Abstract: Structural Analysis of the Indus Basin System from Regional Seismic Data

SOULSBY, ALAN, STEVE LAWRENCE, DAVID SHAW and SIMON TUBB

A database consisting of over 34,000 km of seismic data of various vintages has been interpreted across the Indus Basin System of Pakistan. The Indus Basin occupies the foreland to a collisional zone formed by the Kirthar and Sulaiman foldbelts. Collision tectonics began in the Late Cretaceous and fold/thrust propagation has been active through the Neogene to the present day. The syn-collisional structural history of the Indus foreland has been interpreted from tectono-stratigraphic relationships.

Two prominent unconformities are recognized from seismic interpretation at "Base Tertiary" and "Base Miocene" levels. "Base Tertiary" erosion affects all of the Indus foreland, extending down into the present-day offshore area. Axial zones of "Base Tertiary" erosion, the Jacobabad-Jaiselmer Arch in the center of the basin, and the West Badin Arch in the south both trend WNW-ESE and parallel the Sargodha-Shahpur Arch of the same generation which has been long recognized in the north. We attribute this broad wavelength flexural warping to the first effects of collision in the Late Cretaceous. "Base Miocene" erosion is attributed to typical "forebulge" development, as thrusting/overriding got underway in the Kirthar and Sulaiman foldbelts. The "Base Miocene" unconformity is noticeably diachronous, with overlying section becoming progressively younger updip onto the foreland.

These uplift phases were intervened by a phase of fault-controlled subsidence during the Paleogene, which is attributed to transtensional re-activation of Jurassic-Cretaceous faults as a response to the first effects of collision.

"Late" (Plio-Pleistocene) axes of uplift have a N-S orientation. They have been designated the Dabbo Creek, Badin, Khairpur, Mari, and Qadipir Inversion Axes. These are attributed to inversion-type uplifts, controlled in part by another re-activation of Cretaceous faults, but this time in a transpressional sense, due to late collisional events in the Kirthar (compression) and the Sulaimans (transpression).

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria