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J. E. Case

Publications and source records attributed to J. E. Case.

At least 37 records · Page 2Linked to original sources
USGS1981

The Alaskan Mineral Resource Assessment Program; background information to accompany folio of geologic and resources maps of the Chignik and Sutwik Island quadrangles, Alaska

The Chignik and Sutwik Island quadrangles (1:250,000) are a part of the Alaska Peninsula in southwestern Alaska. This circular and a companion folio of maps represent results of integrated field and laboratory studies by an interdisciplinary team on geology, geophysics, geochemistry, mineral resources, geochronology, and energy resources to provide a modern assessment of the mineral and energy resources of the quadrangles. The maps contain descriptive text, explanatory material, tables and diagrams, and pertinent references. This circular provides the background data for the mineral and energy resource assessment and integrates the component maps. A comprehensive bibliography cites both specific and general references relevant to the geology and resources of the quadrangles.

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USGS1981

Maps showing aeromagnetic survey and geologic interpretation of the Chignik and Sutwik Island quadrangles, Alaska

An aeromagnetic survey over part of the Chignik and Sutwik Island quadrangles, on the southern Alaska Peninsula, was flown in 1977 as part of the Alaska mineral resource assessment program (AMRAP). Maps at scales 1:250,000 and 1:63,360 have been released on open-file (U.s. Geological Survey, 1978a, 1978b). This report includes the aeromagnetic map superimposed on the topographic base (sheet 1) and an interpretation map superimposed on the topographic and simplified geologic base (sheet 2). This discussion provides an interpretation of the aeromagnetic data with respect to regional geology, occurrence of ore deposits and prospects, and potential oil and gas resources. The survey was flown along northwest-southeast lines, spaced about 1.6 km apart, at a nominal elevation of about 300 m above the land surface. A proton-precession magnetometer was used for the survey, and the resulting digital data were computer contoured at intervals of 10 and 50 gammas (sheet 1). The International Geomagnetic Reference Field (IGRF) of 1965, updated to 1977, was removed from the total field data.

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USGS1981

Gravity anomaly and interpretation map of the Chignik and Sutwik Island quadrangles, Alaska

The gravity field of the Chignik and Sutwik Island quadrangles near the center of the Alaska Peninsula represents a complex series of transitions between probable continental crust on the north, probable oceanic crust on the south, sedimentary basins on each side of the peninsula, and a central structural high and volcanic arc. The resulting gravity field may be generalized as a central southwest- to northeast-trending gravity high bordered on both sides by flanking gravity lows over sedimentary basins underlying the lowlands and continental shelf. All three gravitational features show discontinuities and magnitude variations that reflect the complex geologic setting. Data concerning this complex gravity field have accumulated slowly and intermittently since an initial measurement was made at Port Heiden more than 25 years go (Thiel and others, 1958, 1959). A few reconnaissance measurements by R. V. Allen and an offshore traverse conducted by the U.S. Coast and Geodetic Survey R/V Surveyor were made in the early 1960's (Barnes and others, 1966; Barnes, 1967). At about the same time, Gulf Oil Corp. contracted for a relatively detailed survey of the lowlands on the north shore of the peninsula; the map prepared from this survey is now available (Gulf Oil Corp., Port Moller Development Contract Report, available at U.S. Geological Survey, Anchorage, Alaska). In the early 1970's, a few new land measurements were made by P. L. Dobey, of the Alaska Division of Geological and Geophysical Surveys, and an offshore traverse was completed by the R/V C. Greene on contract to the U.S. Geological Survey (Fisher, 1979, and M. A. Fisher, written commun., 1977). The most recent measurements, the basis for this map, were made by M. E. Yount, D. L. Detra, D. R. Jefferis, and J. E. Case during the mineral assessment of the two quadrangles. D. F. Barnes, R. L. Morin, D. R. Jefferis, and R. F. Sikora have shared in the data compilation. Geologic background for the text was provided by R. L. Detterman, T. P. Miller, E. Young, and F. H. Wilson (1979, 1981).

