Black shale xenolith in a Jurassic - Cretaceous kimberlite and organic-rich Upper Ordovician shale on Baffin Island, Canada: A comparison of their organic matter

摘要

Rock-Eval pyrolysis and molecular organic geochemical analyses as well as organic petrographic observations were carried out on a rare black shale xenolith core drilled from a Late Jurassic-Early Cretaceous kimberlite on the Hall Peninsula in southern Baffin Island, Canada. The results are compared with those of outcrop shale samples from the Upper Ordovician Amadjuak Formation, the only organic-rich shale deposit discovered so far in the region. The shale xenolith is found to be organic-rich and thermally mature at the stage of peak oil generation, and contain type II organic matter similar to that of the immature Amadjuak shale. Discounting the differing thermal maturation effect, similar depositional environments and original organic inputs are suggested for both the shale xenolith and the Upper Ordovician shale based on their bulk, molecular and isotopic signatures as well as organic maceral assemblages. The present study cannot exclude the possibility of the shale xenolith being originated from an organic-rich Lower Silurian deposit, as suggested by previous Re-Os isotope dating study. It is clear, however, that depending on their areal distribution and thickness, the lithostratigraphic unit from which the organic-rich black shale xenolith is derived would make an excellent petroleum source rock in the study area.