Subaerial unconformity at the Potsdam-Beekmantown contact in the Quebec Reentrant: regional significance for the Laurentian continental margin history

Abstract

Research Article| September 01, 2002 Subaerial unconformity at the Potsdam–Beekmantown contact in the Quebec Reentrant: regional significance for the Laurentian continental margin history O. Salad Hersi; O. Salad Hersi INRS-Géoressources, Quebec Geoscience Centre, 880 Ch. Ste-Foy, Quebec, PQ G1V 4C7 *Present address: AGAT Laboratories, 3801 - 21 Street NE, Calgary, AB T2E 6T5 Search for other works by this author on: GSW Google Scholar A. Hilowle Mohamed; A. Hilowle Mohamed Department of Earth Sciences, Carleton University, Colonel By Drive, Ottawa, ON K1S 5B6 Search for other works by this author on: GSW Google Scholar D. Lavoie; D. Lavoie Geological Survey of Canada, Quebec Geoscience Centre, 880 Ch. Ste-Foy, Quebec, PQ G1V 4C7 Search for other works by this author on: GSW Google Scholar G.S. Nowlan G.S. Nowlan Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB T2L 2A7 Search for other works by this author on: GSW Google Scholar Author and Article Information O. Salad Hersi *Present address: AGAT Laboratories, 3801 - 21 Street NE, Calgary, AB T2E 6T5 INRS-Géoressources, Quebec Geoscience Centre, 880 Ch. Ste-Foy, Quebec, PQ G1V 4C7 A. Hilowle Mohamed Department of Earth Sciences, Carleton University, Colonel By Drive, Ottawa, ON K1S 5B6 D. Lavoie Geological Survey of Canada, Quebec Geoscience Centre, 880 Ch. Ste-Foy, Quebec, PQ G1V 4C7 G.S. Nowlan Geological Survey of Canada, 3303 - 33 Street NW, Calgary, AB T2L 2A7 Publisher: Canadian Energy Geoscience Association Received: 06 Dec 2001 Revision Received: 17 Jun 2002 First Online: 02 Mar 2017 Online ISSN: 2368-0261 Print ISSN: 0007-4802 © The Society of Canadian Petroleum Geologists Bulletin of Canadian Petroleum Geology (2002) 50 (3): 419–440. https://doi.org/10.2113/50.3.419 Article history Received: 06 Dec 2001 Revision Received: 17 Jun 2002 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation O. Salad Hersi, A. Hilowle Mohamed, D. Lavoie, G.S. Nowlan; Subaerial unconformity at the Potsdam–Beekmantown contact in the Quebec Reentrant: regional significance for the Laurentian continental margin history. Bulletin of Canadian Petroleum Geology 2002;; 50 (3): 419–440. doi: https://doi.org/10.2113/50.3.419 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract The Cambrian–Ordovician Potsdam and Beekmantown groups of the Quebec Reentrant (southwestern Quebec and southeastern Ontario) were deposited during rifting and drifting phases of the Laurentian margin and development of the Iapetus Ocean. Previous studies have generally considered a gradual depositional continuity between the two groups. In contrast, our research on the sedimentology and stratigraphy indicates a regional subaerial unconformity exists between the Potsdam and Beekmantown groups. This unconformable boundary is sharp and associated with an abrupt lithological change. The upper formation of the Potsdam Group (Cairnside Formation) is locally missing, possibly due to erosion, and void-filling, spherulitic, chalcedonic cement is developed less than a metre beneath the unconformity. The void-filling, silica cement is interpreted as pedogenic silcrete. Truncation of the Potsdam Group quartz grains at the contact, along with their silica overgrowths, is also observed. Conodonts from the basal part of the Theresa Formation (lowest formation of the Beekmantown Group) indicate an Early Ordovician (Ibexian, Stairsian) age. No fossils were collected from the underlying Cairnside Formation, but conodonts of Late Cambrian age have been recovered from the Strites Pond Formation of the Philipsburg Group, southern Quebec, a unit that is a possible correlative of the Cairnside Formation. These conodont faunas indicate that the Cairnside–Theresa unconformity ranges from latest Cambrian (Cordylodus proavus Zone) to Early Ordovician age, approximately correlative with the early Stairsian "low diversity interval".We correlate this unconformity with another poorly documented unconformity northeast of Montreal, as well as with other coeval hiatuses exposed elsewhere in the Laurentian margin (e.g. southern Quebec and New York State). Coeval unconformities, interpreted as being the result of a latest Cambrian eustatic sea-level fall, have also been recognized in other parts of North America and abroad. The eustatic fall is also interpreted from Cambro-Ordovician slope-deposited, channel-fill quartz arenites and thick debris flow conglomerates in the Appalachian Humber Zone. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.