--> Facies and Stratigraphic Analysis of the Permian Succession in the Denison Trough, SW Bowen Basin, Queensland, Australia

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Facies and Stratigraphic Analysis of the Permian Succession in the Denison Trough, SW Bowen Basin, Queensland, Australia

Abstract

This paper summarises the outcomes of a long-term project that aims to provide a unified facies scheme for, and stratigraphic analysis of, the Permian sedimentary succession in the Denison Trough of the SW Bowen Basin, to aid in evaluation of petroleum prospectivity in this petroliferous basin. An integrated sedimentological-ichnological study of outcrops and drillcores is combined with the results of subsurface mapping of formations and component members. The Lower Permian succession was accumulated under a regime of modest crustal extension, and was directly affected by glaciation during parts of this time interval. Sediment supply was from the craton to the west of the basin, and from intra-basinal highs bounding extensional depocentres. Alluvial and lacustrine strata (Reids Dome Beds and equivalents) pass upward into an array of coastal plain to shallow marine deposits with several mixed-influence deltaic complexes preserved (Cattle Creek Formation to Lower Aldebaran Sandstone). Isopach maps of these formations illustrate the initially major but over time diminishing influence of extensional accommodation on sediment accumulation. A basinwide discontinuity (intra-Aldebaran unconformity) reflects both basinal reorganization at the end of rifting, and probably also erosion associated with glacial activity. A short-lived Middle Permian period of passive thermal subsidence gave rise to a more sheet-like cross-sectional stratal geometry (Upper Aldebaran Sandstone, Freitag, Ingelara Fms., Catherine Sandstone), and craton-derived sediments accumulated in coastal to shallow marine environments. Isopach maps of these formations show a more even distribution of sediment. This phase was terminated in the late Middle Permian by the onset of the Hunter-Bowen contractional orogeny, causing the transformation of the Bowen Basin into a retroarc foreland basin, with cratonic sediment supply augmented and ultimately overwhelmed by first-cycle volcanic material shed from an emerging continental arc to the east. From this time, a pronounced, north-south-elongate depocentre was located near the eastern basin margin, as indicated by isopach maps. Shallow marine to coastal plain sediments prevailed again (Peawaddy Formation, Black Alley Shale), with periods of oversupply leading to basinwide coastal plain conditions in the latest Permian (Bandanna Formation).