Sedimentation Pattern of Piedmont Alluvial Fan in Sub-mountainous Siwalik Hill Tract of Punjab

摘要

The piedmont zone, located between the foot hills of lower Siwalik Himalayas and the plains in northwest of Punjab is elongated from north east to south east and its average height varies from 250 to 350 m above mean sea level. Based on the interpretation of satellite imageries along with toposheets of the area, in conjunction with ground truth checking i.e. relief, slope and drainage characteristics, the study area was divided into three physiographic units viz., fan head, middle fan and toe fan. The varying distribution patterns of sediments from different units of the alluvial fan in the piedmont plain of lower Siwalik hills were studied and it has been observed that alluvium was heterogeneous in constitution (sand to boulders). The size of sedimentary particles decreased from the fan head or apex towards the fan tail or toe. The total sand content was maximum in fan head soils with weighted mean (WM) = 89.8% followed by middle fan soils (WM = 88.5%) and toe fan soils (WM = 83.2%). The coarse sand content and fine sand content followed the opposite trend, whereas medium sand content did not show any uniform trend. Coarse sand content decreased from fan head soils (WM = 48.2%) to toe fan soils (WM = 34.8%) and fine sand content increased from fan head soils (WM = 20.5%) to toe fan soils (WM = 39.3%). The silt content also showed an increasing trend from fan head soils (WM = 1.9%) to toe fan soils (WM = 6.4%). The clay content was almost similar in fan head (WM = 8.3%) and middle fan (WM = 8.1%)soils and increased in toe fan soils (WM = 10.5%). The soils of the fan head contained medium to very coarse sized abundant gravels and stones (46.8%) in surface horizon. The content of gravels and stones decreased drastically both in the surface as well as sub-surface horizons of middle fan and toe fan soils. The studied pedons from different units of the alluvial fan did not show development of any surface or sub-surface diagnostic horizons and had A-C profiles only and as such qualified for Typic Ustifluvents according to Soil Taxonomy.