The Keepit Conglomerate

Abstract

This thesis presents the results of a detailed sedimentological analysis of the Late Devonian Keepit Conglomerate. The primary aim of the study was to determine the processes and environments of sedimentation of this coarse conglomeratic unit. Furthermore, it was hoped that an understanding of the origin of the Keepit Conglomerate would provide some insight into the palaeobathymetry of the depositional basin during the Late Devonian. The Keepit Conglomerate is of Famennian age, occurring within the Devonian-Carboniferous sequence of the Tamworth Belt, northeast New South Wales. The Tamworth Belt sequence, >9,500 metres thick, is overall regressive, with marine Devonian-Early Carboniferous sediments passing up to Late Carboniferous terrestial sediments. The terrigenous sedimentary detritus was derived by the erosion of a volcanic chain, which lay to the west of the present day western margin of the Tamworth Belt, and deposited within a fore arc basin. Contemporaneous volcanism accompanied sedimentation in many instances. ... The presence of extensive submarine fan deposits in the marine domain of the Keepit Conglomerate containing abundant coarse resedimented conglomerates and sandstones, mostly of proximal character, suggests the depositional basin contained relatively steep intrabasinal slopes, and was of trough rather than shelf nature. While unequivocal pa1aeobathvmetrie data is lacking, the setting is more in character with "deeper" rather than "shallower" basin conditions. The Keepit Conglomerate provides an ancient example of coexisting terrestial and submarine fan sedimentation within a fore arc basin flanking a volcanic chain. The abundant very coarse detritus reflects the proximity of source and depositional basin, and the nature of the sedimentation processes and transporting mechanisms operating in the two domains.