The eastern Lake Mead region, to the north of the belt of metamorphic core complexes that define the Colorado River extensional corridor, underwent large-magnitude extension in the middle to late Miocene. We present two speculative new models for extension in this area that resolve several puzzling and paradoxical relations. These models are based on new field mapping and structural, geochronologic, and thermochronologic data from the northern White Hills, Lost Basin Range, and south Wheeler Ridge. The Meadview fault, a previously underappreciated structure, is an east-side-down normal fault that separates the northern Lost Basin Range to the west from south Wheeler Ridge to the east. Proterozoic crystalline rocks of the northern Lost Basin Range yielded an apatite fission-track (AFT) age of 15 Ma, whereas 2 km to the east, across the Meadview fault, crystalline rocks of south Wheeler Ridge yielded a 127 Ma AFT age. Similarly, at the south end of the Lost Basin Range, crystalline rocks with ca. 15 Ma AFT ages lie within 5 km of crystalline rocks of Garnet Mountain that yielded a 68 Ma AFT age across the Grand Wash fault. Neither of these relations can be explained by existing tilted crustal section or tilt-block models. In our “classic” metamorphic core complex model, the Grand Wash fault (breakaway), the Meadview fault, and the South Virgin–White Hills detachment represent different structural levels of a single, regional detachment that was active between ca. 16 and 11 Ma. The hanging wall of the detachment consists of rocks at south Wheeler Ridge, the Paleozoic ridges, and possibly part of the crystalline basement of the Gold Butte block, sedimentary and volcanic rocks in the hanging walls of the Salt Spring and Cyclopic Mine faults, and possibly stranded tilt blocks beneath the Grand Wash Trough supradetachment basin. The footwall, exhumed by subvertical simple shear and characterized by middle Miocene AFT ages, includes the central and western Gold Butte block, Hiller Mountains, and crystalline rocks of the White Hills and the Lost Basin Range. The east-dipping Meadview fault bounds the crystalline core on the east; the west-dipping South Virgin–White Hills detachment bounds the core on the west. Therefore, the Grand Wash fault represents the structurally highest part of the detachment, and the South Virgin–White Hills detachment represents the structurally deepest exposed part of the detachment. In the modified core complex model, the Grand Wash, Meadview, and South Virgin–White Hills detachment faults are separate structures, and the Grand Wash Trough is a “trailing-edge” basin bound on the east by the Grand Wash fault and on the west by the Meadview fault. The South Virgin–White Hills detachment is the main detachment along which extension was accommodated, and the Meadview fault is a major antithetic normal fault that facilitated exhumation of the core at the trailing edge of the detachment system.

