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At least 307 records · Page 17Linked to original sources
USGS2004

Marine geology and earthquake hazards of the San Pedro Shelf region, southern California

High-resolution seismic-reflection data have been com- bined with a variety of other geophysical and geological data to interpret the offshore structure and earthquake hazards of the San Pedro Shelf, near Los Angeles, California. Prominent structures investigated include the Wilmington Graben, the Palos Verdes Fault Zone, various faults below the western part of the shelf and slope, and the deep-water San Pedro Basin. The structure of the Palos Verdes Fault Zone changes mark- edly southeastward across the San Pedro Shelf and slope. Under the northern part of the shelf, this fault zone includes several strands, but the main strand dips west and is probably an oblique-slip fault. Under the slope, this fault zone con- sists of several fault strands having normal separation, most of which dip moderately east. To the southeast near Lasuen Knoll, the Palos Verdes Fault Zone locally is a low-angle fault that dips east, but elsewhere near this knoll the fault appears to dip steeply. Fresh sea-floor scarps near Lasuen Knoll indi- cate recent fault movement. The observed regional structural variation along the Palos Verdes Fault Zone is explained as the result of changes in strike and fault geometry along a master strike-slip fault at depth. The shallow summit and possible wavecut terraces on Lasuen knoll indicate subaerial exposure during the last sea-level lowstand. Modeling of aeromagnetic data indicates the presence of a large magnetic body under the western part of the San Pedro Shelf and upper slope. This is interpreted to be a thick body of basalt of Miocene(?) age. Reflective sedimentary rocks overlying the basalt are tightly folded, whereas folds in sedimentary rocks east of the basalt have longer wavelengths. This difference might mean that the basalt was more competent during folding than the encasing sedimentary rocks. West of the Palos Verdes Fault Zone, other northwest-striking faults deform the outer shelf and slope. Evidence for recent movement along these faults is equivocal, because age dates on deformed or offset sediment are lacking.

Professional Paper↗
USGS2025

Black abalone (Haliotis cracherodii) population density, recruitment, size structure, and population growth at Naval Base Ventura County, San Nicolas Island, California, 2013–22

The range of the endangered black abalone ( Haliotis cracherodii ) is divided into the North Central California region, the Central California region, the Southern California Mainland region, the Channel Islands region, and the Baja California region by the National Marine Fisheries Service for management purposes. San Nicolas Island is one of eight subregions of the Channel Islands region. The black abalone recovery plan establishes five demographic criteria for the possible delisting or downlisting of the species. The U.S. Geological Survey monitors nine long-term intertidal black abalone sites at San Nicolas Island, California, in cooperation with the U.S. Navy, which owns the island. This report uses data collected between 2013 and 2022 and the delisting criteria to analyze and describe the density, recruitment, size structure, and population trends at the nine U.S. Geological Survey monitoring sites at San Nicolas Island.

California↗
USGS1996

Discrimination among spawning concentrations of Lake Superior lake herring based on trace element profiles in sagittae

Little is known about the stock structure of lake herring Coregonus artedi in Lake Superior, and recent increases in harvestable stock sizes has led to expanded exploitation in some areas. Research on marine teleosts has demonstrated that chemical differences in sagittal otoliths can be used for identification of fish stocks. We used plasma emission spectrophotometry to measure the concentrations of 10 trace elements in the sagittal otoliths from lake herring captured at eight spawning sites in Lake Superior and from Little Star Lake. an inland lake outside the Lake Superior basin. Discriminant function analysis indicated that elemental concentrations provided site‐specific information but that considerable overlap existed among some locations, especially those in western Lake Superior. Correct classification rates varied from 12.0% to 86.1% and were generally higher for spawning locations from embayments in eastern Lake Superior and for the outgroup population from Little Star Lake. The results presented here demonstrate the potential usefulness of this technique for strictly freshwater species, especially those that live in highly oligotrophic waters such as Lake Superior.

