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Rift-related linked depositional systems and their seismic expression. In: Tectonics and Seismic Sequence Stratigraphy
Abstract
The spatial distribution and temporal evolution of depositional systems in active-fault bounded basins are considered to be significantly influenced by tectonics. A four-fold division relating to rift initiation, rift climax, immediate post-rift and late post-rift stages of basin evolution is proposed to characterize most basin infill stratigraphies. The three-dimensional linked depositional systems (systems tracts) associated with each of these stages will vary according to a number of factors. However, a dominant tectonic signature can still be isolated if analysis is undertaken in an appropriate fashion. The general suitability of the application of this new method of describing rift basin stratigraphies in terminal half-graben type basins is demonstrated using case studies and published examples. -from Author
... The evolution of rift basins is commonly characterized by a series of tectonic stages including rift initiation, rift climax, late syn-rift, and a post-rift stage (Prosser, 1991(Prosser, , 1993Ravnås & Steel, 1998;Smyrak-Sikora et al., 2019). The transition from the immediate post-rift to the late post-rift stage has been shown to be manifested by a limited amount of differential subsidence across faults and no signs of fault block tilting (Prosser, 1993). ...
... The evolution of rift basins is commonly characterized by a series of tectonic stages including rift initiation, rift climax, late syn-rift, and a post-rift stage (Prosser, 1991(Prosser, , 1993Ravnås & Steel, 1998;Smyrak-Sikora et al., 2019). The transition from the immediate post-rift to the late post-rift stage has been shown to be manifested by a limited amount of differential subsidence across faults and no signs of fault block tilting (Prosser, 1993). Moreover, studies show that the cessation of rift tectonics allows for eustasy to take control over the larger scale and long-term cyclicity in the basin and thus the resulting basin fill architecture (Bayet-Goll et al., 2018;Collier, 1990;Gawthorpe & Leeder, 2000;Gjelberg & Steel, 1983;Prosser, 1991Prosser, , 1993Smyrak-Sikora et al., 2021;Sorento et al., 2020;Stemmerik & Worsley, 2000). ...
... The transition from the immediate post-rift to the late post-rift stage has been shown to be manifested by a limited amount of differential subsidence across faults and no signs of fault block tilting (Prosser, 1993). Moreover, studies show that the cessation of rift tectonics allows for eustasy to take control over the larger scale and long-term cyclicity in the basin and thus the resulting basin fill architecture (Bayet-Goll et al., 2018;Collier, 1990;Gawthorpe & Leeder, 2000;Gjelberg & Steel, 1983;Prosser, 1991Prosser, , 1993Smyrak-Sikora et al., 2021;Sorento et al., 2020;Stemmerik & Worsley, 2000). ...
The transition from syn‐rift to post‐rift sedimentation in rift basins is difficult to characterize in terms of stratigraphic architecture and dominating control on sedimentation, due to decreasing tectonic activity interplaying with regional subsidence, eustatic sea level changes, and differential compaction of underlying syn‐rift sediments. Our case study of the Late Palaeozoic Inner Hornsund Fault Zone targets late syn‐rift strata recorded in the (?Pennsylvanian – ?lower Permian) Treskelodden Formation in Hornsund, southern Spitsbergen, representing a mixed siliciclastic‐carbonate succession, with siliciclastics primarily sourced from the adjacent Sørkapp‐Hornsund High. We document local scale (<10 km) facies variability, sequence stratigraphy, and evolution of a succession deposited along a flank of the structural high during the late syn‐rift stage. We observe that during the transition towards rift termination (glacio‐)eustatic sea level changes and overall regional flooding became a more prominent forcing factor controlling sedimentation. Our dataset includes sedimentary logs, microfacies analysis, and high‐resolution digital outcrop models. We identify four progressively backstepping stratigraphic sequences, reflecting an evolution from (1) terrestrial siliciclastics through (2–3) nearshore mixed siliciclastic–carbonates, to (4) carbonate ramp deposits. On the small scale (<5 m) the internal sediment cyclicity of the succession was formed by autogenic processes, particularly the changing rate of sediment input from the southwestern source area (the uplifted Sørkapp‐Hornsund basement high). On the larger scale (10s of m), the importance of glacio‐eustatic sea‐level changes, driven by waxing and waning of ice caps in the southern hemisphere (Gondwana), increased as the rift‐related tectonics decreased. The interdisciplinary methods used in this study provide new knowledge of the Middle Pennsylvanian to Permian depositional evolution in southern Spitsbergen, besides a novel framework for comparison to adjacent basins in the region and similar basins elsewhere.
... The kinematics of the listric growth fault may be linked to the deposition of the sedimentary radarfacies ( Table 2). The subaerial evolution of this listric gravitational growth fault can be related to the rift-related depositional systems described by Prosser [19], but 1 -2 orders of magnitude smaller. Open Journal of Geology The evolution of sediment deposition while the listric gravitational fault displacement grows can also be distinguished into stages as proposed by Prosser [19]. ...
... The subaerial evolution of this listric gravitational growth fault can be related to the rift-related depositional systems described by Prosser [19], but 1 -2 orders of magnitude smaller. Open Journal of Geology The evolution of sediment deposition while the listric gravitational fault displacement grows can also be distinguished into stages as proposed by Prosser [19]. The radarfacies underlying the lower lagoonal one is interpretated as a pre-fault sedimentary unit (LP-f n+1 -pf) since its upper boundary displays offlap-toplap reflectors truncation. ...
... Low fault propagation displaces basin depocenter far away from fault and turns the basin geometry more symmetric. All these principles, derived from [19], apply to the Lagoa do Peixe Growth Fault and its local lagoonal basin (Figures 12(A)-(D)). ...
... Notably, the SU6 consists of sub-parallel reflectors onlapping onto the top of the SU5 at the distal basin margin and the eroded fault plan of the F1. The geometry of the SU6 shows some features of the post-rift strata, as addressed in Prosser (1993), which indicates that the basin subsidence in the SU6 stage was not mainly controlled by normal faulting. Our interpreted rift-onset unconformity is close to the intra-rift unconformity (IRU) previously thought to be related to the crustal uplifting and initiation of rifting decline ( Fig. 7b; Lin et al., 2003). ...
... It truncates the underlying reflectors and is onlapped by the overlying reflectors toward the distal part of the basin (Fig. 5a, 7-8). These properties are consistent with the unconformity marking the rift onset (Prosser, 1993). Furthermore, the throw maximum in each T-z plot is located at the rift-onset unconformity , which indicates that the overlying strata are related to the syn-rifting (Meyer et al., 2002;Childs et al., 2003). ...
... 5a,(7)(8). These features are consistent with the characters of the break-up unconformity proposed by Prosser (1993). ...
The growth of normal fault systems affects the development of rift basins. These systems could grow via either non-coherent or coherent models, where segments either develop independently or merge into one fault, respectively. Also, they could experience decreases in fault system lengths, called lateral tip retreat, during the later fault-activity stage. In this study, we investigate the fault growth model by studying the Penghu Basin, a Paleogene rift basin in the western Taiwan Strait, and test the current fault growth models. Our methods include seismic interpretation and fault growth analyses, such as the spatiotemporal distribution of cumulative throw and throw increment and expansion index. In the Penghu Basin, the boundary and transfer fault systems grew via the non-coherent model followed by lateral tip retreat, while other studied fault systems grew via the coherent model before their tips retreated. Furthermore, segments could separate from their parent fault systems prior to the lateral-tip-retreat stage. During the evolution of the fault system, the shifting of a cumulative throw maximum could be accompanied by a throw increment minimum, i.e., segmentation, moving toward the migrated cumulative throw maximum inside segments or by the retreated fault tip of the fault system. This implies a change in the distributions of stress drop and increase regions. Finally, our results indicate that the specific rift phase of basin evolution is highly correlated with the development of fault systems. We suggest that the lateral tip retreat of fault systems marks a change in the rift phase of a basin and implies the end of basin evolution.
... Classical models of rift basin evolution are based on the analysis of the sedimentary record preserved within individual grabens and half-grabens; studies such as these typically allow the timing and duration of these stages to be constrained (e.g. Bosence, 1998;Gawthorpe & Leeder, 2000;Prosser, 1993). In these models, the syn-rift stage is characterised by mechanical subsidence, marked by the generation of large amounts of accommodation over a relatively short period. ...
... basement highs). During this time (named mid-synrift by Bosence, 1998, and rift climax by Prosser, 1993 andScherer, 2010), the greatest thickness of sediment accumulates next to the half-graben border fault; in the case of a symmetrical graben, sediment thicken across the bounding faults, into the intervening depocentre. Following the main syn-rift period or rift climax, active faulting gradually decreases and ceases (Gawthorpe & Leeder, 2000), and mechanical subsidence is replaced by a long-wavelength, relatively slow subsidence driven by cooling of the lithosphere (Bosence, 1998;Prosser, 1993). ...
... During this time (named mid-synrift by Bosence, 1998, and rift climax by Prosser, 1993 andScherer, 2010), the greatest thickness of sediment accumulates next to the half-graben border fault; in the case of a symmetrical graben, sediment thicken across the bounding faults, into the intervening depocentre. Following the main syn-rift period or rift climax, active faulting gradually decreases and ceases (Gawthorpe & Leeder, 2000), and mechanical subsidence is replaced by a long-wavelength, relatively slow subsidence driven by cooling of the lithosphere (Bosence, 1998;Prosser, 1993). In some cases, this transition is associated with plate rupture (i.e. ...
Rift basins typically comprise three main tectono‐stratigraphic stages; pre‐, syn‐ and post‐rift. The syn‐rift stage is often characterised by the deposition of asymmetric wedges of growth strata that record differential subsidence caused by active normal faulting. The subsequent post‐rift stage is defined by long‐wavelength subsidence driven by lithospheric cooling and is typified by the deposition of broadly tabular stratal packages that drape any rift‐related relief. The stratigraphic contact between syn‐ and post‐rift rocks is often thought to be represented by an erosional unconformity. However, the late syn‐rift to early post‐rift stratigraphic record is commonly far more complex since (i) the associated tectonic transition is not instantaneous; (ii) net subsidence may be punctuated by transient periods of uplift; and (iii) strain often migrates oceanward during rifting until continental breakup is achieved with crustal rupture. Previous publications on the Eastern Brazilian marginal basins have not historically used the tripartite scheme outlined above, with the post–pre‐rift interval instead being subdivided into rift, sag and passive margin tectono‐stratigraphic stages. In addition, the sag stage has been previously described as late syn‐rift, early post‐rift or as a transition between the two, with the passive margin stage being equivalent to the classically defined post‐rift, drift stage. Two (rather than one) erosional unconformities are also identified within the rift‐to‐sag succession. In this work, we use 2D and 3D seismic reflection and borehole data to discuss the expression of and controls on the syn‐ to post‐rift transition in the shallow and deep water domains of the south‐central Campos Basin, south‐east Brazil. We identified three seismic–stratigraphic sequences bounded by unconformities, named lower and upper pre‐salt and salt. The lower pre‐salt interval is characterised by wedge‐shaped packages of reflections that thicken towards graben and half‐graben‐bounding normal faults. This stage ends with the development of an angular unconformity, inferred to form as a result of the onset of the oceanward migration of deformation. The upper pre‐salt is typically defined by packages of subparallel and relatively continuous reflections that are broadly lenticular and thin towards fault‐bound basement highs, but that locally contain packages that thicken against faults. The pre‐salt to salt contact is defined by an erosional unconformity that is largely restricted to basement highs, and which is inferred to have formed due to base‐level fall and uplift associated with local fault reactivation, resulting in the formation of channels of possible fluvial origin. Based on its geometries and seismic facies, we conclude that the lower pre‐salt interval is syn‐rifting and syn‐tectonic , deposited during active continental extension and upper crustal faulting affecting the entire evolving margin, whereas the overlying upper pre‐salt is syn‐rifting and post‐tectonic in the Campos Basin, deposited when extension and faulting had migrated seaward to the future location of the spreading centre. The results of our study support the arising notion that the syn‐rift sequence does not only display syn‐tectonic sedimentary packages, and thus the tripartite tectono‐stratigraphic model for rift development is too simplistic and cannot be applied when assessing rifts in the context of the regional development of continental margins.
... Identification of the tectonic episodes was based on subsurface mapping of pre-rift, syn-rift and post-rift deposits due to their characteristic seismic expressions. Pre-rift deposition occur before faulting where uniform basin subsidence is indicated by more or less parallel strata (Prosser, 1993). Syn-rift deposition occurs during active fault movement when sedimentation keep pace with fault movement-induced basin subsidence; is characterised by wedge shaped sedimentary fills with internal strata thickening toward the bounding fault (Prosser, 1993). ...
... Pre-rift deposition occur before faulting where uniform basin subsidence is indicated by more or less parallel strata (Prosser, 1993). Syn-rift deposition occurs during active fault movement when sedimentation keep pace with fault movement-induced basin subsidence; is characterised by wedge shaped sedimentary fills with internal strata thickening toward the bounding fault (Prosser, 1993). The post rift sedimentation occurs after rifting, blankets syn-rift deposits and shows a change in depositional configuration from a saw-tooth geometry to parallel and sub-parallel configurations (Prosser, 1993). ...
