The petroleum geochemistry of Canadian Beaufort Tertiary “non-marine” oils

Abstract

Molecular, isotopic and elemental data for a set of 28 Paleogene and 3 Cretaceous oils from the Mackenzie Delta and offshore Canadian Beaufort Sea have been evaluated. The depositional environment and organic matter characteristics of the source units for these oils have been predicted. The Paleogene oils of the Canadian Beaufort are molecularly distinctive, and clearly contain a major land plant component. Oleanane and the 17α(H)- and 17β(H)-24,28-bisnorlupanes are present, as well as the following compound types: 24-norlupanes (and possibly higher homologues); de-A-lupane; noroleanenes; norursene; dehydroabietane; 28,30-bisnorhopanes. Several molecular and isotopic characteristics are useful in assessing and ordering the extent of biodegradation and thermal maturation of these oils. The Cretaceous oils are separately sourced from the Paleogene oils. The latter oils comprise two distinct land plant-derived genetic families, distinguished by the presence/absence of 24,28-bisnorlupanes, 24-norursene, 24-norlupane and 24-noroleanenes. The Kugmallit/Richards family contains each of these compound types, and is considered to originate from the Eocene Richards Formation. In contrast, lupanoids and noroleanenes are absent in oils of the Reindeer/Moose Channel family; the occurrence of 28,30-bisnorhopane and/or oleanane in these oils suggests a Paleocene origin. Although these source rock predictions are supported by the available data, they must be considered speculative until detailed molecular, isotopic and elemental compositional data are available regionally for potential source rocks of the Eocene and Paleocene source units in the Canadian Beaufort.