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A combined study of radar facies, lithofacies and three-dimensional architecture of an alpine alluvial fan (Illgraben fan, Switzerland)
Abstract
Alluvial fans serve as useful archives that record the history of depositional and erosional processes in mountainous regions and thus can reveal the environmental controls that influenced their development. Economically they play an important role as groundwater reservoirs as well as host rocks for hydrocarbons in deeply buried systems. The interpretation of these archives and the evaluation of their reservoir architecture, however, is problematic because marked heterogeneity in the distribution of sedimentary facies makes correlation difficult. This problem is compounded because the accumulated sedimentary deposits of modern unconsolidated fan systems tend to be poorly exposed and few such systems have been the focus of investigation using high-resolution subsurface analytical techniques. To overcome this limitation of standard outcrop–analogue studies, a geophysical survey of an alpine alluvial fan was performed using ground penetrating radar to devise a scaled three-dimensional subsurface model. Radar facies were classified and calibrated to lithofacies within a fan system that provided outcropping walls and these were used to derive a three-dimensional model of the sedimentary architecture and identify evolutionary fan stages. The Illgraben fan in the Swiss Alps was selected as a case study and a network of about 60 km sections of ground penetrating radar was surveyed. Seven radar facies types could be distinguished which were grouped into debris-flow deposits and stream-flow deposits. Assemblages of these radar facies types show three depositional units which are separated by continuous, fan-wide reflectors; they were interpreted as palaeo-surfaces corresponding to episodes of sediment starvation that affected the entire fan. An overall upward decline in the proportion of debris-flow deposits from ca 50% to 15% and a corresponding increase in stream-flow deposits were identified. The uppermost depositional unit is bounded at its base by a significant incision surface up to 700 m wide, which was subsequently filled up mostly by stream-flow deposits. The pronounced palaeo-surfaces and depositional trends suggest that allocyclic controls governed the evolution of the Illgraben fan, making this fan a valuable archive from which to reconstruct past sediment fluxes and environmental change in the Alps. The results of the integrated outcrop–geophysical approach encourage similar future studies on fans to retrieve their depositional history as well as their potential reservoir properties.This article is protected by copyright. All rights reserved.
... The internal structure of sedimentary fans can be investigated using electrical resistivity tomography (ERT) or ground penetrating radar (GPR) (e.g., Ekes & Friele, 2003;Franke et al., 2015;Hornung et al., 2010), allowing for insights into depositional structures and, hence, processes. Therefore, fans can be valuable sedimentological archives recording environmental conditions during deposition in mountain sediment-source areas (Harvey et al., 1999). ...
... We process our radar data using the ReflexW software (Sandmeier Scientific; processing sequences summarized in Data S12; more details on processing steps in Cassidy, 2009). We analyze and interpret our radar transects based on common terminology for radargram-analysis (Mitchum et al., 1977;Neal, 2004) and reference radar facies linked to sedimentary facies from outcrops in alluvial fan systems (e.g., Franke et al., 2015;Hornung et al., 2010;Mitchum et al., 1977). ...
... Similarly, debris flow channels, boulders and debris flow snouts also point to a dominance of gravitational processes in unit II(Figures 6 and 8). In contrast to unit I, however, channels appear shallower and more persistent, filled with more uniform material indicating a calmer and more confined pattern of deposition.Clusters of boulders stand out of the anthropogenically smoothed fan surface, further supporting the notion of a dominance of gravitational processes during the entire fan formation.In the context of other studies conducting GPR on alluvial fans in alpine environments, the radar facies observed for sedimentary unit I proves exceptional (e.g.,Ekes & Friele, 2003;Franke et al., 2015;Hornung et al., 2010). However, in a similar setting, Hornung et al. (2010) identified two distinct radar facies on an alpine alluvial fan in Switzerland that correspond to debris flows and fluvial T A B L E 2 Characteristics of Goms outsize fans (GOFs) and their feeder catchments, approximated volumes and masses deposited in fans and eroded from catchment. ...
Outsize fans are characterized by seemingly disproportionately small feeder catchments in relation to their fan area. Often having escaped rigorous scientific inquiry, the formative processes of these landforms remain inconclusive, supposedly ranging from catastrophic mass-wasting processes to gradual fluvial formation. Here we apply a multi-method approach, combining morphometric analysis with geophysical subsurface surveys and cosmogenic radionuclide exposure dating, to three outsize fans with hitherto unknown formation history in the Upper Rhone valley, Switzerland. Their feeder catchments are cut into bedrock hillslopes with a lack of indication of both pre-existing catchment structures and/or unconsolidated material that was available after deglaciation.
Focusing our study on the largest of these fans, our findings suggest a fan formation in three phases: In Phase 1, commencing after deglaciation at ~10 ka and ceasing with full catchment development ~6.0 ka, bulk fan bodies were established by deposits of massive high-energy, high-magnitude debris flows exporting sediment with average yields of up to 73 kt km⁻² yr⁻¹. In Phase 2, feeder basins were affected by comparatively lower-magnitude debris flows that distributed a sedimentary facies of debris flow channels, snouts and large boulders across the initial fan. Over time, deposition rates quickly decayed and finally ceased ~0.8 ka, when the system entered the present Phase 3, during which the fan-surface consolidated and fan aggradation terminated. Low gradient and abundant still-water deposits upstream of the fan still attest to the disruption of longitudinal sediment connectivity in the trunk valley.
We conclude that outsize fan formation by massive debris flows in the upper Rhone valley was rapid and massive, but incremental and non-catastrophic. Given the delivery of material at extremely high rates, outsize fans are capable of having a sustained impact on geomorphic systems and, during phases of activity, potentially endangering human livelihoods.
... The probability cumulative curve of this lithofacies presents as a smooth upper arch, while the particle size frequency distribution histogram is zigzag-shaped, and the particle size distribution falls within a wide range (-6u to 6u) ( Figure 4a). This lithofacies is the product of gravity flow sedimentation (Blair, 1999b;Miall, 1985;Nemec & Steel, 1984;Postma et al., 1988) or caused by a debris-flow sedimentation factor (De Haas et al., 2015;Franke et al., 2015; Table 1). ...
... Debris-flow deposition; rapid deposition of a small amount of gravel mixed with finegrained sand after a short-distance debris flow deposition. Rapid deposition of high concentrations of sediments caused by paroxysmal flood events/rainstorms (Franke et al., 2015;Nemec & Steel,1984). Gravel, clast-supported, massive (Gcm) Clast supported; medium to coarse cobble sizes; poor sorting. ...
... Small, limited river channels (shallow channels), small sediments in the low-velocity normal flow unit environment. The fine-grained sediment in the low-flow state in the unrestricted channel (Allen, 1981;Miall, 1996;Franke et al., 2015). ...
Conglomerate reservoirs in alluvial fans commonly contain economic crude oil, but it is challenging to depict the distribution of conglomerate reservoirs or to summarise the sedimentary model in alluvial fans deposits owing to their complex lithofacies changes and variable hydrodynamic conditions. This paper focuses on the Poplar River alluvial fan in the northwest Junggar Basin, China, as a special case to analyse its sedimentary processes and to build a sedimentary model through detailed outcrop mapping and grainsize analysis. The Poplar River alluvial fan is a braided river-dominated fan with the characteristics of a large fan size (approximate 327.6 km²), gentle slope (∼<0.04–0.07°), coarse sediments (mainly cobbles or finer pebbles) and rare fine-mud sediments deposited from floods. In this alluvial fan, 15 lithofacies are identified that mainly formed in five hydrodynamic environments: (i) debris-flow deposits; (ii) high-flow traction current deposits; (iii) low-flow traction current deposits; (iv) still-water deposits; and (v) eolian deposits. Moreover, the sedimentary processes on the Poplar River alluvial fan can be divided into flood and interflood periods. During flood periods, sediment deposition plays a major role on the alluvial fan. From the proximal to distal parts, six lithofacies associations can be identified: feeder-channel and sheet-flow deposits in the proximal part, sheet flood and braided-stream deposits in the intermediate part, and channel deposits and wetland deposits in the distal fan areas. During the interflood periods, sediment reworking is the most important function, and three lithofacies associations are identified: main-channel deposits in the proximal fan, braided-trench deposits in the intermediate fan and wetland deposits in the distal area. The braided-stream deposits, braided-trench deposits and sheet-flood deposits have the best potential for high-quality aquifers or oil reservoirs based on their moderately well-sorted grains and high primary permeable intervals.
• KEY POINTS
• Fifteen lithofacies and eight lithofacies associations are identified in the Poplar River braided river-dominated alluvial fan.
• The aggradation process of the studied alluvial fan can be divided into flood and interflood periods.
• The flood-period braided-fluvial deposits, interflood main-channel and braided-trench channel deposits are the facies with best reservoir potential.
... Chaotic facies have been widely attributed to coarse, poorly sorted deposits (Burke et al., 2008;Pellicer and Gibson, 2011;Franke et al., 2015;Livingstone et al., 2016;Perkins et al., 2016). This is supported by sediment exposures through RF1, which comprise a variety of massive, coarse, gravelly or diamictic deposits interpreted to have formed by the rapid deposition of hyperconcentrated flows (Fig. 5c; d) (Saunderson, 1977;Gorrell and Shaw, 1991;Pellicer and Gibson, 2011;Pellicer et al., 2012;Livingstone et al., 2016;Lang et al., 2017). ...
... Below this bounding surface is a core of RF1 present along the whole esker profile. The chaotic reflections suggest coarser material with a lack of structure, so are interpreted to have formed by rapid deposition during high flow velocities (Burke et al., 2010;Pellicer and Gibson, 2011;Franke et al., 2015;Livingstone et al., 2016). At around 500 m along the profile, side-swipes are observed, likely relating to signal scattering from surface obstacles (Cassidy and Jol, 2009). ...
... At multiple locations, the contact with RF4 and underlying reflectors is erosional (Fig. 6). The reflectors observed in these concave infills are less chaotic, which we interpret to have formed as erosional troughs infilled by finer sediment as flow energy waned (Sambrook-Smith et al., 2006;Franke et al., 2015; closure, leading to increased flow velocities and the erosion of underlying sediments (Perkins et al., 2016). Figure 7 shows a 0.6-km, 160 MHz radar profile taken along the crest of a 1.9-km long, round-crested ridge near the southern end of the simple esker system (northern sector). ...
The architecture and evolution of the subglacial hydrological system plays a key role in modulating ice flow. Eskers provide an opportunity to understand subglacial hydrology at a broader perspective than contemporary studies. Recent research has established a morphogenetic classification for eskers, but these studies have been limited to topographically simple regions of a single ice sheet. We present an updated map of esker distribution in Northern Ireland based on 5-m resolution elevation data. We also present a high-resolution map of the glacial geomorphology of SW Northern Ireland, based on ~ 0.4-m resolution elevation data. Ground Penetrating Radar data from four sites along the > 20-km long Evishanoran Esker system in central Northern Ireland are combined with geomorphological observations to provide insight into depositional processes and controls on esker formation. Esker architecture indicates two styles of deposition, including an initial high energy flow event in a subglacial conduit and delta foreset deposition close to the ice sheet margin during ice margin retreat. These delta foreset deposits can be used to reconstruct former ice margins. We identify that local topographic complexity and geological structures (e.g., faults) are important controls on esker formation. The broad-scale esker architecture remains the same despite variable esker planform morphology, suggesting hydrological conditions alone cannot explain esker morphology. This study provides further evidence that morphogenetic relationships cannot be based solely on remote sensing data and must be supported by robust field observations, especially where post-glacial processes may distort esker morphology (e.g., peat infilling).
... The estimation of the dimensions and spatial distribution of the architectural elements in fluvial reservoirs from 1D core and well data is a notorious problem in reservoir modelling. In this sense, outcrop analogue studies represent a powerful tool, supplementing sparse subsurface data with outcropderived measurements (Miall 1990;Kokureck et al. 1991;Tyler & Finley 1991;Wizevich 1991;Yoshida et al. 2001;Ajdukiewicz & Lander 2010;Scott et al. 2013;Pranter et al. 2014;Franke et al. 2015). Only by integrating both sources of informationoutcrop and subsurfacecan an appropriate database be properly constrained for the reservoir geometry, dimensions and attributes to generate realistic models that include high-resolution facies interpretation and rock heterogeneities (Alpay 1972;Kokureck et al. 1991;Ambrose et al. 1991;Miall 1991;Alexander 1992;Kostic & Aigner 2007; Van den Brill et al. 2007;Calvache et al. 2010;Ozkan et al. 2011;Trendell et al. 2012;Ghinassi et al. 2014;Colombera et al. 2014;Pranter et al. 2014;Klausen & Mork 2014;Shimer et al. 2014). ...
... The parallel or sub-parallel reflectors displayed in the lower part of the channel in the GPR profile (Fig. 9c) correspond to the horizontal lamination of lithofacies (Sh) (Stephens 1994;Bridge & Lunt 2009;Lunt et al. 2013;Reesink et al. 2014). In the upper part of the profile, where mounded (wave reflection or chaotic) and sub-parallel reflectors are observed, interrupted by other concave-up reflectors, trough cross-bedded (St) sandstones Bridge & Lunt 2009;Lunt et al. 2013;Reesink et al. 2014;Franke et al. 2015) with internal erosional scars have been described in outcrop (Fig. 11c). ...
... The GPR profiles acquired across the compound bar architectural element (Fig. 9a, b) show parallel or sub-parallel reflectors with high amplitude and locally with high tilt angles. The GPR profile of the bar head (Fig. 9a) clearly represents the features observed in outcrop, such as the occurrence of different mega-cross-bedded sets and tiered bars as well as internal erosional scars (Bridge & Lunt 2009;Lunt et al. 2013;Reesink et al. 2014;Franke et al. 2015). Towards the south in this profile, there is a change to mounded radar facies due to the proximity to channel south (Bridge & Lunt 2009;Smith et al. 2006;Lunt et al. 2013;Reesink et al. 2014;Franke et al. 2015). ...
The integrated application of advanced visualization techniques – validated against outcrop, core and gamma ray log data – was found to be crucial in characterizing the spatial distribution of fluvial facies and their inherent permeability baffles to a centimetre-scale vertical resolution. An outcrop/behind outcrop workflow was used, combining the sedimentological analysis of a perennial deep braided outcrop with ground-penetrating radar profiles, behind outcrop optical and acoustic borehole imaging, and the analyses of dip tadpoles, core and gamma ray logs. Data from both the surface and subsurface allowed the recognition of two main architectural elements – channels and compound bars – and within the latter to distinguish between the bar head and tail and the cross-bar channel. On the basis of a well-constrained sedimentological framework, a detailed characterization of the gamma ray log pattern in the compound bar allowed several differences between the architectural elements to be identified, despite a general cylindrical trend. A high-resolution tadpole analysis showed that a random pattern prevailed in the channel, whereas in the bar head and tail the tadpoles displayed characteristic patterns that allowed differentiation. The ground-penetrating radar profiles aided the 3D reconstruction of each architectural element. Thus the application of this outcrop/behind outcrop workflow provided a solid database for the characterization of reservoir rock properties from outcrop analogues.
