Imperial College London

PETER A. ALLISON

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Earth Science
 
 
 
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Contact

 

+44 (0)20 7594 6479p.a.allison Website

 
 
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Location

 

4.84Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

101 results found

Collins DS, Avdis A, Wells MR, Dean CD, Mitchell AJ, Allison PA, Johnson HD, Hampson GJ, Hill J, Piggott MDet al., 2021, Prediction of shoreline–shelf depositional process regime guided by palaeotidal modelling, Earth-Science Reviews, Vol: 223, ISSN: 0012-8252

Ancient shoreline–shelf depositional systems are influenced by an unusually wide array of geological, biological and hydrodynamic processes, with sediment transport and deposition primarily determined by the interaction of river, wave (including storm) and tidal processes, and changes in relative sea level. Understanding the impact of these processes on shoreline–shelf morphodynamics and stratigraphic preservation remains challenging. Numerical modelling integrated with traditional facies analysis provides an increasingly viable approach, with the potential to quantify, and thereby improve understanding of, the impact of these complex coastal sedimentary processes. An integrated approach is presented here that focuses on palaeotidal modelling to investigate the controls on ancient tides and their influence on sedimentary deposition and preservation – one of the three cornerstones of the ternary process classification scheme of shoreline-shelf systems. Numerical tidal modelling methodology is reviewed and illustrated in three palaeotidal model case studies of different scales and focus. The results are synthesised in the context of shoreline–shelf processes, including a critique and modification of the process-based classification scheme.The emphasis on tidal processes reflects their global importance throughout Earth’s history. Ancient palaeotidal models are able to highlight and quantify the following four controls on tidal processes: (1) the physiography (shape and depth) of oceans (1000s km scale) determines the degree of tidal resonance; (2) the physiography of ocean connections to partly enclosed water bodies (100–1000s km scale) determines the regional-scale flux of tidal energy (inflow versus outflow); (3) the physiography of continental shelves influences shelf tidal resonance potential; and (4) tides in relatively local-scale embayments (typically 1–10s km scale) are influenced by the balance of tidal amplification

Journal article

Lyster SJ, Whittaker AC, Hampson GJ, Hajek EA, Allison PA, Lathrop BAet al., 2021, Reconstructing the morphologies and hydrodynamics of ancient rivers from source to sink: Cretaceous Western Interior Basin, Utah, USA, Sedimentology, Vol: 68, Pages: 2854-2886, ISSN: 0037-0746

Quantitative reconstruction of palaeohydrology from fluvial stratigraphy provides sophisticated insights into the response, and relative impact, of tectonic and climatic drivers on ancient fluvial landscapes. Here, field measurements and a suite of quantitative approaches are used to develop a four-dimensional (space and time) reconstruction of palaeohydrology in Late Cretaceous palaeorivers of central Utah, USA – these rivers drained the Sevier mountains to the Western Interior Seaway. Field data include grain-size and cross-set measurements and span five parallel fluvial systems, two of which include up-dip to down-dip transects, across seven stratigraphic intervals through the Blackhawk Formation, Castlegate Sandstone and Price River Formation. Reconstructed palaeohydrological parameters include fluvial morphologies (flow depths, palaeoslopes, palaeorelief and planform morphologies) and various hydrodynamic properties (flow velocities, water discharges and sediment transport modes). Results suggest that fluvial morphologies were similar in space and time; median flow depths spanned 2 to 4 m with marginally greater flow depths in southerly systems. Meanwhile palaeoslopes spanned 10−3 to 10−4, decreasing downstream by an order of magnitude. The most prominent spatio-temporal change is an up to four-fold increase in palaeoslope at the Blackhawk–Castlegate transition; associated alluvial palaeorelief is tens of metres during Blackhawk deposition and >100 m during Castlegate Sandstone deposition. This study observed no change in unit water discharges at the Blackhawk–Castlegate transition, which argues against a climatically driven increase in palaeoslope and channel steepness. These findings instead point to a tectonically driven palaeoslope increase, although one limitation in this study is uncertainty in palaeochannel widths, which directly influences total water discharges. These reconstructions complement and expand on extensive p

