V. Paul Wright

National Museum Wales, Cardiff, Wales, United Kingdom

Are you V. Paul Wright?

Claim your profile

Publications (38)80.5 Total impact

  • V. P. Wright · A. J. Barnett ·

    Geological Society London Special Publications 07/2015; 418(1). DOI:10.1144/SP418.3 · 2.58 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The unusual occurrence of calcretes and prominent organic matter in the Middle Jurassic (Lower Bathonian, Serra de Aire Formation) of the Lusitanian Basin of western Portugal (Western Iberian Margin) revealed a complex palimpsest exposure record, here interpreted as reflecting hydrological changes caused by phases of emergence and immersion. It serves as a potential model for understanding strtigraphic development at lowstand surfaces in ther carbonate successions. The exposure-dominated facies association grades upwards into peritidal and lagoonal limestones, and the interval is assigned to the regressive peak of a Transgressive-Regressive Facies Cycle (2nd order) of the thick Middle Jurassic carbonate ramp succession.
    Sedimentary Geology 05/2015; 323. DOI:10.1016/j.sedgeo.2015.04.012 · 2.67 Impact Factor
  • V. Paul Wright · Juan Ignacio Baceta · Philippe A. Lapointe ·

    06/2014; 2(3):SF1-SF16. DOI:10.1190/INT-2013-0175.1
  • A.J. Barnett · V.P. Wright · S.F. Crowley ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Orange to tan weathering ferroan dolomites associated with palaeosols are a volumetrically minor but conspicuous feature of cyclic late Mississippian (Brigantian) icehouse ramp successions in Kentucky, eastern USA. The ferroan dolomites have sharp bases and tops and are intercalated with pedogenic units (e.g. calcretes) or floodplain deposits. Sedimentological and C/O stable isotope data suggest that the dolomiteswere formed in brackish or schizohaline coastal marsh (paludal) environments. This chapter establishes the origin of these ferroan dolomite beds, documents their sequence stratigraphic significance, and draws attention to a potentially wide-spread but rarely documented sub-aerial exposure feature. Paludal dolomite beds associated with well-developed palaeosols and major (Myr-scale) disconformities probably reflect depressed Milankovitch band sea-level oscillations that occurred during third-order lowstands.
    Linking Diagenesis to Sequence Stratigraphy, 05/2013: pages 477-499; , ISBN: 9781118485392
  • L. Cherns · V. P. Wright ·
    [Show abstract] [Hide abstract]
    ABSTRACT: It is now well established that seawater chemistry, as well as influencing non-skeletal marine precipitation ('calcite' and 'aragonite seas'), has affected skeletal mineral secretion in some algal and marine invertebrate groups. Skeletal mineralogy has had a yet more profound consequence on fossil preservation. The realization that the fossil record of marine organisms with an aragonite shell is widely depleted in some shelf settings through early, effectively syn-depositional, dissolution ('missing molluscs' effect) has led to a re-evaluation of the composition, diversity, ecological and trophic structure of marine benthic communities. Comparisons of molluscan lagerstätten from 'calcite' and 'aragonite seas' show a similar pattern of skeletal mineralogical loss, that is, no differences are discernibly linked to changed seawater geochemistry. It is notable that the rare mollusc-rich skeletal lagerstätten faunas in the fossil record include many small individuals. Micromolluscs are quantitatively important among modern shell assemblages, yet small size is a major source of taphonomic and biodiversity loss in the fossil record. In skeletal lagerstätten faunas, micromolluscs contribute variably to mollusc biodiversity but appear particularly significant through at least to Triassic times. They highlight a further 'missing molluscs' effect of taphonomic loss through early dissolution.
