プレートテクトニクスとその原動力に関する研究が進むにつれて, 堆積盆地の進化について統一的な理論ができつつある.
マントルの対流によって起こるグローバルなプレート運動のパターンは常に変化している. トランスフォームあるいは収束や発散するプレートの運動にともなって, いろいろなタイプの堆積盆地が発達する. それらは地殻の引っ張りによってできる extensional basin と, 圧縮と荷重による foreland basin の2つに大別される.
海洋底拡大パターンの変化は海盆の容積や大陸縁辺の形状に影響を与えるので, 超大陸の形成や分裂の結果, 地域的あるいは全地球的規模でさまざまなタイムスケールの周期パターンが地層に記録されることになる. さらに, いわゆるミランコヴィッチ効果とよばれる天体運動によって生じる短時間の周期が加わる. このような周期性は, 地球軌道が傾いていることによって起こる太陽放射の量と分布の変化を示している.

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Three processes in petroleum geology have been tried to be modeled in these decades as a part of computer applications for actual exploration problems. They are generation, migration and accumulation processes. Simulation models have been developed indivisually in each part of these processes. Among them generation model was achieved as a most successful tool for exploration. Geochemical information can be used to predict the timing and amount of hydrocarbon generated in the basin. This model, coupled with fluid flow model in two-dimensional scheme, makes an integrated simulation tool for searching areas of high potential of petroleum accumulations.
However, when the model was applied to the real geologic situation, it was turned out that the results were so dependent upon given lithological distributions which were controled directly by input parametes. As an extention of simulation modeling, the sedimentological approach was then applied to estimate facies distributions within a basin.
The concept of Quantitative Dynamic Stratigraphy (QDS) in recently employed for this type of modeling where three modes exist: geodynamic modeling, purely-sedimentary process modeling and stratigraphical modeling. This paper demonstrates how one of the stratigraphical models works through its application to “Vail's Sequence.” This type of forward modeling functions to test independently a hypothesis proposed by the seismic stratigraphy.
The QDS models should conceptually be applicable to ancient geological deposits, however, we know so little about input parameters in the geologic past. We may be necessary to include some stochastic processes for simulating real sedimentary features as an integration of the present deterministic approaches.

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The Lake Biwa is a deep (up to 100m) tectonic basin with rapid accumulation of muddy sediments, and show an asymmetrical profile with stacked submerged terraces on the east and steep slope on the west.
The results of acoustic survey off the Echi River and the facies analyses of sediment cores show that these terraces are composed of sand-rich deposits formed under delta, barrier, and alluvial plain environments, which are similar to those in the present time and characterized by wave-dominated edimentary structures. They are successively built up 40-m-thick coastal sedimentary prisms, where at least nine sedimentary sequences are identified. Each sequence has dominant regressive facies represented by prograding delta-front and shoreface deposits followed by lagoon or alluvial-plain deposits behind them, but fewer transgressive facies.
In addition to the stacked terraces, barrier-growth, lagoon-filling, overwash, and coastal onlap structures around the sequence boundaries can prove the water-level rise during the last 30, 000yr. Thin sand sheets or reworked sediments on the ravinement surfaces, washover deposits, and well-preserved surface topographic features are suggestive of rapid shoreface retreat or in situ drowning. The average amplitude and period of lake-level rise are estimated as 3.5m and 3, 500yr, respectively.
According to the previous works (TAKAYA and NISHIDA, 1964; YOSHIOKA, 1987; KAWABE, 1989), it is expected that the tectonic block including the drainage channel of the lake water (present Seta River) is uplifted, and that the lake basin is tilting westward to the active faults along the western basin boundary. Therefore, such a periodic rise can be sttributed to tectonically-induced relative subsidence compared to the level of the drainage channel, rather than a climatic control.