Journal article

Jones LA, Dean CD, Mannion PD, Farnsworth A, Allison PAet al., 2021, Spatial sampling heterogeneity limits the detectability of deep time latitudinal biodiversity gradients, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 288, ISSN: 0962-8452

Journal article

Lyster SJ, Whittaker AC, Allison PA, Lunt DJ, Farnsworth Aet al., 2020, Predicting sediment discharges and erosion rates in deep time—examples from the late Cretaceous North American continent, Basin Research, Vol: 32, ISSN: 0950-091X

Depositional stratigraphy represents the only physical archive of palaeo‐sediment routing and this limits analysis of ancient source‐to‐sink systems in both space and time. Here, we use palaeo‐digital elevation models (palaeoDEMs; based on high‐resolution palaeogeographic reconstructions), HadCM3L general circulation model climate data and the BQART suspended sediment discharge model to demonstrate a predictive, forward approach to palaeo‐sediment routing system analysis. To exemplify our approach, we use palaeoDEMs and HadCM3L data to predict the configurations, geometries and climates of large continental catchments in the Cenomanian and Turonian North American continent. Then, we use BQART to estimate suspended sediment discharges and catchment‐averaged erosion rates and we map their spatial distributions. We validate our estimates with published geologic constraints from the Cenomanian Dunvegan Formation, Alberta, Canada, and the Turonian Ferron Sandstone, Utah, USA, and find that estimates are consistent or within a factor of two to three. We then evaluate the univariate and multivariate sensitivity of our estimates to a range of uncertainty margins on palaeogeographic and palaeoclimatic boundary conditions; large uncertainty margins (≤50%/±5°C) still recover estimates of suspended sediment discharge within an order of magnitude of published constraints. PalaeoDEMs are therefore suitable as a first‐order investigative tool in palaeo‐sediment routing system analysis and are particularly useful where stratigraphic records are incomplete. We highlight the potential of this approach to predict the global spatio‐temporal response of suspended sediment discharges and catchment‐averaged erosion rates to long‐period tectonic and climatic forcing in the geologic past.

Journal article

Chiarenza A, Farnsworth A, Mannion PD, Lunt DJ, Valdes P, Morgan JV, Allison PAet al., 2020, Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction, Proceedings of the National Academy of Sciences of USA, Vol: 117, Pages: 17084-17093, ISSN: 0027-8424

The Cretaceous/Paleogene mass extinction, 66 Ma, included the demise of non-avian dinosaurs. Intense debate has focused on the relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms for this event. Here, we combine fossil-occurrence data with paleoclimate and habitat suitability models to evaluate dinosaur habitability in the wake of various asteroid impact and Deccan volcanism scenarios. Asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats. Conversely, long-term forcing from Deccan volcanism (carbon dioxide [CO2]-induced warming) leads to increased habitat suitability. Short-term (aerosol cooling) volcanism still allows equatorial habitability. These results support the asteroid impact as the main driver of the non-avian dinosaur extinction. By contrast, induced warming from volcanism mitigated the most extreme effects of asteroid impact, potentially reducing the extinction severity.

Journal article

Dean C, Allison P, Hampson G, Hill Jet al., 2019, Aragonite bias exhibits systematic spatial variation in the late Cretaceous Western Interior Seaway, North America, Paleobiology, Vol: 45, Pages: 571-597, ISSN: 0094-8373

Preferential dissolution of the biogenic carbonate polymorph aragonite promotes preservational bias in shelly marine faunas. Whilst field studies have documented the impact of preferential aragonite dissolution on fossil molluscan diversity, its impact on regional and global biodiversity metrics is debated. Epicontinental seas are especially prone to conditions which both promote and inhibit preferential dissolution, which may result in spatially extensive zones with variable preservation. Here we present a multi-faceted evaluation of aragonite dissolution within the late Cretaceous Western Interior Seaway of North America. Occurrence data of molluscs from two time intervals (Cenomanian-Turonian boundary, early Campanian) are plotted on new high-resolution paleogeographies to assess aragonite preservation within the seaway. Fossil occurrences, diversity estimates and sampling probabilities for calcitic and aragonitic fauna were compared in zones defined by depth and distance from the seaway margins. Apparent range sizes, which could be influenced by differential preservation potential of aragonite between separate localities, were also compared. Our results are consistent with exacerbated aragonite dissolution within specific depth zones for both time slices, with aragonitic bivalves additionally showing a statistically significant decrease in range size compared to calcitic fauna within carbonate-dominated Cenomanian-Turonian strata. However, we are unable to conclusively show that aragonite dissolution impacted diversity estimates. Therefore, whilst aragonite dissolution is likely to have affected the preservation of fauna in specific localities, time averaging and instantaneous preservation events preserve regional biodiversity. Our results suggest that the spatial expression of taphonomic biases should be an important consideration for paleontologists working on paleobiogeographic problems.

