GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 147-10
Presentation Time: 4:20 PM


MCDOUGALL, Kristin, U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff, AZ 86001

Detailed foraminiferal analysis of the Paleogene strata of the Tumey Gulch section, central California, identified several biotic events reflecting changes in paleobathymetry, faunas, oxygenation, and carbon flux related to the Paleocene-Eocene Thermal Maximum (PETM) along this continental margin. These include the Benthic Extinction Event (BEE), deep water agglutinated faunal acmes, fluctuations in the disaster, opportunistic, and recovery faunas, changes in the dissolved oxygen related to organic carbon and sedimentation rates, and variation in the calcium compensation depth (CCD). These biotic events are present in other Paleogene sections located along the California margin although many of the Paleogene units are discontinuous, sparsely sampled, and separated by faulting. Nevertheless, biotic events can be recognized in sections around the San Francisco Bay area, near Gualala, and in the San Rafael Mountains. Agglutinated foraminiferal faunas are common in the Paleocene portion of the sections and include abundant Cyclammina and Ammoanita which are suggest poorly oxygenated environments. An increase in Glomospira occurs just prior to the PETM signaling an increase in terrestrial organic matter and elevated sedimentation rates. The BEE is recognized by the last appearance of many Paleocene species (e.g. Anomalinoides rubiginosus, Cibicidoides alleni, C. dayi, Gyroidinoides globosus, and Stensioeina beccariiformis) and the first appearance of Eocene species (e.g. Anomalinoides capitatus, Cibicidoides eocaenus, and numerous species of Bulimina and Vaginulinopsis). The abundance of calcareous species, specifically Bulimina alazaensis, followed by the appearance of opportunistic taxa (e.g. Tappanina and Allomorphina) in the PETM interval indicates more oxic conditions. Eocene species characteristic of a recovery fauna (Anomalinoides, Bulimina, Cibicidoides, and Pleurostomella) appear above this event. Although these biotic events are most easily recognized in the Tumey Gulch section, they appear to be widespread in the California sections and allow for a more complete understanding of the impact of the PETM on an active continental margin.