Lake Superior, Little Star Lake↗
USGS2013

Tectonic map of the Circum-Pacific region, Pacific basin sheet

Circum-Pacific Map Project : The Circum-Pacific Map Project was a cooperative international effort designed to show the relationship of known energy and mineral resources to the major geologic features of the Pacific basin and surrounding continental areas. Available geologic, mineral, and energy-resource data are being complemented by new, project-developed data sets such as magnetic lineations, seafloor mineral deposits, and seafloor sediment. Earth scientists representing some 180 organizations from more than 40 Pacific-region countries are involved in this work. Six overlapping equal-area regional maps at a scale of 1:10,000,000 form the cartographic base for the project: the four Circum-Pacific Quadrants (Northwest, Southwest, Southeast, and Northeast), and the Antarctic and Arctic Sheets. There is also a Pacific Basin Sheet at a scale of 1:17,000,000. The Base Map Series and the Geographic Series (published from 1977 to 1990), the Plate-Tectonic Series (published in 1981 and 1982), the Geodynamic Series (published in 1984 and 1985), and the Geologic Series (published from 1984 to 1989) all include six map sheets. Other thematic map series in preparation include Mineral-Resources, Energy-Resources and Tectonic Maps. Altogether, more than 50 map sheets are planned. The maps were prepared cooperatively by the Circum-Pacific Council for Energy and Mineral Resources and the U.S. Geological Survey and are available from the Branch of Distribution, U. S. Geological Survey, Box 25286, Federal Center, Denver, Colorado 80225, U.S.A. The Circum-Pacific Map Project is organized under six panels of geoscientists representing national earth-science organizations, universities, and natural-resource companies. The six panels correspond to the basic map areas. Current panel chairmen are Tomoyuki Moritani (Northwest Quadrant), R. Wally Johnson (Southwest Quadrant), Ian W.D. Dalziel (Antarctic Region), vacant. (Southeast Quadrant), Kenneth J. Drummond (Northeast Quadrant), and George W. Moore (Arctic Region). Project coordination and final cartography was being carried out through the cooperation of the Office of the Chief Geologist of the U.S. Geological Survey, under the direction of General Chairman, George Gryc of Menlo Park, California. Project headquarters were located at 345 Middlefield Road, MS 952, Menlo Park, California 94025, U.S.A. The framework for the Circum-Pacific Map Project was developed in 1973 by a specially convened group of 12 North American geoscientists meeting in California. The project was officially launched at the First Circum-Pacific Conference on Energy and Mineral Resources, which met in Honolulu, Hawaii, in August 1974. Sponsors of the conference were the AAPG, Pacific Science Association (PSA), and the Coordinating Committee for Offshore Prospecting for Mineral Resources in Offshore Asian Areas (CCOP). The Circum-Pacific Map Project operates as an activity of the Circum-Pacific Council for Energy and Mineral Resources, a nonprofit organization that promotes cooperation among Circum-Pacific countries in the study of energy and mineral resources of the Pacific basin. Founded by Michel T. Halbouty in 1972, the Council also sponsors conferences, topical symposia, workshops and the Earth Science Series books. Tectonic Map Series : The tectonic maps distinguish areas of oceanic and continental crust. Symbols in red mark active plate boundaries, and colored patterns show tectonic units (volcanic or magmatic arcs, arc-trench gaps, and interarc basins) associated with active plate margins. Well-documented inactive plate boundaries are shown by symbols in black. The tectonic development of oceanic crust is shown by episodes of seafloor spreading. These correlate with the rift and drift sequences at passive continental margins and episodes of tectonic activity at active plate margins. The recognized episodes of seafloor spreading seem to reflect major changes in plate kinematics. Oceanic plateaus and other prominences of greater than normal oceanic crustal thickness such as hotspot traces are also shown. Colored areas on the continents show the ages of deformation and metamorphism of basement rocks and the emplacement of igneous rocks. Transitional tectonic (molassic) and reactivation basins are shown by a colored boundary, and if they are deformed, a colored horizontal line pattern indicates the age of deformation. Colored bands along basin boundaries indicate age of inception, and isopachs indicate thickness of platform strata on continental crust and cover on oceanic crust. Colored patterns at separated continental margins show the age of inception of rift and drift (breakup) sequences. Symbols mark folds and faults, and special symbols show volcanoes and other structural features. Affiliations are as of compilation of the data. This map was created in quadrants and then compiled together. They are the Northwest land, Northwest Marine (different compilers), Northeast, Southwest and Southeast, and parts in plate-boundary sections.

Circum-Pacific Map↗
USGS2019

Terrestrial lidar data of the February 14, 2019 Sausalito Boulevard Landslide, Sausalito, California

On February 14, 2019, just before 2:56 am local time (Pacific Standard Time), a landslide initiated from the hillslopes above the Hurricane Gulch section of the City of Sausalito, Marin County, California. The landslide, specifically classified as a debris flow, overran a road (Sausalito Boulevard) immediately below the landslide source area and impacted a residential structure that subsequently toppled downslope and collided with another residential structure. The second structure then crossed a lower road (Crescent Avenue) that runs along the base of the slope before the mixture of soil and structural debris came to rest in and near the valley axis that drains the lower area of Hurricane Gulch. The U.S. Geological Survey responded to this event within hours of the landslide and provided situational awareness of possible secondary landslide hazards associated with the unstable slope. The USGS also rapidly mobilized its topographic surveying capabilities (specifically, GPS and terrestrial lidar devices) and collected a three-dimensional point cloud model of the landslide source area and surrounding terrain to capture the as-failed condition of the slope for use in potential future studies. This report summarizes the methods and available data collected during this response.

