Palaeoglaciation of Bayan Har Shan,northeastern Tibetan Plateau: glacial geology indicates maximum extents limited to ice cap and ice field scales

Key locations within an extensive area of the northeastern Tibetan Plateau, centred on Bayan Har Shan, have been mapped to distinguish glacial from non‐glacial deposits. Prior work suggests palaeo‐glaciers ranging from valley glaciers and local ice caps in the highest mountains to a regional or even plateau‐scale ice sheet. New field data show that glacial deposits are abundant in high mountain areas in association with large‐scale glacial landforms. In addition, glacial deposits are present in several locations outside areas with distinct glacial erosional landforms, indicating that the most extensive palaeo‐glaciers had little geomorphological impact on the landscape towards their margins. The glacial geological record does indicate extensive maximum glaciation, with local ice caps covering entire elevated mountain areas. However, absence of glacial traces in intervening lower‐lying plateau areas suggests that local ice caps did not merge to form a regional ice sheet on the northeastern Tibetan Plateau around Bayan Har Shan. No evidence exists for past ice sheet glaciation. Copyright © 2009 John Wiley & Sons, Ltd.     

中国南极冰川学研究10年回顾与展望

扼要回顾中国南极冰川学研究历程,当前国际南极冰川学研究背景和发展趋势,并从南极冰盖雪冰物理特征研究,冰盖气候环境记录的现代过程研究以及冰芯研究等方面总结我国南极冰川学研究取得的成果,认为８０年代后期以来,中国南极冰川研究成果显著,尤其是对南冰盖气候环境记录的现代过程研究取得了很大进展,居于国际研究的前沿地位。     

中国南极冰川学研究10 a回顾与展望

The study of Antarctic glaciology in China is reviewed with the emphasis on the past decade. Much progress has been achieved in the physical characteristics of the Antarctic ice sheet and caps and in the study of climatic and environmental records in Antarctic snow and ice. Through observations of snow profiles of numerous snow-pits and shallow cores in the Wilkes Land and Lambert Glacier basin and along the route of the 1990 International Trans-Antarctica Science Expedition (ITASE), the regional features of snow deposition and densification in Antarctica were revealed. The Nelson Island ice cap in South Shetland Islands was investigated in detail that　greatly enriched the knowledge of glaciers under a sub-Antarctic maritime climate. From the analyses of shallow ice cores and surface snow samples, in particular those taken along the ITASE route, the systematic data of stable isotopes, soluble impurities and heavy metal Pb in present precipitation in Antarctica has been obtained. Some suggestions are proposed through discussing the present hot points in the above fields.     

The glacially sculptured landscape in Dronning Maud Land, Antarctica, formed by wet-based mountain glaciation and not by the present ice sheet

The glacial landscape beneath the Maudheimvidda ice sheet in East Antarctica was most probably formed during a more temperate phase of Antarctic glaciation than the present. Overdeepened glacial cirques and U-shaped valleys are found in the Heimefrontfjella and Vestfjella mountain ranges. These glacial landforms, located beneath the ice sheet, have been mapped with radio-echo sounders. The present ice sheet covering these landforms is cold and frozen to its bed, and has a negligible erosive effect on the substrate. Ice sheet thickening during the Quaternary glacial periods is not believed to have caused any significant increase in erosion at the investigated sites. Instead, the glacial morphology was most likely formed by smaller, temperate glaciers when the Antarctic climate was warmer than at present. Datings of foraminifera and ash layers from the Transantarc-tic Mountains indicate that the present cold ice sheet was formed 2.5 Ma years ago. Other studies imply that a cold Antarctic ice sheet has lasted even longer. The glacial landforms in Maudheimvidda may thus be of a pre-Quaternary age.     

Late Quaternary glaciation in the Hebrides sector of the continental shelf: was St Kilda overrun by the British‐Irish Ice Sheet?