Journal article

Jones LA, Mannion PD, Farnsworth A, Valdes PJ, Kelland S-J, Allison PAet al., 2019, Coupling of palaeontological and neontological reef coral data improves forecasts of biodiversity responses under global climatic change, Royal Society Open Science, Vol: 6, ISSN: 2054-5703

Reef corals are currently undergoing climatically driven poleward range expansions, with some evidence for equatorial range retractions. Predicting their response to future climate scenarios is critical to their conservation, but ecological models are based only on short-term observations. The fossil record provides the only empirical evidence for the long-term response of organisms under perturbed climate states. The palaeontological record from the Last Interglacial (LIG; 125 000 years ago), a time of global warming, suggests that reef corals experienced poleward range shifts and an equatorial decline relative to their modern distribution. However, this record is spatio-temporally biased, and existing methods cannot account for data absence. Here, we use ecological niche modelling to estimate reef corals' realized niche and LIG distribution, based on modern and fossil occurrences. We then make inferences about modelled habitability under two future climate change scenarios (RCP4.5 and RCP8.5). Reef coral ranges during the LIG were comparable to the present, with no prominent equatorial decrease in habitability. Reef corals are likely to experience poleward range expansion and large equatorial declines under RCP4.5 and RCP8.5. However, this range expansion is probably optimistic in the face of anthropogenic climate change. Incorporation of fossil data in niche models improves forecasts of biodiversity responses under global climatic change.

Journal article

Chiarenza A, Mannion P, Lunt D, Farnsworth A, Jones L, Kelland S-J, Allison Pet al., 2019, Ecological niche modelling does not support climatically-driven dinosaur diversity decline before the Cretaceous/Paleogene mass extinction, Nature Communications, Vol: 10, Pages: 1-14, ISSN: 2041-1723

In the lead-up to the Cretaceous/Paleogene mass extinction, dinosaur diversity is argued to have been either in long-term decline, or thriving until their sudden demise. The latest Cretaceous (Campanian–Maastrichtian [83–66 Ma]) of North America provides the best record to address this debate, but even here diversity reconstructions are biased by uneven sampling. Here we combine fossil occurrences with climatic and environmental modelling to quantify latest Cretaceous North American dinosaur habitat. Ecological niche modelling shows a Campanian-to-Maastrichtian habitability decrease in areas with present-day rock-outcrop. However, a continent-wide projection demonstrates habitat stability, or even a Campanian-to-Maastrichtian increase, that is not preserved. This reduction of the spatial sampling window resulted from formation of the proto-Rocky Mountains and sea-level regression. We suggest that Maastrichtian North American dinosaur diversity is therefore likely to be underestimated, with the apparent decline a product of sampling bias, and not due to a climatically-driven decrease in habitability as previously hypothesised.

Journal article

Collins D, Alvdis A, Allison P, Johnson H, Hill J, Piggott Met al., 2018, Controls on tidal sedimentation and preservation: insights from numerical tidal modelling in the late oligocene–miocene South China sea, Southeast Asia, Sedimentology, Vol: 65, Pages: 2468-2505, ISSN: 0037-0746

Numerical tidal modelling, when integrated with other geological datasets, can significantly inform the analysis of physical sedimentation processes and the depositional and preservational record of ancient tide-influenced shoreline–shelf systems. This is illustrated in the Oligo–Miocene of the South China Sea (SCS), which experienced significant changes in basin physiography and where tide-influenced, shoreline–shelf deposition is preserved in ca 10 sub-basins. Palaeogeographic reconstructions, palaeotidal modelling and regional sedimentary facies analysis have been integrated in order to evaluate the spatial–temporal evolution and physiographic controls on tidal sedimentation and preservation during the ca 25 Myr Oligo–Miocene record in the SCS. Palaeotidal modelling, using an astronomically forced and global tidal model (Fluidity) at a maximum 10 km resolution, indicates that spring tides along Late Oligocene–Middle Miocene coastlines were predominantly mesotidal– macrotidal and capable of transporting sand, which reflects two main conditions: (1) increased tidal inflow through wider ocean connections to the Pacific Ocean; and (2) tidal amplification resulting from constriction of the tidal wave in a ‘blind gulf’ type of basin morphology. Since the Middle–Late Miocene, a reduction in the amplitude and strength of tides in the SCS was mainly due to diminishing tidal inflow from the Pacific Ocean caused by the northward movement of the Philippines and Izu-Bonin-Mariana arc. Sensitivity tests to palaeogeographic and palaeobathymetric uncertainty indicate that regional–scale (100–1000s29 km) palaeogeographic changes influencing tidal inflow versus outflow can override local30scale (1–100s km) changes to tidal resonance and convergence effects (funnelling and shoaling), such as shelf width and shoreline geometry. Palaeotidal model results compare favourably to the distribution and sedimenta

Journal article

Collins DS, Johnson HD, Allison PA, Damit ARet al., 2018, Mixed process, humid-tropical, shoreline-shelf deposition and preservation: middle Miocene-modern Baram Delta Province, Northwest Borneo, Journal of Sedimentary Research, Vol: 88, Pages: 399-430, ISSN: 1527-1404

This evaluation of the Miocene–Modern Baram Delta Province (BDP) depositional system provides: (1) a rare case study of outcrop observations that can be directly compared with a closely comparable and geographically adjacent modern analogue; (2) new insights into how deposition and preservation occur across a range of process regimes in a highly aggradational tectono-stratigraphic setting; and (3) an example of a well-exposed mixed-influenced shoreline–shelf depositional system, displaying variable interaction of fluvial, wave, and tidal processes. The exceptionally close relationship between the present-day BDP source-to-sink system and its ancient (Miocene–Pliocene) counterpart is because the climatic (humid-tropical, ever-wet, monsoon-influenced), tectonic (active foreland margin), hydrological (multiple, relatively short rivers), and gross depositional (shoreline–shelf) settings have remained consistent over the past c. 15–20 Myr. This study compares exposure-based analyses of facies and stratigraphic architecture in the middle Miocene Belait Formation (eastern BDP) with process-based geomorphological and sedimentological analyses of coastal–deltaic depositional environments in the present-day BDP. The Belait Formation comprises three distinct types of vertical facies-succession sets: (1) aggradationally-stacked, upward-sanding units (10–50 m thick), dominated by erosionally based sandstone beds showing swaly cross-stratification and gutter casts, record deposition during simultaneously high storm-wave energy and storm-enhanced fluvial discharge (“storm floods”); these are interpreted as analogs for deposits along the present-day open coastline in the BDP (e.g., the present-day, open-shelf Baram delta and flanking strandplain); (2) aggradationally stacked, heterolithic, upward-sanding units characterized by interbedded swaly cross-stratified sandstone and combined-flow-rippled heterolithics, record deposition

Journal article

Collins D, Johnson HD, Allison PA, Guilpain P, Razak Damit Aet al., 2017, Coupled ‘storm-flood’ depositional model: application to the Miocene–Modern Baram Delta Province, north-west Borneo, Sedimentology, Vol: 64, Pages: 1203-1235, ISSN: 0037-0746

