ABSTRACT

A graphic correlation coupled with a Q-mode vector analysis of fossil palynomorph assemblages shows that these microfossils responded to environmental changes within the late Cretaceous sea of southwestern Colorado. The time correlation is based on the occurrence of selected land-derived pollen and spores. The Q-mode vector analysis was performed on percentages of 22 selected microplankton taxa distributed in 72 samples from two stratigraphic sections. These stratigraphic sections lie on a line that is normal to the trend of the late Cretaceous shoreline. The analysis is interpreted by comparing the distribution of end member sample groups in the two sections, as determined by the vector analysis, with a well-documented model of onlapping and offlapping facies based on the literature. Within the relatively homogeneous marine shale, the distribution of three end member sample groups--one that occurs near shore, one that occurs at intermediate distances offshore. and a third that occurs far offshore--parallels the transgression and regression of the shoreline as represented by the distribution of the correlative littoral sandstones and related nonmarine facies.

It is concluded that vector analysis within a well-established time correlation framework is effective in empirically pointing up environmentally-controlled distributions of microfossils.