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1.
Interpretation of weathered glacial and interglacial deposits in the lower King Valley suggests that the Early Pleistocene Thureau Formation is conformably overlain by the Regency Formation. Pollen analysis of the Regency Formation provides evidence of a new climatic stage, the Regency Interglacial. The interglacial deposit consists of humified peat overlain by drifted wood and leaves. The pollen analysis shows a transition from montane scrub rainforest to lowland temperate rainforest dominated by Lagarostrobos franklinii, Nothofagus cunninghamii and Phyllocladus aspleniifolius. Trace quantities of the species Quintinia psi-latispora and Gothanipollis perplexus , now both extinct in Tasmania, were also recorded. On the basis of intense chemical weathering and correlation with sediments that have a reversed magnetization the weathered glacial deposits of the Thureau Formation are thought to be older than 730,000 B.P. The eroded interglacial deposit rests on the weathered deposits and is buried by outwash gravels of the David Formation, which was deposited during an ice advance of the Middle Pleistocene Henty Glaciation (c. 150,000 B.P.). Comparison of the Regency site with a site 2 km to the south at Baxter Rivulet shows that the unconformity between the interglacial deposit and the overlying outwash gravel represents the erosion of the evidence for the Middle Pleistocene Moore Glaciation.  相似文献   

2.
Glaciations of the West Coast Range,Tasmania   总被引：1，自引：0，他引：1  
Geomorphic, stratigraphic, palynologic and 14C evidence indicates that the West Coast Range, Tasmania, was glaciated at least three times during the late Cenozoic. The last or Margaret Glaciation commenced after 30,000 yr B.P., culminated about 19,000 yr B.P., and ended by 10,000 yr B.P. During this period a small ice cap, ca. 250 m thick, and cirque and valley glaciers covered 108 km2. The glacial deposits show little chemical weathering or erosional dissection. The snow line ranged from 690 to 1000 m with an average of 830 m for the ice cap. Mean temperature was 6.5°C below the present temperature. During the preceding Henty Glaciation a 300- to 400-m-thick ice cap and outlet glaciers exceeded 1000 km2. The glacial deposits are beyond 14C assay. They are more weathered chemically and more dissected than Margaret age deposits, and the degree suggests a pre-last interglaciation age (> 130,000 yr B.P.). The snow line of the ice cap lay at 740 m, and annual temperature was reduced by 7°C. Ice of the earliest Linda Glaciation slightly exceeded that of the Henty Glaciation but had a similar distribution. The glacial deposits are intensely weathered, have reversed magnetization, and overlie a paleosol containing pollen of Tertiary type. An early Pleistocene or Tertiary age is indicated.  相似文献   

3.
《Quaternary Science Reviews》2007,26(5-6):743-758
Detailed examination of the Tekapo Formation in the Tasman Valley, New Zealand has identified 20 facies, and five facies associations. These associations are delta foresets and bottomsets, sediment density flows, ice-contact lake sediments with ice-rafted debris and resedimentation deposits, and outwash gravels. Interpretation of the sediment-landform associations informed by observations at modern glacier termini suggests that the Late Pleistocene Tekapo Formation moraines have been formed by downwasting of a more expanded Tasman Glacier. During the early stages of glacier retreat, ponds on the glacier surface develop into thermokarst lakes which enlarge and coalesce to form a large supraglacial lake. Continued downwasting causes the lake outlet river to entrench into the impounding latero-frontal ice-cored moraine, lowering the lake level. This exposes lake-bottom sediments and forms shorelines on the proximal slopes of the ice-cored moraine. As the ice-cored moraine melts, these lake sediments are deformed and deposited against the Mt. John moraine. The observations and interpretations reported here suggest the Late Pleistocene end moraine is a constructional feature not a structural (glaciotectonic) feature as suggested by previous studies.  相似文献   

