Paleoenvironmental and tectonic reconstruction of the lower Eocene Ghazij Formation and related units, Balochistan, Pakistan: Implication for India -Asia collision
Formation and related units exposed along the transpressional suture zone of the western margin of the Indian plate preserve the oldest syntectonic deposits of initial India-Asia collision. Analysis of lithofacies, paleoflow directions, and sandstone petrography indicate that the process of deformation and uplift of the carbonate shelf along the western margin of the Indian continent was started as early as late Paleocene. This tectonic uplift and deformation is documented by several independent lines of evidence: (1) the overall shallowing upward synorogenic sequence of the Ghazij Formation and related units, (2) proximal conglomerate facies (consisting mainly of limestone clasts) dominate in the west, whereas distal facies of sandstone and shale dominate in the east, (3) paleocurrent directions indicate southeastward flowing sediment dispersal paths during late Paleocene-early Eocene time, opposite that found in the late Cretaceous, suggesting a reversal in the depositional slope of the Cretaceous shelf, (4) the existence of an unconformity at the base of the upper part of the late Paleocene-early Eocene Gidar Dhor Formation and newly interpreted Kach Sequence in the Quetta and Kalat regions, and (5) petrographic study of sandstones indicating a collision suture/fold thrust belt provenance for the Ghazij Formation and related units. These results corroborate structural and geophysical evidence for a late Paleocene-early Eocene age for initial India-Asia contact and contradict a late Cretaceous age based on faunal data and a late early Eocene to middle Eocene age based on sedimentary evidence from the Himalayan compressional suture zone in the north. The unroofing pattern and uplift geometry of the western Indian shelf suggests that India first collided in the southern part of the study area (Kalat-Khuzdar area) during the late Paleocene-early Eocene along a transpressional suture and proceeded northward in a time-transgressive fashion. Sandstones from the Ghazij Formation and related units lack continental crystalline material indicating the Afghan-Kabul blocks were sutured to Asia, not India, at this time. These new geological data also serve to strengthen the argument that recently discovered Ghazij fossil mammals record syncollisional dispersal into India.
Networked Digital Library of Theses and Dissertations