Regional-Scale Structural Modelling Along a Geological Transect Across the NW Fold and Thrust Belt, PNG

Abstract

The jungle-covered NW Fold and Thrust Belt (NWFTB) ranges from the platform near sea level in the SW, to mountains over 3000 m high in the NE, with none of it accessible by road, hence the geological structure and evolution are poorly constrained. Field mapping and analysis of remote sensing data tied to wells and available seismic data has facilitated improved local and regional structural models. A 150 km long and 30 km deep cross-section has been constructed from the platform, across the Juha gasfield, the giant Muller Anticline, NW Thrust Belt, the highly elevated terrain of fold and thrust ‘boat-synclines’ and into the Om Metamorphic terrane. A transition from platform to slope to basin is reflected in the stratigraphy. The poor quantity and/or quality of data at depth make it hard to identify the main controls on structural style. Field and seismic data reveals major detachments are widespread, particularly within the Cretaceous Ieru and Jurassic Imburu formations. The massive nature of the Muller Anticline and Om Terrane suggest crustal scale structures. Seismic data across Juha indicate a thick sedimentary section compared to the platform and probable inversion. Geological maps and the Korka well suggest thrusting along multiple detachments in the NW Thrust Belt and boat-synclines. Iterative forward kinematic modelling was used to reproduce the complex fault-by-fault evolution from pre-compression to present day and test the kinematic and geometric validity of the section. Models reveal that structural style, and its variability, relates to the relative influence of basement-connected and detachment faulting. The former is crucial in forming regionally significant structures such as the Muller Ranges and Om Thrust. Reproducing the present day elevation from the Muller Ranges to Om Terrane requires a relatively steep NE dipping basement decollement extending to crustal depths of greater than 30 km. Basement structures may have been Early Mesozoic rifted passive margin features that were reactivated during Late Cenozoic compression. Smaller wavelength structures in the NW Thrust Belt and forelandward of the Juha Anticline are best reproduced by thrusting from multiple detachment-levels, with minimal basement involvement. The models have significant implications for identifying and risking hydrocarbon prospects. They show that for the best chance of exploration success, prospect-scale structural modelling should consider the regional-scale context.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015