... Syn-rift deposition occurs during active fault movement when sedimentation keep pace with fault movement-induced basin subsidence; is characterised by wedge shaped sedimentary fills with internal strata thickening toward the bounding fault (Prosser, 1993). The post rift sedimentation occurs after rifting, blankets syn-rift deposits and shows a change in depositional configuration from a saw-tooth geometry to parallel and sub-parallel configurations (Prosser, 1993). Based on sedimentary fill geometries, the revealed tectonic episodes were then linked to occurrence of magmatic/volcanic deposits in the Tanga offshore basin stratigraphy which correlate with the age equivalent intervals in the EWB. ...
The offshore Tanga Basin of north-eastern Tanzania contains Cenozoic sedimentary successions that have been poorly studied. The basin development was due to an interplay of multiple factors including periods of active fault movement linked to the East African Rift system (EARs) which influenced the Cenozoic development of the offshore Tanga Basin. The EARs recorded several discrete tectonic episodes that were associated with magmatic activities and massive volcanism. However, there is no report on the possible presence of magmatic intrusions indicative of magmatic activities and volcanism in the history of the Tanga Basin. Timing of occurrence and distribution of magmatic intrusions are among the key components needed to evaluate the petroleum potential of the basin. A detailed 2D qualitative seismic interpretation, coupled with core logging data and analysis of elemental proxies, has been employed to evaluate the petroleum potential of the Cenozoic successions of the offshore Tanga Basin considering the presence and timing of occurrence of the magmatic intrusions. These used data and the associated interpretation techniques have not been used before to meet similar objectives. Both core logging and elemental proxies are newly collected information used in this study. Results suggest that the Tanga Basin has been variedly intruded by magmatic sills and dikes. Seismic well tie and correlation to age-equivalent deposits across the onshore successions in the EWB revealed that the volcanic events occurred during tectonic episodes that influenced the development of the East African Rift basins. Seismic interpretation also suggests that these tectonic episodes occurred possibly during the Miocene, Pleistocene and Holocene periods when magmatic intrusions are believed to have promoted source rock maturation and facilitated the formation of structural elements for petroleum preservation.
... The sequence stratigraphic model summarised from marine rift successions suggests that tectonically controlled change in accommodation space is the dominant control in determining sedimentary filling and stratigraphic architecture of rift basins (Martins-Neto & Catuneanu, 2010;Ravnås & Steel, 1998). The rate of sediment supply plays a second-order role in sequence arrangement, whereas climatically forced eustatic fluctuations control the changes of high-frequency (fourth-order and lower rank) sequences (Prosser, 1993;Van Wagoner et al., 1990). Although these models have been suggested to be valid for rift lake systems (Holz et al., 2017), more detailed studies are needed given the considerable differences in the spatio-temporal scale between marine and lacustrine settings. ...
... Following the sequence stratigraphic principles developed for non-marine and rift sequences (Martins-Neto & Catuneanu, 2010;Prosser, 1993;Ravnås & Steel, 1998;Van Wagoner et al., 1995;Wadsworth et al., 2002Wadsworth et al., , 2003, a sequence stratigraphic model for syn-rift lake successions is summarised here based on the Shahezi Formation, as shown in the three sections in Figure 18. Each sequence, bounded by regional unconformities and their correlative conformities, displays typical triplets of LST, TST and HST. ...
Lakes are sensitive indicators of the balance between accommodation and sediment supply, recording high‐resolution changes in palaeoenvironmental conditions. Long‐lived rift lake basins, however, are predominantly controlled by episodic accommodation changes and pronounced basinward facies shifts, complicating the generalisation of tectonic and climatic controls on rift lake successions. This study proposes a sequence framework and depositional pattern for asymmetric half‐grabens in syn‐rift lake basins by characterising the lacustrine fan‐delta deposits of the Lower Cretaceous Shahezi Formation in the Songliao Basin. Detailed sedimentologic and petrographic analyses identified 24 lithofacies categorised into seven facies associations. A sequence stratigraphic framework was constructed to outline the tectono‐stratigraphic evolution during the syn‐rift phase. The results indicate that the syn‐rift Lishu palaeo‐lake is characterised by its relatively small size, steep slopes, poorly developed and siliciclastic‐dominant shoreline strata and significant input of allochthonous biodetritus. The syn‐rift deposits show a distinct threefold conglomerate–sandstone–mudstone motif, with a complete cycle comprising a prolonged retrogradational phase (LST and TST) and a brief progradational phase (HST). Basin‐bounding faults accelerated hinterland erosion and increased sediment feeder system slopes by rotating hangingwall blocks; consequently, rapid sediment transport and localised gravitational collapse caused the common occurrence of soft‐sediment deformation structures and sublacustrine fan conglomerates. The substantial increase in accommodation space, resulting from fault‐generated subsidence, triggered lake expansion and further contributed to the development of transgressive system tracts and continuous mudstone deposition. These mudstones, rich in terrigenous organic matter and allochthonous fossils, correlate with carbonaceous mudstones, coals and conglomeratic sandstones in proximal overfilled sections, indicating a dynamic interplay between fan delta progradation and Lake Shoreline transgressions. This study proposes a depositional model within a sequence stratigraphic framework for non‐marine sediment accumulation in asymmetric half‐grabens bounded by active faults. The findings offer insights that complement existing models developed for marine rift systems.
... Dominance of fine-grained deposits in some of the intervals may be due to deposition in distal basinal areas where gravity flows may have limited energy to deliver course sediment, depletion of the source material, and continued deepening of the basin and drowning of the source area (cf. Prosser, 1993;Ravnås and Steel, 1998;Ravnås et al., 2000). Low energy environment in the distal basinal areas is the likely interpretation since the Oligocene period followed the Late Eocene regression event (Key et al., 2008;Franke et al., 2015;Mvile et al., 2021; this work) with possible gravity flow pulses due to slope instability upon sea level fall (cf. ...
... The Miocene tectonic event, in the offshore Tanzania, which uplifted some of the areas that were eroded to supply sediment to the basinal area (Mvile et al., 2021;this work) influenced the evolution of the Miocene channel system in the study area. This may be explained by the fact that tectonic block movements are known to affect antecedent drainage patterns where drainage trajectories shift from transverse to longitudinal (Prosser, 1993). ...
... The stratigraphic architecture of extensional basins reflects the interplay between tectonics, sedimentation and base-level variations (e.g. Prosser 1993;Schlager 1993;Nottvedt et al. 1995). Seismic and well data interpretation has long highlighted the role of tectonically induced rapid base-level variations resulting in dominantly coarsening-upward successions within the wedge-shaped syn-tectonic strata (Martins-Neto and Catuneanu 2010). ...
... Furthermore, the lateral autocyclic source variations of the feeding deltas create even higher-order cycles both by proximal sedimentation over the flank and by the deposition of sand lobes in the deep basin (Balázs et al. 2017b). Such cycles with different frequences are also reported from syn-rift outcrops from the Pannonian Basin (Andrićet al. 2017; Sebe et al. 2019) and have been interpreted from rift basins worldwide (Prosser 1993;Martins-Neto and Catuneanu 2010;Matenco et al. 2022). ...
The subsidence history and sedimentary architecture of extensional basins are controlled by the interplay between tectonics, mantle dynamics, and climatic variations. Observations from outcrop to regional seismic scales coupled with numerical modelling techniques, including basin-scale stratigraphic, crustal-scale tectonic and mantle-scale subduction models contribute to quantify basin evolution. Here, we review and discuss both tectonic and stratigraphic applications of such models and compare them with observations from the Pannonian Basin system of Central Europe. We show that diachronous localization of back-arc extension, crustal thinning, asthenospheric upwelling and subsequent thermal relaxation are superimposed on an overall slow plate convergence. These processes result in contrasting subsidence and uplift patterns and a variable heat flow evolution in different parts of the basin system. The crustal stress-field of the subbasins does not always reflect their contrasting vertical motions. Extensional deformation generally migrates from the basin margins towards the basin centre. Structural inversion is localized along hot and weak inherited zones from the Middle Miocene to Present. Tectonic subsidence focuses sedimentation along deep depocenters, sourced by exhumed footwalls and from the neighbouring orogens. The overall post-rift sediment progradation are influenced by inherited bathymetries from the preceding syn-rift stage and by enhanced differential vertical motions.
... The tectono-sedimentary history of the PRB was established based on 2D seismic interpretation of fault activity relative to sedimentation, basin geometry, shapes of sedimentary fills, reflection termination patterns relative to the bounding markers, and appearance of key reflectors. Interpretation of reflection termination patterns is based on definitions of Prosser (1993), Holz et al. (2017), and Fyhn et al. (2020). ...
... The horizons irregularities and onlap and toplap stratal termination patterns with respect to the bounding horizons reveal details of sediment erosion and presence of unconformities in the basin stratigraphy (Prosser 1993, Holz et al. 2017. Based on presentations and definitions from these reports, the onlap termination patterns are used to suggest the presence of angular unconformities while toplap termination patterns imply erosional truncations. ...
The sedimentary fills in the Pangani rift basin (PRB) of northeastern Tanzania have not yet been studied in detail and their petroleum potential is poorly understood. This study aims at assessing distribution of magmatic intrusions and key petroleum system elements in the PRB based on 2D seismic, remote sensing, and aeromagnetic data interpretations. Results show that evolution of the basin fill was influenced by sediment supply, magmatism, and tectonics. The PRB contains Pliocene–Holocene clastic, magmatic, and volcaniclastic deposits. The clastic sediment was sourced from the north-northeast and east-southeast of the PRB. The magmatic and volcaniclastic rocks were formed during Pleistocene–Holocene and are increasing in frequency toward the north and northeast of the basin. Tectonics and faulting created depocenters and magma conduits; magmatic intrusions and fault systems form potential petroleum traps. Seismic interpretation has shown that PRB contains potential reservoir and seal rocks for possible petroleum accumulations. Fault systems dissecting the PRB provided petroleum migration pathways from deep buried source rocks to potential reservoirs. For the first time, this study has shown that the PRB contains key petroleum system elements for petroleum accumulations to occur. Our results will be of interest to researchers working in different East African Rift basins.
... These elements have been used to identify petroleum source rocks, reservoir rocks, potential petroleum prospects, and direct hydrocarbon indicators and are widely used to suggest petroleum migration and accumulations in different basins (e.g., Aminzadeh et al., 2002;Pettingill et al., 2019;Schroot & Schüttenhelm, 2003). Seismic stratigraphy, seismic facies analysis, sedimentary fill shapes, and seismic stratal termination patterns may reveal different architectural elements and indicate key factors for basin development (Catuneanu et al., 2009;Ejeke et al., 2017;Mitchum et al., 1977;Nanda, 2016;Nottvedt et al., 1995;Prosser, 1993;Ravnås & Bondevik, 1997;Ravnås & Steel, 1998;Vail, 1987;Van Wagoner et al., 1990). Stratal surfaces through which other strata terminate mark timelines reflecting periods of non-deposition or changes in depositional regimes. ...
... The Jurassic saw-tooth-shaped fills and the Jurassic-Cretaceous wedges with parallel internal strata (lower part, Fig. 7) suggest infill of remnant rift topography. This interpretation is adopted from previous works where similar features have been mapped from different sedimentary basins (e.g., Nottvedt et al., 1995;Prosser, 1993;Ravnås & Bondevik, 1997;Ravnås & Steel, 1998). The mapped rift topographies are interpreted to have resulted from the Middle Jurassic tectonic event reported by Kent et al. (1971) and Kapilima (2003). ...
The Dar es Salaam Platform (DSP) and Mafia Basin are within the Bigwa-Rufiji-Mafia (BRM) hydrocarbon exploration block of the coastal Tanzania basin. The DSP has made insignificant hydrocarbon discoveries despite some exploration campaigns that involved the acquisition of seismic reflection data and exploration drilling. This study used 2D seismic interpretation techniques and well-log analysis to establish depositional and post-depositional architectural elements of the DSP for the purpose of contributing to the understanding of the petroleum prospectivity of the area. Based on well-log analysis, correlation has been made to the Mafia Basin to assess any spatial variability in depositional conditions and processes, which may be key to understanding the petroleum potential of the DSP. Results show that tectonics, sea level changes, and sediment supply mainly controlled the formation of the DSP. Different tectonic events created hydrocarbon migration pathways from deep buried source rocks to shallow seated reservoirs and formed possible petroleum prospects. The revealed petroleum prospects are fault-controlled and have not been tested by drilling. Some of the prospects have been fractured by subsequent faulting. The faulting of the petroleum prospects within the DSP caused hydrocarbon leakages to be revealed by the mapped gas chimneys. These gas chimneys are reported for the first time in the study area. The hydrocarbon leakage from the DSP prospects may be one of the reasons why the previous exploration campaigns ended with some dry wells.
... Given the lack of core material in the Permian-Triassic intervals, our interpretation of the alluvial systems in the study area relies on well-constrained conceptual models (e.g. Gawthorpe & Leeder, 2000;Prosser, 1993) and field-analogues (e.g. Smyrak-Sikora et al., 2019;Würtzen et al., 2022). ...
