Late Wisconsinan glaciation and postglacial relative sea-level change on western Banks Island,Canadian Arctic Archipelago

The study revises the maximum extent of the northwest Laurentide Ice Sheet (LIS) in the western Canadian Arctic Archipelago (CAA) during the last glaciation and documents subsequent ice sheet retreat and glacioisostatic adjustments across western Banks Island. New geomorphological mapping and maximum-limiting radiocarbon ages indicate that the northwest LIS inundated western Banks Island after ~ 31 ¹⁴C ka BP and reached a terminal ice margin west of the present coastline. The onset of deglaciation and the age of the marine limit (22–40 m asl) are unresolved. Ice sheet retreat across western Banks Island was characterized by the withdrawal of a thin, cold-based ice margin that reached the central interior of the island by ~ 14 cal ka BP. The elevation of the marine limit is greater than previously recognized and consistent with greater glacioisostatic crustal unloading by a more expansive LIS. These results complement emerging bathymetric observations from the Arctic Ocean, which indicate glacial erosion during the Last Glacial Maximum (LGM) to depths of up to 450 m.     

A constraint to the Wisconsinan glacial history,Canadian Arctic Archipelago

Thick ice-bearing permafrost is not observed today beneath the deeper channels of the central Queen Elizabeth Islands, Canadian Arctic Archipelago. Analysis of a precision temperature log recently obtained at an offshore well near Ellef Ringnes Island indicates that the thermal regime beneath the seabed is in equilibrium with today's marine environment. If thick permafrost similar to that observed on land today had existed in the Pleistocene in areas that are presently offshore, then such permafrost must have started melting no later than 25000 years ago in order to allow the present thermal regime to evolve. This suggests that the inter-island channels must have been water-filled at least by that date.     

Facies and stratigraphical analyses of glacial and interglacial sediments at Morgan Bluffs,Banks Island,Canadian Arctic Archipelago

Stratigraphical exposures of both glacial and non‐glacial sediments at Morgan Bluffs, a >6‐km long exposure on the east coast of Banks Island, comprise a discontinuous archive of Quaternary environmental change. A detailed facies analysis of the sediments and a new stratigraphical framework is incompatible with the many climatostratigraphical units proposed previously. Instead, three distinct intervals of sedimentation are recognized. The first records the progradation of a delta, followed by fluvial aggradation of a braided river valley perhaps ～1 Ma. The second documents glacigenic sedimentation, including fluctuations of a tidewater glacier margin, in a marine basin more than 0.78 Ma. The third records till deposition by the NW Laurentide Ice Sheet during the Late Wisconsinan, followed by the progradation of a deglacial, ice‐contact delta into an ice‐dammed lake ～12.8 cal. ka BP. The revised stratigraphical framework adds important new terrestrial observations to a sparse and fragmentary data set of Quaternary environmental change in the Canadian Arctic. This study challenges former references and correlations to the previously proposed climatostratigraphical framework and nomenclature.     

Nature and origin of ground ice,Sandhills Moraine,southwest Banks Island,Western Canadian Arctic

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.     

Episodic ice streams and ice shelves during retreat of the northwesternmost sector of the late Wisconsinan Laurentide Ice Sheet over the central Canadian Arctic Archipelago

A complex of glacial landforms on northeastern Victoria Island records diverse flows within the waning late Wisconsinan Laurentide Ice Sheet over an area now divided by marine straits. Resolution of this ice flow pattern shows that dominant streamlined landforms were built by three radically different ice flows between 11,000 and 9000 BP. Subsequent to the glacial maximum, the marine-based ice front retreated at least 300 km to reach northeast Victoria Island by 10,400 BP. Disequilibration at the rapidly retreating margin induced minor surges on western Storkerson Peninsula (Flow 1). Next, a readvance into Hadley Bay transported 10,300 BP shells, while a major ice stream over eastern Storkerson Peninsula (Flow 2) remoulded till into a drumlin field several hundred kilometres long and at least 80 km wide until flow ceased prior to 9600 BP. The ice stream surged into Parry Channel, covering 20,000 km² with the Viscount Melville Sound Ice Shelf. Finally, Flow 2 drumlins on the northwest shore of M'Clintock Channel were cross-cut c . 9300 BP by advance of the grounded margin of a buoyant glacier (Flow 3), possibly an analogue of Flow 2 displaced farther south.     

