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At least 1,675 records · Page 93Linked to original sources
USGS2016

High-resolution seismic-reflection data from offshore northern California — Bolinas to Sea Ranch

The U.S. Geological Survey collected high-resolution seismic-reflection data in September 2009, on survey S-8-09-NC, offshore of northern California between Bolinas and Sea Ranch. The survey area spans about 125 km of California’s coast and extends around Point Reyes. Data were collected aboard the U.S. Geological Survey R/V Parke Snavely . Cumulatively, ~1,150 km of seismic-reflection data were acquired using a SIG 2mille minisparker. Subbottom acoustic depth of penetration spanned tens to several hundred meters and varied by location and underlying sediments and rock types. This report includes maps and a navigation file of the surveyed transects, utilizing Google Earth™ software, as well as digital data files showing images of each transect in SEG-Y and JPEG formats. The images of bedrock, sediment deposits, and tectonic structure provide geologic information that is essential to hazard assessment, regional sediment management, and coastal and marine spatial planning at Federal, State and local levels. This information is also valuable for future research on the geomorphic, sedimentary, tectonic, and climatic record of central California.

California↗
USGS2019

The Mw 6.0 South Napa earthquake of August 24, 2014—Observations of surface faulting and ground deformation, with recommendations for improving post-earthquake field investigations

The M w 6.0 South Napa earthquake of August 24, 2014, produced complex and extensive surface faulting and other ground deformation features. Following the event, geologists made more than 1,200 field observations at locations where tectonic faulting and ground failure produced visible deformation that fractured and disturbed the ground surface. At a few locations, large-scale, detailed, field-based maps of fault rupture and ground deformation were produced. The South Napa earthquake response was one of the first times when post-earthquake reconnaissance data were mostly collected and disseminated electronically. The advantages and opportunities these new methods bring to our research also pose new challenges to large-scale compilation efforts and demonstrate the value of developing guidelines and better standardization across the community to more optimally utilize developing technology in future post-earthquake investigations. Some suggestions for standardizing the collection and dissemination of post-earthquake field reconnaissance data are provided herein. Field observations and maps were integrated with airborne imagery, lidar, and InSAR to produce a comprehensive, large-scale digital map of fault rupture and zones of ground deformation. The map, observations, and photo database are summarized here in appendixes and figures and are also available as a series of digital data products within a companion U.S. Geological Survey data release ( Ponti and others, 2019 ); the characteristics of fault rupture and ground deformation features are summarized in detail in the body of this report. The results of this compilation reveal that faulting occurred within a 2-km-wide zone on six, roughly parallel traces within the West Napa Fault System. Most of the fault slip, and all the afterslip, occurred on the 21-km-long westernmost trace (Trace A). Maximum coseismic slip was greater than 40 cm and possibly as great as 60 cm, with the slip maximum located about 10 km north of the epicenter. Extensive ground deformation also occurred off the principal fault traces. Deformation characteristics of these features were not consistent with either primary faulting or shaking-induced ground failure and remain enigmatic, although this report includes speculation about possible origins. The use of InSAR was invaluable for identifying and mapping secondary traces with small displacements, and for delineating the overall details of the extensive rupture. InSAR data also highlighted other areas with possible ground deformation—some of which are found coincident with previously mapped fault traces, whereas others are in areas where no faults were previously mapped. Several of these regions had no visible ground deformation, whereas others did produce features that were inconsistent with tectonic faulting, so care must be taken not to over interpret the InSAR data without careful, corroborating field investigations.

California↗
USGS2021

Implementation plan for the southern Pacific Border and Sierra-Cascade Mountains provinces

