LODO FORMATION AND THE PALEOCENE-EOCENE THERMAL MAXIMUM IN CENTRAL CALIFORNIA

The faunal expressions of the Paleocene-Eocene Thermal Maximum (PETM), Carbon Isotope Excursion (CIE), and Benthic Foraminiferal Extinction (BFE) are well documented in the deep sea sediments. Few studies, however, have examined continental margin sections. The presence of the CIE was identified based on organic carbon (John et al., 2007) in the Lodo Formation, Central California which was deposited on the Paleocene-Eocene continental margin. We present data on the benthic foraminifers in the Lodo Fm. which record faunal changes related to the PETM and a possible early Eocene hyperthermal. The BFE is not recognized because deposition initially occurred below the calcium compensation depth (CCD) and only long-ranging agglutinated species are present. The Glomospira acme zone is recognized at the base of the CIE and below the red clay. While this event has been attributed to a rise in the CCD, it was more likely due to the opportunistic behavior of these species in a stressed environment during periods of increased input of terrestrial organic matter and elevated sedimentation rates. The abundance of calcareous species, specifically Bulimina alazaensis, followed by the appearance of opportunistic species (Tappanina and Quadrimmorphina) in the overlying samples indicates a drop in the CCD and a return to more oxic conditions. Above the red clay, but still within the CIE interval, a slightly younger secondary extinction event related to the BFE is recognized during which Paleocene species last appear. Eocene species characteristic of a recovery fauna (Anomalinoides, Bulimina, Cibicidoides, and Pleurostomella) appear above this event. Foraminiferal assemblages indicate that deposition in sediments overlying the CIE interval is at abyssal depths and are dominated by agglutinated foraminifers. Calcareous assemblages return when water depths shallow.

A second red clay occurs in the upper part of the Tumey Gulch section and is associated with a decline in δ¹³C. This interval includes an increase in the opportunistic species, is preceded with an increase in Glomospira and disaster species (agglutinated species), and is followed by an increase in recovery fauna. Together these assemblages suggest the presence of another hyperthermal within the Lodo Fm. which we interpret as probably the early Eocene hyperthermal ETM3.