Natural sulfurization of carbohydrates in marine sediments: consequences for the chemical and carbon isotopic composition of sedimentary organic matter

Abstract

Carbohydrates make up the largest part of the organic matter in the biosphere and are used by living organism for many different reasons. They serve, among others, as carbon and energy source as well as metabolic intermediates. Carbohydrates are generally thought to be remineralized during early diagenesis in the water column and in the sediment and thus not preserved in substantial amounts. However, earlier studies have suggested that preservation of carbohydrates through sulfurization could be possible and may be an important pathway for the preservation of sedimentary organic matter. In theory, preservation of carbohydrates through sulfurization would have a significant impact on total organic carbon (TOC) as well as the carbon isotopic composition of the TOC (8 13CTOc) records and could, for example, explain the large variations in both records observed in the Upper Jurassic Kimmeridge Clay Formation (KCF). However, it is still unclear to what extent carbohydrates can be preserved in sedimentary organic material and what the consequence of a substantial preservation of carbohydrates is for the chemical composition of the TOC. Its consequences for the 8l3CTOC record are also unclear since hardly anything is known about the variation in isotopic compositions of carbohydrates in natural systems. The primary goal of the work described in this thesis is to test the hypothesis that preservation of carbohydrates through sulfurization may be an important pathway for the preservation of organic matter and, if so, to determine what the consequences for the TOC and 813CTOC record will be.