... Sequences controlled by tectonic forcing can be distinguished in seismic data by asymmetric sequence geometries, internal onlap relations and stratal growth wedges (e.g. Prosser, 1993;Serck & Braathen, 2019), whereas climatic forcing is reflected rather in well-logs by (cyclic) lithological variations, sandstone stacking patterns and varying clay mineral assemblages (e.g. Abels et al., 2013;Nystuen et al., 2014;Paredes et al., 2020). ...
For the first time, this study presents interpretations of alluvial fans in spectral decomposition RGB Blends, analysed in seismic time slices from the Middle Triassic to Lower Jurassic stratigraphical interval of the Horda Platform (northern North Sea). The time slices record a shifting alluvial fan front, fluvial variability, uplift and erosion and reveals depositional elements that may set the common conception of the geological development of this area during the Early–Middle Mesozoic up for discussion. Results show that the Upper Triassic Lunde Formation in the eastern margin of the Horda Platform was characterized by the deposition of coalesced alluvial fans. A variable extent of the fan front through the Upper Triassic is linked to interplaying allogenic factors: uplifted source areas in the aftermath of Early–Middle Triassic rifting determined sediment availability; climate transitioning from arid to semi-humid, with increasingly fluctuating precipitation, controlled sedimentation, and run-off; provenance dictated bulk sedimentology and affected prevailing alluvial processes. An overall retreat of the fan system through the Late Triassic coincided with a significant change in landscape characteristics at the transition into the overlying Statfjord Group. Uplift and initial tilting of the Horda Platform caused landscape degradation and the formation of plateaus and incised valleys, contemporaneous with increased humidity and marine transgression, forming estuaries. The shift in depositional style has implications for reservoir properties, creating complexity and heterogeneity in terms of facies distribution and connectivity, which may benefit potential CO2 storage. Upper Triassic alluvial fan development in the Horda Platform (northern North Sea) depicted through spectral decomposition of seismic time slices Enhanced level of seismic stratigraphic interpretation with RGB blending Impact of allogenic factors on alluvial depositional development Implications of alluvial variability on reservoir properties
... Similarly, but revealing an angular relationship that is less clear, 2SEQ5 fills the basin lows 440 resulting from the synclinal arching of 2SEQ4, also onlapping the latter 2nd-order sequence 441 (see white arrows in Figs. 10 and 11). These structural and strata relationships allow us to use 442 them as markers for the rift-climax stage sensu Prosser (1993) in the proximal domain of the 443 Santos Basin. Importantly, such a relative chronology is observed throughout the entire 444 proximal domain but is even clearer in evolving depocentres where the stratigraphic surfaces 445 tend to be more clearly separated, in contrast to their adjacent structural highs. ...
This paper uses high-resolution 2D and 3D seismic surveys tied to stratigraphic data from 155 boreholes in the mapping and hierarchization of 1551 extensional faults across the Santos Basin and its Outer High. These faults were able to control deposition in extensional basins with different ages – they are thus classified into three (3) main systems with the aim of understanding their geodynamic significance. Fault system 1 (FS1) controlled the oldest syn-rift sequence and delimits the very first half-graben basins developed during an Early Rift stage. Fault System 2 (FS2) was formed in response to crustal thinning during an Intermediate rifting stage. Fault System 3 (FS3) responded to the migration of the rift axis towards the distal margin in a Late Rift stage. Strikingly, fault reactivation occurred throughout the entirety of the proximal domain of the Santos Basin during the Late Rift Stage. This work is important as each interpreted fault system is understood to have controlled the availability of accommodation space during its peak activity, thereby shaping the inner proximal, outer proximal, and distal domains of the Santos Basin. The evolution these fault systems also resulted in the deposition of syn-rift sequences obeying a specific order or ranking. By correlating fault systems with their adjacent syn-rift strata, we propose 1st-order sequence boundaries that are associated with each stage of the development of the rifted margin of the Santos Basin, formed as a consequence of changes in thermo-mechanical conditions during the evolution of the margins. Identified 2nd-order sequences are attributed to tectonic movements at the crustal block scale. In contrast, stratigraphic sequences of the 3rd- and 4th-orders are associated with localised tectonic inputs. Within this framework, we use stratigraphic surfaces as structural correlation markers across multiple observational scales. Consequently, the sequence 1SEQ1 corresponds to the stretching phase, standing for the initial stages of rifting within an intraplate setting. The sequence 1SEQ2 relates to the necking stage and formation of the outer proximal domain. Whereas sequence 1SEQ3 accompanied the development of the distal domain in the so-called hyperextension and continental breakup stages. Ultimately, this work demonstrates that the tectono-stratigraphic evolution of continental margins, from the onset of rifting to continental breakup, is documented by a clear, diachronic tectono-stratigraphic record. Such a record varies along and across hierarchized fault systems that are developed at multiple scales of observation.
... Oppositely, Cupertino (2000) placed the limit between pre-rift phase and syn-rift phase at the base of the Itaparica Formation. In her work, Wiedekher (2010) classified the Itaparica Formation as belonging to the Early Rift Climax Tectonic System Tract of Prosser (1993), or to the Trough-going Fault Stage of Gawthorpe & Leeder (2000), or to the Half-graben Stage of Morley (2002). ...
Based on the study of a great quantity of ostracods carapaces from 10 cores of the Recôncavo Basin (Bahia, Brazil), this work presents the detailed and revised taxonomy of limnic ostracoda from the Itaparica Formation (Lower Cretaceous). Seven species belonging to four genera have been recovered: Kegelina kegeli, Kegelina depressa, Kegelina bisculpturata, Kegelina armata, Praecypridea acuta, Cypridea brevicornis, Theriosynoecum fittoni. What was once defined as Theriosynoecum varietuberatum proximum and Theriosynoecum varietuberatum varietuberatum is understood here as a difference in ornamental of the Theriosynoecum fittoni due to overall morphological compatibility. This observation is supported by most recent works, as it brings ornamentation itself as an insufficient aspect to distinct and define species for the Theriosynoecum genus. Based on the ostracoda associated with the litologic aspects, the Itaparica Fm represent a lacustrine depositional environment in a freshwater lake with depositions of shales, sandstones, siltstones, carbonatite and limestones in an arid climate.
... Studies of rift basins usually emphasizes the influence of tectonics on basin geometry, distribution and connection of faults, and on the ratio between accommodation and sediment supply during the rifting stages (Prosser 1993, Bosence 1998, Gawthorpe and Leeder 2000, Morley 2002, Kuchle and Scherer 2010, while few works focus on processes responsible for transport, deposition and preserved architectural elements in early rift settings based on outcrop data (e.g. Scherer et al., 2014). ...
The Late Aptian Maceió Formation, part of the Alagoas Basin, is an analogue to offshore reservoirs, representing the fourth supersequence during the basin evolution. The Maceió Formation includes conglomerates, sandstones, shales, calcilutite, and evaporitic deposits. To reach our goals, we use existing and new data, including sedimentary logs, 3D processing images, and gravimetric estimates for shales, as well as petrographic sections for porosity-permeability. The Alagoas Basin exhibits a variety of depositional settings, including braided fluvial channels, delta plains, prodelta, lacustrine environments, and aeolian deposits. The aeolian system forms interdunes and large 3D dunes. The lacustrine system reflects reduced energy, resulting in the deposition of a fine-grained succession. The fluvial-deltaic and aeolian facies show reduced accommodation space due to climate, favoring periods of greater sediment supply. The transition to a fluvial-deltaic context implies an increased subsidence, marking the peak of the early rift phase. The sandstones show angular and poorly selected grains of feldspars, quartz, and lithic fragments. It exhibits typical intergranular primary porosity and intragranular/secondary porosity resulting from the dissolution of feldspars and highly fractured quartz grains, showing high porosity. Excellent hydrocarbon potential 20.0 to 36.0% organic matter in shales, coupled with facies descriptions and distribution, it refines our interpretation of depositional cycles within Maceió Formation.
... Rift basins from continental margins have a consistent stratigraphic pattern that attests to the primarily control exerted by tectonic processes on basin evolution (e.g., Martins-Neto & Catuneanu, 2010;Prosser, 1993;Wescott et al., 1996). The stratigraphy of rift basins is affected by non-tectonic factors such as climate and external sediment supply that are superimposed on subsidence; but because the basin-scale motif of coarse-grained base, fine-grained middle, to coarse-grained top is so common and widespread it is attributed to the genesis of the rift basin itself rather than more random external factors (Blair & Bilodeau, 1988;Gupta et al., 1998;Lambiase & Bosworth, 1995;Nottvedt et al., 1995). ...
A summary of the Jurassic‐Cretaceous rift to breakup tectonostratigraphy of the onshore Sverdrup Basin is correlated to the offshore Amerasia Basin in order to reconstruct a tectonic setting for the High Arctic Large Igneous Province (HALIP). The rift climax from the Canadian rifted margin is correlated with hyper‐extension of the continent‐ocean‐transition zone. Hyper‐extension of the continental lithosphere can accommodate plate motions of Arctic Alaska‐Chukotka away from the Canadian Arctic Islands and Lomonosov Ridge between ∼155 Ma and 135–133 Ma. After lithospheric breakup at ∼135–133 Ma, correlation of the post‐rift stage to the seafloor spreading anomalies M10n to M4n that are associated with oceanic crustal domains can accommodate plate motions from 135–133 Ma to 128 Ma. The uncertainties associated with the earliest magmas of HALIP overlap with the uncertainties on the timing of the latest seafloor spreading. The first main pulse of HALIP in the Aptian at 124–120 Ma post‐dates seafloor spreading and so HALIP was emplaced in a tectonic setting that closely resembles the present state of the south and eastern Amerasia Basin. At the paleogeographic center of the HALIP, the Alpha Ridge complex is consistent with the magmatic character and history of similar Cretaceous oceanic plateau in terms of volume and duration.
... Concerning rift sequence stratigraphy, Prosser (1993) pioneered the approach of advocating for the straightforward identification and description of depositional systems based on facies and stacking patterns. On this basis, Holz et al. (2017) proposed an integrative sequence stratigraphic model that possesses the necessary comprehensiveness and feasibility throughout the entire rifting phase. ...
Sequence architectures along the margins of rift basins are still poorly documented compared to passive continental margin settings. The Eocene Shahejie Formation on the rift margin of the Dongying Depression records a complex sequence stratigraphic distribution of conglomerate, sandy conglomerate, sandstone and mudstone. These facies have been mainly attributed to fan delta and marginal subaqueous fan depositional settings that developed during segmented fault activity along the rift margin. We utilize three‐dimensional (3D) seismic data, conventional cores, and wireline log data to dissect the overall wedge‐shaped upper sub‐member strata of the Shahejie Formation's fourth member. The study interval is a third‐order sequence formed between 45.4 and 42.5 Ma and contains a lowstand–transgressive systems tract (LST–TST) and a highstand systems tract–falling‐stage systems tract (HST–FSST). We found that the LST–TST developed several huge amalgamated depocenters along the Chennan border fault; whereas, these depocenters gradually diminished or even disappeared during the HST–FSST period, illustrating less significant control by the border fault. Through calculations of strata growth rates, we confirmed that the segmented activity of the border fault influences the stratigraphic distribution and facies evolution during these two periods. Specifically, deep‐water depositional systems, represented by marginal subaqueous fans were widely developed in the LST–TST period and were influenced by overall strong tectonic activity, including retrogradational (R) and aggradational (A) patterns. However, the aggradational to progradational (AP) deltas and progradational to degradational (PD) deltas dominated the generally muted tectonic activity setting during the HST–FSST. Additionally, influenced by localized segmented fault activity, these systems tracts exhibit incomplete vertical development, resulting in spatial variability in stratigraphic stacking patterns.
... The upward decrease in grain-size towards the upper part of the lower section and overall dominance of fine-grained deposits in the upper section of the EWB stratigraphy indicate several scenarios. These scenarios include either progressive deepening of the basin, drowning of the source area, source depletion of accessible course material to be supplied to the basin, decreased river energy and influence during dry periods, and change in provenance (e.g., Prosser, 1993;Ravnås & Steel, 1998;Ravnås et al., 2000). The depleted sediment source may have resulted from reduced tectonic movements that created sediment sources and produced sediment to be supplied to the basin. ...
The sedimentary record of the Eyasi-Wembere Basin (EWB) in northeastern Tanzania has not yet been characterized in detail. Previous studies in the EWB focused on tectonic development, basin geometry, planning of seismic surveys, timing of tectonic events and volcanic eruptions, and age assignment to different stratigraphic levels. Little attention has been given to the broad understanding of the overall stratigraphy and factors that controlled the evolution of the basin fill. This work has combined core logging, extensive geological mapping and qualitative analysis of elemental proxies to reconstruct paleodepositional conditions and processes that influenced the sedimentary development of the study area. Evidences of lithologies that were mentioned previously are shown for the first time. This study also describes widespread desiccation marks indicative of dry climate, extensive Holocene limestone beds, localized stromatolites, igneous intrusions, and recent debris flow deposits. Overall, results show that the evolution of the basin fill was controlled by several factors, including tectonics, occasional water-level fluctuations, climate variability, hydrothermal activities, bio-productivity, redox potentials, and sediment gravity flows. Multiple sediment sources existed during basin development; they include regional and local clastic sources, volcanic products, river inputs, biogenic sediment, and hydrothermal precipitates.
