貝形虫およびカイエビ化石の生層序とジルコン―フィッション・トラック法に基づく篠山層群の年代の再考 Revised age of the Sasayama Group, southwest Japan, based on ostracode and conchostracan bio-stratigraphy and zircon fission-track dating
The age of the non-marine Cretaceous Sasayama Group, distributed in western Honshu, Japan, was reassessed based on ostracod and conchostracan bio-stratigraphy, and zircon fission-track dating. The ostracod genera <i>Mongolocypris</i> and <i>Eucypris</i> from the lower part of the Sasayama Group, combined with the conchostracan genera <i>Yanjiestheria</i> and <i>Nemetheria</i> from the upper part of the group, suggest an age range from Albian to Cenomanian. Zircon fission-track dating of the lower and upper parts of the group yields ages of 106±9, 100.9±8.4, and 96.1±7.4 Ma, also indicating a range from Albian to Cenomanian. These data indicate that deposition of the Sasayama Group began about 30 Ma later than previously thought.
地質学雑誌 116(5), 283-286, 2010