A HOLOCENE SOIL-CHRONOASSOCIATION AND NEOTECTONICS IN THE WESTERN GANGETIC PLAINS, INDIA

Abstract

Western Gangetic Plain, lying in the states of Uttar Pradesh, Haryana and Union Territory of Delhi, has been divided into thirteen soil-geomorphic units based on remote sensing techniques, field checks and laboratory investigations. The soil-geomorphic units are: Aeolian Plain, Old Yamuna Plain, Yamuna Floodplain, Lower Ganga-Yamuna Interfluve, Old Ganga Plain, Ganga-Ramganga Interfluve, Old Kosi Plain, Upper Ganga-Yamuna Interfluve, Ganga-Solani Interfluve, Younger Piedmont, Older Piedmont, Ganga Floodplain and Ramganga Floodplain. Field characteristics and laboratory data has been used to determine the degree of soil development on different geomorphic, which is further used to develop a soil-chronoassociation. Soils have been grouped into five members of a soil-chronoassociation QGN1 to QGN5, with QGN5 being the oldest. Soil of different geomorphic units included in different members are: QGN1 ( < 500 BP)- Floodplains of Ganga, Yamuna and Ramganga; QGN2 ( >500 - <2,500 BP) - Aeolian Plain, Old Yamuna Plain, Old Ganga Plain, Old Kosi Plain, Ganga-Solani Interfluve and Younger Piedmont; QGN3 (2,500 BP) - Upper Ganga-Yamuna Interfluve and Ganga-Ramganga Interfluve; QGN4 ( > 5,000 BP) - Older Piedmont; and QGN5 (10,000 BP) - Lower Ganga-Yamuna Interfluve. Tectonics seems to have controlled the shifting of rivers and evolution of soils and morphology in the area during the Holocene. A number of surficial faults, like the Ganga Fault, Yamuna Fault, Solani fault, Ratmau fault, and Ramganga fault etc. have been recognised from the study area. Some of these are not related to any known basement features. Both longitudinal and transverse type faults are present and these have been active at different times for varied periods during the Holocene, leading to shifting of rivers and upliftment or subsidence of large blocks. The Lower Ganga- Yamuna Interfluve, with pedogenic carbonates and a surficial layer of salts, represent a dry cold climate during 9,000 to 11,000 yr BP.