... Electronic copy available at: https://ssrn.com/abstract=4804711 P r e p r i n t n o t p e e r r e v i e w e d Recent studies have proposed refinements on the classification of the Araripe Basin as a rift basin based on modern definitions (i.e., Prosser, 1993). In this sense, ...
... It is generally acknowledged that the tectonostratigraphic evolution of a rifted margin is separated into tectonic sequences with specific structural geometries and stratigraphic patterns (e.g., Bally and Snelson, 1980;Aslanian et al., 2009;Haupert et al., 2016;Neuharth et al., 2022). (I) The syn-rift sequence, related to crustal thinning, normal faulting, and growth strata during which two periods with specific accommodation rates are recognized (e.g., Prosser, 1993;Gawthorpe and Leeder, 2000;Nutz et al., 2022): (i) the rift initiation period, where the accommodation created by basement fault displacement is filled by sedimentation; and (ii) the rift climax, which corresponds to the period of maximum rate of displacement on a fault, where sedimentation is outpaced by the accommodation induced by the tectonic subsidence. (II) The transition sequence, marked by a progressive migration of the deformation towards the distal necking crustal domain. ...
We characterize the eastern Red Sea necking crustal domain through its north-south structural and stratigraphic record. Along-strike margin segmentation occurred during rifting (∼28-14 Ma), with tilted blocks filled by siliciclastic sediments structuring the northern poor-magmatic segment (28°N-21.5°N), while siliciclastic/volcanoclastic sediments and volcanic flows interpreted as SDRs characterize the southern magmatic segment (21.5°N−13°N). Tectonic and magmatic activity stopped in this crustal domain of the margin when a thick salt layer precipitated during the Middle Miocene (∼14-13 Ma). The stratigraphy of the margin then became similar between the two segments suggesting comparable post-salt subsidence and common crustal characteristics throughout the Red Sea. By characterizing its tectonostratigraphic record on a regional scale, this study tests two end-member scenarios for the tectonic evolution of the Red Sea. It also provides new insights into the tectonostratigraphic record of a rift margin system by simultaneously comparing the evolution of a magma-rich and a magma-poor segment.
... The start of the third cycle coincides with the P-T boundary and the third cycle is interpreted to have formed during the Early Triassic rift phase of Müller et al. (2005) and Kiswaka and Felix (2020b). The fining upward sequences infer either the sediment source area being gradually depleted of accessible sediment which could be transported to the depocentres (Prosser, 1993), progressive deepening of the basin (Ravnås et al., 2000) and drowning of source area (Ravnås & Steel, 1998), or lobe switching. ...
The Permo-Triassic organic-carbon-rich rocks (OCRs) offshore mid Norway have been poorly studied and their depositional conditions are not well understood. This study used core logging and analysis of elemental proxies to investigate these rocks based on core 6611/9-U-01 from offshore mid Norway to understand their depositional conditions. Element concentrations were measured using a portable X-ray fluorescence scanner whereby 23 elements have been linked to depositional conditions, grain size distributions and flow processes. Results show that the analysed interval contains four major fining upward cycles dominated by variable amounts of gravity flow deposits and (hemi-)pelagic mudstones. The combination of elemental distributions and facies suggests that the OCRs were formed during periods of anoxia. The OCRs are contained in parts of the sedimentary sequence with significant slump deposits suggesting sediment reworking. A possible explanation for this is that the slumps might have re-transported the organic-rich sediment to the deeper basinal areas where anoxia was well developed, and consequently resulted in preservation of the organic matter. In this study, the environmental conditions of the OCRs have been identified even when this signal is mixed with the element signal caused by variations of grain sizes. This is shown by independence of the concentrations of redox proxies (S, Pb, and Mo) and palaeoproductivity proxies (Ba, Cu, Ni, and Zn), and grainsize distributions reflected by Nd, Pr, Ce, La, Zr, Rb, Fe, and Cl concentrations. An example to this observation is the variation of S content, which is high in both coarse- and fine-grained intervals implying that redox conditions were not influenced by grain size variations. Similarly, palaeoproductivity, based on Ba values, was more or less uniform across the studied interval despite the observed grain size variations.
... (2) its seismic facies character, i.e., laterally continuous, relatively low-to moderate-amplitude reflections; and (3) the fact that syn-rift stratigraphic successions motifs are typically characterised by an upward-deepening motif, Unit 3 is interpreted as representing laterally continuous, pelagic and hemipelagic rocks deposited in an overall lowenergy environment (Figures 9i and 10g) (e.g., Gawthorpe & Leeder, 2000;Prosser, 1993;Ravnås et al., 2000). This interpretation is supported by the regional relative sea level rise that characterised the Middle-Late Jurassic (i.e., J40.0SB horizon; Longley et al., 2002). ...
The syn‐rift architecture of extensional basins records deposition from and interactions between footwall‐, hangingwall‐, and axially‐derived systems. However, the exact controls on their relative contributions and the overall variable depositional architecture, and how their sediment volume varies through time, remains understudied. We undertook a quantitative approach to determine temporal and spatial changes in the contribution of fault‐scarp degradation to the syn‐rift tectono‐stratigraphic development of the Thebe‐0 fault system on the Exmouth Plateau (NW Shelf, offshore Australia), using high‐quality 3D seismic reflection and boreholes data. The magnitude of footwall erosion was measured in terms of vertical (VE) and headward (HE) erosion by calculating the volume of eroded material along the footwall scarp. A detailed seismic‐stratigraphic and facies analysis allowed us to constrain the architectural variability of the hangingwall depositional systems and the types of resulting deposits (i.e., fault‐controlled base‐of‐scarp, settling from suspension, and hangingwall‐derived). After addressing the syn‐rift tectono‐stratigraphic framework, we suggest that periods of significant erosion along the Thebe‐0 fault scarp are related to the accumulation of fault‐controlled base‐of‐scarp deposits characterised by comprising a lower wedge with chaotic to low‐continuity reflections. Footwall‐derived deposits characterised by an upward decrease in stratigraphic dip are interpreted as related to periods of reduced fault activity and sustained sediment delivery sourced from the footwall scarp and systems beyond it (e.g., antecedent systems). We then analysed the tectono‐stratigraphic framework and the volumetric comparison between material eroded from the fault‐scarp and accumulated in the basin, aiming to estimate the contribution of fault‐scarp degradation to the hangingwall syn‐rift fill. Our results suggest periods of enhanced fault activity control fault‐scarp degradation variability through time, and we agree with that described by previous researchers—fault throw variability along‐strike regulates the variability in the magnitude of erosion. However, we propose that fault‐scarp degradation timing and its spatial variability are also influenced by the interaction and linkage with adjacent normal faults and by sea level variations. Lastly, we determine broader similarities and differences with a system located in the same fault array (i.e., Thebe‐2 fault system), aiming to give insights into the tectono‐stratigraphic evolution of a broader area and the spatial variability in fault‐scarp degradation.
... The method used to determine the relative age of rift faults was by observing syn-kinematic sedimentary wedges, which exhibit a divergent pattern in the hanging wall of the faults, with thickening towards the main faults (Prosser, 1993;Strugale et al., 2021). When syn-kinematic wedges were absent in the observed region, we assumed that fault nucleation occurred near to the horizon on which the fault exhibits its maximum throw (Walsh and Watterson, 1988). ...
... Esse padrão sugere estágios finais de quiescência tectônica e clima úmido, seguidos de um aumento na taxa de subsidência e aridez, como observado no arcabouço bacinal [3]. A base dos perfis estratigráficos relaciona-se às fácies lacustres de baixa energia e profundidades elevadas, correlacionáveis ao clímax da fase rifte [11] devido ausência de registros bioestratigráficos o posicionamento temporal é complexa. A análise estratigráfica demonstrou que acima dos limites superiores do trato de lago profundo (1350m; 1390m) as amostragens concentram-se nos reservatórios areníticos e dessa maneira foram desconsideradas para avaliação da geocronologia dos folhelhos, entretanto reavaliação com enfoque na cronologia de geração e migração do óleo utilizando mesma técnica, certamente trará luz a cronologia de eventos na bacia. ...
... For the Northern Fault, the hanging-wall stratal wedge that thickens towards the fault, and the broad fault-parallel hanging-wall syncline associated with SB1 are typical characteristics of border fault evolution in thick-skinned settings free from mobile salt (e.g. Prosser, 1993;Gawthorpe and Leeder, 2000;Young et al., 2001) A C C E P T E D M A N U S C R I P T (Fig. 7a). In contrast, the more complex geometry and hanging-wall architecture of the Southern Coffee-Soil Faults indicate that mobile Zechstein salt exerts a strong control on deposition during fault growth (Fig. 11). ...
We explore how relationships between fault activity, salt movement, and sediment loading impact hanging-wall stratal geometry throughout the evolution of a salt-influenced normal fault system. We examine a ∼65 km long portion of the Coffee-Soil Fault System (CSFS) in the Danish North Sea, the hanging-wall of which has been partially influenced by a pre-rift unit of mobile salt. To constrain the tectono-stratigraphic evolution of the CSFS we combine structural observations with seismic-stratigraphic analysis of hanging-wall growth strata.
We find that the hanging-wall of the CSFS shows major depocentre shifts through time, along with marked variability in along- and across-strike stratal geometries. We explain how the development of these characteristics is influenced by: i) the segmentation and linkage history of the fault system; ii) the evolution of salt-cored cover monoclines above blind basement fault segments; and iii) changes in the locations and rates of accommodation generated by load-driven withdrawal of salt up the hanging-wall dip-slope, and fault-related subsidence. Our findings have implications for structural and stratigraphic studies in salt-influenced rift basins, as well as for understanding the potential distribution of geo-storage and hydrocarbon reservoirs in such settings.
... S4 is marked by a reflector package with a simple parallel infill. Extracted from Prosser (1993). ...
The Búzios Field is one of the most prolific petroleum fields along the Eastern Brazilian Margin. Despite significant research conducted restrictedly on the pre-salt reservoirs, few studies have focused on the threedimensional characterization of the entire Búzios Field area. Therefore this work aims to spatially characterize
a volume along the Búzios Field area using 3D seismic volume interpretation, seismic attributes, and well-log
data. The combined use of these tools allowed the understanding of several parameters concerning the tectonostratigraphic evolution of the Santos Basin. Within the mapped area, we identified five units: Syn-Rift I, SynRift II, Post-Rift I, Post-Rift II, Drift I, and Drift II. The 3D model reveals significant features such as the depth
variation of the Syn-Rift I unit and the heterogeneous morphology of the Post-Rift II unit. The Syn-Rift I unit is
deeper towards the N-NW and shallower towards the S-SE due to a regional half-grabens system. This system
impacts the pre-salt geometry and thickness, as structural highs and lows are relevant factors in sediment accommodation. The Post-Rift I unit has a predominantly regular geometry and thickness but tends to thicken
towards the S-SE and exhibits slight downward flexure towards the NE in the southeast of the Búzios Field. In
three dimensions, the heterogeneous morphology of the Post-Rift II unit is evidenced by the variable thickness
and irregular topography, accounting for the intense halokinesis in the Santos Basin. Above the evaporite layer,
the thickness of the Drift I unit is highly conditioned by salt morphology, with thicker and deformed packages in
areas of thinner salt section. On the other hand, the Drift II unit shows relatively constant thickness with minor
variations near fault zones. Comparisons with other fields within the Santos Basin (Tupi and Sapinho´ a/Lapa)
reveal differences in layer thickness, mobilization, and rotation of the syn-rift blocks. The Post-Rift I layer (Barra
Velha Fm.) and the Post-Rift II package (Ariri Fm.) are thinner and less mobilized in the Búzios Field area.
Moreover, the syn-rift blocks are less rotated, and the internal reflectors have a lower inclination in the study
area when compared to these other fields. Therefore, this research concludes that the lower mobilization of salt,
the lower thickness of the post-rift package, and the minor syn-rift block rotation observed in the Búzios Field
area are associated with the relative distance from the continental margin and, consequently, with the amount of
displacement generated by the South Atlantic Rift. In this case, the Búzios Field is located in a more proximal
portion than the Tupi and Sapinho´ a/Lapa fields, exhibiting features suggestive of a lower displacement.
... Complex seismic-based follow-up is occasionally used to assess seismic characteristics [17]. The seismic features include topographical information such as tremor investigation flagging [24], immediate seismic-based pile evidence characteristics [25], and thinly-distributed strata inside exploration zones [26]. Several aspects of the portrayal of the repository were determined using a variety of seismic-based attributes that were grounded in reality [27]. ...
