There are few studies on paleoenvironment and paleoecology of the early rudists of Late Jurassic to earliest Cretaceous, though Late Cretaceous rudists have attracted much attention as a major contributor to carbonate platform. Rudist and microencruster framestone was discovered from the Late Jurassic Torinosu-type limestone of the Imaidani Group in the Nakatsugawa North Section, Shirokawa area, western Shikoku, Southwest Japan. The limestone succession, 17 m thick is divided into the lower part (9 meters thick from the bottom) composed of coral framestone and pack-grainstone, and the upper part (8 meters thick) consisting of coral-rudist-microencruster framestone. Abundant rudist individuals of a primitive uncoiled form occur in 9-14 m interval from the bottom, where the framestone does not contain corals. The rudist individuals often preserve bivalved appearance with little fragmentation, and were bound by a microencruster Bacinella. Occurrence and texture of the framestone substantiate that the rudists and Bacinella construct a framework structure in a relatively high energy environment Further studies of the rudists of the Torinosu-type limestones will provide clues to the paleoenvironment and paleoecology of the rudists in their early evolutionary phase.
|Number of pages||8|
|Journal||Memoir of the Fukui Prefectural Dinosaur Museum|
|Publication status||Published - Jan 1 2011|
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