4.
Major and trace element chemical analyses of the Plio‐Pleistocene Bardin Bluffs Formation, on the margin of a major ice‐stream of the East Antarctic Ice Sheet, yield an anomalous chemically altered sediment composition. The Bardin Bluffs Formation of the Pagodroma Group is one of the key deposits on the Antarctic continent recording glaciomarine sedimentation under open marine fjord conditions as recently as the Plio‐Pleistocene. In modern fjords occupied by outlet glaciers of ice sheets, the composition of fine‐grained terrigenous sediments approaches that of unweathered rock types exposed upstream. In the Bardin Bluffs Formation, average abundances of stable elements (Ti, Al, Zr) approach average upper crustal compositions and the element ratios are consistent with sediments with a cratonic source, implying glacial dispersal from a large shield area through the Lambert Glacier drainage system. Interestingly, the chemical index of alteration (CIA) of these sediments has values similar to those of average shales formed under conditions of chemical weathering. The sediments are particularly depleted in silicate Ca, which has been observed elsewhere in glacial muds sourced from pre‐glacial saprolites. The anomalous chemistry of the Bardin Bluffs Formation can be explained by a sequence of events, involving chemical weathering prior to glacial expansion and erosion. The presence of a remnant 1·5 m deep late Neogene weathering profile at the base of the Bardin Bluffs sequence corroborates this conclusion. Supply of large quantities of chemically weathered materials to Antarctic marginal basins requires at least partial deglaciation of the continent and was previously regarded as uncharacteristic for late Neogene Antarctica.  相似文献   

5.
During the Itkillik Glaciation the Brooks Range supported an extensive mountain-glacier complex that extended for 750 km between 141° and 158°W longitude. Individual ice streams and piedmont lobes flowed as much as 50 km beyond the north and south margins of the range. Glaciers in the southern Brooks Range were longer than those farther north because of a southerly precipitation source, whereas those in the central and eastern part of the range were larger than glaciers at the extremities of the mountain system because of higher and more-extensive accumulation areas. Glacier equilibrium-line altitudes (ELAs) at the time of greatest advance were depressed 600 ± 100 m below present levels, whereas during a less-extensive late-glacial readvance (Alapah Mountain) ELA depression was about 300 ± 30 m. Radiocarbon dates indicate that Itkillik drift correlates with Late Wisconsin drift along the southern margin of the Laurentide Ice Sheet and with drift of Cordilleran glaciers in southern Alaska and the western conterminous United States deposited during the last glaciation. Itkillik I moraines represent the maximum ice advance under cold full-glacial conditions between about 24,000 and 17,000 14C y. a. Itkillik II sediments, probably deposited close to 14,000 y. a., are characterized by abundant outwash and ice-contact stratified drift implying a milder climate than that of the Itkillik I phase. Alapah Mountain moraines at the heads of valleys draining high-altitude (≥1800 m) source areas record a possible late Itkillik readvance that is not yet closely dated. Itkillik glaciers may have largely disappeared from Brooks Range valleys by the beginning of the Holocene.  相似文献   

6.
An extensive stratigraphic section at Cape Alfred Ernest on the Wootton Peninsula, northwest Ellesmere Island contains six lithofacies which appear to record two glacial phases separated by an organic layer. (1) A lower massive gravel records a pre-ice advance outwash phase; (2) massive fine-grained sediments record a period of non-glacial marine deposition when sea-level was higher than present; (3) a massive diamicton records the advance of ice across the site; (4) intermediate stratified beds record supraglacial and proglacial outwash, and include an organic layer; (5) massive diamicton grading down-valley to stratified diamicton and then massive, sheared diamicton, overlain by laminated fine-grained sediments with dropstones, recording the last (late Wisconsinan) glaciation; (6) upward-coarsening sands and gravels record proglacial outwash and grade to raised marine deltas. Radiocarbon dates of 39270 ± 640 and > 51000 yr BP were obtained on samples from the organic layer by accelerator mass spectrometry and conventional radiocarbon dating, respectively. Palaeoecological data suggest that the organics accumulated in a wet sedge meadow environment when the climate was warmer than present. Stratigraphic considerations suggest that the organic layer represents an interglacial interval which, if valid, indicates that the site constitutes the northernmost interglacial stratigraphy in the Canadian Arctic. Alternatively, the organic layer may date to Plio-Pleistocene times.  相似文献   