Globally, the deep water reservoir systems are comprised of a variety of traps. Lateral and downdip trapping features include sand pinch-outs, truncation against salt or shale diapirs, and monoclinal dip or faulting with any combination of trapping designs; the potential for massive hydrocarbon accumulations exists, representing significant exploration prospects across the planet. However, the deepwater turbidities and the submarine fans are two different types of traps, which are developed along the upslope and the basin floor fans. Among these two traps, the basin floor fans are the most prolific traps as they are not influenced by the sea-level rise, which distorts the seismic signals, and hence provides ambiguous seismic signatures to predict them as the hydrocarbon-bearing zones for future explorations. Therefore, the Deep-water channel-levee sand systems and basin floor fans sandstone establish the cost-economic stratigraphic plays. The subsurface variability is significant, and hence, characterizing the thick (porous) channelized-basin floor fans reservoir is a challenge for the exploitation of hydrocarbons. Present studies aim at the execution of seismic-based attributes and wedge modeling tools to accurately resolve and characterize the porous and gas-bearing reservoirs using the high-resolution seismic-based profiles, in SW Pakistan. The reflection strength slices better delineate the geomorphology of sand-filled channelized-basin floor fans as compared to the instant frequency magnitudes. This stratigraphic prospect has an area of 1180 km2. The sweetness magnitudes predict the thickness of channelized-basin floor fans as 33 m, faults, and porous lithofacies that complete a vital petroleum system. The wedge modeling also acts as a direct hydrocarbon indicator (DHI) and, hence, should be incorporated into conventional stratigraphic exploration schemes for de-risking the stratigraphic prospects. The wedge model resolves a 26-m thick hydrocarbon-bearing channelized-basin floor fans lens with a lateral distribution of ~64 km. Therefore, this wedge model provides ~75 % correlation of the thickness of the LSL as measured by sweetness magnitudes. The thickness of shale that serves as the top seal is 930 m, the lateral mud-filled canyons are 1190 m, and the thick bottom seal is ~10 m, which provides evidence for the presence of vibrant petroleum play. Hence, affirms the bright opportunities to exploit the economically vibrant stratigraphic scheme inside the OIB and other similar global depositional system
... The Araripe Basin (Fig. 1A) is embedded in the Precambrian São José do Caiano Terrane in the Transversal Zone Domain of the Borborema Province (Brito Neves et al., 2000), between the Pernambuco Shear Zone to the south and the Patos Shear Zone to the north. Following the model of Prosser (1993) and the adaptation of Kuchle and Scherer (2010) to the Brazilian basins, the stratigraphy of the Araripe Basin is divided in syneclise, early rift, rift climax and post-rift. The syneclise sequence is represented by the Paleozoic Cariri Formation (Assine, 2007), which outcrops to the east in the Cariri Valley. ...
The Santana Group, consisting of the Barbalha, Crato, Ipubi and Romualdo formations, records the postrift sequence of the Gondwana break-up in the Araripe Basin. The post-rift phase of the South Atlantic rifting is dated as the Alagoas Stage, which corresponds to the ostracod biozone 011. A detailed ostracod
stratigraphical distribution along the Santana Group, allowed to standardise a common ostracod for the biozone name and a code, the Pattersoncypris micropapillosa Biozone (OST-011). Four different ostracod associations were recognized establishing the subzones: Pattersoncypris cucurves (OST-011.1), Pattersoncypris cucurves-Neuquenocypris berthoui (OST-011.2), Damonella grandiensis (OST-011.3) and Pattersoncypris crepata (OST-011.4). Planktic foraminifera were also recovered in different associations,
leading to identify two international biostratigraphic intervals and calibrate the ostracod subzones, the Early Aptian Leupoldina cabri Zone includes the OST-011.1 and OST-011.2 subzones, and the upper Late Aptian Hedbergella infracretacea–Microhedbergella miniglobularis composite zone correlated to the OST-011.4 subzone. Between these zones there is an interval without foraminiferal biostratigraphy resolution, the OST-011.3 subzone which is assigned to the lower Late Aptian. The palaeoenvironmental evolution of
the Santana Group was reconstituted from the integrated study of ostracods, planktic and benthic foraminifera. Through the Aptian, the Araripe Basin evolved from a transitional to a marine environment, recording estuarine, fluvial to bayhead deltas, a bay coastal watershed that reached better-marine conditions under extreme aridity and the full installation of an epeiric sea flooding the area.
The Brazilian paleoxyloflora conspicuously lacks a robust Late Jurassic-Early Cretaceous record. However, several fossil woods have been reported since the 18th century from the Upper Jurassic to Lower Cretaceous deposits of Missão Velha Formation, Araripe Basin, northeastern Brazil, although no taxonomic and systematic analysis has been carried out so far. Here, we provide the first taxonomic and systematic study of these fossil woods, utilizing them for paleoclimatic and paleobiogeographic inferences for this region in equatorial Gondwana. We thus describe a new fossil-species, Metapodocarpoxylon brasiliense, and document, for the first time, the presence of Agathoxylon mendezii in Brazil. They are distinguished by characters of radial pit arrangement, cross-field pits, presence of resin plugs, axial parenchyma, septate tracheids, and ray seriation and height. These fossil-genera have been previously observed in other Mesozoic paleoxylofloras of Gondwana, being Metapodocarpoxylon, in particular, restricted to the tropical belt and coastal areas, and its occurrence in Brazilian paleofloras is unknown to date. Its new occurrence suggests a migration of this element of the paleovegetation towards inland areas likely triggered by paleoclimatic changes from the Late Jurassic onwards. The presence of indistinct and distinct growth rings with narrow late wood in the conifer assemblage suggests a moderately seasonal paleoclimate with rainy and dry seasons, which is also supported by the geological data, probably stimulated by the monsoonal regime in the basinal area. The new wood records, combined with geological and paleoclimatological background information and palynological data obtained from the study area in the early 2000’s allowed for a preliminary reconstruction of a segment of the landscape during deposition of the Missão Velha Formation.
Alkaline lakes hold significant biological, environmental, and economic importance, yet research on their deep-time formation remains limited. This study examines the sedimentary and evolutionary processes of the Permian Fengcheng Formation alkaline lake in the Mahu Sag, Junggar Basin, using seismic, well-log, core, mineralogical, and geochemical data. Results indicate that alkaline mineral formation primarily occurred in rift climax systems, where fan delta plains and lacustrine environments coexisted. Nahcolite (NaHCO3) formed as leafy crystals through evaporation on the outer fan margins, with nucleation at the bottom. Trona (Na2CO3·NaHCO3·2H2O) precipitated as raft-shaped crystals from saline water. Dark sediments interbedded with shortite (Ca2Na2(CO3)3) formed in deepwater environments under arid, cold conditions. The rift expansion facilitated evaporite deposition, and hydrothermal fluids contributed alkaline substances. Late Paleozoic glaciation increased chemical weathering, enhancing lake alkalinity, while arid conditions favored evaporite formation. An impermeable basement and semi-enclosed hydrology were critical for alkaline lake development. This study sheds light on the conditions for ancient sodium carbonate evaporite formation and provides insights into the sedimentary evolution of similar tectonic and climatic lake basins, offering a foundation for hydrocarbon exploration.
We analyse 498 faults identified in satellite imagery and interpret the height and width of associated footwall ranges with respect to co‐seismic elastic rebound from tectonic and erosional unloading. The dynamics of footwall uplift link uplands to catchment patterns and interrelated hanging wall sedimentary fans. Height–length relations of some catchments and associated alluvial fans scale linearly whereas others, such as fault‐slope catchments and related down‐fault fans (building out from faults) show a significant scatter without an obvious trend. Perched basins abandoned in the footwalls of younger faults offer catchment‐fan height–length relations like watergap and dipslope‐related fans and, besides, hint at reduction of dip angle due to rollback of larger faults before abandonment. Analysis of the width‐to‐height ratio ( W / h ) of footwall ranges offer a robust linear statistical trend, h = 0.06 W and is identical between datasets. This trend is valid for both arid and tropical rifts, the latter offering smaller rebounds. Contributions of elastic rebound on fault throw in our data are simplistically considered through comparison to global trends on fault length versus throw. This allows consideration around maximum throw ( T max ) linked to the maximum height of footwall ranges ( h ) and to their width ( W ) above the reference level. Basic calculations indicate that co‐seismic rebound contributes from <1% to 17% of extensional fault throw. Width‐to‐height ratios for large faults ( L > c. 50 km) show less spread than smaller faults. Such large faults expectedly dissect the brittle crust, indicating that these large faults which root in the ductile–brittle transition approach a balanced, steady‐state kinematic pattern. We speculate that significant crustal thinning associated with these large faults triggers the onset of isostatic adjustments that drive fault rotation, instigating fault abandonment and disconnected perched basins.
The Söğüt Mountains is a fault-bounded carbonate range situated between the active Acıgöl and Akgöl grabens in southwestern Türkiye. The southwestern sector of the Acıgöl Graben floor displays an array of faults that have produced peculiar intra-basin half-grabens with local lakes and drainages. The conspicuous geomorphic expression of the intra-basin faults and depressions in this sector of the basin is attributed to low sedimentation rate (i.e., starved basin) related to very limited runoff and sediment supply from the southwestern carbonate margin of the basin, dominated by subsurface drainage in a carbonate bedrock strongly affected by gravitational deformation and karstification. Detailed mapping reveals the presence of large landslides and extensive DSGSDs in the mountain fronts flanking the Söğüt Mountains, showing ridge-top depression, uphill-facing scarps, high-relief downhill-facing scarps, and toe bulges. Cartographic relationships provide insights into the development and evolution of the deformations in the slopes that experience continuous tectonic rejuvenation and debuttressing. DSGSDs and large landslides take advantage of secondary synthetic tectonic faults, in which gravitational and tectonic displacement are superposed. The transformation of DSGSDs into large to giant short runout landslides (up to ca. 3.5 Gm3) occurs mainly on laterally unconfined slopes associated with bends and stepovers in the basin-bounding faults. Seismicity is likely the main triggering factor controlling the kinematics of the gravitational deformations and landslides. Cartographic evidence indicate downslope propagation of the gravitational deformation (uphill-facing-scarps and associated troughs) in the tectonically growing slopes. Additionally, preferential development of solution sinkholes is observed in gravitationally distorted slopes with impeded surface drainage.
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Inherited rift topography controls the sediment routing, timing of sand supply, and sedimentary linkage of early post‐rift depocentres. Exhumed examples of early post‐rift turbidite systems are rare and previous studies have examined the evolution of individual depocentres; in contrast, the detailed evolution of early post‐rift turbidite systems across multiple depocentres has never been documented. Current fill‐and‐spill models do not detail the stratigraphic architecture and evolution of sedimentological characteristics of multiple intraslope fans developed across topography, including bed type distributions. Here, the evolution of three intraslope fans that developed across two early post‐rift depocentres is documented along an 18 km long transect in the southern Neuquén Basin, Argentina. The relative chronology of sand supply in depocentres is constrained with new U–Pb ages, and sediment source areas with provenance analysis. The early post‐rift intraslope fans record progradation of the system and progressive sedimentary linkage of post‐rift depocentres, transverse to local syn‐rift structures, with sediment routing subparallel to the cratonic basin margin. The large‐scale stratigraphic architecture of intraslope fans indicates an evolution as a fill‐and‐spill system, with initial confinement through flow stripping and overspill to spillover with erosion and bypass across a transverse topographic high separating the depocentres. Changes in early post‐rift intraslope fan characteristics, including thickness, sandstone content, lobe complex stacking patterns, stratal termination patterns and bed type distribution, record changing confinement through time within a depocentre, and spatially across depocentres. The strong spatial and vertical stratigraphic variability of transitional flow deposits and hybrid event beds reflects enhanced erosion, sediment bypass and flow transformation across transverse relief between the two depocentres during the spillover phase. These findings advance current understanding of early post‐rift turbidite systems and refine fill‐and‐spill models, which will help the prediction of spatial and vertical changes in rock quality and connectivity in subsurface hydrocarbon reservoirs and CO 2 storage sites.
