http://SaturnianCosmology.Org/ mirrored file For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== SciVerse Home /Marine Geology/, /Volume 59, Issues 1-4/, /27 July 1984/, /Pages 251-269/ Thomas Tung-Hung Lin, Michael T Ledbetter *Abstract* Volcanic ash erupted from vents in Central America, southern Mexico and northern South America has accumulated as discrete layers in sediment of the surrounding ocean basins. Many of these ash layers form acoustic reflectors which are observed on 3.5 kHz seismic records from the eastern equatorial Pacific. Twelve discrete reflectors within 40 m of the seafloor may be traced in the region. Shallow (<20 m) seismic reflectors can be correlated to ash layers in piston cores where some ashes were correlated by Bowles et al. (1973) and Drexler et al. (1980) using geochemical methods. In addition, deeper seismic reflectors (>20 m) can be correlated with ash layers in two DSDP cores and used to indirectly establish that all seismic reflectors in this study are ash layers. Based on areal distribution patterns, most seismic reflectors indicate the direction of possible volcanic sources. Moreover, using an assumed constant sedimentation rate of 3 cm × 10^3 yr^−1 , the average estimated age of each reflector can be calculated. All ash reflectors are Quaternary in age. Reflectors 1 to 3 are correlated to marine ash layers “D”, “I”, and “L”, and the assigned ages correlate well with the previously established ages of 83,000, 133,000 and 230,000 yrs B.P., respectively, for these layers. The importance of carbonate content in the acoustic str... /Marine Geology/ Close You are not entitled to access the full text of this document *The importance of carbonate content in the acoustic stratigraphy of Panama Basin Original Research Article* /Marine Geology/, /Volume 54, Issues 3-4/, /January 1984/, /Pages 237-247/ Juergen Mienert *Abstract* DSDP cores from areas of low (Site 505) and high heat flow (Site 504 B) near the Costa Rica Rift, together with seismic profiles from the Panama Basin, have been studied to determine the relationship between: (1) carbonate content and physical and acoustic properties; and (2) carbonate content, carbonate diagenesis and acoustic stratigraphy. Except for ash and chert layers, bulk density correlates strongly and linearly with carbonate content. Velocity is uniform downcore and only small variations at a small scale are measured. Thus an abrupt change in carbonate content will cause abrupt changes in acoustic impedance and should cause reflectors that can be detected acoustically. A comparison of seismic profiler reflection records with physical properties, carbonate content and reflection coefficients indicates that the main reflectors can be identified with ash layers, diagenetic boundaries, and carbonate content variations. Diagenesis of carbonate sediments is present at Site 504 B in a 260 m-thick ooze—chalk—limestone/chert sequence. These diagenetic sequences occur in areas of higher heat flow (200 mW m^−2 ). Seismic profiler records can be used to map the extent and depth of these diagenetic boundaries. Chemical and optical studies of glass shards in Pleisto... /Journal of Volcanology and Geothermal Research/ Close You are not entitled to access the full text of this document *Chemical and optical studies of glass shards in Pleistocene and Pliocene ash layers from DSDP site 192, Northwest Pacific Ocean Original Research Article* /Journal of Volcanology and Geothermal Research/, /Volume 4, Issues 1-2/, /August 1978/, /Pages 99-116/ K.F. Scheidegger, P.A. Jezek, D. Ninkovich *Abstract* Thirty-four ash layers of Pleistocene and Pliocene age from DSDP Site 192, northwestern Pacific Ocean, have been subjected to detailed chemical and optical study to evaluate: (1) the chemical and optical variability in glass shards from deep-sea ash layers, and (2) secondary changes brought about by prolonged exposure to seawater. Glass shards from approximately half of the ash layers studied were found to have uniform compositions which approach the precision of the microprobe chemical analyses, whereas the remainder are compositionally diverse (e.g., SiO_2 , variations of 5–15% among shards from the same ash layer) and appear to be the eruptive products of compositionally zoned magma chambers. Optical studies of glass shards confirm the absence of devitrification or the formation of pervasive secondary alteration products. By contrast, chemical studies suggest that the glass shards have experienced progressive hydration with possible minor ion exchange of K, Mg, Ca and Si. The hydration occurs rapidly and leads to a rather uniform water content of 4.5–5% after several hundred thousands of years exposure to seawater. Step-wise heating dehydration experiments, optical effects, and published'oxygen isotope studies indicate that the water of hydration is incorporated uniformly within the glass. Systematic chemical differences between electron microprobe analyses of glass shard interiors and corresponding bulk chemical study by atomic absorption lead us to postulate that glass shard margins have undergone a minor chemical exchange with major cations in seawater. They have gained 0.10–0.20 wt. % K_2 0, MgO, and CaO while losing a corresponding amount of Si_2 O. Although the glass shards from DSDP Site 192 are hydrated and may have experienced subtle, surficial ion exchange, we stress that they are the most chemically representative samples available of magmas that were explosively erupted from volcanic arcs. Hawaiian-derived volcanic ash layers in equatorial nort... /Marine Geology/ Close You are not entitled to access the full text of this document *Hawaiian-derived volcanic ash layers in equatorial northeastern Pacific sediments Original Research Article* /Marine Geology/, /Volume 50, Issues 1-2/, /November 1982/, /Pages 25-40/ E Rehm, P Halbach *Abstract* Volcanic ash layers with thicknesses of up to 30 cm and ages between 1 and 2 m.y. were found in equatorial northeastern Pacific sediments. Grain-size distributions, mineralogical composition and alteration of the ashes are described. Chemical analyses of major, trace and rare-earth elements and trace-element correlations indicate a basaltic composition of the ocean-island tholeiitic type. Comparison with Hawaiian tholeiitic rocks indicates the Island of Maui as the source of material for the ash sequence in the investigated area. The composition of an ash layer north of the area indicates it was associated with volcanism of Mauna Loa or Kilauea.