Pdf Download stratigraphy of Pakistan GSP memories Vol 22 by S.M. Ibrahim Shah Government of Pakistan.
Table Of Content
Message of the Advisor to the Prime Minister, Government of Pakistan, Ministry of Petroleum and Natural Resources
Foreword, Secretary, Government of Pakistan, Ministry of Petrolcum and Natural Resources
Preface, Director General, Geological Survey of Pakistan
Prologuc
Contents
SEDIMENTARY BASINS OF PAKISTAN
Tectonics of Pakistan
Indus Basin
Axial Belt
Balochistan Basin
Himalayan Tectonostratigraphic Basin
Kohistan island arc
Karakoram-Hindukush Tectonostratigraphic Basin
PALEOGEOGRAPHY
PRECAMBRIAN
Indus Basin
Indian shield
Lower Indus Basin
Nagar Parkar igncous complex
Upper Indus Basin
Kirana complex
Hachi group
Kirana group
Taguwali formation
SEDIMENTARY BASINS OF PAKISTAN
Sedimentary basin is defined as “Geologically depressed area with thick sediments in the interior and thinner sediments at edges”. This definition is precisely applicable on present day configuration of Indus and Balochistan basins, where stratigraphic sequence is normal and stratigraphic record is not much influenced by tectonic activities. On the other hand, the intervening arca between Indus and Balochistan basins affected by tectonism shows only a linear representation of different attenuated stratigraphic units of both the basins and is called Axial Belt. Similarly, ‘Northern Montane Area’ lacks any true form of sedimentary basin. With this situation in the later two arcas, most workers do not use the word basin, but describe the stratigraphy, where applicable, under various terms like province, block, belt, domains, zones, island are, folded belt, thrust belt, complexes, ridges, terrane, valleys and ranges. Very few workers used the term ‘Basin’ but probably as an informal term, as for example “Peshawar Basin”, “Hazara Basin” etc. Therefore, these areas with sedimentary fill do not conform to the strict sense of sedimentary basin, nevertheless, in one form or the other stratigraphy is there and workers have described it. Stated in other way, originally these haphazardly placed sediments were deposited in a true sedimentary basin but most of them away from their present day situation under different latitudes and longitudes. Now these units are accumulated at one place with long history of tectonism.
As for example, the filled up original basins of “Northern Montane Area”, West Himalaya was subjected to opcirogenic and orogenic movements. The orogenic movement triggered by plate tectonic activities brought in, interalia, heat and upheaval, which obliterated the original sedimentary basins beyond all repairs. Ultimately, the present day scenario presents the area as buckled, folded and faulted with nappe and thrust sheets and warped in a manner of alternating basins and swells. As for example, the southern part of the Himalayan Tectonostratigraphic basin contains, parautochthonous units characterized by folds and wedge structures directed towards south. Compressional forces, post-dating the nappe movements produced, steepening of the beds, steep reverse faults and thrusts, in this region, it is a characteristic of the nappe that their aerial extent shows much variation along the strike. Because of their sheet like form, nappe are eroded in axial culmination and are preserved in depressions, imposing a prerequisite of tectonostratigraphic resolution before the stratigraphy of basin and ridge like structures is worked out. The parautochthonous units override the Tertiary belt along a rather straight thrust line Main Boundary Thrust (MBT), also called Murree Thrust as noted by Fuchs (1982). Displacement in some of these nappes and other faults as measured or indicated, from the Indian side of the basin, is of the order of several kilometres.
Further, north, alien stratigraphic sequences, belonging to different interacting continental plates form a collision zone. Here, presence of abnormal stratigraphic sequences is a common feature. In the entire northern area including Chitral, Gilgit and Hunza, large-scale allochthons are present, which thrust over the apparently normal stratigraphic section, at various places also pinching of the formations, crushing of the strata are seen on the ridges as well as in the valleys.
