DOCUMENTING DIATOM OCCURENCE IN LATE EOCENE MARINE COASTAL SEDIMENTS IN CENTRAL TEXAS

Diatom fossils are rarely reported in Gulf Coast sediments because of their small size and opaline silica composition, but these are significantly important organisms in the ecosystem. The assemblage of diatoms can be found in marine and freshwater environment; particularly in moist soils. Recent work has shown them to occur in abundance in Late Eocene coastal marine strata contaning volcanic ash. The occurence of even a few diatoms in thin section or washed sand fractions is enough to justify a search for them using standard processing methods and the presence of some siliceous sponge spicules in sediments is a useful indicator of abundant diatoms. Coastal deposits can be expected to have much clay present that must be removed. Work with central texas diatomites requires repeated washing and dispersal to decant fine mud particle. Examination of samples shows that only siliceous fossils are preserved in the deposit.The diatomites studied have been subjected to strong oxidation and some of these diatoms contain secondary oxide minerals that interfere with cleaning the diatoms. However, when well cleaned the diatoms show excellent preservation and fine detail is revealed. Preparation of mounting slides and microscopic images have shown various forms, ranging sizes of diatoms.