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USGS1959

Impact mechanics at Meteor Crater, Arizona

Meteor Crator is a bowl-shaped depression encompassed by a rim composed chiefly of debris stacked in layers of different composition. Original bedrock stratigraphy is preserved, inverted, in the debris. The debris rests on older disturbed strata, which are turned up at moderate to steep angles in the wall of the crater and are locally overturned near the contact with the debris. These features of Meteor Crater correspond closely to those of a crater produced by nuclear explosion where depth of burial of the device was about 1/5 the diameter of the resultant crater. Studies of craters formed by detonation of nuclear devices show that structures of the crater rims are sensitive to the depth of explosion scaled to the yield of the device. The structure of Meteor Crater is such as would be produced by a very strong shock originating about at the level of the present crater floor, 400 feet below the original surface. At supersonic to hypersonic velocity an impacting meteorite penetrates the ground by a complex mechanism that includes compression of the target rocks and the meteorite by shock as well as hydrodynamic flow of the compressed material under high pressure and temperature. The depth of penetration of the meteorite, before it loses its integrity as a single body, is a function primarily of the velocity and shape of the meteorite and the densities and equations of state of the meteorite and target. The intensely compressed material then becomes dispersed in a large volume of breccia formed in the expanding shock wave. An impact velocity of about 15 km/sec is consonant with the geology of Meteor Crater in light of the experimental equation of state of iron and inferred compressibility of the target rocks. The kinetic energy of the meteorite is estimated by scaling to have been from 1.4 to 1.7 megatons TNT equivalent.

Open-File Report↗

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↗

USGS1960

Preliminary textures and mineral associations in the ultramafic zone of the Stillwater complex, Montana

This paper presents some results of work done between 1951 and 1955 as a part of a comprehensive investigation of the stratigraphy, geochemistry, and petrography of the Ultramafic zone of the Stillwater complex by the U. S. Geological Survey. Detailed mapping of the chromite deposits of the complex was done between 1939 and 1943, under the supervision of J. W. Peoples. Reports of this work, and geologic maps of most of the complex, have been published: Peoples and Howland (1940); Wimmler (1948); Howland, Garrels, and Jones (1949); Peoples, Howland, Jones, and Flint (1954); Jackson, Howland, Peoples, and Jones (1954); Howland (1955); Jones, Peoples, and Howland (in press). The present investigation has called for additional mapping and study of many problems which had to be bypassed because of the pressure of wartime urgency. I spent a total of about 15 months in the field during the summers of 1951 through 1955; P. R. Vail assisted in the field work in 1952 and 1953, and R. L. Christiansen assisted in 1954.

