新第三系宮崎層群青島層から産出した生痕化石Zoophycos

抄録

Well-preserved many specimens of the trace fossil Zoophycos were found in the Upper Miocene-Lower Pliocene Aoshima Formation of the Miyazaki Group distributed along the Nichinan Coast in southeastern Kyushu, Japan. All of Zoophycos occur in very fine-grained sandstone beds and are of the helical-coil type. The characteristic recurved structure was observed in the lowest spreite of some Zoophycos, although all spreite of many Zoophycos spread obliquely in the downward direction to the bedding plane. The present Zoophycos with recurved spreite is the first record. The depth of the recurved lowest spreite in the sandstone beds shows that the spreading of the lowest spreite is strongly influenced by a change in the grain size; the lowest spreite was recurved upward in the bottom of the very fine grained sandstone beds overlaying on the parallel laminated fine grained sandstone beds.