Abstract There are only three environmental factors necessary for the development of turbidity current flow. These are: sufficient water depth, sufficient slope angle, and an effective regression. The term, “sufficient water depth”, is somewhat controversial. One geologist's definition of deep water coincides with another's concept of shallow water. Examining first, the maximum water depths for marine strata in California, depths associated with Neogene turbidites range down to 1500 or 1800 meters. In modern sediments, turbidites have been cored in water up to 8200 meters deep in the Puerto Rico Trench. Other flat-floored abyssal trenches which are believed to be receiving turbidites are found at still greater depths. Thus, there is no reason to believe that turbidites are restricted by any maximum in terms of water depth, if the other factors necessary for their generation are present. The question then arises as to what is the minimum water depth in which turbidites can develop. In the ancient rocks, pertinent documentation is again found in the Late Tertiary of California. A minimum figure of about 100 to 125 meters is suggested for some Middle Miocene turbidites in the Santa Monica Mountains. These water depths were determined on the basis of benthonic foraminiferal assemblages. In oceanic waters the shallowest occurrence described in the literature (Hand and Emery, 1964) is a graded sand bed, one meter thick, near the head of Newport Canyon off the California coast. This bed occurs in a present day water depth of 184 meters. Presumably, it was deposited

We interpret seismic-reflection profiles to determine the location and offset mode of Quaternary offshore faults beneath the Gulf of Santa Catalina in the inner California Continental Borderland. These faults are primarily northwest-trending, right-lateral, strike-slip faults, and are in the offshore Rose Canyon–Newport-Inglewood, Coronado Bank, Palos Verdes, and San Diego Trough fault zones. In addition we describe a suite of faults imaged at the base of the continental slope between Dana Point and Del Mar, California. Our new interpretations are based on high-resolution, multichannel seismic (MCS), as well as very high resolution Huntec and GeoPulse seismic-reflection profiles collected by the U.S. Geological Survey from 1998 to 2000 and MCS data collected by WesternGeco in 1975 and 1981, which have recently been made publicly available. Between La Jolla and Newport Beach, California, the Rose Canyon and Newport-Inglewood fault zones are multistranded and generally underlie the shelf break. The Rose Canyon fault zone has a more northerly strike; a left bend in the fault zone is required to connect with the Newport-Inglewood fault zone. A prominent active anticline at mid-slope depths (300–400 m) is imaged seaward of where the Rose Canyon fault zone merges with the Newport-Inglewood fault zone. The Coronado Bank fault zone is a steeply dipping, northwest-trending zone consisting of multiple strands that are imaged from south of the U.S.–Mexico border to offshore of San Mateo Point. South of the La Jolla fan valley, the Coronado Bank fault zone is primarily transtensional; this section of the fault zone ends at the La Jolla fan valley in a series of horsetail splays. The northern section of the Coronado Bank fault zone is less well developed. North of the La Jolla fan valley, the Coronado Bank fault zone forms a positive flower structure that can be mapped at least as far north as Oceanside, a distance of ~35 km. However, north of Oceanside, the Coronado Bank fault zone is more discontinuous and in places has no strong physiographic expression. The San Diego Trough fault zone consists of one or two well-defined linear fault strands that cut through the center of the San Diego Trough and strike N30°W. North of the La Jolla fan valley, this fault zone steps to the west and is composed of up to four fault strands. At the base of the continental slope, faults that show recency of movement include the San Onofre fault and reverse, oblique-slip faulting associated with the San Mateo and Carlsbad faults. In addition, the low-angle Oceanside detachment fault is imaged beneath much of the continental slope, although reflectors associated with the detachment are more prominent in the area directly offshore of San Mateo Point. North of San Mateo Point, the Oceanside fault is imaged as a northeast-dipping detachment surface with prominent folds deforming hanging-wall strata. South of San Mateo point, reflectors associated with the Oceanside detachment are often discontinuous with variable dip as imaged in WesternGeco MCS data. Recent motion along the Oceanside detachment as a reactivated thrust fault appears to be limited primarily to the area between Dana and San Mateo Points. Farther south, offshore of Carlsbad, an additional area of folding associated with the Carlsbad fault also is imaged near the base of the slope. These folds coincide with the intersection of a narrow subsurface ridge that trends at a high angle to and intersects the base of the continental slope. The complex pattern of faulting observed along the base of the continental slope associated with the San Mateo, San Onofre, and Carlsbad fault zones may be the result of block rotation. We propose that the clockwise rotation of a small crustal block between the Newport-Inglewood–Rose Canyon and Coronado Bank fault zones accounts for the localized enhanced folding along the Gulf of Santa Catalina margin. Prominent subsurface basement ridges imaged offshore of Dana Point may inhibit along-strike block translation, and thus promote block rotation.

