BACTERIAL AND ALGAL MARKERS IN SEDIMENTARY ORGANIC-MATTER DEPOSITED UNDER NATURAL SULFURIZATION CONDITIONS (LORCA BASIN, MURCIA, SPAIN)

Free lipids, sulphur-bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early d iagenetic carbonates replacing gypsum from a Messinian sequence of Lor ca Basin. The high abundance of phytane, 2,3-dimethyl-5-(2,6,10-trimet hylundecyl)thiophene, mid-chain C-20 isoprenoid thiophenes and bithiop henes and bis-O-phytanyl and O-phytanyl-O-sesterterpanyl glycerol ethe rs indicates that the organic matter in all these samples was deposite d under hypersaline conditions. The isopranyl glycerol ethers are esse ntially found in the sulphur-bound macromolecular matter which contras ts with the low concentrations of these compounds as free lipids. Howe ver, the distributions of these isopranyl glycerols is paralleled by t he occurrence of free phytanic acid (shales and laminated carbonate) a nd 3,7,11,15,19-pentamethyleicosanoic acid (only in the laminated carb onate). The bacterial inputs are represented by 2-hydroxytetracosanoic acid, n-octadec-11-enoic acid, hopanoic acids and the distributions o f iso-and anteiso-C-15 and C-17 homologues and minor amounts of iso-C- 16 and anteiso-C-14. These branched fatty acids are characteristic of sulphate-reducing bacteria. The relative proportions of the iso-and an teiso-compounds in the total fatty acid distributions are correlated w ith the proportion of reduced sulphur in the sediments. (C) 1997 Elsev ier Science Ltd.