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 Montecito, California, has a complicated Quaternary history of debris flows, the most recent being the Montecito debris flows of 9 January 2018, which were wildfire-debris flow–linked events that took 23 lives and damaged or destroyed several hundred homes. Relative flow chronology, based on boulder weathering, incision rates, and soil dates with limited numerical (radiocarbon and exposure) dating, is used to identify paths of prehistoric debris flows. Topography of debris flow fans on the piedmont is significantly affected by the south-side-up reverse Mission Ridge fault system. Examination of weathering rinds from Pleistocene debris flows confirms that the Rattlesnake Creek–Mission ridge debris flows are folded over the ridge, and that lateral propagation linked to uplift of marine terraces (uplift rate of ~0.5–1 m/k.y.) significantly altered debris flow paths. As communities continue to rebuild and live in these hazard-prone areas, disaster risk reduction measures must take into account both spatial and temporal components of vulnerability. This field guide includes four stops from Montecito to Santa Barbara. The first stop will be to observe debris flow stratigraphy over the past ~30 ka beneath an earthquake terrace and a prehistoric Chumash site on the beach near the Biltmore Hotel in Montecito. The second stop will be at San Ysidro Creek in San Ysidro Canyon, the site of the largest Montecito debris flow that occurred on 9 January 2018. We will discuss source area and processes of the debris flow, and take a short hike up the canyon to visit the debris flow basin and a ring net designed to reduce the future hazard. The final two stops will explore the debris flow chronology of Santa Barbara over the past ~100 ka. Figure 1 shows the location of the field-trip stops. There is no road log as field sites can be found with a search on a smartphone.

ABSTRACT Several stratigraphic sections of the Monterey Formation along the coastline west of Santa Barbara are well exposed and easily accessible. The stratigraphic sections between Naples Beach and Gaviota display a similar lithostratigraphic sequence over a twenty mile distance. The basal portion of the Monterey is represented by upper Saucesian and Relizian calcareous-siliceous shales that experienced large-scale soft-sediment deformation. The soft-sediment slumping suggests deposition on a slope in the late early Miocene. The overlying Luisian and lower Mohnian phosphatic shale interval is extremely organic-rich. Several phosphatic hardgrounds occur in the middle of this organic-rich interval (at the Luisian/Mohnian boundary). These hardgrounds correspond with a major depositional hiatus. The hardground interval suggests deposition on a banktop during the late middle Miocene. This hardground interval is absent in coastal exposures in the city of Santa Barbara. Instead, a 100-ftthick porcelanite and chert interval is present at the Luisian-Mohnian boundary. This biogenic silica-rich interval resembles the upper Luisian and lower Mohnian fractured chert reservoirs in oil fields in the Santa Barbara Channel. The upper Monterey is dominated by siliceous shales and porcelanites. An increase in detrital content at the top of the Monterey Formation corresponds with the initiation of uplift of the Santa Ynez Range. Submarine canyon deposits that incise the Monterey Formation and are filled with Monterey chert cobble conglomerates or large blocks of Monterey shale in a matrix of Sisquoc shale suggest that the Santa Barbara coastline was on a shelf edge at the end of the Miocene.

ABSTRACT Natural gamma-ray spectrometry is a powerful addition to the traditional lithostratigraphic analysis of mudrocks. Gamma-ray data can reveal many aspects of mudrock deposition: lithologic variation, organic-matter content, hydrocarbon source quality, bedding thickness, stratal stacking patterns, depositional environments, and significant stratigraphic surfaces and packages and their regional distribution. It is especially valuable in studying the Monterey Formation with its complex composition and lithologic variations. Our studies of the Monterey Formation show that: 1) potassium and thorium are reliable indicators of detritus content (r 2 = 0.75 v. Al 2 O 3 ), 2) high levels of thorium occur coincident with volcanic ash beds, 3) uranium correlates with total-organic-carbon content (TOC, r 2 = 0.80), and 4) K/U correlates well with hydrocarbon source quality measured by Alumina/TOC. Gamma-ray spectra also portray the relative proportions of hemipelagic and pelagic components in these rocks and can reveal the depositional environment when considered along with the stratal stacking patterns (Bohacs, 1990). The data obtained from an outcrop gamma-ray survey is analogous to the data obtained from the NGT or spectral gamma-ray well log from boreholes. This enables a detailed calibration of well-log response with numerous outcrop samples and provides a powerful correlation and interpretation tool for integrating outcrop and subsurface data. Many important stratigraphic surfaces have distinct spectral gammaray signatures. This is a critical element for stratigraphic analysis and developing depositional models: the surfaces approximate time lines whilst lithologic packages often range widely in age. For example, the very organic-rich phosphatic shales at Naples Beach span several million more years than the most enriched rocks at Point Pedernales (Bohacs, 1993); see also Hornafius (1991) for other examples.