The early Carboniferous palaeogeography of the southern New England Belt, New South Wales

Abstract

Early Carboniferous sedimentation in the southern part of the New England Belt reflects the gradual filling of the Tamworth Trough and a change from mainly marine to mainly non-marine deposition. Sedimentation was largely controlled by volcanism along the western and southern margins of the trough, but late in the Early Carboniferous uplifts associated with the emergence of the New England Arch combined with the volcanism to influence the configuration of the shoreline. In the latest Devonian or earliest Carboniferous volcanics and terrestrial sediments were deposited locally in the western part of the region, whereas fine-grained deeper water sediments accumulated to the north and east. A marine transgression early in the Tournaisian moved the shoreline westwards and established a region of shallow marine deposition which was linked with the deeper-water environment. Volcanism and rejuvenation of source areas in the late Tournaisian and early Visean caused a terrestrial piedmont containing a shallow marine embayment to prograde into the marine shelf. Increased volcanism and uplift in the source areas in the early middle Visean enlarged the piedmont and was responsible for deposition of alluvial sediments and ignimbrites. Offshore, because of the intensity of volcanism, ash-bearing silt and mud were deposited on the marine shelf. In the middle Visean the non-marine environment encroached farther into the marine shelf, but in the southwest the shoreline fluctuated across a coastal plain, resulting in the deposition of paralic sediments. The enormous influx of volcanic detritus into the shallow marine shelf resulted in the deposition of a thick succession in a subsiding area around Chichester; a thinner sequence may have been deposited on the incipient Stroud Platform. Late in the Visean the major centres of volcanism shifted from the western to the southern margins of the trough; combined with the emergence of the Stroud Platform the volcanism was responsible for a widespread marine regression. Coarse-grained shallow water sediments were deposited on the platform, and a thicker fine-grained succession accumulated in the subsiding region.