... The estimation of the dimensions and spatial distribution of the architectural elements in fluvial reservoirs from 1D core and well data is a notorious problem in reservoir modelling. In this sense, outcrop analogue studies represent a powerful tool, supplementing sparse subsurface data with outcropderived measurements (Miall 1990;Kokureck et al. 1991;Tyler & Finley 1991;Wizevich 1991;Yoshida et al. 2001;Ajdukiewicz & Lander 2010;Scott et al. 2013;Pranter et al. 2014;Franke et al. 2015). Only by integrating both sources of information -outcrop and subsurface -can an appropriate database be properly constrained for the reservoir geometry, dimensions and attributes to generate realistic models that include high-resolution facies interpretation and rock heterogeneities (Alpay 1972;Kokureck et al. 1991;Ambrose et al. 1991;Miall 1991;Alex- ander 1992;Kostic & Aigner 2007;Van den Brill et al. 2007;Calvache et al. 2010;Ozkan et al. 2011;Trendell et al. 2012;Ghinassi et al. 2014;Colombera et al. 2014;Pranter et al. 2014;Klausen & Mork 2014;Shimer et al. 2014). ...
... The parallel or sub-parallel reflectors displayed in the lower part of the channel in the GPR profile (Fig. 9c) correspond to the horizontal lamination of lithofacies (Sh) (Stephens 1994;Bridge & Lunt 2009;Lunt et al. 2013;Reesink et al. 2014). In the upper part of the profile, where mounded (wave reflection or chaotic) and sub-parallel reflectors are observed, interrupted by other concave-up reflectors, trough cross-bedded (St) sandstones ( Corbeanu et al. 2001;Bridge & Lunt 2009;Lunt et al. 2013;Reesink et al. 2014;Franke et al. 2015) with internal erosional scars have been described in outcrop (Fig. 11c). ...
... The GPR profiles acquired across the compound bar architectural element (Fig. 9a, b) show parallel or sub-parallel reflectors with high amplitude and locally with high tilt angles. The GPR profile of the bar head (Fig. 9a) clearly represents the features observed in outcrop, such as the occurrence of different mega-cross-bedded sets and tiered bars as well as internal erosional scars (Bridge & Lunt 2009;Lunt et al. 2013;Reesink et al. 2014;Franke et al. 2015). Towards the south in this profile, there is a change to mounded radar facies due to the proximity to channel south (Bridge & Lunt 2009;Smith et al. 2006;Lunt et al. 2013;Reesink et al. 2014;Franke et al. 2015). ...
From the geometrical, sedimentological and petrological characteristics derived from an outcrop and the core and well logging data of 4 boreholes in combination with 5 GPR lines (200 MHz), a 3D model of a layer of sandstone in TIBEM (Triassic of the Iberian Meseta, Spain) has been developed.The selected example corresponds to a meander belt. In it we have distinguished for modeling purposes the main highly sinuous channel, two successive point bars,multiple scroll bars and two chute channels, as well as a clay plug marking
the phase of channel inactivity. The model obtained using the Petrel software shows fairly realistic heterogeneities within the reservoir, allowing the identification of areas with quite different values of porosity and permeability, controlled by the distribution of lithofacies among different subenvironments.The example reveals as an interesting outcrop analog to many fluvial reservoirs.
... The interlinked occurrence of different sedimentary facies forms a complex sedimentary architecture of an individual fan (Blair, 1999;Blair & McPherson, 1994;Brenna et al., 2020;Chen et al., 2017;Franke et al., 2015;Zhang et al., 2021). ...
... The ground-penetrating radar (GPR) technique was applied to understand the subsurface geometry of Suhi vrh fan. This geophysical method has been used successfully for alpine alluvial fans (Franke et al., 2015;Mills & Speech, 1997), as well as for coarse-grained sedimentary bodies (talus slopes) built of carbonate gravels (Sass & Krautblatter, 2007). ...
Sieve lobes typically appear in gravel‐rich and matrix‐poor alluvial fans. Despite being extensively studied, the sieve‐lobe facies has been defined largely based on qualitative field observations without quantitative sedimentological analyses. Additionally, depositional activity of sieve lobes has not been monitored over extended periods (monthly to annually) and not directly associated with specific precipitation triggers. Furthermore, the internal geometry of sieve‐lobe built alluvial fans has not yet been imaged by subsurface methods. We performed a multi‐method analysis of sieve lobes in the Julian Alps (NW Slovenia) on an alpine alluvial fan composed of carbonate gravels. We performed a detailed textural and structural sedimentological analysis of 11 recent sieve lobes differing in size and age. A three‐year aerial surveying of the alluvial fan surface with a Small Unmanned Aircraft and photogrammetric modelling was used to detect active sieve‐lobe evolution. Detected sieve‐lobe‐formation events and volumetric surface changes were paired with triggering precipitation events. Ground‐penetrating radar (GPR) profiling depicted the geometry of the sieve‐lobe built alluvial fan. Sieve‐lobe facies consists of over 80% of poorly‐sorted, open‐framework gravels and less than 2% mud. Lobes exhibit downward coarsening and increase in clast mean size. These textural and structural characteristics are present in all sieve lobes regardless of their age and size. Sieve lobes form with a subannual frequency usually following 24‐hour rainfall events exceeding 50 mm. Over 1000 m3 of sediment was deposited during these events. The GPR profiles confirm that the studied alluvial fan is formed predominantly by stacked sieve lobes. Quantitative sedimentary analysis of sieve lobes, monitoring of their recent evolution and depiction of their subsurface geometry, demonstrated in this study, reinforce the challenged concept that sieve lobes are one of the main building blocks of alluvial fans. This work also demonstrates that, under specific conditions, sieving may become the dominant alluvial fan‐forming process.
... The sheet-like, slightly inclined geometry points to fan-head aggradation that resulted either from unchanneled debrisflow or stream-flow depositions (cf. Blair and McPherson 2009;Ventra and Nichols 2014;Franke et al. 2015). ...
... The downslope deposition indicates a phase of fan progradation (cf. Blair and McPherson 2009;Meinsen et al. 2014;Franke et al. 2015). The upslope-stepping lobes may indicate a subsequent phase of aggradation and fan-trench backfilling (e.g., Ventra and Nichols 2014;Meinsen et al. 2014). ...
We present new evidence for neotectonic activity along the Harz Boundary Fault, a Cretaceous reverse fault that represents a key structure in northern Germany. For the fault analysis, we use a multimethod approach, integrating outcrop data, luminescene dating, shear wave seismics, electrical resistivity tomography (ERT) and numerical simulations. A recent sinkhole at the SSW-ward dipping and WNW–ESE striking Harz Boundary Fault exposes a NNE-ward dipping and WNW–ESE striking planar fault surface that cuts through unconsolidated debris-flow deposits thus pointing to young Lateglacial tectonic activity. The fault shows a polyphase evolution with initial normal fault movement and a later reactivation as an oblique fault with reverse and strike-slip components. A shear wave seismic profile was acquired to analyse the geometry of the fault and show that the Harz Boundary Fault is steeply dipping and likely has branches. Partly, these branches propagate into overlying alluvial-fan deposits that are probably Pleniglacial to Lateglacial in age. The outcrop data in combination with the seismic data give evidence for a splay fault system with steep back-thrusts. One of these back-thrusts is most likely the NNE-ward dipping fault that is exposed in the sinkhole. The lateral extent of the fault was mapped with electrical resistivity tomography (ERT) profiles. The timing of fault movement was estimated based on optically stimulated luminescence dating of the faulted debris-flow deposits using both quartz and feldspar minerals. Consistent feldspar and quartz ages indicate a good bleaching of the sediment prior to deposition. The results imply fault movements post-dating ~ 15 ka. Numerical simulations of glacio isostatic adjustment (GIA)-related changes in the Coulomb failure stress regime at the Harz Boundary Fault underpin the assumption that the fault was reactivated during the Lateglacial due to stress changes induced by the decay of the Late Pleistocene (Weichselian) Fennoscandian ice sheet.
... Age constraints for fan surfaces are generally more difficult to obtain as their preservation is limited by the shifts of the active channels, which may lead to erosion or burial of older fan surfaces. Such buried older fan surfaces may be detectable by ground penetrating radar (Hornung et al., 2010;Franke et al., 2014). In arid regions, relative ages for the different parts of a fan surface may be derived from the degree of desert varnish development (Bull, 1991) or differences in the surface roughness (Regmi et al., 2014). ...
... Sedimentologic observations were made at the cliffs at the distal portions of the Ampatune and Mallma fans. To infer the depositional processes as well as the spatiotemporal evolution of the fans, we followed the standard nomenclature of Miall (1996) to classify the different lithofacies types and architectural elements and to interpret them in terms of the depositional environment (e.g., Franke et al., 2014;Meinsen et al., 2014;Ventra and Nichols, 2014). ...
Alluvial fans record climate-driven erosion and sediment-transport processes and allow reconstructing past environmental conditions. Here we investigate the sedimentation history of two alluvial fans located in formerly glaciated valleys of the Cordillera Oriental, Peru. ¹⁰ Be exposure ages from the fan surfaces and radiocarbon ages from the fan interiors constrain the final stages of fan formation. The ¹⁰ Be and ¹⁴ C ages cluster mainly between 13.3–9.3 ka and 11,500–9700 cal yr BP, respectively. Our age data set indicates that—after deglaciation—large amounts of fan sediment were deposited until ∼10 ka, when sedimentation rates declined rather abruptly. This pattern is supported by ¹⁰ Be erosion rates for the fan catchments, because under the assumption of constant erosion the time needed to erode the material stored in the fans significantly exceeds their age. Correlating our ages with regional climate records indicates that precipitation exerts the primary control on fan sedimentation. Two periods with elevated lake levels and increased precipitation between 18 and 14.5 ka and from 13 to 11.5 ka resulted in rapid deposition of large fan lobes. Subsequently, lower precipitation rates decreased erosion in the catchments and sediment delivery to the fans, which have remained largely inactive since ∼9.5 ka.
... Lunt et al. (2004) proposed that the subparallel nature of the reflections was likely due to successive bedload sheets deposition. Structures of facies IIb resemble horizontal and u-shaped fill reflections with convex-upward upper boundary described as overbank deposits and debris-flow lobes in an alluvial fan (Franke et al., 2015). ...
... Facies IIIb consists of locally variable sediments. The convex-upward mound-like reflections may indicate massive deposits Franke et al., 2015). In addition, these features can be interpreted as the depositional signature of small-scale incipient unit bars (Lunt et al., 2004). ...
... Studies of alluvial sequences have been carried out in a wide range of convergent tectonic settings and these deposits are inferred as thick clastic wedges deposited in advance of propagating thrust fronts in orogenic belts (Nichols, 1987a;Platt and Keller, 1992;Sinclair, 1997;Kuhlemann and Kempf, 2002;Clevis et al., 2004;Barrier et al., 2010). Modern examples of such studies are established on the Indo-Gangetic, Po and Mesopotamian plains (Geddes, 1960;Allen, 1965;Baltzer and Purser, 1990;Ori, 1993;Sinha and Friend, 1994;Gupta, 1997;Shukla et al., 2001;Goswami and Mishra, 2013), while ancient sedimentary rock records are well analyzed in the Pyrenean foreland basin (Nichols, 1987b;Marzo et al., 1988;Bentham et al., 1992;Nijman, 1998;Ramos et al., 2002;Luzon, 2005;Nichols and Thompson, 2005;Barrier et al., 2010;Sun et al., 2021) and the Alpine molasse basin (Platt and Keller, 1992;Jin et al., 1995;Schlunegger et al., 1997;Zweigel et al., 1998;Capuzzo and Wetzel, 2004;Fontana et al., 2008Fontana et al., , 2014Franke et al., 2015). ...
The Himalayan foreland basin originated through the India–Asia continent–continent collision driven by downward flexing of the Indian plate. It forms an ideal assemblage to delineate the role of process-controlled sedimentary fill in basin evolution. This paper provides the first comprehensive account of the lithofacies associations and architecture of the Middle Siwalik succession of the Himalayan foreland basin in the south-central Himachal
Pradesh sector, India through detailed sedimentological analysis. Eight lithofacies form three distinct sand, gravel, and silt-mudstone lithofacies associations pertaining to specific depositional environments. Architectural elements have been defined together with bounding surfaces separating them.
Sedimentological investigations reveal that the Middle Siwalik sequence represents a flash flood dominated piedmont fan and proximal to middle megafan. The fan expansion cycles indicate tectono-climatically controlled sedimentation in the Middle Siwalik foreland basin. Frequent flooding and a high sedimentation rate were influenced by the tectonic uplift along the reactivated thrusts in the hinterland coupled with phases of
monsoonal intensification.
... Land based GPR is well established and successfully applied since years in archaeological prospection (e.g. Leckebusch 2001;Wallner et al. 2021), sedimentology (Franke et al. 2015), and engineering geology. Rarely, GPR systems were used already from boats on the water surface (Sambuelli et al. 2009;Baum et al. 2014;Fediuk et al. 2022). ...
The publication at hand are the proceedings of the 15th International Conference on Archaeological Prospection held between March 28 and April 1, 2023, in Kiel, Germany. The content of the articles ranges from local to large-scale case studies all over the world and from various archaeological times, over methodological improvements, new processing and visualization techniques to a special session on marine and wetland prospection. Thus, the collection of articles summarizes the state of the art of prospection methods for on- and offshore archaeological investigations.
... Gmm Matrix-supported conglomerate Structureless, disorganized or weak grading, poorly sorted, clasts are angular to subangular ranging from pebbles to boulders Rapid deposition by debris flow (Shultz, 1984;Costa, 1988;Miall, 1996;Franke et al., 2015) Gmg Matrix-supported conglomerate Inverse poorly sorted clasts, angular to subrounded clasts. Outsized clasts are common towards the top of the facies Rock avalanche deposits (Nemec and Steel, 1984;Blair, 1999aBlair, , 1999bFranke et al., 2015) Gci ...
Alluvial fan deposits record important information about paleoclimate, tectonic setting, and paleogeography that can be deciphered with detailed sedimentological analysis. The late Messinian Chaabet Et Tabbela Formation, in the western part of the Kechabta Basin in northern Tunisia, shows excellent examples of alluvial fans deposited during the latest phase of the Messinian Salinity Crisis, the Lago Mare event. This exposure provides the opportunity to investigate terrestrial depositional conditions during this period. The Chaabet Et Tabbela Formation was investigated through sedimentological logging and detailed facies analysis at eight locations. Sixteen facies types were identified and interpreted along with variation in clast compositions. These facies were further grouped into four facies associations: (1) proximal alluvial fan, dominated by gravity-driven processes, (2) medial alluvial fan, which mainly comprises a mix of debris flow and high-sediment load streamflow deposits, (3) distal alluvial fan, which consists of laterally continuous sheetflood and subordinate channels deposits, and (4) playa and floodplain, which are made of red mudstones with calcareous paleosols. Clast composition of these fan deposits comprises Triassic, Jurassic, and Cretaceous bedrock suggesting that sediment was sourced from the surrounding Maghrebian mountain chain. Two laterally adjacent alluvial fans were identified along the N-S Messeftine Fault. These fans have prograded during the Late Messinian, with an estimated radius of ca 2 km.
The evolution of these alluvial fans is related to a complex interplay of allogenic processes. The uplift related to intra-Messinian tectonic event and climate variation contributed to the formation of these fans during the late Messinian. Although, these deposits are relatively limited in extension, similar continental deposits form synchronously in different marginal Mediterranean basins during the Lago Mare stage, suggesting that the alluvial fans of the Chaabet Et Tabbela Formation should be placed in a context of regionally change climactic and paleogeographic conditions.
