Paleoenvironmental trends in the Lower Cretaceous Upper Member of the Missisauga Formation, Scotian margin, Canada: a sedimentological and ichnological integration.

Basins along the Scotian Margin formed as part of North Atlantic opening, with Middle Triassic rifting leading to eventual Early-Middle Jurassic breakup. In the overlying passive margin succession, the Lower Cretaceous section is dominated by siliciclastic deposits reported from a variety of marine, shallow marine, and fluvial settings. In concert with ongoing palynological analyses, the present study contributes to the development of an event stratigraphic scheme by focussing on paleoenvironmental interpretations. Ichnological and sedimentological analyses were used to build a preliminary facies model, with an initial focus on the Upper Member of the Missisauga Formation conventional cores from Panuke B-90 and Cohasset A-52. Depositional conditions began as wave-influenced normal marine, with a distal Skolithos Ichnofacies. Restricted bay and possible deltaic deposits followed, with wave-influence decreasing up section and the ichnofossil assemblage gradually replaced by an impoverished archetypal expression of the Cruziana Ichnofacies. Overlying sandstone bodies are interpreted as tidally influenced estuarine channels based on the presence of herringbone cross-stratification, cyclical bedding, wood with Teredolites borings, and rare elements of a highly impoverished Skolithos Ichnofacies; however, barrier shoreface and tidal flats are present, suggesting a mixed wave- and tide-influenced estuary. Outer estuary conditions followed, with barrier shoreface, tidal flat and central bay deposits. Impoverished Cruziana Ichnofacies dominate, with elements of the Skolithos Ichnofacies locally present. The top of the Missisauga Formation shows indication of more normal marine conditions, with intermittent marine macrofauna and limited ichnological suites implying some degree of dysoxia. Storm influence is evident near the transition into the overlying Naskapi Member of the Logan Canyon Formation based on the presence of possible hummocky cross-stratification, a weakly stressed Cruziana Ichnofacies and more diverse marine macrofauna. Future work will entail detailed facies analysis and comparison with palynofacies to build a comprehensive paleoenvironmental model and a refined sequence stratigraphic framework. [ABSTRACT FROM AUTHOR]