A new study highlights the significant influence that climate has had on erosion in the Himalayas in pre-historic times1.
Analysing sediment samples from the Ganga Plain from the campus of the Indian Institute of Technology Kanpur, geologists have found that there were two major excursions in the region coinciding with periods of precipitation minima and larger glacial cover (approximately 20 ka and 70 ka ago – ka is kiloannuam, a unit of time equivalent to 1000 years). These excursions were the result of a decrease in proportion of sediment from the higher Himalaya due to a decrease in monsoon precipitation and an increase in glacial cover that are in turn caused by lower solar insolation, the researchers say.
Sediment samples from a 50-m-long core pertaining to around 100 ka of deposition were analysed for strontium (Sr) and neodymium (Nd) isotope compositions.
Both samples had significant variation in core depth within the range for silicate rocks of the higher and the lesser Himalaya. The variations in the isotope compositions reflect variations in the mixing proportion of sediments from the higher and lesser Himalaya, the two major sediment sources to the Ganga. The opposite trends in their depth profiles further confirmed this hypothesis.
The authors of this study are from: Planetary and Geo-Sciences Division, Physical Research Laboratory, Ahmedabad, India; Engineering Geosciences Group, Indian Institute of Technology, Kanpur, India and Department of Geology, University of Delhi, India
