SIERRA BLANCA LIMESTONE AND THE PALEOCENE–EOCENE THERMAL MAXIMUM (PETM) IN CALIFORNIA

Eocene limestones are noted in Paleogene sedimentary rocks throughout California. The most prominent and extensive interval of limestone deposition or transport appears to be associated with the PETM, which is recognized in California by the Benthic Extinction Event (BEE), agglutinated faunas, Glomospira acme zone, distinctive foraminiferal faunas, and rapid changes in the CCD. The distribution and pattern of these unusual occurrence of shallow water limestone sheds considerable light on the climatic and tectonic conditions of the Paleogene in California, provided that the age and paleoenvironment of thee strata are interpreted correctly.

An example is the Sierra Blanca Limestone which is exposed in the San Rafael Mountains and western part of the Transverse Ranges and has long been used as a piercing point to define offset on the Santa Ynez fault which bounds the north side of the range. The limestone was named by Nelson (1925) and the type area was described by Keenan (1932) as a section along Indian Creek in the San Rafael Mountains, California. The limestone unconformably overlies Cretaceous strata and was considered middle Eocene in age (Keenan, 1932) but the age was later revised to early Eocene (Mallory, 1959). The limestone was interpreted as a shallow marine deposit based on the presence of Discocyclinids and stellate orbitoidal foraminifers, and calcareous algae (Arthaeolithamhnium, Lithoithamnium, and Lythophyllum). Lenticular bodies of Sierra Blanca limestone have been identified in the overlying Anita Shale and interpreted as turbidite deposits shed off an algal bank (Chipping, 1972; Whidden, 1994; Whidden et al., 1995a,b). Outcrops of the Sierra Blanca Limestone are not extensive and age interpretations indicate that there are 3 discrete groups: Late Paleocene, early Eocene, and late early Eocene. The late Paleocene limestone may be associated with the warm Middle Paleocene Biotic Event (MPBE) but data is insufficient. The early Eocene limestones are transported and associated with the PETM. The late early Eocene limestones are also transported, include Discocyclinids and occur during the early Eocene Climatic Optimum (EECO).