Seminar

The Miocene limestone of northwestern Sri Lanka, referred to as Jaffna Limestone, contains various vertebrate and invertebrate fossils. The Miocene Jaffna Limestone is sandwiched between the Precambrian basement, referred to as Wanni Complex and the Pleistocene Red Beds. The formation of the vast extent of marine carbonate deposits there might be related to marine transgression. The Miocene fossiliferous limestone may have recorded the isolation of Sri Lanka from India in Miocene. However, detailed investigations concerning the geochronology of the entire Jaffna limestone unit are rare and research was suspended for decades due to the Sri Lankan Civil War. Absolute geochronology would help answer certain fundamental questions related to paleoenvironment of Sri Lanka. This study aims at obtaining the absolute age of the limestone.  Strontium (Sr) isotope analyses, Uranium (U) – lead (Pb) dating and microfossil analysis were applied to obtain a numerical age of the marine biogenic deposit. 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.