... Clast-supported gravel lags or isolated angular outsize Table 3 Characteristics of channel bodies and sheetflood deposits. clasts indicate reworking and winnowing of sediments, probably during "normal" flow conditions (Blair and McPherson, 1994;Franke et al., 2015). The angular clasts have been derived from the adjacent bedrock of the drainage area and may either have resulted from debris fall or snow flow/snow avalanches. ...
Alluvial fans are important paleoclimatic archives, that may record high-frequency climatic oscillations. However, climate signals may be overprinted or even be destroyed by autogenic processes caused by channel avulsion and lobe switching. Here we present new data from two different Late Pleistocene (MIS 3-2) alluvial fan systems in northern Germany and compare these systems to experimental alluvial fans and other field examples. The selected fan systems formed under similar climatic and tectonic conditions, but differ in size, type, and drainage area allowing to estimate the role of climate and autogenic controls on flow processes, facies architecture, and fan-stacking patterns. Luminescence dating is used to determine the timing of fan onset and aggradation. Fan onset occurred in response to climate change at the end of MIS 3 when temperatures decreased and periglacial climate conditions were established in northern central Europe. A related increase in sediment supply and strongly variable precipitation patterns probably promoted fan formation. The major period of fan aggradation was approximately between 33-18 ka, followed by fan inactivity, abandonment, and incision during the Lateglacial. Sand-rich, sheetflood-dominated fans are related to larger, low-gradient fan catchments. Steep depositional fan slopes (5°-17°) and short-lived high-energy floods promoted supercritical flow conditions. Well sorted, sediment-laden, rapidly waning flows favored the deposition and preservation of supercritical bedforms and allowed for the aggradation of stable antidunes. Steep, dip-slope catchments enhanced stream gradients and promoted the transport of coarser sediments. These fans have lower gradient slopes (2-6°) and are dominated by channelized flows, alternating with periods of unconfined sheetfloods. Meter-scale coarsening upward successions, characterized by sandy sheetflood deposits at the base, overlain by multilateral or smaller single-story gravelly channel fills may be related to high-frequency climatic fluctuations or seasonal fluctuations in water and sediment supply. These coarsening-upward successions are commonly bounded by a paleo-active layer, from which ice-wedge casts penetrate downwards. The comparison to experimental fans and other field examples implies that the recurrent pattern of multistory, multilateral and single-story channel bodies with a lateral offset to vertical stacking pattern most probably was controlled by autogenic switch in an avulsion-dominated system. Fan abandonment and dissection probably occurred at the Late Pleniglacial to Lateglacial transition. The change in deposition from alluvial-dominated processes to aeolian sedimentation with minor alluvial influences during the Lateglacial records alternation of dry and ephemeral wetter phases that are related to rapid climatic variations. The main phase of aeolian sand-sheet deposition probably correlates with Heinrich event H1 between approximately 18-16 ka and reflects sedimentation in response to aridification and high mean wind speeds.
... Blair and McPherson, 2009;Harvey, 1999), and stream-flow dominated fans (cf. DeCelles et al., 1991;Colombera and Bersezio, 2011;Franke et al., 2015). Depending on the process regime of a fan, the formative processes, spatial distribution and characteristics of OFGs can vary considerably. ...
Open-framework gravels (OFGs) form common lithofacies of alluvial fans. However, inferences of their mechanisms of transport and deposition, and of controls on their distribution in alluvial-fan successions, remain difficult, limiting our ability to interpret the environmental significance of such deposits and to predict their distributions in ancient successions. From an applied standpoint, such predictions are important in the development of hydrocarbon reservoirs and remediation of aquifers hosted in alluvial-fan strata. To elucidate our understanding of formative conditions of different types of OFGs, a study has been undertaken on the Quaternary Poplar Fan, in the endorheic Heshituoluogai Basin, China.
Based on observations from outcrops and trenches on the Poplar Fan, eight different types of OFGs are identified: these lithofacies types account for 7% of the total deposits of the fan. During high flow stages, OFGs are deposited in association with supercritical sheet-like flow (type 1), unconfined streamflow (type 2), and flow in groundwater-fed channels (type 3). During low flow stages, OFGs are associated with trough cross-stratification (type 4) and sigmoidal cross-stratification (type 5); these types occur over the entire fan. At the fan margins, OFGs are associated with gulleys (type 6), especially at the distal fan toe. Other OFG types are associated with bank collapse (type 7) or intercalated with aeolian deposits (type 8). A model is proposed to account for the distribution of different types of OFGs across the fan, wherein types 1, 2 and 4 seen in the medial fan are dominant. This provides a framework for the identification, prediction and correlation of OGFs in subsurface alluvial-fan successions.
... The sediments belonging to the Bottom Conglomerate Formation is interpreted to be debris flow deposits of an alluvial fan (Blair and McPherson, 1993Sohn et al., 1999;Miall, 2006;Chamyal et al., 1997;Reading, 1996;Collinson et al., 2006;Pundalik et al., 2010;Franke et al., 2015;Chen et al., 2017;Kale and Pundalik, 2019;Davoudi, 2020). The matrix supported conglomerate variety represents the mud flow deposits (Reineck and Singh, 2012). ...
The Late Cretaceous Bottom Conglomerate Formation from Khasi Group occurs as isolated and coalescent cones. Development of three discrete lithofacies namely clast supported and matrix supported boulder conglomerate, interstratified pebbly conglomerate and granule conglomerate, and large scale tabular cross bedded pebbly conglomerate within the Bottom Conglomerate Formation represents the debris flow, mudflow and water-flow deposits of alluvial fan respectively. Proximity of this alluvial fan to Dawki fault indicates that this fault and its associated faults provided the basin depression, geomorphic contrast together with the climate favoring the debris flow process to build an alluvial fan. Thin section studies of the matrix of these conglomerates revealed quartzose wacke nature, indicating mineralogical maturity and textural immaturity of these sediments. The thin section studies also suggest prevalence of humid climate during deposition. The high proportion of zircon, and transparent heavy mineral assemblage of augite, rutile, monazite, sillimanite, spinel, sphene, dumortierite, and anatase, suggests that the sediments under study are derived from mixed provenance such as Proterozoic Supracrustal High Grade Granulite Metasediments, Gneissic Complex, Late Proterozoic Porphyritic Granitoids, Shillong Group, Khasi Metabasics with some inputs from the Sylhet Trap Basalts and their associated intrusives. Geochemical studies of these sediments support the mixed provenance for these sediments, and indicate humid climate during their deposition, thereby supporting the thin section and heavy mineral studies.
... c Cross-correlation between the LR-and RF-based landslide susceptibility maps which shows that 78.03% area is having a perfect match georadar images shown in Fig. 6 exhibit numerous reflections and distortion in the GPR image collected at 9th mile landslide zone. Mainly three radar facies were recognized from the radargram, namely parallel even continuous reflections, low amplitude with discontinuous reflections (WD) and complex sigmoid (CS) (Adepelumi and Fayemi 2012;Franke et al. 2015;Rossetti 2003). In Figs. ...
Landslide susceptibility (LSI) modeling of Darjeeling–Sikkim Himalaya is performed by integrating 28 causative factors on 28C28 combinations on Geographical Information System (GIS) following analytic hierarchy process (AHP)-based multicriteria decision protocol, logistic regression (LR)-based multivariate technique, machine learning data-driven random forest (RF) and artificial neural network (ANN) methods wherein the terrain is classified into ‘None’ (with: 0.0 < LSI ≤ 0.17), ‘Low’ (with: 0.17 < LSI ≤ 0.34), ‘Moderate’ (with: 0.34 < LSI ≤ 0.51), ‘High’ (with: 0.51 < LSI ≤ 0.68),‘Very High’ (with: 0.68 < LSI ≤ 0.85) and ‘Severe’ (with: 0.85 < LSI ≤ 1.00) susceptible zones as validated through standard statistical accuracy tests and direct cross-correlation analysis of all the susceptible zonation maps generated by drawing comparison with the 30% landslide inventory test data. The best integrated thematic RF-based LSI vector layer with an accuracy level of 0.871, in turn, on integration with the vulnerability components like population density, number of households, building types, building height and building density has demarketed approximately 21% of the region under ‘Very High’ to ‘Severe’ socioeconomic risk zone while about 36% area are classified under ‘Very High’ to ‘Severe’ structural risk zone as implicated by devastating landslide hazards in the region. Ground Penetrating Radar Survey has been conducted on all the slopes in the ‘Very High to Severe’ landslide susceptible zones wherein near-surface lithologic setting, presence of paleo-slopes and microstructural features like fractures/faults and poorly stratified debris flow have been imaged that provided favorable subsurface conditions for slope failure. Finite element method-based slope failure analysis for Newmark displacement estimates factor of safety (FoS) value that acts as the proxy in defining the degree of slope instability is seen to vary between 1.905 and 2.357 in the ‘Low to Moderate’ landslide susceptible zone while it ranges between 1.051 and 1.652 in the ‘High’ landslide susceptible zone and between 0.649 and 1.349 in the ‘Very High to Severe’ landslide inventory subset along the slopes under both gravity loading and seismic shaking in the terrain. The slope stability analysis puts the yield acceleration between 0.0012 and 0.11984 m/s2 and the total deformation between 0.0027 and 1.4484 m. All these parameters in the classified landslide susceptible zones in unison demonstrate how unstable are the terrain slopes in the ‘High to Severe’ landslide susceptible zones.
... The interpretation of features in GPR slices involves recognizing variations in reflection continuity, shape, amplitude, internal configuration and external geometries (Beres et al., 1999;González-Villanueva et al., 2011;Franke et al., 2015). Such variations can be categorized into socalled radar facies (Beres and Haeni, 1991;Jol and Smith, 1991). ...
Across the UK, sandy beaches and dunes protect coastal infrastructure from waves and extreme water levels during large‐scale storms, while providing important habitats and recreational opportunities. Understanding their long‐term evolution is vital in managing their condition in a changing climate. Recently, ground‐penetrating radar (GPR) methods have grown in popularity in geomorphological applications, yielding centimetre‐scale resolution images of near‐surface stratigraphy and structure, thus allowing landscape evolution to be reconstructed. Additionally, abrupt changes in palaeo‐environments can be visualized in three dimensions. Although often complemented by core data, GPR allows interpretations to be extended into areas with minimal ground‐truth control. Nonetheless, GPR data interpretation can be non‐intuitive and ambiguous, and radargrams may not initially resemble the expected subsurface geometry. Interpretation can be made yet more onerous when handling the large 3D data volumes that are facilitated with modern GPR technology. Here we describe the development of novel semi‐automated GPR feature‐extraction tools, based on ‘edge detection’ and ‘thresholding’ methods, which detect regions of increased GPR reflectivity which can be applied to aid in the reconstruction of a range Quaternary landscapes. Since reflectivity can be related to lithological and/or pore fluid changes, the 3D architecture of the palaeo‐landscape can be reconstructed from the features extracted from a geophysical dataset. We present 500 MHz GPR data collected over a buried Holocene coastal dune system in North Wales, UK, now reclaimed for use as an airfield. Core data from the site, reaching a maximum depth 2 m, suggest rapid vertical changes from sand to silty‐organic units, and GPR profiles suggest similar lateral complexity. By applying thresholding methods to GPR depth slices, these lateral complexities are effectively and automatically mapped. Furthermore, automatic extraction of the local reflection power yields a strong correlation with the depth variation of organic content, suggesting it is a cause of reflectivity contrast. GPR‐interpolated analyses away from core control thus offer a powerful proxy for parameters derived from invasive core logging. The GPR data collected at Llanbedr airfield highlight a complex dune system to a depth of 2.8 m, probably deposited in several phases over ~700 years, similar to elsewhere in North Wales.
... For the petroleum geological industry and the field of sedimentology, techniques of lithofacies or lithology analysis that use seismic or geophysical prospecting are quite mature [11,12]. Based on the theory of geostatistics, commercial or public software have been able to achieve the establishment of lithofacies or lithology models to better predict its three-dimensional spatial distribution [13][14][15][16]. Of course, it is possible to directly introduce the mature techniques in the field of petroleum geology and sedimentology to the field of engineering geology. ...
Lithology variations, which are recognized as rock type differences, significantly affect the physical properties of rock masses in red beds. In this paper, we introduce a statistical method for quantitatively evaluating the degree of lithology variations in layered red beds with depth. The core of this method is to use borehole logs as random variables for statistical analysis to calculate the percentage of a specified lithology at a given elevation, which involves seven steps of attitude calculation, reference point selection, distance calculation, elevation modification, data discretization, data statistics, and curve plotting. The Yellow River Guxian Dam is chosen as a field case study. We classify rock types of feldspar sandstone, fine sandstone, and conglomerate into hard rocks and that rock types of calcareous siltstone, argillaceous siltstone, and mudstone into soft rocks. Borehole logs recorded during the geological investigation are used to plot the percentage curve of hard rocks. We find that the degree of lithology variations for each lithology group differs greatly, the general behaviors of lithology variations on two sides of the Guxian Dam riverbed are quite similar but still with some differences, and that some thick lithology groups can be finely divided into several subgroups. On the basis of the hard rock percentage curve, we introduce a lithology variation index to quantitatively characterize the degree of lithology variations, which can be used as an important index to supplement the traditional methods when performing rock mass classifications in red beds. We also plot the trilithology percentage curve of sandstone, calcareous siltstone, and argillaceous siltstone, which serves for the determination of physical parameters of the dam foundation rock mass, the identification of the potential shear sliding surface, and the search for an impervious grouting bottom. Moreover, we find that the crest and trough, which are local high and low points in the hard rock percentage curve, can be used to show some characteristics of shear zones. The locations of shear zones are well represented in the form of troughs and that the development of shear zones has a good linear relationship with the hard rock percentage of the corresponding crest. The method proposed in this paper can be promoted and applied in similar projects or studies.
... Geoscanner Gekko-80 (Geoscanners, Boden, Sweden) antennas in bistatic mode were used for data collection and GPRSoft® was used to filter and topographically correct the data. Radar facies were identified based on distinctive reflection packages observed within the profiles, similar to studies carried out on alluvial fans by É kes & Friele (2003), Hornung et al. (2010) and Franke et al. (2015). Penetration depths reached 4-7.5 m, below which the data became too noisy to interpret. ...
Alluvial fans often support ephemeral streams whose flow regimes and sediment dynamics are strongly controlled by fan sedimentary characteristics and interactions with shallow groundwater aquifers. The hydrogeology of such fans has most often been documented for large fans located within arid climate zones. This research focuses on a small (0.075 km²) alluvial fan situated in a temperate, high rainfall climate (the Lake District, North West England). An ephemeral stream flowing across this alluvial fan plays a key role in supplying water and sediment to the River Ehen, which is the focus of a habitat restoration initiative. This study combines high spatial resolution, near surface geophysics and outcrop data with hydrological data to characterise the hydrogeological properties of the alluvial fan. A conceptual hydrogeological model was developed to understand the hydrology across the alluvial fan and how that affects water and sediment supply to the River Ehen. The alluvial fan is composed predominantly of permeable debris flow deposits and numerous palaeochannels which may provide preferential groundwater flow paths. During streamflows, partial to full stream-aquifer connectivity occurs, especially in the distal fan where groundwater discharges back into the stream. Streamflows occur when the fan apex infiltration rate/capacity threshold of approx. 60 l/s⁻¹ is exceeded, typically following rainfall events >9-11 mm. Understanding interactions between ephemeral streams and their underlying aquifers enables better predictions of the timing and magnitude of future flows, and in-turn, their likely impacts on the water courses into which they discharge.
