INTERTIDAL AND SUBTIDAL SEDIMENTATION DURING A MIDPROTEROZOIC MARINE TRANSGRESSION, REYNOLDS RANGE GROUP, ARUNTA BLOCK, CENTRAL AUSTRALIA

In the Reynolds Range (central Arunta Block), a series of mid-Proterozoic, clastic shallow marine metasediments, the Reynolds Range Group, unconformably overlies a sedimentary and granitic basement and is intruded by granites. The group comprises five distinct stratigraphic units: a quartzite, a lower calc-silicate, a pelite, an upper calc-silicate and a felsic volcanic unit. The quartzite unit that extends along the northeastern flank of the Reynolds Range, and the lower calc-silicate unit that occurs to the southwest, represent lateral transitions of a basal unit which was deposited on a metamorphic basement in an epicontinental shallow marine basin. A series of northeast-directed marine transgressions resulted in a deepening of the marine basin which is reflected in the transition to the pelite unit. The upper calc-silicate occurs as a lens within the pelite unit and represents carbonate build-ups that were deposited on a raised platform free from siliciclastic input. During the initial stages of the depositional cycle, a thick rhyolitic unit was deposited in the northwest Reynolds Range. The Reynolds Range Group, which represents division 3 sediments in the Arunta Block, correlates with the 10 000 m thick Hatches Creek Group in the Davenport province. The implication is that the entire Arunta Block might have been covered by a potentially thick sequence of sediments that were comparable with the Reynolds Range Group. Such a thick sequence largely explains the lithostatic pressures that existed during subsequent granulite facies metamorphism in the area.