FIRST EXAMPLE OF AN ALGAENAN YIELDING AN AROMATIC-RICH PYROLYSATE - POSSIBLE GEOCHEMICAL IMPLICATIONS ON MARINE KEROGEN FORMATION

Non-hydrolysable macromolecules were isolated from the marine green mi croalga Chlorella marina where they represent ca. 5% by weight of the dry biomass. Such resistant biomacromolecules, termed algaenans, were previously identified in numerous microalgae (mostly comprising freshw ater species) and they were shown to play a major role in the formatio n of a number of source rocks and oil shales via the selective preserv ation pathway. Scanning and Transmission Electron Microscopy revealed that the algaenan of C. marina is located in the cell wall but is comp letely amorphous once isolated. All the previously studied algaenans w ere also cell wall constituents but they always retained some morpholo gical features of the initial walls. Another conspicuous difference wa s also observed regarding chemical structure. In agreement with spectr oscopic observations, the pyrolysate of C. marina algaenan is sharply dominated by compounds comprising various aromatic units whereas all t he so far studied algaenans appeared highly aliphatic and based on lon g polymethylenic chains. As a result, the selective preservation of al gaenans could not be restricted to the formation of aliphatic sediment ary organic matter. In fact, it can be anticipated that some aromatic fractions of kerogens should also be derived from such a pathway, as s uggested in recent studies. Copyright (C) 1996 Elsevier Science Ltd