| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1992: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1991: ¥1,700,000 (Direct Cost: ¥1,700,000)
|
|---|
| Research Abstract |
The objective of this research is to study the formation mechanism of sedimentary cycles within marginal sea sand to clarify what kind of paleoceanographic information is extractable from it. I studied the Japan Sea sediments as an example, and followings are major results of the research. (1)The Quaternary sediments recovered from the deeper part of the Japan Sea show distinct dark and light color cycles, which were caused by fluctuation in the bottom water oxygenation condition and surface productivity. Such fluctuation in paleoceanographic conditions in the Japan Sea was affected by the nature and amount of the surface current flowing into the Japan Sea which were regulated by glacio-eustatic sea-level oscillations. (2)The mode of circulation of the deep water within the Japan Sea in response to glacio-eustatic sea-level oscillations are strongly dependent on the positions and the depths of straits which have been changed through time. Drastic changes of such conditions seem to have
… More
occurred at 2.5Ma, 5Ma, 10.5Ma, and 15.5Ma. (3)Such changes in the positions and the depths of straits seem to have influenced both by global eustatic sea-level changes and local tectonics. (4)Semienclosed marginal seas such as the Japan Sea respond sensitively to Milankovitch scale short term climatic and oceanographic oscillations and the result of such responses are expressed as sedimentary cycles. However, the origin of such sedimentary cycles is not unique but it is variable depending on the location and the age of the sediments within the marginal sea. For example, during the intervals of semi-isolation of the Japan Sea (0 - 2.5Ma, 5 - 10.5Ma), dark and light color cycles caused by fluctuation of the bottom water oxygenation level developed in the deeper part of the sea, on which biogenic silica productivity cycle was superimposed. On the other hand, during the intervals of more open configuration of the Japan Sea (5 - 2.5Ma) when deep water was produced within the sea, dark and light cycles reflecting fluctuation of the bottom water oxygenation level disappeared and only biogenic silica productivity cycle could be recognized. At the sites closer to the Japanese Islands, cyclic change in biogenic silica content is ovserved which was rather caused by fluctuation of terrigenous material input reflecting climatic changes on land. Less
|
