GEOCHEMISTRY OF SOME K T SECTIONS IN INDIA

A number of marine as well as continental K/T sections in India, parti cularly around the Deccan volcanic regime, have been analyzed to obtai n concentration profiles of some platinum group and other trace elemen ts, specifically to search for anomalous levels of iridium. Except for the Um Sohryngkew River (USR) section in Meghalaya, where iridium is found to occur at an anomalously high level in the K/T boundary layer, all other sections show low levels in the range of 10 to approximatel y 120 pg/g. The iridium profile in the USR section is characterized by a sharp peak of 12.1 ng/g in a 1.5 cm thick limonitic layer, superimp osed on a broad band of approximately 0.2 ng/g extending over a 50+/-2 0 cm thick section, beyond which Ir decreases to the base level of app roximately 0.02 ng/g, both in the Tertiary as well as in the Cretaccou s. High Ir is accompanied by high Os but the Os/Ir ratio in the peak ( 0.37) is different from the Os/Ir ratio of approximately 2 measured in the broad band. The Ir profile in the USR section seems to be consist ent with fallout of cometary debris preceding and following the main i mpact. The measurements at other sites in the Deccan suggest that the iridium inventory of the Deccan is too low to account for the high iri dium observed in the KTB layer all over the world, but may be sufficie nt to give rise to its enhancement adjacent to the KTB peak.