Montana↗

USGS1962

Bedrock geology of the Mount Carmel and Southington quadrangles, Connecticut

New data concerning the geologic structure, stratigraphy, petrography, origin, and ages of bedrock formations in an area of approximately 111 square miles in south-central Connecticut were obtained in the course of detailed geologic mapping from 1957 to 1960. Mapping was done at a scale of 1:24,000 on topographic base maps having a 10-foot contour interval. Bedrock formations are classified in two principal categories. The first includes metasedimentary, meta-igneous, and igneous rocks of Precambrian to Devonian age, which crop out in the western parts of both quadrangles. The second includes sedimentary and igneous rocks of the Newark Group of Late Triassic age, which crop out in the eastern parts of the quadrangles. Diabase dikes, which are Late Triassic or younger in age, intruded rocks in both the western and eastern parts of the map area. Rocks in the western part of the area underwent progressive regional metamorphism in Middle to Late Devonian time. The arrangement of the chlorite, garnet, biotite, staurolite, and kyanite zones here is approximately the mirror-image of metamorphic zones in Dutchess County, New York. However, garnet appeared before biotite in politic rocks in the map area, because the ration MgO/FeO is low. Waterbury Gneiss and the intrusive Woodtick Gneiss are parts of a basement complex of Precambrian age, which forms the core of the Waterbury dome. This structure is near the southern end of a line of similar domes that lie along the crest of a geanticline east of the Green Mountain anticlinorium. The Waterbury Gneiss is believed to have been metamorphosed in Precambrian time as well as in Paleozoic time. The Woodtick Gneiss also may have been metamorphosed more than once. In Paleozoic time, sediments were deposited in geosynclines during two main cycles of sedimentation. The Straits, Southington Mountain, and Derby Hill Schists, which range in age from Cambrian to Ordovician, reflect a transition from relatively clean politic sediments to thinly layered sediments that contained rather high percentages of fine-grained volcanic debris. Metadiabase and metabasalt extrusives above Derby Hill Schist south of the map area represent more intense volcanic activity before or during the early stages of the Taconic disturbance in Late Ordovician time. Impure argillaceous, siliceous, and minor calcareous sediments of the Wepawaug Schist, which is Silurian and Devonian in age, were deposited unconformably on older rocks during renewed subsidence of a geosyncline. The Wepawaug now occupies the trough of a tight syncline, which formed before and during progressive regional metamorphism at the time of the Acadian orogeny in middle to Late Devonian time. Felsic igneous rocks were intruded into the metasedimentary formations of Paleozoic age before the climax of the latest progressive regional metamorphism. Intrusives that gave rise to the Prospect and Ansonia Gneisses were emplaced mainly in the Southington Mountain Schist, and the igneous rocks as well as the host rocks were metamorphosed in the staurolite zone. Although it is possible that these two intrusives were emplaced during the Taconic disturbance, the writer believes it more likely that the igneous rocks from which the Prospect and Ansonia Gneisses formed were emplaced during the Acadian orogeny. Woodbridge Granite, which intruded the Wepawaug Schist, is Devonian in age and undoubtedly was emplaced during the Acadian orogeny. In this area the granite is essentially unmetamorphosed, because it is in the chlorite, garnet, and biotite zones. Southwest of the map area, however, metamorphic equivalents of the Woodbridge are found in Wepawaug Schist in the staurolite zone. The Ansonia Gneiss, therefore, may be a metamorphic equivalent of the Woodbridge Granite. Rocks of Late Triassic age formerly covered the entire map area, but were eroded from the western part after tilting and faulting in Late Triassic time. The New Haven Arkose of the Newark

Open-File Report↗

USGS1963

Astrogeologic studies, annual progress report, August 25, 1961 - August 24, 1962

This report, which covers the period August 25, 1961 to August 24, 1962, is the third of a series describing the program of research conducted by the U.S. Geological Survey on behalf of the National Aeronautics and Space Administration. The major long-range objectives of the program are to determine and map the stratigraphy and structure of the Moon's crust, to work out from these the sequence of events that led to the present condition of the Moon's surface, and to determine the processes by which these events took place. This report is presented in four parts with a separate summary. Part A: Lunar and planetary investigations (with map supplement). Geologic mapping of the Moon involves discrimination of the different materials exposed on the lunar surface and their assignment to geologic units, the determination of the photometric characteristics of these materials, delineation of the boundaries of the units and determination of their stratigraphic sequence. Part B: Crater investigations. These include field studies of terrestrial craters, hypervelocity impact experiments with rocks and other materials, studies of the behavior of rocks under high shock loads, and experimental and field studies of shock metamorphism in rocks. Part C: Cosmochemistry and petrography. Studies are being made of the chemical, petrographic, and physical properties of materials of extraterrestrial origin and of certain materials associated with terrestrial impact structures. The studies reported in Part C are concerned with tektites, terrestrial impactites, metallic spherules formed by the Meteor Crater impact event, and particles of possible cosmic origin. Part D: Studies for space flight program. These studies are undertaken to aid in the design of space flight experiments and the planning of space missions. The report that makes up Part D is an evaluation of the lunar flux of secondary particles derived from primary impact events on the lunar surface.

Open-File Report↗

USGS1965

The correlation of coal beds in Squaw Basin and part of Eden Ridge, T. 33 S., R. 11 W., W. M., southwestern Oregon

A conflict in correlation of coal beds dating from 1914 is reexamined-with the aid of new. core hole data, photogeologic interpretation, a broader understanding of the stratigraphy, and brief field studies. It is concluded that the known coal beds in Squaw Basin area of limited lateral extent and are older than those exposed at Eden Ridge. Similar coal beds may be found in other rocks of the Tyee Formation in this area. More core drilling could be justified.

