THE PILBARA COAST - A RIVERINE COASTAL-PLAIN IN A TROPICAL ARID SETTING, NORTHWESTERN AUSTRALIA

The unifying feature of the Pilbara Coast of northwestern Australia is that it is a sedimentary repository for a range of rivers that drains a high-relief Precambrian rocky hinterland and discharges sediments along a coastal plain which fronts a wave-dominated environment in a tropical arid climate. The combination of fluvial and shoreline accretion processes, coastal cementation, coastal erosion, and ancestral landform architecture, such as residual Pleistocene limestone ridges and large outcrops of Precambrian bedrock, has produced a complex coastal system during the Quaternary. As a result, the coast is dominated by active deltas, beach/dune shores, inactive, eroding parts of deltas and their barriers, limestone barrier coasts, bays associated with eroded limestone barriers, and archipelago/ria coasts. Quaternary sediments throughout the area, while varied in their distribution and history at the smaller scales, exhibit a recurring pattern of lithotopes and lithologies in the region. There are three main Quaternary suites: Pleistocene red siliciclastic sediments (alluvium, deltaic sediments, and aeolian sand) that form an inland zone; Pleistocene limestones that form local barriers; and a Holocene system, within which are the sedimentary suites of deltas, beach/dunes, tidal-flats, and tidal-embayments.