Biological markers for anoxia in the photic zone of the water column

Abstract

In this chapter we review the current state of knowledge on the occurrence of anoxic conditions in the water column of past depositional systems using biomarkers. The recognition of such conditions is important for a better understanding of the deposition of petroleum source rocks and periods of widespread water column anoxia in the geological past (so-called oceanic anoxic events). The most reliable biomarkers for this purpose are specific pigments and bacteriochlorophylls derived from photosynthetic green and purple sulfur bacteria, which require both light and sulfide. These proxies for water column anoxia have been well tested in present-day lakes, fjords and stratified basins. With increasing burial in the sediment, the pigments and bacteriochlorophylls undergo a myriad of transformation reactions, but the products are in most cases still specific enough to use them as environmental indicators. In this way, the occurrence of photic zone euxinia has been demonstrated for a wide variety of settings (e.g. shelf seas, enclosed basins, open ocean systems) and during geological eras as old as the Precambrian. © Springer-Verlag Berlin Heidelberg 2005.