ABSTRACT: Tertiary carbonate sedimentation and petroleum systems in the Papuan Fold Belt

Allan, Tony L., Julie A. Trotter, Michael J. Korsch, David J. Whitford , CSIRO, North Ryde NSW, Australia

Strontium isotope chronostratigraphy has been extensively applied to Oligocene-Miocene platform carbonates of the Darai Limestone that form the surface carapace in much of the Papuan Fold Belt (PFB) in Papua New Guinea. The technique gives excellent chronostratigraphic subdivision with an age resolution of ca. +1 Ma. Ongoing research has incorporated limestone microfacies and biostratigraphy with isotopic analysis. Recent models of hydrocarbon entrapment in the PFB emphasize the importance of pre-Tertiary basin architecture both in trapping early migrating hydrocarbons prior to deformation, and its influence on structural style in the PFB. Chronostratigraphic study reveals substantial intra-Darai variation in sedimentation rate, with broad strike-parallel domains of rapid sedimentation at the leading edge of the Fold Belt flanked by domains of slower deposition in areas including the producing fields. Facies analysis indicates dominantly shallow water aggradational carbonate deposition in most areas, and the variation in depositional rates may reflect syndepositional fault movement in a pre-Tertiary halfgraben-like setting. Accepting recent Fold Belt "play" models, areas of slower deposition and younger basal Darai, such as observed in the producing fields, may therefore indicate pre-existing highs (potential footwall structures) in extensional settings. Across-strike structures have influenced carbonate facies and thickness, which in turn are reflected in the deformational style observed at the surface.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia