Microfacies and microstructures of subglacial and deglacial sediments from the Pingualuit Crater Lake (Ungava Peninsula, Canada)

Abstract

International audienceAbstract: The Pingualuit Crater (Ungava Peninsula, Canada) hosts a freshwater basin in which a subglacial lake subsisted under the Laurentide Ice Sheet during the last glacial period. Microfacies and microstructures of a 9mlong sediment core are presented to discuss the depositional environment of deformed glacigenic and postglacial sequences deposited in the deep basin of the lake. Five distinct lithofacies are characterized. The range of glacial microstructures observed in the lower facies (Facies IV) reveals that high stress level occurred outside the crater during the formation of this diamicton released by the ablation of debris-rich basal glacier ice in an ice contact subglacial–proglacial lacustrine environment. The overlying subaqueous and glacigenic sediment gravity flow (Facies IIIb) is associated with a temporary absence of ice cover over the coring site, and likely results from the efflux plume and the associated suspension sedimentation produced during the retreat of the ice margin. Then, the finely laminated (<1–2 mm) and normally graded meltout silts (Facies IIIa) containing dropstones and load cast featuressuggest underflows in an unstable ice marginal lacustrine environment hydrologically separated from the retreating glacier but containing floating glacial ice blocks. Microstructures within occasional diamictic layers indicate sudden meltout deposits from these drifting ice blocks. The above finer-grained sediments (Facies Ib) lack typical glacial microstructures, marking the onset of postglacial organic sedimentation. These postglacial sediments are affected by post-depositional deformations due to an overlying rotational slide (Facies II) that may have perturbed the associated environmental record

Composition, geometry, and emplacement dynamics of a large volcanic island landslide offshore Martinique: From volcano flank‐collapse to seafloor sediment failure?

“…Data were processed using the Osirix software and the resulting longitudinal images are displayed in greyscale, with the darker grey representing lower X‐ray attenuation and lower bulk density values [e.g., Boespflug et al ., ; Duliu , ]. This nondestructive and high‐resolution method allows especially to visualize and characterize deformation microstructures associated with the dynamic of sedimentary mass‐movements [e.g., Duliu , ; Guyard et al ., ; St‐Onge et al ., ].…”

Late-Quaternary glacial to postglacial sedimentation in three adjacent fjord-lakes of the Québec North Shore (eastern Canadian Shield)

“…Rhythmically laminated silts and clays (U3) sampled in Lake Pentecôte correspond to sedimentation controlled by glacial-melt runoff (i.e., ice-distal varves?) (Powell, 1983;Ó Cofaigh and Dowdeswell, 2001;Guyard et al, 2011Guyard et al, , 2014Ridge et al, 2012;Boes, 2014). The lower thick laminations (PC15-04B-P; Fig.…”

Holocene history of the eastern side of Novaya Zemlya from glaciomarine sediment records in the Tsivol’ki Fjord

“…The rhythmically laminated LF1 may indicate sedimentation controlled by pulses of glacial meltwater (Powell 1983; Ó Cofaigh & Dowdeswell 2001; Guyard et al . 2011, 2014; Ridge et al . 2012; Boes 2014).…”

“…2, Table S1). The rhythmically laminated LF1 may indicate sedimentation controlled by pulses of glacial meltwater (Powell 1983;O Cofaigh & Dowdeswell 2001;Guyard et al 2011Guyard et al , 2014Ridge et al 2012;Boes 2014). Distal glaciomarine LF1 sediments show a higher biodiversity of the microfossils and a limited water exchange with the Kara Sea.…”