Microfacies and microstructures of subglacial and deglacial sediments from the Pingualuit Crater Lake (Ungava Peninsula, Canada) (original) (raw)
Related papers
Glacitectonized lake sediments, Barrier Lake, Kananaskis Country, Canadian Rocky Mountains
Canadian Journal of Earth …, 1999
Stratigraphic and sedimentological analyses of exposures through a glacilacustrine sedimentary sequence along the south shore of Barrier Lake, Kananaskis Country, reveal evidence of glacitectonic disturbance, relating to a readvance of the Bow Valley glacier at the end of the last glaciation. Prior to disturbance, palaeocurrent measurements in gravel and sand foreset beds record the deposition of subaqueous fans-deltas from a glacier lobe retreating eastwards along the Barrier Lake depression. The fan-delta sediments fine upwards into ripple-and cross-bedded sands and laminated muds with dropstones, documenting progressively distal sedimentation. Palaeostress directions measured from large-scale folds, shear zones and glacitectonites, and deformation tills indicate that glacier ice readvanced southwards from a glacier lobe located over the Barrier Lake depression. These stress directions are used to reconstruct the flow lines within the southern margin of a low-profile glacier lobe that terminated halfway up lower Barrier Lake, a more extensive readvance than previously envisaged in the area for this period. Comparisons of diamicton and glacitectonite fabric shapes with similar sediments elsewhere indicate that the subglacially deformed material that caps some of the sections is immature and has undergone short travel distances. Although the exact age of the readvance is unknown, it probably represents the Canmore Readvance of the Late Wisconsinan glaciation.
The Pingualuit Crater was formed by a meteoritic impact ca. 1.4 million years ago in northernmost Ungava (Canada). Due to its geographical position near the center of successive North American ice sheets and its favorable morphometry, the Pingualuit Crater Lake (water depth ¼ 246 m) promises to yield a unique continuous sedimentary sequence covering several glacial/interglacial cycles in the terrestrial Canadian Arctic. In this paper, we suggest the existence of a subglacial lake at least during the Last Glacial Maximum (LGM) by hydraulic potential modeling using LGM ice-surface elevation and bed topography derived from a digital elevation model. These results support the hypothesis that the bottom sediments of the Crater Lake escaped glacial erosion and may contain a long-term continental sedimentary sequence. We also present the stratigraphy of a 9 m-long core retrieved from the deep basin of the lake as well as a multiproxy reconstruction of its deglacial and postglacial history. The base of the core is formed by very dense diamicton reflecting basal melt-out environments marking the end of subglacial conditions at the coring site. The overlying finely laminated silt are related to the onset of proglacial conditions characterized by extremely low lacustrine productivity. Infra Red Stimulated Luminescence and AMS 14 C dating, as well as biostratigraphic data indicate sediment mixing between recent (e.g. Holocene) and much older (pre-to mid-Wisconsinan) material reworked by glacier activity. This process prevents the precise dating of these sediments that we interpret as being deposited just before the final deglaciation of the lake. Two finer grained and organic-rich intervals reflect the inception of lacustrine productivity resulting from the cessation of glacial meltwater inputs and ice-free periods. The lower organic interval corresponds to the early postglacial period (6850e5750 cal BP) and marks the transition between proglacial and postglacial conditions during the Holocene Thermal Maximum, while the uppermost organic-rich core section represents late Holocene sediments (w4200e600 cal BP). The organic intervals are separated by a basin-scale erosive slide occurring around 4200 cal BP and likely related to 1) a seismic event due to the glacio-isostatic rebound following the last deglaciation or 2) slope instabilities associated with rapid discharge events of the lake.
Advance and retreat glacigenic deformation at Williams Lake, British Columbia
Canadian Journal of Earth Sciences, 1987
Glacigenic deformation structures at Williams Lake, British Columbia, occur within stratified Quaternary sediments that both overlie and underlie lodgement till of the last (Fraser = Late Wisconsinan) glaciation. The main structures in sediments below the lodgement till are faults, joints, and clastic dikes produced by glacier overriding during Late Wisconsinan time. The orientation of these structures is closely related to the direction of glacier flow at Williams Lake. Their character and stratigraphic position suggest that the substrate in this area was partly frozen and partly unfrozen when covered by ice during the Fraser Glaciation.