Until recently, the British‐Irish Ice Sheet (BIIS) was thought to have reached no farther than a mid‐continental shelf position in the Hebrides Sector, NW Britain, during the last glaciation (traditional model). However, recent discovery of widespread shelf‐edge moraines in this sector has led to a suggestion of much more extensive ice (Atlantic Shelf model). The position of the St Kilda archipelago, approximately mid‐way between the Outer Hebrides and the continental shelf edge, makes it ideal as an onshore location to test which of the two competing models is more viable. To this end, we (i) reassessed the characteristics, stratigraphy and morphology of the Quaternary sediments exposed on the largest island (Hirta), and (ii) applied time‐dependent 2D numerical modelling of possible glacier formation on Hirta. Instead of three glaciations (as previously suggested), we identified evidence of only two, including one of entirely local derivation. The numerical model supports the view that this glaciation was in the form of two short glaciers occupying the two valleys that dominate Hirta. The good state of preservation of the glacial sediments and associated moraine of this local glaciation indicate relatively recent formation. In view of the low inferred equilibrium line altitude of the glacier associated with the best morphological evidence (～120 m), considerable thickness of slope deposits outside the glacial limits and evidence of only one rather than two tills, a Late Devensian rather than Younger Dryas age is preferred for this glaciation. Re‐examination of the submarine moraine pattern from available bathymetry suggests that the ice sheet was forced to flow around St Kilda, implying that the ice was of insufficient thickness to overrun the islands. Accepting this leaves open the possibility that a St Kilda nunatak supported local ice while the ice sheet extended to the continental shelf edge.     

Early Permian climate change in the Falkland Islands

An Early Permian glacial diamictite forms a distinctive unit within the Falkland Islands sedimentary succession and two aspects of its significance have recently been serendipitously enhanced. Fossil discoveries in exotic limestone clasts bear on palaeogeography, whilst a series of mineral‐exploration borehole cores have allowed a detailed study of the sedimentary record of deglaciation that followed deposition of the diamictite. Statistical analysis of reflectance and XRF core‐scanning data has identified likely Milankovitch periodicities and enabled tentative time‐scale modelling. The ‘icehouse to greenhouse’ transition appears to have spanned approximately 1.2 million years, with waning cycles of re‐advance superimposed on overall glacial retreat. The new results play into a long‐debated geological paradox: although the Falkland Islands are now proximal to the South Atlantic coastline of South America, their geology bears an uncanny resemblance to that of the Cape Fold Belt and Karoo Basin in South Africa. This puzzled the geological pioneers, but became readily explicable when first continental drift and then plate tectonics were invoked to reconstruct the break‐up of the Gondwana supercontinent—although the details remain controversial. One of the key stratigraphical correlation levels throughout the major fragments of southern Gondwana—South Africa, South America, Antarctica and Australia—is the glacigenic deposit left behind by the extensive, Late Carboniferous to Early Permian regional glaciation; in the Falkland Islands it is designated the Fitzroy Tillite Formation.     

IX. The St. Vincent Basin

Late Palaeozoic glaciation in Australia, discovered over a century ago, is now known to have covered a large part of the continent. In South Australia, tillite and outwash debris lie upon clearly striated pavements within glacial valleys, and show that ice sheets with valley tongues moved northward from sources now occupied by deep ocean south of the continent. These glaciers reached into the Cooper, Arckaringa, and Pedirka Basins at the end of the Carboniferous and laid down patches of till in the Early Permian, now preserved largely in the subsurface. In Tasmania, an ice sheet waxed in the latest Carboniferous from sources to the west of the island, and deposited till and “drop‐stones” into fossiliferous marine strata until well into the Late Permian. In Victoria, the ice cap laid down till on a striated floor, and here and there sequences of outwash, including boulder pavements. In New South Wales, continental glaciation expanded eastward to the sea early in the Permian, and left a record intercalated with volcanics and coal beds into the Late Permian. Bordering the Tamworth Trough of northern New South Wales, and occurring also in the highlands of New England, alpine glaciers left a record in the form of striated stones and dropstones, in very thick sequences of fluviatile, lacustrine, and marine clastic sediments. The mountains existed in Middle and early Late Carboniferous times, and were largely worn down to gentle relief when continental glaciers expanded northward in the Early Permian. A non‐glacial interval at the end of the Carboniferous therefore probably occurred in New South Wales. In Queensland, alpine glaciers occupied mountains at the western rim of the Bowen Basin at the end of the Carboniferous. Large blocks carried by icebergs from glaciers of unknown locations were dropped into Lower and Upper Permian strata of the Bowen Basin as well. In Western Australia Early Permian ice centres were located on the Yilgarn Block, east of the Perth Basin, on the Pilbara Block southwest of the Canning Basin, and on the Kimberley Block. Evidence for this glaciation consists mostly of ice‐rafted debris and fluvial‐glacial and glacial‐marine strata that reached as far north as the Bonaparte Gulf Basin.

