EVOLUTION OF THE LOWER GANGETIC PLAIN LANDFORMS AND SOILS IN WEST-BENGAL, INDIA

Three major landforms, Uplands, Old Fluvial/Deltaic Plains and Young F luvial Plains are identified from the Lower Gangetic Plains of West Be ngal, India, on the basis of remote sensing and field studies. Morphol ogic, quantitative and thermoluminescence studies of soils of the stud y area have been conducted. Two types of Uplands are recognised: Uplan d in the west overlain by red soils (autochthonous and allochthonous t ypes) and upland in the north (Barind Tract), characterised by three t opographic levels. Aspects of the autochthonous Upland Red Soils (Lowe r to Middle Pleistocene age) show the ferrugination (ferrisol) phase o f development. Soils of the Old Fluvial/Deltaic Plains (6-3 ka) and Lo wer Level of the Barind Tract have argillic horizons and exhibit the f ersiallitisation phase of development. Development of ferrugination an d fersiallitisation phases was favored due to the pre-weathered nature of the parent material. Soils of the Old Fluvial/Deltaic Plains, Bari nd Tract (Lower Level) and Young Fluvial Plains show effects of hydrom orphism due to waterlogging in the form of segregations of Fe-Mn oxide s/gleying and chloritisation, probably due to ferrolysis in the upper horizons of some of these soils. Neotectonics seems to have affected d evelopment of landforms and soils significantly. Due to reactivation o f some basement faults in the western region, some tectonic blocks sub sided, causing transgression during the Early Pleistocene and at ca. 7 ka. Subsequent uplift of these blocks caused regressions and developm ent of soils on the exposed landscapes. Episodic uplift of the Barind Tract in the northern region may have given rise to three topographic levels. Some faults confine the courses of the Damodar, Ganga and Bhag irathi rivers. (C) 1998 Elsevier Science B.V. All rights reserved.