Introduction The National Cooperative Geologic Mapping Program (NCGMP) is publishing a strategic plan titled Renewing the National Cooperative Geologic Mapping Program as the Nation’s Authoritative Source for Modern Geologic Knowledge (Brock and others, in press). The plan provides a vision, mission, and goals for the program during the years 2020–2030, which are: Vision .—Create an integrated, three-dimensional, digital geologic map of the United States. Mission .—Characterize, interpret, and disseminate a national geologic framework model of the Earth through geologic mapping. Goal .—Focus on geologic mapping as a core function of the U.S. Geological Survey (USGS) within the long-term vision of adequately mapping the Nation’s geologic framework in three dimensions. In order to achieve the goals outlined in the strategic plan, the NCGMP has developed an implementation plan. This plan will guide the annual review of projects carried out by USGS staff (FEDMAP) described in the plan and the development of the annual FEDMAP prospectus that will ensure the effective application of the NCGMP strategy. This publication describes the implementation plan of the NCGMP strategy for the southern Pacific Border and Sierra-Cascade Mountains provinces, as defined by Fenneman (1917, 1928, and 1946). This implementation plan focuses on the geology of California and a sliver of Nevada surrounding Lake Tahoe. The southern Pacific Border and Sierra-Cascade Mountains provinces encompass the varied landscapes of the high Sierra Nevada, the Central Valley, and Coast Ranges in northern and central California and the Peninsular Ranges, Continental Borderland, Los Angeles Basin-San Gabriel-San Bernardino valleys, western and central Transverse Ranges, and northernmost Salton Trough in southern California. Societal demands create a need for earth-science data in each of these landscapes. The broader San Francisco Bay area, Central Valley, Los Angeles-San Gabriel-San Bernardino lowlands, and the coastal lowlands that border the Peninsular Ranges are densely populated (about 30 million people) areas at high risk of natural hazards. The mountains of the Sierra Nevada, Peninsular Ranges, and Transverse Ranges, and the coast all provide numerous recreational opportunities that attract visitors from around the world, whereas previously these ranges attracted people to mine their resources. The agricultural capacity of the Central Valley is a critical resource for the Nation that is increasingly water limited. The southern. Pacific Border and Sierra-Cascade Mountains provinces, at the edge of the North American continent, were profoundly influenced by subduction zone tectonics during the Mesozoic and early Cenozoic (ongoing in northernmost California) and subsequently by the inception, development, and present activity of the San Andreas transform margin system. Although the geology of this region is the poster child of fundamental conceptual models of subduction zone complexes, forearc basins, ophiolite obductions, magmatic arcs, and suspect terranes, as well as hosting one of Earth’s most notorious continental transform faults—the San Andreas Fault—important questions that have important societal consequences remain to be answered. Most of California’s population reside in these provinces and live within 30 miles of an active fault (according to www.earthquakeauthority.com ) yet new faults continue to be discovered, highlighting the importance of deformation off the main San Andreas Fault. Bedrock, surficial, and three-dimensional (3D) geologic maps depicting stratigraphic structure and depth to crystalline basement rocks provide critical context and information for understanding fault rupture, distributed deformation, fault connectivity, and history in addition to providing crucial data that enable forecasting of shaking amplitude and length from hypothetical earthquake scenarios. The tectonic evolution of California produced not only stunning mountains, with associated hazards from landslides and active volcanoes, but also fertile valleys that make California the top agricultural producer in the country in terms of cash receipts (according to www.ers.usda.gov/faqs ). These valleys lie atop large basins that not only store groundwater but, in many cases, host oil and gas fields, contributing to the fourth highest hydrocarbon production by State in the country in 2016 (according to https://www.aei.org/carpe-diem/animated-chart-of-us-oil-production-by-state-1981-2017 ). Water is a key resource increasingly stressed by growing agricultural, industrial, and residential needs. Warmer and drier conditions have led to an increased reliance on extracting groundwater resources, whose availability and quality are dictated at the first order by the 3D spatial distribution of bedrock and Quaternary surficial deposits. Thus, assessment of this critical resource is inextricably tied to knowledge of the surficial and subsurface geologic structure and material types.

California, Nevada↗
USGS2023

Preliminary geologic map of the Southern Santa Rosa Mountains and Borrego Badlands, San Diego County, Southern California

This investigation delineates the geologic framework of an area of 75 square kilometers (km 2 ) located west of the Salton Sea in southern California (fig. 1, on sheet 1). The study area encompasses the south flank of the Santa Rosa Mountains and the eastern part of the Borrego Badlands (sheet 1). In this study area, regionally important stratigraphic and structural elements collectively inform the late Cenozoic geologic evolution of the Anza-Borrego sector of the Salton Trough province. Critical stratigraphic and structural elements in the map area include the following: The well exposed sequence of late Cenozoic, nonmarine sedimentary rocks that filled the Anza-Borrego subbasin (fig. 1) of the Salton Trough; A tectonic boundary that—in the southern Santa Rosa Mountains—separates the sedimentary strata from underlying crystalline rocks of Peninsular Ranges type. This tectonic boundary, named the West Salton Detachment Fault System by Axen and Fletcher (1998), is projected to underlie all late Cenozoic sedimentary strata in the Anza-Borrego subbasin of the Salton Trough; A variety of transpressional, transtensional, and strike-slip structures that have deformed the late Cenozoic sedimentary strata and collectively guided syntectonic and posttectonic depositional events within the Anza-Borrego subbasin of the Salton Trough; and The southeasternmost surface expression of the Clark Fault, a major strand of the dextral San Jacinto Fault Zone. Geologic mapping and analysis for this investigation focused on clarifying geologic relations among these four stratigraphic and structural aspects in the map area.

