Radiocarbon dating and sedimentation rates in the Holocene alluvial sediments of the northern Bihar plains, India

Abstract

Seven radiocarbon dates of carbonate shells and charcoal from the upper two metres of sediment in the Indo-Gangetic plains of northern Bihar, eastern India, can be divided into three groups, with the following approximate ages: 2400±45 a BP (two samples), 1100±45 a BP (four samples) and 765±45 a BP (one sample). This evidence for at least three episodes of sedimentation in the last 2400 a contrasts with evidence of greater ages from similarly near-surface sediments in the middle Gangetic plains of Uttar Pradesh, further west. In these more westerly areas, greater ages and well-developed river terraces point to much more restricted late Holocene sedimentation. Rates of net sediment accumulation calculated using our Bihar ages, spanning a period of the order of 103–104 a, are similar to those calculated for periods of the order of 105–106 a for the Himalayan foreland basin. This suggests that, in the whole basin case, short-period rates higher than the Bihar rates have been compensated by longer than Bihar periods of non-deposition or erosion.