STUDIES ON THE LANDFORM DEVELOPMENT AND QUATERNARY GLACIATIONS IN NORTH PAKISTAN
Li Ji-jun Xu shu-ying (Lanzhou University)
The landform development and Quaternary Glaciations in Northern Pakistan are of great significance to the Pleistocene Chronology and Geomorphology of High Asia. Based on the data collected during our visiting Pakistan in 1981, two main erosion surfaces are identified in the piedmont belt of the Himalayas. One is the Potwar Plateau, with an average elevation about 500 meters, and the other a dissected planation surface at an elevation about 1,600m above sea level They are progressively younger from north to south, ranging from 1.5 M. Y. B. P. to 0.4 M. Y. B. P. This reflects the southward expansion of the rising Hima-layas. As an erosion surface, the Porwar Plateau ought to having been formed before that time, probably of early Pleistocene Age. The 1,600 m surface is situated north of Potwar Pla-teau and possibly of Pliocene Age, because it trunctes the Murree Series (N1) and is dis-sected by a mature broad valley system which plunges into Potwar plateau Surface south-ward. The paleomagnetic data of the Late Cenozoic sediments obtained both from the inte-rior part of the Qinghai-xizang Plateau and the foot hills of the Himalayas show that the violent uplift of the Himalayas and Qinghai-xizang Plateau as a whole has been taken place proximately since the beginning of the Quaternary. Chief morphological events in Hunza Valley are as follows: (1) A planation surface developed after the intruded Karakoram granodiorite bearing a Rb/Sr dating age of 8.6 M. Y. B. P. Only small fragments of this surface can now be found on the tops of the Karakoram, while its equivalent is well preserved in the piedmont belt of the Himalayas (1, 600 m surface). (2) Strong uplifting took place on the turn between the Tertiery and Quaternary, ushered in a downcutting period. The 4,200 m Patundas Surface could be correlated to Bot-war plateau Surface, and thus both are of Early Pleistocene Age. (3) Then followed by successve upheavals and incisions by the Hunza River and its tributaries, the landscape was transformed into ragged mountians and deep gorges. We can recognize four glaciations in the Hunza Valley during Pleistocene Period. The known earli-est glaciation seems to be of semi-covered type, followed by two main trunk valley glacia-tions which ocurred before 139,000 yr. B. P. (TL). (4) The fourth glaciation in the Hunza Valley has rather a small dimension. Glaciers often advanced into the main valley and blocked it here and there, but they had never jo-inted together into a trunk valley glacier. The Minapin Glacier advanced about 47,000 yrs ago (TL), and glaciers in Pasu area advanced in twice in Last Glaciation. (5) After the optimum period in Holocene, began the neoglaciation and ice advances .are bracketted by C14 dates of 2,265 ?65, 685 ?45 and 325 ?60 yr. B. P.