Recent-to-Late Pleistocene Sedimentary Organic Matter in the Gulf of Papua, Papua New Guinea

Lawrence A. Febo¹, Samuel J. Bentley¹, Gerald R. Dickens², André W. Droxler², Larry C. Peterson³, and Bradley N. Opdyke^4
1 Louisiana State University, Baton Rouge, LA
² Rice University, Houston, TX
³ University of Miami, Miami, FL
⁴ The Australian National University, Canberra, Australia

The Gulf of Papua is a ~2000 m deep basin situated along the northeastern Australia and Papua-New Guinea margin, which is one of the largest mixed siliciclastic/carbonate depositional systems in the world. In this study, the origin, flux, and distribution of sedimentary organic matter (SOM) were analyzed in 54 core tops and two jumbo piston cores. Analyses of multicores provide modern organic matter flux data for the shelf-edge to basin in the Gulf of Papua, whereas piston-core sediments provide past flux over longer time scales. SOM was analyzed using Total Organic Carbon (TOC), Rock-Eval Pyrolysis (REP), C/N, δ¹³C, and kerogen petrography.

Coretop TOC values are low and range from 0.18 - (avg. 1.0) - 1.14 wt. %. TOC values are highest in the northeastern Pandora Trough and decrease towards the southwest in the central Pandora Trough. Lowest TOC values occur in the carbonate dominated Ashmore and northern Pandora troughs. REP indicates type 3 kerogens for most coretops, which may be derived either from woody organic matter or from highly oxidized marine SOM. Kerogen analysis shows that SOM in the northeastern Pandora Trough and Eastern Plateau is dominated by autochthonous marine amorphous organic matter (AOM), suggesting that the type 3 kerogen is highly oxidized SOM. Sediments in the northern Ashmore and Pandora troughs contain more marine palynomorphs than AOM. Downcore changes in TOC, C/N, δ¹³C, and palynofacies are interpreted to indicate climatically driven changes in organic matter flux from varied sources.