    Geological Society London Special Publications 12/2011; 358(1):9-17. DOI:10.1144/SP358.2 · 2.58 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Current classifications of carbonate platforms use depositional gradient as the main criterion for separating systems into two end-member types, ramps and flat-topped platforms (FTPs). However, many examples do not conform to this simple classification. To investigate why this is and to better understand probable controls on platform development, we have used a series of 2D numerical forward model runs to investigate how sediment production, diffusional sediment transport, and other controls such as tectonic subsidence, antecedent topography, and relative sea-level oscillation interact to determine platform geometry. Modeling results reaffirm that rates of down-dip sediment transport relative to rates of autochthonous production are a critical factor in maintaining a ramp profile in stable cratonic settings under a constant rate of relative sea-level rise. Type of carbonate production versus water-depth curve, for example euphotic versus oligophotic, is not a significant control in our model cases. Both euphotic and oligophotic production profiles produce FTPs when diffusion coefficients are low relative to production rates, and ramps when diffusion coefficients are relatively high. These results suggest a continuum of platform types, ranging from transport-dominated, low-gradient systems at one end of the spectrum, to in situ accumulation dominated systems at the other. A system may be transport-dominated because high-energy processes are able to break down and transport even bound sediment, or because carbonate factories produce only sediment that is easily transportable under even low-energy conditions. Time evolution is also probably important. Initially low gradient systems will, in the absence of sufficiently high sediment transport rates, tend to evolve towards high-gradient flat-topped steep-margined platforms. Many observed or inferred platform geometries are therefore likely to be transient forms, and this could complicate interpretation. Investigating how basin bathymetry and style of subsidence control platform geometry suggests that, in transport-dominated systems, strata simply drape the underlying topography, and that pre-existing breaks of slope and differential fault subsidence are a stronger control on platform geometry in in situ accumulation dominated systems. Rotational subsidence tends to create transport-dominated systems during rotation as the topographic gradient increases and transport rate increases and outpaces in situ production rate. Relative sea-level oscillations tend to move the locus of sediment production laterally along any slope present on the platform, distributing the sediment accumulation across the whole width of the platform, suppressing progradation and steepening, and so favoring development of low-gradient systems. Based on all these results, we suggest that a simple cutoff classification into ramp and flat-topped platform types can still be useful in some circumstances, but a more meaningful approach may be to describe and predict platform strata in terms of a multiple-dimension platform parameter space containing a continuum of geometries controlled by sediment production, sediment diffusion coefficient, antecedent topography, differential subsidence effects, relative sea-level oscillations and perhaps other as yet unappreciated controls.
    Journal of Sedimentary Research 01/2011; 81(1-2). DOI:10.2110/jsr.2011.6 · 1.79 Impact Factor
  • Lesley Cherns · James R. Wheeley · V. Paul Wright ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Early diagenetic dissolution of skeletal carbonate in environments from seafloor to shallow burial has the potential to skew the marine fossil record of aragonitic shells, particularly molluscs. Taphonomic windows leading to the preservation of labile skeletal components include relatively rare occurrences of early mineral replacement by silica (skeletal lagerstätten). Another, much more frequent process is event deposition where dissolution is halted by rapid burial of shells. Shell plasters form in basinal mud or low energy lagoonal environments during temporary dysoxic episodes, such as are caused by algal blooms. Preservation potential for aragonitic fossils may be enhanced by early cementation during shallow burial (hardgrounds) that protects the delicate dissolution moulds from destruction by bioturbation, or in high energy shoal environments where the drive for microbial dissolution is reduced. A data-based environmental model summarizes the main taphonomic zones, and illustrates significant taphonomic bias against aragonitic shells in lower energy settings of platform interiors and mid-outer ramps/shelves. The temporal distribution of various taphonomic windows shows the limited occurrence of silicified faunas, while the nature and extent of shell beds also change, but there is no obvious correlation with periods of ‘calcite’ and ‘aragonite seas’.
    11/2010: pages 79-105;
  • Lesley Cherns · V. Paul Wright ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Quantitative analysis of rare skeletal Lagerstatten of Paleozoic-early Mesozoic ages indicates that early dissolution of aragonite has seriously skewed community structures. The consequences of this widespread diagenetic process effectively preclude accurate interpretation and reconstruction of many fossil faunas in shelf settings. Trophic and ecologic loss focuses on the shallow infaunal tier of burrowing bivalves and the epifaunal vagrant detritus-feeding tier represented by gastropods. Case studies of the Ordovician-Carboniferous suggest that sequences with apparently typical Sepkoski Paleozoic faunas dominated by brachiopods were originally molluscan-dominated and included significant infaunal components. Early Mesozoic faunas dominated by epifaunal and semi-infaunal bivalves are similarly severely skewed by loss of ecologic diversity. Molluscan biodiversity appears more strongly affected in Paleozoic times. Such lower-energy environments as lagoons and mid-to-outer carbonate ramp settings are especially prone to dissolution loss. It is perhaps important to question for such faunas whether trophic tiers are reduced or missing.
    Palaios 10/2009; 24(11):756-771. DOI:10.2110/palo.2008.p08-134r · 1.79 Impact Factor
  • Susan B. Marriott · V. Paul Wright · Brian P. J. Williams ·
    [Show abstract] [Hide abstract]
    ABSTRACT: As much as 80% of the 4.5-km-thick succession of alluvial sediments of late Silurian to early Devonian age in South Wales is composed of mudstone, generally regarded as overbank suspension deposits. Studies of selected formations reveal a variety of lithofacies associations in these mud-dominated intervals, which suggest diverse mechanisms for mud emplacement. For example, there are distinct fining upward units, 2.5–5 m thick, that represent ephemeral channel-zone deposits in which extensive reworking of palaeo-Vertisols took place as clay pellet bedload material. The overall depositional system has many similarities with that described from the Channel Country of central Australia, where anastomosing fluvial systems are associated with distal mud sheetflood deposits. The exact channel planforms for the Old Red Sandstone systems, however, cannot be readily determined, although where larger channel sandbodies exist they have a sheet-like occurrence with a high width/depth ratio, and possibly may be the result of large-scale, low-frequency sheet-flood events. The development of palaeosols with vertic features, calcretes, alternations of desiccation and burrowing in the channel deposits suggests marked seasonality with a flashy regime. The Channel Country represents a fairly stable low-relief cratonic interior, whereas the Old Red Sandstone in South Wales was deposited on a coastal-plain in a subsiding basin setting. There are, however, similarities in terms of depositional products despite the disparity in morpho-tectonic setting, which may reflect extremely low gradients and climatic influences such as frequency and magnitude of flood events.
    Fluvial Sedimentology VII, 03/2009: pages 517 - 529; , ISBN: 9781444304350
  • Source
    Lesley Cherns · James R. Wheeley · V. Paul Wright ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent studies on silicified fossil biotas have suggested that substantial skewing of the molluscan record resulted from early aragonite dissolution in mid-outer carbonate ramp settings. If those rare skeletal lagerstätten are representative, then the quality and completeness of the molluscan record are thrown into doubt. Yet database studies suggest that the bivalve fossil record is actually relatively complete. If so, then biodiversity must be captured by other processes that preserved shells vulnerable to early dissolution, and which operated on a relatively high frequency, i.e., less than the species duration for bivalves.Storm beds, shell plasters and submarine hardgrounds are identified as fossil deposits that can preserve the labile aragonitic component of the fauna and thus represent potential taphonomic windows. Many storm event beds include rich accumulations of shelly benthos. Differences between storm bed faunas and those of the background facies could reflect transportation effects. However, some storm bed assemblages are rich in originally aragonitic infaunal bivalves that are not represented in background facies or more proximal shelf equivalents, and here rapid burial and removal of organic matter by winnowing may be the keys to aragonite shell preservation. Despite Palaeozoic to Cenozoic changes in the thickness and frequency of shell beds that reflect the predominant bioclast producers, shallow infaunas are commonly concentrated together with epifauna in such deposits.Some low energy, organic-rich mud-dominated settings are associated with preservation of aragonitic molluscs. Infaunal bivalves are a prominent component of shell plasters or pavements in such settings, linked to episodic bottom water anoxia. Decaying algal blooms drew the redox boundary up above the sediment–water interface, and brought populations of infaunal bivalves to the surface where they died. Isolated from the oxic taphonomically active zone, the shells were not dissolved and were buried as thin shell layers. In similar settings, aragonitic shells were preserved as moulds through early pyritisation, or even through preservation of original shell aragonite.In oxic environments, bioturbational reworking of surface sediment destroyed moulds of aragonitic shells after early dissolution. In some hardgrounds, these delicate moulds were preserved due to synsedimentary cementation, probably using carbonate released by aragonite dissolution. The examples included here come from both intervals of “calcite” and “aragonite” seas, and it is not possible to assess whether the saturation state (with respect to aragonite) of the ambient sea water played a role in the selective removal of aragonitic shells.While taphonomic windows may have captured the diversity of individual groups, it is clear from quantitative data involving skeletal lagerstätten that the scale of loss from early aragonite dissolution has drastically altered the trophic composition of some fossil assemblages commonly used as the basis for reconstructions of past communities.