California↗
USGS1960

An aeromagnetic reconnaissance of the Cook Inlet area, Alaska

Forty-two east-west aeromagnetic lines were flown across the Cook Inlet-Susitna Lowland between Chelatna Lake and Seldovia at a flight altitude of approximately 2,500 feet. The lines traverse all or part of five Mesozoic tectonic elements that dominate the structure of the Cook Inlet area. Each of these tectonic elements, the Alaska Range geosyncline, the Talkeetna geanticline, the Matanuska geosyncline, the Seldovia geanticline, and the Chugach Mountains geosyncline, has a characteristic magnetic pattern. The aeromagnetic data, compiled as total intensity aeromagnetic profiles, show several significant features which are consistent with the structural grain of the area. A two-dimensional anomaly was observed near the east edge of the area on all but the southernmost profiles, where it becomes obscure. Geologic evidence suggests that this feature, the Knik Arm anomaly, is produced by plutonic rocks that have been intruded along the Seldovia geanticline. Southeast of this anomaly the profiles are almost flat. This flatness indicates that magnetic rocks are deeply buried in this area, which is underlain by slate and graywacke deposited in the Chugach Mountains geosyncline.

Alaska↗
USGS1972

Geology and mineral deposits of the Wadi an Nuqumi quadrangle, Kingdom of Saudi Arabia

The rocks, structures, and mineral deposits of the Wadi an Nuqumi quadrangle were formed during three periods of deformation, two of Precambrian age and one of Tertiary and Recent age. The older Precambrian Halaban cycle produced the thick eugeosynclinal suite of interlayered metasedimentary and metavolcanic rocks comprising the Halaban Formation, the numerous synorogenic granitic masses which intrude the layered rocks, and the northward-trending tectonic, plutonic, and metamorphic features of all these rocks which constitute the basic grain of the area. The older Halaban features are everywhere strongly transected, but only slightly deformed and offset, by many eastward-northeastward-, and northwestward-striking fractures and strike-slip faults. Silicic dikes are emplaced in these fractures, and several kinds of barren and metalliferous veins are closely associated with them. All these features are here thought to have formed during a period of deformation of late Precambrian age which produced the Najd Wrench Fault Zone; therefore, these features are named for it. Sporadic remnants of once far more extensive basaltic lava fields and the north-northwestward-striking vertical fractures which occur in them and contain volcanic vents from which they were extruded are the youngest rocks and structures in the Wadi an Nuqumi area. They are thought to have formed during the period of tectonic and volcanic activity which also produced the Red Sea graben. The principal mineral deposits of the Wadi an Nuqumi area are silicified-carbonate breccia veins which occur in structures of the Najd Wrench Fault deformation and metalliferous quartz veins which are closely associated with them. Only the latter possesses any economic potential, the most promising being the gold and silver-bearing quartz-base metal veins of the Al Numrahniyah and Muthaheel ancient mines.

Open-File Report↗
USGS1975

Preliminary description and interpretation of cores and radiographs from Clear Lake, Lake County, California: Core 7

Clear Lake, California is located in the California Coast Ranges about 120 km north of San Francisco and is the largest freshwater lake wholly within California. The lake basin is tectonically controlled (Anderson, 1936; Brice, 1953, Sims and Rymer, 1974) and the area seismically active (Coffman and von Hake, 1973). Interest in this lake was stimulated by hypotheses developed from a study of sediments in Van Norman Reservoir after the 1971 San Fernando earthquake (Sims, 1973). During this study three zones of deformational structures were found in the 1 m-thick sequence of sediments exposed over about 2 km 2 of the reservoir bottom. These zones were correlated with moderate earthquakes that shook the San Fernando area in 1930, 1952, and 1971. Results of this study, coupled with the experimental formation of deformational structures similar to those from Van Norman Reservoir, led to a search for similar structures in Pleistocene and Holocene lakes and lake sediments in other seismically active areas. Clear Lake, California was chosen specifically because of .:s location near the San Andreas fault and the San Francisco-Oakland urban complex, and the probability of obtaining an uninterrupted sediment record from the present into Pleistocene time. Eight 12 to 15 cm diameter continuous cores were taken from the lake sediments (fig. 1) as part of a study of earthquake induced structures in sediments and the tectonic framework of the Clear Lake basin. The eight cores range in length from 13.87 m to 133.09 m (Table 1).