California↗
USGS1979

Depositional environments of the uranium-bearing Cutler Formations, Lisbon Valley, Utah

The Cutler Formation in Lisbon Valley, San Juan County, Utah, is composed predominantly of fluvial arkosic sandstones, siltstones, shales, and mudstones that were deposited by meandering streams that flowed across a flood plain and tidal flat close to sea level. Two types of channel deposits are recognized from their sedimentary structures: meandering and distributary. The flood plain was occasionally transgressed by a shallow sea from the west, resulting in the deposition of several thin limestones and marine sandstones. The marine sandstones were deposited as longshore bars. Wind transported sand along the shoreline of the shallow sea, forming a coastal dune field. Marine sandstones and eolian sandstones are more common in the upper Cutler in the southern part of the area, whereas in the central and northern part of the area the formation is predominantly fluvial. Crossbed orientation indicates that Cutler streams flowed S. 67? W. on the the average, whereas marine currents moved sediment S. 36? E. and N. 24? W., and wind transported sand S. 800 E. The uranium in the Cutler is found in the central and northern part of the area, in the upper part of the formation, in small fluvial sandstone bodies that were deposited predominantly in a distributary environment. No uranium is known in the marine or eolian sandstones. Petrographically, the uranium-bearing sandstones are identical to other Cutler fluvial sandstones except that they contain less calcite and more clay and are slightly coarser grained. Ore formation has modified the host sandstones very little.

Open-File Report↗
USGS1967

Stratigraphic and tectonic framework of Libya

Libya is situated on the Mediterranean foreland of the African shield. Marine strata of Paleozoic, Mesozoic, and Cenozoic ages abound in northern Libya, but continental rocks of Paleozoic and Mesozoic ages predominate in southern Libya. Marine incursions in Ordovician, Silurian, Devonian, Carboniferous, late Cretaceous, and early Tertiary times reached far into the country, some crossing the southern border. Compressional folds are almost wholly absent, but uplift, subsidence, block faulting, and tilting have occurred, and angular and parallel unconformities are common. The major diastrophic disturbances include the Caledonian and Hercynian, as well as disturbances during late Cretaceous and Oligocene through Miocene or Recent times. The chief regional structures are the Gefara basin, Hamada basin, Gargaf arch, Marzuq basin, Tibesti-Haruj uplift, Kufra basin, Cyrenaican uplift, and Sirte embayment. Several large basalt flows of Cenozoic age are present. Sand and gravel conceal the bedrock in about a third of the country. In the Sirte embayment marine sedimentation, differential compaction, reef development, subsidence, and block faulting, beginning in late Cretaceous time, favored the development of source and reservoir rocks. Recoverable oil has been found chiefly in limestone and sandstone of early and late Cretaceous and Tertiary ages, and in knobs of probable early Paleozoic sandstone and in fractured granite. In the Hamada basin oil accumulations have been found in sandstones of Triassic age and of several Paleozoic systems. Most of the oil and gas discovered to date in Libya are in anticlinal structures, but several unconformities within the section probably influenced these accumulations; oil and gas may well await discovery in other types of traps.

AAPG Bulletin↗
USGS1994

Identification of tire leachate toxicants and a risk assessment of water quality effects using tire reefs in canals

Cover is an important component of aquatic habitat and fisheries management. Fisheries biologists often try to improve habitats through the addition of natural and artificial material to improve cover diversity and complexity. Habitat-improvement programs range from submerging used Christmas trees to more complex programs using sophisticated artificial habitat modules. Used automobile tires have been employed in the large scale construction of reefs and fish attractors in marine environments (D'Itri 1985) and to a lesser extent in freshwater (Johnson and Stein 1979) and have been recognized as a durable, inexpensive and long-lasting material which benefits fishery communities. Recent studies by the U.S. Bureau of Reclamation (Mueller and Liston 1991) have quantified the importance of tire reeds to enhancing freshwater canal fisheries in the southwestern United States. These studies have demonstrated that fisheries and aquatic macroinvertebrates are attracted to these structures, increasing species diversity, densities and biomass where reefs are places in canals. Potential benefits to fishermen are great in the form of recreational fishing. However, the use of tire reefs in aquatic environments which have relatively small volumes compared to marine or reservoir environments has raised water quality concerns. Effects of tires on water quality have not typically been studied in the part because of the obvious presence of fishes and other aquatic organisms that make use of tire reefs; the implication being that tires are intert and non-toxic. Little information on effects of tires on water quality is contained in the literature. Stone et al. (1975) demonstrated that tire exposure had no detrimental effects on two species of marine fish while results of Kellough's (1991) freshwater tests were inconclusive, but suggested that some factor in tire leachate was toxic to rainbow trout ( Oncorhynchus mykiss ). Nozaka et al. (1973) found no harmful substances leached from tire material soaked in fresh water. Because there are few data on toxicity associated with tires, this became the focus of our study. Toxicity Identification Evaluation (TUE) procedures developed by the EPA (1991) were used to evaluate water quality impacted by tires.

