Diachronism of drowning event on Baturaja limestone in the tertiary Palembang sub-basin, South Sumatra, Indonesia

Abstract

New ages for sediments of the Palembang sub-basin are presented. The combined application of grade-dating, strontium isotope stratigraphy and biostratigraphy allowed dating of eustatic events in the Talang Akar, Baturaja and Gumai formations. The Oligocene-early Miocene transgression occurred in the Lahat and Talang Akar formations from west to east. The deposition of Baturaja carbonate on tectonic uplift structures is intepreted as representing a lowstand system tract. The drowning of this carbonate platform by the Gumai shales is a record of important subsidence and climatic changes. A maximum flooding surface above the limestone is characterized by a great abundance and maximum diversity of planktonic foraminifera, calcareous nannofossils and benthonic foraminifera of deep water environment. Above this, the highstand system tract comprises the shales. The decreasing age of Gumai formation shales overlying the limestones shows a diachronism of the Baturaja unit and drowning event. These two formations from a third-order sequence documenting early-middle Miocene transgression. The carbonate drowning event coincides with a renewal of volcanic and tectonic activities and climatic cooling. A relative sea level curve is proposed.