    Palaeogeography Palaeoclimatology Palaeoecology 12/2008; 270(3-270):220-229. DOI:10.1016/j.palaeo.2008.07.012 · 2.34 Impact Factor
  • P. M. Burgess · V. P. Wright · D. Emery ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The mechanisms responsible for formation of peritidal parasequences have been a focus of debate between proponents of contrasting autocyclic and allocyclic models. To contribute to this debate a three-dimensional numerical forward model of carbonate production, transport and deposition has been developed. Shallowing-upward parasequences are produced in the model via carbonate island formation and progradation, with an element of self-organization, and no external forcing. These autocyclic parasequences have characteristics comparable with peritidal parasequences observed in outcrop. Modelled parasequence thickness and duration depend primarily on subsidence rate and sediment transport rate, illustrating the significance of sediment flux in formation of peritidal parasequences. Adding an element of stochastic variation of sediment transport rate and transport path leads to formation of nonuniform-thickness parasequences that generate Fischer plots showing apparent hierarchies similar to those often interpreted as evidence of eustatic forcing. The model results do not rule out allocylic mechanisms, but suggest that shoreline and island progradation are also plausible mechanisms to create variable-thickness, shallowing-upward peritidal parasequences and should be considered in interpretations of such strata.
    Basin Research 10/2008; 13(1):1 - 16. DOI:10.1046/j.1365-2117.2001.00130.x · 2.73 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Study of four closely-spaced El Garia Formation reservoirs (offshore Tunisia) has identified diagenetic controls on variation in reservoir quality. The Ashtart, Didon and Zarat Fields have been affected by significant dissolution porosity, which occurred during burial diagenesis, with vuggy pores preferentially forming in micritic sediment. However, inter-crystalline porosity due to dolomitisation is the principal control on reservoir quality in the Hasdrubal Field. This spatial variation in porosity type reflects, to some extent, the structural and sedimentological isolation of Hasdrubal within the facies trend, surrounded by deep water embayments and, unlike the other studied fields, not directly underlain by salt diapirs.Burial corrosion appears to have formed where mid to outer ramp, mud-rich El Garia Formation facies directly overlie salt domes, a consequence of the circulation of aggressive fluids related to increased heat flow above the salt. Inorganic CO2, focused into the reservoir prior to hydrocarbon emplacement by faults related to salt movement, is the most likely candidate responsible for the burial dissolution porosity observed in the Ashtart, Didon and Zarat fields. A salt diapir does underlie the most basinward (north-east) margin of Hasdrubal, and minor dissolution porosity is present, but we conclude that the absence of significant dissolution in Hasdrubal is due to its offset position, away from the highly faulted roof zone immediately above the salt. Although we favour this model, we cannot rule out that the absence of dissolution porosity in Hasdrubal may reflect the early emplacement of hydrocarbons from an older (non-Bou Dabbous Formation) source, or differences in the timing of salt movement and consequent fault creation below Hasdrubal compared to the other fields, local temperature and/or acid concentration effects, or a different source of CO2. Differences in the distribution of dissolution porosity in the Ashtart, Didon and Zarat Fields may be related to the presence of intra-reservoir permeability barriers, due to increased nummulithoclastic (= fragmented Nummulites) content. This may also explain the strata-bound nature of the dolomite in Hasdrubal, which, like the dissolution porosity in Ashtart, is overlain by sediments with an increased nummulithoclastic content. Although dolomite is present in variable quantities in all of the studied fields, the significant volume of dolomite in Hasdrubal may reflect a local ‘plumbing’ effect, with dolomitising fluids entering the reservoir via a fault network that does not affect the other fields.