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USGS1979

Geologic interpretation of the gravity anomaly map of the Seward and Blying Sound quadrangles, Alaska

For more than 20 years, gravity surveys have been conducted in the vicinity of Prince William Sound, the epicentral region of the great Alaska earthquake of March 27, 1964. Some of the major regional gravity anomalies were outlined by Thiel, Ostenso, Bonini (1960), and additional anomalies were defined by pre- and post-earthquake gravity studies reported by Barnes and Allen (1965) and Case, Barnes, Plafker, and Robbins (1966). Another gravity anomaly map was prepared by personnel of the U.S. Coast and Geodetic Survey (now the National Oceanic and Atmospheric Administration) (Wood, 1966, p. 131; Rice, 1969, p. 5-20). Anomalies shown by Rice (1969) are broadly similar to those shown by Case, Barnes, Plafker, and Robbins (1966); Rice's interpretations concerned mainly gravity changed related to the earthquake, and the data were not interpreted in terms of regional geology. New gravity stations were established in 1976 as part of the mineral resource appraisal of the Seward and Blying Sound quadrangles. This report incorporates the new data obtained in 1976, reinterprets some anomalies previously discussed by Case, Barnes, Plafker, and Robbins (1966), and interprets other anomalies not previously discussed. Descriptions of the major rock units and structural features are found in the companion report by Tysdal and Case (in press). An interpretation of the aeromagnetic map of the region has been prepared by Case, Tysdal, Hillhouse, and Gromme (1979).

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USGS1979

Geologic interpretation of aeromagnetic map of the Seward and Blying Sound quadrangles, Alaska

An aeromagnetic survey of the Seward and northern part of the Blying Sound quadrangles was flown by Geometrics, Inc., during 1975-77 to provide magnetic data to aid in an appraisal of the mineral resources. Background details of the regional geology and major structures are described in a companion report by Tysdal and Case (1979), and interpretation of the gravity data are described in a report by Case and others (1979). Preliminary reports of a paleomagnetic investigation have been reported by Hillhouse and Gromme (1977), and a more complete analysis of the results is in preparation. The aeromagnetic survey was flown at a nominal height of 300 m above the surface and flight lines were spaced about 1.7 km apart. Total magnetic field was measured by a proton-precession magnetometer. The International Geomagnetic Reference Field (IGRF), updated to 1976, was removed, and the residual values were computer-contoured to produce the aeromagnetic map (sheet 1). Detailed aeromagnetic maps at scale 1:63,360 and a map at scale 1:250,000 have been released as Open File Reports 78-1080 through 1083 (U.S. Geological Survey, 1978). Magnetic anomalies in the Seward-Blying Sound region are somewhat less complex than in other parts of south-central Alaska, primarily because of the huge volume of relatively nonmagnetic flysch that constitutes the Valdez and Orca Groups. Several rather isolated groups of mafic-ultramafic rocks are significantly more magnetic than the flysch assemblages, and cause distinctive patterns of magnetic anomalies. A few of the granitic plutons are magnetic, but most appear to have little or no magnetic expression.

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USGS1977

Sheeted dikes, gabbro, and pillow basalt in flysch of coastal southern Alaska

A Paleocene to Eocene(?) mafic sequence of igneous rocks on Knight Island and a Cretaceous mafic and ultramafic sequence of the Resurrection Peninsula in coastal southern Alaska are characterized by pillow basalts, sheeted dikes, and gabbro intrusions. At both localities, pillow basalts are interbedded with flysch, and the gabbros intrude both the sheeted dikes and the immediately overlying sedimentary rocks. At the Resurrection Peninsula, small bodies of serpentinized dunite are present in the gabbro, and overlying low-grade metasedimentary rocks and mafic tuffs are interbedded with sedimentary rocks. At Knight Island the sheeted dikes intrude Paleocene and Eocene(?) sedimentary rocks. These igneous rocks have petrographic features similar to those of oceanic tholeiites and have some of the characteristics of ophiolites. They apparently were formed near the continental margin, because both sequences intrude and are interlayered with flysch. We believe the igneous rocks were intruded along faults (perhaps leaky transform faults) of ocean floor that happened to be near the continental margin; the faults were oriented parallel to the depositional strike and subsequent deformational strike of the Valdez(?) and Orca Groups.

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USGS1977

The Alaskan Mineral Resource Assessment Program; background information to accompany folio of geologic and mineral resource maps of the McCarthy Quadrangle, Alaska

The McCarthy 1? by 3? quadrangle, in eastern south-central Alaska, contains potentially significant resources of copper and possibly of a few other commodities. This circular and a companion folio of maps represent results of integrated field and laboratory studies in the disciplines of geology, geophysics, geochemistry, and satellite imagery that are designed to provide a modern mineral resource assessment of the quadrangle. The maps are accompanied by descriptive texts, explanatory material, pertinent references, and by a few auxiliary tables and diagrams. This circular provides background information for the mineral resource assessment and integrates the component maps. It also includes a master list of references (see 'Bibliography') relevant to the geology and mineral deposits of the quadrangle.

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