Glaciotectonised Quaternary sediments at Cape Shpindler,Yugorski Peninsula,Arctic Russia: implications for glacial history,ice movements and Kara Sea Ice Sheet configuration

The coastal cliffs of Cape Shpindler, Yugorski Peninsula, Arctic Russia, occupy a key position for recording overriding ice sheets during past glaciations in the Kara Sea area, either from the Kara Sea shelf or the uplands of Yugorski Peninsula/Polar Urals. This study on Late Quaternary glacial stratigraphy and glaciotectonic structures of the Cape Shpindler coastal cliffs records two glacier advances and two ice‐free periods older than the Holocene. During interglacial conditions, a sequence of marine to fluvial sediments was deposited. This was followed by a glacial event when ice moved southwards from an ice‐divide over Novaya Zemlya and overrode and disturbed the interglacial sediments. After a second period of fluvial deposition, under interstadial or interglacial conditions, the area was again subject to glacial overriding, with the ice moving northwards from an inland ice divide. The age‐control suggests that the older glacial event could possibly belong to marine oxygen isotope stage (MOIS) 8, Drenthe (300–250 ka), and that the underlying interglacial sediments might be Holsteinian (>300 ka). One implication of this is that relict glacier ice, buried in sediments and incorporated into the permafrost, may survive several interglacial and interstadial events. The younger glacial event recognised in the Cape Shpindler sequence is interpreted to be of Early‐to‐Middle Weichselian age. It is suggested to correlate to a regional glaciation around 90 or 60 ka. The Cape Shpindler record suggests more complex glacial dynamics during that glaciation than can be explained by a concentric ice sheet located in the Kara Sea, as suggested by recent geological and model studies. Copyright © 2003 John Wiley & Sons, Ltd.     

Late glacial and holocene lake level fluctuations in Lake Biel,western Switzerland

Cores and outcrops from the southern shore of Lake Biel were studied to reconstruct the nearshore environment of the lake between ca. 12000 and 5000 yr BP. Core correlations were established by lithostratigraphical and pollen analytical correlations. From the Allerød to the Preboreal time quiet hydrodynamic conditions favoured the deposition of lake marl in the littoral zone and peat on the shore. Between the Preboreal(?) and the Atlantic the littoral zone shows a higher hydrodynamic environment with allochthonous material, whereas peat and clay layers are recorded from the shore. During the Older Atlantic severe erosional episodes caused the erosion of Boreal, Preboreal and Younger Atlantic layers. The previously described long hiatus between the Allerød and the Boreal time can now be connected with these erosional episodes. From Younger Atlantic to Subboreal time the littoral zone displays quiet conditions again with sedimentation of lake marl. On the basis of these results a lake level curve for Lake Biel is proposed: high lake level stands can be traced during the Allerød, Boreal, Older Atlantic and Younger Atlantic biozones; low lake level stands are found during the Allerød, Younger Dryas, Preboreal and Older Atlantic biozones.     

Radiocarbon Geochemistry of Modern and Ancient Arctic Lake Systems, Baffin Island, Canada

The accuracy of Arctic lake chronologies has been assessed by measuring the¹⁴C activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials. Small (<1 km²) shallow (<25 m) Arctic lakes with watersheds <12 km²have soil and peat stratigraphic sections with¹⁴C activities ranging from 98 to 51% Modern. The¹⁴C activity of particulate organic carbon, dissolved organic carbon, and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95% Modern. The sediment–water interface of the studied lakes shows consistent¹⁴C ages of ∼1000¹⁴C yr, although the¹⁴C activity of living aquatic vegetation is 115% Modern. Radiocarbon measurements of components of the lacustrine carbon pool imply that the ∼1000¹⁴C yr age of the sediment–water interface results from deposition of¹⁴C-depleted organic matter derived from the watershed.     

Geochemistry of ice-covered, meromictic Lake A in the Canadian High Arctic

The geochemical processes occurring within meromictic Lake A (maxdepth 120 m) on northern Ellesmere Island, Canada, were investigated to determinethe history of the lake and to provide a baseline for future studies. The lake contained seawaterdiluted by freshwater input that had been mixed prior to the lake's isolation from tidalaction. Input of freshwater after isolation of the lake created vertical stratification resultingin the creation of distinct oxic, suboxic and anoxic zones. Dissolved oxygen was present to 13 m,and sulphide beneath 32 m. Manganese and iron cycling dominated the redox chemistrybetween these depths. Total manganese concentrations reached 176 M, higher thanin most other natural stratified lake or marine environments.     