Bulletin of Environmental Contamination and Toxico↗
USGS2002

Preliminary geologic map of the Santa Barbara coastal plain area, Santa Barbara County, California

This report presents a new geologic digital map of the Santa Barbara coastal plain area at a compilation scale of 1:24,000 (one inch on the map = 2,000 feet on the ground) and with a horizontal positional accuracy of at least 20 m. This preliminary map depicts the distribution of bedrock units and surficial deposits and associated deformation underlying and adjacent to the coastal plain within the contiguous Santa Barbara and Goleta 7.5' quadrangles. A planned second version will extend the mapping westward into the adjoining Dos Pueblos Canyon quadrangle and eastward into the Carpinteria quadrangle. The mapping presented here results from the collaborative efforts of geologists with the U.S. Geological Survey Southern California Areal Mapping Project (SCAMP) (Minor, Kellogg, Stanley, Stone, and Powell) and the tectonic geomorphology research group at the University of California at Santa Barbara (Gurrola and Selting). C.L. Powell, II, performed all new fossil identifications and interpretations reported herein. T.R. Brandt designed and edited the GIS database,performed GIS database integration and created the digital cartography for the map layout. The Santa Barbara coastal plain is located in the western Transverse Ranges physiographic province along a west-trending segment of the southern California coastline about 100 km (62 mi) northwest of Los Angeles. The coastal plain region, which extends from the Santa Ynez Mountains on the north to the Santa Barbara Channel on the south, is underlain by numerous active and potentially active folds and partly buried thrust faults of the Santa Barbara fold and fault belt. Strong earthquakes that occurred in the region in 1925 (6.8 magnitude) and 1978 (5.1 magnitude) are evidence that such structures pose a significant earthquake hazard to the approximately 200,000 people living within the major coastal population centers of Santa Barbara and Goleta. Also, young landslide deposits along the steep lower flank of the Santa Ynez Mountains indicate the potential for continued slope failures and mass movements that may threaten urbanized parts of the coastal plain. Deformed sedimentary rocks in the subsurface of the coastal plain and the adjacent Santa Barbara Channel contain deposits of oil and gas, some of which are currently being extracted. Shallow, localized sedimentary aquifers underlying the coastal plain provide limited amounts of water for the urban areas, but the quality of some of this groundwater is compromised by coastal salt-water contamination. The present map compilation provides a set of uniform geologic digital coverages that can be used for analysis and prediction of these and other geologic hazards and resources in the coastal plain region. In the map area the oldest stratigraphic units consist of resistant Eocene to Oligocene marine and terrestrial sedimentary rocks that form a mostly southward-dipping and laterally continuous sequence along the south flank of the Santa Ynez Mountains. Less resistant, but more variably deformed, Miocene, Pliocene, and Pleistocene marine sedimentary rocks and deposits are exposed in the lower Santa Ynez foothills and in the coastal hills and sea cliffs farther south. Pleistocene and Holocene surficial alluvial, colluvial, estuarine, and marine-terrace deposits directly underlie much of the low-lying coastal plain area, and similar-aged alluvial and landslide deposits locally mantle the lower flanks of the Santa Ynez Mountains. Structurally, the Santa Barbara coastal plain area is dominated by the Santa Barbara fold and fault belt, an east-west-trending zone of Quaternary, partly active folds and blind and exposed reverse and thrust faults. The dominant trend of individual structures within the belt is west-northwest -- slightly oblique to the overall trend of the fold and fault belt. A conspicuous exception, however, is the More Ranch fault system, which strikes east-northeast across the fold and f

Open-File Report↗
USGS2008

Stratigraphy and structural setting of Upper Cretaceous Frontier Formation, western Centennial Mountains, southwestern Montana and southeastern Idaho

Stratigraphic, sedimentologic, and palynologic data were used to correlate the Frontier Formation of the western Centennial Mountains with time-equivalent rocks in the Lima Peaks area and other nearby areas in southwestern Montana. The stratigraphic interval studied is in the middle and upper parts (but not uppermost) of the formation based on a comparison of sandstone petrography, palynologic age data, and our interpretation of the structure using a seismic line along the frontal zone of the Centennial Mountains and the adjacent Centennial Valley. The Frontier Formation is comprised of sandstone, siltstone, mudstone, limestone, and silty shale in fluvial and coastal depositional settings. A distinctive characteristic of these strata in the western Centennial Mountains is the absence of conglomerate and conglomeratic sandstone beds. Absence of conglomerate beds may be due to lateral facies changes associated with fluvial systems, a distal fining of grain size, and the absence of both uppermost and lower Frontier rocks in the study area. Palynostratigraphic data indicate a Coniacian age for the Frontier Formation in the western Centennial Mountains. These data are supported by a geochronologic age from the middle part of the Frontier at Lima Peaks indicating a possible late Coniacian-early Santonian age (86.25 ?? 0.38 Ma) for the middle Frontier there. The Frontier Formation in the western Centennial Mountains is comparable in age and thickness to part of the Frontier at Lima Peaks. These rocks represent one of the thickest known sequences of Frontier strata in the Rocky Mountain region. Deposition was from about 95 to 86 Ma (middle Cenomanian to at least early Santonian), during which time, shoreface sandstone of the Telegraph Creek Formation and marine shale of the Cody Shale were deposited to the east in the area now occupied by the Madison Range in southwestern Montana. Frontier strata in the western Centennial Mountains are structurally isolated from other Cretaceous rocks in the region and are part of the Lima thrust sheet that lies at the leading edge of the Sevier-style overthrusting in this part of southwestern Montana and adjacent southeastern Idaho.