    Sedimentary Geology 09/2008; 209(1-209):42-57. DOI:10.1016/j.sedgeo.2008.06.006 · 2.67 Impact Factor
    [Show abstract] [Hide abstract]
    ABSTRACT: The Mississippian - Pennsylvanian Global Stratotype Section and Point (GSSP) are hosted within a shallow-water, dominantly carbonate succession in the lower part of the Bird Spring Formation at Arrow Canyon, Nevada, USA. The boundary is marked by the first appearance datum (FAD) of the conodont Declinognathodus noduliferus sensu lato. It is shown that the boundary interval is punctuated by numerous subaerial hiatuses represented by palaeokarstic surfaces and palaeosols, which divide strata at this location into fourth-order glacio-eustatic cycles. A well-developed palaeosol horizon occurs <1 m above the FAD of D. noduliferus. It also coincides with a very marked facies change and a second-order shift in cycle-stacking patterns. These characteristics violate International Commission on Stratigraphy guidelines, which state that GSSPs should be chosen in sections showing continuous sedimentation and lacking vertical facies changes at or near the boundary. Because the Mid-Carboniferous is an icehouse interval, cyclostratigraphy is a powerful tool for high-resolution correlation. A comparison of the cyclostratigraphy of Mid-Carboniferous strata at Arrow Canyon and in northern England indicates that a large number of glacio-eustatic sea-level oscillations are not recorded at Arrow Canyon and that this section contains over 25 missed beats of Milankovitch band duration equating to a hiatus of ≥1 Ma.
    Journal of the Geological Society 07/2008; 165(4):859-873. DOI:10.1144/0016-76492007-122 · 2.64 Impact Factor
  • Source
    James R. Wheeley · Lesley Cherns · V. Paul Wright ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Aragonite derived from marine molluscs is evaluated as the source for microcrystalline carbonate cements of limestone-mar] alternations (LMA). Calculations demonstrate that extremely low levels of mollusc-derived aragonite, well below the production rates of molluscs in modem marine settings, could have provided sufficient carbonate to cement examples of Ordovician, Silurian and Jurassic LMA in non-tropical or tropical settings. It is likely that even in the Palaeozoic molluscs provided sufficient carbonate entirely to source microcrystalline cements of LMA. Autochthonous molluscan aragonite is the only viable aragonite precursor for LMA microcrystalline cements of cool-water settings where temperatures precluded calcified algae and abiotic carbonate precipitation. In 'calcite seas' where Mg:Ca ratios inhibited both abiogenic aragonite precipitation and aragonite generation by calcified algae, molluscan aragonite was again the most likely main contributor. In some epeiric seas where brackish wedges switched off the shallow-water carbonate mud factories molluscan aragonite is the parsimonious source of carbonate for LMA microcrystalline cements.
    Journal of the Geological Society 01/2008; 165(1):395-403. DOI:10.1144/0016-76492006-160 · 2.64 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Early Devonian Conigar Pit Sandstone Member (CPSM) of the Freshwater West Formation (Lower Old Red Sandstone, Lochkovian age) at Freshwater West in south Wales comprises a heterolithic, predominantly alluvial suite (mudstones, fine to coarse-grained sandstones, conglomerates) with varying depositional architecture. A number of discrete facies associations are observed. The fine-grained, inclined- and non-inclined heterolithic association is dominant within the CPSM. It represents dryland sinuous channelized flow (IHS bedsets) and unconfined flow (non-inclined bedsets) at terminal and intermediate floodouts deposited under semi-arid conditions. Mudstones were deposited in two distinct environments associated with this semi-arid river system. Laminated and burrowed, reddish brown mudstones were deposited in shallow semi-permanent lakes or pools on the floodplain. Massive mudstones were deposited as within-channel muddy braid-bars, with sedimentary structures being lost during subsequent compaction. The mudstones exhibit Vertisol pedogenesis reflecting the seasonal wetting and drying associated with the semi-arid climate. Periods of intense desiccation are indicated by deep desiccation cracks and associated rubbly surfaces. Possible, though unproven tidal conditions influenced a small percentage of the heterolithic channels at Freshwater West. The extent of these channels is uncertain. The coarser-grained multi-storey sandstone association was deposited by low-sinuosity rivers with a fluctuating, but perennial discharge. Associated with these laterally extensive sandbodies was a high water table with surface ponding (wetlands) that enabled the preservation of plant detritus. During high discharge events, flow expanded over the contemporaneous floodplain depositing the sheet sandstone association within splay complexes. The interpretation that perennial discharge may have been triggered by basin-wide climate change challenges the long-held view that the Lower ORS climate was continuously semi-arid in nature. The spatial/temporal extent of this climate change is uncertain, as it is possible that the multi-storey sandbodies were deposited by allogenic rivers draining a distant, possibly uplifted source area. A decrease in the observed frequency and maturity of Vertisol profiles, and a corresponding increase in multi-storey sandbodies upward through the succession may reflect a long-term, episodic pattern of climate change.
