北海道空知層群からの浮遊性有孔虫 Leupoldina cabri (Sigal, 1952) の発見とその北太平洋の白亜紀における年代学的意義

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概要

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• Leupoldina cabri (Sigal) has a very unique outer morphology that makes it one of the most easily identifiable species among the Cretaceous planktonic foraminifers. The species is also very short-ranging, with its occurrence being restricted to the mid-Aptian interval of the Lower Cretaceous System. Despite its wide geographic distribution in the Atlantic and European realms, the species has not been recorded from the broad Pacific region until its discovery in 1999 from northern California. L. cabri was recovered from a short stratigraphic interval of siliciclastic sequences that brackets the boundary between the Sorachi and Yezo Groups in the axial zone of central Hokkaido, the northernmost island of Japan. The present report of L. cabri from the northwestern Pacific serves to confirm a wide geographic distribution of this species in the early Cretaceous ocean and enables to unequivocally identify the mid-Aptian interval in the Hokkaido sequence. With the recognition of L. cabri in the Hokkaido sequence, a possible "Livello Selli inerval", detected by a parallel, independent carbon isotope study undertaken on the same sequence, can be confirmed to be time-correlative with the actual Selli Level observed in the Mediterranean type region. This confirmation clearly establishes that the ocean-wide shoaling event of oxygen-deficient waters, called the "Oceanic Anoxic Event (OAE), " had also taken place in the Pacific region during the correlative time period of Aptian age.

• 国立科学博物館の論文
• 2000-12-22

著者

• 安渡 敦史

  Institute Of Geology And Paleontology Graduate School Of Science Tohoku University

• 斎藤 常正

  Department Of Geology And Paleontology National Science Museum

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