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Late Oligocene Clastic Depositional System in Saurashtra-Dahanu Area, Western Offshore Basin, India

Jitendriya Mishra
KDMIPE, ONGC, Dehradun, India

The Late Oligocene sands within Daman Formation are important exploration plays in Saurashtra- Dahanu area of Western Offshore Basin, India. The formation is represented by alternation of sandstone, siltstone and shale along with limestone streaks towards the base. The sands are medium to fine grained, moderately sorted and calcareous. The shales are dark to olive grey, carbonaceous and contain sideritic nodules. Sedimentary structures including cross lamination, flaser bedding and cut and fill structures are observed. Smaller benthic foraminifera are present in the lower part of the formation indicating shallow inner neritic environment.

The formation is divisible in to three sedimentary sequences based on litho-facies and electrolog correlation. The lower sequence comprises of mainly shale and siltstone along with sandstone. Distinct facies variation is observed from clastic sandy facies to limestone facies from east to west. The middle sequence is represented dominantly by alternations of sandstone, siltstone and shale. The upper sequence comprises mainly thick sands and shale. The log motifs include mainly coarsening up, serrated and spiky log motifs for the lower and middle sequence and fining up and serrated motifs for the upper sequence.

On the basis of litho-association, electrolog motifs and paleontological data, deltaic depositional system with tidal influence is envisaged for the Late Oligocene Daman Formation. The sands were deposited as distributary channels, crevasse splays in the upper sequence, whereas the sands within middle sequence were deposited as distributary mouth bars and delta front sands. The sands within lower sequence were deposited in a distal delta front regime in Dahanu and shallow marine environment in Saurashtra area to the east and west respectively.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery