Abstract:
The Upper Cretaceous Bibai Formation is exposed in Kach-Ziarat and Spera Ragha-Chinjun valleys and near Muslimbagh, within the western part of the Sulaiman Thrust-Fold Belt. The formation generally comprises basic volcanic rocks, volcanic conglomerate and breccia, sandstone, mudstone and ash beds. Within the Kach-Ziarat valley it is dominantly composed of volcaniclastic sediments and rarely lava flows, while, within the Spera Ragha-Chinjun valley dominantly the in-situ basaltic volcanic rocks. Volcaniclastic succession of the Kach-Ziarat valley may be categorized into various facies like volcanic conglomerate (VC), volcanic breccia (VB), sandstone(SS), sandstone rhythmically interbedded with mudstone (SSMS), mudstone (MS), limestone(LS) and lava flows (VOL).. These facies posses characters which indicate deposition by sediment gravity flows and slumping. Volcanic conglomerate and sandstone (VC-SS) association of facies, their stacking pattern, erosive bases and fining-upward trends suggest deposition within a channelized complex anastomosing on a submarine fan system. The SSMS facies of sandstone rhythmically interbedded with mudstone, is characterized by grading, Bouma Tabcde, Tbcde, Tcde and Tde sequences, sole marks, soft sediment deformation, pinch-and-swell and general thinning-and fining-upward trends of 2nd-order-cycles. It indicates deposition by turbidity currents in overbank (-levee) complex between channels. The mudstone (MS) facies, possessing occasional thin sandstone and siltstone beds in lower part and profusion of shallow marine fauna in upper part, indicate deposition in lower fan/basin plane conditions and also an overall shallowing-up trend of the succession. Limestone (LS) facies, interbedded with volcaniclastic facies in lower part of the formation, is very finely crystalline (bio-micritic) possessing foraminifera of the Globotruncana family suggest deposition during calm periods when gravity flows had been suspended intermittently. Paleocurrent pattern indicate a south-southwest paleo-flow direction and a source area to the north-northeast of Bibai Peak. Based on characters of various facies associations, their vertical and lateral organization, paleocurrent pattern and composition of detritus, it is proposed that the Bibai formation comprises a special category of “channel (-levee) –overbank complex”, we name it the Bibai Submarine Fan, which developed on the slope of a series of seamounts (hotspot volcanos). Lithofacies and their associations clearly define the mid-fan, overbank (-levee) and lower-fan basin plain components of the submarine fan. Seamounts developed on sea floor of the northwestern margin of the Indo-Pakistan Plate, which later on emerged and provided detritus to the Bibai Submarine Fan. It is proposed that the present trend of paleocurrents, generally sourthward, has been rotated anticlockwise along with the north and northwastward drift and anticlockwise rotation of the Indo-Pakistan Plate towards Eurasia during the Upper Cretaceous and later periods till present time. Its clockwise rotation back to its Upper Cretaceous (71.4±3.4 My) position would give its original west-northwestward paleoslope at the northwestern margin of the Indo-Pakistan Plate.
Page(s):
1-24
DOI:
DOI not available
Published:
Journal: Acta mineralogica pakistanica, Volume: 11, Issue: 1, Year: 2000