Sequence Stratigraphic Framework and Geochemical Characterization of the Neoproterozoic Old Fort Point Formation, Windermere Supergroup, Southern Canadian Cordillera: Examination of a Deep-Water Source Rock Analogue from an Ancient Passive-Margin Setting

Smith, Mark D.¹, R.W.C. (Bill) Arnott¹, Gerry M. Ross² (1) University of Ottawa, Ottawa, ON (2) Consultant, Kula, HI

With the continued growth of frontier deep-water exploration, it has become increasingly important to integrate reservoir outcrop analogues with stratigraphic and geochemical data from associated organic-rich mudrock facies that would form the potential source rock for the hydrocarbon system. The Neoproterozoic Old Fort Point Formation (OFP) is a regionally widespread (>35,000 km²), distinctive fine-grained stratigraphic marker horizon within the predominantly coarse-grained siliciclastic turbidites of the ancient passive-margin Windermere Supergroup (WSG), southern Canadian Cordillera. The OFP is part of a 2nd or 3rd order sequence deposited along a basin-slope to basin-floor transect and is interpreted to be related to a major eustatic rise attributed to deglaciation that terminated coarse siliciclastic input into the basin. This rapid rise in sea-level likely facilitated water-column stratification with the development of bottom-water anoxia below a postulated pycnocline. The organic-rich middle member of the OFP is a black shale highstand deposit characterized by enriched TOC values (up to 3%, ~10% at deposition) and distinctive chemical and isotopic (e.g. Mo, V, Sb, ¹³C_org, ³⁴S_py) signatures unlike other fine-grained units from the WSG. The middle member of the OFP may have formed a potential source rock for the surrounding basin-floor sandy turbidites of the WSG. Therefore, it provides an excellent opportunity to improve our understanding of deep-water black shale depositional processes and their stratigraphic and geochemical evolution over the extent of an ancient sedimentary basin.