Dinoflagellate cysts as indicators of palaeoenvironmental and sea-level change : a critical assessment from the Late Cenomanian - Early Coniacian (Cretaceous) of Europe

Olde, Kate (2014) Dinoflagellate cysts as indicators of palaeoenvironmental and sea-level change : a critical assessment from the Late Cenomanian - Early Coniacian (Cretaceous) of Europe. (PhD thesis), Kingston University, .


The Late Cretaceous represented a period of greenhouse climate of Earth history, and was characterised by high temperatures, high atmospheric CO2 and high eustatic sea-level, with larege areas of shallow warm epicontinental seas. Understanding the dynamics of the Late Cretacious oceans led to the deposition of a large portion of the world's petroleum reserves, so reconstruction of depositional environments and refinement of stratigraphical correlation are important for this field as well. Dinoflagellates were a prolific and diverse group within the plankton throughout Late Cretaceous oceans, and their cysts display good preservation across different facies, and so are a good group for biostratigraphical and palaeoenvironmental study. A high-resolution quantitative study of the palynomorphs from five European sections of Late Cenomanian to Early Coniacian (Late Cretaceous) age is presented, along with elemental and stable-isotope geochemistry. The sections are from a range of palaeolatitudes and basins, including the North Sea Basin, the Anglo-Paris Basin, the Bohemian Basin, the Polish Trough and the Vocontian Basin. High-resolution [delta]13C curves (derived from carbonate and organic carbon) enable the recognition of major isotope events, despite offsets in absolute values and variation in amplitude between the sections, providing support for the hypothesis that such curves can be used in detailed chemostratigraphical correlation. Dinoflagellate cyst (dinocyst) biostratigraphical markers that correlate between basins prove to be good tie-points, though the positions of several previously recognised dinocyst markers are shown to differ between basins. Acmes of dinocyst species are considered to be of potentially better use than first or last occurences. Hypotheses for the processes leading to widespread black shale deposition and carbon isotope excursion that characterise Oceanic Anoxic Event 2 (OAE2), at the Cenomanian-Turonian boundary, have focussed on increased productivity versus increased preservation of organic matter. High dinocyst abundance, and particularly a high proportion of peridinoid cysts, (which are thought to be derived from eutrophy-adapted heterotrophic dinoflagellates), at the onset of OAE2, support the notion of increased productivity. However, as OAE2 progressed, changes in dinocyst assemblages relfect a cessation of high productivity. Dinocyst distribution is considered to be controlled largely by nutrient levels, but is also impacted by temperature, sea level, and water mass changes. Influxes of certain species are related to changes in salinity, changes in temperature, and water mass change, and increased communication between basins.

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