Cretaceous Research↗
USGS2015

Evaluating habitat associations of a fish assemblage at multiple spatial scales in a minimally disturbed stream using low‐cost remote sensing

Habitat heterogeneity at multiple scales is a major factor affecting fish assemblage structure. However, assessments that examine these relationships at multiple scales concurrently are lacking. The lack of assessments at these scales is a critical gap in understanding as conservation and restoration efforts typically work at these levels. A combination of low‐cost side‐scan sonar surveys, aerial imagery using an unmanned aerial vehicle, and fish collections were used to evaluate the relationship between physicochemical and landscape variables at various spatial scales (e.g. micro‐mesohabitat, mesohabitat, channel unit, stream reach) and stream–fish assemblage structure and habitat associations in the South Llano River, a spring‐fed second‐order stream on the Edwards Plateau in central Texas during 2012–2013. Low‐cost side‐scan sonar surveys have not typically been used to generate data for riverscape assessments of assemblage structure, thus the secondary objective was to assess the efficacy of this approach. The finest spatial scale (micro‐mesohabitat) and the intermediate scale (channel unit) had the greatest explanatory power for variation in fish assemblage structure. Many of the fish endemic to the Edwards Plateau showed similar associations with physicochemical and landscape variables suggesting that conservation and restoration actions targeting a single endemic species may provide benefits to a large proportion of the endemic species in this system. Low‐cost side‐scan sonar proved to be a cost‐effective means of acquiring information on the habitat availability of the entire river length and allowed the assessment of how a full suite of riverscape‐level variables influenced local fish assemblage structure.

Texas↗
USGS2002

Mesozoic and Cenozoic tectonics of the eastern and central Alaska Range: Progressive basin development and deformation in a suture zone

Analysis of late Mesozoic and Cenozoic sedimentary basins, metamorphic rocks, and major faults in the eastern and central Alaska Range documents the progressive development of a suture zone that formed as a result of collision of an island-arc assemblage (the Wrangellia composite terrane) with the former North American continental margin. New basin-analysis, structural, and geochronologic data indicate the following stages in the development of the suture zone: (1) Deposition of 3-5 km of Upper Jurassic-Upper Cretaceous marine strata (the Kahiltna assemblage) recorded the initial collision of the island-arc assemblage with the continental margin. The Kahiltna assemblage exposed in the northern Talkeetna Mountains represents a Kimmeridgian-Valanginian backarc basin that was filled by northwestward-flowing submarine-fan systems that were transporting sediment derived from Mesozoic strata of the island-arc assemblage. The Kahiltna assemblage exposed in the southern Alaska Range represents a Valanginian-Cenomanian remnant ocean basin filled by west-southwestward-flowing submarine-fan systems that were transporting sediment derived from Paleozoic continental-margin strata uplifted in the along-strike suture zone. A belt of retrograde metamorphism and a regional anticlinorium developed along the continental margin from 115 to 106 Ma, roughly coeval with the end of widespread deposition in the Kahiltna sedimentary basins. (2) Metamorphism of submarine-fan deposits of the Kahiltna basin, located near the leading edge of the island-arc assemblage, occurred at ca. 74 Ma, as determined from a new U-Pb zircon age for a synkinematic sill. Coeval with metamorphism of deposits of the Kahiltna basin in the southern part of the suture zone was development of a thrust-top basin, the Cantwell basin, in the northern part of the suture zone. Geologic mapping and compositional data suggest that the 4 km of Upper Cretaceous nonmarine and marginal marine sedimentary strata in this basin record regional subaerial uplift of the suture zone. (3) Shortening and exhumation of the suture zone peaked from 65 to 60 Ma on the basis of metamorphic and geochronologic data. In the southern part of the suture zone, submarine-fan deposits of the Kahiltna basin, which had been metamorphosed to kyanite schists at ???25 km depth and ???650 ??C, were exhumed and cooled through the biotite closure temperature (???300 ??C) by ca. 62 Ma. In the northern part of the suture zone, this time period was marked by shortening, uplift, and erosion of sedimentary strata of the Cantwell basin. (4) From 60 to 54 Ma, ???3 km of volcanic strata were deposited over deformed sedimentary strata of the Cantwell basin, and several granitic plutons (the McKinley sequence) were emplaced along the suture zone. (5) Following igneous activity, strikeslip displacement occurred from ca. 54 to 24 Ma along the Denali fault system, which had developed in the existing suture zone. Late Eocene-Oligocene strike-slip displacement resulted in the formation of several small sedimentary basins along the Denali fault system. (6) Regional transpressive shortening characterized the suture zone from ca. 24 Ma to the present. Flexural subsidence, related to regional shortening, is represented by late Eocene to Holocene nonmarine deposits of the Tanana foreland basin. Regional subsidence resulted in Miocene coal seams up to 20 m thick and well-developed lacustrine deposits. Overlying the Miocene deposits are ???1.2 km of Pliocene and Holocene conglomeratic deposits. Compositional and paleocurrent data from these younger deposits record regional Neogene uplift of the suture zone and recycling of detritus from older basins to the south that had become incorporated into the uplifted suture zone. Geologic mapping of major thrust faults along the northern and southern margins of the suture zone documents Paleozoic strata thrust over both Pliocene fluvial deposits and Quaternary glacial deposits of the Tanana basin.

