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1.
A reconstruction of deglaciation and associated sea-level changes on northern James Ross Island, Antarctic Peninsula, based on lithostratigraphical and geomorphological studies, shows that the initial deglaciation of presently ice-free areas occurred slightly before 7400 14C yr BP. Sea-level in connection with the deglaciation was around 30 m a.s.l. A glacier readvance in Brandy Bay, of at least 7 km, with the initial 3 km over land, reached a position off the present coast at ca. 4600 yr BP. The culmination of the advance was of short duration, and by 4300 yr BP the coastal lowlands again were ice-free. A distinct marine level at 16–18 m a.s.l. was contemporaneous with or slightly post-dates the Brandy Bay advance, thus indicating the relative sea-level around 4600–4500 yr BP. Our results from James Ross Island confirm that over large areas in this part of Antarctica the last deglaciation occurred late. © 1997 John Wiley & Sons, Ltd.  相似文献   

2.
The Northern Prince Gustav Ice Stream located in Prince Gustav Channel, drained the northeastern portion of the Antarctic Peninsula Ice Sheet during the last glacial maximum. Here we present a chronology of its retreat based on in situ produced cosmogenic 10Be from erratic boulders at Cape Lachman, northern James Ross Island. Schmidt hammer testing was adopted to assess the weathering state of erratic boulders in order to better interpret excess cosmogenic 10Be from cumulative periods of pre-exposure or earlier release from the glacier. The weighted mean exposure age of five boulders based on Schmidt hammer data is 12.9 ± 1.2 ka representing the beginning of the deglaciation of lower-lying areas (< 60 m a.s.l.) of the northern James Ross Island, when Northern Prince Gustav Ice Stream split from the remaining James Ross Island ice cover. This age represents the minimum age of the transition from grounded ice stream to floating ice shelf in the middle continental shelf areas of the northern Prince Gustav Channel. The remaining ice cover located at higher elevations of northern James Ross Island retreated during the early Holocene due to gradual decay of terrestrial ice and increase of equilibrium line altitude. Schmidt hammer R-values are inversely correlated with 10Be exposure ages and could be used as a proxy for exposure history of individual granite boulders in this region and favour the hypothesis of earlier release of boulders with excessive 10Be concentrations from glacier directly at this site. These data provide evidences for an earlier deglaciation of northern James Ross Island when compared with other recently presented cosmogenic nuclide based deglaciation chronologies, but this timing coincides with rapid increase of atmospheric temperature in this marginal part of Antarctica.  相似文献   

3.
The recent disintegration of Antarctic Peninsula ice shelves, and the associated accelerated discharge and retreat of continental glaciers, has highlighted the necessity of quantifying the current rate of Antarctic ice mass loss and the regional contributions to future sea-level rise. Observations of present day ice mass change need to be corrected for ongoing glacial isostatic adjustment, a process which must be constrained by geological data. However, there are relatively little geological data on the geometry, volume and melt history of the Antarctic Peninsula Ice Sheet (APIS) after Termination 1, and during the Holocene so the glacial isostatic correction remains poorly constrained. To address this we provide field constraints on the timing and rate of APIS deglaciation, and changes in relative sea-level (RSL) for the north-eastern Antarctic Peninsula based on geomorphological evidence of former marine limits, and radiocarbon-dated marine-freshwater transitions from a series of isolation basins at different altitudes on Beak Island. Relative sea-level fell from a maximum of c. 15 m above present at c. 8000 cal yr BP, at a rate of 3.91 mm yr?1 declining to c. 2.11 mm yr?1 between c. 6900–2900 cal yr BP, 1.63 mm yr?1 between c. 2900–1800 cal yr BP, and finally to 0.29 mm yr?1 during the last c. 1800 years. The new Beak Island RSL curve improves the spatial coverage of RSL data in the Antarctic. It is in broad agreement with some glacio-isostatic adjustment models applied to this location, and with work undertaken elsewhere on the Antarctic Peninsula. These geological and RSL constraints from Beak Island imply significant thinning of the north-eastern APIS by the early Holocene. Further, they provide key data for the glacial isostatic correction required by satellite-derived gravity measurements of contemporary ice mass loss, which can be used to better assess the future contribution of the APIS to rising sea-levels.  相似文献   

