MICROFOSSILS OF THE DUCK CREEK FORMATION: A DETAILED ANALYSIS OF CALCISPHERES AND THEIR BIOSTRATIGRAPHIC SIGNIFICANCE

Marine microfossils were a major component of the phytoplankton in the basal portion of the Duck Creek Formation in North Texas. Through micropaleontological analysis, samples from various outcrop locations of the Duck Creek Formation in North Texas were observed in order to classify and correlate specific marine microfossils, known as calcispheres. Calcispheres are accepted as calcareous dinoflagellate remains and possess unique morphological and internal structures, and are useful in biostratigraphy and paleoenvironmental research.

The Duck Creek Formation is greatly composed of marine limestones and shales and is paleogeographically located along the eastern edges of the Cretaceous Western Interior Seaway. The Duck Creek Formation is on the upper part of the Comanche Series, part of the Washita Group in the Lower Cretaceous; specifically, from the upper Albian. It overlies the Kiamichi Formation and itself is overlain by the Fort Worth Formation.

Samples from field locations in Grayson County and Tarrant County were brought back to the University of Texas at Dallas and prepared for imaging with a Scanning Electron Microscope. There is an overwhelming abundance of Pithonella spherica, which are incredibly spherical in morphology, (as indicated by their name) and tend to be found with recrystallized outer shells and have an internal structure of calcareous radially dispersed plates. Other microfossils found within the samples, such as Favusella washitensis have helped to further understand the paleoenvironment the calcispheres occupied, as well as constrain the depositional time periods. The overwhelming abundance of calcispheres over other microfossils such as foraminifera which are very abundant on adjacent levels suggests episodic algal blooms.

Continuing studies will apply the observations of calcispheres from these sampled sections to other stratigraphic profiles of the Duck Creek Formation.Correlation of the calcispheres over the continuous profile of the Duck Creek FM. as a whole will establish a detailed look at the faunal events of calcisphere deposition. The calcispheres and the related microfossils found will be used to further detail the boundaries between Washita Group depositional cycles and boundaries between the Kiamichi and Fort Worth Formations.