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

Abstract

High-resolution swath bathymetry imagery allowed mapping in great detail the sublacustrine geomorphology of lakes Pentecôte, Walker and Pasteur, three deep adjacent fjord-lakes of the Québec North Shore (eastern Canada). These sedimentary basins have been glacio-isostatically uplifted to form deep steep-sided elongated lakes. Their key geographical position and limnogeological characteristics typical of fjords suggest exceptional potential for long-term high-resolution paleoenvironmental reconstitutions. Acoustic subbottom profiles acquired using a bi-frequency Chirp echosounder (3.5 & 12 kHz), together with cm-and m-long sediment core data, reveal the presence of four acoustic stratigraphic units. The acoustic basement (Unit 1) represents the structural bedrock and/or the ice-contact sediments of the Laurentide Ice Sheet and reveals V-shaped bedrock valleys at the bottom of the lakes occupied by ice-loaded sediments in a basin-fill geometry (Unit 2). Moraines observed at the bottom of lakes and in their structural valleys indicate a deglaciation punctuated by short-term ice margin stabilizations. Following ice retreat and their isolation, the fjord-lakes were filled by a thick draping sequence of rhythmically laminated silts and clays (Unit 3) deposited during glaciomarine and/or glaciolacustrine settings. These sediments were episodically disturbed by mass-movements during deglaciation due to glacial-isostatic rebound. AMS 14 C dating reveal that the transition between deglaciation of the lakes Pentecôte and Walker watersheds and the development of para-and post-glacial conditions occurred around 8000 cal BP. The development of the lake-head river delta plain during the Holocene provided a constant source of fluvial sediment supply to the lakes and the formation of turbidity current bedforms on the sublacustrine delta slopes. The upper sediment succession (i.e., ∼4-∼6.5 m) consists of a continuous para-to post-glacial sediment drape (Unit 4) that contains laminated and massive sediment and series of Rapidly Deposited Layers. These results allow establishing a conceptual model of how a glaciated coastal fjord develops during and after deglaciation in a context of rapid glacio-isostatically forced regression.

Highly variable sediment deposition in Lake Imandra, NW Russia, since the Late Pleistocene

“…central part of Fig. 3B) may be a result of either deformation by dead‐ice blocks (Eyles et al ., 1991; Yevzerov and Nikolaeva, 2008) or strong channelled meltwater flows (Kleman et al ., 1997; Hättestrand and Clark, 2006a,b; Poiré et al ., 2018). The latter is indicated by sediment deposits in core Co1410 that also comprise a fining‐upward sequence towards the top of SU Id (Lenz et al ., 2021).…”

Late Wisconsinan grounding zones of the Laurentide Ice Sheet margin off the Québec North Shore (NW Gulf of St Lawrence)

“…incised glacial valleys of lakes Walker and Pentecôte (Poiré et al 2018), in association with the GZ2 and GZ3 systems, and of Ste Marguerite River, with the GZ2 system (Figs 3a & 6). They are also observed in 'channels' between some islands of the Sept-Îles archipelago at depths of c. 120 m, in association with the GZ2 system (Fig.…”

Post‐Last Glacial Maximum evolution of a “fjord‐type” lake based on high‐resolution seismic data: the Lago Roca/Acigami (southern Tierra del Fuego, Argentina/Chile)

“…These basins often contain thick and well‐preserved infills which record the depositional processes that occurred during and after deglaciation (Finckh et al ., ; Mullins and Eyles, ). These successions also provide important information for palaeoenvironmental and palaeoclimatological reconstructions (i.e., Anselmetti et al ., ; Pinson et al , ), reconstruction of glacier or lake‐level fluctuations (Waldmann et al ., ; Poiré et al ., ; Lebas et al ., ), palaeoseismological analyses (Schnellmann et al ., ; Chapron et al ., ; Praet et al ., ) and morphotectonic studies (Lodolo et al ., ; Lozano et al ., ).…”