The rapid growth northward of continental glaciers in Australia near the end of the Carboniferous corresponds with a rapid shift of palaeolatitude as judged from Irving's palaeomagnetic studies. The ice sheet grew quickly upon upland areas when Gondwanaland moved to a near polar position and the unfrozen Palaeo‐Pacific lay near at hand to provide an abundant source of moisture.     

Causes of Antarctic glaciation in the cenozoic

The causes of Antarctic glaciation are analyzed by means of numeral experiments based on the three-dimensional thermodynamic model of a large ice sheet. Refrigeration of the climate between the Eocene and the Oligocene was due to the opening of the passage south of Australia and to the formation of the South Ring Stream. Calculations have shown that this led to the development of the East Antarctic Ice Sheet which might have existed in spite of relatively high temperatures of the surrounding ocean air. A new cooling of the climate in the Middle Miocene is connected with the fact that the South Ring Stream found its way through the Drake Passage glaciers spreading on to the Western Antarctic. Between Miocene and Pliocene, glaciation of the South Polar regions was at its maximum due to the regression of the world ocean. In Quaternary time, sea level was lowering due to the glaciation of the Northern Hemisphere, which resulted in glacier growth in the Antarctic. The anticipated warming of the climate due to the activity of man is not likely to bring about any considerable change in the size of the East Antarctic Ice Sheet.     

Bathymetric and geological maps from the British Antarctic Survey

Since my 2012 feature about British Antarctic Survey (BAS) geological maps, the survey has continued to produce a series of ad hoc maps highlighting the results of their ongoing research, often in collaboration with their international colleagues. Not only has BAS added to their geological mapping series with James Ross Island off the Antarctic Peninsula, they have also produced a map of the bedrock topography of the entire continent, together with two bathymetric and geological settings sheets of the seas to the north of Antarctica. The first oceanographic map focuses on the South Sandwich Islands, some of the most remote United Kingdom overseas territories, roughly 700 km south‐east of South Georgia. Finally, the Drake Passage sheet shows the sea bed morphology from the Falklands and Tierra del Fuego to the South Shetland Islands just off the Antarctic Peninsula, spanning 70–50°W in longitude and 52–63°S in latitude. Below 60° south, all international territorial claims have been frozen by the Antarctic Treaty, which has demilitarized the entire continent since 1961 and ensured it remains untainted by mineral exploration and which has now expanded to a membership of over 50 nations.     

The Polonez Cove Formation of King George Island, Antarctica: stratigraphy, facies and implications for mid-Cenozoic cryosphere development

The middle to late Oligocene Polonez Cove Formation, exposed on south‐eastern King George Island, South Shetland Islands, provides rare evidence of mid‐Cenozoic West Antarctic cryosphere evolution. A revised lithostratigraphy and facies analysis and a review of the palaeoenvironmental significance of the formation are presented here. The diamictite‐dominated basal member of the formation (Krakowiak Glacier Member) records the presence and retreat of marine‐based ice on a shallow continental shelf. Five overlying members are recognized. These consist of basaltic‐sourced sedimentary rocks and lavas and represent a variety of shoreface and shallow continental shelf environments in an active volcanic setting. These units contain diverse reworked and ice‐rafted exotic clasts that become sparse towards the top of the formation, suggesting a continuing but waning glacial influence. New ⁴⁰Ar/³⁹Ar dates from interbedded lava flows indicate a late Oligocene age (25·6–27·2 Ma) for the Polonez Cove Formation, but are slightly younger than skeletal carbonate Sr‐isotope ages obtained previously (28·5–29·8 Ma). There is evidence for wet‐based subice conditions at the base of the Polonez Cove Formation, but no sedimentary facies to suggest substantial meltwater. This may reflect a subpolar setting or may result from lack of preservation or a high‐energy depositional environment. A northern Antarctic Peninsula/South Shetland Islands provenance is probable for most non‐basaltic clasts, but certain lithologies with possible origins in the Transantarctic and Ellsworth Mountains also occur sparsely throughout the formation. There is evidence to suggest that the presence of such far‐travelled clasts within subglacially deposited facies at the base of the formation reflects the advance of a local ice cap across marine sediments containing the clasts as ice‐rafted material. The presence of these clasts suggests that extensive marine‐based ice drained into the southern Weddell Sea region and that a strong Weddell Sea surface current operated both before and during deposition of the Polonez Cove Formation.     