Oregon↗

USGS1970

Morphology, sedimentation, and seismic characteristics of an arctic beach, Nome, Alaska - with economic significances

Arctic beaches exhibit characteristics that do not occur on beaches in more temperate zones. In the summer of 1967 morphological, sedimentological, and seismic refraction studies were made on an arctic beach near Nome, Alaska, in order to better define these distinguishing characteristics. Several distinct microrelief structures are developed during ice break-up and the melting of ice and snow on the beaches including ice-pushed ridges, kaimoo ridge and deposits, sea-ice kettles, sea- ice sand and sea-ice gravel cones, micro-outwash deposits, and microdeltaic deposits. Sedimentological studies showed that sediment distribution along the beach is random with no increasing or decreasing median diameters, or sorting coefficients, or sand-gravel percentages, either along the strandline or along the beach profile. This random grain size distribution is attributed to the relatively low energy along the coast of the Seward Peninsula. Further, the beaches are insulated from the elements by ice for about 6 months out of the year and the beach sediments are disturbed annually by ice-push. Longshore drift appeared to vary from east to west during the summer of 1967 with a net transport to the east. The seismic refraction study on the Nome beach indicated that internal stratigraphy of the overburden could be interpreted and correlated with known onshore and offshore stratigraphic units. Bedrock was well defined in the seismograms and exhibited a gently undulating topography with several buried channels that may be sites of gold placer deposits.

Alaska↗

USGS1970

Geology of the north end of the Ruby Range, southwestern Montana

This study consists of two parts: stratigraphy and sedimentation, and structure of rocks in the northern one-third of the Ruby Range of southwestern Montana. Detailed studies of Cambrian marine dolomite rocks in the Red Lion Formation and in the upper part of the Pilgrim Limestone resulted in their division into distinct rock units, termed lithofacies. These lithofacies contain features suggestive of subtidal, intertidal, and supratidal environments similar to those presently forming in the Persian Gulf. Stromatolltic structures occurring in the uppermost part of the Red Lion Formation are similar to those presently forming in Shark Bay, Australia. The Ruby Range within the map area is broken into a series of northwest-plunging basement (Precambrian metamorphic rock) blocks, differentially uplifted during the Cretaceous-Tertiary orogenic period. These blocks are bordered by upthrust faults, which are nearly vertical in their lower segments and are .low-angle in their uppermost parts. Asymmetrical folds in Paleozoic sedimentary rocks formed in response to the differential uplift of the blocks; thus they too plunge to the northwest. Displaced masses of rock border the range on the three sides within the map area and are interpreted as gravity-slide features resulting from uplift of the range. Normal faulting began blocking out the present range margins by Oligocene time.

Open-File Report↗

USGS1972

A preliminary study of peat resources in eastern Maine

Nineteen peat deposits in southeastern Aroostook County (fig. 1) contain an estimated 4,987,000 tons of peat. The location, size and quality data for each deposit are given in tables 1, 2 and 3. Thirty-eight deposits in Washington County (fig. 2) contain an estimated 20,041,000 tons of peat. The location, size and quality data for each deposit are given in tables 4, 5 and 6. Twenty additional deposits containing estimated 3,802,000 tons in Washington County (fig. 2) were not sampled in detail but are described in tables 7 and 8. In addition to the deposits studied, it is estimated that there are at least as many more deposits of similiar size and quality in the area studied. Data in this study were obtained by conducting pace and compass traverses across swamps, marshes and heaths. Auger holes were put down by hand using a Davis sampler and Macaulay peat borer along the traverses to collect samples of the peat and to determine the thickness and stratigraphy of the deposits and the configuration of the depression in which they lie. The amount of peat was estimated from auger hole data and from the surface area measured on topographic and air photo maps. In calculating tonnages, 1 acre-foot of peat in place was considered equivalent to 200 tons of air-dried peat. Samples from all of the deposits were analyzed under the supervision of Irving May in the laboratories of the U.S. Geological Survey for moisture, ash, organic content, water-holding capacity, fiber size (exceeding 0.15mm),and acidity.

Maine↗

USGS1973

Salt deposits in Los Medanos area, Eddy and Lea Counties, New Mexico

The salt deposits of Los Medanos area, in Eddy and Lea Counties, southeastern New Mexico, are being considered for possible use as a receptacle for radioactive wastes in a pilot-plant repository. The salt deposits of the area. are in three evaporite formations: the Castile, Salado, and Rustler Formations, in ascending order. The three formations are dominantly anhydrite and rock salt, but some gypsum, potassium ores, carbonate rock, and fine-grained clastic rocks are present. They have combined thicknesses of slightly more than 4,000 feet, of which roughly one-half belongs to the Salado. Both the Castile and the Rustler are-richer in anhydrite-and poorer in rock salt-than the Salado, and they provide this salt-rich formation with considerable Protection from any fluids which might be present in underlying or overlying rocks. The Salado Formation contains many thick seams of rock salt at moderate depths below the surface. The rock salt has a substantial cover of well-consolidated rocks, and it is very little deformed structurally. Certain geological details essential for Waste-storage purposes are unknown or poorly known, and additional study involving drilling is required to identify seams of rock salt suitable for storage purposes and to establish critical details of their chemistry, stratigraphy, and structure.