O Grupo Brotas representa a fase de início de rifte na evolução tectono-sedimentar das bacias da Depressão Afro-Brasileira (Sequência Início de Rifte). A Formação Aliança compreende argilitos e folhelhos calcíferos castanho-avermelhados, maciços a laminados, siltitos cinza-esbranquiçados a esverdeados e níveis delgados de calcarenitos, arenitos calcíferos e, principalmente, calcários bioclásticos argilosos (grainstones), com feições de exposição subaérea (gretas de contração), fossilíferos e com forte diagênese ou localmente silicificados e, mais raramente, níveis centimétricos de evaporitos (gipsita), intercalados nos pelitos (argilitos e folhelhos). As intercalações de rochas carbonáticas são ricas em fósseis de ostracodes, conchostráceos e diversos fragmentos ósseos de peixes como Mawsonia gigas, escamas de Lepidotes sp, dentes isolados e espinhos de nadadeira dorsal de tubarão hybodontiforme, bem como Crocodylomorpha e abundantes traços fósseis (icnofósseis). A associação de ostracodes é característica de corpos lacustres permanentes de água-doce alcalina (e.g. Theriosynoecum pricei, T. uninodosa e Alicenula spp). A presença de formas fósseis exclusivamente não marinhas indica sedimentação de água doce. Assim, a paleogeografia da Formação Aliança inclui a presença de sistema lacustre, com aporte de sedimentos trazidos por rios efêmeros, que evaporavam pelas condições climáticas áridas predominantes e pelo tectonismo divergente atuante no Andar Dom João, formando a Depressão Afro-Brasileira. A Formação Sergi corresponde à unidade estratigráfica superior do Grupo Brotas. Caracteriza-se por arenitos, de granulação grossa a fina, por vezes conglomeráticos, com algumas intercalações de siltitos de coloração creme com tons avermelhados, apresentando estratificação cruzada acanalada. Característica importante dessa formação é o abundante conteúdo de lenhos fósseis silicificados e concreções de silexito. Os arenitos dessa unidade são interpretados como depositados em sistemas fluviais entrelaçados de alta energia com retrabalhamento eólico, representando
As the most prolific basin, Central Sumatra Basin is a very mature basin for hydrocarbon exploration. Most of the productive reservoir came from Neogen deposits therefore the stratigraphic reconstruction for depositional environment distribution focused on this deposits. Meanwhile the Paleogene deposits distribution and gross depositional environment (GDE) has not been explore further especially on the southern part on the basin. Paleogen deposits like Kelesa Formation is a syn rift deposition which was deposited in the center of the basin. The lithofacies development of the Kelesa Formation consist of 3 major lithofacies associations: (1) thick-bedded mudstone, (2) Interbedded sandstone and conglomerate, (3) Interbedded sandstones and mudstones. The thick-bedded mudstone is deposited in deep lake setting; interbedded sandstone and conglomerate is interpreted as alluvial fan deposit and interbedded sandstones and mudstones as a fluvial channel. GDE map of Kelesa Formation indicate that sandstones facies developed in fluvial and alluvial fan setting near the basin boundary consider as a potential for future hydrocarbon exploration. Keywords: Kelesa Formation; lithofacies; gross depositional environment; Paleogene deposits
Located in the Gulf of Guinea, the Kribi-Campo sub-basin belongs to the Aptian salt basins along the West African Margin. In this paper, we investigated the tectono stratigraphic architecture of the basin, focusing on the role of
salt tectonics and strike-slip faults along the Kribi Fracture Zone with implications for reservoir prediction.
Using 2D seismic data and well data interpreted through sequence stratigraphy with integrated seismic attributes analysis with Python Programming and unsupervised Machine Learning, at least 6 s-order sequences, indicating three main stages of tectono-stratigraphic evolution were determined: pre-salt syn-rift, post-salt rift climax and post-rift stages. The pre-salt syn-rift stage with KTS1 tectonosequence (Barremian-Aptian) reveals a transform rifting along NE-SW transfer faults associated with N–S to NNE-SSW syn-rift longitudinal faults bounding a NW-SE half-graben filled with alluvial to lacustrine-fan delta deposits. The post-salt rift-climax stage (Lower to Upper Cretaceous) includes 2 s-order tectonosequences (KTS2 and KTS3) associated to the salt tec-
tonics and Campo High uplift. During the rift-climax stage, the growth of salt diapirs developed syncline with-drawal basins filled by early forced regression, mid transgressive and late normal regressive systems tracts. The
early rift climax underline some fine grained hangingwall fan or delta deposits and coarse grained fans from the footwall of fault scarps. The post-rift stage (Paleogene to Neogene) contains at least three main tectonosequences KTS4, KTS5 and KTS6-7. The first one developed some turbiditic lobe complexes considered as mass transport complexes and feeder channel-lobe complexes cutting the unstable shelf edge of the Campo High. The last two developed submarine Channel Complexes associated to lobes towards the southern part and braided delta to tidal channels towards the northern part of the Kribi-Campo sub-basin.
The reservoir distribution in Kribi-Campo sub-basin reveals some channels, fan lobes reservoirs and stacked channels reaching up to the polygonal fault systems.
Fluvio-aeolian and lacustrine depositional systems are commonly associated with the initial sedimentary processes in rift-type basins, typically indicative of relatively calm tectonic settings. Fluvio-aeolian sandstones from the Boipeba Member of the Aliança Formation have been documented in well-drilled samples from the Recˆ oncavo and Tucano basins, with thicknesses decreasing progressively from south to north. These units constitute the Brotas Group, encompassing deposits from the Jurassic period (Dom Jo ̃ ao local Brazilian stage). However, due to the absence of any records within the Jatob ́ a Basin up until now, its occurrence in this basin remains uncertain. Based on facies analysis and depositional architectural elements, the fluvio-aeolian system of the Boipeba Member can be categorized into four associations (1) medium to low energy fluvial channels, (2) floodplains, (3) dunes and (4) sand sheets. Palaeocurrent data have indicated a variable paleoflow direction ranging from SW and NW, which is expected for the rift-onset phase fluvial system. Within the broader context of the Recˆ oncavo-Tucano-Jatob ́ a Rift System (RTJ), five distinct fluvial and/or aeolian units can be identified: the Tacaratu Formation (Syneclisis), the Boipeba Member (the basal unit of the Aliança Formation), the Sergi Formation (Early Rift), the S ̃ ao Sebasti ̃ao Formation (Rift), and the Marizal Formation (Post-Rift). The Boipeba Member is the first unit of the Early Rift Sequence in the RTJ, deposited in a fluvio-aeolian environment until it evolves to the exclusively lacustrine deposition of the Capianga Member (the upper unit of the Aliança Formation). The subsequent recurrence of the fluvio-aeolian cycle is evident in the Sergi Formation. Faciological and petrographic analyses of outcrops in drainage channels in the Tacaratu municipality, located in the southeastern part of the Jatob ́a Basin, were performed. The rock formations appear as whitish-gray sandstones, typically thin to medium, subrounded, and consistently sorted. Some samples exhibit clay matrix and contain feldspars. Notably, the presence of planar cross-stratifications and a distinct upper contact with sediments of lacustrine origin provide diagnostic features indicating the Boipeba Member. Based on the facies, depositional system and palaeocurrent analyses, the deposits of the Boipeba Member in the Jatob ́ a Basin were interpreted as resulting from fluvial channel sedimentation, followed by subsequent aeolian reworking. This process transitioned gradually to a lacustrine infilling, exemplified by the Capianga Member. Therefore, the Aliança Formation within the Jatob ́a Basin signifies the complete deposition of a fluvio-aeolian and lacustrine system, exhibiting both of its members, as observed in the other basins of the RTJ.
The Neo-Tethys margin evolution is preserved in the Northern Calcareous Alps (Eastern Alps), from Late Permian crustal stretching to Late Triassic oceanization. The Northern Calcareous Alps represent the salt-floored fold-and-thrust developed from the salt-influenced Triassic carbonate sedimentary cover of the ancestral European margin of the Neo-Tethys Ocean. A crustal scale model for the margin has been obtained by restoration of regional cross-sections of the Northern Calcareous Alps carbonate platforms. Lithospheric break-up was investigated from remnants of exhumed mantle found within an evaporitic melange, suggesting hyperextended crust underneath the distal Triassic platforms of the Northern Calcareous Alps preceding breakup. By modelling the thermal evolution of the margin in combination with excellent stratigraphic control, a detailed timeline has been established for the evolution of the Neo-Tethys margin, especially around the period of rapid mantle exhumation. Our study indicates that salt-floored carbonate shelfs can be used as a proxy to characterize the margins evolution, from crustal stretching to continental breakup. Diagnostic stratigraphic records are preserved in the carbonate platforms: pre- mantle exhumation carbonates are represented by aggrading isolated carbonate platforms first, followed by expanding and margin wide prograding carbonate shelfs once thermal subsidence dominates. In addition, a distinct clastic sequence is deposited as an immediate response to mantle exhumation, in between the pre- and post-mantle exhumation carbonate factory. Our study proposes a new refined model for the formation of the Neo-Tethys margin and provides new insights for the dynamic coupling of salt-controlled carbonate shelfs and the underlying lithosphere during continental breakup
Marine basin margins are characterized by repetitive episodes of progradation punctuated by periods of transgression and flooding of the depositional platform. The repetetitive stratigraphic architecture is the product of the ongoing interplay among sediment supply, basin subsidence (and uplift), and eustatic sea level change. A genetic stratigraphic sequence is the sedimentary product of a depositional episode. The sequence incorporates and reconciles depositional systems, bedding geometries, and bounding surfaces within the framework of cycles of basin-margin offlap and flooding. Each sequence consists of the progradational, aggradational, and retrogradational or transgressive facies deposited during a period of regional paleogeographic stability. The defining genetic stratigraphic sequence boundary is a sedimentary veneer or surface that records the depositional hiatus that occurs over much of the transgressed shelf and adjacent slope during maximum marine flooding. -from Author
Depositional sequences are composed of genetically related sediments bounded by unconformities or their correlative conformities and are related to cycles of eustatic change. The bounding unconformities are inferred to be related to eustatic-fall inflection points. They are either type 1 or type 2 unconformities, depending on whether sea-level fall was rapid (i.e., rate of eustatic fall exceeded subsidence rate at the depositional shoreline break) or slow (i.e., rate of eustatic fall was less than subsidence rate at the depositional shoreline break). Type 1 and type 2 unconformities are each characterized by a basinward shift of coastal onlap concomitant with a cessation of fluvial deposition. The type of subaerial erosion characterizing each unconformity is different. Type 1 unconformities are characterized by stream rejuvenation and incision, whereas type 2 unconformities typically are characterized by widespread erosion accompanying gradual denudation or degradation of the landscape. Timing of fluvial deposition is also a function of eustatic change insofar as global sea level is the ultimate base level to which streams will adjust. The elevations of stream equilibrium profiles are affected by eustatic change, and, assuming constant sediment supply, streams will aggrade or degrade in response to eustatically induced shifts in these profiles. Fluvial deposition occurs at different times in type 1 and type 2 sequences and is characterized by different geometries within each type of sequence. -from Authors
The steady state exists in a system of fans when all of the fans are increasing in thickness at approximately the same rate. Laboratory and field observations suggest that the steady-state slope of an alluvial fan is determined by debris size, depositional process, and water discharge. Large fans have larger drainage basins and hence larger discharges than small fans. Consequently, fan slope generally decreases with increasing fan area. Under otherwise equivalent conditions, fans composed of coarse material are steeper than those composed of fine material, and fans built largely by debris flows or sieve deposition are steeper than fans on which fluvial processes dominated.
A study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes, in which M sub o varies as L sup 2 or u = alpha L where L is rupture length and u is slip. In contrast to interplate earthquakes, for which alpha approximately equals 1 x .00001, for the intraplate events alpha approximately equals 6 x .0001, which implies that these earthquakes have stress-drops about 6 times higher than interplate events. This result is independent of focal mechanism type. This implies that intraplate faults have a higher frictional strength than plate boundaries, and hence, that faults are velocity or slip weakening in their behavior. This factor may be important in producing the concentrated deformation that creates and maintains plate boundaries.
Utilizes a new model of continental rift sedimentation that has been developed in the Tertiary to Recent rifts of East Africa. The structure of the Firth appears to have resembled the simple half-graben that makes up the great East African rift system. The fluvial sediments show evidence of tectonically induced cycles of sedimentation which are interpreted in terms of waves of detritus working down the drainage system. Suggests only small-scale fault activity and a relatively subdued topography during Triassic times. This is supported by evidence of extensive calichification during the Rhaetic which produced a top-Trias marker horizon found throughout the Inner Moray Firth. -from Authors
The (?) Permo-Triassic Stornoway Formation is c . 4000 m thick and consists mainly of conglomerates.
The sediments were deposited on alluvial fans as mudflow, streamflood and braided stream deposits, and on floodplains as channel and overbank sediments. In each of the lower, middle and upper units of the Formation there is evidence of two major phases of alluvial fan-building. It is suggested that these phases were tectonically controlled and that within each alluvial fan sequence the time-trend of sedimentation reflects the rate of basin subsidence. Fining-upwards fan sequences suggest basin-margin faulting of gradually decreasing intensity; coarsening-upwards sequences suggest a history of increasing fault intensity. Floodplain deposits, overlying either type of sequence, indicate a cessation of tectonism and a gradual overlap of the old fault lines by fine-grained sediment.
The Stornoway Formation is seen as the sedimentary fill within the deep, western margin of an asymmetrical North Minch (Permo-Triassic) Basin. Palaeogeographic reconstructions through time suggest that this western margin shifted westwards as the locus of faulting and fault-generated sedimentation migrated by 15 km from the Minch Fault.
Hornelen Basin (Devonian) is filled with ∼25 km of sediments, mostly sandstones. These sedimentary rocks are spectacularly organized into more than 150 basin-wide cycles, each on the order of 100 m thick, most of which coarsen upward. The cycles are otherwise complex, consisting of marginally derived fanglomerates and laterally equivalent, longitudinally dispersed alluvial plain sediments. The basin-wide nature of the cycles, the fact that the coarsening upward occurred at the same time in both marginal and axial facies, and because successive alluvial fan bodies coarsen upward whether they are composed of debris flow or of stream deposits suggest that the cycles are allocyclic and that they are the basin's response to the lowering of its floor. In their marginal development, the cycles are commonly segmented, consisting of coarsening-upward subcycles of the order of 10 to 25 m thick. The geometry and internal details of these suggest that they also were tectonically generated. It is likely that the 10 to 25-m coarsening-upward sequences, representing aggrading base-level conditions, were the basic sedimentary response to basin-floor subsidence. The 100-m cycles represent additional complexity in style of subsidence. Progressive eastward overlap of successive 100-m units suggests that at this interval the locus of subsidence abruptly shifted in a proximal direction, by ∼0.25 km. A dextral wrench fault model is proposed to account for this pattern of basin filling.
