Planktic Foraminiferal Biostratigraphy and Biochronology of the Post-Miogypsina Neogene of Bombay Offshore Basin

Neogene planktic foraminiferal events and biostratigraphy of four deep well sections viz. D1-A-1, SS-1, R-13-1 and D-4-1 in the Bombay Offshore Basin have been established. A pronounced and regiona lunconformity separates the post-Miogypsina (post Zone N10 or N12, Middle Miocene) clay/claystone succession from the underlying carbonates. In most of the studied wells the hiatus covers a time span of 6.5 Ma (or 9.7 Ma) involving part of Middle Miocene and entire Late Miocene except in well D-4-1 where its span is greatly reduced. Three planktic foraminiferal datums viz. LAD of Globigerina nepenthes (3.78 Ma), LAD of Dentoglobigerina altispira (2.6 Ma) and LAD of Globigerinoides fistulosus (1.6 Ma) have been demarcated in the Pliocene. A comparison of these biochronologic datums with those recorded from the DSDP sites in northern Indian Ocean is made. The delayed Last Occurrence of Globoquadrina dehiscens in Bombay Offshore is attributed to its reworking in Pliocene.