Pakistan Research Repository

THE GENESIS OF THE QUATERNARY DEPOSITS OF THE VALE OF PESHAWAR, SOUTH OF KABUL RIVER

Khan, Inam Ullah (1990) THE GENESIS OF THE QUATERNARY DEPOSITS OF THE VALE OF PESHAWAR, SOUTH OF KABUL RIVER. PhD thesis, University of Peshawar, Peshawar.

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Abstract

The vale of Peshawar is located in the youngest collision zone in the north-west of Pakistan. It remained a locus of various tectonic and geomorphological activities throughout its geological history. The present bas in which was filled in with a variety of sediments, during the Quaternary period has been carved out of Tertiary mountain system as a result of long phase of erosion which lasted for about 15 to 19 m.y.s. The study area which is located south of the river Kabul forms an integral part of the vale and possesses a complete record of such tectonic and geomorphological episodes which are preserved in various litho-stratigraphic units and exposed in different sections along the channels of present torrents, draining the northern slopes of the Attock-Cherat range. The study shows that the Pleistocene glaciations had a direct influence over the climate and geomorphological pattern of the vale, which resulted in the establishment of such morphogenetic conditions that remained in tune with the changing climate pattern of the interpretation of lithological characteristics of different beds, it was possible to identify four major facies, e.g. lacustrine, flood plain, alluvial fan and Aeolian (loess). The oldest sediments (Lower Pleistocene) of the value are exposed on the croded bed rock of Murree formation of Miocene age at Garhi Chandan, south of Peshawar city. These sediments are composed of lacustrine and over-bank and channel facies of Kabul river. Vast deposits of volcanic ash, dated as 2.7+-0.3 m.y. are embedded in these sediments and considered contemporaneous to the Soan Formation of the Potwar plateau. These deposits are overlain by the material of older fans with an erosional unconformity which on the Lei Conglomerate Complex of the Potwar plateau. Evidence suggest that the vale was transformed into lakes at least four times during the Pleistocene due to different causes. In the first two phases, lakes were formed as a result of the effect of tectonics, while the latter phases seem to occur due to the northward prograding Younger alluvial fans in two phases which blocked the flow of Kabul river. The various erratic blocks lying along the northern foot-slopes of the Attock-Cherat range are suggested to be deposited on the lake bed by the floating ice blocks during one of the stades of the Middle Pleistocene. The geomorphological behaviour of Kabul river appears to be controlled by the oscillating climate as well as by the tectonic events which also resulted in the draining of the lakes. Due to the lowering of local base level, Kabul river started aggradations by building its flood-plain. Near its outlet from the mountain, it behaved like a braiding stream. In the main vale, water in excess of channel capacity resulted in over-bank deposition while the migrating slow moving meandering channel developed point bar facies during which huge amount of sand was deposited in the vale on a very large area. Besides the deposition of glacio-fluvial material, the vale also received a large amount of sediments, released by the slopes of the Attock-Cherat range deposited as facies of alluvial fans. Their formation seems to be triggered by suitable climate conditions as well as by rapid uplift of the Attock-Cherat range. Their deposition appears to be contemporaneous with climate amelioration as is evidenced by the formation of different soil horizons and growth of rich vegetation on the fan material. It may be noted that each of these phases of deposition in the vale was followed by a phase of erosion in order to achieve a profile of equilibrium. There are evidence to believe that during the Plesistocene, loess was deposited in the vale in three phase. The earliest two loess are found embedded in the first and second lake phases, while the third (youngest) loess appears to blanket the entire topography during the late phase of the upper Pleistocene. The detailed analyse of mineral and physical characteristics of the loess Peshawar vale, suggest it to be as rock flour produced by the grinding action of glaciers in the northern provenance during glacial advance. This material was deposited by the winds during the glaciations phase in warm dry/semi-dry climatic conditions with occasional wet spells. This is indicated by the development of soil horizons, the deposition of recent gravels and lenses of sand within the loess. The Holocene is marked by a large scale erosion of loess, the piedmont and the development of badland topography. There is also evidence to suggest that the vale is presently passing through a phase of aggradation

Item Type:Thesis (PhD)
Uncontrolled Keywords:Quaternary deposits, Peshawar, Peshawar Vale, Geomorphological studies, Geology, Pleistocene, Holocene, Tectonic, Geomorphological activities, Geological history, Basin, Sediments, Teritary mountain, Lito-stratigraphic, Attock-Cherat, Pleistocene glaciation, Climatic pattern, Glacial Himalayes, Lacustrine, Flood plain, Alluvial fan, Aeolian (loess),
Subjects:Social Sciences(g) > Geography (g7)
ID Code:255
Deposited By:Mr Ghulam Murtaza
Deposited On:17 Jun 2006
Last Modified:04 Oct 2007 21:00

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