    Sedimentary Geology 11/2007; 202(1):35-57. DOI:10.1016/j.sedgeo.2007.05.006 · 2.67 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An extensive palaeokarst porosity system, developed during a pronounced mid-Paleocene third-order lowstand of sea level, is hosted in Danian limestones of the Urbasa–Andia plateau in north Spain. These limestones were deposited on a 40–50 km wide rimmed shelf with a margin characterised by coralgal buildups and coarse-grained bioclastic accumulations. The sea-level fall that caused karstification was of approximately 80–90 m magnitude and 2.5 Ma in duration. During the exposure, a 450 m wide belt of sub-vertical margin-parallel fractures developed a few hundred metres inboard of the shelf edge. Most fractures are 90–100 m deep, average 1 m in width, and are associated with large erosional features created by collapse of the reefal margin. Inland from the fracture belt, three superimposed laterally extensive cave systems were formed over a distance of 3.5 km perpendicular to shelf edge, at depths ranging from 8–31 m below the exposure surface. The palaeocaves range from 0.3 to 2 m in height, average 1.5 m high. They show no evidence of meteoric processes and are filled with Thanetian grainstones rich in reworked Microcodium, a lithology that also occurs infilling the fractures. The caves are interpreted as due to active corrosion at the saline water–fresh-water mixing zone. Caves are missing from the shelf edge zone probably because the fractures beheaded the meteoroic lens preventing mixing-zone cave development beyond the fracture zone. Towards the platform interior, each cave system passes into a prominent horizon, averaging 1 m in thickness, of spongy porosity with crystal silt infills and red Fe-oxide coatings. The spongy horizons can be traced for 5.5 km inboard from the cave zone and occur at 10.5 m, 25 m and 32 m below the exposure surface. In the inland zone, two additional horizons with the same spongy dissolution have been recognised at depths of 50 m and 95 m. All are analogous to Swiss-cheese mixing-zone corrosion in modern carbonate aquifers and probably owe their origins to microbially-mediated dissolution effects associated with a zone of reduced circulation in marine phreatic water. In the most landward sections a number of collapse breccia zones are identified, but their origin is unclear. The palaeokarst system as a whole formed during the pulsed rise that followed the initial sea-level drop, with the three main cave-spongy zones representing three successive sea-level stillstands, recorded by stacked parasequences infilling large erosional scallops along the shelf margin. The geometry of the palaeo-mixing zones indicates a low discharge system, and together with the lack of meteoric karstic features favours a semi-arid to arid climatic regime, which is further supported by extensive calcrete-bearing palaeosols occurring in coeval continental deposits.
    Sedimentary Geology 07/2007; 199(3-199):141-169. DOI:10.1016/j.sedgeo.2007.01.024 · 2.67 Impact Factor
  • V. Paul Wright ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Needle-fibre calcite occurs in association with root structures in a Lower Carboniferous calcrete crust. The origin of this form of calcite is discussed and the scattered literature from soil science, microbiology and geology is reviewed. It is concluded that while needle-fibre calcite is not diagnostic of any environment its origin is related to the activities of various micro-organisms, especially fungi. The use of needle-fibre calcite as a climatic indicator is reviewed and it is used, with other criteria, as evidence of fluctuating climates in the Lower Carboniferous.
    Geological Journal 04/2007; 19(1):23 - 32. DOI:10.1002/gj.3350190103 · 1.63 Impact Factor
  • V. Paul Wright · Susan B. Marriott ·
    [Show abstract] [Hide abstract]
    ABSTRACT: Mudrocks are a prominent feature of many ancient dryland successions but they are not always a product of the settling out of suspension load. From studies of the late Silurian–early Devonian Old Red Sandstone mudrocks of South Wales it has been shown that many were not overbank sediments deposited from suspension on floodplains, but were emplaced as sand- and silt-sized aggregates transported as bed load and deposited in sinuous channels and as braid-bar complexes on multi-stage floodplains in dryland river systems. Using the Old Red Sandstone examples criteria are provided for the recognition of similar deposits in the sedimentary record. One important aspect of these mudrocks is that they can represent multiple recycling events and can constitute condensed deposits that may be characteristic of closed alluvial basins with periodically limited sediment supply.
