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Introduction

Core-log-seismic data integration method is an interdisci-plinary strategy, integrating core measurements, logging dataand seismic data (e.g., Goldberg, 1997). The investigation byuse of multiple scales of data such as seismic (2 or 3 dimen-sional information reflecting regional geologic structure),downhole logging (continuous information in intermediatescale surrounding of the borehole), and core data (detailedphysical properties and geologic age information), contributesto improve the confidence of each data set.

Our study was initiated at the margins of the Yamato Basin,Japan Sea to obtain the high-resolution seismic stratigraphyand to conduct silica diagenesis characterization, and thenextended to the Shatsky Rise to clarify the paleoceanographicevents based on the Ocean Drilling Program (ODP) data sets.

Data and method

All the data sets, core, physical properties, well-log andreflection seismic data, used in this study, are taken fromOcean Drilling Program Leg 127 in the Japan Sea (NationalGeophysical Data Center, 1992) and Leg 198 in the ShatskyRise (Shipboard Scientific Party, 2002). Gamma-ray Attenua-tion Porosity Evaluator (GRAPE), P-wave Logger (PWL) andwet bulk density data were obtained from the physical proper-ty measurements, while gamma-ray, lithodensity, neutronporosity, resistivity and sonic velocity were measured by theborehole logging. They were used to define, interpret andcharacterize seismic units, and to calculate and model the syn-thetic seismograms.

Integration of core-log-seismic data does not necessary leadto significant results without careful adjustments of the data incases where you have large differences in resolution. Toreduce the resolution differences, single-channel seismicreflection data were reprocessed with reference to syntheticseismograms made from density and velocity data sets takenby well-log and physical property measurements (Moe et al.,2002). Seismic stratigraphic units are at first established byintegrating the physical properties of core samples, well-log-ging data and seismic reflection data. Synthetic seismogramsare used to correlate different scales of data at the integration.

The units are applicable to wider area seismic profiles andhave close relationship with the representative lithology.

Since the data obtained by the high-resolution seismic,well-log and physical property data measurements are highlysensitive to sedimentation, silica diagenesis and lithologicvariations, these data sets are very useful for examining thedetails of lithologic and diagenetic processes.

Silica diagenetic process in the Yamato basin,Japan Sea

Marine sediments indurate through dissolution and partialreprecipitation of biogenic silica, which are occurred in thedepositional process to the depths. This indurational process iscalled the silica diagenesis. Opal-A (biogenic silica) is dis-solved with various changes in environmental factors such astemperature, time, host rock lithology and pore water chem-istry, and is partly reprecipitated as Opal-CT (metastable dia-genetic silica- cristobalite), and is then transformed to quartz(microcrystalline quartz) (e.g., Hein et al., 1978; Tada, 1991).Among the few silica diagenetic locations, the Japan Sea is thearea most studied with systematic geophysical surveys andseveral deep-sea drilling sites. In this paper we report on thestudy for Site 797 at the western margin of the Yamato Basin(Fig. 1).

To characterize the seismic units and their unit boundariesby means of lithologic and physical property data, we selectedfour kinds of properties (density, velocity, gamma-ray andresistivity) together with core lithology determined onboard(Fig. 2). Silica diagenetic boundaries sometimes vary on theindex of physical properties (GRAPE and PWL), well-log dataand seismic profiles. Even though both boundaries, opal-A/CTand opal-CT/microcrystalline-quartz, are identified at the ODPsites in the Japan Sea, the opal-A/CT boundary is more promi-nent with changes marked in core-log-seismic data.

Silica diagenesis produces three diagenetic zones: opal-A,opal-CT and quartz zones. Their characteristics are clearly dif-ferent in core lithology, seismic and well-log profiles. Well-log and physical properties data were useful to characterizeopal-A zone due to the very weak reflectors on seismic pro-files, while seismic data was used to identify chert layers andopal-A/CT boundaries as prominent reflectors. Characteriza-tion in quartz zone, however, was difficult in this study due tothe high instability of these data.

Core- log- seismic data integration for high-resolution seismicstratigraphy

MOE Kyaw Thu1, Kensaku Tamaki2, Shin-ichi Kuramoto3,*, Ryuji Tada4,Saneatsu Saito5 and Trevor Williams6

1 Center for Data and Sample Analyses, Institute for Frontier Research on Earth Evolution (IFREE)2 Ocean Research Institute, University of Tokyo, Tokyo, Japan3 National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan4 Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan5 Deep Sea Research Department, Japan Marine Science and Technology Center, Yokosuka, Japan6 Borehole Research Group, Lamont-Doherty Earth Observatory, New York, USA

* Present Address: Center for Deep Earth Exploration, Japan MarineScience and Technology Center, Yokosuka, Japan

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Paleoceanographic events in the Shatsky Rise

The purpose of core-log-seismic integration in Shatsky Riseis to relate paleoceanographic events found in the core sample,to the seismic record. By using logging data as an intermedi-ary between the core and seismic data, the spatial and tempo-ral extent of these events can be traced from the borehole loca-tion to the whole study area along the seismic profiles.

