Organic carbon as a palaeoenvironmental indicator in the marine realm
1995
Recent developments in biogeochemistry have made accessible all information
currently known to be present in sedimentary organic compounds, i. e. the carbon skeleton
structure, the positions of functional groups and stable carbon isotope ratios. This combined
information has strengthened the applications of sedimentary organic compounds as
biomarkers and palaeoenvironmental indicators. This review summarizes the most
important biomarkers and their applications in reconstructing marine palaeoenvironments
and processes. The marine environment is characterized by the combined presence of specific
compounds, such as organic sulphur compounds, dinosteroids, 24-n-propylsteroids (even in
trace amounts), high amounts of C₂₅ HBI hydrocarbons and the absence of long chain
n-alkanes with odd over even predominance, bicadinanes and specific higher-plant
triterpenoids (e. g. oleanane). Furthermore, palaeoenvironmental conditions, such as photic
zone anoxia, hypersalinity, microbial sulphate-reducing activity, algal blooming, palaeo-upwelling
and palaeo-surface seawater temperature are indicated by molecular and/or
isotopic characteristics. Biomarkers from terrestrial sources are included because land-derived
organic matter is an important contributor to coastal and shallow-marine
environments. A short case study, within a Holocene terrestrial/marine setting (Florida
Bay, USA), is also presented to illustrate the reconstruction of transgressive-regressive
trends using selected organic compounds.
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