Paleoenvironment and biostratigraphy of foraminifers at Sites 794, 795, 796, and 797 in the Japan Sea

Abstract

Biostratigraphy and paleoenvironmental history of deep and surficial waters of the Japan Sea are addressed using sequences recovered from the floor of the backarc basin. The study is divided into two parts: 1) foraminifer biostratigraphy and paleoenvironmental assessment of sedimentary sequences recovered from above igneous basement at the four sites and 2) detailed planktonic foraminifer paleoenvironmental analysis of Quaternary and Pliocene sequences from Sites 794 and 797 in the Yamato Basin. A sequence of Neogene paleoenvironmental events were identified: 1) deepening of the Yamato basins to middle bathyal depths by the early to middle Miocene, an event contemporaneous with the age of some deep basins known from uplifted sections adjacent to the Japan Basin; 2) cooling of the Japan Sea in the early middle Miocene; 3) oxygenation of deep waters in the late Miocene; 4) further cooling of surficial water masses between the Olduvai Subchron and the Brunhes/Matuyama Boundary; and 5) extermination of lower middle bathyal faunas and replacement by upper middle bathyal faunas near the base of the Quaternary. -from Author