Beringia and beyond: Papers celebrating the scientific career of Andrei Vladimirovich Sher, 1939–2008     

Scott Elias  Svetlana Kuzmina  Mary E. Edwards  Adrian M. Lister 《Quaternary Science Reviews》2011,30(17-18):2037-2038

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Pattern and chronology of glacial Lake Peace shorelines and implications for isostacy and ice‐sheet configuration in northeastern British Columbia,Canada          下载免费PDF全文

Adrian S. Hickin  Olav B. Lian  Victor M. Levson  Yao Cui 《Boreas: An International Journal of Quaternary Research》2015,44(2):288-304

Recognition of positions of glacial lakes along the margin of continental ice sheets is critical in reconstructing ice configuration during deglaciation. Advances in remote sensing technology (e.g. LiDAR) have enabled the generation of accurate digital‐elevation models (DEMs) that reveal unprecedented geomorphic detail. Combined with geographical information systems, these tools have considerably advanced the mapping and correlation of geomorphic features such as relict shorelines. Shorelines of glacial Lake Peace (GLP) developed between the Laurentide and Cordilleran ice sheets in northeastern British Columbia and northwestern Alberta. Shoreline mapping from high resolution DEMs produced more than 55 500 elevation data points from 3231 shorelines, enabling the identification of four major phases of GLP: Phase I (altitude 960–990 m a.s.l.); Phase II (890–915 m a.s.l.); Phase III (810–865 m a.s.l.); and Phase IV (724–733 m a.s.l.). The timing of Phase II of GLP is estimated by two optical ages of <16.0±2.5 and 14.2±0.5 ka BP. Extensive mapping of the shorelines allows for measuring of glacial isostatic adjustment as ice retreated. Shorelines currently dip to the northeast at around 0.4–0.5 m km^?1. This slope reflects the asynchronous retreat of the Cordilleran (CIS) and Laurentide (LIS) ice sheets. The relative uplift in the southwest of the study area within the Rocky Mountains and foothills suggests that the Late Wisconsinan (MIS 2) CIS persisted in the foothill after the LIS lost mass and retreated, or that the Late Wisconsinan CIS was very thick and caused deep crustal loading, which resulted in more uplift in the southwest before reaching equilibrium during, or shortly after deglaciation.  相似文献   

Significance of post‐peak metamorphic reaction microstructures in the ultrahigh temperature Eastern Ghats Province,India          下载免费PDF全文

David E. Kelsey  Laura J. Morrissey  Martin Hand  Chris Clark  Renee Tamblyn  Adrian A. Gaehl  Sarah Marshall 《Journal of Metamorphic Geology》2017,35(9):1081-1109

Ultrahigh temperature (UHT) granulites in the Eastern Ghats Province (EGP) have a complex P–T–t history. We review the P–T histories of UHT metamorphism in the EGP and use that as a framework for investigating the P–T–t history of Mg–Al‐rich granulites from Anakapalle, with the express purpose of trying to reconcile the down‐pressure‐dominated P–T path with other UHT localities in the EGP. Mafic granulite that is host to Mg–Al‐rich metasedimentary granulites at Anakapalle has a protolith age of c. 1,580 Ma. Mg–Al‐rich metasedimentary granulites within the mafic granulite at Anakapalle were metamorphosed at UHT conditions during tectonism at 960–875 Ma, meaning that the UHT metamorphism was not the result of contact metamorphism from emplacement of the host mafic rock. Reworking occurred during the Pan‐African (c. 600–500 Ma) event, and is interpreted to have produced hydrous assemblages that overprint the post‐peak high‐T retrograde assemblages. In contrast to rocks elsewhere in the EGP that developed post‐peak cordierite, the metasedimentary granulites at Anakapalle developed post‐peak, generation ‘2’ reaction products that are cordierite‐absent and nominally anhydrous. Therefore, rocks at Anakapalle offer the unique opportunity to quantify the pressure drop that occurred during so‐called M2 that affected the EGP. We argue that M2 is either a continuation of M1 and that the overall P–T path shape is a complex counter‐clockwise loop, or that M1 is an up‐temperature counter‐clockwise deviation superimposed on the M2 path. Therefore, rather than the rocks at Anakapalle having a metamorphic history that is apparently anomalous from the rest of the EGP, we interpret that other previously studied localities in the EGP record a different part of the same P–T path history as Anakapalle, but do not preserve a significant record of pressure decrease. This is due either to the inability of refractory rocks to extensively react to produce a rich mineralogical record of pressure decrease, or because the earlier high‐P part of the rocks history was erased by the M1 loop. Irrespective of the specific scenario, models for the tectonic evolution of the EGP must take the substantial pressure decrease during M2 into account, as it is probable the P–T record at Anakapalle is a reflection of tectonics affecting the entire province.  相似文献   

