Formation mechanism of sedimentary cycles in the marginal sea and application of the result to paleoceanography

本研究的目的是研究边缘海砂沉积旋回的形成机制，以明确从中提取什么样的古海洋学信息。我以日本海沉积物为例进行了研究，主要研究成果如下：(1)日本海深层第四纪沉积物表现出明显的暗色和浅色旋回，这是由于海底氧合条件和表层生产力的波动所致。日本海古海洋学条件的这种波动受流入日本海的表面流的性质和数量的影响，而流入日本海的表面流又受冰川-海平面波动的调节。(2)随着时间的推移，海峡的位置和深度发生了变化，而日本海深水环流对冰川-海平面波动的响应模式与海峡的位置和深度密切相关。在2.5Ma、5Ma、10.5Ma和15.5Ma时，这种情况发生了较大的变化。(3)这种海峡位置和深度的变化似乎既受到全球海平面上升变化的影响，也受到局部构造的影响。(4)日本海等半封闭边缘海对米兰科维奇尺度短期气候和海洋振荡的响应较为敏感，其响应结果表现为沉积旋回。然而，这种沉积旋回的起源并不是唯一的，而是根据边缘海中沉积物的位置和年龄而变化的。例如，在日本海半隔离期（0 ~ 2.5Ma, 5 ~ 10.5Ma），由于海底氧合水平的波动，在海的较深处形成了暗色和浅色循环，并在此基础上叠加了生物成因二氧化硅生产力循环。另一方面，在日本海较为开放的配置区间（5 ~ 2.5Ma），当海内产生深水时，反映底水氧合水平波动的暗循环和光循环消失，只识别生物成因二氧化硅生产力循环。在靠近日本群岛的地点，观察到生物源二氧化硅含量的循环变化，这是由反映陆地气候变化的陆源物质输入的波动引起的。少

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