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 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 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.