4.
Brenda L. Hall   《Quaternary Science Reviews》2009,28(21-22):2213-2230
A history of Holocene glaciation in the Antarctic and sub-Antarctic affords insight into questions concerning present and future ice-sheet and mountain-glacier behavior and global climate and sea-level change. Existing records permit broad correlation of Holocene ice fluctuations within the region. In several areas, ice extent was less than at present in mid-Holocene time. An important exception to this is the West Antarctic Ice Sheet, which has undergone continued recession throughout the Holocene, probably in response to internal dynamics. The first Neoglacial ice advances occurred at 5.0 ka, although some sites (e.g., western Ross Sea) lack firm evidence for glacial expansion at that time. Glaciers in all areas underwent renewed growth in the past millennium, and most have subsequently undergone recession in the past 50 years, ranging from near-catastrophic in parts of the Antarctic Peninsula to minor in the western Ross Sea region and sections of East Antarctica. This magnitude difference likely reflects the much greater warming that is taking place in the Antarctic Peninsula region today as compared to East Antarctica.  相似文献   

5.
The volume of Antarctic ice at the Last Glacial Maximum is a key factor for calculating the past contribution of melting ice sheets to Late Pleistocene global sea level change. At present, there are large uncertainties in our knowledge of the extent and thickness of the formerly expanded Antarctic ice sheets, and in the timing of their release as meltwater into the world’s oceans. This paper reviews the four main approaches to determining former Antarctic ice volume, namely glacial geology, glacio-isostatic studies, glaciological modelling, and ice core analysis and attempts to reconcile these to give a ‘best estimate’ for ice volume. In the Ross Sea there was a major expansion of grounded ice at the Last Glacial Maximum, accounting for 2.3–3.2 m of global sea level. At some time in the Weddell Sea a large grounded ice sheet corresponding to c. 2.7 m of global sea level extended to the shelf break. However, this ice expansion has not yet been confidently dated and may not relate to the Last Glacial Maximum. Around East Antarctica there was thickening and advance offshore of ice in coastal regions. Ice core evidence suggests that the interior of East Antarctica was either close to its present elevation or thinner during the last glacial so the effect of East Antarctica on sea level depends on the net balance between marginal thickening and interior thinning. Suggested East Antarctic contributions vary from a 3–5.5 m lowering to a 0.64 m rise in global sea level. The Antarctic Peninsula ice sheet thickened and extended offshore at the Last Glacial Maximum, with a sea level equivalent contribution of c. 1.7 m. Thus, the Antarctic ice sheets accounted for between 6.1 and 13.1 m of global sea level fall at the Last Glacial Maximum. This is substantially less than has been suggested by most previous studies but the maximum figure matches well with one modelling estimate. The timing of Antarctic deglaciation is not well known. In the Ross Sea, terrestrial evidence suggests deglaciation may have begun at c. 13,000 yr BP1 but that grounded ice persisted until c. 6,500 yr BP. Marine evidence suggests the western Ross Sea was deglaciated by c. 11,500 yr BP. Deglaciation of the Weddell Sea is poorly constrained. Grounded ice in the northern Antarctic Peninsula had retreated by c. 13,000 yr BP, and further south deglaciation occurred sometime prior to c. 6,000 yr BP. Many parts of coastal East Antarctica apparently escaped glaciation at the LGM, but in those areas that were ice-covered deglaciation was underway by 10,000 yr BP. With existing data, the timing of deglaciation shows no firm relation to northern hemisphere-driven sea level rise. This is probably due partly to lack of Antarctic dating evidence but also to the combined influence of several forcing mechanisms acting during deglaciation.  相似文献   

