The sedimentary sequence at Site 1010 (Fig. 2) consists of an apparently continuous, 185-m-thick interval of Quaternary to middle Miocene sediments. They are divided into four lithologic units. Unit I (0-18.5 meters below seafloor [mbsf]) consists of siliciclastic sediments (silty clays and clayey silts) with abundant vitric ash layers and disseminated volcanic glass throughout. The top of Unit II (18.5-66.0 mbsf) is defined by increased biogeneous sediment components and consists of interbedded units alternating between nannofossil ooze and silty clay. Volcanic ash layers (both vitric volcanic ash and altered) are abundant. Unit III (66.0-178.0 mbsf) represents increased siliceous components interbedded throughout with clay and nannofossil sediments. Interbedding occurs on a scale of 20-80 cm. Unit IV (178.0-basement) is composed of alternating porcellanite, nannofossil chalk, and clay. The tagged basement consists of basalt.
The section includes an upper 60-m-thick sequence containing variable but often abundant planktonic foraminifers and few diatoms, radiolarians, and calcareous nannofossils from the Quaternary through the lowermost Pliocene and uppermost Miocene (Fig. 2). This is underlain by a 70-m-thick sequence of late Miocene to late middle Miocene age marked by an almost complete absence of planktonic foraminifers and generally uncommon calcareous nannofossils, diatoms, and radiolarians. This is underlain by a 55-m-thick sequence of rapidly deposited diatom ooze of middle middle Miocene age (base: diatom Denticulopsis hyalina Zone, 13.1-13.9 Ma; Nannofossil Zone CN4, 13.6 to 15.8 Ma). These diatom oozes contain assemblages of diatoms, radiolarians, and planktonic foraminifers indicative of extensive upwelling of cool waters associated with the California Current. The radiolarian assemblages are the best-preserved Miocene examples from an intense upwelling province, and include numerous new species never observed before. Likewise, the planktonic foraminifer assemblages provide a rare insight into the characteristics of faunas associated with intense Miocene upwelling. The sequence of changes in planktonic foraminifers suggests the need to establish a new zonation for the southern California Current system.
A complete magnetostratigraphy was determined from Holes 1010C and 1010E (Fig. 2). All chrons from the Brunhes to the top of Chron C3Bn (7 Ma) could be identified in the upper 75 mbsf. The age-depth plot based on magnetic reversals shows three linear segments, representing 3 different sedimentation rates in the upper 75 mbsf. Below 75 mbsf, the intensity of magnetization decreases. The drilling-induced remanent magnetization dominates between 75 and 160 mbsf and prevents the identification of polarity reversals.
No significant amounts of gas were measured in the sediment column. Carbonate contents vary strongly between 0 and 80 wt% in the upper 110 mbsf. Below this depth, carbonate contents are generally higher than the upper section because of higher nannofossil concentration. Organic carbon values decrease with depth from about 0.4 to less than 0.2 wt%.