California↗
USGS1975

Reconnaissance geology of the Central Mastuj Valley, Chitral State, Pakistan

The Mastuj Valley in Chitral State is a part of the Hindu Kush Range, and is one of the structurally most complicated areas in northern Pakistan. Sedimentary rocks ranging from at least Middle Devonian to Cretaceous, and perhaps Early Tertiary age lie between ridge-forming granodiorite intrusions and are cut by thrust faults. The thrust planes dip 10? to 40? to the north- west. Movement of the upper thrust plates has been toward the southeast relative to the lower blocks. If this area is structurally typical of the Hindu-Kush and Karakoram Ranges, then these mountains are much more tectonically disturbed than previously recorded, and suggest compression on a scale compatible with the hypothesis that the Himalayan, Karakoram, and Hindu Kush Ranges form part of a continental collision zone. The thrust faults outline two plates consisting of distinctive sedimentary rocks. The lower thrust plate is about 3,000 feet thick and consists of the isoclinally folded Upper Cretaceous to perhaps lower Tertiary Reshun Formation. It has overridden the Paleozoic metasedimentary rocks of the Chitral Slate unit. This thrust plate is, in turn, overridden by an 8,000-foot thick sequence consisting largely of Devonian to Carboniferous limestones and quartzites. A key factor in the tectonic processes has been the relatively soft and plastic lithology of the siltstone layers in the Reshun Formation which have acted as lubricants along the principal thrust faults, where they are commonly found today as fault slices and smears. The stratigraphic sequence, in the central Mastuj Valley was tentatively divided into 9 mapped units. The fossiliferous shales and carbonates of the recently defined Shogram Formation and the clastlcs of the Reshun Formation have been fitted into a sequence of sedimentary rocks that has a total thick- ness of at least 13,000 feet and ranges in age from Devonian to Neogene. Minerals of potential economic significance include antimony sulfides which have been mined elsewhere in Chitral, the tungstate, scheelite, which occurs in relatively high concentrations in heavy-mineral fractions of stream sands, and an iron-rich lateritic rock.

Open-File Report↗
USGS1976

Preliminary description and interpretation of cores and radiographs from Clear Lake, Lake County, California: Core 3

Clear Lake, California is located in the California Coast Ranges about 120 km north of San Francisco and is the largest freshwater lake wholly within California. The lake basin is tectonically controlled (Anderson, 1936; Brice, 1953; Sims and Rymer, 1974) and the area seismically active (Coffman and von Hake, 1973). Interest in this lake was stimulated by hypotheses developed from a study of sediments in Van Norman Reservoir after the 1971 San Fernando earthquake (Sims, 1973). During this study three zones of deformational structures were found in the 1 m-thick sequence of sediments exposed over about 2 km2 of the reservoir bottom. These zones were correlated with moderate earthquakes that shook the San Fernando area in 1930, 1952, and 1971. Results of this study, coupled with the experimental formation of deformational structures similar to those from Van Norman Reservoir, led to a search for similar structures in Pleistocene and Holocene lakes and lake sediments in other seismically active areas. Clear Lake, California was chosen specifically because of its location near the San Andreas fault and the San Francisco-Oakland urban complex, and the probability of obtaining an uninterrupted sediment record from the present into Pleistocene time. Eight 12 to 15 cm diameter continuous cores were taken from the lake sediments (fig. 1) as part of a study of earthquake induced structures in sediments and the tectonic framework of the Clear Lake basin. The eight cores range in length from 13.87 m to 115.21 m (Table 1).

