Sr isotope numerical depositional age of Miocene marine strata (Quilon Formation), Kerala–Konkan Basin, India

The large offshore and marginal marine Kerala–Konkan basin consists mainly of the Warkalli Group, of which the Quilon Formation represents a transgressional facies of carbonates and siliciclastics with a distinct marine biota consisting of ostracods, foraminifers, otoliths, echinoderms, bryozoans, etc. Depositional ages initially assigned to this formation varied from Eocene to Pliocene, although subsequent estimates favoured an early or middle Miocene age. Based on strontium isotopic compositions ( 87 Sr/ 86 Sr) measured from well preserved, marine, unaltered aragonitic molluscs from the Quilon Formation of Kerala basin, we report a precise numerical age and prefer a depositional age between 17.08 and 17.13 Ma, which is in agreement with the Burdigalian Stage assigned to this formation on the basis of paleontological data. The new-age data suggest that the Quilon Formation records the onset of Mid-Miocene Climatic Optimum (MMCO).