Geological Society of America Bulletin↗
USGS2015

Geologic map of the southern White Ledge Peak and Matilija quadrangles, Santa Barbara and Ventura Counties, California

This report presents a digital geologic strip map of the southern parts of the contiguous White Ledge Peak and Matilija 7.5’ quadrangles in coastal southern California. With a compilation scale of 1:24,000 (one inch on the map to 2,000 feet on the ground), the map depicts the distribution of bedrock units, surficial deposits, and associated deformation adjacent to and south of the Arroyo Parida fault and in the southern Ojai Valley east of the Ventura River. This new compilation, combined with a recently published geologic map of the Santa Barbara coastal plain (U.S. Geological Survey Scientific Investigations Map 3001), completes a 69-km-long east-west mapping transect from Goleta to Ojai by the U.S. Geological Survey. These two contiguous geologic maps provide new insights and constraints on Neogene-through-Quaternary tectonic deformation and consequent landscape change, including geohazards in the urbanized southern flank of the Santa Ynez Mountains. A principal aim of the new mapping and associated fault-kinematic measurements is to document and constrain the nature of transpressional strain transfer between various regional, potentially seismogenic faults. In the accompanying pamphlet, surficial and bedrock map units are described in detail as well as a summary of the structural and fault-kinematic framework of the map area. New biostratigraphic and biochronologic data based on microfossil identifications are presented in expanded unit descriptions of the marine Neogene Monterey and Sisquoc Formations. Site-specific fault kinematic observations are embedded in the digital map database. This compilation provides a uniform geologic digital geodatabase and map plot files that can be used for visualization, analysis, and interpretation of the area’s geology, geologic hazards, and natural resources.

California↗
USGS1999

The origin and paleoecologic significance of the trace fossil Asteriadtes in the Pennsylvanian of Kansas and Missouri

The trace fossil Asteriacites , recorded in Cambrian to Recent shallow- and deep-marine facies, is traditionally interpreted as the resting trace of asterozoans. Well-preserved specimens of A. lumbricalis are abundant in Pennsylvanian (Upper Carboniferous) shallow- and marginal-marine siliciclastic deposits of eastern Kansas and western Missouri. Detailed morphologic analysis of these specimens suggests that they record the activities of mobile epifaunal ophiuroids. Evidence of a brittle star (ophiuroid) producer rather than sea star (asteroid) is provided by (1) trace-fossil morphologic features reflecting the anatomy of the producer (e.g., well-differentiated central structure, slender vermiform arms) and ophiuroid burrowing technique (e.g., proximal arm expansion, arm branching), and (2) mode of occurrence (e.g., gregarious behavior, horizontal and vertical repetition). Vertical and horizontal repetition produces complex aggregates of A. lumbricalis that are interpreted either as escape structures (fugichnia) or as feeding structures, respectively. Ophiura texturata is proposed as a modern analogue for the A. lumbricalis producer, based on inferred life habit and feeding behavior. Asteriacites lumbricalis is present in two different intertidal trace-fossil assemblages. The first assemblage is characterized by high diversity and records tidal flats developed outside of embayments under normal marine conditions. The second assemblage consists of A. lumbricalis together with a few other ichnotaxa and represents a depauperate association that developed in restricted tidal flats within an embayment or estuarine setting. This challenges the conventional view of Asteriacites as a normal-marine salinity indicator. Some echinoderms, and particularly asterozoans, penetrate and inhabit modern environments of depressed salinity. The presence of Asteriacites in Pennsylvanian marginal-marine facies of Kansas and Missouri provides evidence that ophiuroids had adapted to brackish-water conditions by the late Paleozoic.

