Depositional Environments and Reservoir Assessment of Late Cretaceous Sandstones in the South Central Kirthar Foldbelt, Pakistan

Abstract

Sandstones of Late Cretaceous (Campanian-Maastrichtian) age constitute much of the Pab and Mughal Kot Formations, which are well exposed in western Pakistan. In the south central part of the Kirthar foldbelt, these units attain thicknesses ranging up to 350m and are dominated by quartzose sandstones with subordinate argillites and marls, all deposited on the western continental margin of the Indo-Pakistan Plate. Seven sedimentologic logs, measured through this sandy sequence along a strike-wise extent of some 290 km, provide new data on the palaeoenvironments and dispersal patterns represented in these rocks and on their reservoir potential.The eight main facies were formed by a range of sand-transporting mechanisms that includes classical turbidity flows, storm-and river flood-generated underflows, high and low-energy tractional flows, storm-and fair weather wave reworking, and local slope failure and remobilisation. The four facies associations comprise a Shoreface Association, a Shelfal Delta Lobe Association, a Deeper Shelf/ Ramp Association (the distal equivalent of the Shelfal Delta Lobe Association), and a deep-water Submarine Fan Lobe Association.Facies distributions and palaeoflow patterns demonstrate the existence of two depositional systems in this area during the Late Cretaceous. Sandbodies formed in a NW-prograding submarine fan dominate a southern system, while in the north of the study area, storm-and river flood-influenced shelfal sands were conveyed to the west and WNW. Here, sediment-gravity flows evolved from east to west, following a broadly across-shelf pattern from cross-bedded sandstones to graded turbidites. Sandstone petrography suggests supply from the uplifting Indo-Pakistan Shield to the east, feeding a broad, west-facing shelf or clastic ramp characterised by Mutti-type "shelf-lobes". At outcrop, these sandstones possess low porosities but other reservoir characteristics (total sand thickness, percent sand, vertical and lateral connectivity, Late Cretaceous sandstones, South Central Kirthar Foldbelt, Pakistan 374 etc.) are closely linked to dominant facies types and their inferred paleoenvironments. Using these attributes, sandstones formed in the western, mid-shelf, settings of the northern system display the most promising reservoir properties.

Signatures of Late Neoproterozoic Gondwana assembly and Maronian glaciation in Lesser Himalaya: a palaeogeographical and stratigraphical approach

“…The beds are characterized by regular and laterally continuous geometry at outcrop scale. The limited extent of this facies and its occurrence with parallel-laminated and cross-bedded sandstones suggest its origin during alternate calm intervals (Umar et al 2011a;Khan et al 2002).…”

“…A number of processes may be responsible for slumping at this scale (Lewis 1971). Liquefaction, steep gradient and rapid deposition on slopes can trigger slumping of sediments (Umar et al 2011a, b;Khan et al 2002). The local preservation and complete absence of this facies in most of the measured sections suggest its origin either by slumping along a channel margin or an over steepened part of the slope.…”

“…7B). Largescale cross-bedding and hummocky cross-stratification indicate deposition during strong traction flows under high velocity conditions (Collinson et al 2006), such as those produced by storm-or river-induced currents (Khan et al 2002).…”

Contrasting Late Cretaceous–Palaeocene lithostratigraphic successions across the Bibai Thrust, western Sulaiman Fold–Thrust Belt, Pakistan: Their significance in deciphering the early-collisional history of the NW Indian Plate margin

“…On the basis of the foraminiferal assemblage reported from its type locality (in the Kirthar Belt), Vredenburg (1908), Williams (1959) and Hunting Survey Corporation (1960) have assigned it a Late Maastrichtian age. Smewing et al (2002), Khan et al (2002) and Fitzsimmons et al (2005) have assigned Maastrichtian age to the succession of Pab formation.…”

The effects of diagenesis on the reservoir characters in sandstones of the Late Cretaceous Pab Formation, Kirthar Fold Belt, southern Pakistan

“…The formation was deposited on the tectonically controlled western margin of Indian Plate. Two contrasting depositional systems were identified (Khan et al, 2002;Umar, 2007), as shallow marine (Northern Depositional System) and fluviodeltaic to deep marine turbidites (Southern Depositional System). Three facies associations were identified as transitional from proximal to distal settings as shoreface, shelf delta lobe and deeper shelf facies associations in the Northern Depositional System.…”