Wind-driven bottom currents and related sedimentary bodies in Lake Saint-Jean (Québec, Canada)

Alexis Nutz 1 M. Schuster 1 J.-F. Ghienne 1 C. Roquin 1 M.B. Hay 2 F. Rétif 3 R. Certain 4 Nicolas Robin 4 O. Raynal 4 P.A. Cousineau 2 Sirocco Team F. Bouchette 3
1 IPGS - Institut de physique du globe de Strasbourg
2 UQAC - Université du Québec à Chicoutimi
3 Géosciences Montpellier
4 CEFREM - Centre de Formation et de Recherche sur les Environnements Méditérranéens
Abstract : Lakes are major depositional systems for which the related depositional processes have long been considered relatively simple. Breaking this statement, this study presents a detailed analysis of deposits in Lake Saint-Jean, the third largest natural lake in Québec. In addition to postglacial deltaic and coastal depositional systems fringing the lake, current-controlled features such as a large subaqueous prograding wedge and three sediment drifts have been identifi ed in its central portion based on two-dimensional (2-D) acoustic high-resolution subbottom profiles. The large subaqueous prograding wedge is a 4-km-long and up to 15-m-thick heterolithic shelf-like construction in the southeastern part of the lake. The three sediment drifts are 0.1–0.5-km-long and 2–5-mthick mud mounds distributed on the lake floor in the central portion of the lake. Diatom analyses and radiocarbon dating show that the development of these current-controlled features occurred during the lacustrine phase, after the disconnection with the postglacial marine Laflamme Gulf at 8.5 cal. k.y. B.P. Depositional facies show evidence of recurrent bottom-current activity. Related deposits alternate with pelagic sedimentation stages characterized by the settling of mud and biogenic accumulations. We investigated the origin of bottom currents using a numerical simulation (SYMPHONIE, an oceanographic model), with the aim of modeling wind-induced lake-scale water circulation. Simulations suggest that the subaqueous prograding wedge and the three sediment drifts result from wind-induced bottom currents generated by storm events having wind speed greater than 10 m s–1. Such strong winds are able to significantly affect sedimentation in the central portion of Lake Saint-Jean. The resulting wind-induced sedimentary features were integrated into a refi ned lacustrine depositional model that summarizes the evolution of a group of water bodies referred to as “wind-driven water bodies.” This study applies a new tool for lake strata characterization and highlights the potential diffi culty in differentiating them from marine deposits in the geological record.
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Submitted on : Monday, August 17, 2015 - 2:27:30 PM
Last modification on : Wednesday, August 14, 2019 - 2:10:02 PM

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Alexis Nutz, M. Schuster, J.-F. Ghienne, C. Roquin, M.B. Hay, et al.. Wind-driven bottom currents and related sedimentary bodies in Lake Saint-Jean (Québec, Canada). Geological Society of America Bulletin, Geological Society of America, 2015, pp.1-15. ⟨10.1130/B31145.1⟩. ⟨insu-01184724⟩

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