California↗
USGS1976

Geology of the Deep Creek area, Washington, and its regional significance

This report, although primarily concerned with the stratigraphy and structure of a lead-zinc mining district in northern Stevens County, Washington, discusses and integrates the geology of the region about the Deep Creek area. Although the study centers in an area of about 200 square miles immediately south of the International Boundary, the regional background comes from: (1)the previously undescribed Northport quadrangle to the west, (2) published reports and reconnaissance of the Metaline quadrangle to the east, and (3) from published reports and maps of a 16 mile wide area that lies to the north adjacent to these three quadrangles in British Columbia. The report is divided into three parts: (1) descriptions of rocks and structures of the Deep Creek area, (2) descriptions of the regional setting of the Deep Creek area, and (3) an analysis and interpretation of the depositional and tectonic events that produced the geologic features exposed today. In the Deep Creek area surficial deposits of sand and gravel of glacial origin cover much of the consolidated rocks, which range in age from greenschist of the late Precambrlan to albite granite of the Eocene. Three broad divisions of depositional history are represented: (1) Precambrian, (2) lower Paleozoic and (3) upper Paleozoic; the record of the Mesozoic and Eocene is fragmentary. The lower Paleozoic division is the only fossil-controlled sequence; the age of the other two divisions were established by less direct methods. Both Precambrian and upper Paleozoic sequences are dominated by fine-grained detrital sediments, the Precambrian tending towards the alumina-rich and the upper Paleozoic tending towards the black shale facies with high silica. Neither sequence has more than trivial amounts of coarse clastics. Both include limestones, but in minor abundance. The lower Paleozoic sequence, on the other hand, represents a progressive change in deposition. The sequence began during the very late Precambrian with the deposition of clean quartz sand. This was followed by the accumulation of a comparatively thin limestone unit succeeded by a thick shale. The shale grades into a thick carbonate unit which in turn is overlain by black graptolitic slates (Ordovician). This general order of deposition holds for the Cambro-Ordovician throughout the area. Precambrian rocks indigenous to the Deep Creek area, have undergone at least six tectonic events of greatly different intensities. The first three of these events are epeirogentic, the fourth involves intense folding, the fifth, crossfolding, and the sixth, block faulting without folding. These events are dated with varying degrees of precision. The two epeirogentic events of the Precambrian, one gentle folding at the beginning of Windermere time and the other high angle faulting and volcanism in mid-Windermere time, did little to deform or metamorphose the rocks. The third event consists of uplift of northern Idaho and adjacent Montana and westward decollement thrusting of essentially unfolded lower Paleozoic rocks. The decollement faulting is inferred to explain anomalous rock distribution and cannot be accurately dated. It occurred sometime after the Devonian and before the Jurassic. A late Paleozoic age is favored.

British Columbia, Idaho, Washington↗
USGS1977

Catalog of earthquakes in the Santa Barbara Channel area for the period January 1, 1972 to December 31, 1973

The Santa Barbara Channel region forms the western most area of the Transverse Ranges, and is one of the most seismically active areas in the State of California. Instrumentally recorded earthquakes throughout southern California have been reported by the Seismological Laboratory of the California Institute of Technology (CALTECH) since 1932. Earthquake data for the period 1934 to 1963 were analyzed by Allen and others (1965) and related to regional geologic structures in southern California. Sylvester and others (1970) discussed the earthquake swarm that occurred in the Santa Barbara channel during the period from June 26 to August 3, 1968 with respect to the seismic history of the channel. The U. S. Geological Survey (USGS) (Vedder and others, 1969a) prepared a report on the geology, petroleum development, and seismicity of the Santa Barbara Channel region subsequent to an offshore oil-well blowout in the Dos Cuadras Offshore oil field. In that report, Hamilton and others (1969) reviewed the regional seismicity and its possible effects on the region. They noted that the existing seismic network precluded identification of individual active faults within the channel. A network of seismograph stations was established in late 1969 by the U. S. Geological Survey to monitor earthquakes in and around the Santa Barbara Channel. The purpose of this network is to provide data to gain insight into the tectonic and physical processes responsible for the generation of damaging earthquakes in the Santa Barbara Channel region. Lee and Vedder, (1973) reported the earthquakes located by this network for the period from January 1, 1970 to December 31, 1971, and showed that the earthquake activity appears to be spatially related to recognized faults in the region. This report contains a catalog of earthquakes in the Santa Barbara Channel region for the period from January 1, 1972 to December 31, 1973. It is prepared in a manner similar to that of the catalog contained in Lee and Vedder (1973) for the preceding two year period. These catalogs contain the basic study of seismicity in the Santa Barbara Channel region. The data contained in these catalogs provides a foundation for further study of the seismicity in tectonics of the Santa Barbara Channel region.