Sedimentary Geology, 2011
There has been considerable interest in recent years in the development of theoretical models of subglacial transport and deposition of sediment, but relatively few studies report field documentation of the resultant sediment stratigraphies. This paper presents detailed sedimentological description and analysis of a succession of late Quaternary deposits interpreted to record subglacial overriding and deformation of previously deposited lacustrine sediments exposed in the Vineland Quarry that sits close to the crest of the Niagara Escarpment within the Lake Ontario basin. The predominately fine-grained sediments record deposition under glaciolacustrine conditions followed by deformation and deposition by overriding glacial ice. Laminated silt and clay deposits overlie the striated bedrock surface and were deposited within a lake that formed as the Ontario Lobe of the Laurentide Ice Sheet advanced during the Port Huron stadial and ponded water against the Niagara Escarpment. The laminated silt and clay facies show increasing amounts of deformation up-section, passing from planar through ductile to brittle deformation. This succession of deformed facies is overlain by a macroscopically massive clay-rich diamict that caps the section. This pattern of sediment deposition and deformation is consistent with that proposed by current models of subglacial sediment deformation with the disrupted laminated silts and clays representing 'glacitectonites' resulting from downward penetrating stresses imparted by an overriding ice sheet. The uppermost massive diamict unit represents full macroscopic homogenization of the overridden sediment and is classified as a subglacial 'traction till'. The gradual transition from undisturbed laminated deposits through increasingly deformed sediment to structureless, diamict suggests that these deposits record a single episode of ice advance across the region. This ice advance was probably the short-lived advance of the Ontario Lobe of the Laurentide Ice Sheet that occurred at approximately 13,000 ybp.
The interrelation of glaciotectonic and glaciodepositional processes within the glacial environment
1991
In recent years it has been recogmsed that ice/sediment couphng occurred beneath the Quaternary ice sheets that advanced over the soft sediments of lowland areas This paper looks m detail at the effects of this coupling on the sediments, which results m glaootectomc deformation, and also discusses the interaction of deformation and deposition within the subglaclal environment Two types of glacmtectonic deformation are discussed that are produced by the active movement of ice (1) proglaclal tectonics at the margin, which include compressive fold styles such as hstnc thrusts and faults and open folding, (2) subglacial tectonics formed beneath the glacier, which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone Styles of deformation associated with stagnant Ice are also investigated We argue that glaootectomc deformation is a common phenomenon and an integral part of geological record from continental ice sheets It is suggested that zones of deformation within the sediment are related to s~miiar zones of strain m the ice sheet, and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats It Is also argued that subglacial deposition and deformation are related and that on soft beds undeformed till is rare, whilst deformed till ts very common
Canadian Journal of Earth Sciences, 2013
The deposits identified as being the Drift des Demoiselles, which is the upper unit of the southern Magdalen Islands (Québec, Canada), belong to two units of different origin, glacial and glaciomarine. At Anse à la Cabane, the glacial deposit comprises two subunits: a glacitectonite at the base and a subglacial traction till at the top. Numerous glaciotectonic deformation structures suggest ice flow towards the southeast. The till is above an organic horizon dated to ϳ47-50 ka BP. New data presented here show that the southern part of the Magdalen archipelago was glaciated during the Late Wisconsinan. We relate this ice flow to the Escuminac ice cap, whose centre of dispersion was located in the Gulf of St. Lawrence, northwest of the islands. At Anse au Plâtre, the top of the Drift des Demoiselles is a glaciomarine deposit. At Anse à la Cabane, the till is covered by a stratified subtidal unit located at ϳ20 m above sea level. Both were deposited during the marine transgression that followed deglaciation. At Anse à la Cabane, three ice-wedge casts truncate the till and the subtidal unit, providing evidence that periglacial conditions occurred on the archipelago after deglaciation.