Multiple glaciations and sea level changes, northern Ellesmere Island, high arctic Canada

Along the northern coasts of Ellesmere Island, at least two glaciations are recognized on the basis of morphostratigraphy. The early Holocene ice limit lay only 5 to 60 km beyond present glaciers due to constraints imposed by aridity and calving. This limited ice advance likely extended beyond any Wisconsinan glacial limit. Marine limits established during, retreat from the last glacial maximum reach 148 m a.s.l. In contrast, earlier, more extensive glaciations inundated the coastlines and are associated with former relative sea levels now reaching 286 m a.s.l. Correlation of these pre-Wisconsinan glaciations is based upon amino acid ratios. However, this approach is severely limited by slow rates of racemization, a lack of in situ samples, and complex thermal histories owing to multiple transgressions. Models favoring extensive regional glaciation of northern Ellesmere Island and Greenland must include a glacioclimatic scenario recognizing the constraint that aridity places on glaciation. We suggest that the large ice volume associated with the oldest recognized glaciation relates to a period of reduced sea-ice cover, possibly >400,000 BP, and may correlate with an interglacial stage of the marine oxygen isotope record.     

Late Quaternary glaciation of the northern Urals: a review and new observations

This is a synthesis of the glacial history of the northern Urals undertaken using published works and the results of geological surveys as well as recent geochronometric and remote sensing data. The conclusions differ from the classical model that considers the Urals as an important source of glacial ice and partly from the modern reconstructions. The principal supporting evidence for the conventional model – Uralian erratics found on the adjacent plains – is ambiguous because Uralian clasts were also delivered by a thick external ice sheet overriding the mountains during the Middle Pleistocene. Alternative evidence presented in this paper indicates that in the late Quaternary the Ural mountains produced only valley glaciers that partly coalesced in the western piedmont to form large piedmont lobes. The last maximum glaciation occurred in the Early Valdaian time at c. 70–90 ka when glacial ice from the Kara shelf invaded the lowlands and some montane valleys but an icecap over the mountains was not formed. The moraines of the alpine glaciation are preserved only beyond the limits of the Kara ice sheet and therefore cannot be younger than MIS 4. More limited glaciation during MIS 2 generated small alpine moraines around the cirques of the western Urals (Mangerud et al. 2008: Quaternary Science Reviews 27, 1047). The largest moraines of Transuralia were probably produced by the outlet glaciers of a Middle Pleistocene ice sheet that formed on the western plains and discharged across the Polar Urals. The resultant scheme of limited mountain glaciation is possibly also applicable as a model for older glacial cycles.     

Late Quaternary glacial–interglacial variations in sediment supply in the southern Drake Passage

Geochemical characteristics of marine sediment from the southern Drake Passage were analyzed to reconstruct variations in sediment provenance and transport paths during the late Quaternary. The 5.95 m gravity core used in this study records paleoenvironmental changes during the last approximately 600 ka. Down-core variations in trace element, rare earth element, and Nd and Sr isotopic compositions reveal that sediment provenance varied according to glacial cycles. During glacial periods, detrital sediments in the southern Drake Passage were mostly derived from the nearby South Shetland Islands and shelf sediments. In contrast, interglacial sediments are composed of mixed sediments, derived from both West Antarctica and East Antarctica. The East Antarctic provenance of the interglacial sediments was inferred to be the Weddell Sea region. Sediment input from the Weddell Sea was reduced during glacial periods by extensive ice sheets and weakened current from the Weddell Sea. Sediment supply from the Weddell Sea increased during interglacial periods, especially those with higher warmth such as MIS 5, 9, and 11. This suggests that the influence of deep water from the Weddell Sea increases during interglacial periods and decreases during glacial periods, with the degree of influence increasing as interglacial intensity increases.     