7.
This paper records the findings at a temporary exposure at Thorpe St Andrew near Norwich, Norfolk, UK in Early and early Middle Pleistocene Crag deposits. The British Geological Survey (BGS) describes the particular formation exposed as Norwich Crag consisting of Early Pleistocene shallow marine sediments. The section shows a succession of sorted sands and gravels overlain by a sandy diamicton. Based on field evidence and clast analysis, the sands and gravels are interpreted as the product of point bar and overbank sedimentation and represent the product of a river cutting into and aggrading within the more widespread shallow marine deposits. Composition of the sediments indicates derivation, primarily from Wroxham Crag Formation, with a contribution from Norwich Crag. The sandy diamicton is interpreted as late Middle Pleistocene Corton Till that is recorded in the area. A distinct pattern of colour changes at the top of the sands and gravels is interpreted as a soil that developed on the fluvial sediments before being overridden by the glacier that deposited the Corton Till. The existence of the fluvial sediments within the regional shallow marine deposits suggests that a fall of sea-level, possibly due to climate cooling, while the elevation of the sediments and the adjacent Crag implies that the site has been uplifted since sedimentation. This is the first observation of terrestrial sediments within the shallow marine Crag. The paper also makes a contribution to understanding the diagenetic processes that give deposits within this region some distinctive colour and sediment patterns.  相似文献   

8.
Two widespread tephra deposits constrain the age of the Delta Glaciation in central Alaska. The Old Crow tephra (ca. 140,000 ± 10,000 yr), identified by electron microprobe and ion microprobe analyses of individual glass shards, overlies an outwash terrace coeval with the Delta glaciation. The Sheep Creek tephra (ca. 190,000 yr) is reworked in alluvium of Delta age. The upper and lower limiting tephra dates indicate that the Delta glaciation occurred during marine oxygen isotope stage 6. We hypothesize that glaciers in the Delta River Valley reached their maximum Pleistocene extent during this cold interval because of significant mid-Pleistocene tectonic uplift of the east-central Alaska Range.  相似文献   

9.
The Sandhills Moraine is a Late Wisconsinan lateral moraine complex on southwest Banks Island. The occurrence of ice-ablation landforms, ground ice slumps, kettle lakes and catastrophic lake drainage in winter suggests the presence of substantial bodies of massive ground ice. The distinctive hummocky topography of the Sandhills Moraine is thought to reflect partial melt-out of this ice. Stratigraphic observations indicate that the ice is overlain irregularly and unconformably by glacigenic sediments, notably pebbly clay (till) and/or sandy gravels (outwash), while the ice itself possesses numerous and variable mineral inclusions, faults and foliations. Petrofabric analyses indicate a strongly preferred orientation to the ice crystals. It is suggested that these characteristics are best explained if the ground ice is interpreted as relict glacier ice.  相似文献   

10.
Glaciotectonized sediments and palaeosol at Great Sampford, western Suffolk, England are reconstructed to their original positions in order to determine the form of the original land surface and the associated soil development. The restored stratigraphy consists of Early Pleistocene Kesgrave Sands and Gravels which were deposited by the 'pre-glacial' river Thames, with the Early-Middle Pleistocene Valley Farm Soil developed on a terrace surface. These units are overlain by Sampford Deformation Till and Lowestoft Till, which were formed during the Middle Pleistocene Anglian glaciation. The micromorphological features of the reconstructed soil are interpreted in terms of three climatic cycles, each comprising a period of temperate climate soil formation followed by cold climate soil disruption. The final stage of disruption is associated with the periglacial climate that preceded Anglian glacierization. This pedological reconstruction is the most complex yet recognized from British Early and Middle Pleistocene palaeosols and provides an insight into major climatic oscillations prior to the Anglian Glaciation. The surface upon which the soil developed is one of the oldest terraces of the 'pre-glacial' River Thames that were formed when this river flowed northwards through East Anglia.  相似文献   

