Abstract: Magnetic Stratigraphy of the Type Refugian Stage (late Eocene-early Oligocene), Western Santa Barbara County, California
THOMPSON, MATTHEW, and DONALD PROTHERO
The age of the Refugian Stage in California has long been controversial, largely because it is defined on depth-dependent benthic foraminifera. Since Schenck and Kleinpell (1936) named the Refugian, authors have correlated it with either the late Eocene or early Oligocene or both. McDougall (1980) showed that the Refugian was time-transgressive between California and Washington. Calcareous nannoplankton (Warren and Newell, 1980; Almgren and Filewicz, 1984) show that the Arroyo el Bulito section through the Gaviota Formation correlated with late Eocene and early Oligocene nannofossil Zones NP19-20 and CP16a.
Magnetostratigraphic sections of the Sacate, Gaviota, and Alegria formations were taken in the type area in Canada de Santa Anita, in Arroyo el Bulito, and at Gaviota Gorge. Most samples produced a stable primary remanence that passed a fold and reversal test, and showed a clockwise rotation of about 83.3 degrees plus or minus 6.1 degrees (consistent with the 92 degrees plus or minus 7 degrees rotation reported from the overlying Miocene Monterey Formation). Based on calibration from the plankton, the type Refugian spans Chron C16r to late Chron C13r (36.5-33.7 Ma), or late Eocene and earliest Oligocene. However, in the San Lorenzo Formation near Santa Cruz, and in the Lincoln Creek Formation in Washington, the Refugian starts about 2 million years later than in the type section, and ends about a million years later, so the Refugian is highly time-transgressive.
Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California