Cenomanian and Turonian palynology and palaeoceanography of the western interior basin, United States of America

Abstract

$$a The Cretaceous geological record of the Western Interior Seaway of North America has been extensively studied and suggests a complex and dynamic history of interrelated tectonic, custatic, oceanographic and climatic changes. This seaway linked the Arctic ocean with the subtropical Tethyan ocean and custatic fluctuations caused mixing of the two very different water masses affecting the sedimentological and palaeontological record. Extensive work on the lithostratigraphy, biostratigraphy framework allowing precise bed-by-bed correlation between section hundreds of kilometres apart. Cenomanian to Turonian strata from four sections and one care, from Arizona, Utah, Colorado and Kansas have been studied for their marine palynomorph and palynofacies assemblages and the biostratigraphy is described. Precise correlation of samples between the sites shows that many biostratigraphically useful taxa have synchronous ranges and that many taxa also had environmental preferences. These are subsequently used for paleoenvironmental interpretations. Strata from the core record the second-order transgressive-regressive custatic Greenhorn marine cycle with superimposed third- and fourth-order fluctuations. The range of paleoenvironments studied here include probable freshwater through near-shore to distal pelagic environmental interpretation and a direct comparison shows that the dinoflagellate cyst assemblages are equally as good at tracing sea-level and water mass fluctuations. A global marine oxygen depletion event is suggested to have occurred at the Cenomanian - Turonian boundary. Integration of palynological data with previous work suggests that burial of amorphous organic matter at this time was related to primary productivity which increased with expansion of the Tethyan water mass at times of third- and fourth-order transgression. This integrated, high-resolution study with tight chronostratigraphic control credits the use of dinoflagellate cysts, not only as a biostratigraphic tool but also with a very real and precise potential for paleoenvironmental and palaeoecologically interpretation.

Date of Award	1997
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Bruce Tocher (Supervisor)