Abstract The present bathymetry, basin geometries, and spatial earthquake distribution in the inner California borderlands reflect complex basin inversion processes that reactivated two low-angle Miocene extensional detachments as blind thrust faults during the Pliocene to Holocene. The Oceanside and the Thirtymile Bank detachments comprise the inner California blind thrust system. These low-angle detachments originated during Neogene crustal extension that opened the inner California borderlands, creating a rift system that controlled the deposition of early to late Miocene sedimentary units and the exhumation of the metamorphic Catalina schist. During the Pliocene, a transpressional regime induced by oblique convergence between the Pacific and the North American plates reactivated the Oceanside and the Thirtymile Bank detachments as blind thrust faults. This reactivation generated regional structural wedges cored by faulted basement blocks that inverted the sedimentary basins in the hanging wall of the Miocene extensional detachments and induced contractional fold trends along the coastal plain of Orange and San Diego counties. Favorably oriented high-angle normal faults were also reactivated, creating zones of oblique and strike-slip faulting and folding such as the offshore segments of the Rose Canyon, San Diego, and the Newport-Inglewood fault zones. We evaluate several different styles of geometric and kinematic interactions between these high-angle strike-slip faults and the low-angle detachments, and favor interpretations where deep oblique slip is partitioned at shallow crustal levels into thrusting and right-lateral strike-slip faulting. Analyses of seismic reflection profiles, well data, earthquake information, and sea-floor geology indicate that the Oceanside and the Thirtymile Bank blind thrust faults are active and represent important sources of earthquakes in this region. Restored balanced cross sections provide a minimum southwest-directed slip of 2.2–2.7 km (1.4–1.8 mi) on the Oceanside thrust and illustrate the function of this detachment in controlling the processes of basin inversion and the development of the overlying fold and thrust belt.

ABSTRACT This atlas of foraminifera is designed to update and enhance biostratigraphic correlations in the California Miocene. The study focuses primarily on the Monterey Formation, because it is a major source and reservoir of petroleum, and exclusively on the time interval during which it was deposited, 17.9 to 6.0 million years ago. Most of the recovered fauna derives from nine outcrop sections or areas in central and southern California, representing four Neogene coastal basins: Graves Creek (Salinas Basin), Indian Creek (Salinas Basin), Laguna Hills (Los Angeles Basin), Manville Quarry access road (Santa Maria Basin), Monterey County roadcuts (Salinas Basin), Naples Beach (Ventura Basin), Upper Newport Bay (Los Angeles Basin), San Clemente Island (Los Angeles Basin), and Topanga Canyon (Los Angeles Basin). The collections yield 112 genera and 391 (350 benthic, 41 planktic) species-group taxa. Eleven new species are described: Astacolus naplesensis, Bolivina exilicostata, Bolivina isaacsi, Bolivina woodruffi, Cancris lippsi, Evolutononion dumonti, Lenticulina barroni, Lenticulina douglasi, Lenticulina indianensis, Neoeponides navarrettei, and Valvulineria mcdougalli. Sequence checklists for each section tabulate the occurrences and relative abundances of species, the data from which are composited in faunal checklists that reveal provincial trends in the spatial and temporal distribution of each species. Illustrations of all recorded species should enable workers to compare taxa in order to evaluate and incorporate new information into preexisting data banks. They also provide the means for conformity among workers and serve as a training guide for new students. Future applications in geologic correlation should benefit from the greater degrees of precision and confidence afforded by the revised foraminiferal taxonomy and biostratigraphy presented in this compendium.

Abstract Detailed marine geophysical surveys of the inner California Continental Borderland west of northern Baja California show that the region is underlain by two major northwest-trending Quaternary dextral wrench fault systems. The San Clemente fault system lies along the western part of the inner borderland and comprises the San Clemente and San Isidro fault zones. Together, these fault zones connect to form a long (>300 km), narrow (<5 to 10 km), continuous zone of shear similar to the longer San Andreas transform system onshore. The Agua Blanca fault system is a complex northwest-trending zone of dextral shear delineated by three or more subparallel wrench fault zones in the eastern part of the inner borderland. The westernmost, San Diego Trough-Bahia Soledad fault zone, consists of relatively long (-50 km), continuous main fault traces which cut the Quaternary sediments of the nearshore basin trough. The Coronado Bank-Agua Blanca fault zone is more complicated, with numerous discontinuous, subparallel, right- and-left-stepping, en echelon and anastomosing fault traces which are associated with substantial structural relief. A nearshore zone of faulting, marked by the Estero-Descanso fault zone in the south and the Newport-Inglewood-Rose Canyon fault zone in the north, parallels the coast and defines the eastern boundary of the California Continental Borderland structural province. All of these eastern fault zones merge into the transpeninsular Agua Blanca fault, and their N30°W trend differs significantly (>20°) from the trend of the major Peninsular Ranges fault zones. The ridge-and-basin physiography of the inner borderland and transtension evident along the Agua Blanca fault system show that dextral oblique rifting has dominated the late Cenozoic tectonic style of the inner California Continental Borderland. Systematic differences in the post-Miocene style of deformation, with extension in the south, right-slip in the center, and convergence in the north, imply that Transverse Ranges convergence is affecting inner borderland tectonism. Historical earthquake activity shows that the inner borderland is an active part of the present-day Pacific-North American plate boundary, with focal mechanisms generally consistent with the tectonism inferred from the geologic structure. Counterclockwise rotation of a semirigid “Southern California Shear Zone,” which is the splintered northern end of the long, narrow, Baja California microplate, explains the observed patterns of deformation within the region. Because significant right-slip may occur to the west of Baja California along the San Clemente fault system, and does not cross the peninsula to the Gulf of California transform system, estimates of Pacific-North American relative plate motion based on sea-floor-spreading rates at the mouth of the Gulf of California may be in error.