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Recent progress in oceanography, marine sedimentology, and organic geochemistry enables us to evaluate, quantitatively, factors which control the process of marine organic matter production and its degradation during settling through the water column as well as within the surface sediment. Since many of the factors could be evaluated through detailed geological observation and paleoceanographic reconstruction of the depositional setting, it seems possible to incorporate mathematical formulation of this process into the pre-existing models of source rock evaluation.In this paper, I will propose the mathematical formulation of the marine organic matter production-settling-degradation process based on recently accumulating oceanographic data, and try to apply this formulation to evaluate the source rock potential of the Miocene Onnnagawa Formation, northeast Japan.

Sedimentary rhythm analysis is a method to study sedimentary cycles through the systematic sampling and analysis of the sequences, derivation of multiple paleoenviron-mental parameters from the analytical data, and examination of the frequencies in variation of these parameters and their phase relationships. Through sedimentary rhythm analyses, it is possible to study the dynamics of paleo-ocean circulation. In this short paper, I would like to show the application of this method to reconstruct dynamic behaviour of the surface and deep water circulation within the Japan Sea corresponding to the glacial-interglacial sea-level oscillations during late. Quaternary. Reconstruction of this sort is useful to understand the paleoenvironment as well as mechanism(s) of the petroleum source rock deposition within marginal seas.

Pore-size distribution of natural sandstones was analyzed by mercury poro-simetry. Cumulative pore-size distribution curves drawn on the log-probability diagram can be regarded as consisting of two to five linear segments which reflect the porosity and petrographic types of Sandstones. Effects of grain size, sorting, roundness, matrix and porous mudrock fragments on the cumulative curves were experimentally elucidated by UCHIDA and TADA (1991) with investigating five series of artificially packed sands as follows: (1) ES series composed of equigranular glass beads, (2) VS series composed of variably sorted glass beads, (3) BS series bimodally composed of two mixtures of sand-size glass beads and either 4-phi glass beads or normally distributed matrix-size glass beads, (4) VR series composed of mixtures of equigranular sphere glass beads and angular quartz grains, and (5) PRF series composed of equigranular glass beads and porous mudrock fragments.Natures of pores in various petrographic types of natural sandstones, such as Mississippian and Tertiary quartz arenites, Miocene lithic arenites and Miocene lithic wacke, were estimated from the cumulative pore-size distribution curves based on the experimental results of UCHIDA and TADA (1991). As a matter of fact, cumulative distribution curves of these sandstones are regarded as consisting of two to five linear segments, which designate the framework distribution and the toroidal void distribution of intergranular porosities, the framework distribution and the toroidal void distribution of matrix and the intragrain distribution of lithic fragments of mudrocks including in sandstones, respectively.The gradient and position of the segments are influenced by grain size, sorting and porous mudrock fragments as well as by porosity types. Consequently, shapes of the cumulative curves should correspond to rock types of sandstones. Thus, porosity properties, such as the intergranular porosities, matrix porosities and intragrain porosities of mudrock fragments can be quantitatively estimated from the pore-size distribution analyses.

Japan Sea Legs 127 and 128 of Ocean Drilling Program were conducted in the summer of 1989. The drilling results at 6 sites during the cruises gained our understanding on the history of the Japan Sea. Based on the new chrono-stratigraphic informations, opening of the Japan Sea started at least before 18 to 20Ma, which is much older than the age of 15Ma estimated from paleomagnetic evidence by OTOFUJI and MATSUDA (1983).Lithostratigraphy of the sediments above the acoustic basement was established, which was proved to be correlatable throughout the Japan Sea. The lithostratigraphy is also correlatable with that in oilfield areas in the Tohoku region. The change in lithology through time is probably influenced by global changes in sea level as well as climate.Seismic stratigraphy is correlated with lithostratigraphy at 3 sites drilled during Leg 127. The result suggests remarkable coincidence of opal-A/CT diagenetic boundary with the Bottom Simulating Reflector [BSR].These results will have profound influences on stratigraphic studies in the Japan Sea and its environs.

Cumulative pore-size distribution curves of natural sandstones analyzed by mercury porosimetry generally consist of two to five linear segments on the log-probability diagram, which may reflect the nature of porosity and petrographic types of sandstones. In order to clarify the significance of these segmentations in pore-size distribution curves of natural sandstones, effects of grain size, sorting, roundness, presence of matrix and porous mudrock fragments were analyzed for artificially packed sands as follows: (1) equigranular glass beads (ES series), (2) variably sorted glass beads (VS series), (3) bimodal mixtures of sand-size glass beads and either 4-phi glass beads or normally distributed matrix-size glass beads (BS series), (4) mixtures of equigranular sphere glass beads and angular quartz grains (VR series), and (5) equigranular glass beads and porous mudrock fragments (PRF series).Cumulative curves of ES, VS and VR series consist of two to three segments corresponding to the framework distribution attributed to the main part of intergranular pores built up by grain packing and the toroidal void distribution attributed to the subordinate part of intergranular pores around grain contacts. Gradients of the framework distribution segments decrease as sorting index increases. Effect of roundness on shapes of the cumulative curves is negligible. Two more segments appear in the smaller pore-size range of the cumulative curves of BS series, and are attributed to the framework and toroidal void distributions of matrix, respectively. In PRF series, porous mudrock fragments also yield an additional segment in the smaller pore-size range of the curve which is attributed to the intragrain pore-size distribution.The gradient and position of the segments are influenced by grain size, sorting and porous mudrock fragments as well as by porosity types. Consequently, shapes of the cumulative curves correspond to rock types of sandstones. Thus, porosity properties can be semiquantitatively estimated from the pore-size distribution analysis.