New Mexico↗

USGS1975

Origin and significance of natural gases of Montana

About two years ago, I was assigned to a project to evaluate the hydrocarbon potential of the Cretaceous system of the northern Rocky Mountains; namely, in Montana, North Dakota, and South Dakota. I had no problem identifying potential traps; both structural and stratigraphic, but recognized the fact that most of the production from the Cretaceous in Montana is natural gas. More important, this production is from relatively shallow depths, often less than 2,000 feet. I realized that not only stratigraphy and structure, but also the origin, migration, and accumulation of hydrocarbons must be fully understood for effective exploration of new resources in the northern Rocky Mountains and elsewhere.

Montana↗

USGS1975

Geophysical logs from a geologic test hole near Charleston, South Carolina

On March 2, 1975, the U.S. Geological Survey completed a series of geophysical well logs in the Charleston Project Deep Core Hole No. 1 located at Latitude 32° 53.2 'N and Longitude 80° 21 . 5'W in Dorchester County near Charleston, South Carolina. The land surface is at an elevation of 5.4 m (18 ft) above mean sea level. The total depth of the test hole is 793 m (2,600 ft) and the geophysical logs were recorded through fresh barite mud to the bottom. The deep geologic. test hole penetrated the entire section of Atlantic Coastal Plain sediments and extended about 40 m (130 ft) into basement rock composed of basalt flows. The purpose of the logging is to assist in the interpretation of the depositional environments, stratigraphy, structural, and geological history of the onshore and offshore areas surrounding Charleston, S.C. The purpose of this report is to make the uninterpretated geophysical recordings of the entire log suite publicly available . The logs available are shown in table 1, along with the operating depth intervals, total footage, scale, units of measure, combination log, and other pertinent data.

South Carolina↗

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

Preliminary report on radioactive conglomerates of Middle Precambrian age in the Sierra Madre and Medicine Bow Mountains of southeastern Wyoming

Middle Precambrian miogeosynclinal metasedimentary rocks o# the Sierra Madre and Medicine Bow Mountains of southeastern Wyoming contain radioactive quartz-pebble conglomerates of possible economic interest. These conglomerates do not contain ore-grade uranium in surface outcrops, but an earlier report on the geochemistry of the Arrastre Lake area of the Medicine Bow Mountains shows that ore-grade deposits may be present in the subsurface. This report describes the stratigraphy of the host metasedimentary rocks and the stratigraphic setting of the radioactive conglomerates in both the Sierra Madre and Medicine Bow Mountains, and compares these rock units with those of the Blind River-Elliot Lake uranium district in Canada. The location of radioactive .conglomerates is given so that further exploration may be undertaken by interested parties.

Wyoming↗

USGS1977

Geology of the Midnite uranium mine area, Washington — Maps, description, and interpretation

