Sedimentology of the continental end‐Permian extinction event in the Sydney Basin,eastern Australia     

Christopher R. Fielding  Tracy D. Frank  Allen P. Tevyaw  Katarina Savatic  Vivi Vajda  Stephen McLoughlin  Chris Mays  Robert S. Nicoll  Malcolm Bocking  James L. Crowley 《Sedimentology》2021,68(1):30-62

Upper Permian to Lower Triassic coastal plain successions of the Sydney Basin in eastern Australia have been investigated in outcrop and continuous drillcores. The purpose of the investigation is to provide an assessment of palaeoenvironmental change at high southern palaeolatitudes in a continental margin context for the late Permian (Lopingian), across the end‐Permian Extinction interval, and into the Early Triassic. These basins were affected by explosive volcanic eruptions during the late Permian and, to a much lesser extent, during the Early Triassic, allowing high‐resolution age determination on the numerous tuff horizons. Palaeobotanical and radiogenic isotope data indicate that the end‐Permian Extinction occurs at the top of the uppermost coal bed, and the Permo‐Triassic boundary either within an immediately overlying mudrock succession or within a succeeding channel sandstone body, depending on locality due to lateral variation. Late Permian depositional environments were initially (during the Wuchiapingian) shallow marine and deltaic, but coastal plain fluvial environments with extensive coal‐forming mires became progressively established during the early late Permian, reflected in numerous preserved coal seams. The fluvial style of coastal plain channel deposits varies geographically. However, apart from the loss of peat‐forming mires, no significant long‐term change in depositional style (grain size, sediment‐body architecture, or sediment dispersal direction) was noted across the end‐Permian Extinction (pinpointed by turnover of the palaeoflora). There is no evidence for immediate aridification across the boundary despite a loss of coal from these successions. Rather, the end‐Permian Extinction marks the base of a long‐term, progressive trend towards better‐drained alluvial conditions into the Early Triassic. Indeed, the floral turnover was immediately followed by a flooding event in basinal depocentres, following which fluvial systems similar to those active prior to the end‐Permian Extinction were re‐established. The age of the floral extinction is constrained to 252.54 ± 0.08 to 252.10 ± 0.06 Ma by a suite of new Chemical Abrasion Isotope Dilution Thermal Ionization Mass Spectrometry U‐Pb ages on zircon grains. Another new age indicates that the return to fluvial sedimentation similar to that before the end‐Permian Extinction occurred in the basal Triassic (prior to 251.51 ± 0.14 Ma). The character of the surface separating coal‐bearing pre‐end‐Permian Extinction from coal‐barren post‐end‐Permian Extinction strata varies across the basins. In basin‐central locations, the contact varies from disconformable, where a fluvial channel body has cut down to the level of the top coal, to conformable where the top coal is overlain by mudrocks and interbedded sandstone–siltstone facies. In basin‐marginal locations, however, the contact is a pronounced erosional disconformity with coarse‐grained alluvial facies overlying older Permian rocks. There is no evidence that the contact is everywhere a disconformity or unconformity.  相似文献   

Detailing the impact of the Storegga Tsunami at Montrose,Scotland     

Mark D. Bateman  Tim C. Kinnaird  Jon Hill  Robert A. Ashurst  Jenna Mohan  Rebecca B. I. Bateman  Ruth Robinson 《Boreas: An International Journal of Quaternary Research》2021,50(4):1059-1078

The Storegga tsunami, dated in Norway to 8150±30 cal. years BP, hit many countries bordering the North Sea. Run-ups of >30 m occurred and 1000s of kilometres of coast were impacted. Whilst recent modelling successfully generated a tsunami wave train, the wave heights and velocities, it under-estimated wave run-ups. Work presented here used luminescence to directly date the Storegga tsunami deposits at the type site of Maryton, Aberdeenshire in Scotland. It also undertook sedimentological characterization to establish provenance, and number and relative power of the tsunami waves. Tsunami model refinement used this to better understand coastal inundation. Luminescence ages successfully date Scottish Storegga tsunami deposits to 8100±250 years. Sedimentology showed that at Montrose, three tsunami waves came from the northeast or east, over-ran pre-existing marine sands and weathered igneous bedrock on the coastal plain. Incorporation of an inundation model predicts well a tsunami impacting on the Montrose Basin in terms of replicate direction and sediment size. However, under-estimation of run-up persisted requiring further consideration of palaeotopography and palaeo-near-shore bathymetry for it to agree with sedimentary evidence. Future model evolution incorporating this will be better able to inform on the hazard risk and potential impacts for future high-magnitude submarine generated tsunami events.  相似文献   