11.
The sedimentology and stratigraphy of a multi‐phase glaciation sequence dating to Marine Isotope Stage 6 in the Rakaia Valley, South Island, New Zealand, is presented. This outcrop presents an example of the depositional signature of an end member of temperate valley glaciation, where voluminous sediment supply in a tectonically active setting combines with high annual temperatures and low seasonality to generate significant year‐round glacifluvial activity. Such glacial systems produce geological–climatic units that are dominated by thick sequences of aggradational gravels and proglacial lake sediments trapped behind outwash heads during deglaciation. At Bayfields Cliff, outwash sequences record an oscillating glacier margin marked by a sequence of glacier‐fed, Gilbert‐type deltas. The deltas are cut by numerous small‐scale, syndepositional, normal faults indicating both loss of glacier support and melt‐out of buried ice. A larger‐scale thrust fault system reflects late‐stage ice overrun. Braid plain gravels and chaotic disturbed glacial lake sediments are also recorded. A notable feature of these systems is the virtual absence of till in an environment with much other evidence for proximal ice. Cumulatively we regard these sediment–landform associations as diagnostic of debris‐laden, perhumid, temperate valley glacier systems. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
The Mt Giluwe shield volcano was the largest area glaciated in Papua New Guinea during the Pleistocene. Despite minimal cooling of the sea surface during the last glacial maximum, glaciers reached elevations as low as 3200 m. To investigate changes in the extent of ice through time we have re-mapped evidence for glaciation on the southwest flank of Mt Giluwe. We find that an ice cap has formed on the flanks of the mountain on at least three, and probably four, separate occasions. To constrain the ages of these glaciations we present 39 new cosmogenic 36Cl exposure ages complemented by new radiocarbon dates. Direct dating of the moraines identifies that the maximum extent of glaciation on the mountain was not during the last glacial maximum as previously thought. In conjunction with existing potassium/argon and radiocarbon dating, we recognise four distinct glacial periods between 293–306 ka (Gogon Glaciation), 136–158 ka (Mengane Glaciation), centred at 62 ka (Komia Glaciation) and from >20.3–11.5 ka (Tongo Glaciation). The temperature difference relative to the present during the Tongo Glaciation is likely to be of the order of at least 5 °C which is a minimum difference for the previous glaciations. During the Tongo Glaciation, ice was briefly at its maximum for less than 1000 years, but stayed near maximum levels for nearly 4000 years, until about 15.4 ka. Over the next 4000 years there was more rapid retreat with ice free conditions by the early Holocene.  相似文献   

13.
Terminal-moraine ridges up to 6 m high have been forming at the snout of Styggedalsbreen for two decades. Based on intermittent observations during this period, combined with a detailed study of ridge morphology, sedimentary structures and composition during the 1993 field season, a model of terminal-moraine formation that involves the interaction of glacial and glacio-fluvial processes at a seasonally oscillating ice margin is presented. In winter, subglacial debris is frozen-on to the glacier sole; in summer, ice-marginal and supraglacial streams deposit sediments on the wasting ice tongue. The ice tongue overrides an embryonic moraine ridge during a late-winter advance and a double layer of sediment (diamicton overlain by sorted sands and gravels) is added to the moraine ridge during the subsequent ablation season. Particular ridges grow incrementally over many years and exert positive feedback by enhancing snout up-arching during the winter advance and constraining the course of summer meltwater streams close to the ice margin. The double-layer annual-meltout model is related to moraine formation by the stacking of subglacial frozen-on sediment slabs (Krüger 1993). Moraine ridges of this type have a complex origin. are not push moraines, and may be characteristic of dynamic high-latitude and high-altitude temperate glaciers.  相似文献   