The early Aptian black shale recovered in Hole 1207 isclearly characterized by a large peak in gamma radiation at566 mbsf (meter below seafloor) (Fig. 3). Uranium, an associ-ate with the black shales, is the main contributor to the gammaradiation peak, and the black shale itself is also clear on densi-ty and porosity logs with lower and higher values, respective-ly. According to the logs of uranium, porosity, and density, theshale layer is estimated to be about 1.2-m thick. However,only 40cm of shale was recovered from the core.

In addition to identifying the paleoceanographically impor-tant black shale layer, we estimated total organic carbon(TOC) content from the density log, which is useful for theevaluation of hydrocarbon generation. The result is onlyapproximate, because we assumed that the shale and the back-ground sediments had the same porosity, and adopted densitiesthat were not necessarily well constrained (e.g., that of theorganic matter). Following Rider (1996), we used densities ofthe background sediment and the black shale from the densitylog, density of organic matter by assumption, density of matrixfrom grain density and seawater density for calculation. 15%TOC from the log-based calculation is the average of TOCmeasured by Rock-Eval pyrolysis.

Unlike the Hole 1207, black shales recovered in Hole 1213are represented by two large peaks in gamma radiation at257.5 and 259.5mbsf (Fig. 3). However, only the lower of thetwo uranium peaks is accompanied by low density values. Theshale layer is about 0.9-m thick, according to log data of theuranium, porosity, and density. Using the same calculations byRider, the density indicates that the peak has an organic mattercontent of approximately 9% that is close to the Rock-Evalpyrolysis measurement.

Conclusions

Lithological implications of seismic stratigraphic units aremade clear by integrating core lithology, the physical proper-ties of core samples, and borehole well-logging data. Theresults are applicable to the interpretation of the seismicreflection data acquired over a much wider area. Not only thelithologic features of the seismic stratigraphic units but alsotheir physical properties were characterized. Furthermore, sili-ca diagenetic boundaries and stages were defined, and com-plete diagenetic processes were traced including regionallysignificant opal-A/CT boundary appearance.

The results of this study lay the groundwork for interpretingreflectors associated with biogenic silica over the entire Yam-ato Basin and for tracing reflectors associated with paleo-ceanographic events in the Shatsky Rise. The core-log-seismicintegration is an important method that provides not onlystratigraphic correlation with high resolution but also newinformation on paleoceanography such as global change inmarine environment, marine productivity and so on.

Acknowledgements. We thank the captain, crew and technicians ofthe JOIDES Resolution from Ocean Drilling Program for the dataacquisition, scientists from Ocean Research Institute, Geological Sur-vey of Japan, Borehole Research Group and Institute of FrontierResearch on Earth Evolution for technical assistance to process seis-mic and downhole logging data.

References

Goldberg, D., GRL special section on core-log-seismic data integration,Geophys. Res. Lett., 24, 315, 1997.

Hein, J. R., D. W. Scholl, J. A. Barron, M. G. Jones, and J. Miller,Diagenesis of late Cenozoic diatomaceous deposits and formationof the bottom simulating reflector in the southern Bering Sea,Sedimentology, 25, 155-181, 1978.

Moe, K. T., K. Tamaki, S. Kuramoto, R. Tada, and S. Saito, High-res-olution seismic stratigraphy of the Yamato Basin, Japan Sea andits geological application, The Island Arc, 11, 1, 61-78, 2002.

National Geophysical Data Center (NGDC), Ocean Drilling ProgramCD-ROM version 1.0 data set, National Oceanic and AtmosphericAdministration (NOAA), 1992.

Rider, M., The geological interpretation of well logs, Gulf publishing,UK, 1996.

Shipboard Scientific Party, Leg 198 Preliminary Report, ODP Prelim.Rpt., 98, Online, 2002.

Tada, R., Compaction and cementation in siliceous rocks and theirpossible effect on bedding enhancement, in Einsele, Ricken andSeilacher, eds., Cycles and events in stratigraphy, 480-491,Springer, 1991.

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Figure 1. Location and bathymetric map illustrating ODP Site 797 in theYamato Basin, Japan Sea and Sites 1207 and 1213 in the Shatsky Rise.

Figure 3. Downhole gamma radiation, density and porosity logs fromHoles 1207B and 1213B illustrating the form and setting of the OAE1ablack shale. Gamma radiation peaks in the logs, which are representa-tive of black shale, indicate early Aptian black shales.

Figure 2. Results from the core-log-seismic data integration in ODP Site 797. (a) Lithologic and physical properties characterization of the seismicunits. Seismic stratigraphic units, their core lithology, synthetic seismogram modeled from velocity and density data, and selected logs: velocity (red),density (green), gamma-ray (black) and resistivity (blue). (b) Defined seismic units (numbers) and silica diagenetic boundaries (labeled lines) areclearly divided on density and velocity well-log cross-plots. (c) Chert layers(resistive light color thin layers) are observed in Formation Micro-scannerresistivity images and calculated their content in the formation.