High-resolution chronostratigraphy based on cyclic sedimentation.

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Cyclic lithologic changes in sediments can be used a chronometer spanning 1/2 day through 100, 000 of years in the geological column. Here we reviews some examples of cyclic sediments, related to tidal currents, seasonal changes, and glacio-eustacy. Particular attention is paid to the oxygen isotope study of turbidites of the Otadai and Umegase Formations drilled through by the study well TR-3, Boso Peninsula. The data clearly demonstrate that the sedimentation of turbidites was closely related to glacio-eustatic changes.All these examples of sediment cyclicity are controlled by constant, cyclic movements of astronomical bodies. Therefore, their signatures in sediments should be very stable through time. For this reason, each astronomically-induced cyclicity in sediments represents a definite time interval, which is useful for high-resolution chronostratigraphy. For example, fluctuations in oxygen isotope data from deep-sea pelagic sediments can be interpreted as an end result of astronomically-induced cyclicity of various origin. Recognition of these cyclicities provides a tool for sequencial dating of the sediments. This article reviews the sequencial dating of the TR-3 by determining the interval sedimentation rates. For this calculation, TR-3 oxygen isotope records were correlated to those of DSDP Site 607 which were well interpreted in terms of the astrochronologic method.
石油技術協会の論文