秋田県海域および沿岸地域における鮮新世〜更新世の浮遊性有孔虫化石マーカーの出現パターンと集油構造形成時期

Abstract

Planktonic foraminiferal marker beds such as Globorotalia ikebei bed, No.3 and No.2 Globorotalia inflata beds and Neogloboquadrina asanoi bed, have been useful for correlation and age determination of the marine Plio-Pleistocene formations along the coast of the Japan Sea in northeast Japan. All the marker beds are not necessarily found in the oil exploratory wells, however, although the formations are inferred to be deposited under the deep sea environment (the Uvigerina akitaensis Zone of benthic foraminifera). The N. asanoi and No.2 G. inflata beds are more occasionally missing at offshore wells, Akita Prefecture.The distribution maps of each marker bed were made based on biostratigraphic data of 80 wells, and they suggest that regional deep sea erosion and/or non-deposition occurred at topographic highs of anticlinal structures which had been formed in relation to compressional foldings since early Pliocene.The occurrence patterns of the marker beds were divided into five patterns based on their combination of existence and missing. The patterns could be closely related with the timing of structure growths. It is interpreted that major scaled erosions occurred at the Marker A and around the Pliocene-Pleistocene boundary, where they eroded the No.2 G. inflata bed and the N. asanoi bed, respectively. Structural uplift is considered to be the important factor for the deep sea erosion of the marker beds.