Eastward tilting of the Death Valley-Panamint Range structural block has resulted in segmentation of alluvial fans in south-central Death Valley. The youngest segment is generally near the fanhead on the east side and always near the toe on the west side. Six episodes of tilting have occurred, three of which postdate the last major high stand of Lake Manly, herein named the Blackwelder stand, which ended about 10,500 yrs ago. Estimates of the volume of sediment deposited after each episode of tilting suggest that distinct tectonic events occurred approximately 200, 1,000, 6,000, 17,000, 30,000, and 42,000 yrs ago. The average tilting rate appears to have increased exponentially with time. On the Black Mountains, immediately east of the structural block, deposits of tufa and of carbonate-cemented lacustrine, alluvial, and colluvial gravel of diverse age are presently perched at elevations up to 100m above present fans in positions where they could not have formed without support from older fans. On the west side of the valley, shorelines cut during the Blackwelder stand are about 30 m lower than these perched tufa and gravel deposits. Calculations based on these observations suggest that the average tilting rate doubled every 23,000 yrs during the late Wisconsin. The present rate is about 0.016 degrees/1,000 yrs.
Transfer zones in extensional regions display a wide range of geometries from discrete fault zones to zones of broad warping. The classification of extensional fault displacement transfer zones developed in this paper includes three main criteria: (1) primary subdivision of transfer zones by relative attitude and direction of throw of the major faults (synthetic and conjugate); (2) secondary subdivision of conjugate transfer zones into transfer zones where the normal faults dip toward each other (convergent) and where the transfer zones occur between faults that dip away from each other (divergent); (3) the tertiary subdivision of conjugate relationships of transfer zones and secondary subdivision of synthetic transfer zones are by the fault terminations in plan view; fault tips approach, or they overlap, completely overlap (termed collateral), or are in line (termed collinear). A high abundance of overlapping transfer zones occur in the East African rift where extension is low and large-scale cross faults (photo-transform faults?) are uncommon. Commonly, transfer zones in this region are relatively high areas with complex internal fault geometries flanked by deeps. Transfer zones in rifts contain complex but somewhat predictable structural geometries that make them optimum locations for structural hydrocarbon traps. The classification presented can help define and delineate those zones and to some degree predict their internal structural geometry.
The southern Alps of Italy preserve a tectonically intact array of Jurassic facies that record the evolution of a part of the margin of the Apulian plate from its ancestral beginnings in a complex of Permian and Triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform. Breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs. Then, as the new Ligurian oceanic basin began to open farther west and, as subsidence gradually slowed, accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility, carbonate dissolutio levels, and the strength of bottom currents. Estimates of the history of seafloor depths, based on a simple subsidence law of the form Subsidence = K(Age)12/, provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the Jurassic in this region. The rapid 1-km deepening of the compensation depth for calcite during the Late Jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling (fertile, silica-rich, carbonate dissolving) to downwelling (less fertile, silica-poor, carbonate preserving).
The Danish sector occupies a key position in the North Sea Rift at the junction of the NW-SE trending UK-Norwegian Central Graben and N-S trending Dutch Central Graben. The change of trend is accomplished through the activity of several closely spaced WNW trending zones of basement fracturing, which transect the transition area between the 2 rift elements. These WNW transverse zones combine with NNW fault trends to form a rhombohedral mosaic of structural highs and depocentres. Activity along the WNW trending faults dates from the Earth Carboniferous or possibly earlier, which is prior to the onset of rifting (Late Carboniferous-Early Permian). It is proposed that the WNW transverse zones are the W continuation of deep structures controlling the margins of the Ringkobing-Fyn High, which in turn form part of a splaying network of shear zones corresponding to the Tornquist Zone. The abrupt change of course of the North Sea Rift in the Danish sector is attributed to activity along the Tornquist Zone. In a wider context, the overall rift- rift offset pattern of the rift may reflect the original arrangement of localized pull-apart basins that formed along this crustal lineament during Late Variscan shear deformation.-Author
Tectonic control of alluvial architecture is commonplace in extensional, transcurrent and compressional tectonic terrains. The primary influence of tectonic activity on floodplain behavior is tilting, which varies areally and temporally and is superimposed on the pre-existing channel gradient. These effects are considered theoretically and illustrated by Pleistocene and Holocene examples from southwest Montana and the Mississippi Valley.
A transverse slope will cause the movement of channel belts toward the area of maximum subsidence either 1) by processes of downslope cutoff and preferential erosion, producing an abnormally wide and asymmetric sandstone body, or 2) in steps, by avulsion. Avulsion may be triggered by tilting or may occur subsequently through preferential flooding of the down-tilted side of the floodplain. Although the channel will move toward the position of maximum subsidence, it will often be offset by fans constructed from the footwall or it may flow into a lake occupying the floodplain low. Differential subsidence strongly affects deposition rates, groundwater behavior, pedogenesis and flood distribution, in addition to channel migration.
Submarine syn-rift deposits are commonly characterized by turbiditic assemblages. The sedimentary processes and the nature and organization of the depositional systems are governed by a variety of partly interrelated factors such as regional and local tectonic style, subsidence rate, sedimentation rate, compaction, composition of source terrain, base and sea-level, rate of sea-level change, climate, inclination and length of slopes, and depth and morphology of receiving basin. A major Mesozoic rift event in the northern North Sea-North Atlantic realm was initiated in mid-to-late Jurassic times, climaxed in the Early-Middle Volgian, and gradually abated in the early Cretaceous. The tectonic leitmotif was the tilted fault block. A variety of syn-rift turbidite systems was deposited in the basins formed over the hangingwall blocks. A number of examples have been selected to illustrate the great variation and difficulties of sediment-body correlation in these systems. Their main similarities and differences are highlighted and related to sea-level stand, tectonic style, provenance area and sedimentary processes. The relative effects of the governing factors are then isolated, and a number of predictions made concerning the facies types and architecture of clastic submarine syn-rift sequences in general. Predictions are strongly improved by precise dating and time-stratigraphic correlation within and between systems. -Author
The very rapid subsidence, sediment accumulation, and hydrocarbon maturation observed in many small extensional or 'pull-apart' basins can be explained using a McKenzie-type model. It has been shown that in basins of 100km width or less, lateral heat loss is quite important and accelerates lithospheric cooling and subsidence. We show here that cooling that is simultaneous with stretching is very important for basins formed by stretching of lithospheric blocks that are 10km to several tens of kilometers wide. In fact, for most of these very narrow basins, most of the anomalous heat introduced by stretching is also dissipated during the stretching event. We have calculated the effect of alternate short periods of stretching and cooling to approximate simultaneous stretching and cooling. The results show, for example, that for a block, initially 10km wide and stretched uniformly at 3cm/yr, sufficient subsidence will take place in 200 000yr to accumulate 4-5km of sediment. A consequence of this rapid subsidence is initial sediment starvation. These results may be applicable to many of the small extensional basins associated with the San Andreas transform system.-Authors
Thick nonmarine sequences with similar facies and geometry may accumulate in basins that develop adjacent to strike-slip faults. Herein we compare 3 basins of different age and size whose tectonic and depositional characteristics suggest a similar origin and history. The Hornelen Basin developed during the Middle and possibly Early Devonian in W Norway. The basin is 60-70km long, 15-25km wide, and approx 1250km2 in areal extent; its cumulative fill of 25 000m was deposited at an estimated rate of 2.5m/1000yr. The Ridge Basin developed during the Miocene and Pliocene between the right-lateral San Gabriel and San Andreas faults in S California. The basin is 30-40km long, 6-15km wide, and approx 400km2 in areal extent; its cumulative fill of 7000-11 000m was deposited at an estimated rate of approx 3m/1000yr. The 3 Little Sulphur Creek Basins probably developed between 4-2Ma along the E side of the right-lateral Maacama fault zone in N California. These basins cumulatively are approx 12km long, 1.5-2km wide, and approx 15km2 in areal extent; their cumulative fill of 5000m was deposited at an estimated rate of approx 2.5m 1000yr.-from Authors
The Barrow province lies at the transition between the western and northwestern rift domains of the Australian continental margin. As these domains evolved during the Mesozoic, five depositional wedge sequences developed in the eastern half of the province. Each sequence possesses distinct stratigraphic and sedimentological characteristics, which differs from the others as a function of proximity, direction, and style of rift-related diastrophism along the evolving margin. -from Authors
The Gulf of Suez is an active rifted basin which originated in the early Miocene after a phase of Eocene shallowing and Oligocene emergence. The rift cuts across the Precambrian basement and the E- W facies belts of the sedimentary cover. Initial rifting produced a fault-bounded trough; the preliminary fill comprises basalts and red-beds and is followed by more extensive marine trangressive clastics that pass up into deep-water marls. Later Miocene uplift generated spreads of coarse gravels representing fan and fan-delta deposits with associated coral reefs. Downwarping in the Middle Miocene allowed tilted fault blocks to be draped by basinal evaporites. Thus, this rift has a complex geological history which cannot be readily modelled by reference to either the simple stretching or doming models that are currently popular. -R.A.H.
The quantitative model presented simulates the development of a two-dimensional alluvial sedimentary succession beneath a floodplain traversed by a single major river. Several inter-related effects which influence the distribution of channel-belt sand and gravel bodies within overbank fines are accounted for. These are (a) laterally variable aggradation, (b) compaction of fine sediment, (c) tectonic movement at floodplain margins, and (d) channel avulsion. Selected experiments with the model show how the interconnectedness and areal density of channel-belt deposits decrease with increasing floodplain width/channel-belt size, mean avulsion period, and channel-belt aggradation rate. Separation of stream patterns based on interconnectedness and channel deposit density is difficult. Tectonic movements do not have a significant influence upon the successions unless a preferred direction of tilting is maintained (half-graben). Then channel-belt deposits showing offlap tendencies tend to cluster adjacent to the active floodplain margin, leaving dominantly fine-grained alluvium to accumulate on the inactive side. Individual channel-belt deposits thicken during aggradation, although a self-regulating limit to such thickening is likely to operate. ‘Multistorey’features resulting from aggradation may be difficult to tell apart from those arising through superposition of distinct channel-belt deposits of avulsive origin.
The age and significance of sequence boundaries on Jurassic to Early Cretaceous rifted continental margins in three ocean basins have been documented. The margins are the Santos basin in the South Atlantic, the Grand Banks in the North Atlantic, and the Beaufort Sea in the Arctic Ocean. Large industry data bases were used for the interpretation of each area. Megasequence boundaries separate the major phases of basin evolution, for example syn-rift and post-rift. Boundaries developed with an average periodicity of 49 m.y. Sequence boundaries define the component parts of each megasequence and developed with a modal periodicity of 10-15 m.y. Out of 27 total boundary ages, most (16) are developed on just one margin. Only two possible age ranges overlap on all three margins. 80% of the megasequence boundaries and 50% of the sequence boundaries show a direct causal connection with coveal faulting and/or folding. The rest of the boundaries appear as unstructured surfaces separating transgressive and/or regressive sedimentary wedges and are interpreted to result from changes in the rate of basin subsidence, sediment input, and long-term eustatic sea level. These data do not support theories advocating synchronous worldwide boundary development resulting from periodic, short-term falls in global eustatic sea level. Only in like basins of the same age, with identical subsidence and sediment input rates, are boundaries likely to develop synchronously. Hence, the concept of global synchroneity of sequence boundary development may well be an illusion created by the similarity in age of the majority of basins studied. As a result of this study, it seems wise to discard the global approach to basin analysis. 13 figures, 1 table.
The subsidence history of Australia's southern margin is shown to consist of two distinct tectonic phases and has important implications for models of sedimentary basin formation. The first phase is characterized by rapid tectonic subsidence (about 50 m/m.y) which lasted for about 25-30 m.y. during the Early Cretaceous. The period of rapid subsidence represents the rifting phase of margin development. This early stage is correlated with associated rifting phenomena: faulting and extension of the brittle upper crust, formation of grabens and half-grabens, and the rapid accumulation of volcanogenic detritrus (Otway Group). The amount of extension (20-50%) is estimated from a comparison of observed and modeled tectonic subsidence at several exploratory wells along the margin. The model includes uniform extension and thinning of the continental lithosphere, a prolonged extensional event followed by simple cooling, horizontal and vertical conduction of heat, and radioactive heat production by the crust. The rift phase may have begun earlier, but the most rapid and widespread subsidence occurred during the Early Cretaceous. The end of rapid and widespread subsidence occurred during the Early Cretaceous. The end of rapid subsidence coincides closely with the age of the oldest sea floor spreading magnetic anomaly (about 90 Ma) adjacent to the continent-ocean boundary (COB). The second state of margin development is the post-rift (or drift) phase, a period of much slower rates of subsidence and relative tectonic quiescence. Subsidence during the post-rift stage is modeled as cooling and contraction of extended continental lithosphere. Estimates of extension and thinning from subsidence modeling agree with seismic refraction measurements of the thickness of continental crust near the COB.