Late Quaternary glaciation of Tibet and the bordering mountains: a review

Abundant glacial geologic evidence present throughout Tibet and the bordering mountains shows that glaciers have oscillated many times throughout the late Quaternary. Yet the timing and extent of glacial advances is still highly debated. Recent studies, however, suggest that glaciation was most extensive prior to the last glacial cycle. Furthermore, these studies show that in many regions of Tibet and the Himalaya glaciation was generally more extensive during the earlier part of the last glacial cycle and was limited in extent during the global Last Glacial Maximum (marine oxygen isotope stage 2). Holocene glacial advances were also limited in extent, with glaciers advancing just a few kilometers from their present ice margins. In the monsoon-influenced regions, glaciation appears to be strongly controlled by changes in insolation that govern the geographical extent of the monsoon and consequently precipitation distribution. Monsoonal precipitation distribution strongly influences glacier mass balances, allowing glaciers in high altitude regions to advance during times of increased precipitation, which are associated with insolation maxima during glacial times. Furthermore, there are strong topographic controls on glaciation, particular in regions where there are rainshadow effects. It is likely that glaciers, influenced by the different climatic systems, behaved differently at different times. However, more detailed geomorphic and geochronological studies are needed to fully explore regional variations. Changes in glacial ice volume in Tibet and the bordering mountains were relatively small after the global LGM as compared to the Northern Hemisphere ice sheets. It is therefore unlikely that meltwater draining from Tibet and the bordering mountains during the Lateglacial and early Holocene would have been sufficient to affect oceanic circulation. However, changes in surface albedo may have influenced the dynamics of monsoonal systems and this may have important implications for global climate change. Drainage development, including lake level changes on the Tibetan plateau and adjacent regions has been strongly controlled by climatic oscillations on centennial, decadal and especially millennial timescales. Since the Little Ice Age, and particularly during this century, glaciers have been progressively retreating. This pattern is likely to continue throughout the 21st century, exacerbated by human-induced global warming.     

The Falkland Islands’ palaeoecological response to millennial‐scale climate perturbations during the Pleistocene–Holocene transition: Implications for future vegetation stability in the southern ocean islands

Oceanic island flora is vulnerable to future climate warming, which is likely to promote changes in vegetation composition, and invasion of non‐native species. Sub‐Antarctic islands are predicted to experience rapid warming during the next century; therefore, establishing trajectories of change in vegetation communities is essential for developing conservation strategies to preserve biological diversity. We present a Late‐glacial‐early Holocene (16 500–6450 cal a bp ) palaeoecological record from Hooker's Point, Falkland Islands (Islas Malvinas), South Atlantic. This period spans the Pleistocene‐Holocene transition, providing insight into biological responses to abrupt climate change. Pollen and plant macrofossil records appear insensitive to climatic cooling during the Late‐glacial, but undergo rapid turnover in response to regional warming. The absence of trees throughout the Late‐glacial‐early Holocene enables the recognition of far‐travelled pollen from southern South America. The first occurrence of Nothofagus (southern beech) may reflect changes in the strength and/or position of the Southern Westerly Wind Belt during the Late‐glacial period. Peat inception and accumulation at Hooker's Point is likely to be promoted by the recalcitrant litter of wind‐adapted flora. This recalcitrant litter helps to explain widespread peatland development in a comparatively dry environment, and suggests that wind‐adapted peatlands can remain carbon sinks even under low precipitation regimes. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.     

