HOLOCENE EVOLUTION OF THE WESTERN GANGETIC PLAIN, INDIA

Abstract

Western part of the Upper Gangetic Plain marked by upland interfluves and covered by moderately to well developed soils between Ganga and Yamuna Rivers have been taken up for detailed investigations. Although a number of studies in this particular area has been carried out but regional perspective from the point of view of style of deposition, soil formation and role of climate and tectonics responsible for shaping the present day landscape during the Holocene period is still missing. The present research is an attempt in this direction using latest techniques of remote sensing, GIS, luminescence dating, morphological studies of soils in the field and Ground Penetrating Radar (GPR) studies across the faults - . ^ catrsfwi ou:. Different soil-geomorphic units (river flood plains, aeolian ridges, terminal fans, palaeochannels, piedmont plain, plains associated with rivers and plains) were identified using the above techniques. Three major blocks, piedmont block in the north, the Muzaffarnagar- Meerut (Old Ganga-Yamuna Plain) Block further south and Mainpuri Block hqv«- (Ganga-Yamuna Interfluve) Block in the south nas been recognized. Further 33 soil-geomorphic units were identified, which are grouped into five morphostratigraphic sequence members viz. QGMS-I to V(with ages <1.7, 1.8- 3.6, 3.6-6.5, 6.5-9.6, >10 ka, respectively). Soil morphological characters of soils of QGMS-I and II show apedal to weak pedality nature, whereas QGMS-I11 to V shows moderately to well developed pedality. Sixteen faults (3-longitudinal and 13-transverse) are identified through remote sensing satellite image analysis and Geographical Information System

techniques by creating digital elevation models and geomorphic evidences. Longitudinal faults (Ganga and Yamuna system of faults) are curvilinear in nature and transverse faults are nearly normal or at large angles to the former. Parkash et al. (2000) modeled the stress pattern in the region and suggested that the longitudinal faults were formed by compression from the southwest. Thus, transverse faults formed in an extensional regime perpendicular to the compressional regime and are steeply dipping normal faults. The downthrown sides of the transverse faults are towards south and east in the northern and southern regions of the study area, respectively with the exception of the Fatehpur fault and Aliganj-Mainpuri fault with the downthrown block to the west and northwest, respectively. The transverse normal faults in the northern region are in the third stage of development while those in the central and eastern part are in the first and second stages of fault development respectively (Gawthorpe and Leeder, 2000). Ground Penetrating Radar studies along Muzaffarnagar (transverse) and Solani-ll (longitudinal) faults indicate that the major fault is always associated with numerous small faults in the downthrown block and most of the faults are steeply dipping normal faults at least up to a depth of 20 m. Activities along the transverse normal faults have led to the deposition of the terminal fans on the downthrown blocks mainly on the Ganga-Yamuna interfluve. Repeated activity along the transverse normal faults followed by periods of stability led to the formation of sequences of terminal fan deposits consisting of small deposits topped by soils. Similar sequences of deposits were also observed in the vertical sections along the bounding Ganga and Yamuna Rivers, inland Sengar River and also in the shallow (<50 m) boreholes within the IV interfluve, which suggests that marginal parts of the interfluve (<14% of the total interfluve area) were inundated by the large rivers only for short intervals during the Holocene, deposition was mainly in the form of terminal fans formed by the activity of the transverse normal faults.