COMPOSITIONAL TRENDS IN THE PERMIAN SANDSTONES FROM THE DENISON TROUGH, BOWEN BASIN, QUEENSLAND REFLECT CHANGING PROVENANCE AND TECTONICS

Point-count data of sandstone samples collected from six sedimentary f ormations encountered in boreholes in the Permain sequence of the Deni son Trough (an Australian backarc/retroarc foreland basin) provide inf ormation about the tectonic evolution of their source areas and the de positional sites. Plots of the detrital compositions of these Permian sandstones against borehole depths indicates that the Reids Dome Beds sandstones, containing highly abundant lithic/volcanolithic grains, ma rk the onset of intense compressional tectonics and arc volcanic activ ities to the east accompanied by extensional tectonics and subsidence in the trough. Folding and thrusting owing to intense compressional te ctonics in the New England Fold Belt and Arc volcanism in the Camboon Volcanic Arc region to the east generated a great supply of recycled s ediment and volcanic detritus that led to a rapid infilling of the sub siding Dension Trough during formation of the Reids Dome Beds sandston es in Early Permian time. The detrital composition of the sandstones o f the overlying Cattle Creek Formation, Aldebaran Sandstone, and the F reitag Formation indicate gradually decreasing compressional tectonics and arc volcanism accompanied by increasingly dominant sediment-suppl y from the stable continental craton to the west. The Freitag Formatio n sandstone compositions mark the quietest tectonic and volcanic episo de in the region, accompanied by subsidence of the Denison Trough owin g to thermal cooling during the Middle Permian. The Peawaddy Formation and the Bandanna Formation sandstone compositions represent a Late Pe rmian renewal of compressional tectonics and arc volcanism to the east accompanied by uplift and folding of the sedimentary strata, resultin g in the formation of largely fluvial depositional environments in the Denison Trough. Modal compositions of the Bandanna Formation sandston es indicate that renewed arc volcanism and compressional tectonic acti vity attained maximum intensities during the Late Permian.