ABSTRACT The Monterey Formation, consisting of siliceous and calcareous biogenic sediments, was deposited during the transition from a relatively warm greenhouse climate in the early Miocene to the cooler temperatures of icehouse climatic conditions during the early middle to late Miocene. This cooling event was associated with global paleoclimatic and oceanic changes assumed to be related to the deposition of organic carbon–rich sediments into the marginal basins of California. This chapter introduces an age model for the Miocene strata at Naples Beach based on a composite stratigraphic section and standardized data set, providing the framework for the integration of biostratigraphic zones with a series of astronomically tuned siliceous and calcareous microfossil bioevents, an updated strontium isotope stratigraphy, new tephrochronology ages, and ages from specific magnetostratigraphic units. This multidisciplinary approach, utilizing the integration of microfossil disciplines with independent age controls, is critical to obtaining an age resolution of ~200 k.y. for the majority of the Monterey Formation section. This chronostratigraphic framework improves the age control of the boundaries between the California benthic foraminiferal stages and provides more age refinement for the possible hiatus and condensed interval within the Carbonaceous Marl member of the Monterey Formation. The recalibrated ages for the tops of the Miocene benthic foraminiferal stages are Saucesian (ca. 17.4 Ma), Relizian (15.9 Ma), Luisian (13.1 Ma), and Mohnian (7.7 Ma). Also, the time missing in the hiatus between the Luisian and Mohnian is <200 k.y., and the duration of the condensed interval is from 13.0 to 11 Ma. This refined age model provides a correlation of the organic carbon–rich intervals occurring in the Luisian and lower Mohnian stages within the Naples Beach strata to the deep-sea δ 13 C maxima events CM5 (ca. 14.7 Ma) and CM6 (ca. 13.6 Ma), suggesting episodic increases in organic carbon deposition along the continental margins coincided with the Miocene carbon isotope excursion found in deep-sea cores. The transition from the Miocene climatic optimum to the icehouse world consisted of four climatic and oceanic phases (from ca. 17.5 to ca. 7 Ma), which are represented in the onshore section by variations in the organic carbon and phosphate contents, the occurrence of calcareous and siliceous lithologic facies, and the distribution of microfossils, especially changes in the benthic foraminiferal assemblages.

Abstract Over 165 species of megainvertebrates, mostly mollusks, from the lowest three (of approximately 17) emergent marine terraces along the southwestern coast of Santa Barbara County, California, provide the basis for both paleoecological and paleoclimatic interpretation. Most of the fossiliferous exposures on the two lowest terraces at Canada de Alegria, Gaviota, and Arroyo Hondo are situated at or very near to the original shoreline angle (i.e., base of the fossil sea cliff) of their respective terraces, physically constraining any interpretation of their depositional setting. The overall composition of their faunas, however, suggests sources from several near-shore marine habitats, all at intertidal to shallow inner sublittoral depths (0 to 18-27 m). Only the sandy bottom faunas from localities at Cojo Bay differ, representing a position about 700 to 750 m from shore and a water depth of about 15 m. Composite faunas from localities on the first terrace at Cojo Bay, Gaviota, and Arroyo Hondo, and from the second terrace at Canada de Alegria contain from four to 12 extralimital northern species each, indicative of slightly cooler water paleoclimatic conditions, comparable to those occurring today in the vicinity of Monterey Bay, central California. The fauna from the third terrace at Arroyo Hondo contains four extralimital southern gastropods, whose zoogeographic ranges suggest a more southerly geographic equivalency and slightly warmer water conditions, comparable to those occurring today between San Diego, California, and Ensenada, Baja California. On the basis of terrace mapping, uranium-series age estimates of bones, amino-acid racemization and epimerization analyses of bivalve mollusks, long-term uplift studies, and the zoogeographic signatures of the terrace faunas, the three lowest terraces are assigned ages of 85 to 80 ka (Cojo Bay, Gaviota, and lower Arroyo Hondo localities), 105 to 100 ka (Canada de Alegria second terrace locality), and 130 to 120 ka (Arroyo Hondo upper terrace localities), correlative with dated sea-level highstands recorded elsewhere as reef terraces, and in deep-sea sediments as marine oxygen isotope substages 5a, 5c, and 5e, respectively.

ABSTRACT Paleobathymetric and paleoenvironmental analyses of upper Cretaceous and Cenozoic sediments of the Santa Ynez Mountains and adjacent Ventura Basin illustrate that Paleogene, Neogene, and Quaternary depositional cycles have produced the widespread stratigraphic patterns present in the northern portion of the continental borderland of southern California. Cretaceous through Eocene sedimentation was centered in an east-west structural trough termed the Santa Barbara Embayment. This feature was filled from east-to-west as rates of sedimentation exceeded rates of subsidence in Paleogene time. Abyssal basin plain deposits were sequentially buried by prograding fan, slope, and shelf deposits terminating in widespread non-marine deposition and erosion in Oligocene time as documented by the Sespe Formation. Upper Eocene and Oligocene alluvial deposits of this latter unit neatly partition Paleogene and Neogene depositional packages in this area. Rapid subsidence and marine transgression occurred over wide areas of the California margin in latest Oligocene and early Miocene time initiated by collision of the Pacific and North American plates with subsequent birth of the San Andreas fault zone, translational margin tectonics, and creation of a complex series of bathyal Neogene basins. Continued subsidence of these basins and eustatic drowning of the adjacent Miocene strandline created a series of mid Miocene silled basins starved of terrigenous debris allowing relatively undiluted deposition of diatomites during a period of climatic deterioration and consequent intensified diatom productivity in the California Current system. A well developed oxygen minimum layer allowed preservation of laminated diatomites and diatomaceous muds in these basins ultimately forming the characteristic lithologies of the mid and upper Miocene Monterey Formation. Further tectonic reorganization of the continental borderland occurred in Pliocene time with uplift of the Santa Ynez Mountains and other highs and simultaneous acceleration of subsidence in adjacent synclinal areas including the Ventura Basin. These events led to the rapid progradation of Plio-Pleistocene terrigenous debris into the Ventura Basin, capping underlying diatomaceous basin muds, and filling the basin just prior to a late Pleistocene tectonic event which uplifted portions of these deposits to their present position above sea level initiating the present phase of borderland deposition.