Origin of oils in the Eastern Papuan Basin, Papua New Guinea

The geochemical characteristics of 16 oils/condensates/seep oil/oil shows (collectively called oils) from the Eastern Papuan Basin (EPB) and one seep oil from the Western Papuan Basin (WPB) are integrated with data from previous studies of oils, fluid inclusion oils and solid bitumens from the EPB and WPB, Papua New Guinea. The combined set of samples can be divided in two major families of hydrocarbons. The Family A oils, mostly occurring in the WPB region, were generated from clay rich marine source rocks, containing predominantly terrigenous higher plant derived organic matter (OM) deposited in a sub-oxic to oxic environment. Source rock(s) for Family A oils are likely to be of Middle to Upper Jurassic, e.g., the Upper Jurassic Imburu Formation. The Family B oils, distributed mainly in the EPB region, were generated from Cretaceous or younger marine carbonate source rock(s) deposited under anoxic to sub-oxic conditions, and containing predominantly prokaryotic OM with some terrigenous higher plant inputs. The EPB natural gases analyzed in this study may be co-genetic to the co-occurring Family B oils in the EPB. Both Family A and B oils were generated at similar thermal maturities of 1.0–1.3% vitrinite reflectance equivalent. Although no source interval to date has been firmly identified in the EPB, post-Jurassic strata are a viable option, because (1) Late Cretaceous and Paleogene carbonate and clastic marine sediments including possible source lithologies are present, and (2) this section of the Papuan Basin sustained rapid sedimentation and tectonic loading, particularly in the Cenozoic.