    Sedimentary Geology 02/2007; 195(1-195):91-100. DOI:10.1016/j.sedgeo.2006.03.028 · 2.67 Impact Factor
  • Source
    Simon James Beavington-Penney · Victor Paul Wright · Andrew Racey ·
    [Show abstract] [Hide abstract]
    ABSTRACT: The middle Eocene Seeb Formation represents deposition on one of the earliest "modern" style carbonate platforms, i.e., influenced by seagrasses and mangroves, and presents an opportunity to explore controls on the preservation of Cenozoic carbonate lithofacies. In the study area, the Seeb Fm. is dominated by an anomalously thick (approximately 250 m) and uniform package of shallow marine, platform-interior sediments. These nodular, indistinctly bedded shallow-subtidal sediments display no evidence for relative sea-level change (such as subaerial exposure features), and lack the shallowing-upwards cyclothems that have characterized carbonate sediments deposited in platform-interior settings throughout much of the rock record (particularly during greenhouse periods). We conclude that this is a consequence of thorough bio-retexturing of the sediment by burrowing organisms and the roots of marine vegetation, which destroyed primary fabrics, facies diversity, evidence for cyclicity, and "missing time" horizons such as cycle-bounding exposure surfaces. It seems possible that the remarkable thickness of apparently acyclic Seeb Fm. sediment that built up may reflect increased bio-disturbance of the shallow marine environment following the Late Cretaceous expansion of seagrasses and mangroves. A similar lack of peritidal cyclothems may be common to many Cenozoic shallow marine carbonate deposits. "Missing time" horizons in limestones, reflecting erosion or nondeposition, have been identified by some authors to explain discrepancies between low calculated accumulation rates of ancient sediments and higher rates measured in comparable modern environments. However, our studies of the Seeb Fm. suggest that the significance of such "missing time" horizons in ancient sediments may have been overstated, and that apparent differences between modern and ancient accumulation rates are a consequence of the extrapolation of unrepresentative, localized high rates of modern sediment production to large (platform-scale) areas. Our study reinforces the idea that modern sediment production and accumulation rates may be much lower than previously thought because they are typically measured in highly productive areas such as seagrass beds and do not take into account the highly variable nature of carbonate production, storage, erosion, and destruction across platforms. Therefore, far less "missing time" needs to be inferred for ancient sediments to account for any imbalance between modern and ancient sediment accumulation rates.
    Journal of Sedimentary Research 10/2006; 76(10). DOI:10.2110/jsr.2006.109 · 1.79 Impact Factor
    [Show abstract] [Hide abstract]
    ABSTRACT: ABSTRACT A thin calcrete-crust horizon from the Lower Carboniferous Llanelly Formation of South Wales consists of two parts; an upper laminated unit and a lower peloidal unit. The former is interpreted as a subaerial stromatolite and the latter as an A horizon of a palaeosol. Comparisons are made with the A horizons of rendzinas and it is concluded that the calcrete-crust represents a complete rendzina profile. This fossil rendzina contains abundant evidence of a soil fauna in the form of fecal pellets and small burrows.
    Sedimentology 06/2006; 30(2):159 - 179. DOI:10.1111/j.1365-3091.1983.tb00663.x · 2.95 Impact Factor

Publication Stats

899 Citations
80.50 Total Impact Points


  • 2015
    • National Museum Wales
      • Department of Natural Sciences
      Cardiff, Wales, United Kingdom
  • 2001-2011
    • Cardiff University
      • School of Earth and Ocean Sciences
      Cardiff, Wales, United Kingdom
  • 2006-2007
    • Milton Keynes College
      Milton Keynes, England, United Kingdom
    • University of Bristol
      Bristol, England, United Kingdom
  • 2002-2007
    • University of Wales
      Cardiff, Wales, United Kingdom
  • 2003
    • University of South Wales
      Понтиприте, Wales, United Kingdom