6.
Detailed sedimentological and microtextural analyses of newly-discovered late Neogene diamictites and other coarse-grained facies, mostly sandwiched between hyaloclastite of the James Ross Island Volcanic Group and Cretaceous sandstone and mudstone, indicate deposition mainly by glacigenic debris flows. The deposits on James Ross Island (northern Antarctic Peninsula) constrain the depositional setting, ice–bed dynamics and regional palaeoclimate. The sequences on James Ross Island vary in age but are mainly late Miocene and Pliocene. Unlike Neogene sedimentary sequences elsewhere in Antarctica, those on James Ross Island are unusually well-dated by a combination of 40Ar/39Ar and 87Sr/86Sr analyses on fresh interbedded lavas and pristine bivalve molluscs, respectively. The Sr isotopic ages of the debris flows cluster around 4.74, 4.89, 5.44, 5.78, and 6.31 Ma and probably date relatively warm periods in the northern Antarctic Peninsula region, when the bivalves lived under ice-poor or seasonally ice-free conditions. The bivalves are often remarkably well-preserved, lack adhering lithified sediment and, in at least two locations, are large, mainly unfragmented and sometimes articulated, suggesting that they were alive immediately prior to their incorporation in subaqueous debris flows at the margins of an advancing glacier. These fossiliferous glacigenic debris flows signify episodes of ice expansion during relatively warm periods, or “interglacials”, of the late Miocene and Pliocene. The James Ross Island glacigenic sedimentary successions attain thicknesses of up to 150 m and extend over 4 km laterally. The high volume of glacigenic sediment delivery implicit in the James Ross Island successions indicates that a series of dynamic ice fronts crossed the region during the late Miocene and Pliocene epochs. Associated evidence, in the form of clast abrasion (including striations and faceting) and bedrock erosion, is indicative of basal sliding and subglacial sediment deformation active at the ice–bed interface and wet-based temperate or polythermal regimes, prior to remobilisation. The evidence further suggests two local ice caps on James Ross Island during the warm periods, as well as ice-overriding by the Antarctic Peninsula Ice Sheet from the west and northwest.  相似文献   

7.
Glaciomarine surficial sediments in cores taken from Bransfield Strait, adjacent to the Antarctic Peninsula, have yielded abundant recycled and contemporaneous (Pleistocene–Holocene) palynomorphs. The former are derived principally from Late Cretaceous–Palaeogene sediments and provide information on glaciomarine depositional conditions and sediment source areas. The composition of the assemblages suggests that they reflect vegetation that was endemic to the Weddellian Biogeographic Province, which includes what is now Seymour Island, James Ross Island and other parts of the Antarctic Peninsula region. The sediments concerned are considered to have accumulated as a result of ice-rafting and discharge of subglacial meltwater.  相似文献   

8.
Back in the mid-nineteenth century British explorer James Clark Ross took his ships, HMS Terror and HMS Erebus , farther south than anyone else had been. He now lends his name to James Ross Island, a part-volcanic edifice that rises out of the sea off the north-east tip of the Antarctic Peninsula. The island records a geological history dating back to the Cretaceous, though its great peaks are volcanic. The most recent rocks of the island record a monumental struggle between fire and ice, the volcanoes, and the ice sheets that cover them. The glacigenic sediments that are interspersed with the volcanic rocks contain rich fossil assemblages which suggest that at times, the climate was warmer, with the ice retreating. Their study may help us to delimit the patterns of climate change in the Antarctic Peninsula region as Earth's global climate warms.  相似文献   

9.
A high-resolution record of Holocene deglacial and climate history was obtained from a 77 m sediment core from the Firth of Tay, Antarctic Peninsula, as part of the SHALDRIL initiative. This study provides a detailed sedimentological record of Holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula. A robust chronostratigraphy was derived from thirty-three radiocarbon dates on carbonate material. This chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including: magnetic susceptibility, electric resistivity, porosity, ice-rafted debris content, organic carbon content, nitrogen content, biogenic silica content, and diatom and foraminiferal assemblages. The core bottomed-out in a stiff diamicton interpreted as till. Gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal. yr BP and its subsequent landward retreat. This was approximately 5000 yr later than in the Bransfield Basin and South Shetland Islands, on the western side of the peninsula. The Firth of Tay core site remained in a proximal glaciomarine setting until 8300 cal. yr BP, at which time significant glacial retreat took place. Deposition of diatomaceous glaciomarine sediments after 8300 cal. yr BP indicates that an ice shelf has not existed in the area since this time.The onset of seasonally open marine conditions between 7800 and 6000 cal. yr BP followed the deglacial period and is interpreted as the mid-Holocene Climatic Optimum. Open marine conditions lasted until present, with a minor cooling having occurred between 6000 and 4500 cal. yr BP and a period of minor glacial retreat and/or decreased sea ice coverage between 4500 and 3500 cal. yr BP. Finally, climatic cooling and variable sea ice cover occurred from 3500 cal. yr BP to near present and it is interpreted as being part of the Neoglacial. The onset of the Neoglacial appears to have occurred earlier in the Firth of Tay than on the western side of the Antarctic Peninsula. The Medieval Warm Period and Little Ice Age were not pronounced in the Firth of Tay. The breadth and synchroneity of the rapid regional warming and glacial retreat observed in the Antarctic Peninsula during the last century appear to be unprecedented during the Holocene epoch.  相似文献   