Reply to Comment on “Post‐impact event bed (tsunamite) at the Cretaceous–Palaeogene boundary deposited on a distal carbonate platform interior”          下载免费PDF全文

Tvrtko Korbar  Iain McDonald  Vlasta Premec Fućek  Ladislav Fuček  Hrvoje Posilović 《地学学报》2017,29(5):332-334

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Validation of MODIS Vegetation Continuous Fields for monitoring deforestation and forest degradation: two cases in Mexico     

Yan Gao  Adrian Ghilardi  Jaime Paneque-Galvez  Margaret Skutsch  Jean François Mas 《国际地球制图》2016,31(9):1019-1031

This study assesses whether MODIS Vegetation Continuous Fields percent tree cover (PTC) data can detect deforestation and forest degradation. To assess the usefulness of PTC for detecting deforestation, we used a data set consisting of eight forest and seven non-forest categories. To evaluate forest degradation, we used data from two temperate forest types in three conservation states: primary (dense), secondary (moderately degraded) and open (heavily degraded) forest. Our results show that PTC can differentiate temperate forest from non-forest categories (p = 0.05) and thus suggests PTC can adequately detect deforestation in temperate forests. In contrast, single-date PTC data does not appear to be adequate to detect forest degradation in temperate forests. As for tropical forest, PTC can partially discriminate between forest and non-forest categories.  相似文献   

Evaluation of Strength Characteristics of Tropical Black Clay Treated with Locust Bean Waste Ash     

Kolawole J. Osinubi  Adrian O. Eberemu  Olusegun B. Akinmade 《Geotechnical and Geological Engineering》2016,34(2):635-646

An expansive tropical black clay (also known as black cotton soil because the cotton plant thrives well on it) was treated with up to 15 % locust bean waste ash (LBWA) to assess its soil improvement potential. Samples were subjected to index, compaction using three energy levels (British Standard light, BSL, West African Standard, WAS or ‘Intermediate’ and British Standard heavy, BSH), shear strength (unconfined compressive strength, UCS), California bearing ratio, CBR and durability tests. Results obtained show that the natural soil is not suitable for road construction. The maximum dry density (MDD) and optimum moisture content (OMC) decreased and increased, respectively. Regardless of the compactive effort and curing period, strength and durability properties increased with higher LBWA content with the BSL effort recording the best improvement. However, based on durability results, the optimal 12.5 % LBWA treatment of black cotton soil did not satisfy criteria for its use in road construction as a stand alone additive. Also, significant improvement in soil properties was obtained using the BSL compactive effort, which is easily achieved in the field. The benefits of the application include reduction in the cost of soil improvement and the adverse environmental impact of locust bean waste.  相似文献   

Fish,Macroinvertebrate and Epifaunal Communities in Shallow Coastal Lagoons with Varying Seagrass Cover of the Northern Gulf of Mexico     

Rachel B. McDonald  Ryan M. Moody  Ken L. Heck  Just Cebrian 《Estuaries and Coasts》2016,39(3):718-730

Coastal lagoons are ubiquitous along coastlines worldwide. Here, we compare the abundance of epifauna, seagrass-associated macroinvertebrates, and small fish across a gradient of seagrass cover in shallow coastal lagoons of the northern Gulf of Mexico. Two of the lagoons had little or no seagrass cover (0–18.8 %), and four had high cover (83.8–97.5 %). All of the lagoons were partially covered with fringing marsh. We hypothesized that, due to habitat redundancy between seagrass beds and fringing marshes, seagrass-associated fish and macroinvertebrates would not be largely reduced despite the large differences in seagrass cover among the lagoons. Our results support this hypothesis. For most sampling dates, we did not find significant differences in fish and macroinvertebrate abundance among the lagoons and, when we did, several highly vegetated lagoons did not have larger abundances than sparsely vegetated lagoons. The extreme shallowness of the lagoons studied (<1 m) may also provide further protection from large predatory fishes in the absence of seagrasses. Our results also suggest that marsh detritus, by providing habitat for epifauna and helping maintain prey availability, may further temper reductions in seagrass-associated fishes and macroinvertebrates following seagrass decline. The results highlight the importance of marsh-bordered, shallow lagoons as habitat for small fish and macroinvertebrates regardless of seagrass cover. This study contributes to the characterization of habitat redundancy in coastal ecosystems and pinpoints the importance of considering all habitats in concert for the proper understanding and management of coastal ecosystems.  相似文献   