Quaternary glaciation of Mt. Qomolangma-Xixabangma region

The uplift of the Himalaya and Qinghai-Xizang plateau began at the end of Pliocene to the beginning of Early Pleistocene, changing the atmospheric circulation in Asia, enhancing the South Asian monsoon and enormously effecting the climatic conditions and glacial development.According to the evidence of glacial deposits, geomorphology, paleobiology, paleopedology, etc., at least four glaciations can be recognized. The uplift of the Himalayas was earlier than that of other mountains, so that the glaciation occurred in Early Pleistocene, forming small piedmont glaciers on the N slope, whilst at the same time there were wide short valley glaciers on the S slope. During the Middle Pleistocene, the height of Himalaya was about 4000 m a s l, the monsoon was strong, and much water vapour reached the interior of the plateau, the most favourable period for glacial development. Great piedmont glaciers and small ice caps formed on the mountains N of Himalayas and great valley glaciers occurred on the S slope, but no great ice sheet covered the plateau.During the early Late Pleistocene, the Himalayas had risen to over 5000 m asl, forming a barrier against the incursion of the Indian monsoon, so that the precipitation decreased sharply on the plateau N of Himalayas, thus diminishing the extent of the glaciation. But on the high mountains of the S part of Xizang and on several high mountains of the S slope of the Great Himalaya, the precipitation increased and the extent of glaciation reached a maximum. Since Last Glaciation, the precipitation of the alpine zone has decreased more sharply, the climate has become drier and colder, becoming unfavourable for glacial development.During the Holocene, three stages may be distinguished, i.e. the recession in Early Holocene (10,000-8000 BP); the disappearance of most glaciers in the Hypsithermal period in Middle Holocene, (8000-3000 BP); and the neoglacial fluctuations in Late Holocene (3000 BP up to present). The glaciers of the Neoglaciation advanced several hundred meters or even 3–5 km farther than existing glaciers.     

Carboniferous diamictite dykes in the Falkland Islands

Sedimentary dykes hosted in ? Ordovician-Devonian strata on the Falkland Islands contain diamictite. The dykes, which are discordant to the host rocks, are sub-vertical, parallel-sided sheets formed by downward injection of a semi-fluidized sediment. On West Falkland palynomorphs present in 2 of the 11 dykes located demonstrate a Late Visean-Early Namurian age. This is older than the main Lafonian Diamictite Formation (Permian) and indicates that the dykes are a rare preservation of sediments formed during the main ice coverage of the Gondwana glaciation. Vitrinite reflectance from organic matter in the dykes indicates a shallow burial history (< 2–3 km) for the southwest Falkland Islands implying deposition of an incomplete or condensed sequence during Late Palaeozoic times, although the stratigraphical relationship of the dykes indicates that this may be extended back into the Mid Palaeozoic. The two diamictite dykes located on East Falkland are shown to be younger; probably Permian in age.     

First cosmogenic 10Be constraints on LGM glaciation on New Zealand's North Island: Park Valley,Tararua Range

We report the first direct ages for late Quaternary glaciation on the North Island of New Zealand. Mt Ruapehu, the volcanic massif in the North Island's centre, is currently glaciated and probably sustained glaciers throughout the late Quaternary, yet no numeric ages have been reported for glacial advances anywhere on the North Island. Here, we describe cosmogenic ¹⁰Be ages of the surface layers of a glacially transported boulder and glacially polished bedrock from the Tararua Range, part of the axial ranges of the North Island. Results indicate that a limited valley glaciation occurred, culminating in recession at the end of the last glacial coldest period (LGCP, ca. 18 ka). This provides an initial age for deglaciation on the North Island during the last glacial–interglacial transition (LGIT). It appears that glaciation occurred in response to an equilibrium‐line altitude (ELA) lowering of ～1400 m below the present‐day mean summer freezing level. Ages for glaciation in the Tararua Range correspond closely to exposure ages for the last glacial maximum (LGM) from the lateral moraines of Cascade Valley in the South Island, and in Cobb Valley, in northern South Island. The corollary is that glaciation in the Tararua Range coincided with the phase of maximum cooling during MIS 2, prior to the Antarctic Cold Reversal (ACR), during the LGCP. Copyright © 2008 John Wiley & Sons, Ltd.     

滇西北山地末次冰期冰川发育及其基本特征

对滇西北海拔4 000~4 500 m 山地的第四纪冰川发育和平衡线高度进行了研究. 结果表明: 古冰川发育主要依托海拔4 000~4 300 m的夷平面,早中期发育小型的冰帽以及流入四周谷地的山谷冰川,晚期主要发育规模较小的冰斗冰川. 冰川主要发育期为末次冰期,古冰川平衡线、山体最高峰以及夷平面的高度显示,冰川发育所依托的夷平面在末次冰期时超过古平衡线,二者差值为50~400 m,为冰川发生提供了良好的地形与地势条件. 冰川规模演化表明,滇西北地区多处山地MIS 3中期的冰川规模大于末次冰盛期（LGM）,可能与MIS 3中期较强南亚季风带来较丰富的降水有关. 古气候研究资料以及研究区的冰期系列表明,滇西北海拔4 000~4 500 m山地末次冰期的冰川作用是构造和气候相耦合的结果.