STRATIGRAPHIC SEDIMENTOLOGY OF TERTIARY COOL-WATER LIMESTONES, SE AUSTRALIA

Mid-Tertiary limestones, exposed as sea cliffs along the coast of Vict oria, southeastern Australia, accumulated on the inner part of a cool- water, distally steepened ramp or open shelf. All sediments are bioela stic, dominated by particles of bryozoans, echinoderms, benthic forami nifers, brachiopods, and molluscs. Shallow, grainy facies also contain coralline algae, quartz, and glauconite, while deep, muddy facies inc lude ahermatypic corals, ostracodes, sponge spicules, planktic foramin ifers, and terrigenous clays. The fundamental depositional unit is a m eter-scale, subtidal cycle or rhythm. Shallow-shelf cycles are shallow ing-upward, cross-bedded or burrowed grainstone capped by a marine-cem ented hardground or quartz-granule lag, while mid-shelf cycles are upw ard-coarsening and thickening, proximal to distal tempestites. Such cy cles are interpreted to form by eustatically driven, climatically cont rolled oscillations in abrasion wave base and swell wave base. Deep sh elf rhythms are interbedded bryozoan marl and calcareous clay, thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution. Lowstand systems tracts are dep ositional or erosional. Sequence boundaries are complex, multigenerati on, mostly submarine surfaces (condensed cycle boundaries) that can be traced offshore into multiple Omission surfaces and conformable conta cts. Basinward facies shifts result in deposition of condensed lowstan d wedges of stacked, shallowing-uwpard grainstone cycles. Transgressiv e systems tracts are thick bryozoan marl-calcareous clay rhythms assoc iated with facies backstepping and abrupt deepening. Such rhythmites t ypically grade stratigraphically upward into tempestite cycles. Highst and systems tracts are highly progradational, wedge-shaped rock bodies of shallowing-upward grainy cycles. These limestones provide the crit ical link of stratigraphy between modern cool-water carbonate shelf de posits and the older Mesozoic and Paleozoic record of similar sediment s.