California↗
USGS1978

Depositional history and fault-related studies, Bolinas Lagoon, California

Studies of core sediments and seismic reflection profiles elucidate the structure and depositional history of Bolinas Lagoon, Calif., which covers 4.4 km 2 and lies in the San Andreas fault zone at the southeast corner of the Point Reyes Peninsula 20 km northwest of San Francisco. The 1906 trace of the San Andreas fault crosses the west side of the lagoon and was determined from (1) tectonically caused salt-marsh destruction indicated by comparison of 1854 and 1929 U.S. Coast and Geodetic Survey (U.S.C. & G.S.) topographic surveys, (2) formation of a tidal channel along the border of destroyed salt marshes, and (3) azimuths of the trend of the fault measured in 1907. Subsidence in the lagoon of 30 cm occurred east of the San Andreas fault in 1906. Near the east shore, seismic-reflection profiling indicates the existence of a graben fault that may connect to a graben fault on the Golden Gate Platform. Comparison of radiocarbon dates on shells and plant debris from boreholes drilled on Stinson Beach spit with a relative sea-level curve constructed for southern San Francisco Bay indicates 5.8 to more than 17.9 m of tectonic subsidence of sediments now located 33 m below mean sea level. Cored sediments indicate a marine transgression dated at 7770?65 yrs B.P. overlying freshwater organic-rich lake deposits. Fossil pollen including 2 to 8 percent Picea (spruce) indicate a late Pleistocene (?)-Early Holocene climate, cooler, wetter, and foggier than at present. Above the transgression are discontinuous and interfingering sequences of transgressive-regressive marine, estuarine, and barrier sediments that reflect rapid lateral and vertical shifts of successive depositional environments. Fossil megafauna indicate (1) accumulation in a protected, shallow-water estuary or bay, and (2) that the lagoon was probably continuously shallow and never a deep-water embayment. Analysis of grain-size parameters, pollen frequencies, and organic remains from a core near the north end of the lagoon indicates (1) that mid-nineteenth-century redwood logging correlates with rates of sediment accumulation of l.3 to 1.9 cm/yr that are three to 6 times higher than post-1906 rates of 0.3 to 0.4 cm/yr, (2) accumulation of up to 115 cm of sediment since 1849, and (3) an anomalously coarse-grained sediment that may correlate with the 1906 earthquake.

Open-File Report↗
USGS1978

Regional and local networks of horizontal control, Cerro Prieto geothermal area, Mexico

The Cerro Prieto geothermal area in the Mexicali Valley 30 km southeast of Mexicali, Baja California, is probably deforming due to (1) the extraction of large volumes of steam and hot water, and (2) active tectonism. Two networks of precise horizontal control were established in Mexicali Valley by the U.S. Geological Survey in 1977-78 to measure both types of movement as they occur. These networks consisted of (1) a regional trilateration net brought into the mountain ranges west of the geothermal area from survey stations on an existing U.S. Geological Survey crustal-strain network north of the international border, and (2) a local net tied to stations in the regional net and encompassing the area of present and planned geothermal production. Survey lines in this net were selected to span areas of probable ground-surface movements in and around the geothermal area. Electronic distance measuring (EDM) instruments, operating with a modulated laser beam, were used to measure the distances between stations in both networks. The regional net was run using a highly precise long-range EDM instrument, helicopters for transportation of men and equipment to inaccessible stations on mountain peaks, and a fixed wing airplane flying along the line of sight. Precision of measurements with this complex long-range system approached 0.2 parts per million of line length. The local net was measured with medium range EDM instrument requiring minimal ancillary equipment. Precision of measurements with this less complex system approached 3 parts per million for the shorter line lengths. The detection and analysis of ground-surface movements resulting from tectonic strains or induced by geothermal fluid withdrawal is dependent on subsequent resurveys of these networks.

Baja California↗
USGS1979

Proterozoic sedimentary rocks and basins of the Arabian shield and their evolution

Proterozoic sedimentary rocks of the Arabian Shield consist of three depositional phases. Phase I (the oldest) includes the Baish, Bahah, and Jiddah groups, which consist of an immature assemblage dominated by fine-grained metagraywacke, graphitic schist, chert, marble, and subordinate polymictic conglomerate and metasiltstone. Clastic rocks of Phase I are composed solely of volcanic material and do not contain plutonic or sialic detritus. Metasandstone, polymictic conglomerate, coarse-grained metagraywacke, and abundant marble (stromatolitic in places) constitute Phase II, the Ablah, Halaban, and Murdama groups. Plutonic and volcanic components are abundant in the clastic suite; K-feldspar detrital fragments are common in the Halaban and Murdama. The Shammar and Jubaylah groups form Phase III. Sedimentary rocks of this phase are fine- to coarse-grained terrigenous clastic rocks, boulder conglomerate, and stromatolitic limestone and dolomite. All phases include abundant volcanic rocks. Sedimentary basins, excluding those containing Phase III rocks, generally trend north, especially in the central and southern parts of the shield. In the central and northern parts of the shield, north-trending basins and structures are truncated abruptly by parallel northwest-trending sedimentary troughs (Jubaylah basins) formed by sinistral wrench-fault tectonics. Textural and compositional characteristics of the Proterozoic sedimentary rocks together with spatial relations of the depositional basins document a progressive change from oceanic to shallow marine and continental sedimentation with time, and a shift in the basin axes from west to east. Sedimentary parameters during this lengthy timespan show general increases in compositional and textural maturity, carbonate content, grain size, the ratio of sedimentary rocks to volcanic rocks, and plutonic and K-feldspar-bearing detritus. The sedimentary style of each phase was a function of tectonic conditions during deposition.

