Paleoclimatic Changes and Global Changes of Sea Level as a Method to Establish Interregional Correlation and Chronostratigraphy

SAITO Tsunemasa

doi:10.3720/japt.48.21

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Other Title

年代層序樹立の手法としての古気候変遷と海水準変動
ネンダイソウジョジュリツノシュホウトシテノコキコウヘンセント

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Description

This paper presents a review of two recent and important approaches to interregional stratigraphic correlation and chronostratigraphy. These approaches are 1) the use of oxygen isotopic variations for stratigraphic correlation in marine sequences containing calcareous microfossils and 2) the stratigraphic interpretation of seismic reflection patterns to deduce time-synchronous unconformities and their correlative conformities.<br>The method of seismic stratigraphy developed by Vail and others (1977, 1980) is primarily based on studies of shallow continental margin seismic data and correlates the reflection boundaries with sea-level changes.<br>Because the melting and freezing of high-latitude ice sheets are the primary factor controlling 18O/16O ratio variations in the calcareous tests of foraminifera, the record of isotopic changes in deep open ocean sediments is globally synchronous. This approach is particularly useful to stratigraphic studies of the late Cenozoic when large ice sheets occurred in the polar regions and fluctuated in volume. Since the ice volume fluctuations are also responsible for eustatic sea-level changes, the oxygen isotope study can be used to reconstruct past changes in sea-level.<br>A sharp change in oxygen-isotopic values near the beginning of the Middle Miocene at about 14Ma brought about an influx of siliceous microfossils in Japanese Miocene sediments by establishing a region of upwelling over much of the northeastern Japan owing to the development of a cool, southward-flowing current. Another marked change in the oxygen isotope record at about 3.2Ma has been interpreted to have caused a sea-level lowering of as much as 40m. A paraconformity separating the non-marine Mukaiyama Formation from the subjacent marine Tatsunokuchi Formation in the environs of Sendai City is considered to have resulted from this large sea level drop. On the other hand, the method of seismic stratigraphy has so far received little attention in Japan.

Journal

Journal of the Japanese Association for Petroleum Technology

Journal of the Japanese Association for Petroleum Technology 48 (1), 21-34, 1983

The Japanese Association for Petroleum Technology