Miocene foraminifera from the Finniss Clay and Cadell Marl, western Murray Basin: taxonomic and taphonomic contrasts and their environmental significance.

Abstract

Sandwiched between Miocene limestones of the Mannum Formation and Morgan Limestone in the western Murray Basin, the Finniss Clay and Cadell Marl contain different foraminiferal faunas with varying taphonomic grades. At the Mannum Pumping Station section, the Finniss Clay fauna has a low diversity, frequent shallow-water forms, and a poor taphonomic grade. In what was the deeper part of the basin at Waikerie, a diverse fauna with well-preserved small species is recorded in sediments equivalent to the Finniss Clay. In contrast, the Cadell Marl from various localities comprises a well-preserved and diverse biofacies with both shallow and deeper water taxa. These contrasts suggest different depositional environments: shallower and warm during deposition of the Finniss Clay and nutrient-rich, dysaerobic and deeper water during deposition of the Cadell Marl. The shallowing event indicated by faunas from the Finniss Clay was due to falling sea level close to the early/middle Miocene boundary, whereas the Cadell fauna appears to reflect the global carbon buildup at the peak of the Monterey carbon excursion during the Miocene climatic optimum, about 16 million years ago. © 1999 Association of Australasian Palaeontologists.