Early Himalayan Orogeny and Its Influence on Carbonate-Clastic Sedimentation: The Middle-Late Eocene Kirthar Formation of the Indus Foreland Basin, Pakistan

Ghulam Abbas¹ and Osman Salad Hersi^2
1 AGAT Laboratories, Calgary, AB
² University of Regina, Regina, SK

The Kirthar Formation (Middle – Late Eocene) accumulated in the Sulaiman sub-basin of the Indus Foreland Basin. It conformably overlies Early Eocene evaporites of Ghazij Formation and unconformably underlies sandstones of Oligocene Nari Formation.

 The Kirthar Formation consists of four alternating members of Habib Rahi and Pirkoh limeostones and Sirki and Drazinda shales. The vertical stacking pattern of the four members defines generally two third-order deepening-upward sequences characterized by basal carbonate members grading upward to the shales (i.e., Habib Rahi-Sirki and Pirkoh-Drazinda sequences). The Habib Rahi Member is proven gas reservoir in the southern part of the Sulaiman sub-basin. The limestones consist of shelf marine foraminiferal wackestone, packstone and grainstone with mollusks and echinoids. The shale members are greenish-gray to brown and chocolates, and with subordinate fossiliferous limestone interbeds in their upper parts suggesting high order sea level fluctuations. The formation thickens from 250 m in the south (e.g., Mari-X3 well) to 851 m (Thak Section) in the eastern Sulaiman Range. The shale members become thicker basin-ward whereas the limestone members become thinner along this trend.

 The accumulation of the Kirthar Formation resulted from the interplay among carbonate production, tectonics and fine siliciclastics dumped from the Himalyan orogenic belt. The carbonate members represent periods of tectonic quiescence accompanied by low siliciclastic input, high carbonate production and pro-gradation. On the other hand, periods of tectonic accretion was followed by erosion, further sagging of the basin and high siliciclastic input causing retro-gradation of the carbonates and accumulation of the shale wedges.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005