2024 Volume 78 Issue 1 Pages 1-14
The horseshoe furrows and ridge structures were observed around the mound that contained the trace fossil (burrow) from the Toyohama Formation of the Miocene Morozaki Group in the Chita Peninsula, Aichi Prefecture, Japan. The morphological characteristics of these structures were examined and determined as obstacle scours. However, no rigid bodies, such as gravel or shell or obstacles from the bottom surface were observed on the mound that contained the burrow. It might be highly probable that the halo core of the burrow which was hardened by the mucus of the trace-former, or the trace-former itself or both, played the role of an obstacle in this structure.
In the upper deep-sea zone, benthic animals formed burrows and colonies on the seafloor surface, where the bottom sediment consisted of silt. The obstacle scours were formed by horseshoe vortexes around the obstacles due to turbidity currents, which contained medium-grained sand flowing onto the seafloor surface from S15˚W direction.
