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K. J. Murata

Publications and source records attributed to K. J. Murata.

At least 19 recordsLinked to original sources
USGS1979

Origin of dolomite in Miocene Monterey Shale and related formations in the Temblor Range, California

Dolomites in thick sections of Miocene Monterey Shale and related formations in the Temblor Range of California acquired their isotopic compositions as they formed at shallow depth in the original sediment rich in organic matter, and retained the composition against the vicissitudes of burial diagenesis. The oxygen isotopes of dolomites of successive beds record changes in temperature of bottom water while the carbon isotopes of the same samples indicate changes in the kind of microbial activity (sulfate reduction vs carbohydrate fermentation) that prevailed at shallow depths in the sediment. In an auxiliary study, two samples of dolomite from sediments of Cariaco Basin off Venezuela (DSDP site 147) were found to have ??5C13 of -14.1 and -9.8 per ml PDB, although they occur in a heavy-carbon zone containing bicarbonate as heavy as +8.4 per ml. These dolomites probably originated at shallow depth in the light-carbon zone of microbial sulfate reducers and were buried under later sediments down into the heavy-carbon zone of microbial fermenters of carbohydrates without losing their original light-carbon composition. ?? 1979.

Geochimica et Cosmochimica Acta↗
USGS1977

Occurrence of bloedite and related minerals in marine shale of Diablo and Temblor Ranges, California

Bloedite, epsomite, and related minerals occur in small amounts throughout the arid eastern foothills of the Diablo and Temblor Ranges, as efflorescences on siliceous shale and as deposits around small springs and a brine pond. These minerals ultimately are products of weathering of underlying organic shale, and they are reminders that the chemistry of weathering of reduced organic shale is largely a reversal of the chemistry of its early diagenesis.

California↗
USGS1975

Diagenesis of Miocene siliceous shales, Temblor Range, California

Siliceous Monterey Shale and related shales of the Temblor Range, Calif., are subdivided into three depth-controlled zones characterized by different forms of silica. These are, in descending stratigraphic order: (1) Biogenic opal zone, with remains of diatoms and other siliceous organisms, (2) diagenetic cristobalite zone, and (3) diagenetic quartz zone. Using the top of the youngest marine unit, the overlying Etchegoin Formation, as datum, the transition from biogenic opal to disordered cristobalite occurs within the Monterey Shale of Chico Martinez Creek at -730 m, and the ordered cristobalite-to-microquartz transition at about -2,030 m. Temperatures that prevailed at these transition depths while the sedimentary pile lay at the bottom of the sea are estimated at about 50° and 110°C, respectively. Diagenetic cristobalite manifests, downward through a 1,300-m interval of section, a progressive decrease in its d (101) spacing because of a gradual ordering of its internal structure through adjustments in the solid state. Diagenetic microquartz forms only from well-ordered cristobalite that provides the most appropriate concentration of dissolved silica for precipitation of microquartz. Scanning electron micrographs of the silica mineral in pores of rocks made up of disordered cristobalite show aggregates of well-formed bladed crystals, like those described from deep-sea cherts. The pore silica minerals in rocks made up of ordered cristobalite occur as dendritic growths of poorly formed stubby crystals, and the change in crystal habit could be an external expression of the internal ordering process.

California↗
USGS1974

Cristobalitic stage in the diagenesis of diatomaceous shale

With increasing depth of burial, diagenetic cristobalite in the Monterey Shale of California shows a decrease in the d (101) spacing from 4.115 to 4.040 angstroms, indicative of a progressive change in its internal structure. The spacing is 0.004 to 0.015 angstrom smaller in porcellanite than in associated chert, probably because the cristobalite of porcellanite formed later than that of chert.

California↗
USGS1973

Zeolites in the Miocene Briones Sandstone and related formations of the central Coast Ranges, California

Authigenic zeolites present in the generally tuffaceous Miocene Briones Sandstone and related formations of the central Coast Ranges of California indicate three stages of diagenetic history: (1) Initial alteration of pyroclastic materials to clinoptilolite (and montmorillonite) that is widely distributed in small amounts throughout the region. (2) Subsequent crystallization of heulandite followed by stilbite in fractures at a few places. (3) Widespread development of laumontite in only the southern part of the region, where the sandstone appears to have been downfolded and faulted to greater depths than elsewhere. Laumontite occurs both as pervasive cement of sandstone and as filling of fractures, and was produced through the reaction of interstitial solutions with other zeolites and with such major constituents of the sandstone as plagioclase, montmorillonite, and calcite at temperatures of 100° C or higher. Mordenite was found at only one locality, closely associated with clinoptilolite and opal. Analcite occurs in diverse settings, and its relation to the other zeolites is obscure. Sparry calcite and coexisting stilbite, laumontite, or analcite in veins seem to make up nonequilibrium assemblages.

California↗
USGS1970

Tholeiitic basalt magmatism of Kilauea and Mauna Loa volcanoes of Hawaii

The primitive magmas of Kilauca and Mauna Loa are generated by partial melting of mantle peridotite at depths of −60 km or more. Results of high-pressure melting experiments indicate that the primitive melt must contain at least 20% MgO in order to have olivine as a liquidus mineral. The least fractionated lavas of both volcanoes have olivine (Fa 13 ) on the liquidus at 1 atmosphere, suggesting that the only substance lost from the primitive melt, during a rather rapid ascent to the surface, is olivine. This relation allows the primitive composition to be computed by adding olivine to the composition of an erupted lava until total MgO is at least 20 percent. Although roughly similar, historic lavas of the two volcanoes show a consistent difference in composition. The primitive melt of Mauna Loa contains 20% more dissolved orthopyroxene, a high-temperature melting phase in the mantle, and is deficient in elements such as potassium, uranium, and niobium, which presumably occur in minor low-melting phases. Mauna Loa appears to be the older volcano, deriving its magma at higher temperature and greater depth from a more depleted source rock.

Hawaii↗
USGS1967

Carbon-13-rich diagenetic carbonates in miocene formations of California and Oregon

Carbon unusually rich in C 13 (δC 13 = +5.4 to +19.0 per mil relative to the Peedee belemnite carbonate standard of the University of Chicago) is characteristic of certain diagenetic limestones and dolomites in the Miocene Monterey Shale of California and the Nye Mudstone of Oregon. This heavy carbon may have originated through low-temperature equilibration between CO 3 - - and CO 2 in migrating carbonated waters or between CH 4 and CO 2 in natural gas. Light carbon (δC 13 = -5.6 to -18.2 per mil) derived through nonequilibrium oxidation of organic matter also occurs in the carbonate of Monterey Shale in some localities, but at most places it is much less common than heavy carbon.

California, Oregon↗
USGS1966

The 1963–65 eruption of Irazú volcano, Costa Rica (the period of March 1963 to October 1964)

The 1963–65 eruption of Irazú, like all others of this volcano during the historic period, produced only ash and other fragmental ejecta without lava. The initial outbreak on March 13, 1963 started with a series of great explosions that hurled out much ash, blocks, and bombs, but the activity soon settled down to alternating periods of explosive cruptions and quiet emission of steam. Ash was deposited mostly along a zone that extended westward from the summit to and beyond the city of San Jose, 24 km away. The prolonged ashfall severely damaged dairy, vegetable, and coffee farms, and for a while made daily life in the affected cities extremely difficult. Accelerated runoff of rainwater from the ash-covered slopes of the volcano caused destructive floods, mudflows, and landslides. The climax of the cruption probably occurred during December 1963 and January 1964, when ash and incandescent scoria were erupted voluminously and the magma rose to within 100 meters of the lip of the vent. Precise levelling along the highway to the summit in May 1964 by the Geographic Institute revealed the upper part of the volcano upheaved as much as 11 cm above levels determined in 1949. A repetition of the levelling in September 1964 showed a subsidence to approximately the 1949 configuration, indicating a distinct reduction of pressure in the magma chamber. Substantial amounts of pulverized wallrock were present in the ash along with fragments of scoria and pumice. Progressive caving of the vent walls, which enlarged the diameter of the vent from 200 meters to 525 meters, kept dropping wallrock down onto the exploding magma, and at times stopped the eruption for a day or two by plugging the vent. The scoriaceous and pumiceous bombs were porphyritic two-pyroxene olivine basaltic andesite, and their composition remained remarkably constant throughout the eruption. The ash section was about 2 meters thick, 800 meters downwind from the vent in June 1964. In the section, deposits of the rainy season could be distinguished by their well developed stratification from those of the dry season. A zone containing three persistent pumice horizons represents the climactic period of December 1963 to January 1964. The cloudburst of December 10, 1963 is recorded by a highly rilled surface, and the strong winds of the dry season of 1964 are indicated by a rippled lag deposit.

Bulletin Volcanologique↗
USGS1961

Magmatic differentiation in the Uwekahuna Laccolith, Kilauea Caldera, Hawaii

Petrographic and chemicoal studies of a suite of rocks from the Uwekahuna laccolith of Kilauea Volcano show that the original mafic tholeiitic magma differentiated into tholeiitic picrite, tholeiitic olivine gabbro, and an aphanitic rock approaching quartz-basalt in composition. Mechanisms involved were an initial gravity settling of olivine and a final filter pressing of the residual liquid. The range of composition represented by the rocks of the laccolith is as great as that found among all hitherto analysed lavas of the volcano.

Hawaii↗
USGS1960

How volcanoes grow

Geology, geochemistry, and geophysics disclose the constitution and eruption mechanism of Hawaiian volcanoes.

Hawaii↗