14.
本文主要描述和讨论了四川省攀枝花市沿金沙江分布、并以炳草岗地龙箐剖面为代表的昔格达组湖相沉积下伏的砾石层的沉积特征及其河流相成因.根据前人对昔格达组湖相沉积的磁性地层学研究结果,为4.2/3.28～2.6/2.12/1.78 MaBP的上新世中、晚期或至早更新世早期,表明其下伏厚达50 m的砾石层的形成时代约为4.2～4.5/5 MaBP的上新世早期.早上新世金沙江河流相砾石层在接近金沙江谷底位置的发现,表明金沙江很早就已经从青藏高原主夷平面下切了2000 m以上、已在接近其现今谷底的位置上存在.这对于探讨古金沙江的河谷发育及其与青藏高原隆升的关系,具有重要的指示意义.  相似文献   

15.
希夏邦马峰东南富曲河谷的冰川沉积和冰川构造   总被引：2，自引：0，他引：2  
在希夏邦马峰（海拔８０１２ｍ）东南富曲河谷，中更新世以来有三次冰期；即聂拉木、富曲和普罗冰期。它们均可再分为两个亚阶段。聂拉木南的高冰碛平台长３.５ｍ，宽１.５ｋｍ，厚２００ｍ。属于中更新世聂拉木冰期（聂聂雄拉冰期）的巨大山谷冰川沉积，中尼公路从高冰碛平台尾端通过，形成数公里长的冰碛剖面，呈现出美丽多姿的冰川成因类型沉积和冰川构造现象，包括冰下，冰上融出碛，冰内.冰下河道沉积，冰湖沉积，坠碛，流磺等。冰川运动时造成的冰川构造，如断层、滑动面-…等也很清楚，代表了海洋型（暖冰川）冰川沉积和冰川构造特征，是中国目前研究冰川构造最理想的场所。  相似文献   

16.
Although substantial work has been done on the pre-glacial terraces of East Anglia, very little systematic work has been done to understand the origin of river terraces in East Anglia that have formed since ice last covered the region. This paper records the results of studies of exposures and borehole records in ‘classical’ Quaternary terrace landforms that are considered to have formed since the Anglian (MIS 12) Glaciation, in the middle Waveney Valley. These features have been examined in terms of their morphological and sedimentological properties, in order to provide a detailed record of their form and composition, understand their processes of formation, and identify their stratigraphical status. The results show that the main body of the highest terrace (Homersfield Terrace, Terrace 3) is not composed of river sediments, but of shallow marine sediments, and is a remnant of early Middle Pleistocene Wroxham Crag. River sediments, in the form of Anglian age (MIS 12) glaciofluvial Aldeby Sands and Gravels also exist in the area as a channel fill, cut through the Wroxham Crag, and reflect outwash erosion and sedimentation from a relatively proximal ice margin to the west. The results mean that the interpretations previously presented for the terrace landforms of the middle Waveney valley are not applicable. The issue of why the terrace stratigraphy, hitherto identified in East Anglia cannot be related to that for the River Thames to the south and the rivers of Midland England to the west, still requires further research.  相似文献   

17.
A Pleistocene drift sequence in hummocky terrain along part of the southern Avalon Peninsula of Newfoundland is interpreted to comprise complexly interrelated lodgement till, melt-out till, flow till, supraglacial and proglacial outwash, and supraglacial rhythmites. The gray and tan melt-out tills are stacked in imbricate fashion, giving rise to exceptionally thick stratigraphic sections. Contacts between melt-out tills are interpreted as remnants of shear planes because they are sharp, they dip in the up-ice direction, and they converge toward valley margins. Overlying flow tills interdigitate with supraglacial outwash. The drift sequence was deposited during a single episode of glaciation, rather than by repeated glacier advance, as previously proposed. It is the product of thrusting of englacial debris along ice-marginal shear planes, subsequent melting-out of englacial debris, and formation of supraglacial flow till and outwash. Preservation of this sequence probably is due to high content of englacial debris within the Wisconsinan ice. The sedimentary, glacitectonic, and morphologic features of this sequence are similar to those found at the margins of certain Arctic glaciers of subpolar thermal regime which have recently been the subject of Pleistocene glacial sedimentation models for west-central Canada and Great Britain. Recognition of these distinct elements indicates wisconsinan glacier lobes were of the cold Arctic type in southeastern Newfoundland. Alternative explanations for this sequence, such as deposition by glaciers of temperate thermal regime or by surging glaciers, are discounted. Because the features described here are complex and difficult to recognize, they may be more widespread in Pleistocene drift than has previously been interpreted.  相似文献   