Evidence reviewed in this paper indicates that intraplate stresses in the lithosphere are of substantial magnitude. Numerical modelling and observation of modern and paleo-stress fields demonstrate the existence of stress provinces of great areal extent in the interiors of the plates. The interaction of intraplate stresses with basin subsidence provides a new element in basin analysis. Fluctuations in intraplate stress fields influence basin stratigraphy and provide a tectonic explanation for short-term, relative sea-level variations inferred from the sedimentary record. Modelling shows that the incorporation of intraplate stresses in models of basin evolution can predict a succession of onlap and offlap patterns similar to those observed at basin flanks. Such a stratigraphy can be interpreted as the natural consequence of short-term changes in basin shape by moderate fluctuations in intraplate stresses, superimposed on long-term broadening of the basin with cooling since its formation. Basin stratigraphy could provide a new source of information for paleo-stress fields.
Multifold seismic reflection and geologic mapping in part of the eastern branch of the East African Rift system of northern Kenya reveal a major rift structure containing at least 3 km of Neogene sediment fill beneath Lake Turkana. This includes a series of half-graben basins, with centrally located Quaternary volcanic centers, which are linked end-to-end by structural accommodation zones. Whereas the geometry of rifting is similar to that of the nonvolcanic western branch of the East African Rift system, the Turkana half-grabens are much smaller and may reflect extension of a thinner lithosphere or development of more closely spaced fracture patterns during rift evolution, or both.
The nonmarine Upper Jurassic-lowermost Cretaceous Todos Santos Formation of central Chiapas, Mexico, was deposited in half-graben basins formed during the early rifting stage of the southern Gulf of Mexico Basin. This formation consists of alluvial-fan, fluvial, and lacustrine sequences that were deposited under arid climatic conditions. Alluvial fans were built outwardly from the elongate basin margins by runoff that flowed transverse to the basin axis, whereas fluvial units were deposited by rivers that flowed parallel to the basin axis. Lacustrine deposition took place in a topographic depression adjacent to the basin margin. The presence of alluvial-fan and fluvial or lacustrine deposits in vertically stacked, cyclic megasequences hundreds of meters thick indicates that the basin opography changed through time. This cyclicity denotes that periodically fluvial or lacustrine environments occupied the basin-margin position and at other times alluvial-fan sedimentation occurred there. Cyclicity was caused by periodic changes from high to low rates of basin subsidene. The response of these three depositional environments to basin subsidence differed due to the unique hydrologic controls on sediment transport and deposition in each environment. Lakes were maintained by springs that emanated from the fractured fault margin and by fluvial discharge. Fluvial discharge and deposition resulted from precipitation or annual snowmelt anywhere in the river's expansive drainage basin, whereas alluvial-fan sedimentation occurred only when there was infrequent, significant precipi ation in the small drainage basin from which fan sediment was derived. As a result of these hydrologic controls, the lacustrine or fluvial environments responded more quickly to periods of active tectonic subsidence and migrated over the fans to occupy the basin-margin depression. Aided by a decrease in basin subsidence, alluvial fans eventually prograded and displaced the fluvial or lacustrine environments away from the basin margin.
This paper addresses the problem of the dating of motion on large, extensional faults, from the seismic expression of the sedimentary sequences deposited during and after the extensional deformation. A general discussion of the interpretational methods and pitfalls involved in a seismically based, kinematic analysis is made by reference to a case study of the Coffee Soil Fault, which forms the eastern boundary of the Central Graben of the North Sea Rift. The case study is used to demonstrate that onlap of remnant fault scarps can easily be mistaken for syn-rift deposition, and that this can lead to considerable errors in the timing of the end of rifting. -from Author
Extensional tectonism produces characteristic half-graben/tilt-block systems whose facies mosaics are influenced by tectonically induced slopes resulting from hanging wall downtilting and footwall uplift. The characteristic asymmetrical subsidence vectors that therefore develop across the graben also exert a fundamental control upon facies distributions. A number of predictive tectono-sedimentary facies models are presented in which these various influences are explored. Alluvial fans and cones react to tilting by becoming segmented, those in the hanging wall showing down-dip hanging wall off-lap and those sourced in the footwall showing progradation from the apex. Lake and coastal waters react instantly to tilting, causing transgression and seiche-induced erosion. Axial through-flowing river channels and delta lobes tend to migrate or avulse towards the axis of maximum subsidence but may be constrained by the toes of footwall-sourced fans. Peat accumulation or soil development are accentuated up the hanging wall dip slope away from the locus of maximum deposition. In coastal areas, fan deltas sourced in the footwall pass offshore into small submarine fans whilst axial fans issue from delta fronts where individual fan lobes may migrate under fault control. In carbonate provinces the footwall scarp may become a bypass margin whilst the hanging wall dip slope may undergo a ramp-to-rimmed shelf evolution with time.
A preliminary interpretation of a deep seismic reflection profile across the N North Sea provides an insight into the crustal structure beneath the major extensional rift, the Viking graben. The Viking graben was initiated during the early Mesozoic and evolved during the Jurassic-Cretaceous into an asymmetrical half-graben, fault-bounded on its W side. Deep seismic reflections enable an interpretation of the position of the Moho to be made, and an estimate of the amount of crustal extension, within the plane of the section, of 50% has been calculated.-from Authors
The Orcadian Basin of northern Scotland (largely of Middle Devonian age) is a major lacustrine rift basin, with the widely correlateable, Achanarras/Sandwick lake bed extending for at least 800 km along the rift. Above this lake bed, there are about 540 m of cyclic lacustrine sediments, with lake sedimentation terminated by alluvial fan progadation. The Upper Stromness Flagstone Formation and the Rousay Flagstone Formation making up this lacustrine sequence are given revised and precise definitions within four reference sections from the Orkney Islands. The sequence consists of about 45 first-order cycles averaging about 12 m in thickness, which resulted from long-term climatic fluctuations in rainfall with a cycle time-scale of about 25 000 years. Longer climatic fluctuations of about 100000 and 400000 years are also present. These periods correspond to the precession and two eccentricity orbital cycles.
Detailed knowledge of the stratigraphy constrains the structural and maturation history of the basin. The basin formed in a series of extensional half graben, and the Orkney area suffered later inversion. The lake sediments first reached the oil window at relatively shallow depths ( c . 2000 m), probably in the early Carboniferous, implying very high geothermal gradients during the early part of the basin history as corroborated by the presence of Devonian volcanics in the region. In the Orkney area, uplift probably started in the late Carboniferous.
The Mesozoic tilted fault block in Norwegian North Sea block 30/6 containing the giant Oseberg oil and gas field is used to illustrate basin development during the Jurassic and Cretaceous. There is seismic evidence for an early rifting phase in the N Viking Graben, on which the Jurassic/Cretaceous rifting phase (early Bathonian to Berriasian) is overprinted. Planar normal faults and listric faults which were restricted to the rifting phase dominate. The topography, defined by the post-rift unconformity, is a composite surface which formed in response to subsidence proceses.-from Authors
The thickest part of asymmetric rift, pull-apart, and foreland basin fills commonly consists of large-scale (hundreds to thousands of metres thick), tectonically generated cyclothems of fine-grained marine, lacustrine, or longitudinal fluvial deposits and coarse-grained transverse braid-plain or alluvial-fan deposits. The appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source-area uplift, based on the conceptual tie between relief and coarse grain size, and on the application of the Davis theory of landform development. We propose the opposite interpretation: that the commencement of fine-grained sedimentation above coarse-grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity. This reinterpretation is more consistent with (1) modern examples, (2) the consideration of source-area and sedimentary-basin geomorphology, (3) the disparity between the reaction rates of the various environments to subsidence, (4) the disparity between the rates of tectonic uplift and erosion, and (5) the controls on elastic-wedge progradation. In our model, extensive coarse-grained clastic-wedge progradation is an indicator of tectonically quiescent phases.
In the seismically active Malaŵi rift (Africa), uplifted segments of the border fault system flank basins with different acoustic stratigraphies, sediment thicknesses and styles of faulting. Regionally curvilinear border fault segments bound sigmoidal-shaped basins linked along the length of the rift in accommodation zones. Accommodation zones that trend oblique to the approximately N-S trend of the rift system occur within the rift valley bounded by border fault segments, suggesting little thinning occurs beneath the elevated rift flanks. Cross-sectional morphologies and fault patterns within Malaŵi rift basins depend on the geometrical arrangement of border fault segments and these patterns are similar to those observed in the Tanganyika rift. Border fault segments locally may reactivate or have an orientation sub-parallel to Proterozoic-Mesozoic structures, but the border fault segmentation and alternating asymmetries of rift basins show no consistent relationship with pre-existing faults and lithologic contacts. The central parts of border fault segments, where maximum vertical displacements have been observed, are separated from any adjacent segment by 50–90 km in both the Malaŵi and Tanganyika rifts. The uniform separation of border fault segments in both the Malaŵi and Tanganyika rifts, despite their differences in age and geologic setting, suggests stress concentrations with an average spatial wavelength of 70 km occur along the length of the Tanganyika and Malaŵi rifts.
The Tertiary Bohai rift system of the eastern part of China consists of several rift basins and represents one of the important petroleum provinces of China. Four major aspects of sedimentology of the rift basins are summarized and discussed in this paper: (1) facies types and their characteristics; (2) the pattern of spatial distribution and temporal evolution of sedimentary facies, facies associations and sequences of the basins; the typical depositional models and facies associations have been established and are illustrated according to different evolutionary stages of the rift basins; (3) two main controlling factors—tectonics and paleoclimate; and (4) relationships between the distribution of oil and gas and the sedimentary facies and depositional models of the rift basins and how to apply them to predict the occurrence of oil and gas.
A review of selected subsurface data (mostly seismic-reflection data) from the Great Basin indicates that the basins form in one of 3 ways. Historic, Holocene, or latest Pleistocene surface ruptures are associated with each type of basin. Indentification of the type of normal faulting associated with each basin, as well as with the province boundaries, is critical to accurate assessment of both earthquake hazards and resource potential. As basins mature, they grow larger by one or more of 4 sedimentary or structural processes and as they grow broader or coalesce, the deformation style becomes less complex. Evolutionary trends also reflect a broadening of the spacing between the faults that play an active role in basin development. The possibility exists that, in some areas, extension on widely spaced, steep, deeply penetrating faults is a late-stage process that evolved from earlier large-magnitude extension on shallow listric faults, rotated planar faults, and/or detachment faults that developed near sites of strong thermal (magmatic) disturbance. -from Authors
Detailed studies of high-resolution and multifold seismic reflection
data from the two largest East African rift lakes, Malawi and
Tanganyika, reveal a complex suite of coarse-grained depositional
facies. These facies occur within specific regions of the controlling
half grabens that compose the rift lakes. Sand-prone environments
include subaqueous channels and small drowned fluvial complexes. Channel
systems range from large erosional canyons to deep-water turbidite
channel-levee systems. Lowstand and highstand deltas of axial and
shoaling-side rivers are volumetrically important coarse-grained facies.
Fan deltas develop along the base of major border faults during lake
lowstands; subaqueous talus fan deposits occur along the base of the
border faults during lake highstands. Lowstand deltas are the
best-preserved progradational facies in these rift lakes. In addition to
simple tectonic control, drastic tectonically or climatically induced
lake-level change significantly regulates the production of
coarse-grained lacustrine synrift deposits.
The response to extensional stresses that deformed and finally ruptured
the northwest Australian passive margin was achieved by an interplay of
simple and pure shear mechanisms. The results of a two-ship seismic
reflection and refraction experiment show that the outer Exmouth Plateau
is dominated by large rotated blocks bounded by deeply penetrating
normal faults, some of which are heavily intruded. Magmatic underplating
attended this extension but is absent in the central region where a set
of prominent, subhorizontal, mid-crustal arrivals are interpreted to be
detachment surfaces. Extensive exploration seismic coverage, drilling,
and sampling suggest that deformation on the outer plateau postdates
that in the central plateau. We propose that initial deformation of the
region was dominated by a simple shear detachment system along low-angle
fault planes. This passed laterally and temporally into a region of pure
shear deformation characterized by high-angle normal faults and
magmatism, and this became the locus of final rupture.
Transfer zones form important structural elements in extensional basins, accommodating displacement changes between individual fault and basin segments. Transfer zone geometry is related to the extension direction and the displacement, dip polarity, overlap and overstep of fault/basin segments adjacent to the zone. Topographic changes associated with transfer zones have a direct influence on drainage basin evolution, sediment transport and stratigraphy.
Two main categories of transfer zone can be identified: (i) interbasin transfer zones, linking individual half graben, and (ii) intrabasin transfer zones, linking individual fault segments within a half graben. Interbasin transfer zones range from interbasin ridges to broad faulted highs and major relay ramps. They have a marked influence on basin stratigraphy and drainage evolution, often separating half graben with distinct stratigraphies and acting as conduits through which major axial depositional systems enter the rift zone. Intrabasin transfer zones range from relay ramps separating adjacent en echelon normal faults to discrete fault jogs. Intrabasin transfer zones commonly act as a conduit for local sediment transport, but have minimal effect on basin-scale stratigraphy. Transfer zones also affect early post-rift sedimentation and are important elements in controlling fluid migration in the subsurface.