... in the Rhône river for over 6 km downstream (e.g., Franke et al., 2015;Schlunegger et al., 2009). The elevation ranges from 886 m a.s.l. at the base of the fan to a maximum of 2,645 m a.s.l. ...
Climate change impacts on sediment production and transfer processes on hillslopes and through channels are governed by possible changes in precipitation, runoff, and air temperature. These hydrological and geomorphological impacts are difficult to predict in temperature‐sensitive Alpine environments. In this study, we combined a stochastic weather generator model with the most current climate change projections to feed a hillslope‐channel sediment cascade model for a major debris‐flow system in the Swiss Alps (the Illgraben). This allowed us to quantify climate change impacts and their uncertainties on sediment yield and the number of debris flows at hourly temporal resolution. We show that projected changes in precipitation and air temperature lead to a reduction in both sediment yield (−48%) and debris‐flow occurrence (−23%). This change is caused by a decrease in sediment supply from hillslopes, which is driven by frost‐weathering. Additionally, we conduct model experiments that show the sensitivity of projected changes in sediment yield and debris‐flow hazard to basin elevation, with important implications for assessing natural hazards and risks in mountain environments. Future changes in hydrological and sediment fluxes are characterized by high uncertainty, mainly due to irreducible internal climate variability. Therefore, this stochastic uncertainty needs to be considered in climate change impact assessments for geomorphic systems.
... Debris-flow avulsions can be particularly dangerous, because mitigation measures in the active channel may not be able to reduce risk on other areas of the fan after avulsion De Haas, Kruijt, et al., 2018;Pederson et al., 2015). In addition, debris-flow fan deposits are archives of past flow processes (e.g., De Haas, Braat, et al.,2015;Dühnforth et al., 2007;Whipple & Dunne, 1992) and sediment supply (e.g., Dietrich & Krautblatter, 2017;Franke et al., 2015;McDonald et al., 2003), and they may therefore record sedimentary signals of past climate changes (e.g., D'Arcy et al., 2017). The frequency of avulsion determines the revisiting time of each location on the fan surface, and thus the utility of the surface in recording past environmental conditions (e.g., Dühnforth et al., 2007). ...
Debris‐flow fans form by shifts of the active channel, termed avulsions. Field and experimental evidence suggest that debris‐flow avulsions may be induced by depositional lobes that locally plug a channel or superelevation of the channel bed above the surrounding fan surface, by analogy to fluvial fans. To understand debris‐flow avulsion processes, we differentiate between these controls by quantifying the spatial distribution of debris‐flow lobe and channel dimensions, along with channel‐bed superelevation, on nine debris‐flow fans in Saline Valley, California, USA. Channel beds are generally superelevated by 2–5 channel depths above the fan surface, and locally by more than 7 channel depths, thereby substantially exceeding superelevation on fluvial fans. Depositional‐lobe thickness and channel depth decrease with distance from the fan apex, although both are highly variable across the fans. Median channel depths roughly correspond to the 50th–75th percentiles of lobe thicknesses, while minimum channel depths roughly correspond to the 10th–25th percentiles. In contrast, the thicknesses of lobes that have triggered avulsions roughly equal local channel depths and are on average twice as thick as the local median lobe thickness. The spatial correspondence between avulsion locations and thick lobe deposits, and the lack of correlation with channel‐bed superelevation, leads us to infer that avulsions on these fans are mostly caused by thick lobes forming channel plugs. Although results may vary with climatic and tectonic setting, our findings indicate that avulsion hazard assessment on populated fans should include mapping and monitoring of channel depths relative to typical deposit thicknesses on a given fan.
... Yet beyond the favourability of the site conditions for using GPR, the use of quantitative data analysis by means of k-means clustering of structure-parallel vectors allowed for semi-automatic determination of radar facies from the CIT survey. Classical studies have made use of manual tracing of GPR reflection patterns and geometries for geologic interpretation (Martinez et al. 1998;Asprion & Aigner 2000;Asprion et al. 2009;Bennett et al. 2009;Jorry & Biévre 2011;Franke et al. 2015). Such methods may be beneficial for unambiguous reflection geometries and/or small-scale studies. ...
The study of exposed carbonate platforms provides observational constraints on regional tectonics and sea-level history. In this work Miocene-aged carbonate platform units of the Seroe Domi Formation are investigated on the island of Bonaire, located in the Southern Caribbean. Ground penetrating radar (GPR) was used to probe near-surface structural geometries associated with these lithologies. The single cross-island transect described herein allowed for continuous mapping of geologic structures on kilometre length scales. Numerical analysis was applied to the data in the form of k-means clustering of structure-parallel vectors derived from image structure tensors. This methodology enables radar facies along the survey transect to be semi-automatically mapped. The results provide subsurface evidence to support previous surficial and outcrop observations, and reveal complex stratigraphy within the platform. From the GPR data analysis, progradational clinoform geometries were observed on the northeast side of the island which support the tectonics and depositional trends of the region. Furthermore, several leeward-side radar facies are identified which correlate to environments of deposition conducive to dolomitization via reflux mechanisms.
... While additional information can be collected through several very-high-resolution geophysical techniques (e.g., seismic imaging and ground-penetrating radar), alluvial and debris-flow fans so far have mainly been studied using the ground-penetrating radar. This technique can resolve depositional structures down to the decimeter scale, but can only penetrate the topmost 10 to 30 m in the best-case scenario (e.g., Ékes and Hickin, 2001;Ékes and Friele, 2003;Franke et al., 2015;Friele et al., 1999;Hornung et al., 2010). More penetrative geophysical surveys, such as active seismic techniques, can resolve the complex architecture of alluvial fans and the hosting valley fills, but the approach is challenging and costly. ...
High-resolution active-source seismic surveys target the stratigraphic and structural configuration of the mid-Venosta Valley, which hosts two mega fans located at the confluence between the Adige River and its tributaries: the Gadria-Strimm fan and the Lasa fan. We aimed at imaging with high detail: 1) the postglacial sediment accumulation within the fans, 2) the characteristics of Adige river deposits, and 3) the stratigraphic/structural relationships among fans, alluvial deposits and top of the bedrock (i.e. Ötztal- Ortles-Campo Nappe units). Alluvial and debris-flow fan environments often pose significant challenges to high-resolution seismic exploration, due to the high heterogeneity and the rugged topography of the near surface. We processed our data by integrating first-arrivals refraction tomography with Common Midpoint, and Common Reflection Surface seismic reflection techniques. All methods produced complementary results which allowed us reaching a well-constrained imaging of the internal architecture of the Quaternary sedimentary cover, as well as of the geometry of the hosting bedrock surface. Our result show that the sedimentary record investigated by our profiles is nested in a strongly asymmetrical valley geometry, suggesting that the tectonic forcing associated with the contact between Ötztal- Ortles-Campo Nappe units has interacted closely with fluvial and/or glacial valley incision over the past millennia. We provide also a quantitative estimation of the overall thickness of sediment accumulation in the valley and allow to evaluate the complex postglacial sediment dynamics between the Adige River and the Gadria and Lasa fans, with the Gadria system playing a dominant role in terms of sediment supply.
... The mounded-to-hummocky reflectors are interpreted as debris-flow depositional lobes (with channels and levees), originating from the Gadria-Strimm system. Similar facies, albeit resolved at much higher resolution via GPR surveys, have also been described as debris-flow deposits (e.g., Ekes and Friele, 2003;Hornung et al., 2010;Franke et al., 2015). Similar facies were not observed in the Lasa fan, where the geometry of the reflectors documents that most of the fan was built by streamflows, alternating with hyperconcentrated flows. ...
We reconstruct the post−Last Glacial Maximum (LGM) evolution of the upper Adige River floodplain, Eastern Italian Alps. In particular, we are interested in constraining the time scales associated with fan building and understanding how the relevant sediment supply at tributary confluences has interacted with the Adige River to form the present landscape configuration. By combining high-resolution seismic imaging with drillhole data and radiocarbon dating, we show (i) that ∼80% of the valley fill was deposited in post-LGM times, (ii) that sediment evacuation from tributaries began with local deglaciation at the end of the Younger Dryas; and (iii) that tributary basin aspect and size, by controlling the local pattern of deglaciation, may have delayed fan building by up to two millennia. Debris-flow sediment supply from the Gadria-Strimm system drove the evolution of this valley segment between 12 and 6.25 k.y. B.P., first deflecting, then damming the course of the Adige River, forming a lake, and affecting the shape and size of the neighboring fans. Our data show an anisotropic development of the Gadria fan, with growth focused on the central and eastern portion of the fan between 10 and 8.5 k.y. B.P., followed by gradual lateral shifting toward west for about the next two millennia. The estimated sediment yield associated with the fan formation describes a debris flow−driven paraglacial sedimentary wave that conforms to the conceptual model originally proposed by Church and Ryder (1972), but never tested before in upland basins with empirical data. The wave lasted for ∼4 k.y. and around 9 k.y. B.P. peaked at ∼390,000 m3yr−1. At the valley profile scale, results suggest that similar fans functioned as effective sediment traps, which prevented, and still limit, fluvial reworking and valley floor incision. We argue that these geomorphic barriers, which have enhanced fragmentation of the valley long profile, with knickpoints located at major tributary fans, have delayed postglacial landscape recovery until today.
https://doi.org/10.1130/B31924.1
... Radar facies are defined in terms of reflection continuity, shape, dip, internal reflection configuration and external form (Neal 2004), following the terms used in seismic stratigraphy (Mitchum et al. 1977), and have been widely used to describe and classify different sedimentary structures (e.g. Van Heteren et al. 1998;Van Overmeeren 1998;Beres et al. 1999;Ekes & Hickin 2001;Moysey et al. 2006;Franke et al. 2015). ...
We evaluate the applicability and the effectiveness of integrated GPR attribute analysis to image the internal sedimentary features of the Piscinas Dunes, SW Sardinia, Italy. The main objective is to explore the limits of GPR techniques to study sediment-bodies geometry and to provide a non-invasive high-resolution characterization of the different subsurface domains of dune architecture. On such purpose, we exploit the high-quality Piscinas dataset to extract and test different attributes of the GPR trace. Composite displays of multi-attributes related to amplitude, frequency, similarity, and textural features are displayed with overlays and RGB mixed models. A multi-attribute comparative analysis is used to characterize different radar facies to better understand the characteristics of internal reflection patterns. The results demonstrate that the proposed integrated GPR attribute analysis can provide enhanced information about the spatial distribution of sediment-bodies, allowing an enhanced and more constrained data interpretation
... In civil engineering we also find various examples, such as calibration of measurements in bridges (Heikkilä et al., 2010), and assessment of bridge decks (Varnavina et al., 2015), among others. Other interesting works of varied nature have also used GPR images and 3D analysis; among these, it is worthwhile quoting the retracing of natural river courses (Slowik, 2013) the alluvial fan studies (Franke et al., 2015), and the interesting uses in humanitarian assistance and security (Núñez-Nieto et al., 2015). In these scenarios, volumes, on which profiles are taken, either in depth or surface layers, are built. ...
In this paper, a ground penetrating radar (GPR) is used as a non-destructive method to assess the buried elements of water supply systems (WSSs). The aim is the detection of various pipe materials (such as plastic and metallic, among others), and the identification of other important aspects (e.g. water leakage). This work seeks to use the visualization advantages of the subsoil characteristics provided by pre-processed GPR images. These features, which are represented as anomalies into the images, are extracted and merged to generate 3D models. The 3D representations obtained facilitate elucidation by personnel non-highly skilful in the interpretation of data from non-destructive techniques. The work is performed on GPR images of WSS pipes taken from strategic locations of urban environments. The goal is to promote the use of these technologies in the WSSs intended to generate relevant information that allows the adequate and dynamic technical management of these systems. The results and analyses are presented in this paper.
... The characteristics, morphology, and patterns and mechanisms of erosion and deposition in these flows have been very well documented (McArdell et al., 2007;Berger et al., 2011;Schürch et al., 2011), as have their contributions to catchment-scale sediment transfer (Schlunegger et al., 2009;Bennett et al., 2013Bennett et al., , 2014Burtin et al., 2014). Previous studies of the fan, however, are limited to quantification of the near-surface stratigraphy (Franke et al., 2014) and ...
Debris-flow fans form a ubiquitous record of past debris-flow activity in mountainous areas, and may be useful for inferring past flow characteristics and consequent future hazard. Extracting information on past debris flows from fan records, however, requires an understanding of debris-flow deposition and fan surface evolution; field-scale studies of these processes have been very limited. In this paper, we document the patterns and timing of debris-flow deposition on the surface of the large and exceptionally active Illgraben fan in southwestern Switzerland. We use terrain analysis, radiocarbon dating of sediment fill in the Illgraben catchment, and cosmogenic ¹⁰Be and ³⁶Cl exposure dating of debris-flow deposits on the fan to constrain the temporal evolution of the sediment routing system in the catchment and on the fan during the past 3200 years. We show that the fan surface preserves a set of debris-flow lobes that were predominantly deposited after the occurrence of a large rock avalanche near the fan apex at about 3200 years ago. This rock avalanche shifted the apex of the fan and impounded sediment within the Illgraben catchment. Subsequent evolution of the fan surface has been governed by both lateral and radial shifts in the active depositional lobe, revealed by the cosmogenic radionuclide dates and by cross-cutting geometrical relationships on the fan surface. This pattern of frequent avulsion and fan surface occupation provides field-scale evidence of the type of large-scale compensatory behavior observed in experimental sediment routing systems.
... Alluvial fan topographic responses to sediment transport are often represented via three distinct, but often interconnected ways: vertical accretion, lateral accretion, and progradation. The scale of these topographic changes can be on the order of fine-scale changes such as particle roughness (Frankel and Dolan, 2007) or coarse-scale topographic changes associated with fan-lobe formation (Franke et al., 2015) or fan segmentation (Hooke and Dorn, 1992). ...
... Unter dem Begriff Radarfazies werden abgrenzbare Bereiche gleicher Reflexionsmuster verstanden und nach folgenden Kriterien beschrieben (Payton 1977): -Amplitudenstärke, -Reflektorschärfe, -Laterale Kontinuität der Reflektoren, -Geometriebeziehung der Reflektoren zueinander. Diese Methode findet bei der sedimentologischen Analyse von Radargrammen breite Anwendung (Salat 2010, Neal 2004, Bristow & Jol 2003, Hornung et al. 2010, Franke et al. 2014, Ékes & Hickin 2001, Kjaer et al. 2004, Kostic & Aigner 2007. Sie ermöglicht es geologische Einheiten (Geokörper) auszukartieren, die aufgrund Ihrer einheitlichen Ablagerungsprozesse auch einheitliche und typische Ausbildungen ihrer Reflexionsmuster in Radargrammen zeigen. ...
