Lithofacies and Lateral Extension of latest Cretaceous Dinosaur beds from Sulaiman Foldbelt, Pakistan

Abstract

The Late Cretaceous Pab Formation consists of quartzose sandstone with subordinate muds, deposited on the western continental margin of Indo-Pakistan plate, is well exposed in the Sulaiman and Kirthar foldbelts, and coeval strata like upper part of Lumshiwal and lower part of Hangu Formation are also exposed in the upper Indus basin like Trans Indus, Salt Range, Kohat and Potwar regions. The Pab Formation of Dhaola Range of central Sulaiman foldbelt is divided. into three members namely Dhaola, Kali and Vitakri members. Vitakri member is the host of Latest Cretaceous (Maestrichtian) dinosaurs and other archosaurs from Sulaiman fold belt. Vitakri member or dinosaur beds will be used synonymous. Eight lithologic sections have been measured through the upper part of Pab Formation. Out of these, five lithologic sections across strike extent of some 80 km, and four (one is overlaping) lithologic sections along a strikewise extent of some 250 Km, provide new data on the depositional environments, lateral extention and depositional pattern of Latest Cretaceous dinosaur beds and their coeval sequences in the Sulaiman foldbelt. The four main facies of Latest Cretaceous strata of upper part of Pab Formation identified in the Sulaiman foldbelt are; Facies F1 (Trough cross and planner laminated/bedded sandstone), Facies F2 (Massive reddish brown to red muds), Facies F3 (Carbonaceous shale) and Facies F4 (Tabular/planner and trough cross bedded sandstone interlayered with the subordinate greenish grey and minor reddish brown muds). These facies formed by a range of sand transporting mechanisms that includes classical meandering and overbank flood flows, oxbow and crevasse splays lakes, storm and river flood generated flows, and high and low energy tractional flows. Three facies associations identified in the upper part of Pab Formation are, meandering river and overbank flood association well exposed in the southern part of central Sulaiman foldbelt, oxbow lake and Crevasse splays lacustrine association found in the Kingri area of northern part of central Sulaiman foldbelt, and alluvial deltafan beech association (mostly submarine and rarely subaerial) located in the Kaha-Harrand section of southern Sulaiman foldbelt and in the Musa Khel and Mughal Kot sections of the northern Sulaiman foldbelt. Facies association patterns demonstrate the existence of three depositional systems in the Sulaiman foldbelt during the Latest Cretaceous. Sandbodies with subordinate muds formed in westward prograding mostly submarine and partly subaerial dominate north and south systems, while the central system like meandering river and associated flood bank, oxbow and crevase'splays lacustrine environments deposited the sandstone, reddish brown muds, coal,carbonaceous shale and green muds in the central part of Sulaiman foldbelt. Quartzose nature of sandstone and paleoflow suggest supply from the uplifting Indo-Pakistan Shield to the eastward. Sediment gravity flow generally evolved from east-west. The Dinosaur beds/Vitakri beds thickness varying from 15 meter(m) to 35 m, is increasaing toward WSW and decreasing ENE directions. The lateral extension of Latest Cretaceous (Maestrichtian) dinosaur beds of the Pab Formation have been observed in major four anticlinorium named as Vitakri-Mari Bohri anticlinorium (Barkhan and Kohlu districts), Dhaola anticlinorium (Barkhan and Kohlu districts), Phulali anticlinorium (Barkhan, Dera Bugti and Kohlu districts) and Fort Munro anticlinorium (Dera Ghazi Khan and Rajan Pur districts). A model of meandering river named as D.G.Khan-Vitakri river forming lobate belt shape, flowing EW from Indian shield to Fort Munro, and flowing ENE to WSW from Fort Munro to Mari Bohri via Vitakri. The exposed strata of dinosaur beds (Vitakri member) of southern part of central Sulaiman foldbelt is surrounded by coeval strata like the lacustrine charged by overbank flood in the near north(Badhi and Kingri), mostly submarine and partly subaerial alluvial deltafan in the farther north (Musa Khel and Mughal Kot area), deltafan and shelf marine in west, deltafan in the south(Kaha-Harrand area), and terrestrial paleoland (and Indo-Pakistan Shield) in the east.