Open-File Report↗
USGS1979

Preliminary report on an exploratory drill hole: New Madrid test well-1-X in Southeast Missouri

As part of the U.S. Geological Survey's investigation of earthquake hazards in the upper Mississippi embayment, a test well (NMTW-l-X) was drilled in the "bootheel" of Missouri, 21 km south-southwest of the town of New Madrid. The primary purpose of the well was to obtain in situ stress measurements from zones within subsurface Paleozoic rocks using the hydraulic fracturing (hydrofracture) technique. Such measurements determine the character and magnitude of the active tectonic stress field in an area and are helpful in evaluating the potential for faulting (Zoback and others, 1978). The new data about the active tectonic stress field can then be used to evaluate the various theories that have been proposed to explain the genesis and characteristics of the upper Mississippi embayment earthquakes. A second goal of the test well was to extensively study the post-Paleozoic stratigraphy in the area. Detailed stratigraphic information would provide a better understanding of the structural framework of the upper Mississippi embayment. Accurate knowledge of the stratigraphy would also help to identify the reflecting horizons that were recorded in a series of seismic reflection profiles that the U.S. Geological Survey had previously run throughout the upper Mississippi embayment. To strengthen the correlation between reflecting horizons and stratigraphic units, one of the reflection profiles was run within 10 m of the well. The stratigraphy and structure of the New Madrid, Mo., area are, at present, poorly understood. Only a handful of deep wells and test holes, some with only generalized driller's logs and few with accompanying geophysical logs, are available to aid in interpreting the subsurface geology of the upper Mississippi embayment. Extensive paleontologic and palynologic studies are planned to assist in identifying formal stratigraphic units and to help define the depositional history of the sediments. For the Tertiary and Cretaceous sequences, these investigations will also yield valuable biostratigraphic data by defining the biofacies changes that occur between the well-studied marine facies in the southern part and the time-equivalent, continental and nearshore-deltaic facies in the northern part of the embayment. This report was prepared to release preliminary data obtained during the drilling phase of the test well. It includes a short text describing mechanical operations and history of the drilling, some initial stratigraphic interpretations of the test-well data, and a brief discussion of studies generated by the project which are now in progress. Attached appendices contain a field driller's log and geophysical logs. In order to maintain consistency with standard drilling usage, measurements related to drilling operations are cited in English units.

Missouri↗
USGS1980

Intrusions and intrusive complexes in an ophiolite near San Luis Obispo; a chemical and petrologic study

The San Luis Obispo ophiolite is a sequence of mafic and ultramafic rocks that lie as a thrust-like slice on top of Franciscan melange in the southern California Coast Range. The ophiolite comprises the classic Steinmann Trinity of basal serpentinized ultramafic rocks overlain sequentially by spilitized pillow lavas and cherts. The ophiolite is intruded by numerous diabasic dikes and several large intrusive complexes that contain peridotite, gabbro, diabase and felsic rocks. Field relations indicate that this ophiolite originated as a sequence of submarine volcanic flows and breccia units extruded onto an ultramafic basement. Later the volcanic and ultramafic rocks were intruded along their contact by mafic magma that crystallized as a stratiform complex of cumulate peridotite and gabbro. Next, this stratiform complex was intruded by diorite and albite-granite (trondhjemite) sills, which may have been produced by partial melting of gabbros in the upper levels of the stratiform complex. Finally all earlier units were intruded by diabasic sills and dikes that probably were late feeders for the pre-existing volcanic unit. All the ophiolite rocks underwent subsequent highly localized brecciation, under greenschist-facies conditions, in which felsic rocks were incipiently melted by frictional heating. The host rocks and intrusions were metamorphosed at low temperature and the mafic rocks were altered by Na- and Si-metasomatism. Despite this pervasive alteration, evidences of the formational stages of the ophiolite are preserved in disequilibrium mineral assemblages, primarily within mafic and ultramafic rocks of the intrusive complexes. Whole-rock analyses of the ophiolite suite indicate that alteration has obscured but not obliterated the original chemical character of the mafic rocks. The ophiolite diabases and basalts contain up to 6 weight percent Na 2 0 and 58 percent Si0 2 , in contrast to normal Si0 2 contents of 50 percent or less and Na 2 0 contents of less than 3 percent for unaltered oceanic and continental tholeiite basalts. However, the low K 2 0 contents (less than 0.8 percent) of all units in the ophiolite suite indicate that these rocks are not part of an alkalic kindred, but rather are altered tholeiites. Compositions of relict amphibole and plagioclase in the mafic rocks indicate that the ophiolite formed in a high-temperature environment and the deep seated rocks were metamorphosed under amphibolite-facies conditions. A later change in the environmental conditions allowed subsequent low-temperature (greenschist facies) metamorphism and metasomatism. The structure and chemistry of the San Luis Obispo ophiolite support the hypothesis that this body may represent a fragment of oceanic crust and mantle. The volcanic rocks and the intrusive complexes probably formed at a mid-ocean ridge, where conditions of high heat-flow provided the requisite high-temperature environment and promoted the production of mafic magmas. The change to low-temperature conditions probably was due to inception or acceleration of crustal spreading at that portion of the ridge where this ophiolite formed. The nature of brecciation in the ophiolite indicates that the low-temperature environment also was one of greater tectonic disturbance, relative to conditions at the ridge. This tectonically active environment probably corresponds to an island arc where the ophiolite-bearing plate was subducted in an adjacent trench. The absence of a high-pressure mineral assemblage in the San Luis Obispo ophiolite suggests that this segment of ocean-crust and upper mantle was not buried in a subduction zone, but rather was rafted on top of subduction melange (Franciscan Formation) into its present position.

