Absolute Dating of Recent Sediments in the Cyclone-Influenced Shelf Area off Bangladesh: Comparison of Gamma Spectrometric (137Cs, 210Pb, 228Ra), Radiocarbon, and 32Si Ages

Abstract

A geochronological survey of the Bengal shelf area involved results from more than 20 sediment cores dated using gamma spectrometry and the nuclides 137Cs, 228Ra, 226Ra, and 210Pb. In some cores, which contained older sediments, 32Si and 14C were determined to examine the possibility to extrapolate the obtained chronologies to century and millennial scale. Geochronological work in this region is faced with problems of cyclone-induced sediment reworking, grain-size effects on fallout nuclides, scarcity of carbonates, unknown 14C reservoir effect and sedimentation rates that are too high to obtain sediment cores long enough to establish a chronology. Despite these problems, comparison between the results of the different dating methods provided the most reliable sediment balance to date for the submarine delta of the Ganges-Brahmaputra river system and indicated that on a time scale of several centuries at least 35% of the annual sediment load is deposited.