Bedrock geology of about 12 km 2 near the Midnite mine has been mapped at the surface, in mine exposures, and from drilling, at scales from 1:600 to 1:12,000 and is presented here at 1:12,000 to provide description of the setting of uranium deposits. Oldest rocks in the area are metapelitic and metacarbonate rocks of the Precambrian (Y) Togo Formation. The chief host for uranium deposits is graphitic and pyritic mica phyllite and muscovite schist. Ore also occurs in calc-silicate hornfels and marble at the western edge of a calcareous section about 1,150 m thick. Calcareous rocks of the Togo are probably older than the pelitic as they are interpreted to be near the axis of a broad anticline. The composition and structural position of the calcareous unit suggests correlation with less metamorphosed carbonate-bearing rocks of the Lower Wallace Formation, Belt Supergroup, about 200 km to the east. Basic sills intrusive into the Togo have been metamorphosed to amphibolite. Unmetamorphosed rocks in the mine area are Cretaceous(?) and Eocene igneous rocks. Porphyritic quartz monzonite of Cretaceous age, part of the Loon Lake batholith, is exposed over one third of the mine area. It underlies the roof pendant of Precambrian rocks in which the Midnite mine occurs at depths of generally less than 300 m. The pluton is a two-mica granite and exhibits pegmatitic and aplitic textural features indicative of water saturation and pressure quenching. Eocene intrusive and extrusive rocks in the area provide evidence that the Eocene surface was only a short distance above the present uranium deposits. Speculative hypotheses are presented for penesyngenetic, hydrothermal, and supergene modes of uranium emplacement. The Precambrian Stratigraphy, similar in age and pre-metamorphic lithology to that of rocks hosting large uranium deposits in Saskatchewan and Northern Territory, Australia, suggests the possibility of uranium accumulation along with diagenetic pyrite in carbonaceous muds in a marine shelf environment. This hypothesis is not favored by the author because there is no evidence for stratabound uranium such as high regional radioactivity in the Togo. A hydrothermal mode of uranium emplacement is supported by the close apparent ages of mineralization and plutonism, and by petrology of the pluton. I speculate that uranium may have become enriched in postmagmatic fluids at the top of the pluton, possibly by hydrothermal leaching of soluble uranium associated with magnetite, and diffused outward into metasedimentary wall rocks to create an aureole about 100 m thick containing about 100 ppm uranium. Chemistry of the hydrothermal process is not understood, but uranium does not appear to have been transported by an oxidizing fluid, and the fluid did not produce veining and alteration comparable to that of base-metal sulfide deposits. Uranium in the low-grade protore is believed to have been redistributed into permeable zones in the Tertiary to create ore grades. Geologic and isotopic ages of uranium mineralization, and the small volume of porphyritic quartz monzonite available for leaching, are not supportive of supergene emplacement of uranium.

Washington↗

USGS1977

Geology of the Monterey Bay region

Geophysical data and sea floor samples collected from the continental shelf and slope between Ano Nuevo Point and Point Sur, California indicate that the Monterey Bay region has had a complex late Cenozoic tectonic history. Uplift and depression have produced a succession of regressive and transgressive sedimentary units, while contemporaneous right-slip along faults of the San Andreas system have offset major structural and lithologic elements. This deformation produced three regional and several local unconformities within upper Tertiary rocks and initiated development of a canyon system that today includes the Monterey, Ascension, Carmel, and other large submarine canyons. The Tertiary stratigraphy of the offshore Monterey Bay area is divided into two provinces by a major structural boundary, the north-trending Palo Colorado-San Gregorio fault zone. East of this zone in the offshore are four seismically distinct sequences that can be correlated with major sequences onshore. These sequences comprise (1) pre-Tertiary basement, and (2) middle Miocene, (3) upper Miocene to Pliocene, and (4) upper Pliocene to Holocene sedimentary intervals. Each of the latter three sequences is bounded by unconformities, as is its counterpart on land. Only Neogene sedimentary rocks are present offshore; Paleogene units, if originally present, have been removed completely by pre-middle Miocene erosion. An extensive erosional surface was cut during Zemorrian time into the late Mesozoic granitic basement rocks. Incised into this surface are the ancestral Monterey Canyon and an unnamed canyon. Marine sedimentary rocks of upper Miocene and Pliocene age overlie this unconformably and fill the unnamed canyon. Similar rocks also may have once filled Monterey Canyon. Near shore these strata are covered by terrestrial alluvial and eolian deposits, deltaic deposits, marine canyon fill, landslide and slump deposits, and unconsolidated sediments that range in age from upper Pliocene to Holocene. Monterey Canyon appears to have been filled and exhumed at least twice since its inception in Oligocene time, once in late Miocene and once in Pleistocene time. Three major seismic stratigraphic units are apparent in continuous seismic reflection profiles from the offshore area west of the Palo Colorado-San Gregorio fault zone. These are (1) acoustical basement, and (2) middle Tertiary and (3) late Tertiary to Quaternary sedimentary intervals. Acoustical basement comprises Cretaceous to early Tertiary sedimentary rocks, Mesozoic or older metamorphic rocks, and Cretaceous or Jurassic rocks of the Franciscan assemblage. The middle Tertiary sequence consists of sedimentary rocks of questionable Miocene age. The late Tertiary to Quaternary sequence is composed of Pliocene sedimentary rocks and unconsolidated marine sediments, and submarine landslide and slump deposits. Seismic reflection surveys indicate two major, intersecting, northwest-trending fault zones to be present in the offshore Monterey Bay area. The Palo Colorado-San Gregorio fault zone may be more than 200 km long; it is narrow (approximately 3 km wide) and is represented in most places by one or two faults. This zone appears to connect with faults mapped on land near Ano Nuevo Point and Point Sur. The Monterey Bay fault zone, located in the area between Santa Cruz and Monterey, is a diffuse zone, approximately 10 to 15 km wide, of en echelon faults. Faults within this zone appear to connect with faults on land near Monterey, and the zone appears to be truncated by the Palo Colorado-San Gregorio fault zone west of Santa Cruz. Locations of more than 110 earthquakes (1968-1976) show that the newly mapped fault zones in Monterey Bay are seismically active. Epicenters in the bay form two clusters, one at the intersection of the Monterey Bay and Palo Colorado-San Gregorio fault zones, and the other in a linear belt that trends northwest along the Palo Colorado-San Gregorio fault zone. Faults within th

