Offshore Indus Basin

[7] Seismic data in the offshore Indus basin show evidence of an early rift geometry below the Deccan volcanics.

Imaging is hampered by the presence of volcanics, which partly infill the rifts and by the thick overlying Indus Fan section of Oligocene to Recent age.

This was accompanied by major clastic influx from the Indus river and leading to deposition of up to 9 km of Oligocene to Recent sediments.

[2] Seismic and gravity data suggest that the underlying crust in the offshore Indus basin is of three types: continental, transitional and oceanic.

Continental crust is interpreted for the area below the shelf and upper slope based on the presence of deep rift geometries on seismic lines.

Transitional crust occurs on the slope in water depths of 1500–3000 m and is characterized by a prominent gravity low and a northeast-southwest-trending chain of seamounts of Late Cretaceous-Paleocene age.

The Makran accretionary wedge, north of the Murray ridge, developed in response to the subduction of the Gulf of Oman oceanic crust beneath Eurasia from about 14 Ma onwards.

Nari (Oligocene in age), Gaj (Miocene) and recent sediments, were brought down by the Indus river after the Himalayan uplift and deposited over the Eocene carbonates.

[12] The Indus fan was deposited in an unconfined setting on the continental slope, rise and basin floor, covering much of the Arabian Sea.

The entire fan extends over an area of 110,000 square kilometers with greater than 9 km of sediment accumulating near the toe-of-slope.

[6][13] Fan sedimentation is estimated to have begun at the end of the Oligocene or beginning of the Miocene, during a period of faster Himalayan exhumation, possibly linked to Monsoon intensification.

This arrangement of sediments is ideal for stratigraphic plays and that is why these channel-levee systems are of utmost importance to the petroleum industry.

Four types of traps have been identified in offshore Indus: an extensional rollover anticline trend in the upper slope, drape structures over the Eocene carbonate banks and seamounts, stratigraphic traps formed by sands pinching out against the Murray Ridge and folds associated with the Murray Ridge shear faults and shale diapirs.