Kansas, Missouri↗
USGS2003

Geologic framework and hydrogeologic characteristics of the Edwards aquifer, Uvalde County, Texas

The Edwards aquifer in Uvalde County is composed of Lower Cretaceous carbonate (mostly dolomitic limestone) strata of the Devils River Formation in the Devils River trend and of the West Nueces, McKnight, and Salmon Peak Formations in the Maverick basin. Rocks in the Devils River trend are divided at the bottom of the Devils River Formation into the (informal) basal nodular unit. Maverick basin rocks are divided (informally) into the basal nodular unit of the West Nueces Formation; into lower, middle, and upper units of the McKnight Formation; and into lower and upper units of the Salmon Peak Formation. The Edwards aquifer overlies the (Lower Cretaceous) Glen Rose Limestone, which composes the lower confining unit of the Edwards aquifer. The Edwards aquifer is overlain by the (Upper Cretaceous) Del Rio Clay, the basal formation of the upper confining unit. Upper Cretaceous and (or) Lower Tertiary igneous rocks intrude all stratigraphic units that compose the Edwards aquifer, particularly in the southern part of the study area. The Balcones fault zone and the Uvalde salient are the principal structural features in the study area. The fault zone comprises mostly en echelon, high-angle, and down-to-the-southeast normal faults that trend mostly from southwest to northeast. The Uvalde salient—resulting apparently from a combination of crustal uplift, diverse faulting, and igneous activity—elevates the Edwards aquifer to the surface across the central part of Uvalde County. Downfaulted blocks associated with six primary faults—Cooks, Black Mountain, Blue Mountain, Uvalde, Agape, and Connor—juxtapose the Salmon Peak Formation (Lower Cretaceous) in central parts of the study area against Upper Cretaceous strata in the southeastern part. The carbonate rocks of the Devils River trend and the Maverick basin are products of assorted tectonic and depositional conditions that affected the depth and circulation of the Cretaceous seas. The Devils River Formation formed in a fringing carbonate bank—the Devils River trend— in mostly open shallow marine environments of relatively high wave and current energy. The West Nueces, McKnight, and Salmon Peak Formations resulted mostly from partly restricted to open marine, tidal-flat, and restricted deep-basinal environments in the Maverick basin. The porosity of the Edwards aquifer results from depositional and diagenetic effects along specific lithostratigraphic horizons (fabric selective) and from structural and solutional features that can occur in any lithostratigraphic horizon (non-fabric selective). In addition to porosity depending upon the effects of fracturing and the dissolution of chemically unstable (soluble) minerals and fossils, the resultant permeability depends on the size, shape, and distribution of the porosity as well as the interconnection among the pores. Upper parts of the Devils River Formation and the upper unit of the Salmon Peak Formation compose some of the most porous and permeable rocks in Uvalde County.

Texas↗
USGS1959

Geology of the upper Killik-Itkillik region, Alaska

The upper Killik-Itkillik map area is a 2,500 square mile segment of foothills along the north front of the Brooks Range on the Arctic Slope of Alaska. The rocks exposed in this area include eleven formations of sedimentary rocks, three types of surficial deposits, and one igneous rock unit. The oldest rocks are a 2,500-foot sequence of limestone which belongs to the Lisburne group (Mississippian). The Lisburne is succeeded by the Siksikpuk formation (Permian ?), a 300-foot unit of variegated shale and siltstone. The Shublik formation (Triassic), composed of 200 to 750 feet of fossiliferous dark shale, limestone, and chart, rests upon the Siksikpuk. Next above the Shublik is a sequence, more than 13,000 feet thick, of marine shale and graywacke which is subdivided into four formations: Tiglukpuk (Late Jurassic), Okpikruak (earliest Cretaceous), Fortress Mountain (late Early Cretaceous), and Torok (late Early Cretaceous). The youngest rocks comprise the Nanushuk group (late Early to Late Cretaceous) which consists of 5,000 feet of interfingering marine and non-marine clastic rocks and is subdivided into three formations: Tuktu, Chandler, and Ninuluk. Small diabase sills, thought to be of latest Jurassic age, intrude the Tiglukpuk and older formations in the western part of the map area. The rocks of the map area have been deformed by north-south tectonic forces in such a way that the upper part of the crust appears to have moved northward relative to deeper parts. Five east-trending zones of distinctive lithology and structure are recognizable: zone I, at the mountain front-massive strata of the Lisburne group sliced by southward dipping imbricate faults and locally thrust upon the younger strata of the dipping imbricate faults and locally thrust upon the younger strata of the foothills, zone II—relatively incompetent interfolded late Paleozoic and Mesozoic strata characterized by isoclinal folds and by small, closely spaced high-angle faults, zone III--chiefly rocks of the Fortress Mountain formation which, although folded and faulted, are not as complexly deformed as the rocks of zone II, zone IV - highly crenulated shale of the Torok formation, and zone V, at the northern edge of the map area--gently folded strata of the Nanushuk group. A seismograph survey across zone IV suggests that, although the incompetent Torok formation is highly crenulated, the subsurface strata lie nearly flat. The character of the subsurface structure in zones II and III is uncertain. However, it is believed that some of the high-angle faults in these two zones may flatten in the subsurface and merge into large sole faults beneath thrust plates of Paleozoic limestone. Such a fault pattern has been found in the foothills of the Alberta Rockies, where the surface structure, stratigraphy and geologic history are remarkably similar. The depositional history of the Paleozoic and Mesozoic strata is divided into a shelf phase during late Paleozoic and Triassic and a geosynclinal phase during Late Jurassic and Cretaceous. The shelf sediments were chiefly marine carbonates and fine clastics, apparently derived largely from the north. The geosynclinal sediments consisted of marine graywacke "flysch" deposits overlain by littoral marine and non-marine coal-bearing "molasse" deposits and were derived mainly from the south. Several periods of emergence and erosion interrupted the shelf and geosynclinal deposition; evidently some folding and faulting occurred during deposition of the "flysch". The principal deformation is believed to have coincided with the Laramide orogeny in Late Cretaceous or Tertiary. In the Pleistocene the Brooks Range was intensively glaciated, and at times of maximum advance, ice tongues along the major river valleys pushed northward into the foothills.

