LONG-CHAIN ALKENONES AND ALKYL ALKENOATES AND THE FOSSIL COCCOLITH RECORD OF MARINE-SEDIMENTS

Long-chain (n-C37-C39) alkenones and alkyl alkenoates are biological markers for sediment inputs of algae from the Class Prymnesiophyceae, which includes the coccolithophorids. These compounds have been recognized in many recent and ancient marine sediments, but in only a few living algal species, notably the ubiquitous coccolithophorid Emiliania huxleyi. The proven value of long-chain alkenones in palaeotemperature assessment prompts an evaluation of their sedimentary record, especially their correspondence with coccolithophorid fossils in ancient marine sediments. Synthesis of available micropalaeontological and molecular data suggests that morphologically related species of the genera Crenalithus, Dictyococcites, Emiliania, Gephyrocapsa, Pseudoemiliania and Reticulofenestra, all belonging to the family Gephyrocapsaceae, were potential biological sources of alkenones and alkyl alkenoates in marine sediments deposited since the Eocene (∼45 Ma). The occurrence of alkenones in Cenomanian and Albian sediments devoid of nannofossils may be presumed to reflect contributions from ancestors of the Gephyrocapsaceae, although an investigation of Cretaceous samples containing both coccoliths and alkenones would provide further evidence of this proposed correspondence. The combination of palaeontological and molecular chemotaxonomic information offers a novel approach to the evaluation of the phylogenetic lineages that link living and extinct algae. © 1990.