Bioerosion and encrustation rates in recent mollusk death assemblages on a supratidal siliciclastic setting,Playa Norte,Veracruz State,Mexico     

Catalina Gómez-Espinosa  F. Raúl Gío-Argáez  Ester A. Farinati  Salvador Aliotta  Sergio Adrian Salgado-Souto 《Arabian Journal of Geosciences》2018,11(8):188

This study presents both qualitative and quantitative data regarding marine mollusk (gastropods and bivalves) shell bioerosion and encrustation based on death assemblages obtained from a recent supratidal environment in Playa Norte, Veracruz State. The objectives of this study were to assess the nature of bioerosion and encrustation processes and to investigate the role of these taphonomic features contributing to the deterioration of natural shell accumulations within a tropical siliciclastic tidal environment. The assemblage comprises 31 species: 13 gastropods and 18 bivalves. The bioerosion and encrustation degrees were low to moderate for both types. The most abundant traces were predatory gastropod structures (Oichnus paraboloides and O. simplex), whereas sponge borings (Entobia isp.), polychaete dwellings (Caulostrepsis taeniola), and echinoid raspings (Gnatichnus isp.) were less frequent. The encrusting organisms include polychaete serpulids, bryozoans, and rare foraminifers (Homotrema rubrum). Because of the low bioerosion and encrustation degrees occurring in this area, accumulation is expected to predominate over biotic destruction. As deposition conditions (richly fossiliferous carbonate sandstone beds) were similar to those prevailing in the Tuxpan Formation during the Miocene (Langhian), it is suggested that this study provides an equivalent reference to interpret mollusk fossil assemblages located in this site.  相似文献   

Tellurium,selenium and cobalt enrichment in Neoproterozoic black shales,Gwna Group,UK: Deep marine trace element enrichment during the Second Great Oxygenation Event          下载免费PDF全文

Joseph G. T. Armstrong  John Parnell  Liam A. Bullock  Magali Perez  Adrian J. Boyce  Jorg Feldmann 《地学学报》2018,30(3):244-253

Black shales of the late Neoproterozoic Gwna Group (570–580 Ma), UK, contain enrichments of tellurium (Te), selenium (Se) and cobalt (Co) relative to average shale compositions. The Te and Co enrichments bear comparison with those of ferromanganese crusts in the modern deep ocean. Gwna Group deposition coincides with the Second Great Oxidation Event, which had a significant effect on trace element fixation globally. Selenium and Te concentrations within these black shales indicate increased continental weathering rates, high biological productivity and corresponding increases in atmospheric O₂ concentrations. Cobalt, nickel (Ni) and arsenic (As) enrichments in this succession are secondary mineralisation phases. Demand for many of the trace elements found enriched in the Gwna Group black shales make their mechanisms of accumulation, and variations through the geological record, important to understand, and suggests that new resources may be sought based on black shale protoliths from this period.  相似文献   

Pattern,style and timing of British–Irish Ice Sheet advance and retreat over the last 45 000 years: evidence from NW Scotland and the adjacent continental shelf     

Tom Bradwell  Derek Fabel  Chris D. Clark  Richard C. Chiverrell  David Small  Rachel K. Smedley  Margot H. Saher  Steven G. Moreton  Dayton Dove  S. Louise Callard  Geoff A. T. Duller  Alicia Medialdea  Mark D. Bateman  Matthew J. Burke  Neil McDonald  Sean Gilgannon  Sally Morgan  David H. Roberts  Colm ó Cofaigh 《第四纪科学杂志》2021,36(5):871-933

