Age for the Miocene Jaffna Limestone in Sri Lanka

Abstract

The 80-100 m thick Jaffna Limestone is widely distributed in the northwestern Sri Lanka. Abundant and varied fossils, including foraminifera, gastropods, corals, calcareous algae, bryozoa, anthozoa, lamellibranch and echinoids, have been discovered from the Jaffna Limestone. Previous studies suggested that the formation of these marine carbonate deposits might be related to marine transgression. Based on fossil correlations, researchers generally accepted that the Jaffna Limestone was formed around Miocene. However, absolute age determinations for these deposits are lacking. A reliable chronostratigraphic constraint will allow to understand the depositional history of the Jaffna Limestone. Furthermore, establishing the high-resolution ages for the Jaffna Limestone will enable to test the relationship between sea level change and the mid-Miocene Climatic Optimum in South Asia. This study provides the first robust age calibration for the limestone in the Jaffna Peninsula. The measured 87Sr/86Sr ratios (0.708721 – 0.708228), which correspond to 15.5 – 23.5 Ma, indicate that the age of Jaffna Limestone ranged from late Oligocene to middle Miocene. The U-Pb dating result of calcite minerals generated an age of 16.5+/-2.0 Ma. Our results indicate that the depositional history of the Miocene Jaffna Limestone is more complicated than previous thought