Deccan basalts in and around Koyna — Warna region, Maharashtra: Some reflections

In this paper, an attempt is made to review the current status of chemo-and magnetostratigraphy of the Deccan Traps, particularly in the Western Province, and to interpret geomorphological and borehole data in relation to the earlier known structural data in the whole region, to that of the Koyna-Warna region, covering Deccan Traps and part the Archean basement. Koyna and Warna region comprises of chemically defined younger Formations of Wai Subgroup and Lonawala Subgroup displaying over-stepping arrangement from older Formations further north in the Nasik area and younger Formations down south. This is further corroborated by a single polarity change from reversed to normal, all the way to Belgaum. This is considered as a time marker around 65Ma (Chron C29r /C29n) matching with the K-T boundary. The Deccan Trap contact with the Archean basement in the 7 boreholes shows a plateau around 200m in the western section but a variation ranging up to 500m in the eastern side of the Warna region. These variations may be due to faulting or upwrap in this region. It is to be noted that the Koyna–Warna volcanic pile is similar to the thick sequences of the Mahabaleswar Ghat section further north in terms of their chemistry and magnetostratigraphy. A combination of surface and sub-surface data of the Koyna-Warna region may not show the presence of older volcanic formations such as Kalsubai Subgroup nor ages older than 65Ma.