Sedimentology and history of a Late Wisconsinan glacial lake, Grande Prairie, Alberta, Canada

The Grande Prairie region of northwestern Alberta was partially covered by glacial Lake Peace, which was dammed against the retreating Laurentide ice sheet. Two levels of glacial Lake Peace are identified in the study are by closely spaced groups of strandlines and minor deltas lying at 805 to 840 m a. s. l., and 655 to 710 m a.s.l. Sedimentation associated with the upper of the two lake levels is marked by rhythmites of silt and clay deposited by turbid underflow, interbedded with diamicton deposited by debris flow. Dropstones and dump structures indicate common ice-rafting. Thick sequences are only found on the axes of major valleys, where sediment gravity flows were concertrated. Thin sequences of ice proximal glaciolacustrine sediments reflect topographic setting and do not indicate a short-lived lake. Retreat of the ice front resulted in a decrease in ice-rafted material and diamicton in sediments. The fall in lake level to the second stage resulted in deposition of sequences of vaguely laminated silt and clay close to the modern Beaverlodge River. These sediments were deposited by suspension settling from interflow or overflow of the Beaverlodge River as it entered the lake. Lake sedimentation was dominated by inflow from unglaciated areas, rather than the ice front.     

A geochemical evaluation of perennial spring activity and associated mineral precipitates at Expedition Fjord,Axel Heiberg Island,Canadian High Arctic

Two groups of perennial springs are observed in the Canadian High Arctic at Expedition Fjord on Axel Heiberg Island at Colour Peak and Gypsum Hill. Saline discharge (∼1.3–2.5 molal NaCl) produces a variety of calcite (travertine) and gypsum-rich precipitates. Saturation index calculations of the spring waters at Colour Peak suggest CO₂ degassing from the waters causes calcite precipitation. Gypsum precipitation dominates at Gypsum Hill, where spring waters have lower alkalinity and higher SO₄ concentrations. Mineral accumulations form both channel and rimstone pool morphologies as a result of varying slope conditions. At Colour Peak, confined flow in steep slope areas develop massive structures in contrast to more friable, porous accumulations in areas where waters fan out on shallower slopes; these morphological variations lead to corresponding varying apparent rates of mineral precipitation. Mineral precipitation at Gypsum Hill is far less notable as a result of lower discharge rates and annual degradation by icing formation. Microscopic observations and geochemical analyses of the channel precipitates at Colour Peak reveal alternating light (calcite spar) and dark (anhedral microcrystalline calcite combined with organic matter and non-carbonate minerals) laminae. Rimstone pools forming in lower sections of spring discharge are composed of accumulations of large euhedral calcite crystals interbedded with allochthonous inputs. High concentration of dissolved solids is responsible for slow travertine precipitation rates, which occurs during winter. This precipitation is further retarded during summer months by the introduction of crystal growth inhibitors such as Fe³⁺ and deposition of organic matter and soil sediments.     

A new Isochirotherium trackway from the Triassic of Vieux Emosson, SW Switzerland: stratigraphic implications

The footprint assemblage of Vieux Emosson, located at 2400 m altitude in the Swiss Alps, was first described in 1982. The assemblage was regarded as Late Ladinian or Carnian in age, but the dating was questioned because the taxa show few affinities with other Triassic assemblages. Here we describe a short trackway with shallow but well-preserved tracks referred to the ichnogenus Isochirotherium, showing affinities with Isochirotherium soergeli and Isochirotherium lomasi. The trackway is present on a piece of slab ex situ lying on a mass of fallen rocks, but the slab can be attributed with confidence to the same level as the main one previously mapped. Preliminary observations in situ and of the footprint casts made in 1979 and deposited in the Natural History Museum of Geneva suggest that none of these are attributable to dinosaurs and that the Vieux Emosson footprints are mainly “track preservation variations” of chirotherian tracks. The occurrence of the ichnogenus Isochirotherium favours an older age, probably Early or Middle Triassic, than previously suggested for the Vieux Emosson tracksite.     

Submarine and onshore end moraines in southern Newfoundland: implications for the history of late Wisconsinan ice retreat

Recessional positions of the Newfoundland ice sheet 14-9 ka BP are represented by fjord-mouth submarine moraines, fjord-head emerged ice-contact marine deltas, and inland moraine belts. The arcuate submarine moraines have steep frontal ramparts and comprise up to 80 m of acoustically incoherent ice-contact sediment (or till) interfingered distally with glaciomarine sediment that began to be deposited c. 14.2 ka BP. The moraines formed by stabilization of ice that calved rapidly back along troughs on the continental shelf. The ice front retreated to fjord-heads and stabilized to form ice-contact delta terraces declining in elevation westward from +26 m to just below present sea level. Stratified glaciomarine sediments accumulated in fjords, while currents outside fjords eroded the upper part of the glaciomarine deposits, forming an unconformity bracketed by dates of 12.8 and 8.5 ka BP. The delta terraces are broadly correlated with the 12.7 ka BP Robinson's Head readvance west of the area. The ice front retreated inland, pausing three or four times to form lines of small bouldery stillstand moraines, heads of outwash, sidehill meltwater channels, and beaded eskers. Lake-sediment cores across this belt yield dated pollen evidence of three climatic reversals to which the moraines are equated: the Killarney Oscillation c. 11.2 ka BP, the Younger Dryas chronozone 11.0-10.4 ka BP, and an unnamed cold event c. 9.7 ka BP. Relative sea level fell in the early Holocene because of crustal rebound, so that outwash and other alluvium accumulated in deltas now submerged due to relative sea-level rise.     