California↗
USGS1981

Proceedings of Conference XIII, evaluation of regional seismic hazards and risk

The participants in the conference concluded that a great deal of useful research has been performed in the national Earthquake Hazards Reduction Program by USGS and non-USGS scientists and engineers and that the state-of-knowledge concerning the evaluation of seismic hazards and risk has been advanced substantially. Many of the technical issues raised during the conference are less controversial now because of new information and insights gained during the first three years of the expanded research program conducted under the Earthquake Hazards Reduction Act. Utilization of research results by many groups of users has also improved during this period and further improvement in utilization appears likely. Additional research is still required to resolve more completely the many complex technical issues summarized above and described in the papers contained in the proceedings. Improved certainty of research results on the evaluation of regional seismic hazards and risk is required before full utilization can be made by state and local governments who deal. with people frequently having a different perception of the hazard and its risk to them than that perceived by scientists or engineers. Each of the papers contained in the proceedings contain throughtful recommendations for improving the state-of-knowledge. Two papers, in particular, focussed on this particular theme. The first was presented by Lynn Sykes in the Geologic Keynote Address. He identified geographic areas throughout the world which may be considered as counterparts or analogues of seismic zones in the United States. He concluded that much can be learned about prediction, tectonic settings, earthquake hazards, and earthquake risk for sites in the United States by studying their tectonic analogues in other countries. The second paper was presented by John Blume in the Engineering Keynote Address. He suggested 20 specific research topics that, in his opinion, will significantly advance the state-of-the-art in earthquakeresistant design. The papers by Sykes and Blume are presented in the front of the proceedings.

Open-File Report↗
USGS1982

Lineaments derived from analysis of linear features mapped from Landsat images of the Four Corners region of the Southwestern United States

Linear features are relatively short, distinct, non-cultural linear elements mappable on Landsat multispectral scanner images (MSS). Most linear features are related to local topographic features, such as cliffs, slope breaks, narrow ridges, and stream valley segments that are interpreted as reflecting directed aspects of local geologic structure including faults, zones of fracturing (joints), and the strike of tilted beds. 6,050 linear features were mapped on computer-enhanced Landsat MSS images of 11 Landsat scenes covering an area from the Rio Grande rift zone on the east to the Grand Canyon on the west and from the San Juan Mountains, Colorado, on the north to the Mogollon Rim on the south. Computer-aided statistical analysis of the linear feature data revealed 5 statistically important trend intervals: 1.) N. 10W.-N.16E., 2.) N.35-72E., 3.) N.33-59W., 4.) N. 74-83W., and 5.) N.89-9-W. and N. 89-90E. Subsequent analysis of the distribution of the linear features indicated that only the first three trend intervals are of regional geologic significance. Computer-generated maps of the linear features in each important trend interval were prepared, as well as contour maps showing the relative concentrations of linear features in each trend interval. These maps were then analyzed for patterns suggestive of possible regional tectonic lines. 20 possible tectonic lines, or lineaments, were interpreted from the maps. One lineament is defined by an obvious change in overall linear feature concentrations along a northwest-trending line cutting across northeastern Arizona. Linear features are abundant northeast of the line and relatively scarce to the southwest. The remaining 19 lineaments represent the axes of clusters of parallel linear features elongated in the direction of the linear feature trends. Most of these lineaments mark previously known structural zones controlled by linear features in the Precambrian basement or show newly recognized relationships to geological and/or geophysical patterns that suggest probable influence by buried basement features. The remaining few lineaments are not strongly correlative with geological or geophysical patterns, but on the basis of existing data they cannot be dismissed as being possible expressions of basement features.

Open-File Report↗