Sulfurized carbohydrates: an important sedimentary sink for organic carbon?

In contrast to the general belief that carbohydrate carbon (C-CHO) is prefe rentially degraded and is not extensively preserved in the sedimentary reco rd, it is shown here that C-CHO forms a large fraction of the organic matte r (OM) of the total organic carbon (TOC)-rich upper Jurassic Kimmeridge Cla y Formation as a result of early diagenetic sulfurization, a previously unr ecognized pathway of OM preservation. This is evident from both changes in the molecular composition of the insoluble OM and from delta(13)C(TOC) shif ts Of 6 parts per thousand With varying CCHO contents. Furthermore, experim ents simulating the natural sulfurization of the CCHO-rich alga Phaeocystis spp. demonstrated that sulfurization can indeed lead to a substantial pres ervation of C-CHO With a molecular fingerprint identical to that of the Kim meridge Clay and many other Recent and ancient marine OM-rich sediments. Th ese results imply that preservation of CCHO can exert a fundamental control on delta(13)C(TOC) in OM-rich sediments, complicating the interpretation o f delta(13)C(TOC) records with regard to estimating terrestrial versus aqua tic OM fractions, reconstruction of past atmospheric CO2 levels and global carbon budget models. (C) 1998 Elsevier Science B.V. All rights reserved.