Miocene climatic oscillations recorded in the Lakes Entrance oil shaft, southeastern Australia: benthic forminiferal response on a mid-latitude margin

Abstract

The Lakes Entrance oil shaft section in east Gippsland, southeastern Australia, spans most of the second-order rise and fall in sea level and climate known as the Miocene oscillation. For this section, we have established time series of taxic changes and relative abundances of benthic foraminifera. Metrics reflecting the Miocene oscillation are changes in the profiles of inner, middle and outer neritic species, infauna and epifauna, and first and last appearances of species, as well as the numerous intervening comings and goings. A paleodepth curve is derived from shifts in the dominance of ecological groups. The inferred pattern of transgression/regression shows good agreement with third-order sequences. The pattern of first and last appearances shows three levels of particular interest. Two major changes are close by correlation to second-order sequence boundaries, early in the early Miocene and at the middle/late Miocene boundary respectively. Whereas the planktonic succession peaks in all measures at the Miocene optimum, the equivalent but muted benthic peaking leads it by some 2 m.y., peaking at the beginning of the Monterey carbon excursion. Thus the neritic record is more in tune with the deep-ocean record than with the plankton, and we suggest that fluctuations in nutrient supply had their major impact on the rising side (early Miocene) of the Miocene oscillation.