INTEGRATED ORGANIC/INORGANIC GEOCHEMISTRY, PETROLOGY AND PALYNOLOGY FOR INTERPRETATION OF DEPOSITIONAL CONDITIONS OF ORGANIC RICH MUDSTONES OF THE TURONIAN - CENOMANIAN SECOND WHITE SPECKS FORMATION, SK AND MB CANADA (Invited Presentation)

The Upper Cretaceous Second White Specks Formation (2WS) and the overlying and underling units were studied in two areas along the eastern margin of the Western Interior Seaway (WIS) in Canada. Core description was complemented with petrography, XRF and organic geochemistry (Rock-Eval pyrolysis and optical maceral petrography) to determine organic matter composition, depositional paleoenvironment, oceanographic conditions, and hydrocarbon potential. In the two study areas, Waskada Field (WF) in southwestern Manitoba and Pasquia Hills area (PH) in east-central Saskatchewan, cores were sampled for a total of 80 and 21 samples for Rock-Eval and palynology, respectively.

The 2WS sediments are thermally immature with mean vitrinite reflectance (VRo) of 0.54% and mean Tmax values of 408°C. The strata has excellent petroleum source rock potential with an average 7% total organic carbon, with a dominance of marine (type II) kerogen. Maceral analyses show kerogen is dominated by marine liptinite with subordinate amount of vitrinite and inertinite components. Palynology show a variable assemblage of organic matter of polymorphs, phytoclasts and amorphous organic matter (AOM), with AOM being the most dominant. These likely represents periods of phytoplanktonic bloom associated with dysoxic/anoxic bottom-water conditions, during the Upper Cretaceous maximum transgression, corresponding with the 2WS deposition.

Autochthonous pyrite is abundant within the 2WS, with high TOC commonly associated with high S contents, suggesting dominant anoxic/euxinic character at the sediment-water interface at the time of deposition in both areas. Similarly, the relationship between pyritic iron (Fe_pyrite) versus total iron (Fe_total) and total organic carbon (TOC) versus total sulfur content (TSC) cross plots supports periodic anoxia during deposition. Also, different ratios of Fe_pyrite/Fe_total shows upper unit of the 2WS was deposited in a less oxygenated environment compared to the lower unit. Result provide insights into the basin history and depositional environments of the studied successions within the Cretaceous epicontinental seaway and its potential from oil and gas exploration perspectives.