Filtering and storage of precipitation, runoff, and subsequent groundwater recharge is governed by the structure and properties of the shallow subsurface and the soils formed therein. Hence, detailed knowledge about the three-dimensional structure, thickness and composition of the shallow subsurface is essential to quantify these processes; special benefit can be derived in connection with the hydraulic and material-specific properties. Geobodies can be mapped by complementary, non-invasive, geophysical methods. Associated with lithofacies, geophysical and other properties these "geobothes" can be fingerprinted. A 3D model containing e.g. porosity, field capacity, permeability, grain size and soil chemistry can be build. Geoelectrical resistance tomography and three-dimensional (3D) ground-penetrating radar surveys have been carried out in the catchment of the "Seebach" (Forbach, Bunter, Black Forest, Southern Germany). A test field was established and investigated with respect to the sedimentological and pedological architecture of the shallow subsurface, going along with lithofacies mapping, granulometry, and permeability investigations. The synthesis of all data resulted in a three-dimensional quantitative subsurface model of the shallow subsurface architecture. Together with the associated hydrological characteristics, this can serve as input parameters for water budget and sorption models.
Debris flows typically originate in mountainous watersheds. At the base of these watersheds and where not truncated by a higher order stream or discharging into a body of still water, repeated debris-flow deposition often forms semi-conical debris-flow fans. To mitigate debris-flow hazards, it is important to identify debris flow-prone watersheds and to understand their dynamics. This chapter reviews the morphology, sedimentology and dynamics of debris-flow watersheds and associated fans. Debris flow-generating watersheds are generally smaller and steeper than those dominated by floods and debris floods, and host less well-developed drainage networks. They can be roughly categorized into transport-limited systems (in which each hydroclimatic event producing high discharge triggers debris flows due to an abundance of sediment and high recharge rates) or supply-limited systems (in which debris-flow activity is limited by sediment availability and corresponding slow recharge rates). Debris-flow fans have typical lengths of 0.5–10 km and slopes of 5–15° and develop through spatio-temporal shifts of the locus of deposition through avulsion. Their surface topography and stratigraphy consist of stacked and amalgamated lobe, levee, and channel deposits, with sediment of mud to boulder grade. They provide archives of past flow processes and sediment supply indicative of past climate and environmental change. However, our ability to interpret debris-flow successions is still limited by relatively poor knowledge of how catchment geology and flow properties and composition affect resulting depositional features, from bed scale to fan scale. Recent field-based, experimental, and numerical advances on these topics are starting to fill this knowledge gap.
Sedimentary units in alluvial fans may record gradual transport and deposition during multiple floods or sediment‐laden flows or, conversely, during few catastrophic events. While outcrops are a valuable source of direct information to constrain past geomorphic and hydrologic processes, such exposures are scarce, especially along aggrading rivers or those that have been subject to recent catastrophic sedimentation. In this context, near‐surface geophysical techniques can constrain the dimensions, internal architecture, composition, and petrophysical properties of different sedimentary units. We consider the Grimmbach alluvial fan in the cuesta landscape of southwestern Germany, which was heavily impacted by sediment and wood loads during a flash flood in 2016; published radiocarbon dates indicate that at least three floods similar to the one in 2016 may have occurred since the 17th century. To test whether and to which detail near‐surface geophysics might reveal the sedimentary legacy of these floods, we survey the Grimmbach alluvial fan using detailed topographic data and geophysical imaging based on electromagnetic induction, electrical resistivity tomography (ERT), and ground‐penetrating radar. Our geophysical results indicate former channel courses and two coarse bar deposits up to 3 m below the surface, which are comparable with the more extensive bar deposits of the 2016 flood. From the ERT models, we interpret coarse, up to 5 m thick, gravel lag overlying bedrock at a maximum depth of 10 m. Our geophysical results also highlight patches of finer materials derived from gradual sedimentation and soil development. Overall, our results show that the Grimmbach alluvial fan may have formed and reshaped during catastrophic flows, which likely caused channel avulsions. Our findings point to the need to reconsider flash flood and debris‐flow hazards in similar headwaters and fans of this seemingly quiescent cuesta landscape in southern Germany.
Debris flows in alpine environments are prone to occur in the context of global climate change (i.e., elevated air temperature and higher frequency of strong precipitation events). (Alluvial) Fans often develop at the outlet of tributaries after high‐intensity debris flows. Most debris‐flow fans in alpine canyon areas extend directly to the main river channel and become the forefront of the interaction between the tributary gully and the main river channel. Clarifying the development processes/dynamics, evolutionary mechanisms and driving factors of alluvial fans would shed light on understanding the geomorphological effects and genesis of river valleys in alpine canyon areas. Here, we report the development of debris‐flow fan at the outlet of the Tianmo Gully, a formerly hazard‐free but currently hazard‐active tributary of the Parlung Tsangpo Basin, Southeast Tibet, where debris flows have occurred frequently in the last two decades. Combining remote‐sensing images, DEM data, UAV aerial photography, RTK topographic survey and other fieldwork, the development processes and morphological characteristics of the Tianmo fan under the influence of four large debris flows were analysed. Both primary events (described as episodic debris‐flow events characterized by high‐magnitude mass movement) and secondary events (corresponding to perennial stream flow processes with much lower sediment concentrations) affected the development of the Tianmo fan. Episodic debris‐flow events drastically shape the macroscopic morphology of the fan, with rapid deposition and expansion of the fan body, whereas perennial stream flow processes slowly modulate the fan during the intermittent period between debris flows, mainly with gradual retrogressive incision and lateral migration of flow channel on the fan body. Influenced by the strong sediment‐transport process of debris flows and the alluvial fan development, the planform of the Parlung Tsangpo River evolved from a relatively narrow and single‐thread pattern to an alternating‐wide‐and‐narrow pattern, with a corresponding staircase‐like longitudinal profile.
Alluvial fans are found across a range of climates and are built from a combination of fluvial and debris flow processes. Correct identification of process is critical to reconstructing the climate and water histories of alluvial fans on Earth and Mars. Theory and data from subaerial Earth fans are often used to estimate paleoflow discharges and sediment fluxes for martian fans; however, most terrestrial work has been conducted on fans that are in hot, dry climates with runoff sourced from rainfall. This differs from the prevailing interpretation that martian fans were sourced from snowmelt under warming periglacial conditions. To characterize processes and rates of periglacial fan formation, we conducted a field-based study of the Black Mountain alluvial fan in the Aklavik Range, Canada. We observed active fluvial bedload transport as well as several small debris flows that had initiated from ice-filled gullies. Following a runoff event of ∼0.005 mm/hr to ∼0.2 mm/hr across the fan, we estimated sediment fluxes of ∼0.04 m3/hr. Under bankfull conditions, we estimated runoff rates between ∼0.01 mm/hr to ∼14 mm/hr and corresponding sediment fluxes of ∼0.3 m3/hr to ∼550 m3/hr. This suggests that moderate flow events, well below the maximum runoff production rates suggested for Mars, are capable of entraining and transporting appreciable amounts of sediment by fluvial processes. However, sedimentological and geomorphological observations suggest that ∼67% of the fan was deposited fluvially; the remainder was deposited by mass flows. Our results emphasize the need to take care in interpreting martian sedimentary processes and climate from fan surface morphology alone.
Ground Penetrating Radar (GPR) is a geophysical method that uses antennas to transmit and receive high-frequency electromagnetic waves to detect the properties and distribution of materials in media. In this paper, geological observation, UAV detection and GPR technology are combined to study the recent sediments of the Yungang braided river study area in Datong. The application of the GPR technique to the description of fluvial facies and reservoir architecture and the development of geological models are discussed. The process of GPR detection technology and application includes three parts: GPR data acquisition, data processing and integrated interpretation of GPR data. The geological surface at different depths and scales can be identified by using different combinations of frequencies and antenna configurations during acquisition. Based on outcrop observation and lithofacies analysis, the Yandong Member of the Middle Jurassic Yungang Formation in the Datong Basin has been identified as a typical sandy braided river sedimentary system. The sandy braided river sandbody changes rapidly laterally, and the spatial distribution and internal structure of the reservoir are very complex, which has a very important impact on the migration and distribution of oil and gas as a reservoir. It is very important to make clear the characteristics of each architectural unit of the fluvial sand body and quantitatively characterize them. The architectural elements of the braided river sedimentary reservoir in the Datong-Yungang area can be divided into three types: channel unit, bar unit and overbank assemblages. The geological radar response characteristics of different types of sedimentary units are summarized and their interfaces are identified. The channel sediments form a lens-shaped wave reflection with a flat at the top and convex-down at the bottom in the radar profile, and the angles of the radar reflection directional axes are different on both sides of the sedimentary interface. In the radar profile, the deposit of the unit bar is an upward convex reflection structure. The overbank siltation shows a weak amplitude parallel reflection structure. The flood plain sediments are distributed continuously and stably in the radar profile, showing weak reflection characteristics. Different sedimentary units are identified by GPR data and combined with Unmanned Aerial Vehicle (UAV) detection data, and the establishment of the field outcrop geological model is completed. The development pattern of the diara is clarified, and the swing and migration of the channel in different stages are identified.
The Illgraben catchment is one of the most active torrents in the European Alps, with between 2 and 7 debris flows or similar debris floods occurring every year since the start of systematic observations from 2000 to the present. The ultimate cause of the debris-flow activity is the presence of a variety of rock types, which have been substantially deformed and fractured due to tectonic processes. The change in the orientation of the major Alpine Simplon fault line resulted in the development of many additional faults, which is the cause of the highly fractured bedrock. Sediment delivery to the torrent-channel system is dominated by landslides, the deposits of which are temporarily stored within the channel. Subsequent mobilization of sediment, mainly by intense rainfall, results in the formation of debris flows and debris floods, which entrain the sediment within the torrent system and potentially endanger the community.
Exploration and production from formations deposited in low‐gradient fluvial systems is typically associated with a high degree of uncertainty; a reflection of the inherent characteristics of these environments, notably the dominance of non‐reservoir floodplain fines, rapid lateral facies variations and associated heterogeneities at different scales. However, for a field development to be successful it becomes crucial to know the location, geometry, dimensions and connectivity of the most permeable facies, related to the main channel and the associated proximal overbank deposits (crevasse‐splay complexes). With the aim of addressing this problem, a multi‐disciplinary study is presented, combining outcrop data, high‐resolution sedimentological descriptions and advanced visualization techniques based on Digital Outcrop Models. This is compared with subsurface data from behind the outcrop (core, gamma ray and borehole images logs). The Mudstone–Sandstone Unit of the Triassic Red Beds of Iberian Meseta formation in south‐central Spain was selected for the present study. The unit is characterized by the lateral and vertical stacking of four architectural elements: (i) channelized sandstone bodies; (ii) asymmetrical sigmoidal‐shaped sandstone bodies; (iii) lobe‐shaped to sheet‐like sandstone bodies; and (iv) sheet‐like mudstones. These elements represent meandering channel, crevasse‐channel‐splay and floodplain sub‐environments, comprising a distal, low‐gradient meandering fluvial system. Together with well‐documented outcrop and core facies, calibrated log responses are also presented for the channel bodies (bell‐shape Gamma Ray profile, random azimuths and low to high dip angles), the crevasse‐splay bodies (funnel‐shape Gamma Ray profile, unidirectional azimuths and low dip angles) and the floodplain deposits (serrated Gamma Ray profile, unidirectional azimuths and very low dip angles). The full integration of outcrop and subsurface datasets has enabled generation of a robust conceptual model with predictive potential when establishing the three‐dimensional stacking of facies, distribution of heterogeneities and the connectivity between reservoir rock geobodies of primary (channel) and secondary (crevasse complex) interest in this type of fluvial reservoir.
Models to explain alluvial system development in rift settings commonly depict fans that are sourced directly from catchments formed in newly uplifted footwalls, which leads to the development of steep‐sided talus‐cone fans in the actively subsiding basin depocentre. The impact of basin evolution on antecedent drainage networks orientated close to perpendicular to a rift axis, and flowing over the developing hangingwall dipslope, remains relatively poorly understood. The aim of this study is to better understand the responses to rift margin uplift and subsequent intrabasinal fault development in determining sedimentation patterns in alluvial deposits of a major antecedent drainage system. Field‐acquired data from a coarse‐grained alluvial syn‐rift succession in the western Gulf of Corinth, Greece (sedimentological logging and mapping) has allowed analysis of the spatial distribution of facies associations, stratigraphic architectural elements and patterns of palaeoflow. During the earliest rifting phase, newly uplifted footwalls redirected a previously established fluvial system with predominantly southward drainage. Footwall uplift on the southern basin margin at an initially relatively slow rate led to the development of an overfilled basin, within which an alluvial fan prograded to the southwest, south, and southeast over a hangingwall dipslope. Deposition of the alluvial system sourced from the north coincided with the establishment of small‐scale alluvial fans sourced from the newly uplifted footwall in the south. Deposits of non‐cohesive debris flows close to the proposed hangingwall fan apex pass gradationally downstream into predominantly bedload conglomerate deposits indicative of sedimentation via hyperconcentrated flows laden with sand‐ and silt‐grade sediment. Subsequent normal faulting in the hangingwall resulted in the establishment of further barriers to stream drainage, blocking flow routes to the south. This culminated in the termination of sediment supply to the basin depocentre from the north, and the onset of underfilled basin conditions as signified by an associated lacustrine transgression. The evolution of the fluvial system described in this study records transitions between three possible end‐member types of interaction between active rifting and antecedent drainage systems: (i) erosion through an uplifted footwall, (ii) drainage diversion away from an uplifted footwall, (iii) deposition over the hangingwall dip‐slope. The orientation of antecedent drainage pathways at a high angle to the trend of a developing rift axis, replete with intrabasinal faulting, exerts a primary control on the timing and location of development of overfilled and underfilled basin states in evolving depocentres. This article is protected by copyright. All rights reserved.
A multi‐approach study is presented by combining outcrop information with data from four fully recovered cores, gamma‐ray logs, acoustic and optical tele‐viewers and five Ground‐Penetrating Radar profiles (GPR) performed behind the outcrop (so‐called Outcrop/Behind Outcrop [OBO] characterisation). A detailed analysis of tadpoles corresponding to the surfaces identified at the well walls was carried out by coupling core data with well logging and borehole imaging. GPR information allows correlation among wells in addition to providing three‐dimensionality to the architectural elements identified. All these techniques were applied to a 6.3 m‐thick and 100 m‐wide, asymmetric wedge‐shaped sandstone geo‐body interpreted as a single‐storey meander belt in the distal alluvial plain of the Triassic Red Beds of the Iberian Meseta (TIBEM formation) in south‐central Spain. The architectural element analysis on outcrop allowed differentiation of the subenvironments of the main channel, point bars and chute channels. The main‐channel element was characterised by a fining and thinning upward succession in which three parts can be distinguished corresponding to the active‐channel stage, the progressive abandonment and a final mud plug. The tadpoles on the margin of the channel indicate a consistent dip with the underlying lateral accretion units (LAUs) with a decreasing inclination upward. The heterolithic interval of the progressive abandonment is characterised by radar facies in which mounded and subparallel reflectors alternate. The lateral accretion units of the point bars are characterised by a poorly defined bell‐shaped GR curve with anomalously high API values at the lowermost 50 to 60 cm due to the abundance of mud clasts. Other intervals of unexpectedly high API values at the intermediate‐upper part of the curve correspond to small, hanging excavated channels. The cross beds, that result from the migration upward of megaripples over the LAUs, appear both in the core and in the GPR to be false horizontal bedding. The erosional scars identified in outcrop and core at the base and within the chute channels correspond to concave‐up reflectors in GPR. These channels are filled with rippled sandstones that give rise to very low‐amplitude radar facies. The high‐resolution characterisation derived from this workflow highlights its great applicability to the study of other non‐outcropping ancient meander belts in which more robust sedimentary models are required, such as in geo‐steering operations for enhanced oil recovery.
