RADIOLARIAN BIOSTRATIGRAPHIC AND PALEOCEANOGRAPHIC STUDIES OF MONTEREY-LIKE ROCKS OF THE HUMBOLDT BASIN, NORTHERN CALIFORNIA
NELSON, CARL OWEN
Doctor of Philosophy
The middle and upper Miocene sediments of the Humboldt Basin, northern California, have been investigated for the presence of radiolarian fauna. The vast majority of the radiolaria found are cold water indicators, however there are four distinct periods of invasion of warm water fauna. Two minor ones occurring at 11.5ma and approximately 8.0ma and two major events at 5.0ma and approximately 5.5ma. Occurrences of radiolaria indicative of low oxygen conditions, cold deep forms, and radiolarians associated with the California Current indicate that Paleoceanic circulation in the Humboldt Basin region at 6.5ma was similar to "normal" (anti-El Nino-like) circulation of Recent time. Depositional environments and paleoceanographic circulation are modeled from information obtained from 192 Miocene to Pliocene samples of five stratigraphic sections across the subaerially exposed southern margin of the paleo-basin. Radiolarian fauna indicate that initial deposition was in a basin open to deep marine waters. Through time and in a west to east direction, the radiolarian populations exhibit increasingly shelfal characteristics as shallow water sediments prograded to the west. Total organic carbon data from key chronozones support the models of oceanic circulation developed for the key time planes. The fluctuations in the California Current System are the dominant controls on faunal distribution and organic carbon preservation. An example of doming of deep water masses (Weinheimer et al., 1986) indicating analogous El Nino-like circulation is detected and differentiated from other similar appearing events of a different nature (normal, anti-El Nino circulation).