10.
The Gustav Group of the James Ross Basin, Antarctic Peninsula, forms part of a major Southern Hemisphere Cretaceous reference section. Palynological data, chiefly from dinoflagellate cysts, integrated with macrofaunal evidence and strontium isotope stratigraphy, indicate that the Gustav Group, which is approximately 2.6 km thick, is Aptian–Coniacian in age. Aptian–Coniacian palynofloras in the James Ross Basin closely resemble coeval associations from Australia and New Zealand, and Australian palynological zonation schemes are applicable to the Gustav Group. The lowermost units, the coeval Pedersen and Lagrelius Point formations, have both yielded early Aptian dinoflagellate cysts. Because the overlying Kotick Point Formation is of early to mid Albian age, the Aptian/Albian boundary is placed, questionably, at the Lagrelius Point Formation–Kotick Point Formation boundary on James Ross Island, and this transition may be unconformable. Although the Kotick Point Formation is largely early Albian on dinoflagellate cyst evidence, the uppermost part of the formation appears to be of mid Albian age. This differentiation of the early and mid Albian has refined the age of the formation, previously considered to be Aptian–Albian, based on macrofaunal evidence. The Whisky Bay Formation is of late Albian to latest Turonian age on dinoflagellate cyst evidence and this supports the macrofaunal ages. Late Albian palynofloras have been recorded from the Gin Cove, lower Tumbledown Cliffs, Bibby Point and the lower–middle Lewis Hill members. However, the Cenomanian age of the upper Tumbledown Cliffs and Rum Cove members, based on molluscan evidence, is not supported by the dinoflagellate cyst floras and further work is required on this succession. The uppermost part of the Whisky Bay Formation in north-west James Ross Island is of mid to late Turonian age and this is confirmed by strontium isotope stratigraphy. The uppermost unit, the Hidden Lake Formation, is Coniacian in age on both palaeontological and strontium isotope evidence. The uppermost part of the formation appears to be early Santonian based on dinoflagellate cysts, but strontium isotope stratigraphy constrains this as being no younger than late Coniacian. This refined palynostratigraphy greatly improves the potential of the James Ross Basin as a major Cretaceous Southern Hemisphere reference section.  相似文献   

11.
Pollen analysis, glacial varve chronology and palaeomagnetic measurements were carried out on Late Weichselian lake sediments from southwestern Smaland, south Sweden. The sequence is correlated to the GRIP event stratigraphy, expressed in calendar years BP, and covers the period from the deglaciation at c. 14 400 to 11 300 calendar years BP. The series encompasses c. 930 varves and has been connected to the local varve chronology. Varve thickness increases markedly after the Older Dryas stadial, which indicates an accelerated deglaciation and melting of dead ice. The pollen diagram displays the vegetation development from the deglaciation at c. 14 400 calendar years BP to the transition to the Holocene. The vegetation succession starts with an arctic pioneer vegetation at the deglaciation, changes to a more stable tundra environment and displays a development which concurs with the traditional lateglacial pollen stratigraphy for southern Sweden. A palaeo-magnetic secular variation curve is presented displaying two westerly declination swings at 14200-13800 and 12 800-11 600 calendar years BP, respectively. The upper one can be recognized from other palaeomagnetic stratigraphies from southern Sweden and Estonia.  相似文献   