The paper reviews an application of non-destructive electromagnetic imaging of shallow bedrock and landslide colluvium horizons performed with ground-penetrating radar (GPR) technique on mass movement-affected mountain slope. We used a non-shielded 52 MHz GPR equipment to study an area of a shallow translational landslide, which developed on steeply inclined gneissic bedrock on Mt. OEredniak slopes (1210 m a.s.l.) in the OEnie¿nik Massif. This landslide originated at the boundary zone between intact bedrock comprising Proterozoic gneisses and uppermost slope cover, as a result of continuous rainfall during July of 2011. Furthermore , to better understand and examine a landslide area on Mt. OEredniak slopes we also applied structural geological and geomorphological methods. The GPR analyses resulted in high-resolution imaging of internal slope structure and gravitational deposit architecture in the range of 0.5-5 m below surface level. Electromagnetic sounding performed directly above the landslide source area elucidated a set of bedrock discontinuities with a possible direct impact on water aggregation and migration during the rainfall episodes. Furthermore, a GPR profile performed in a landslide toe area, showed subsurface reflection horizons to be correlated with a colluvium/bedrock transitional zone and internal heterogeneous architecture of colluvial deposits. Ground-penetrating radar proved to be both powerful and an easy-maintained 'on-site' method for steep mountain slope analysis, with a potential for high-resolution imaging of shallow-seated gravitational slope deformations.
In alpine environment, alluvial fan architecture can reveal important information about the landscape geomorphic evolution and the climate change. The information about alluvial fan morphology and sedimentology can be obtained by a high-resolution geophysical approach. In this work, we acquired and processed a ∼4 km long high-resolution seismic reflection profile across a representative transect of Val Venosta, over the Gadria fan, Eastern Alps, Italy, using non-conventional acquisition and processing approaches. We tested Dense-wide aperture arrays (DWA) and Common Reflection Surface stack (CRS) in a complex environment, in order to obtain seismic data with a quality and resolution adequate to: 1) study the internal reflective configuration of the fan; 2) image both the pattern of the bedrock below the valley and thickness of the sediment accumulation above it; 3) evaluate the geometrical relationships between the Gadria Fan and the Adige River sediments. By the analysis of our results, we can deduce that DWA seismic data in combination with high-resolution CDP/CRS processing can provide complimentary and low-cost information to aid the study of alluvial fans in alpine environments.
Ground-penetrating radar (GPR) was used to explore alluvial-fan complexes on the piedmont slopes of higher mountains in the
Blue Ridge province of North Carolina. On young fans with relatively unweathered surfaces, GPR penetration reached 16 m with
100 MHz antennae and 25 m with 25 MHz antennae. Penetration appears to be deepest near fan apexes. As the fans are composed
mainly of bouldery debris flow deposits, the internal structures revealed by GPR profiles are few. The typical profile has
a chaotic appearance and is composed of numerous discontinuous reflectors with varying dips and diffraction hyperbolas produced
by boulders. On old abandoned fans that have been subjected to intense weathering, boulders in the deposits have decomposed
and structures subparallel to the surface are more likely to be seen. Continuous reflectors that may indicate contacts between
depositional units, buried soils, or groundwater tables, however, are rare in both kinds of fans. Generally radar velocity
and penetration are greatest on young fans, less on old fans, and least on saprolite.
Rapid mass movements such as avalanches, debris flows, and rock fall are periodic or episodic phenomena that occur in alpine
regions. Recent studies have shown that debris flows generate characteristic signals in the low-frequency infrasonic spectrum
(4–15 Hz). Infrasound can travel thousands of kilometers and can still be detectable. This characteristic provides a basis
for the development of wide area automated monitoring systems that can operate in locations unaffected by the activity of
the process. This study focuses on the infrasound vibrations produced by a debris flow at the Lattenbach torrent, Tyrol (Austria),
and by two events at the Illgraben torrent, Canton of Valais (Switzerland). The Lattenbach torrent is a very active torrent,
which is located in the west of Tyrol in a geologic fault zone between the Silvrettakristallin and the Northern Limestone
Alps. It has a large supply of loose sediment. The Illgraben torrent, which is well known for its frequent sediment transport
and debris flow activity, has been equipped with instruments for debris flow monitoring since the year 2000. This study shows
that debris flow emits low-frequency infrasonic signals that can be monitored and correlated with seismic signals. During
the passage of the debris flow, several surges were identified by ultrasonic gauges and detected in the time series and the
running spectra of infrasonic data.
Book synopsis: Ground-penetrating radar (GPR) is a rapidly developing field that has seen tremendous progress over the past 15 years. The development of GPR spans aspects of geophysical science, technology, and a wide range of scientific and engineering applications. It is the breadth of applications that has made GPR such a valuable tool in the geophysical consulting and geotechnical engineering industries, has lead to its rapid development, and inspired new areas of research in academia. The topic of GPR has gone from not even being mentioned in geophysical texts ten years ago to being the focus of hundreds of research papers and special issues of journals dedicated to the topic. The explosion of primary literature devoted to GPR technology, theory and applications, has lead to a strong demand for an up-to-date synthesis and overview of this rapidly developing field. Because there are specifics in the utilization of GPR for different applications, a review of the current state of development of the applications along with the fundamental theory is required. This book will provide sufficient detail to allow both practitioners and newcomers to the area of GPR to use it as a handbook and primary research reference.
The Swiss historical earthquake catalogue and the macroseismic database have not been significantly improved since 1978. We therefore revised the catalogue and concluded this work in 2002. Three levels of investigation were conducted, depending on the size and location of an event: historical, macroseismic and seismological. For the earthquakes of the last 1000 years with Intensity VI or higher, all available historical information was collected and macroseismic fields were established. The source parameters (epicenter, hypocentral depth class, epicentral intensity, maximum intensity, macroseismic magnitude) and their uncertainties were then determined. Earthquakes with epicentral intensity smaller than VI that occurred inside Switzerland have been reviewed for the period since 1878, or when information was found in historical sources. In total, more than 600 events have been reassessed through historical investigations. Of these events, 177 earthquakes reach intensity VI in the new catalogue and therefore caused damage. About 260 events could be identified as fake events or multiple entries for the same event due to different calendar styles, misprints, or misinterpreted compilations. The catalogue provides a uniform estimate of the moment magnitudes Mw for all events. This uniform earthquake size estimate in terms of magnitude required a magnitude/intensity calibration and reassessment of the instrumental magnitude. Our new earthquake catalogue and the related macroseismic database can be accessed via the Webpage of the Swiss Seismological Service (http://seismo. ethz.ch) The catalogue covers the region included in the Swiss national map at the scale of 1:500'000 (Swiss km-coordinates: 460-880/20-310; Geographic coordinates: 5.6-11.1E/45.3-47.9N).
The Neogene Betic Basins. Geological Context. During the Neogene, sedimentation in the Betic Cordillera took place in two geody-namically different phases. During the first of these (Early and Middle Miocene) the Betic basins evolved simultaneously with the main movements of orogenic structur-ing of the Cordillera, which were the collision between the Alboran Microplate (that would later make up the Internal Zones) and the South-Iberian Palaeomargin (whose deformed rocks made up the External Zones), together with the extensional detach-ments of the former and overthrusts in the latter of these domains (Vera, 2001). In this first, markedly synorogenic phase, a number of basins formed within the orogene (to the South), known as Intrachain Basins, as well as a foreland basin outside it (to the North), known as the North-Betic Strait, Proto-Guadalquivir Basin and North-Betic Foreland Basin (Sanz de Galdeano and Vera, 1992; Soria, 1993; Viseras et al., 2004). The sediments filling them, particularly the intrachain basins, are intensely deformed by Betic orogeny, which prevents detailed understanding of their original palaeogeo-graphic boundaries. The second geodynamic phase in which Neogene sedimentation occurred coincided with the Neotectonic Stage (Late Miocene to Quaternary). The main features of the orogene had already been determined and tectonic activity cen-tred on the convergence of Africa and Iberia. This was the context in which the Pos-torogenic Basins formed, which are located on both Internal and External Zones and on the contact between the two.
Difficulty in successfully applying time-independent equilibrium concepts to the alluvial fan problem required the integration of equilibrium and evolutionary approaches. Reconciliation of these two competing concepts was achieved by considering the time span over which equilibrium is viewed. The resulting integrated approach to the fan dynamics paradigm involves the investigation of depositional processes in different environments and the historical analysis of long-term fan evolution. -from Author
This paper evaluates the recent claim made by Weissmann et al. (2010) that deposits of “Distributive Fluvial Systems” (DFS) may form the bulk of the continental fluvial record. Weissmann et al. (2010) define DFS as “a pattern of channel and floodplain deposits that radiate outward from an apex that is located where the river enters the sedimentary basin”. As such, DFS are fan-like systems on which multiple channels coexist and distribute water and sediment across the fan. Published criteria for the recognition of DFS (Weissmann et al., 2010) are 1) a radial pattern of channels from the DFS apex; 2) downslope decreases in channel size; 3) down-DFS grain-size decreases; and 4) a lack of lateral channel confinement.
Within sedimentological studies, ground penetrating radar (GPR) is being used with increasing frequency because it yields images of the shallow subsurface that cannot be achieved by any other non-destructive method. The purpose of this paper is to provide an introduction to the collection, processing and interpretation of GPR data so that future sedimentary studies can be improved. With GPR equipment now being lightweight, robust and portable, proper data collection and survey design methods need to be followed in order to acquire high resolution, subsurface digital data. Various factors are discussed including: Reflection profiling, velocity soundings, test surveys, topography, logistics, data quality and extreme environments. Basic data processing and visualization are then reviewed, followed by a discussion on GPR interpretation strategies including a background to radar stratigraphy. For the sedimentary geologist or geomorphologist, GPR offers unique data of the shallow subsurface including stratigraphy, geometry, architecture and structure.
Extract
This Special Publication is a collection of papers which identifies, describes, and interprets the occurrence of palaeosurfaces in the geological record. The concept of a palaeosurface is one which is generally understood across the geomorphological and geological sciences but, according to discipline and application, often differs in the emphasis and detail of its interpretation. In order to encompass the widest range of contributions and views upon the subject of palaeosurfaces, a broad remit was deliberately adopted during the preparation of this volume.
Background and objectives
Many working groups within the geological and geomorphological sciences share a common link through the Geological Society, and it is hoped that this volume will further illustrate the potential of cross-disciplinary study. Geology and geomorphology, though often approached by different research schools, are both expressions of complex Earth systems and as such can rarely be treated independently. Since the investigation of palaeosurfaces requires an understanding of both geomorphological and geological processes, their study is clearly a theme which demands this type of cross-disciplinary approach. Therefore, the aim of this volume is to bring together expertise from a variety of fields by researchers in both the geological and geomorphological disciplines who have adopted such a combined approach to palaeosurface research.
Contributions have been encouraged from the fields of geomorphology, geology, geochemistry, palynology and palaeoenvironmental studies. The papers include studies of geomorphological evolution, reconstruction of palaeolandscapes, lateritization and bauxitization, palaeo-karstification, sequence stratigraphy, geochemistry of rock alteration, the preservation of palaeosurface elements in both glaciated and sub-tropical regions, and the use
Sieve deposits were once considered to be one of the building blocks in alluvial fan stratigraphy. Later reinterpretation of sieve lobes as debris-flow deposits, favored because no visual records of active sieve deposition had been reported, undermined their significance, divided opinions, and left this issue unresolved. Here I document active deposition of sieve lobes in natural settings, in support of the original model. Sieve deposition can easily occur in natural settings such as proglacial outwash fans, small arid alluvial fans, or perennial streams when there is a scarcity of fine material, significant bedload, high slope, permeable ground, and discharges moderate enough to allow infiltration. The only hydrodynamic requirement for sieve deposition is a high rate of water loss promoted by permeable bed sediments. Under some circumstances alluvial fans can be built almost entirely of sieve deposits, as shown here. One effect of the rapid extraction of water is the creation of sigmoidal fan profiles. A gradation from sieve deposition to sheetflood occurs if sediment becomes progressively less permeable or if water flow increases, overcoming bed permeability. Sieve deposition is a universal depositional process based simply on infiltration, and it explains matrix-poor clast-supported gravels, while alternative hypotheses, such as matrix winnowing of debris flows used to dispute the sieve model, still need to be proven by observations in nature.
Alluvial fans were studied in the field, largely in the desert regions of California, and in the laboratory. Field study consisted of detailed mapping of parts of four fans and reconnaissance work on over one hundred additional fans. Features mapped included the nature and age of deposits, material size, and channel pattern. In the laboratory small alluvial fans were built of mud and sand transported through a channel into a 5-foot by 5-foot box under controlled conditions. Material is transported to fans by debris flows or water flows that follow a main channel. This channel is generally incised at the fanhead, because there water is able to transport on a lower slope the material deposited earlier by debris flows. The main channel emerges onto the surface near a midfan point, herein called the "intersection point." On laboratory fans most deposition above the intersection point is by debris flows that exceed the depth of the incised channel. Fluvial deposition dominates below the intersection point. This depositional relation probably also occurs on natural fans. On fans deficient in fine material large discharges may infiltrate completely before reaching the toe of the fan. Coarse debris is then deposited as lobate masses, herein called "sieve deposits." In many respects sieve deposits resemble debris-flow deposits, but they lack primary fine material, and fresh lobes are highly permeable.
Using results from an 8 m2 instrumented force plate we describe field measurements of normal and shear stresses, and fluid pore pressure for a debris flow. The flow depth increased from 0.1 to 1 m within the first 12 s of flow front arrival, remained relatively constant until 100 s, and then gradually decreased to 0.5 m by 600 s. Normal and shear stresses and pore fluid pressure varied in-phase with the flow depth. Calculated bulk densities are rho b = 2000-2250 kg m-3 for the bulk flow and rho f = 1600-1750 kg m-3 for the fluid phase. The ratio of effective normal stress to shear stress yields a Coulomb basal friction angle of $\phi$ = 26° at the flow front. We did not find a strong correlation between the degree of agitation in the flow, estimated using the signal from a geophone on the force plate, and an assumed dynamic pore fluid pressure. Our data support the idea that excess pore-fluid pressures are long lived in debris flows and therefore contribute to their unusual mobility.
The alluvial-fan deposits in the Cretaceous Yongdong Basin, Korea, consist of conglomerates with a muddy or sandy matrix and sandstones with thick or thin laminations. The conglomerates and sandstones occur commonly in couplets, constituting apparently single sedimentation units. Facies transitions in the deposits can be summed up in a tripartite facies sequence: (1) a clast-supported conglomerate with a muddy or sandy matrix and parallel clast alignment (facies A and B), (2) a matrix-supported coarse-tail normally graded conglomerate with random clast orientation (facies C) and thickly stratified pebbly sandstone (facies D), and (3) laminated sandstone (facies E). The clast-supported conglomerate is interpreted as deposits of debris flows dominated by frictional grain interactions. Development of pervasive parallel clast alignment, lacking large floating clasts and inverse grading, suggests deposition via incremental aggradation rather than en masse freezing. The matrix-supported conglomerate and thickly stratified sandstone are interpreted as deposits of dense inertia layers or traction carpets developed beneath a high-concentration bipartite flow. The laminated sandstone indicates traction sedimentation associated with dilute flows. The facies sequence therefore suggests deposition from a composite sediment flow that comprises a preceding debris flow, a trailing watery flow, and an intermediate flow between. The intermediate flow is regarded as a hyperconcentrated flow on the basis of its bipartite nature because a hyperconcentrated suspension has a meager yield strength and is prone to be density stratified. The measured section comprises three depositional sequences, decameters thick and separated by thick mudstone beds, which could be interpreted in terms of fan evolution (progradation and retreat) under an influence of changing sediment supply from a drainage basin. Close association of sediment type with constituent facies in the three sequences suggests that composite sediment-flow deposits are favorably developed by sand-matrix debris flows drained from large and less rugged catchments.
