Unexpected events are not exceptional in geological processes, and could be detected even in well-ordered sedimentary systems. Deposition of sandstone beds intercalated in reef limestones is a typical example of an occurrence of disorderly events in a highly ordered sedimentary process.
In this study we have considered mathematical properties of the van del Pol's equation in which sea-level fluctuations and metabolic activities of reef-building organisms are included as indispensable parametric factors controlling limestone deposition. Analytical results infer that the unexpected intercalation of sandstone beds in reef limestones has been a consequence of nonlinear reciprocal behavior between geological and biological agencies.

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Our purpose is to clarify Late Oligocene to Early Miocene paleoceanographic changes in the back-arc region of the Kuril Arc. We have only a few of reports on sedimentological and organic geochemical considerations as the Paleogene formations around the Sea of Okhotsk, which prompted us to research.
Kitami area, our research field, is located on the back-arc region of the Kuril Arc (Fig. 1), and has Tatsukobu-Tsubetsu biosiliceous deposit whose thickness attains more than 2500m. Based on biostratigraphic and rediometric ages, Tatsukobu-Tsubetsu biosiliceous deposit appears to be accumulated during the period ranging from Late Oligocene to earliest Early Miocene. This biosiliceous deposit begins with a basal sandstone including glauconite, which rests unconformably upon the Wakamatsuzawa Formation including silicified woods and roots. According to lithostratigraphic correlations, andesitic volcaniclastic bed of the upper part and acidic tuff bed of the middle part of the Tatsukobu Formation in the Kitami area are correlated to biotite-rich acidic tuff bed and hornblende-rich welded tuff bed in the Ponki-Ashoro area. Radiometric ages of acidic tuff bed and welded tuff bed in the Ponki-Ashoro area indicate 23.8Ma (fission track age) and 27.4Ma (K-Ar age).
To clarify the marine primary production of Tatsukobu-Tsubetsu biosiliceous deposit, we measured organic carbon congtents, C-H-N-O compositions of kerogen (insoluble organic matter) and Sulphur contents. Atomic composition analysis of kerogen concentrates is to examine the presence of terrigenous organic carbon. Plotted in a “van Krevelen Diagram” (i.e., H/C vs. O/O), estimated marine organic carbon (EMOC) and estimated non -marine organic carbon (ENOC) were calculated.
Based on stratigraphic changes in the amount of EMOC and ENOC, Tatsukobu biosiliceous deposit was divided into three stages.
In Depth 1335m-1450m and Depth 0m-350m (Fig. 5), stratigraphic variations in the amount of EMOC are parallel to those of ENOC. However, increase in EMOC are associated blosely with decrease in ENOC within Depth 350m-1335m. EMOC/ENOC ratios indicate that organic matter within Depth 350m-1335m included higher contents of marine-origin organic materials than those within other horizon. According to sedimentary petrological investigations, this deposit also contains larger volume of non-siliceous rocks in Depth 350m-1335m than in other horizon. In the past ocean, we conclude that amount of nutrients and dissolved silica components derived from land were parallel to those of ENOC. If this had happened at the back-arc region of the Kuril Arc during Late Oligocene to earliest Early Miocene, nutrients of deep water-origin contributed more to marine primary production than those of land-origin at the time of Depth 350m-1335m. This presumption suggests that the proto form of the Kuril Basin served as a vessel of nutrient-rich and silica-poor deep water at about 27.4Ma (Fig. 2).

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The present study reports on the method for estimating the water depth from wave-formed ripple marks, using data obtained from field and laboratory. Ripples having crestlines approximately parallel to each other and to wave crestlines are classified into four types based on the relationship between ripple spasing and orbital diameter and on the ripple morphology-orbital vortex ripples (OVR), suborbital vortex ripple (SVR), anorbital vortex ripples, and anorbital planar ripples (APR). OVR form under short-period waves in the limited-fetch coast (lakes and bays) or in lagoon inside reef. The other three are observed in the exposed coast where long period waves prevail.
The water depth of formation of OVR can be calculated using the method for orbital ripples (e.g., Komar, 1974). As to SVR, the following relationship is established: λ/wT=8h/L, where λ is the ripple spacing, w is the sediment fall velocity, T is the wave period, L is the wave length. Based on this equation, the combinations of T and h for given λ and w (which is convertible into sediment grain size) can be obtained. Also the T-h relation can be obtained from AVR, because the following relation is found for AVR: λ/wT=6.6h/L. These results enable us to estimate the ancient water depth from ripple marks preserved in strata. Because APR may not be preserved in deposit, we are unable to use APR as an indicator showing the ancient water depth.

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Paleo-wave conditions were estimated from wave ripples in the shallow marine sediments of the Pleistocene Osaka Group. Using new method by Takeda (1992), we can subdivide ancient ripples into four types, based on the relationship between orbital diameters and ripple spacings. Four types of wave ripples are discriminated in the group. Wave ripples in Neyagawa City are “anorbital vortex ripples” and “anorbital planar ripples”. Waves of 0.7-1.5m high in wave height and 2-4sec in wave period are calculated from those ripples. Wave ripples in Toyonaka City are “suborbital vortex ripples”, and 0.2-0.4m in wave height and 0.5-1sec in wave period are obtained. Wave ripples in Izumi City are “orbital vortex ripples”, and 0.1-0.9m in wave height, 2-4sec in wave period are calculated. Those wave conditions are similar to modern waves in the Sennan region, southern part of Osaka Bay. The minimum lengths of fetches for each reconstructed wave are also estimated.

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High-resolution seismic reflection profiles of the shelf off the Kuji River in northeast Japan show unconforming two sedimentary units lying on Tertiary basement rocks. The boundary surface of both units, which clearly truncates seismic reflections in the lower unit, is a ravinement surface created during the Late st Pleistocene-Early Holocene transgression.
These units are Unit Ka and Unit Kb in ascending order. Unit Ka consists of fluvial and coastal sediments deposited during the last period of low sea levels, which is estimated to be 80-85m below the present level and during the following transgression. Unit Kb, which overlies Unit Ka, is composed of shelf sediments deposited during the transgression after the formation of the ravinement surface and present high sea levels. As the distribution and thickness of Unit Kb show ridge and trough topography, 0-5m high, 1-3km apart, angles of 15-25° with the regional trend of depth contours, it is concluded that Unit Kb consists of transgressive sand ridges.
These transgressive sediments and a characteristic bounding surface indicate that the ravinement surface can be distinguished from the transgressive surface and that transgressive sediments can be divided into two units bounded by the diachronous ravinement surface.

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Gravel beds with superimposed boulders were observed in the Seto Group which is composed of fluvio-lacustrine deposits of the Upper Miocene-Pliocene in Central Japan. The gravel beds with boulders are different from very poorly sorted gravel beds such as debris flow deposits, because the gravel beds, with exception of the boulders, are well sorted.
In this paper, occurrences of the gravel beds with boulders in the Seto Group and recent fluvial gravel deposits with boulders are described. Sedimentary environments of the gravel beds in the Seto Group are discussed in comparison with the recent fluvial gravel deposits.
The gravel beds with boulders in the Seto Group are considered as the gravel channel bar deposits with superimposed residual boulders that are supplied from adjacent weathered basement rocks. The gravel beds are deposited along the periphery of tectonic sedimentary basin, in where a piedmont line was formed.

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