Study of Ocean Floor Structure and Evolution by Drilling

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The purpose of this research project is to investigate the history of Earth's environmental changes and geodynamics of the Earth interior through ocean drilling. This year, the following four main themes were investigated.1) Study of sea level changes and carbonate platform sequence stratigraphy based on the drilling in the Bahama bank. The study showed that progradation, agradation and hiatus formation were closely related to sea level changes and verified the use of sequence stratigraphy in this kind of setting.2) Investigation of the records and causes of rapid climatic and paleoceanographic changes recorded in the high-resolution core samples of the California margin and Sanich Inlet. The results showed that both rapid cooling and warming events were recorded in these cores suggesting that similar rapid events revealed by ice cores and hig latidude ocean such as Heinrich Event are in global scale nature.3) Study of hydrothermal system and ore deposits in the Juan de Fuca Ridge and its sedimented part based on a long-term borehole observatory (CORK). The area of hydrothermal fluid discharge and recharge was specified and the magnitude of circulation cell was determined. This result contributed significantly to the simulation of the hydrothermal system.4) Study of plate subduction, accretionary prism hydrogeology, tectonic erosion in the Barbados and Costa Rica margins. The CORK experiment and logging while drilling was found to be extremely useful for the study of fluid flow and physical properties of the subduction complex. The Costa Rica margin turned out to be a boundary which is dominated by large-scale subduction erosion, not by sediment underplating which was preferred interpretation before drilling.