In the Obernberg valley, the Eastern Alps, landforms recently interpreted as moraines are re-interpreted as rock avalanche deposits. The catastrophic slope failure involved an initial rock volume of about 45 million m³, with a runout of 7.2 km over a total vertical distance of 1330 m (fahrböschung 10°). 36Cl surface-exposure dating of boulders of the avalanche mass indicates an event age of 8.6±0.6 ka. A 14C age of 7785±190 cal yr BP of a palaeosoil within an alluvial fan downlapping the rock avalanche is consistent with the event age. The distal 2 kmof the rock-avalanche deposit is characterized by a highly regular array of transverse ridges that were previously interpreted as terminal moraines of Late-Glacial. ‘Jigsaw-puzzle structure’ of gravel to boulder-size clasts in the ridges and a matrix of cataclastic gouge indicate a rock avalanche origin. For a wide altitude range the avalanche deposit is preserved, and the event age of mass-wasting precludes both runout over glacial ice and subsequent glacial overprint. The regularly arrayed transverse ridges thus were formed during freezing of the rock avalanche deposits.
Classifications of flowing sediment-water mixtures have, in the past, been based primarily on relative, qualitative differences in the style and rate of movement as well as on morphology and sedimentology of deposits. A more quantitative and physically relevant classification is presented here, based on thresholds in rhéologie behavior. The classification is constructed on a two-dimensional matrix in which flows are located according to deformation rate (mean velocity) and sediment concentration, with composition of the mixture constant. Three major rhéologie boundaries are crossed as sediment concentration increases from 0 (clear water) to 100 percent (dry sediment): (1) the acquisition of a yield strength-the transition from liquid "normal streamflow" to plastic "hyperconcentrated streamflow"; (2) an abrupt increase in yield strength coinciding with the onset of liquefaction behavior-the transition to "slurry flow"; and (3) the loss of the ability to liquefy-the transition of "granular flow." These three rhéologie boundaries shift according to particle-size distribution and composition of the mixture. Processes controlling flow behavior depend on deformation rate (velocity). Rateindependent frictional and viscous forces dominate at lower velocities and in finer grained mixtures; rate-dependent inertial forces dominate at higher velocities and in coarser grained mixtures. As velocity increases, grain-support mechanisms change from low-energy varieties (buoyancy, cohesion, structural support) to progressively higher energy mechanisms (turbulence, dispersive stress, fluidization). Existing nomenclatures of geologic flow phenomena can fit within this rhéologie classification. The morphology and sedimentology of flow deposits commonly can be used to deduce rhéologie behavior, but caution needs to be exercised in inferring processes from deposits.
This is the first book to deal comprehensively with Spain's tectonic and sedimentary history over the past sixty or so million years. During Tertiary times, Spain had suffered compressional collision between France and Africa, and its Atlantic and Mediterranean coasts had been further modified by extensional rifting. This study will therefore be of interest to earth scientists generally because of the insights it provides into continental crustal deformation. Spain contains some of the best exposed outcrop geology in Europe. Because it includes sectors of two separate foreland basins, and an intervening craton with basins that have been influenced by extensional and strike-slip deformation, it provides excellent material for the development and testing of theories on the study of sedimentary basin formation and filling.
Many friction relations or flow laws have been proposed to describe the flow and stopping behavior of debris flows. Practical application requires knowledge of the typical range of parameters as well as knowledge of the suitability of the flow laws to the torrent under investigation. Here we systematically compare a wide variety of debris flow laws using two one dimensional numerical simulation models of debris flows and field data from an automated debris flow observation station at the Illgraben torrent, Switzerland. Both models solve the shallow water equations and incorporate a frictional resistance term that describes the properties of flowing debris. The DFEM model uses the finite element method; debris flow friction relations, or flow laws, include the Voellmy fluid, simplified Bingham, and dilatant/grain shearing relations. The WAF-DF is based on the Weighted Average Flux method and has been successfully applied to describe debris flow propagation and the propagation of roll waves superimposed on debris flows. Debris flow laws include the Herschel-Bulkley and general viscoplastic formulations. Both models are compared with field observations to provide the closest match with the observations, providing typical values of debris flow parameters for the various flow laws.
Presents details of the processes and products of present-day alluvial systems which are divided for convenience into 4 groups, namely bedload streams, alluvial fans, meandering streams and anastomosing streams. Interchannel processes and products are treated separately. Examines the array of facies present in ancient alluvial sequences and explores the ways in which they are organized, giving a basis for interpreting the rock record in terms of present-day systems and also pointing to ways in which some ancient systems must have differed from present-day examples. - after Author
Recent development of fluvial facies models has been due to improved description of natural river and floodplain processes and deposits using: (1) ground-penetrating radar (GPR) combined with cores and trenches to describe modern deposits in 3D; (2) study of frozen rivers to allow easy access to the entire channel belt and procurement of undisturbed cores; (3) optically stimulated luminescence (OSL) for improved dating of deposits; (4) high-resolution remote sensing over large areas and at short time intervals in order to determine temporal changes in channel and floodplain geometry due to erosion and deposition; (5) new measuring equipment such as acoustic Doppler current profilers (ADCP), high-resolution multibeam sonar, and GPS, for measuring surface topography, flow, and sedimentary processes. However, there is still a lack of studies of river geometry, flow, and sedimentary processes at the all-important high flow stages, especially on big rivers and floodplains.
Laboratory studies of bed geometry, flow, and sediment transport, erosion, and deposition have been undertaken for a range of scales, from small bedforms such as ripples, dunes, and antidunes, to bars and channels, to whole channel belt–floodplain systems. Controls on river and floodplain mechanics such as sediment supply, base level ,and tectonism have also been evaluated. However, there are scaling problems with laboratory experiments that become more acute as the scale of the system increases.
The new field and laboratory data have allowed development of new qualitative and quantitative fluvial depositional models. Such models account for the fact that: (1) there are different superimposed scales of fluvial forms and associated stratasets in rivers and floodplains; (2) the geometry and mode of migration of any scale of fluvial form (e.g., dune, bar, channel, channel-belt) is closely related to the geometry and internal character of the associated strataset, which allows development of generalized depositional models for the different scales; (3) changes in flow stage over various time scales affect the nature of deposits. These new models use consistent descriptive terminology and dispel many of the extant misconceptions about fluvial deposits.
Quantitative, process-based models of fluvial deposits exist, but are not well developed, especially for the longer-term and larger-scale processes and deposits. Process-based models of the effects of tectonism, climate, and base-level change on fluvial deposits are in their infancy. Furthermore, most models are difficult to test. These problems with quantitative models are due to lack of appropriate quantitative data, and difficulties in mathematical modeling of complex natural systems. As a result of this, stochastic models are commonly used to represent fluvial stratigraphy, given initial data from wells, cores, and geophysical surveys. Development of quantitative models is essential if we are to understand and predict the nature and spatial distribution of ancient fluvial deposits, and to characterize aquifers and hydrocarbon reservoirs for subsurface fluid flow simulations. Such development will require more studies of rivers and floodplains during floods, and more mathematical sophistication.
Major interruptions to the sediment cascade occur at a variety of temporal and spatial scales, ranging from small, short-term and ephemeral zones of deposition to larger more persistent features in the landscape. Sediment storage zones often occur at changes or breaks in the boundary conditions of the sediment pathway. Such zones are characterized by distinctive landforms (debris cones and alluvial fans) and have important effects on the dynamics of the system, which produce 'coupling or buffering' relationships within the sediment pathway. To understand sediment flux through alluvial-fan and debris-cone environments requires consideration of the controls involved, their spatial-temporal relationships and their relations with an absolute chronology. Past research has followed separate lines focusing on geology and sedimentology, with emphasis on tectonic controls, or on geomorphology, with emphasis on climatic controls. More recent approaches allow a quantitative treatment of debris cones and alluvial fans as part of a continuum within the sediment cascade.
The fan formed on 15 July 1982 by a catastrophic flood that was generated by a dam failure. The fan covers an area of 0.25 square km, has a radial length of 0.7 km, and is up to 14 m thick. Sedimentation occurred in three phases, each producing a distinct fan lobe. Much of the present fan surface consists of braided channels that formed by erosion into the sheetflood deposits by noncatastrophic discharge. -from Author
We document initiation and flow processes, deposit facies, and geomorphic effects of forest-fire-related sedimentation on small alluvial fans in Yellowstone National Park. Brief, intense convective-storm precipitation on steep basins burned in the 1988 fires produced sedimentation events involving a variety of depositional processes on fans. Over the course of all documented events, flows on fans progressed from higher to lower sediment concentration. Events were often dominated by either debris flows or relatively sediment-poor streamflow processes; in some events, however, flows ranging a over wide spectrum of sediment concentration produced significant fan deposits. Debris flows were generated by progressive sediment bulking involving pervasive surface runoff and rill erosion on steep upper basin slopes, followed by deep incision as flows progressed down channels. Debris-flow deposits show a marked decline in thickness and coarse gravel content downfan, often with extensive distal gravel-poor facies. We recognized a relatively minor percentage of noncohesive debris-flow and hyperconcentrated-flow facies, with sorting and stratification intermediate between muddy debris-flow and streamflow facies; these were deposited where dilute flows bulked with coarse sediment by eroding channel alluvium or earlier deposits of the event. Below incised fan channels, streamflows expanded as sheetfloods, which prograded lower fans with distally fining deposits. Basins > 3 km 2 typically produced streamflow events on fans, but sediment texture and availability on slopes and in channels are primary factors determining flow processes on fans of smaller basins. Burned soil surfaces provided abundant silt and clay for debris-flow generation, but because soil surface sediment was stripped and/or compacted over time, the lack of available fines resulted in dominance of streamflow processes in later events.
We present a probabilistic sediment cascade model to simulate sediment transfer in a mountain basin (Illgraben, Switzerland) where sediment is produced by hillslope landslides and rockfalls and exported out of the basin by debris flows and floods. The model conceptualizes the fluvial system as a spatially lumped cascade of connected reservoirs representing hillslope and channel storages where sediment goes through cycles of storage and remobilization by surface runoff. The model includes all relevant hydrological processes that lead to runoff formation in an Alpine basin, such as precipitation, snow accumulation, snow melt, evapotranspiration, and soil water storage. Although the processes of sediment transfer and debris flow generation are described in a simplified manner, the model produces complex sediment discharge behavior which is driven by the availability of sediment and antecedent wetness conditions (system memory) as well as the triggering potential (climatic forcing). The observed probability distribution of debris flow volumes and their seasonality in 2000-2009 are reproduced. The stochasticity of hillslope sediment input is important for reproducing realistic sediment storage variability, although many details of the hillslope landslide triggering procedures are filtered out by the sediment transfer system. The model allows us to explicitly quantify the division into transport and supply-limited sediment discharge events. We show that debris flows may be generated for a wide range of rainfall intensities because of variable antecedent basin wetness and snowmelt contribution to runoff, which helps to understand the limitations of methods based on a single rainfall threshold for debris flow initiation in Alpine basins.
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SE - 248
ID - 683
This paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research. Sediments are a product of mass dispersal at the Earth surface and take part in global cycles. Sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface. This involves fundamental questions about the interplay of uplift, climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion, reservoir siltation, and coastal protection. First, after introducing basic concepts, relevant scales and methodologies, the different components of Quaternary routing systems from erosion in headwaters, river systems, glacial and paraglacial systems, lakes, deltas, estuaries, coasts, shelves, epicontinental seas, and deep-sea fans are discussed in terms of their sediment budget. Most suitable are sedimentologically closed or semi-closed depositional environments e.g. alluvial fans, lakes, deltas and deep-sea fans. In a second step, the dynamics of passive, active, and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced. Ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings. In terms of sedimentary basin types, rifts, intracontinental and epicontinental settings are preferred objects of sediment budgets, because of their persistence and relatively simple overall sedimentary architecture. However, closing basins, such as foreland, forearc, retroarc, piggy-back and wedge-top basins may provide excellent snapshots of orogenic sediment fluxes. In a third step, the large long-lived routing systems of the Amazon, the Ganges-Brahmaputra, and the Rhine are reviewed. For each system estimates of either sediment volumes (mass) or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the Late Glacial Maximum as well as the Cenozoic. Following lessons can be taken from these case studies: (i) depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems, (ii) the response times of these large systems are within the Milankovich time interval, thus lower than predicted from diffusion models, (iii) cyclic routing of sediments in continental basins is much more dominated by climate (human) control than by eustacy. and (iv) at long time scales, ultimate sinks win over intermittent storage. It is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles. This includes (i) to better determine response times of large routing systems by linking Quaternary with Cenozoic sediment budgets and continental with marine sub-systems, (ii) to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems, (iii) to study sediment partitioning at the basin scale, (iv) to reconcile continental, supply-dominated sequence stratigraphy with the eustatic-dominated marine concept, and (iv) to account for non-actualism of ancient systems with respect to their erosion and transport mode, in particular, during glaciations and pronounced arid intervals. Glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins, thus challenging the principle of mass conservation.
Dendrogeomorphological analyses of trees affected by debris flows have regularly been used to date past events. However, while previous studies in the Swiss Alps have focused primarily on granitic and gneissic debris-flow material and on Larix decidua Mill. and Picea abies (L.) Karst. trees, they have – at the same time – widely disregarded torrents dominated by finely fractured calcareous and dolomitic lithologies and forests populated with Pinus sylvestris L. In this paper, we report on results obtained from a debris-flow cone in the Rhone valley (Valais, Switzerland) where very fine and muddy material (limestone, dolomite, quartzite and calcite) occasionally affects P. sylvestris trees. Based on the results of a geomorphic map, 1004 increment cores from 451 disturbed P. sylvestris, 37 L. decidua and five P. abies trees were sampled, allowing reconstruction of 15 events between AD 1793 and 2005 as well as the determination of breakout locations of events. From the data, it also appears that debris-flow material only rarely left the incised channel over the last 200 years and that overbank sedimentation events did not occur after 1961, when a rockslide delivered large amounts of erodible material and subsequent debris flows caused an important incision of the canyon on the cone.
