Abstract:
The neritic stratigraphic record in southern Australia sorts into four cycles or sequences which resemble global second-order cycles based on sequence stratigraphy. The record is highly incomplete at the second order, due especially to a 9 my gap in the middle Eocene and poor and restricted records of the early Oligocene and the late Miocene series, and at the third order where hiatuses become more apparent as stratigraphy advances. Correlations and age determinations are based mostly on micropalaeontology and are limited by the neritic facies, the extratropical situation and the lack of a local or regional geomagnetic pattern. In this composite regional succession, we have had to proceed from regional stages based only loosely on fossils, to biostratigraphic ranges and formal zones (of planktonic foraminifera), to faunal associations based on transgressions and regressions, so that we are but a short step from a revision of the regional stages in terms of sequence biostratigraphy. This geochronological scaffolding is important not only to the neritic realm itself, but to the neritic-oceanic link and ODP drilling in one direction and to the terrestrial environmental and paleobiological realm in the other. The Cenozoic record of global climatic deterioration has temporary reversals punctuated by four sharp coolings ("chills") in the early middle Eocene, earliest Oligocene, middle Miocene and late Pliocene, and they too are chronologically consistent with the regional neritic record. In the oldest cycle, the sediments are marginal marine siliciclastics with several very brief transgressions with marine microfaunas and rare macrofossils but no limestones. Extratropical carbonates begin abruptly in the late middle Eocene series at the base of the second cycle and the Wilson Bluff transgression, which is the Khirthar Restoration of the Indo-Pacific region. At the same time there develops a distinction between warmer and cooler intermediate watermasses in the Indian Ocean, and the Leeuwin Current is born. These events are responses to accelerated Australia/Antarctica separation from 43-42 Ma. The third-order components of this cycle are marked by marine transgressions; they are consistent in number and timing with the putative late Eocene global pattern. The third cycle is the Miocene oscillation which begins in late Oligocene time and peaks in sea level and warming at the Miocene climatic optimum in early middle Miocene time. As shown in a correlation chart, the extratropical "cool-water carbonates" are mostly in the second and third cycles, although there are carbonates in the extensive marine horizons of the Pliocene reversal. The Eocene-Miocene neritic carbonate record comprises third-order sequences, seen most clearly as marine transgressions. The transgressions can be related to third-order glaciations and eustatic cycles in plausible if not always compelling correlations. Horizons of warming, upwelling, and siliceous facies complete a framework of an outstanding extratropical, neritic carbonate record.