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Active sediment accretion in the landward slope of the Nankai Trough off SW Japan has been documented by multichannel seismic reflection data which show a development of accretionary prism associated with landward dipping thrusts. It has been difficult to know the lateral extend and configuration of these thrusts which have relatively small displacement even by means of the Sea Beam survey. An oceanfloor imaging sonar system, IZANAGI, however revealed detail structures of the prism and the trough floor. Mud volcano-like morphologies were detected at the trough floor, one of which reaches 2km diameter. Deformation at the toe of the prism is characterized by ramp anticlinal ridges due to thrusting. The trend of thrust faults is affected by the orientation of oceanic basement as well as convergence direction and slope orientation. Toward the interior region of the prism, slope sediments composed of fine grained materials modify the relief of anticlinal ridges.

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The detail observation using soft-x radiography is carried out for a cross-stratification formed in the Upper Pleistocene tidal inlet exposured at Uchijuku, Ibaraki, Japan. The foreset laminae of the cross-stratification are characterized by thin, sharp and fine-grained heavy mineral layers. The dip of laminae is constant thoughout the outcrop. These layers are straight and do not disappear even near the base of foreset. The thickness of each lamina is almost the same thoughout one set. These foreset structures indicate that each foreset lamina is formed by a grain flow.

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The ultrasonic sieving method is a new and useful tool for grainsize analysis of fine-grained muddy sediments. The new method was compared with the traditional hydrometer method. The ultrasonic sieving method shows a little wide variation. Ultrasonic vibration is often used to disperse the sample before the hydrometer analysis. It decreasea the grainsize of muddy sediments, but the sediments attains a “terminal distribution” in grain size after about 30 minutes of vibration. The weigted mean of the analysis by ultrasonic sieving method is smaller than the analysis of unvibrated sample by the hydrometer method, and is concordant with the analysis of sample in terminal distribution by the hydrometer method.

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1990年8月に神戸で開催された「世界閉鎖性海域環境保全会議」のプログラムが示すように, 人口が集中する閉鎖性海域の環境を保全し, 津波や高潮の被害あるいは気候温暖化に伴う海水準の上昇がもたらす被害などから沿岸住民を保護することは, 国際的に緊急の課題となっている.
大阪湾は典型的な閉鎖性海域であり, 歴史的に津波や高潮の被害を受けてきた. 現在では, 大阪市をはじめとする大都市が連なり, ますます沿岸人口は増加しつつあり, 海洋への汚染物質の放出量も増大する一方である. こうした海域で, 海洋環境改善と沿岸防災にまつわる基礎研究を実施することは, その結果を直ちに他海域に適用できる点で, 世界的にも重要な意味をもつ.
従来わが国では, 沖合の海底地質は地質学者によって, 海流や潮流などの水力学的研究は地球物理学者によって研究されてきたが, 沿岸の堆積学的問題や水力学的問題はもっぱら土木工学者によって扱われてきた. しかし, 海洋環境は一つの複合的システムとして存在しており, 一分野からのアプローチだけではその動態を充分に把握することは難しい. 上記のような課題を追求するには学際的なアプローチが必要で, 実際, オランダやアメリカ, ニュージーランドなどの諸外国では, 異分野の研究者が参加する学際的総合研究が主流となっている.
そうした経験からもたらされた学際的海洋環境研究の基本的枠組と手順は以下のようなものである. (1) 公表された研究成果のレビューと既存資料の統合, (2) 水深, 海底地形の進化, 並びにそれらの変化, (3) 底質の堆積相, 堆積物輸送経路及び堆積収支の決定, (4) ウォータコラムの温度, 塩分濃度などの研究, 並びに堆積物の地球化学と生物毒性の研究, (5) 湾口の水力, 潮汐, 海流及び波浪気象の測定, (6) 海流の水力学に関する数理モデルの作成, (7) 水質及び汚染拡散に関する数理モデルの作成, (8) 津波や高潮などの破壊的事件, 及びそうした出来事が水力学, 汚染, 堆積物に与える影響に関する数理モデルの作成, (9) フィールドデータと実験データに基づくこうした数理モデルの有効性に関するレビュー. すなわち, モデルが「現実」とどの程度適合するかの確認.
本論では, こうした枠組をもつ学際的総合研究を大阪湾の環境問題について実施することを提案する.

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