1.1.3 Geology


The Gloucester subregion is underlain by the geological Gloucester Basin, an elongated northerly trending sedimentary basin. It contains up to 2500 m of faulted, deformed and eroded coal-bearing Permian sedimentary and volcanic rocks that rest unconformably on Carboniferous strata of the Late Paleozoic New England Fold Belt.

The Gloucester Basin is interpreted as a fault-bounded depositional trough that was active during the Permian period. It presently contains steeply dipping beds and faults on its flanks that flatten towards the central basin axis. These structural elements suggest that the regional structural architecture was either synclinal or a reactivated extensional graben.

Early normal and syn-depositional faults occur commonly in the basin and in many cases have been reactivated by later tectonism of the Hunter-Bowen Orogeny. This resulted in normal, strike-slip and reverse faults, with an apparent high density near the flanks of the basin. Throughout the basin north-east, north-west and east striking normal and strike-slip faults also occur. Coal exploration drilling on the eastern basin flank has shown local duplication of coal seams, suggesting the presence of low angle thrust faults parallel to the basin axis. These may be attributed to compressional tectonism during the Late Permian orogenic phase.

The Permian coal measures (Dewrang Group and Gloucester Coal Measures) overlie the Alum Mountain Volcanics. These stratigraphic units consist of coal-bearing shallow marine, deltaic and alluvial sedimentary rocks that were deposited in a tectonically active basin. By the Late Permian period, following the cessation of deposition, deformation and uplift during the early stages of the Hunter-Bowen Orogeny resulted in partial erosion of the Permian rock units.

The Dewrang Group includes two coal seams that are mined at the Duralie Coal Mine in the southern closure of the main synclinal structure of the Gloucester Basin. The Stratford and Bowen Road open-cut operations extract coal from upper and middle seams of the Gloucester Coal Measures. To date, the basin is an area of significant interest for coal seam gas exploration.

Last updated:
5 January 2018