From greenhouse to icehouse; organic-walled dinoflagellate cysts as paleoenvironmental indicators in the Paleogene

Dinoflagellates are an important component of the extant eukaryotic plankton. Their organic-walled, hypnozygotic cysts (dinocysts) provide a rich, albeit incomplete, history of the group in ancient sediments. Building on pioneering studies of the late 1970s and 1980s, recent drilling in the Southern Ocean has provided a wealth of new dinocyst data spanning the entire Paleogene. Such multidisciplinary studies have been instrumental in refining existing and furnishing new concepts of Paleogene paleoenvironmental and paleoclimatic reconstructions by means of dinocysts. Because dinocysts notably exhibit high abundances in neritic settings, dinocyst-based environmental and paleoclimatic information is important and complementary to the data derived from typically more offshore groups as planktonic foraminifera, coccolithophorids, diatoms and radiolaria. By presenting case-studies from around the globe, this contribution provides a concise review of our present understanding of the paleoenvironmental significance of dinocysts in the Paleogene (65-25 Ma). Representing Earth's greenhouse-icehouse transition, this episode holds the key to the understanding of extreme transient climatic change. We discuss the potential of dinocysts for the reconstruction of Palcogene sea-surface productivity, temperature, salinity, stratification and paleo-oxygenation along with their application in sequence stratigraphy, oceanic circulation and general watermass reconstructions. (C) 2004 Elsevier B.V. All rights reserved.