DEVONIAN FLUVIODELTAIC SEDIMENTATION IN HONG-KONG

Twenty-three distinct sedimentary facies have been distinguished in th e Devonian Bluff Head Formation exposed around the Tolo Channel area o f northeastern Hong Kong. These facies have been combined into five fa cies associations: channel, aeolian, sheetflood, deltaic and palaeosol , with the bulk of the formation belonging to the channel association. The lower part of the Bluff Head Formation, around Plover Cove, consi sts of upwards-coarsening cycles, each typically 3 m thick. The basal parts of some cycles contain distinctive marine fossils of Early to Mi ddle Devonian age. Sedimentation occurred on a marine-influenced delta plain, with eustatic sea level rises controlling cycle development. T he middle and upper parts of the formation contrast strongly with the lower part and show a distinct change to alluvial plain sedimentation. Upward-fining cycles, each approximately 40 m thick, comprise basal m ultistorey, braided, conglomerate-filled channel deposits at the base passing upwards into finer-grained sheetflood, aeolian and channel san dstones at the top. Palaeosols in the higher parts of the cycles indic ate periods of non-deposition under semi-arid climatic conditions. The se cycles represent repeated abandonments of the fluvial system which we suggest were controlled by tectonic pulses. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.