Paleocene Silverado Formation, Orange County, California

The late Paleocene Silverado Formation of the Santa Ana Mountains in Southern California is one of the few Paleocene sedimentary units in the West Coast. Up to 1700 feet thick, it records a marine transgression from non-marine fluvial sandstones to shallow marine sandstones. However, its precise age has been poorly constrained in the past. Magnetostratigraphic samples taken at type section east of Irvine Lake and in Silverado Canyon were analyzed in a cryogenic magnetometer, using both alternating field and thermal demagnetiztion. The samples showed stable remanence held mainly in hematite or goethite which passed a reversal test and showed 60+/-17 degrees clockwise rotation (consistent with the late Paleocene Santa Susana Formation in Simi Valley). Both sections were entirely of reversed polarity. Based on the mollusks and foraminifera they correlate with Chron C25r (56.6-57.7 Ma)