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

这项研究的目的是研究边缘海砂内部沉积旋回的形成机制，以阐明从中可以提取哪些古海洋信息。我以日本海沉积物为例进行了研究，主要研究成果如下：(1)从日本海深部回收的第四纪沉积物具有明显的暗色和浅色旋回，这是由于底层水的氧合条件和表层生产力的波动造成的。日本海古海洋学条件的这种波动受流入日本海的表层流的性质和数量的影响，而流入日本海的表面流受冰川-海平面波动的调节。(2)日本海深水环流对冰川-海平面波动的响应强烈依赖于随时间变化的海峡位置和深度。这些条件的剧烈变化似乎让…在2.5 Ma、5 Ma、10.5 Ma和15.5 Ma出现较多。(3)海峡位置和深度的这种变化似乎既受全球海平面变化的影响，也受局部构造的影响。(4)半封闭边缘海，如日本海，对米兰科维奇尺度的短期气候和海洋振荡反应敏感，其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，在日本海半隔离期间(0~2.5 Ma，5~10.5 Ma)，由于底水氧合水平的波动，在深海形成了暗色和浅色旋回，并在其上叠加了生物硅生产力旋回。另一方面，在日本海较开放的构造时期(5-2.5 Ma)，当海内产生深水时，反映底层水氧水平波动的暗旋回和光旋回消失了，只能识别出生物硅生产力旋回。在靠近日本群岛的地点，生物硅含量的周期性变化是由反映陆地气候变化的陆源物质输入的波动引起的。较少

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