12.
A 4.96-m-long sediment core from the Hanon paleo-maar in Jeju Island, Korea was studied to investigate the paleoclimatic change and East Asian monsoon variations during the latest Pleistocene to early Holocene (23,000-9000 cal yr BP). High-resolution TOC content, magnetic susceptibility, and major element composition data indicate that Jeju Island experienced the coldest climate around 18,000 cal yr BP, which corresponds to the last glacial maximum (LGM). Further, these multi-proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14,000 cal yr BP, which represents the commencement of the last major deglaciation. After the last major deglaciation, the TOC content decreased from 13,300 to 12,000 cal yr BP and from 11,500 to 9800 cal yr BP, thereby reflecting the weakening of the summer monsoon. The LGM in Jeju Island occurred later in comparison with the Chinese Loess Plateau. Such a disparity in climatic change events between central China and Jeju Island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central China and by the buffering effect of the Pacific Ocean.  相似文献   

13.
Here we present new relative sea-level (RSL) curves developed from Holocene-aged raised beaches along the southern Scott Coast of the western Ross Sea, Antarctica. Fifty-four dates of marine shells, seal skin and elephant seal remains incorporated within raised beaches during storms afford a chronology for these curves. All of the curves show the same pattern and timing of RSL change within a small range of error. The best-dated curve suggests that final unloading of grounded Ross Sea ice from the southern Scott Coast and McMurdo Sound region occurred shortly before 6500 14C yr BP. This age is consistent with glacial geological evidence that places deglaciation between 5730 and 8340 14C yr BP. Our data strongly suggest that grounding-line retreat of the Ross Sea ice sheet southward through the McMurdo Sound region occurred in mid- and late Holocene time. If this is correct, then rising sea level could not have driven ice recession to the present-day grounding line on the Siple Coast, because global deglacial sea-level rise was essentially accomplished by mid-Holocene time. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

14.
Cosmogenic 10Be surface exposure ages for bedrock sites around Torridon and the Applecross Peninsula in Wester Ross, northwest Scotland, provide new insights into the Lateglacial transition. Accounting for postglacial weathering, six statistically comparable exposure ages give a late Younger Dryas (G‐1) exposure age of 11.8 ± 1.1 ka. Two further outliers are tentative pre‐Younger Dryas exposure ages of 13.4 ± 0.5 ka in Torridon, and 17.5 ± 1.2 ka in Applecross. The Younger Dryas exposure ages have compelling implications for the deglaciation of marginal Loch Lomond Stadial ice fields in Torridon and Applecross. Firstly, they conflict with predictions of restricted ice cover and rapid retreat based on modelling experiments and climate proxies, instead fitting a model of vertically extensive and prolonged ice coverage in Wester Ross. Secondly, they indicate that >2 m of erosion took place in the upper valleys of Torridon and Applecross during the Younger Dryas, implying a dominantly warm‐based glacial regime. Finally, the exposure ages have clarified that corrie (cirque) glaciers did not readvance in Wester Ross, following final deglaciation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
This study reports on the most stratigraphically extensive nannofloras yet recovered from the Lachman Crags Member of the Santa Marta Formation, James Ross Island, Antarctic Peninsula. The productive samples are dated as early Campanian. These ages are in accord with those provided by ammonites, foraminifera, ostracods and radiolarians from the same locality. The consistent and relatively abundant presence of Gephyrobiscutum diabolum throughout the productive part of the section, a species that has previously only been documented from the Falkland Plateau, extends its geographic distribution to higher latitudes, at least to the Antarctic Peninsula area.  相似文献   

16.
Fine fractions of soils on the Barton Peninsula, King George Island, West Antarctica have been forming during the last 6000 yr since the last deglaciation. Texturally, they are mostly composed of mineral and rock fragments with some volcanic ashes, which are also indicated by geochemical compositions representing for the nonclay silicate minerals and low values of chemical index of alteration. No significant changes are observed in major- and trace element abundances. Such geochemical characteristics suggest that chemical weathering of bedrocks on the Barton Peninsula seems insignificant and that the soils are composed of physically weathered mineral and rock fragments which are mixed with eolian additions of volcanic ashes and Patagonian dusts. Chondrite-normalized rare earth element (REE) distribution patterns of the Barton Peninsula soils are slightly different from those of bedrocks, indicating that the REE abundances and characteristics were influenced by eolian additions. Mixing calculations, which mass-balance the REEs, suggest that volcanic ashes blown from Deception Island were the major eolian contributor, followed by atmospheric dusts sourced from Patagonia, South America. Even in the warmer and humid climatic conditions in the maritime Antarctic region, the chemical weathering of bedrocks appears to be insignificant, probably due to the relatively short duration of weathering since the last deglaciation.  相似文献   