Cheekye River fan is the best-studied fan complex in Canada. The desire to develop portions of the fan with urban housing triggered a series of studies to estimate debris-flow risk to future residents. A recent study (Jakob and Friele 2010) provided debris-flow frequency-volume and frequency-discharge data, spanning 20-year to 10,000-year return periods that form the basis for modeling of debris flows on Cheekye River. The numerical computer model FLO-2D was chosen as a modelling tool to predict likely flow paths and to estimate debris-flow intensities for a spectrum of debris-flow return periods. The model is calibrated with the so-called Garbage Dump debris flow that occurred some 900 years ago. Field evidence suggests that the Garbage Dump debris flow has a viscous flow phase that deposited a steep-sided debris plug high in organics in centre fan, which then deflected a low-viscosity afterflow that travelled to Squamish River with slowly diminishing flow depths. The realization of a two-phase flow led to a modelling approach in which the debris-flow hydrograph was split into a high viscosity and low viscosity phase that were modelled in chronologic sequence as two separate and independent modelling runs. A perfect simulation of the Garbage Dump debris flow with modelling is not possible because the exact topography at the time of the event is, to some degree, speculative. However, runout distance, debris deposition and deposit thickness are well known and serve as a good basis for calibration. Predictive analyses using the calibrated model parameters suggest that, under existing conditions, debris flows exceeding a 50-year return period are likely to avulse onto the southern fan sector, thereby damaging existing development and infrastructure. Debris flows of several thousand years return period would inundate large portions of the fan, sever Highway 99, CN Rail, and the Squamish Valley road and would impact existing housing development on the fan. These observations suggest a need for debris-flow mitigation for existing and future development alike.
In recent years the upper Rhone Valley has been one of the most intensively investigated regions by the Swiss Seismological Service. The high seismicity in the region encourages research in the seismological field and one main focus has been historical seismology. This report presents the state of the art of our historical investigations by giving an overview of the effects of four damaging earthquakes with intensity larger than VII, for which a fairly large number of documents could be found and analyzed. The overview includes the events of 1584 (Aigle, epicentral intensity VIII), 1755 (Brig, epicentral intensity VIII), 1855 (Visp, epicentral intensity VIII), and 1946 (Sierre, epicentral intensity VIII for the main shock and intensity VII for the largest aftershock). The paper focuses mainly on primary and secondary effects in the epicentral region, providing the key data and a general characterization of the event. Generally, primary effects such as the reaction of the population and impact on buildings took more focus in the past. Thus building damage is more frequently described in historic documents. However, we also found a number of sources describing secondary effects such as landslides, snow avalanches, and liquefaction. Since the sources may be useful, we include citations of these documents. The 1584 Aigle event, for example, produced exceptional movements in Lake Geneva, which can be explained by an expanded sub aquatic slide with resultant tsunami and seiche. The strongest of the aftershocks of the 1584 event triggered a destructive landslide covering the villages Corbeyrier and Yvorne, VD. All macroseismic data on the discussed events are accessible through the webpage of the Swiss Seismological Service (http://www.seismo.ethz.ch).
Complex and rugged topography induces large variations in erosion and sediment delivery in the headwaters of alpine catchments. An effective connection of hillslopes with the channel network results in highly efficient sediment transfer processes, such as debris flows. In contrast, morphological conditions producing decoupling of hillslopes from channels (e.g. glacial cirques) may exclude large areas of the catchment from sediment delivery to its lower parts. Moreover, an efficient connection between hillslopes and channel network does not always ensure an effective downstream transfer of sediment. Low-slope channel reaches (e.g. in hanging valleys) cause sediment deposition, which often results in changes of the sediment transport processes, typically from debris flow to streamflow with low bedload and suspended load rates. The availability of high-resolution digital terrain models, such as those derived from aerial LiDAR, improves our capability to quantify the topographic controls on sediment connectivity. A geomorphometric index, based on the approach by Borselli et al. (2008), was developed and applied to assess spatial sediment connectivity in two small catchments of the Italian Alps featuring contrasting morphological characteristics. The results of the geomorphometric analysis were checked against field evidences, showing good performance and thus potential usefulness of the index.
Erosional denudation of the Alps and their role as sediment source underwent major changes throughout the Quaternary, by repeated glaciation and deglaciation. The sediment fluxes of 16 major Alpine drainage basins were quantified by determining the sediment volumes which have been trapped in valleys and lake basins. These became sedimentologically closed after the last glacier retreat around 17 000 cal. BP. The sediment volumes distributed over their provenance areas yield mean mechanical denudation rates between 250 to 1060 mm ka–1. In contrast, modern denudation rates, derived from river loads and delta surveys, range from 30 to 360 mm ka–1. Relief, such as mean elevation and slope, turned out to be the primary control of both modern and Late Glacial mechanical denudation. Rock types seem to be responsible for some scatter of the data, but their role is masked by other factors. Modern denudation rates increase with higher proportions of bare rocks and glaciated area, but decrease with forest cover. An area-weighted extrapolation of the studied drainage basins to the entire Alps on the basis of major morphotectonic zones yields a mean denudation rate of 620 mm ka–1 over the last 17 000 years. This rate clearly exceeds the modern rate of 125 mm ka–1. Lake sediments and palaeoclimatic reconstructions confirm that the sediment yield of the Alps reached a maximum during deglaciation when large masses of unconsolidated materials were available, vegetation was scarse, and transport capacities were high. During the early Holocene sediment yield declined to a minimum before some climate deterioration and human activities again accelerated erosional processes. Assuming a denudation rate in the early Holocene half of the modern one, the Late Glacial denudation rates must have been in the order of 1100 to 2900 mm ka–1. Consequently, denudation rates during a glacial/interglacial cycle probably varied by a factor of 14, which lies well within the range of other studies in central Europe, Scandinavia and North America. From large scale sediment budgets of perialpine sedimentary basins the overall denudation rate of the Alps during the Quaternary has been c. 400 mm ka–1, i.e. about one third lower than the estimate for the last 17000 years. This can be well explained by the outstanding role which deglaciation played in the time span studied here.
This study combines ground-penetrating radar (GPR) and capacitively coupled resistivity (CCR) for geophysical architecture-analysis of a bar platform and channel bend on the floodplain of a poorly organized wandering gravel-bed river. An important objective of fluvial architectural analysis is linking fluvial style with preserved subsurface sedimentology. However, architectural analysis relies on opportunistic outcrops with locations or orientations that may not provide appropriate data. GPR is a well-established geophysical method that images reflections interpreted to represent bed geometry and bounding surfaces and is therefore ideal for imaging fluvial architecture. Unfortunately, grain-size information, which is integral to architectural classification, is more elusive using GPR. Resistivity data can be used as a proxy for sediment grain size. When GPR and CCR are combined they offer an effective tool for geophysical fluvial architectural analysis. Five trenches provided direct observation of the subsurface sedimentology and are used to calibrate the two geophysical methods. Eight radar facies and one radar element are classified from the GPR survey and grouped into four categories: horizontal and subhorizontal, laterally continuous reflections (Group 1), clinoform reflections (Group 2), discontinuous reflections (Group 3), and concave-up elements (Group 4). The 2-D resistivity data are combined in a GIS to establish a 3-1) resistivity model for the upper 5 in of the floodplain. Resistivity values correlate well with grain size and are categorized into fine-grained (< 400 ohm-m), sand-size (400 to 800 ohm-m) and gravel-sized (> 800 ohm-m) sediments. In general, resistivity values indicate coarse sediment in the bar platform and sand to fine-grained material in the main channel and subordinate depressions. Resistivity profiles were extracted from the 3-D model along the GPR lines so that resistivity values could be directly compared to radar facies. The shape and spread of the resistivity distributions provide dominant grain size as well as an indication of sediment sorting for individual radar facies. In some cases, the same radar facies is associated with markedly different grain sizes, indicating different architectural elements (i.e., horizontally bedded gravel verses horizontally bedded sand or fine-grained sediment). This demonstrates the utility of combining GPR and CCR, insomuch as radar architecture alone is not diagnostic of fluvial architectural elements. In this case study, the bar platform and channel have a planform that might suggest a meandering fluvial style. However, GPR-CCR results indicate that the dominant depositional process across the bar platform was vertical accretion of gravel sheets, an architecture more consistent with a wandering gravel-bed fluvial style. Lateral migration was limited to the outer downstream margin of the platform, a location dominated by a mix of sand and gravel. Coarse gravel likely occupies the base of the main channel, with fine-grained sediment contributing to the remainder of the channel fill. A four-phase history is presented where the initial phase of development involves vertical accretion and migration of stacked gravel-sheets during floods, forming the core of the bar platform. After flooding subsides and the interior bar emerges, the channel becomes established and lateral migration becomes the dominant depositional process. The evolution concludes with avulsion and eventual abandonment of the channel.
Closely spaced (1 m) ground penetrating radar (GPR) profiles were used for a three-dimensional characterization and comparison of glaciofluvial gravel-bed deposits in palaeodischarge zones of the Würmian Rhine glacier (southwestern Germany). Previous sedimentological outcrop investigations revealed three regionally reoccurring architectural styles of gravel bodies. For each of these styles a three-dimensional GPR dataset has been acquired in active gravel pits in order to calibrate the radar profiles with outcrop walls and to analyse, in three dimensions, the depositional elements and their stacking pattern in the subsurface.
The GPR data were interpreted by mapping reflection terminations in order to delineate genetically related units. In particular, radar facies types and radar sequence boundaries were used to define and map depositional elements. Both accretionary and cut-and-fill depositional elements could be identified. Accretionary elements are characterized by horizontally to low-angle inclined (1–3°) and moderately continuous reflections (5–30 m) terminating on flat sequence boundaries; they represent the deposits of gravel sheets and traction carpets. In contrast, cut-and-fill elements are characterized by low to steeply inclined (3–25°), often discontinuous reflections terminating on concave to trough-shaped lower truncation boundaries; these are interpreted as scour-pool fills and small dissection elements (e.g. chutes and lobes).
The three basic architectural styles of gravel bodies can be distinguished on the basis of the size and proportion of cut-and-fill elements mapped within the radar images. One type of gravel body is composed of an amalgamation of large cut-and-fill elements whereas the other two types are dominated by accretionary elements and differ by the proportion of smaller cut-and-fill elements.
The results show that GPR is an adequate technique to illuminate the sedimentary architecture of the various types of gravel bodies. GPR data allow detailed three-dimensional reconstruction of depositional elements and their stacking pattern in the subsurface.
The purpose of this paper is to examine the internal architecture and post-glacial evolution of Cheekye fan, British Columbia, Canada. Analysis of a large database of ground penetrating radar (GPR) profiles has allowed the identification of ten reflection configurations that characterize this high-energy environment. GPR profiles augmented with test-pit, well-log and radiocarbon data provided detailed subsurface information and revealed the large-scale internal architecture and Holocene sedimentation history of Cheekye fan. Based on a shift in reflection configuration with depth. GPR data appears to record a change in the mode of deposition through time. This data suggests that Cheekye fan is a paraglacial fan, largely a product of the geological past. This fact should be taken into consideration when making future hazard estimates.
The facies sequences and fan entrenchment are here primarily affected by thresholds related to catchment geomorphology, by the type of sediment available, and by the position within the storm cell.-from Authors
The central interior plateau of British Columbia, Canada, is dissected
by numerous elongate, glacially overdeepened lake basins akin to coastal
fiords. An air-gun seismic-reflection investigation (242 km of
trackline) of Okanagan Lake (120 km long, ˜3.5 km wide) shows that
the Pleistocene sediment fill is up to 792 m thick and that bedrock has
been excavated by repeated Pleistocene glacial erosion to nearly 650 m
below sea level. The depth of bedrock incision
below the surrounding plateau is more than 2000 m, exceeding that of the
Grand Canyon in Arizona. The total volume of sediment infill within the
narrow trenchlike basin is more than 90 km3, and several
lines of evidence suggest that this fill accumulated rapidly during a
single phase of glaciolacustrine sedimentation during late Wisconsin
deglaciation of the region after 15 ka. Similar fiord-lake basins, up to
100 km long, are common in the interior of British Columbia. If the data
from Okanagan are representative, these basins may represent a major
previously unrecognized component of the total glacial sediment flux to
the ocean. Overdeepening below sea level and the focusing of large
volumes of glacial sediment and meltwater into such basins are of
considerable glaciologic significance and may record the fast, unstable
flow of "ice streams" during deglaciation of the Cordilleran ice sheet.
Glaciation is schematically considered as a perturbation of "normal" fluvial conditions. Drift is unstable in a proglacial or postglacial fluvial environment, resulting in heightened sediment movement that continues as long as drift material remains easily accessible for fluvial erosion and transportation. Sediment yield bears no relation to concurrent primary production of weathered debris. Examples of such "paraglacial" denudation and sedimentation are reported from two contrasting areas. Postglacial valley alluvial deposits are widespread in central Baffin Island where rapid sedimentation continues today; estimated denudation rates are an order of magnitude higher than in comparable unperturbed areas. In south-central British Columbia, rapid sedimentation during the paraglacial period contrasts sharply with present-day conditions.
The sedimentary architecture of an alpine alluvial fan with a surface of 300,000m2 near Samedan, Switzerland, was three-dimensionally investigated using 9km of ground penetrating radar sections with a penetration depth of 10m. Radar facies patterns could be very well calibrated to sedimentology and dated horizons due to a 300m long outcrop section at the foot of the fan. Six major reflectors have been identified and represent first order, fan-wide palaeosurfaces. They are made up of up to 20cm thick fine-grained deposits partly with initial pedogenetic structures and wood remains which yielded ages between 5670±60 and 7515±65 a 14C BP. Between these surfaces different depositional lobes and specific architectural elements like channels, levees or snouts of debris flows could be identified. All these data were geo-referenced to establish a complete quantitative 3-D time-stratigraphic framework. This allowed us to calculate deposited sediment volumes and sediment fluxes for different time slices between the dated palaeosurfaces. Sediment fluxes show an overall decline during the Holocene which we interpret as the decling sediment production in the catchment area—a function of the paraglacial cycle. Since the middle Atlantic period, the aggradation of the fan almost ceased and climate perturbations are no longer reflected in the sedimentary record since then. Within the aggradation period, distinct peaks of high sediment fluxes could be correlated with known periods of glacier retreats in the Swiss Alps, which points to a high sensitivity of the system to climate changes. The results of our study give valuable new insights into thresholds of activity and quiescence of an alpine catchment-fan system and its stage in the course of a paraglacial cycle. Although very important for the understanding of such dynamic systems under global warming scenarios and geo-risk assessment, such data sets are rarely available.
Ground penetrating radar (GPR) measurements have been carried out on an outwash plain and in the rim of an adjacent ice-push ridge in northwest Zealand, Denmark. The radar profiles are differentiated into radar facies with distinct reflection characteristics. The lithology and depositional environment of the radar facies is interpreted by correlating information from profiles in gravel pits, geological maps and bore hole data. The GPR profiles reveal sedimentary structures and glaciotectonic deformation structures. Several thrust planes and folds are interpreted from the GPR data. The deformation style of the tectonised glaciofluvial sediments is a pro-glacial thin-skinned thrust complex, with associated folding. The deformations have resulted in the present ridge morphology seen in the rim of the ice-push ridge. On top of the deformed sediments and in front of them penecontemporaneous and post tectonic sediments are deposited, smoothing the ridge relief created by the thin-skinned thrust complex.
Paraglacial geomorphology is the study of earth-surface processes, sediments, landforms, landsystems and landscapes that are directly conditioned by former glaciation and deglaciation. The withdrawal of glacier ice exposes landscapes that are in an unstable or metastable state, and consequently liable to modification, erosion and sediment release at rates greatly exceeding background denudation rates. This paper (1) reviews research on paraglacial processes, landforms and landscape change in a range of geomorphological settings; (2) explores the importance of paraglacial landscape modificat