ABSTRACT

For many years, algal limestone bodies have been known in the Point Peak and San Saba Members of the Wilberns Formation (Late Cambrian (Dresbachian) to Early Ordovician) in the Llano Uplift region of central Texas, but they have never been studied in detail. The relationships between environment, fossil algae, and algal structures are not well understood, and the descriptive terminology is becoming more complicated.

The writer has examined algal macrostructures along with their corresponding microfabrics and fossil algae from a paleoecologic viewpoint. Several previously unknown microfabrics have been found that reflect the growth patterns of various algal taxa in response to different hydrologic conditions. For example, fossil algae with wispy or tufted growth forms are found in nonlaminated algal macrostructures (limited hydrologic stress) while laminated macrostructures such as stromatolites exhibit tightly laminated microfabrics (considerable hydrologic stress). The various environmentally produced structures are found commonly in sequences that depict the long-term paleoecologic history of the algal reefs from their inception (commonly in the sublittoral) to their culmination (commonly in th intertidal). Four different genera of fossil algae, Girvanella, Epiphyton, Renalcis and Nuia, were found in this study.