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1 January 2016 Spathian (Late Olenekian, Early Triassic) Ammonoids from the Artyom Area, South Primorye, Russian Far East and Implications for the Timing of the Recovery of the Oceanic Environment
Yasunari Shigeta, Taro Kumagae
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Abstract

Five Spathian (late Olenekian) ammonoids are newly reported from the Zhitkov Formation in the Artyom section, South Primorye, Russian Far East. They include the early Spathian taxa Bittnerites pacificus and Tirolites longilobatus from the middle part of the formation, and Ussuriphyllites amurensis, Leiophyllites sp. and Keyserlingites sp. from the upper part. The Ussuriphyllites amurensis Zone was previously correlated with the lower Anisian, but we herein correlate it with the upper Spathian. As a consequence of this age assignment, the weakly bioturbated offshore mudstone in the middle and upper parts of the formation is correlated with the Spathian. In contrast, the Smithian (early Olenekian) offshore laminated mudstone in the lower part of the formation lacks any sign of bioturbation. These mudstones suggest that the oxygen-deficient sea floor was transformed into an aerobic environment inhabitable to benthic organisms at the Smithian-Spathian boundary.

© by the Palaeontological Society of Japan
Yasunari Shigeta and Taro Kumagae "Spathian (Late Olenekian, Early Triassic) Ammonoids from the Artyom Area, South Primorye, Russian Far East and Implications for the Timing of the Recovery of the Oceanic Environment," Paleontological Research 20(1), 48-60, (1 January 2016). https://doi.org/10.2517/2015PR023
Received: 8 April 2015; Accepted: 1 July 2015; Published: 1 January 2016
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