POSSIBLE ALGAL ORIGIN OF LONG-CHAIN ODD N-ALKANES IN IMMATURE SEDIMENTS AS REVEALED BY DISTRIBUTIONS AND CARBON-ISOTOPE RATIOS

A Pliocene oil shale (Pula, Hungary), a C-3 plant Triticum aestivum an d a C-4 plant Zea mays were compared using isotopic composition of bul k organic matter, along with distributions and individual carbon isoto pe ratios of n-alkanes from organic extracts. The microalga Botryococc us braunii (A race) was thus shown to be the main source of the predom inant 27, 29 and 31 n-alkanes of Pula sediment Therefore, the dominanc e of odd carbon-numbered n-alkanes in the range C-25-C-35 in extracts from immature sediments shall not be systematically assigned to higher plant contribution but algal input is also possible. In fact, the lon g chain n-alkanes with an odd predominance previously observed in extr acts of various immature sediments are likely to be derived at least p artially, from algae.