--> Swath Topographic Analysis, Critical Taper, and Structural Styles of the Papua New Guinea Fold-Thrust Belt: Influence of Mesozoic Stratigraphic Architecture?

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Swath Topographic Analysis, Critical Taper, and Structural Styles of the Papua New Guinea Fold-Thrust Belt: Influence of Mesozoic Stratigraphic Architecture?

Abstract

Hydrocarbon exploration of the Papua New Guinea (PNG) Fold-Thrust Belt (FTB) is heavily reliant upon structural models of the subsurface due to generally poor quality seismic data and limited well control available to constrain subsurface architecture. Given this uncertainty, a wide variety of the structural styles have been applied to the PNG FTB which range from Canadian Rockies-style thin-skinned deformation to detachment folding and basement-involved inversion. This is not surprising, but has significant implications for trap geometry. Still, several first-order observations can be made which may have implications for the deformation style of the FTB: 1. The topographic expression of the thrust belt changes significantly from northwest (high relief) to southeast (low relief), 2. Basement is involved in FTB deformation in northwestern regions (confirmed by wells and outcrops), 3. Regional trends of Upper Jurassic to Lower Cretaceous strata show a substantial increase in thickness from northwest to southeast. Analysis of ten regional swath topographic profiles show a general decrease in slope of the frontal portion of the thrust belt from northwest to southeast and a decrease in wavelength of structures which may suggest a decrease in friction along the basal thrust belt decollment per critical taper theory. These along strike changes in the topographic expression and map pattern of the FTB are likely a function of variations in the pre-FTB mechanical stratigraphy- i.e. the thickness and facies distribution of strata which are related to Mesozoic extensional architecture and associated syn-and post rift sedimentation along the northern margin of the Australian plate. Regions to the southeast with thicker pre-FTB strata have the potential for multiple detachment zones within the sedimentary section and are likely to be dominated by thin-skinned style deformation. In contrast, the NW FTB has thinner pre-FTB strata and fewer potential detachment zones requiring faults to involve basement or reactivate pre-existing structures. The along strike FTB structural transitions from thin to thick syn-and post rift strata and associated changes in structural style are likely dominated by lateral ramps rather than tear faults or vertical transfer zones.