The evolution of the terrestrial-terminating Irish Sea glacier during the last glaciation     

Richard Christopher Chiverrell  Geoff Stephen Powell Thomas  Matthew Burke  Alicia Medialdea  Rachel Smedley  Mark Bateman  Chris Clark  Geoffrey A. T. Duller  Derek Fabel  Geraint Jenkins  Xianjiao Ou  Helen Marie Roberts  James Scourse 《第四纪科学杂志》2021,36(5):752-779

Here we reconstruct the last advance to maximum limits and retreat of the Irish Sea Glacier (ISG), the only land-terminating ice lobe of the western British Irish Ice Sheet. A series of reverse bedrock slopes rendered proglacial lakes endemic, forming time-transgressive moraine- and bedrock-dammed basins that evolved with ice marginal retreat. Combining, for the first time on glacial sediments, optically stimulated luminescence (OSL) bleaching profiles for cobbles with single grain and small aliquot OSL measurements on sands, has produced a coherent chronology from these heterogeneously bleached samples. This chronology constrains what is globally an early build-up of ice during late Marine Isotope Stage 3 and Greenland Stadial (GS) 5, with ice margins reaching south Lancashire by 30 ± 1.2 ka, followed by a 120-km advance at 28.3 ± 1.4 ka reaching its 26.5 ± 1.1 ka maximum extent during GS-3. Early retreat during GS-3 reflects piracy of ice sources shared with the Irish-Sea Ice Stream (ISIS), starving the ISG. With ISG retreat, an opportunistic readvance of Welsh ice during GS-2 rode over the ISG moraines occupying the space vacated, with ice margins oscillating within a substantial glacial over-deepening. Our geomorphological chronosequence shows a glacial system forced by climate but mediated by piracy of ice sources shared with the ISIS, changing flow regimes and fronting environments.  相似文献   

Three decades of landslide activity in western Nepal: new insights into trends and climate drivers     

Muñoz-Torrero Manchado  A.  Allen  S.  Ballesteros-Cánovas  J. A.  Dhakal  A.  Dhital  M. R.  Stoffel  M. 《Landslides》2021,18(6):2001-2015

In recent decades, landslide disasters in the Himalayas, as in other mountain regions, are widely reported to have increased. While some studies have suggested a link to increasing heavy rainfall under a warmer climate, others pointed to anthropogenic influences on slope stability, and increasing exposure of people and assets located in harm’s way. A lack of sufficiently high-resolution regional landslide inventories, both spatially and temporally, has prevented any robust consensus so far. Focusing on Far-Western Nepal, we draw on remote sensing techniques to create a regional inventory of 26,350 single landslide events, of which 8778 date to the period 1992–2018. These events serve as a basis for the analyses of landslide frequency relationships and trends in relation to precipitation and temperature datasets. Results show a strong correlation between the annual number of shallow landslides and the accumulated monsoon precipitation (r = 0.74). Furthermore, warm and dry monsoons followed by especially rainy monsoons produce the highest incidence of shallow landslides (r = 0.77). However, we find strong spatial variability in the strength of these relationships, which is linked to recent demographic development in the region. This highlights the role of anthropogenic drivers, and in particular road cutting and land-use change, in amplifying the seasonal monsoon influence on slope stability. In parallel, the absence of any long-term trends in landslide activity, despite widely reported increase in landslide disasters, points strongly to increasing exposure of people and infrastructure as the main driver of landslide disasters in this region of Nepal. By contrast, no climate change signal is evident from the data.

