CALCISPHERES FROM THE LOWER CRETACEOUS, NORTH TEXAS DUCK CREEK FORMATION

Through micropaleontological analysis, samples of marly limestone were analyzed in order to classify and correlate marine microfossils, known as calcispheres. These microfossils were a major component of the phytoplankton in the upper Albian (Lower Cretaceous) basal portion of the Duck Creek Formation in North Texas.

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

Calcispheres are accepted as calcareous dinoflagellate remains. It has been shown that these forms possess unique morphological and internal structures and are useful in biostratigraphy and paleoenvironmental research.

Samples from the field location in North Texas were brought back to the University of Texas at Dallas and prepared for imaging with a Scanning Electron Microscope. Our calcispheres are spherical in morphology and generally have a recrystallized outer shell with an internal structure of radially dispersed plates. Spherical dents within this internal structure are also interpreted to be archeophyles. The abundant calcispheres are predominantly Pithonella sp.; this is a sign of algal bloom episodes, showing also an overwhelming abundance over other microfossils, such as foraminifera and ostracods, which are very abundant on adjacent levels.

Future studies will aim to apply the observations from this section to other profiles of the Duck Creek Fm. in the area, establishing faunal events with temporal and ecological connotations. Correlation with other marine basins with Aptian units is a distinct possibility, i.e. Aurora Formation in the eastern Sierra de Parras, southeastern margin of the Coahuila block, Mexico.