California↗

USGS1978

Potential sites for a spent unreprocessed fuel facility (SURFF), southwestern part of the Nevada Test Site

In the absence of specific criteria, the topography, geomorphology, and geology of Jackass Flats and vicinity in the southwestern part of the Nevada Test Site are evaluated by arbitrary guidelines for a Spent Unreprocessed Fuel Facility. The guidelines include requirements for surface slopes of less than 5 percent, 61 m of alluvium beneath the site, an area free of active erosion or deposition, lack of faults, a minimum area of 5 km2, no potential for flooding, and as many logistical support facilities as possible. The geology of the Jackass Flats area is similar to the rest of the Nevada Test Site in topographic relief (305-1,200 m), stratigraphy (complexly folded and faulted Paleozoic sediments overlain by Tertiary ash-flow tuffs and lavas overlain in turn by younger alluvium), and structure (Paleozoic thrust faults and folds, strike-slip faults, proximity to volcanic centers, and Basin and Range normal faults). Of the stratigraphic units at the potential Spent Unreprocessed Fuel Facility site in Jackass Flats, only the thickness and stability of the alluvium are of immediate importance. Basin and Range faults and a possible extension of the Mine Mountain fault need further investigation. The combination of a slope map and a simplified geologic and physiographic map into one map shows several potential sites for a Spent Unreprocessed Fuel Facility in Jackass Flats. The potential areas have slopes of less than 5 percent and contain only desert pavement or segmented desert pavement--the two physiographic categories having the greatest geomorphic and hydraulic stability. Before further work can be done, specific criteria for a Spent Unreprocessed Fuel Facility site must be defined. Following criteria definition, potential sites will require detailed topographic and geologic studies, subsurface investigations (including geophysical methods, trenching, and perhaps shallow drilling for faults in alluvium), detailed surface hydrologic studies, and possibly subsurface hydrologic studies.

Nevada↗

USGS1978

Site evaluation for U.S. Bureau of Mines experimental oil-shale mine, Piceance Creek basin, Rio Blanco County, Colorado

The U.S. Geological Survey is cooperating with the U.S. Bureau of Mines in the selection of a site for a shaft and experimental mine to be constructed in the Piceance Creek basin, Rio Blanco County, Colo. The Piceance Creek basin, an asymmetric, northwest-trending large structural downwarp, is located approximately 40 km (25 mi) west of the town of Meeker in Rio Blanco County, Colo. The oil-shale, dawsonite, nahcolite, and halite deposits of the Piceance Creek basin occur in the lacustrine Green River Formation of Eocene age. In the basin the Green River Formation comprises three members. In ascending order, they are the Douglas Creek, the Garden Gulch, and the Parachute Creek Members, Four sites are presented for consideration and evaluated on geology and hydrology with respect to shale-oil economics. Evaluated criteria include: (1) stratigraphy, (2) size of site, (3) oil-shale yield, (4) representative quantities of the saline minerals dawsonite and nahcolite, which must be present with a minimum amount of halite, (5) thickness of a 'leached' saline zone, (6) geologic structure, (7) engineering characteristics of rock, (8) representative surface and ground-water conditions, with emphasis on waste disposal and dewatering, and (9) environmental considerations. Serious construction and support problems are anticipated in sinking a deep shaft in the Piceance Creek basin. The two major concerns will be dealing with incompetent rock and large inflow of saline ground water, particularly in the leached zone. Engineering support problems will include stabilizing and hardening the rock from which a certain amount of ground water has been removed. The relative suitability of the four potential oil-shale experimental shaft sites in the Piceance Creek basin has been considered on the basis of all available geologic, hydrologic, and engineering data; site 2 is preferred to sites 1, 3, and 4, The units in this report are presented in the form: metric (English). Both units of measurement are necessary as measurements were taken in English units, and most of the contracting agencies involved are using predominantly English units.

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