17.
《Quaternary Science Reviews》2007,26(17-18):2113-2127
We compare numerical predictions of glaciation-induced sea-level change to data from 8 locations around the Antarctic coast in order to test if the available data preclude the possibility of a dominant Antarctic contribution to meltwater pulse IA (mwp-IA). Results based on a subset of 7 spherically symmetric earth viscosity models and 6 different Antarctic deglaciation histories indicate that the sea-level data do not rule out a large Antarctic source for this event. Our preliminary analysis indicates that the Weddell Sea is the most likely source region for a large (∼9 m) Antarctic contribution to mwp-IA. The Ross Sea is also plausible as a significant contributor (∼5 m) from a sea-level perspective, but glacio-geological field observations are not compatible with such a large and rapid melt from this region. Our results suggest that the Lambert Glacier component of the East Antarctic ice sheet experienced significant retreat at the time of mwp-IA, but only contributed ∼0.15 m (eustatic sea-level change). All of the ice models considered under-predicted the isostatic component of the sea-level response in the Antarctic Peninsula and the Sôya Coast region of the East Antarctic ice sheet, indicating that the maximum ice thickness in these regions is underestimated. It is therefore plausible that ice melt from these areas, the Antarctic Peninsula in particular, could have made a significant contribution to mwp-IA.  相似文献   

18.
Rock samples from the Kanin Peninsula and the Timan Ridge were analysed for in situ cosmogenic 10Be for exposure age dating purposes. Crystalline rocks were sampled at four sites on the Kanin Peninsula, either from bedrock outcrops or from glacial erratics, giving overall similar 10Be ages. Outcropping sandstone and crystalline erratics were available from three sites at the Timan Ridge. The highly weathered sandstone gives substantially younger 10Be ages than the adjacent erratics. The exposure ages from the Kanin Peninsula suggest that the last deglaciation of this area took place between 55 and 37 10Be kyr ago, in agreement with a preceding Kara Sea glaciation (55-45 kyr BP). The northwest coast of the peninsula was probably just outside the maximum limit of the last Scandinavian glaciation (20-17 kyr BP). Glacial erratic exposure ages from the Timan Ridge suggest that the 55-45 kyr BP Kara Sea glaciation reached the northern part of the ridge. The exposure dates do not show conclusive evidence regarding the existence of a Timan Ridge ice cap.  相似文献   

19.
We review the post-glacial climate variability along the East Antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere. Nearly all East Antarctic records show a near-synchronous Early Holocene climate optimum (11.5–9 ka BP), coinciding with the deglaciation of currently ice-free regions and the optimum recorded in Antarctic ice and marine sediment cores. Shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the Early Holocene warm period, and show complex regional patterns, but an overall trend of cooling in the terrestrial records. A Mid to Late Holocene warm period is present in many East Antarctic lake and shallow coastal marine records. Although there are some differences in the regional timing of this warm period, it typically occurs somewhere between 4.7 and 1 ka BP, which overlaps with a similar optimum found in Antarctic Peninsula terrestrial records. The differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify. Nearly all records show a neoglacial cooling from 2 ka BP onwards. There is no evidence along the East Antarctic coastline for an equivalent to the Northern Hemisphere Medieval Warm Period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the Northern Hemisphere's Little Ice Age. There is a need for well-dated, high resolution climate records in coastal East Antarctica and particularly in Terre Adélie, Dronning Maud Land and Enderby Land to fully understand the regional climate anomalies, the disparity between marine and terrestrial records, and to determine the significance of the heterogeneous temperature trends being measured in the Antarctic today.  相似文献   

20.
The Nordenskjöld Formation is a sequence of thinly interbedded ash beds and black, radiolarian-rich mudstones which is exposed on the eastern coast of the Antarctic Peninsula. As a result of recent field work, the Nordenskjöld Formation has been re-examined and redefined with three new members recognized — the Longing, Ameghino, and Larsen members. The age of the formation, based on its macrofossil content, is Kimmeridgian to Berriasian, although reworked clasts from James Ross Island suggest it might range down into the Oxfordian.  相似文献   

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