ABSTRACT Sedimentation after wildfire is a profound disturbance to the biogeomorphic character of fluvial systems. Despite this significant alteration, field data focusing on the geomorphic processes and bed morphology that form the physical structure of habitat are limited, especially over a longer-term perspective. We report results of detailed field studies following two wildfires in the same steep fluvial system in the southern California Transverse Ranges three decades apart. Substantial channel sedimentation during storms following both fires altered physical elements of habitat, which included bed elevation, step height and spacing, pool depth and spacing, grain-size distribution (D 84), and transport capacity (τ o /τ c). The postfire sediment deposits buried bedforms, decreased D 84 , and increased τ o /τ c by an order of magnitude. Incision during subsequent storms initiated recovery that depended on the attributes of post-wildfire climate variability that characterize the semiarid Mediterranean-type environment. Step-pool bedforms reappeared or reformed during the decades between wildfires as the relatively fine gravel-sized post-wildfire sediment was transported downstream, thus reestablishing the physical elements of habitat characterizing the dynamic system.

ABSTRACT Rock properties play a critical role in dictating styles of deformation at all spatial scales, yet the effect of changes across and within diagenetic transition zones has been little studied, despite profound impact on resulting mechanical stratigraphy. Our analysis of the variation of fold strain at map scale and outcrop scale of the highly siliceous Monterey and Sisquoc Formations in the southern Santa Maria Basin, California, provides insight into the interplay among deformation, diagenesis, and rock composition. Diagenetic modification of these rocks has created intervals with high interstratal and interformational contrasts in competence. Map-scale analysis showed large variation in fold strain within the same area, with shortening values ranging from 5.5% to 21.1% between siliceous formations of different diagenetic grade and competence. Apparent shortening in the competent, diagenetically altered, thinly bedded Monterey Formation is twice as high as that in the overlying highly porous, diatomaceous, more massive Sisquoc Formation. The large difference in measurable apparent shortening suggests that the same amount of actual strain was chiefly accommodated by folding in the Monterey Formation versus horizontal compaction in the Sisquoc Formation, since there is no evidence of a detachment between the units. Strain analysis at outcrop scale provided insight into the ways in which both units express such different shortening ratios without having an unconformity or detachment fault between them.

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 Tuff beds (volcanic ash beds and tuffs) have been known in the Miocene Monterey and Modelo Formations since they were initially described nearly 100 yr ago. Yet, these tephra layers have remained largely ignored. The ages and correlation of the Monterey and Modelo Formations are predominantly based on associated biostratigraphy. Here, we combined tephrochronology and biostratigraphy to provide more precise numerical age control for eight sedimentary sequences of the Monterey and Modelo Formations from Monterey County to Orange County in California. We correlated 38 tephra beds in the Monterey and Modelo Formations to 26 different dated tephra layers found mainly in nonmarine sequences in Nevada, Idaho, and New Mexico. We also present geochemical data for an additional 19 tephra layers in the Monterey and Modelo Formations, for which there are no known correlative tephra layers, and geochemical data for another 11 previously uncharacterized tephra layers in other areas of western North America. Correlated tephra layers range in age from 16 to 7 Ma; 31 tephra layers erupted from volcanic centers of the Snake River Plain, northern Nevada to eastern Idaho; 13 other tephra layers erupted from the Southern Nevada volcanic field; and the eruptive source is unknown for 12 other tephra layers. These tephra layers provide new time-stratigraphic markers for the Monterey and Modelo Formations and for other marine and nonmarine sequences in western North America. We identified tephra deposits of four supereruptions as much as 1200 km from the eruptive sources: Rainier Mesa (Southern Nevada volcanic field) and Cougar Point Tuff XI, Cougar Point Tuff XIII, and McMullen Creek (all Snake River Plain).