The Miocene to Modern Baram Delta Province is a highly efficient source to sink system that has accumulated 9 to 12 km of coastal-deltaic to shelf sediments over the past 15 Myr. Facies analysis based on ca 1 km of total vertical outcrop stratigraphy, combined with subsurface geology and sedimentary processes in the present-day Baram Delta Province, suggests a ‘storm-flood’ depositional model comprising two distinct periods: (i) fair-weather periods are dominated by alongshore sediment reworking and coastal sand accumulation; and (ii) monsoon-driven storm periods are characterised by increased wave energy and offshore-directed downwelling storm flow that occur simultaneously with peak fluvial discharge caused by storm-precipitation (‘storm-floods’). The modern equivalent environment has the following characteristics: (i) humid-tropical monsoonal climate; (ii) narrow (ca <100 km) and steep (ca 1°), densely vegetated, coastal plain; (iii) deep tropical weathering of a mudstone-dominated hinterland; (iv) multiple independent, small to moderate-sized (102 to 105 km2) drainage basins; (v) predominance of river-mouth bypassing; and (vi) supply-dominated shelf. The ancient, proximal part of this system (the onshore Belait Formation) is dominated by strongly cyclical sandier-upward successions (metre to decametre-scale) comprising (from bottom to top): (i) finely laminated mudstone with millimetre-scale silty laminae; (ii) heterolithic sandstone-mudstone alternations (centimetre to metre-scale); and (iii) sharp-based, swaley cross-stratified sandstone beds and bedsets (metre to decimetre-scale). Gutter casts (decimetre to metre-scale) are widespread, they are filled with swaley cross-stratified sandstone and their long-axes are oriented perpendicular to the palaeo-shoreline. The gutter casts and other associated waning-flow event beds suggest that erosion and deposition was controlled by high-energy, offshore-directed, oscillatory-dominated, s

Journal article

Collins DS, Avdis A, Allison PA, Johnson HD, Hill J, Piggott MD, Amir Hassan M, Damit ARet al., 2017, Tidal dynamics and mangrove carbon sequestration during the Oligo–Miocene in the South China Sea, Nature Communications, Vol: 8, ISSN: 2041-1723

Modern mangroves are among the most carbon-rich biomes on Earth, but their long-term (≥106 yr) impact on the global carbon cycle is unknown. The extent, productivity and preservation of mangroves are controlled by the interplay of tectonics, global sea level and sedimentation, including tide, wave and fluvial processes. The impact of these processes on mangrove-bearing successions in the Oligo–Miocene of the South China Sea (SCS) is evaluated herein. Palaeogeographic reconstructions, palaeotidal modelling, and facies analysis suggest that elevated tidal range and bed shear stress optimised mangrove development along tide-influenced tropical coastlines. Preservation of mangrove organic carbon (OC) was promoted by high tectonic subsidence and fluvial sediment supply. Lithospheric storage of OC in peripheral SCS basins potentially exceeded 4000 Gt (equivalent to 2000 ppm of atmospheric CO2). These results highlight the crucial impact of tectonic and oceanographic processes on mangrove OC sequestration within the global carbon cycle on geological timescales.

Journal article

parkinson SD, Funke SW, Hill J, Piggott MD, Allison PAet al., 2017, Application of the adjoint approach to optimise the initial conditions of a turbidity current with the AdjointTurbidity 1.0 model, Geoscientific Model Development, Vol: 10, Pages: 1051-1068, ISSN: 1991-9603

Turbidity currents are one of the main drivers ofsediment transport from the continental shelf to the deepocean. The resulting sediment deposits can reach hundredsof kilometres into the ocean. Computer models that simulateturbidity currents and the resulting sediment deposit can helpus to understand their general behaviour. However, in orderto recreate real-world scenarios, the challenge is to find theturbidity current parameters that reproduce the observationsof sediment deposits.This paper demonstrates a solution to the inverse sedimenttransportation problem: for a known sedimentary deposit, thedeveloped model reconstructs details about the turbidity cur-rent that produced the deposit. The reconstruction is con-strained here by a shallow water sediment-laden density cur-rent model, which is discretised by the finite-element methodand an adaptive time-stepping scheme. The model is differ-entiated using the adjoint approach, and an efficient gradient-based optimisation method is applied to identify the turbidityparameters which minimise the misfit between the modelledand the observed field sediment deposits. The capabilities ofthis approach are demonstrated using measurements taken inthe Miocene Marnoso-arenacea Formation (Italy). We findthat whilst the model cannot match the deposit exactly dueto limitations in the physical processes simulated, it providesvaluable insights into the depositional processes and repre-sents a significant advance in our toolset for interpreting tur-bidity current deposits.

