Contrasting Depositional Systems Within the Gas-prone Late Cretaceous Sequences of Western Pakistan: Influence of Regional and Local Tectonic Controls in a Pre-Collisional Margin Setting

Khan, Abdul Salam¹, Gilbert Kelling², Akhtar Mohammad Kassi³, Mohammad Umar¹, Mohammad Afzal Kakar¹ (1) University of Balochistan, Quetta, Pakistan (2) Keele University, Staffordshire, England (3) University of Balochistan, Quetta,

Sand-rich Late Cretaceous (Campanian -Maastrichtian) formations in the Sulaiman and Kirthar foldbelts of western Pakistan were deposited on the north-facing passive margin of the Indo-Pakistan continent. These sequences mark a major influx of coarse terrigenous clastics and formed in a range of environments from fluvio-deltaic to deepwater slope and basin-floor. Two partly coeval depositional systems occur in the Kirthar foldbelt. Deposits of the northern system formed on a storm and flood dominated clastic ramp whereas the southern system is dominated by channelised and lobate sand-bodies formed within confined slope-basins. Late Cretaceous clastics are absent from the northernmost Kirthar foldbelt (Khuzdar- Quetta). Here, thin coeval shelf carbonates include numerous diastems, reflecting deposition on a long-lived palaeobathymetric high, the Paleo-Jacobabad Mari Arch. Late Cretaceous sequences in the eastern sector of the Sulaiman foldbelt represent fluvial to shallow marine settings, associated with northwesterly progradation of a major delta, while coeval sequences in the western part of the Suleiman foldbelt represent outer shelf and submarine slope settings. Here, thick slumped units and large olistoliths of Turonian-Campanian limestone attest to collapse and rapid subsidence of the local margin. These sequences thin southwestwards, towards Quetta, and are replaced by volcaniclastic turbidites and debrites, formed on slopes around a large submarine volcano. The distribution, composition and architecture of these Late Cretaceous clastics have been strongly influenced by regional and local tectonic factors (e.g. ophiolite obduction, thermal uplift of the Indian Shield, inherited basement lineaments, etc.) and their specific effects on this evolving margin will be discussed.