High‐resolution seismic stratigraphy of the Yamato Basin, Japan Sea and its geological application

Abstract

High‐resolution seismic stratigraphy of the Yamato Basin, Japan Sea, was successfully established using core‐log‐seismic data integration. The construction of synthetic seismograms by the combination of physical properties and well‐log data from the Ocean Drilling Program (ODP) Site 797 was the key to accomplishing the high‐resolution seismic stratigraphy. To achieve resolution comparable with well‐log data and core lithology, single channel seismic reflection data taken from ODP underway geophysics were reprocessed, and then carefully compared with synthetic seismogram, core and well log profiles to identify seismic units. Ten seismic stratigraphic units were identified at the site, and seismic stratigraphic interpretation was successfully extended from the site to the nearby area along the Yamato Basin margin. The opal‐A/opal‐CT (biogenic silica/metastable diagenetic silica) boundary has different appearances at places from strong to weak, and mostly discontinuous. One of the significant results achieved from this study is clear distinction of the opal‐A/CT boundary from a very strong reflector, which appears at 22 m below the opal‐A/CT boundary. Through well‐log and physical properties characterization of the different units, resistivity was found to be the best indicator of diatom content and with gamma‐ray it also is an indicator of chert layers in the opal‐CT zone. Velocity is not greatly effected by diatom ooze in the opal‐A zone, however, it shows strong peaks and has an indirect relationship with gamma‐ray in the opal‐CT zone. Finally, successful correlation of Gamma‐ray Attenuation Porosity Evaluator density and resistivity peaks with strong seismic reflectors from upper and lower stratified layers may provide new information on the late Neogene paleoceanography of the Japan Sea in high‐resolution scale.

Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: a case study for the COSC-1 borehole, Sweden

“…The concept of integration and cross-calibration of data sets across different scales is well established in sedimentary basins of marine and lake environments (e.g., Bloomer and Mayer, 1997;Miller et al, 2013;Riedel et al, 2013;Thu et al, 2002), where it was successfully used to better characterize the subsurface seismic stratigraphy using both core and downhole logging data. But to date, there are only few studies that have adapted this concept in hard-rock environments and similar metamorphic complexes.…”

Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden

“…Other studies have shown that differences in seismic properties are generally due to depressurization and formation of microcracks after the core extraction (e.g., Wolter and Berckhemer, 1989;Zang et al, 1989). Especially in sedimentary rocks, the mechanical rebound of pore spaces due to decompression is a primary correction factor when comparing core to in situ data (Urmos et al, 1993). For crystalline, metamorphic rocks, the effect of volume expansion is relatively small.…”

“…The concept of integration and cross-calibration of data sets across different scales is well established in sedimentary basins of marine and lake environments (e.g., Bloomer and Mayer, 1997;Miller et al, 2013;Riedel et al, 2013;Thu et al, 2002), where it was successfully used to better characterize the subsurface seismic stratigraphy using both core and downhole logging data. But to date, there are only few studies that have adapted this concept in hard-rock environments and similar metamorphic complexes.…”

Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden

“…This involves comparison of seismic velocities from different measurements and scales with both lithological and structural characteristics of cored rocks. This concept of integration and cross-calibration of data sets across different scales is well established in sedimentary basins of marine and lake environments (e.g., Bloomer and Mayer, 1997;Miller et al, 2013;Riedel et al, 2013;Thu et al, 2002), where it was successfully used to better characterize the subsurface seismic stratigraphy using both core and downhole logging data. But to date, there are only few studies that adapted this concept in hard-rock environments and metamorphic complexes (e.g., Emmermann et al, 1990;Xu et al, 2009).…”