Journal article

Amir Hassan MH, Johnson HD, Allison PA, Abdullah WHet al., 2016, Sedimentology and stratigraphic architecture of a Mioceneretrogradational, tide-dominated delta system: BalingianProvince, offshore Sarawak, Malaysia, Geological Society, London, Special Publication

Journal article

Jordan N, Allison PA, Hill J, Sutton MDet al., 2015, Not all aragonitic molluscs are missing: taphonomy and significance of a unique shelly lagerstatte from the Jurassic of SW Britain, Lethaia, Vol: 48, Pages: 540-548, ISSN: 1502-3931

The Blue Lias Formation at Lyme Regis (Dorset, UK) includes an exceptional pavement of abundant large ammonites that accumulated during a period of profound sedimentary condensation. Ammonites were originally composed of aragonite, an unstable polymorph of calcium carbonate, and such fossils are typically prone to dissolution; the occurrence of a rich association of aragonitic shells in a condensed bed is highly unusual. Aragonite dissolution occurs when pore-water pH is reduced by the oxidization of hydrogen sulphide close to the sediment-water interface. Evidence suggests that, in this case, the oxygen concentrations in the overlying water column were low during deposition. This inhibited the oxidation of sulphides and the associated lowering of pH, allowing aragonite to survive long enough for the shell to be neomorphosed to calcite. The loss of aragonite impacts upon estimates of past biodiversity and carbonate accumulation rates. The preservational model presented here implies that diagenetic loss of aragonite will be greatest in those areas where dysoxic-anoxic sediment lies beneath an oxic waterbody but least where the sediment and overlying water are oxygen depleted. Unfortunately, this implies that preservational bias through aragonite loss will be greatest in those biotopes which are typically most diverse and least where biodiversity is lowest due to oxygen restriction.

Journal article

Martin-Short R, Hill J, Kramer SC, Avdis A, Allison PA, Piggott MDet al., 2015, Tidal resource extraction in the Pentland Firth, UK: potential impacts on flow regime and sediment transport in the Inner Sound of Stroma, Renewable Energy, Vol: 76, Pages: 596-607, ISSN: 0960-1481

Large-scale extraction of power from tidal streams within the Pentland Firth is expected to be underway in the near future. The Inner Sound of Stroma in particular has attracted significant commercial interest. To understand potential environmental impacts of the installation of a tidal turbine array a case study based upon the Inner Sound is considered. A numerical computational fluid dynamics model, Fluidity, is used to conduct a series of depth-averaged simulations to investigate velocity and bed shear stress changes due to the presence of idealised tidal turbine arrays. The number of turbines is increased from zero to 400. It is found that arrays in excess of 85 turbines have the potential to affect bed shear stress distributions in such a way that the most favourable sites for sediment accumulation migrate from the edges of the Inner Sound towards its centre. Deposits of fine gravel and coarse sand are indicated to occur within arrays of greater than 240 turbines with removal of existing deposits in the shallower channel margins also possible. The effects of the turbine array may be seen several kilometres from the site which has implications not only on sediment accumulation, but also on the benthic fauna.

Journal article

Jacobs CT, Goldin TJ, Collins GS, Piggott MD, Kramer SC, Melosh HJ, Wilson CRG, Allison PAet al., 2015, An improved quantitative measure of the tendency for volcanic ash plumes to form in water: implications for the deposition of marine ash beds, JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 290, Pages: 114-124, ISSN: 0377-0273

Journal article

Parkinson SD, Hill J, Piggott MD, Allison PAet al., 2014, Direct numerical simulations of particle-laden density currents with adaptive, discontinuous finite elements, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 7, Pages: 1945-1960, ISSN: 1991-959X

Journal article

Hiester HR, Piggott MD, Farrell PE, Allison PAet al., 2014, Assessment of spurious mixing in adaptive mesh simulations of the two-dimensional lock-exchange, Ocean Modelling, Vol: 73, Pages: 30-44, ISSN: 1463-5003