Predicting the future response of ice sheets to climate warming and rising global sea level is important but difficult. This is especially so when fast-flowing glaciers or ice streams, buffered by ice shelves, are grounded on beds below sea level. What happens when these ice shelves are removed? And how do the ice stream and the surrounding ice sheet respond to the abruptly altered boundary conditions? To address these questions and others we present new geological, geomorphological, geophysical and geochronological data from the ice-stream-dominated NW sector of the last British–Irish Ice Sheet (BIIS). The study area covers around 45 000 km² of NW Scotland and the surrounding continental shelf. Alongside seabed geomorphological mapping and Quaternary sediment analysis, we use a suite of over 100 new absolute ages (including cosmogenic-nuclide exposure ages, optically stimulated luminescence ages and radiocarbon dates) collected from onshore and offshore, to build a sector-wide ice-sheet reconstruction combining all available evidence with Bayesian chronosequence modelling. Using this information we present a detailed assessment of ice-sheet advance/retreat history, and the glaciological connections between different areas of the NW BIIS sector, at different times during the last glacial cycle. The results show a highly dynamic, partly marine, partly terrestrial, ice-sheet sector undergoing large size variations in response to sub-millennial-scale climatic (Dansgaard–Oeschger) cycles over the last 45 000 years. Superimposed on these trends we identify internally driven instabilities, operating at higher frequency, conditioned by local topographic factors, tidewater dynamics and glaciological feedbacks during deglaciation. Specifically, our new evidence indicates extensive marine-terminating ice-sheet glaciation of the NW BIIS sector during Greenland Stadials 12 to 9 – prior to the main ‘Late Weichselian’ ice-sheet glaciation. After a period of restricted glaciation, in Greenland Interstadials 8 to 6, we find good evidence for rapid renewed ice-sheet build-up in NW Scotland, with the Minch ice-stream terminus reaching the continental shelf edge in Greenland Stadial 5, perhaps only briefly. Deglaciation of the NW sector took place in numerous stages. Several grounding-zone wedges and moraines on the mid- and inner continental shelf attest to significant stabilizations of the ice-sheet grounding line, or ice margin, during overall retreat in Greenland Stadials 3 and 2, and to the development of ice shelves. NW Lewis was the first substantial present-day land area to deglaciate, in the first half of Greenland Stadial 3 at a time of globally reduced sea-level c. 26 kabp , followed by Cape Wrath at c. 24 kabp. The topographic confinement of the Minch straits probably promoted ice-shelf development in early Greenland Stadial 2, providing the ice stream with additional support and buffering it somewhat from external drivers. However, c. 20–19 kabp , as the grounding-line migrated into shoreward deepening water, coinciding with a marked change in marine geology and bed strength, the ice stream became unstable. We find that, once underway, grounding-line retreat proceeded in an uninterrupted fashion with the rapid loss of fronting ice shelves – first in the west, then the east troughs – before eventual glacier stabilization at fjord mouths in NW Scotland by ~17 kabp. Around the same time, ~19–17 kabp , ice-sheet lobes readvanced into the East Minch – possibly a glaciological response to the marine-instability-triggered loss of adjacent ice stream (and/or ice shelf) support in the Minch trough. An independent ice cap on Lewis also experienced margin oscillations during mid-Greenland Stadial 2, with an ice-accumulation centre in West Lewis existing into the latter part of Heinrich Stadial 1. Final ice-sheet deglaciation of NW mainland Scotland was punctuated by at least one other coherent readvance at c. 15.5 kabp , before significant ice-mass losses thereafter. At the glacial termination, c. 14.5 kabp , glaciers fed outwash sediment to now-abandoned coastal deltas in NW mainland Scotland around the time of global Meltwater Pulse 1A. Overall, this work on the BIIS NW sector reconstructs a highly dynamic ice-sheet oscillating in extent and volume for much of the last 45 000 years. Periods of expansive ice-sheet glaciation dominated by ice-streaming were interspersed with periods of much more restricted ice-cap or tidewater/fjordic glaciation. Finally, this work indicates that the role of ice streams in ice-sheet evolution is complex but mechanistically important throughout the lifetime of an ice sheet – with ice streams contributing to the regulation of ice-sheet health but also to the acceleration of ice-sheet demise via marine ice-sheet instabilities.  相似文献