The Siluro-Devonian clastic wedge of Somerset Island,Arctic Canada,and some regional paleogeographic implications

Upper Silurian and Lower Devonian rocks on Somerset Island were derived from Boothia Uplift, a linear tectonic belt that underwent a pronounced period of positive movement commencing in the Pridolian. The lower part of the clastic wedge is a succession of predominantly intertidal to supratidal dolomite and siltstone 150–400 m thick (Somerset Island Formation). Markov analysis documents the presence of tidal cycles in these rocks. The succession changes eastward, away from the uplift, into subtidal marine limestone indistinguishable from that of the underlying Read Bay Formation. The Somerset Island Formation grades vertically and laterally westward into alluvial deposits of the Peel Sound Formation, which consists of red sandstoné of braided river and possibly eolian origin, and two fanglomerate members. A variety of fluvial fining-upward and thinning-upward cycle types has been documented by Markov analysis of a lower sand member of the formation. The Peel Sound reaches a maximum thickness of 600 m in northern Somerset Island.Paleocurrent analysis of crossbedding indicates eastward transport directions in the fluvial rocks, except for cosets of very large scale crossbeds (up to 6 m thick) in the northwestern part of the island, which indicate northwesterly flow. The large sets are interpreted as the deposits of eolian dunes, or of sand waves in a large trunk river which carried clastic detritus northward, parallel to Boothia Uplift.The Peel Sound Formation and its lateral facies equivalents on Prince of Wales Island, west of Boothia Uplift, contain coarser conglomerates and a higher sandstone/carbonate ratio, indicating deposition under higher energy conditions than are thought to have prevailed in Somerset Island. Relief may have been greater and depositional slope steeper in the west, an asymmetry in Boothia Uplift that is reflected in the present-day structural style of a narrow zone of tilting and reverse faulting in the west, and a broad zone of gentle folding and normal faulting in the east. The similarity in structural and stratigraphic asymmetry indicates a genetic link, which is further suggested by the presence of syndepositional folds and unconformities at a few localities within the clastic wedge.An estimate of the volume of sediment removed from Boothia Uplift indicates that approximately one third can be accounted for in the present clastic wedge on either side of the Uplift. Either the Lower Paleozoic formations were attenuated over the Uplift, or rivers such as the hypothetical trunk river were effective in the dispersal of material beyond the region of the clastic wedge.     

Taxonomic composition,paleoecology and biostratigraphy of Late Cretaceous diatoms from Devon Island,Nunavut, Canadian High Arctic

Upper Cretaceous sediments of the Kanguk Formation exposed in Eidsbotn and Viks Fiord grabens on Devon Island, Nunavut, Canadian High Arctic, yielded 91 fossil marine diatom species and varieties (including indeterminate taxa), representing 41 genera. Excellent preservation of the assemblages was aided by shallow burial, protection in downfaulted linear grabens, and the presence of abundant volcanic material. Planktonic species and resting spores comprise nearly 70% of the diatom assemblage, and provided abundant food resources for the Late Cretaceous Arctic ecosystem. Deposition of the approximately 225 m-thick stratigraphic sequence was predominantly in a shallow marine neritic setting, with an upward progression to interbedded terrestrial deposits of the Expedition Fiord Formation, reflecting a regression and eventual persistence of terrestrial facies into the Early Cenozoic. The Kanguk Formation is widespread across the Canadian Arctic, and diatom biostratigraphy indicates a Santonian–Campanian age for the sequences reported herein, based on the presence of Gladius antiquus in the lowermost strata and occurrence of Costopyxis antiqua throughout the succession. However, Amblypyrgus sp. A and Archepyrgus sp. aff. A. melosiroides, encountered in the lower part of the succession, are known exclusively from the Lower Cretaceous. This may suggest a slightly older age. New information on shallow shelf diatom assemblages from this study is compared to reports on two other Late Cretacous Arctic diatom assemblages. These three sites represent an environmental transect from shallow to distal shelf settings and into the oceanic realm.     