Abstract More than 6 ½ billion barrels of oil have been discovered in the San Joaquin Valley. Approximately 4 ¼ billion barrels have been produced and there is a reserve of 2 ¼ . billion barrels. San Joaquin Valley oil fields account for 42 per cent of the annual production, and contain 45 per cent of the reserves of the state. Ninety per cent of the oil produced to date has come from rocks which are Miocene or younger in age. Nonmarine sediments, largely of Miocene or later age, have accounted for 1 ½ billion barrels of oil, or 35 per cent of the total production of the valley. Oligocene and Eocene reservoirs are assuming importance as deeper drilling is done and new areas are explored. The pre-Tertiary sediments have accounted for less than one per cent of the oil produced. However, Cretaceous rocks are now being actively prospected. The San Joaquin Valley is a synclinorium some 250 miles long and 50–60 miles wide, lying between the Sierra Nevada Mountains to the east and the Coast Ranges to the west. The maximum depth to the basement is estimated to be in excess of 30,000 feet with the thickest sedimentary section being on the western side of the valley. Oil production is confined mainly to the southern portion which contains a thick section of organic Tertiary sediments. The San Joaquin Valley does not lend itself well to the basin analysis suggested by authors. The geosynclinal trough is present, as is the Sierra Nevada foreland to the east. Numerous faults of minor displacement along the east side of the valley might be termed a "hingebelt" but they interrupt the regional dip in only a minor way. The San Andreas and other faults of large lateral displacement have probably altered or removed the "geanticlinal welt," if it ever existed, on the west side of the valley. Furthermore, the western boundary of the valley has been transgressed many times by Tertiary seas making it difficult to determine the exact outline of the San Joaquin "basin." In the San Joaquin Valley, oil is found in almost every type of trap. Anticlinal structures with complications either by faulting or stratigraphic changes have accounted for the major volume of production. Examples of this type of accumulation are fields on the Coalinga-Kettleman Hills anticline, the Elk Hills-Coles Levee anticline, the Rio Bravo-Greeley trend, the Wheeler Ridge-Tejon Ranch anticline and the Belridge anticline. Oil occurs in faulted homoclines on the east side of the valley at Round Mountain, Kern Front, Fruitvale, Mount Poso, and Mountain View. Sands open to outcrop but with low fluid level produce at East Coalinga. The Lakeview area of the Midway-Sunset field appears to be synclinal. Although sand is the reservoir rock for 95 per cent or more of the fields, significant accumulations also occur in fractured shales at Elk Hills and Buena Vista Hills and in fractured schist basement at Edison. Inclined water tables have been noted in the Coalinga Nose, North Dome of Kettleman Hills, Paloma, Coles Levee, Elk Hills, and other fields. Advocates of the hydrodynamic theory are opposed by those who consider such inclined water surfaces due to differences in permeability. In some cases water encroachment is opposed to direction of inclination. In the future, stratigraphic and fault traps should account for a larger percentage of oil discovered in the San Joaquin Valley than in the past. Obscure structural highs revealed by subsurface geology, detailed geophysics, or other methods will undoubtedly contribute future discoveries. Recently, extensions and deeper drilling of known structures have accounted for substantial amounts of new oil and should continue to do so in the future.

Active tectonics, tectonic geomorphology, and fault system dynamics investigate deformation of continental crust over late Quaternary to annual time scales. These interdisciplinary endeavors require joint analysis of diverse data sets and model results. Data gathering and analysis driven by EarthScope and other large solid earth science initiatives motivates a discussion of how to apply geoinformatics tools to enhance these efforts. I use three information integration scenarios for earthquake geology site context, basic digital elevation model (DEM) analysis, and tectonic geomorphology (all located in southern California) to show the kinds of analyses, integrations, and visualizations that are commonly employed. Earthquake geology site context along the San Jacinto fault ranges in scale from the San Andreas transform boundary to high-resolution topography and balloon aerial photography. Manipulations of a DEM for the Carrizo Plain illustrate the basic record of deformation and surface processes recorded in the topography. Tectonic geomorphologic investigations at Wheeler Ridge include visualization of imagery and geology with topography, raster calculations to produce a map of local relief, and the integration of fault model calculations for surface uplift. Necessary data sets for these and other scenarios include seismicity; crustal motion; stress; topography; remotely sensed imagery; and maps of Quaternary faults, late Cenozoic subsidence and uplift, and Quaternary geology. Necessary geoinformatics capabilities include visualization and cartography, file format and database conversion, geostatistics, comprehensive data query capability, data capture, field data capture, and physics-based deformation and landscape development models. Collaborations will improve earth scientists' ability to create knowledge, while providing domain challenges for information technologists.

