Alternative biological sources for 1,2,3,4-tetramethylbenzene in flash pyrolysates of kerogen

Pyrolysates of kerogens isolated from Indian Ocean surface sediments and from Black Sea Unit II contain abundant 1,2,3,4-tetramethylbenzene (1,2,3,4-TMB) suggesting the presence of macromolecularly-bound isorenieratane skeletons derived from isorenieratene biosynthesized by green sulphur bacteria (cf. Hartgers et al., 1994c). However, the 13C content of 1,2,3,4-TMB is identical to that of algal lipids, excluding an origin from green sulphur bacteria. The presence of 1,2,3,4-TMB in pyrolysates of stable residues of several marine algae indicates that it can also have an algal origin. Therefore, the assessment of photic zone anoxia on the basis of the abundant presence of 1,2,3,4-TMB in the pyrolysate is not possible without determination of its stable carbon isotopic composition and comparison with those of algal lipids.