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Late pleistocene (Devensian) glaciofluvial outwash at Banc-y-Warren,near Cardigan (west Wales)     

J. R. L. Allen 《Geological Journal》1982,17(1):31-47

On the southwest-facing slopes of a bedrock ridge lying between Cardigan Bay to the north and the Afon Teifi to the south stands a group of hills in which 30-35 m of cross-laminated and parallel-laminated sands with lenticular upward-fining gravel sequences are overlain by 10-12 m of gravel in a single foreset bed. The sediments mantle a surface of till sloping gently toward the southwest, were transported toward the southwest (across one margin of the Afon Teifi valley), and were cut by a system of densely arranged conjugate normal faults striking northwest-southeast. The lenticular gravels and fault system suggest that the deposits accumulated as a glaciofluvial outwash spread, and on top of an ice-lobe that became isolated in the Teifi valley during the downwasting of a glacier which had occupied Cardigan Bay and much of the country to the south. The large gravel foresets capping the succession are the only indication at Banc-y-Warren of the former existence of a lake, but neither a large nor deep body of water need be envisaged.  相似文献   

Preliminary investigation of the surficial sediments in the Cap-Breton Canyon (southwest France) and the surrounding continental shelf     

George P. Allen  Patrice Castaing  Andre Klingebiel 《Marine Geology》1971,10(5):M27-M32

A total of 120 grab samples of the surficial sediments in the Cap-Breton submarine canyon and surrounding continental shelf were collected and analyzed by grain-size sieving. A Q-mode Factor Analysis was made on the grain-size data in order to define the most meaningful facies types. Four distinct lithological facies were found to exist: silt and clay, very fine sand, fine sand, and coarse sand. Comparison with previous work and a ¹⁴C date on the silt and clay facies showed that the facies are not contemporaneous. The sands and coarse sands on the shelf were emplaced during the pre-Würm and Würm regressions, and later probably reworked during the Holocene (Flandrian) transgression. The silty clays found in the canyon and on the shelf to the south are younger and represent sediments brought in as suspended load by the Adour and other nearby rivers during the Holocene (Flandrian) transgression.  相似文献   

Can marine fisheries and aquaculture meet fish demand from a growing human population in a changing climate?     

Gorka Merino  Manuel Barange  Julia L. Blanchard  James Harle  Robert Holmes  Icarus Allen  Edward H. Allison  Marie Caroline Badjeck  Nicholas K. Dulvy  Jason Holt  Simon Jennings  Christian Mullon  Lynda D. Rodwell 《Global Environmental Change》2012,22(4):795-806

Expansion in the world's human population and economic development will increase future demand for fish products. As global fisheries yield is constrained by ecosystems productivity and management effectiveness, per capita fish consumption can only be maintained or increased if aquaculture makes an increasing contribution to the volume and stability of global fish supplies. Here, we use predictions of changes in global and regional climate (according to IPCC emissions scenario A1B), marine ecosystem and fisheries production estimates from high resolution regional models, human population size estimates from United Nations prospects, fishmeal and oil price estimations, and projections of the technological development in aquaculture feed technology, to investigate the feasibility of sustaining current and increased per capita fish consumption rates in 2050. We conclude that meeting current and larger consumption rates is feasible, despite a growing population and the impacts of climate change on potential fisheries production, but only if fish resources are managed sustainably and the animal feeds industry reduces its reliance on wild fish. Ineffective fisheries management and rising fishmeal prices driven by greater demand could, however, compromise future aquaculture production and the availability of fish products.  相似文献   

Estimation of source water to cedar elm in a central Texas riparian ecosystem     

Ranjan S. Muttiah  Joseph D. White  Jacquelyn R. Duke  Peter M. Allen 《水文研究》2005,19(2):475-491

A riparian ecosystem downstream of a small dam in central Texas was instrumented for sap flow, soil moisture content, and stream level from 2001. Stable isotopes in water (D and ¹⁸O) were analysed from rainfall, stream, lake, and cored sapwood cellulose from cedar elm (Ulmus crassifolia). The isotope signature of water source to cedar elm was identified by back calculation starting with the water isotopes in cellulose, and accounting for leaf‐water evaporation and biological fractionation during cellulose synthesis. The estimated mean isotope of the source water to cedar elm was enriched above rainfall in similarity to stream water during 2002. Flow paths that may have contributed to estimated variability from regional base flow and recharge water were identified using the variably saturated HYDRUS‐2D model. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Reproducible Well-Purging Procedures and VOC Stabilization Criteria for Ground-Water Sampling   总被引：3，自引：0，他引：3  

Michael J. Barcelona  H. Allen Wehrraann  Mark D. Varljen 《Ground water》1994,32(1):12-22

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Specific Yield as Determined by Type-Curve Analysis of Aquifer-Test Data   总被引：4，自引：0，他引：4  

Allen F. Moench 《Ground water》1994,32(6):949-957

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