PALEOENVIRONMENT AFTER MAIN DECCAN VOLCANISM ENDED AT KT MASS EXTINCTION: EVIDENCE FROM THE KRISHNA-GODAVARI BASIN, SE INDIA

The two largest and most extensive Deccan volcanic eruptions extended 1000 km across India and are exposed in outcrops of the Krishna-Godavari Basin, SE India. These two Deccan traps are in magnetic polarity C29r and C29n, respectively, with ⁴⁰Ar³⁹Ar and ⁴⁰K/⁴⁰Ar ages of 65.0±0.6 m.y. Paleontologic investigations of the intertrappean sediments show that the main volcanic phase (lower trap) ended at the K-T boundary and that the intertrappean unit spans the early Danian zone P1a (Keller et al., abstract this vol.). Here we present the sea level changes and environmental conditions that prevailed during deposition of the intertrappean sediments based on sedimentologic, and mineralogic analyses. The four outcrops analyzed indicate that deposition occurred in shallow estuarine to inner neritic environments with periods of subaerial deposition marked by paleosoils. The regional geometry of sediments suggests deposition in incised valleys. In this environment, the alternating terrestrial and shallow marine conditions reflect sea-level fluctuations. The lower basalt trap shows a weathered and fractured surface that suggests subaerial exposure and possibly deposition in a continental environment. The overlying dolomitic mudstone with clasts of earliest Danian planktic foraminifera (zone P1a) indicates a very shallow marginal marine environment. A calcrete breccia at the top of this unit marks a drop in sea level and subaerial exposure. This is followed by a series of shallow restricted marine environments with high detrital influx and deposition in a semi-arid climate. A change to more humid conditions is indicated by increased quartz and abundant iron nodules, followed by a rising sea level depositing laminated mudstone in an open coastal environment with low hydrodynanic conditions and seasonally contrasted climate. Deeper open marine environments are indicated by chalky bioclastic limestones, though storm deposits suggests a maximum depth of 40-80 m. Sea level drops are marked by erosion, karstification and paleosoil deposition. These sea level fluctuations and climate changes frequently exposed extensive areas of the basalt flows to weathering and may may have played a key role in the global climate and ocean chemistry during the early Danian leading to the delayed biotic recovery of marine biota.