Origin and formation pathways of kerogen-like organic matter in recent sediments off the Danube delta (northwestern Black Sea)

The chemical structure, source(s), and formation pathway(s) of kerogen-like organic matter (KL) were investigated in recent sediments from the northwe stern Black Sea, off the Danube delta. Three sections from a sediment core collected at the mouth of the Sulina branch of the delta, under an oxic wat er column, were examined: S-0 (0-0.5 cm bsf), S-10 (10-13 cm bsf), and S-20 (20-25 cm bsf). The bulk geochemical features of these sediments (total or ganic carbon, organic C/N atomic ratio, delta C-13(org)) were determined. T hereafter, KL was isolated from the samples, as the insoluble residue obtai ned after HF/HCl treatment. KL chemical composition was investigated via sp ectroscopic (FTIR, solid state C-13 and N-15 NMR) and pyrolytic (Curie poin t pyrolysis-gas chromatography-mass spectrometry) methods, and the morpholo gical features were examined by scanning and transmission electron microsco py. Similar morphological features and chemical composition were observed f or the three KLs and they suggested that the selective preservation of land -plant derived material as well as of resistant aliphatic biomacromolecules (probably derived from cell walls of freshwater microalgae) was the main p rocess involved in KL formation. Besides, some melanoidin-type macromolecul es (formed via the degradation-recondensation of products mainly derived fr om proteinaceous material) and/or some encapsulated proteins also contribut ed to the KL chemical structure. (C) 2000 Elsevier Science Ltd. All rights reserved.