ABSTRACT The major and trace element composition of seventy whole-rock samples of volcanic ash, tuff, and bentonite from beach outcrops of the Monterey Formation west of Santa Barbara were analyzed to determine if these tephra layers could be used as a stratigraphic correlation tool. Five broad groups of ashes can be distinguished based on the abundance of seven elements that are immobile during alteration of the ashes to bentonites (La,Sm,Yb,Nb,Th,Ti,Zr). Lower to middle Miocene ash beds that are correlative with the Tranquillon, Obispo, and possibly the Santa Cruz Island Volcanics are found in the lower Monterey Formation. Upper Miocene ashes that are correlative with ash beds in the type section for the Monterey Formation in Monterey County, as well as ashes from a nonmarine sequence north of the Garlock fault, are found in the upper Monterey Formation at Naples Beach. An ash bed zonation was developed for the Monterey Formation which was used to correlate between stratigraphic sections along the Santa Barbara coastline. The concurrent range zonation developed for these ashes has a resolution that is comparable to the resolution achievable with benthic foraminifera in this part of the time scale.

ABSTRACT A petrographic study of the Wildcat Group was undertaken to determine the sediment provenance of the Late Miocene to Pleistocene marine sediments within the Eel River basin. Previously, it was believed that the principle source terrane was the Franciscan and Yager complexes exposed to the south and to the southeast. The potassium feldspar content within the Wildcat Group appears high (range = 0.7% - 12.3%) for these sources. Compositional data plotted on ternary diagrams suggest sand derivation from transitional continental and mixed origin sources. 40 Ar/ 39 Ar laser probe analyses of Scotia Bluffs Sandstone micas yield ages of approximately 52-57 Ma. Analyses of Pullen Formation micas yield three groups of ages: approximately 66-75 Ma, 128.5 Ma, and 299-303 Ma. A logical source for the younger dates are late Cretatious-Eocene plutonic rocks in Idaho. The source of the older micas remains enigmatic, but may be reset Devonian Abrams Schist of the Klamath Mountains central metamorphic terrane.