18.
The Lleiniog Sand and Gravel Formation, of late Devensian age, has been divided into four Members. The sediments are interpreted as the sequential products of the wasting of a single ice lobe. Member I formed where subglacial streams debouched into a pro-glacial lake and is noteworthy for the occurrence of a bedform, hitherto undescribed but which may be common in many outwash sequences; Member 2 consists of channel sands and gravels deposited by pro-glacial streams; Member 3 has the characters of a melt-out till deposited after a readvance; and Member 4 accumulated in pools of meltwater on the irregular surface of Member 3. Clasts above granule grade are dominantly of locally-derived Carboniferous rocks although a far travelled component from northern England and southern Scotland can be distinguished as well as a small but constant input of Lower Palaeozoic rock types from the Conwy area. The sand grade is dominated by quartz grains released from Permo-Triassic sandstones. Clay grade material has been derived from Carboniferous shales.  相似文献   

19.
Pleistocene sediments at Leet Hill, southern Norfolk are examined in terms of their sedimentary structures, palaeocurrent indicators, clast and heavy mineral lithology and litho- and morphostratigraphic position. Colour of the quartzite and vein-quartz clasts is used to differentiate the Bytham and the Kesgrave sands and gravels, with the Bytham sands and gravels having a significantly higher proportion of coloured material. The Kirby Cane sands and gravels are the lower sedimentary unit and were deposited by the Bytham river, which drained a catchment extending into central England. At Leet Hill, erosion of the Kesgrave Sands and Gravels by the Bytham river has given the Kirby Cane sands and gravels a distinctive lithological assemblage. Trace clast lithologies suggest that the Kesgrave Sands and Gravels in the region of Leet Hill were deposited in a coastal location with an input from northern sources as well as southern and Welsh sources diagnostic of the Thames catchment. The glaciofluvial Leet Hill Sands and Gravels were deposited by outwash from the Anglian Scandinavian ice sheet. Initially the flow direction of the outwash was determined by the Bytham river valley, but this changed to a southerly direction once the valley had been infilled. This paper provides the first indication of the location of the boundary (Early Pleistocene coastline) between the fluvial Kesgrave Sands and Gravels and the marine equivalent reworked by coastal processes, and demonstrates the way the pre-glacial relief initially controlled patterns of glaciofluvial sedimentation during the early part of the Anglian glaciation. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

20.
Glaciotectonic structures in subglacial till and substrate, as well as stone fabric, provenance and surface features in till, indicate that complex interactions of late Wisconsinan glacial lobes occurred along a mountain front in the western Fraser Lowland of southwestern British Columbia. Tills of this study represent subglacial deposition through the maxima of two stades in the Fraser Glaciation, the Coquitlam and the Vashon. Through each stadial maximum, temperate glacial ice was grounded and commonly overrode proglacial outwash while superimposing deformations in subglacial till during three phases: (1) pre-maximum glacier flow down valleys and into lowland piedmont ice, (2) coalescent piedmont ice during stadial maxima when flow was westward along the mountain front and across valley mouths, and (3) post-maximum glacier flow down valleys into lowland piedmont ice but prior to general deglaciation. Valley glaciers appear to have shifted flow directions during phases 1 and 3. During stadial maxima (phase 2), Fraser Lowland piedmont ice may have been part of an outlet glacier-ice stream complex that terminated in salt water over the continental shelf.  相似文献   

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