Alaska↗
USGS2005

Crystalline-rock ejecta and shocked minerals of the Chesapeake Bay impact structure, USGS-NASA Langley core, Hampton, Virginia, with supplemental constraints on the age of impact

The USGS-NASA Langley corehole at Hampton , Va., was drilled 2000 as the first in a series of new coreholes drilled in the late Eocene Chesapeake Bay impact structure to gain a comprehensive understanding of its three-dimensional character. This understanding is important for assessing ground-water resources in the region, as well as for learning about marine impacts on Earth. We studied crystalline-rock ejecta and shock-metamorphosed minerals from the Langley core to determine what they reveal about the geology of crystalline rocks beneath the Atlantic Coastal Plain and how those rocks were affected by the impact . An unusual polymict diamicton, informally called the Exmore beds (upper Eocene), is 33.8 meters (m; 110.9 feet (ft)) thick and lies at a depth of 269.4 to 235.65 m (884.0 to 773.12 ft) in the core . This matrix-supported sedimentary deposit contains clasts of Tertiary and Cretaceous sediment (ranging up to boulder size) and sparse pebbles of crystalline rock . The matrix consists of muddy sand that contains abundant quartz grains and minor glauconite and potassium feldspar. Significantly, the sandy matrix of the Exmore beds contains sparse quartz grains (0.1 to 0.3 millimeter (0.004 to 0.012 inch) in diameter) that contain multiple sets of intersecting planar deformation features formerly referred to as shock lamellae. As many as five different sets have been observed in some quartz grains. Planar deformation features also occur in quartz grains in reworked crystalline-rock clasts in the Exmore beds. Such grains are clearly of shock-metamorphic origin. The presence of these features indicates that the quartz grains have experienced pressures greater than 6 gigapascals (GPa) and strain rates greater than 10 6 /second. Thus, the shock-metamorphosed quartz grains, although rare, provide clear and convincing evidence that the Exmore beds are of hybrid impact origin. Identification of shocked quartz grains in the Langley core adds to the number of sites in the structure where their presence is confirmed. Most of the clasts of crystalline rock that are in and just below the Exmore beds are rounded, detrital, and typical of coastal plain sediments. However, a few have angular shapes and consist of cataclastically deformed felsite having aphanitic-porphyritic to aphanitic texture and peraluminous rhyolite composition. Three of these clasts contain quartz grains that display two sets of planar deformation features of shock-metamorphic origin. Shock-metamorphosed quartz is an integral part of the cataclastic fabric in these three clasts, indicating that both the fabric and the shocked quartz were produced by the same high-energy impact event. Some felsite clasts have spherulitic textures that may be features either of an impact melt or of preimpact volcanic rocks. A weighted-mean total-fusion 40 Ar/ 39 Ar age of 35.3±0.1 Ma (±lσ) for 19 analyses of 4 North American tektites records the age of the late Eocene Chesapeake Bay impact event.

Chesapeake Bay↗
USGS1974

Mariner 10 pictures of Mercury: First results

Mercury has a heavily cratered surface containing basins up to at least 1300 kilometers diameter flooded with mare-like material. Many features are closely similar to those on the moon, but significant structural differences exist. Major chemical differentiation before termination of accretion is implied.

Science↗