ABSTRACT In this paper, we analyze source, seal, trap, reservoir, timing, and migration to explain petroleum occurrence and exploration prospectiveness in the southernmost San Joaquin basin. The factors that control oil occurrence and field size vary greatly among the three productive geologic domains in the area. We term these three domains the Foothills, the Basin, and the Upturn. The Upturn lies in between the structurally high Foothills and the structurally low Basin, and is a near-vertical panel of highly faulted strata with 5,000’-15,000’ of structural relief. Monterey Formation source rock in the southernmost San Joaquin basin has reached oil maturity mainly within the Basin. Oil generation there began about 4 Ma and continues today. However, the onset of anticlinal growth in the Basin at about 1 Ma dramatically changed oil migration pathways and delivery destinations. Prior to 1 Ma, oil migrating out of the Basin was delivered broadly across the entire east-west extent of the Upturn and Foothills. After 1 Ma, migration pathways became more complex and more east to west, resulting in very large oil pools in the southwestern San Joaquin basin. In the Basin, abundant oil has been generated, seal is ubiquitous, and early-formed traps are present. However, reservoir presence, reservoir quality, and the availability of migration pathways limit the amount of commercial production. Commercial oil is found mainly within gently dipping upper Miocene Reef Ridge and Stevens submarine-fan sand stratigraphic traps. The upper Miocene is sand poor, so sand mapping is critical. Fortunately, modern 3-D seismic combined with well data allow reliable mapping of sand fairways and fan facies. Little oil production exists above the upper Miocene because the high-angle faults that facilitate migration from the lower Monterey hydrocarbon kitchen do not penetrate high enough to allow charging of shallower strata. Little commercial production exists below the upper Miocene because depths are too great for sands to retain reservoir quality. The Upturn is well charged with oil, has abundant migration pathways, and contains numerous fault traps, many of which formed before oil migration began. However, it is sparsely drilled and difficult to image seismically, so exploration for the fault-footwall traps that are the typical targets is risky. Perhaps surprisingly given the active dense faulting, the presence of several oil fields in the Upturn indicates that seals can be effective. As in the Basin, sand is generally sparse, so sand presence is an important play control. The eastern Upturn toward the Tejon embayment is sandy, but the western and central parts generally are not. Where sand is present, reservoir quality is adequate even in lower Monterey and older strata that are tight in the Basin because burial of these strata was never deep. Most Foothills fields are located in Quaternary surface anticlines. However, central and eastern Foothills anticlines are undercharged because their present-day fetch areas are small and their trap timing is late: most of the anticlines are extremely young, so were not available to capture early-generated oil migrating from the Basin. To date more oil has been produced in the eastern than in the western Foothills, partly because sand content increases eastward.

This field trip is an overview and reappraisal of the prolific oil basins of southern California (Fig. 1A) using exploration methods now commonly used in international exploration. As a result of the dramatic decline in oil and gas exploration in California during the last decade these mature and well known basins have received limited modern hydrocarbon research and it is hoped that our field trip and guidebook will outline some of the important aspects and questions of these intriguing petroleum systems. We have used balanced cross sections and other types of structural analyses integrated with basin modeling, geochemical and geophysical data to gain new insights into the structure, trapping mechanisms, and petroleum systems (Magoon and Dow, 1994) in a setting combining strike-slip and convergence (transpression). Southern California geology also has the scientific advantage, but societal disadvantage, of earthquakes (Fig. IB) which provide useful data about the deeper structure which will be presented during the trip. Our field examples are in the eastern Ventura basin, Ridge Basin, southern San Joaquin basin, Cuyama basin and western Ventura basin as well as a transect of the western Transverse Ranges (Fig. 1A).

Abstract The conventional Wheeler diagram aids the construction of a spatiotemporal framework of strata. The diagrams are created manually by studying outcrops, wells, or seismic data. For the latter case, automated methods now exist, which support the construction of 2D, as well as 3D Wheeler diagrams. Seismic data contains information in three dimensions, X , Y and Z , where ‘ Z ’ is either two-way time or depth. Seismic horizons are correlated surfaces that often follow geological time lines. In this case, a set of interpreted seismic horizons contains information in four dimensions ( X , Y , Z , and Geological Time). In the mapping from the structural domain to Wheeler space, information about Z (thickness) is lost. This means that one dimension is missing in the conventional Wheeler diagram. This paper describes a method to add information from the Z dimension to the Wheeler domain. It is done by computing stratigraphic thicknesses per sequence stratigraphic unit and displaying these as colour-coded overlays in the Wheeler domain. Thus displayed, thickness variations help in understanding changes in accommodation, sedimentation rate, and depositional trends. 3D Wheeler displays with colour-coded thickness information are referred to as 4D Wheeler diagrams. In this article, the method is described and applied to a case study from the southern North Sea.