Journal article

Jordan N, Allison PA, Hill JH, Sutton MDet al., 2012, Carbonates, ammonites and the fate of aragonite: a new perspective from the Lower Jurassic of Lyme Regis, British Sedimentological Research Group Annual Meeting

The Lower Jurassic Blue Lias Formation at Lyme Regis, Dorset, preserves a diverse assemblage of invertebrate and vertebrate fossils within rhythmic packages of shales, marls and carbonates. One limestone bed in particular, Bed 29, preserves a unique pavement of very large (up to 72 cm) ammonites, initially buried in carbonate mud before diagenetic cementation. The ammonite accumulation is most likely due to sedimentological condensation but the mechanisms for preserving an aragonitic shell long enough for it to be neomorphosed to calcite on the seabed are a challenge for conventional taphonomic models. It has been suggested that early dissolution of aragonite is a major process in offshore deeper ramp settings, resulting in the removal of sediment prior to lithification. We present field-based evidence for a new model of aragonite preservation within a cyclic oxic-anoxic carbonate environment, using ammonite preservation to track the fate of aragonite in different depositional environments. The carbonate sediment provides a short-term geochemical buffer that militates against the dissolution of aragonite sediment and molluscs, allowing neomorphism to calcite under some conditions. The broader implications of this model for the preservation of molluscan shells and reduced sediment dissolution in carbonate environments under variably oxygenated conditions are evaluated.

Conference paper

Hiester H, Piggott MD, Allison PA, 2011, The impact of mesh adaptivity on the gravity current front speed in a two-dimensional lock-exchange, Ocean Modelling, ISSN: 1463-5003

Journal article

Brett CE, Allison PA, Hendy AJW, 2011, Comparative taphonomy and sedimentology of small-scale mixed carbonate/siliciclastic cycles: Synopsis of Phanerozoic examples, Taphonomy: Bias and Process Through Time (Volume 32 in the Topics in Geobiology series), Editors: Allison, Bottjer, Publisher: Springer, Pages: 107-198, ISBN: 978-90-481-8642-6

Book chapter

Fang F, Pain CC, Navon IM, Gorman GJ, Piggott MD, Allison PAet al., 2011, The independent set perturbation adjoint method: A new method of differentiating mesh-based fluids models, International Journal for Numerical Methods in Fluids, Vol: In review

Journal article

Allison PA, Bottjer DJ, 2011, Taphonomy: Process And Bias Through Time (Volume 32 in the Topics in Geobiology series), Publisher: Springer, ISBN: 978-90-481-8642-6

Book

Mitchell AJ, Allison PA, Gorman GJ, Piggott MD, Pain CCet al., 2011, Tidal circulation in an ancient epicontinental sea: The Early Jurassic Laurasian Seaway, Geology, Vol: 39, Pages: 207-210, ISSN: 0091-7613

Journal article

Allison PA, Bottjer DJ, 2011, Taphonomy: Bias and Process Through Time, Taphonomy: Process and Bias Through Time (Volume 32 in the Topics in Geobiology series), Editors: Allison, Bottjer, Publisher: Springer, Pages: 1-18, ISBN: 978-90-481-8642-6

Book chapter

Wells MR, Allison PA, Piggott MD, Hampson GJ, Pain CC, Gorman GJet al., 2010, Tidal modeling of an ancient tide-dominated seaway, part 1: model validation and application to global early Cretaceous (Aptian) tides, Journal of Sedimentary Research, Vol: 80, Pages: 393-410, ISSN: 1527-1404

Journal article

Wells MR, Allison PA, Piggott MD, Hampson GJ, Pain CC, Gorman GJet al., 2010, Tidal modeling of an ancient tide-dominated seaway, part 2: the Aptian Lower Greensand seaway of northwest Europe, Journal of Sedimentary Research, Vol: 80, Pages: 411-439, ISSN: 1527-1404

Journal article

Mitchell AJ, Allison PA, Piggott MD, Gorman GJ, Pain CC, Hampson GJet al., 2010, Numerical modelling of tsunami propagation with implications for sedimentation in ancient epicontinental seas: the Lower Jurassic Laurasian Seaway, Journal of Sedimentary Geology, Vol: 228, Pages: 81-97, ISSN: 0037-0738

Journal article

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