Abstract
The Papuan Basin is the largest petmliferous basin in Papua New Guinea (PNG), where developed several sets of potential source rocks (SRs). The Jurassic SRs are clay-rich shales, whose organic matter (OM, mainly type II2-III) is predominantly derived from terrestrial higher plants deposited in a more oxic environment with relatively high maturity (0.35% < Ro < 2.03%). The Cretaceous SRs contain mixed inputs of terrigenous and marine OM (type II2-III) formed in sub-oxidized to oxidized depositional conditions with moderate maturity (0.33% < Ro < 1.58%). Whereas the Paleocene-Miocene SRs are predominant marine calcareous shales with subsidiary terrigenous OM inputs. These SRs containing type III kerogen are mostly immature (0.21% < Ro < 0.70%). The Papuan Basin oils were classified into three distinct genetic families based on biomarkers and stable carbon isotopes. Family A oils, with heavy carbon isotopes, low Pr/Ph ratios, C-29/C-27 alpha alpha alpha 20 R sterane <1.0, are likely originated from autochthonic Paleogene-Neogene mature marine OM. Family B oils have the characteristics of high Pr/Ph, moderate carbon isotopes, the dominance of C-29 alpha alpha alpha 20 R sterane, and are predominantly derived from autochthonous Jurassic SRs. Family C oils in the Eastern Papuan Fold Belt (EPFB) can be further subdivided into three subtypes by more subtle differences in specific biomarkers. Type C-1 oils, most likely stemmed from the Lower Cretaceous SRs, are characterized by light stable carbon isotopes, Pr/Ph > 2, the mild dominance of C-29 aaa 20 R sterane and the absence of oleanane +/- lupane. Type C-2 oils can be clearly distinguished from Type C-3 by C-19/(C-19 + C-23) tricyclic terpane <0.5, while the latter ones have higher abundances of oleanane +/- lupine and diahopanes as well as C-24 tetracyclic/C-23 tricyclic terpane ratios. Type C2-3 oils are originated from calcareous SRs that deposited in Late Cretaceous or younger age.
NSTL
Elsevier