ABSTRACT We present here a comprehensive record of Miocene terrestrial ecosystems from exposures of the Monterey Formation along the Naples coastal bluffs, west of Santa Barbara, California. Constrained by an updated chronology, pollen analyses of 28 samples deposited between 18 and 6 Ma reflect the demise of mesophytic taxa that grew in a warm, wet environment during the late early and early middle Miocene and the development of a summer-dry/winter-wet Mediterranean climate during the late Miocene. Broadleaf tree pollen from mesophytic woodlands and forests now found in the southeastern United States and China (Liquidambar , Tilia , Ulmus , Carya) characterized the Miocene climatic optimum (16.9–14.7 Ma), the middle Miocene climate transition (14.7–13.8 Ma), and the interval up to ca. 13.0 Ma. Subsequently, during the late middle to early late Miocene, between 13.3 and 9.0 Ma, oak woodlands and herbs (Asteraceae, Amaranthaceae, Poaceae) from beach scrub and chaparral increased as ocean temperatures cooled and the climate became drier. Between ca. 8.9 and 7.6 Ma, pine increased mostly at the expense of oak (Quercus) and herbs, suggesting a period of increasing precipitation. During the latest Miocene (7.5–6.0 Ma), an increase of herb-dominated ecosystems (chaparral, coastal scrub) at the expense of pine reflects the full development of a summer-dry/winter-wet climate in coastal southern California.

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 An integrated biostratigraphic and paleoecologic study of the Naples Bluff coastal section was completed utilizing diatoms, calcareous nannoplankton, and benthlc foraminifera. This section is 1800 ft. thick and represents one of the most completely exposed marine Neogene sections along the central coast of California. This sequence contains well preserved diatom floras and benthic foraminiferal faunas that enabled the integration of diatom biochronology with the provincial Miocene benthic foraminiferal stages of Kleinpell (1938, 1980) and the construction of a sediment accumulation curve for the stratigraphic section. Benthic foraminiferal biofacies provide a detailed analysis of the paleoenvironmental and paleobathymetric history for the sediments of the Naples Bluff section. The biofacies demonstrate that the depositional setting changed several times throughout the section, ranging from lower middle bathyal to upper bathyal. The top of the section shallowed to neritic depths.

ABSTRACT The Los Angeles basin is one of the Neogene basins along the Califomia continental margin that was formed by extension related to complex wrench-fault mechanisms. These extensional mech- anisms caused the pull-apart tectonics that resulted in rapid deepening of many of the continental margin basins in the late Oligocene to early Miocene. For the last 60 years, the biostratigraphic framework for correlation between the oil fields of the Los Angeles basin has been based on the benthic foraminiferal zones and divisions first published by Wissler (1943,1958). These biostratigraphic units are used to correlate the upper middle Miocene to upper Pliocene clastic reservoirs across the basin. The benthic foraminiferal zones of Wissler (1943, 1958) were correlated to the Miocene benthic foraminiferal zones of Kleinpell (1938, 1980) and the Pliocene- Pleistocene stages of Natland (1952). With the utilization of other microfossil disciplines (e.g., siliceous and calcareous planktonic microfossils), a more refined biostra- tigraphic scheme has been developed. Correlation of plankton biostratigraphies with the radiometric time scale has in tum allowed correlation and calibration of benthic foraminiferal zonations. Application of this new biostratigraphic- chronostratigraphic scheme can now be used to constrain the timing and magnitude of tectonic and depositional events marking basin development. Benthic foraminiferal assemblages from three stratigraphic sections, located around the margins of the Los Angeles basin, were correlated to siliceous microfossils, calcareous nannofossils, planktonic foraminifers, and radiometric dates to determine the age relationships of the different benthic foraminiferal zonations. Three regional cross sections were constructed based on the thickness of the Neogene sedimentary package and based on the chronostratigraphic relationships between the benthic foraminif- eral zones and the other fossil groups. These regional cross sections illustrate the shifting of the central basin depocenter through the late Neogene. The pre-late Miocene deposits are thickest along the basin margin, especially in the northwestern part of the central block, the Puente Hills, and the Capistrano embayment. The sediments that were deposited during the late Miocene through the early Pleistocene were deposited in the central trough, bounded by the Newport−Inglewood, Santa Monica-Raymond Hill, and the Whittier fault systems. Unconformities and hiatuses are associated with each tectonic block. Some of these unconformities are local events related to structural growth or fault movement. The hiatuses are regional events caused by changes in ocean chemistry or velocity of bottom currents. The unconformities that occur in the late Miocene to early Pliocene are related to local structural growth in the Palos Verdes Hills area and the Anaheim nose area of the southeastern portion of the basin. Other unconformities that occur in the late Miocene are related to movement along the Newport−Inglewood fault and the Whittier fault. In the late middle Miocene a hiatus occurs within the Monterey Formation in the Palos Verdes Hills and the Newport Bay area. This hiatus is thought to be related to climatic and oceanic events associated with continental and oceanic glaciation.

ABSTRACT Prevalent concepts of foraminiferal paleobathymetric interpretations are based on the modern distribution of living benthic faunas and assume that species depth habitat have not changed with time. Recent studies by Streeter (1973), Schnitker (1974), and Lohmann (1978), suggest that the distribution of benthic foraminifera is not as static in space and time as had been previously believed. Present-day deep sea benthic foraminiferal assemblages appear to be controlled more by the distribution of bottom water masses than by bathymetry. Melonis pompilioides (Fichtel and Moll) is a benthic foraminifer presently inhabiting lower bathyal to abyssal environments. The species is described by Bandy and Chierici (1966) as a typical example of an isobathyal species. The use of M. pompilioides as a bathymetric indicator in modern and ancient environments rests upon two assumptions: First, that it is an isobathyal species and its upper depth limit is approximately the same in different oceans. Second, that the depth habitat of the species, at least its upper depth limit, has not changed with time. Data from the southern California Borderland support a different model, one which explains the Pleistocene distribution of M. pompilioides as the result of faunal migration. Late Pleistocene and Holocene occurrences of the species in basins with sill depths shallower than 2,300 m, the present-day upper depth limit of the species, is evidence of water-mass changes in the last 16,000 years. The apparent bathymetric change of the species is a faunal response to changing environmental conditions rather than evidence of tectonic uplift of the seafloor.