1995 Volume 1995 Issue 180 Pages 296-302
Colonization by an endobyssate bivalve Modiolus kurilensis was possible only in shelly softground conditions, that is, on a soft bottom with the shells being slightly buried with fine sediment. The Pleistocene Omma Formation, Kanazawa, generally exhibits a shelly bottom carpeted by shells (shell pavement) or a shelly bottom covered by soft sediment too thick to allow colonization by Modiolus. The described Modiolus colony was found in the lower unit of the Omma Formation, where sealevel change was relatively small and where shelly softground conditions were present. In contrast, Modiolus is much less common in the shell beds in the cyclothemic middle unit of the formation. An important environmental factor accounting for the uncommon occurrence of Modiolus in cycle-bounding shell beds is their repeated physical reworking followed by deposition of soft sediment too thick to be colonized by Modiolus.
