Hydrogen-pyrolysis/biomarker analysis of organic matter composition in Ganges-Brahmaputra Delta sediments

Andrew R. Zimmerman University of Florida – Department of Geological Sciences
Siddhartha Mitra, Department of Geological Sciences, East Carolina University

The Ganges-Brahmaputra (GB) River complex delivers more sediment to the ocean than any other river system and is also a globally significant contributor of organic carbon. About half of the river’s sediment is intercepted by a submarine channel and dispersed to the deep-sea Bengal Fan, about half is deposited on the prograding shelf clinoform, and a smaller amount is transported back onshore by flood-dominated tidal currents.  Biomarker studies have found that Bengal Fan sediment organic matter (OM) is predominantly terrestrially-derived and buries this OM with extremely high efficiency (as suggested by constant ratios of OC to Al/Si, ie. OM-mineral surface loadings, from river to Fan sediments. If true, the GB presents a strong contrast to the ‘OM incinerator’ of the Amazon Fan which exchanges terrestrial for marine OM upon entering the marine environment and remineralizes much of this OM. The distinct character of the GB system as a terrestrial OM ‘burial machine’ may be due either to its large component of refractory OM, to unique physical/sedimentolgical processes occurring on this continental margin, or to a lack of understanding due to under-sampling, particularly in the sub-aqueous GB Delta.

The goal of this research is to understand the OM composition and diagenetic processes in the sub-aqueous delta region of the GB inner shelf. We use a biomarker/stable isotopic approach to examine the labile OM portion of GB river and shelf surface sediments for evidence of marine OM and diagenetic processing and hydropyrolysis and black carbon analysis to provide compositional and source information on the refractory and macromolecular OM component of these sediments.