The Interplay of Pre-existing Sedimentary Architecture, and its Controls on the Structural Styles in the Eastern Papuan Basin
Spatial and temporal controls of the Cenozoic mixed-carbonate–and-clastic system in the Eastern Papuan Basin are complex. The variability and organisation of sediment type and systems tract are delimited by the antecedent basement architecture and its response to a developing mountain belt and associated foredeep system from the Middle Miocene times. Evidence presented here shows that the syn-depositional structural architecture is regionally variable, and sedimentary accommodation space is controlled in part by localized depo-centres with complex stratigraphic histories. The focus of this paper is to explore the interplay of this pre-existing structure and sediment type, in the context of mechano-stratigraphic contrast, and explore the associated variability in structural styles in the developing Fold-and-Thrust Belt (FTB) in the Eastern Papuan Basin. It is shown here that during the onset of contractional deformation, multiple detachment levels facilitated displacement in the evolving FTB. Balanced cross sections, controlled by seismic, outcrop, well and potential fields data, provide an important solution to the spatial variability in thin-skin and thick-skin, and hard- and soft-linked structural styles evident in these data. Structural styles vary and become more complex from the (1) foreland, to the (2) foreland FTB to the (3) hinterland FTB. The foreland is characterised by far-field strain, which is manifested as inversion of pre-existing normal faults; the presence of this inversion provides evidence of shortening along deep, un-imaged detachment(s). The foreland FTB shows textbook evidence of thin-skin faulting and tectonic wedging with the formation of blind-thrusting, passive-hinterland-verging roof-thrusts, and disharmonic folding in specific horizons. The Eastern Papuan Basin hinterland FTB shows evidence for partial inversion, in addition to shortening accommodated through multiple shallow detachments leading to the development of complex fold trains at present-day surface. This change in structural styles has a significant impact on the explorability of hydrocarbon accumulations and traps. Although the foreland area is structurally simple, the lack of significant structuration results in trapping configurations with limited potential hydrocarbon-column heights. The foreland FTB has imaging challenges, but the relatively well understood detachment levels reduces structural complexity. Furthermore, the tracking of displacement lengths assists in segmenting and defining individual fault strands. The hinterland FTB is, by far, the most complex due to the stratigraphic heterogeneity and currently poorly understood detachment levels. Its structural architecture is manifested and evidenced by large, uplifted possibly inversion domains, with superimposed high-frequency fold trains. Results from this work characterise and quantify structural risk in the Eastern Papuan Basin and will guide our exploration effort in the foreseeable future.
AAPG Datapages/Search and Discovery Article #90371 © 2020 AAPG Asia Pacific Region, The 1st AAPG/EAGE PNG Geosciences Conference, PNG’s Oil and Gas Industry: Maturing Through Exploration and Production, Port Moresby, Papua New Guinea, February 25-27, 2020