Palaeocurrent and palaeohydrologic analysis of some vertical profiles through a Cretaceous braided stream deposit, Banks Island, Arctic Canada

A study of directional variability has been carried out on five vertical profiles containing a total of approximately 195 superimposed planar crossbed sets. The latter are interpreted as the deposits of braid bars. Detailed measurements on one set revealed within-set variance of 93. Within river tract, between-bar variance was obtained by calculating a ten-point moving average for each profile, and subtracting the actual azimuth at each point from the moving average value. Variance at this level is 980, which compares closely with data obtained from modern braided streams. Variability in the moving average azimuth is interpreted as the result of meander migration in the entire channel system. Sinuosity can be estimated from this variability, using a geometrical approximation. It ranges from 1.03 to 1.13. Changes in stream competency with time are indicated by vertical changes in directional variance and set thickness. When accompanied by changes in mean azimuth, as in one of the present five profiles, the data suggest successive deposition by two distinct stream systems. A Markov chain analysis of the data sequence indicates a weak memory effect. Short sequences of bar deposits were formed by streams which varied little in orientation, and these are separated from one another by sequences showing random directional fluctuation. The hydrology of the Isachsen rivers was investigated using Schumm's (1968a, b, 1969, 1972) empirical relationships for modern rivers. Owing to inherent uncertainties in these relationships and a wide margin of error in the input data (principally associated with estimates of depth and width of the Isachsen streams), the results have a validity only at the order-of-magnitude level. Individual Isachsen rivers are estimated to have had drainage areas of between 5000 and 30,000 km²; this information is of use in reconstructions of palaeogeography and tectonic history.     

Luminescence chronology of non‐glacial sediments in Changeable Lake,Russian High Arctic,and implications for limited Eurasian ice‐sheet extent during the LGM

A 10.5 m core from Changeable Lake in the Severnaya Zemlya Archipelago just north of the Taymyr Peninsula intersects ca. 30 cm of diamicton at its base, interpreted as a basal till. Because the upper 10.13 m of this core consists of non‐glacial sediments, a maximum numeric age for these non‐glacial sediments would provide a clear lower limit to the timing of the last glaciation in the area of Changeable Lake. Radiocarbon (¹⁴C) dating of several materials from this core yielded widely scattered results. Consequently we applied photonic dating to sediments above the diamicton. The experimental single‐aliquot‐regenerative (SAR) dose fine‐grain method was applied to two samples, using the ‘double SAR’ approach. With one exception, these fine‐grain SAR results and the results of application of the SAR method to sand‐sized quartz grains from two samples, at ca. 9.95 m and ca. 10.05 m depth, are discrepant with age estimates from the multi‐aliquot infrared‐photon‐stimulated luminescence (IR‐PSL) method applied to fine grains. Multi‐aliquot IR‐PSL dating of 10 samples produces ages increasing monotonically from ca. 4 ka at 2 m to 53 ± 4 ka at 9.97 m. These self‐consistent multi‐aliquot IR‐PSL ages, along with limiting ¹⁴C ages of >47 ka at ca. 10 m, provide direct evidence that glacial ice did not advance over this lake basin during the Last Glacial Maximum, and thus delimit the northeastern margin of the Barents–Kara Sea ice‐sheet to somewhere west of this archipelago. The last regional glaciation probably occurred during marine isotope stage (MIS) 4 or earlier. Copyright © 2004 John Wiley & Sons, Ltd.     

西北冰洋加拿大海盆MIS 8期以来的物源变化及其指示的北极冰盖和洋流的演化

基于对中国第七次北极考察在西北冰洋获得的ARC7-LIC岩芯上部1 m（加拿大海盆近阿尔法脊一侧）自MIS 8期（约300 ka）以来的粘土矿物和全样Sr-Nd-Pb同位素的分析,判断北冰洋中心沉积物源的变化及其所反映的冰盖和表层洋流的演化。结果显示：在MIS 8、MIS5.4、MIS5.1、MIS3期中期冰筏事件以及末次冰消期,北美劳伦冰盖生长规模较大,研究区域的沉积被北美物源主导;相对地,MIS 6、MIS4期的沉积由西伯利亚物源-穿极流模式主导,反映了欧亚大陆冰盖的大规模发育。同时,研究区域在MIS 7、MIS5期的间冰期/间冰阶的沉积也与MIS 3、MIS1期的沉积有所区别。MIS 7、MIS5期的间冰期/间冰阶表现为西伯利亚物源以及穿极流控制下的沉积,而MIS 3期和全新世则表现为北美物源以及波弗特环流作用下的沉积特征,这一差异说明中-晚第四纪间冰阶段北冰洋表层洋流的位置在晚更新世前后发生了变迁。