Mesozoic limestone from the Vema offset zone, Mid-Atlantic Ridge?

Abstract

A shallow-water, indurated limestone, consisting of fossil benthic foraminifera, calcareous green algae, fragments of gastropods, thalassinid crab coproliths, as well as inorganic ooids and pelloids, and containing detrital grains of quartz, orthoclase, and microcline, was dredged from the summit of a transverse ridge within the Vema offset zone of the Mid-Atlantic Ridge. Subaerial and submarine recrystallization, suggesting past emergence of the limestone, is indicated by oxygen and carbon isotope analysis. The occurrence in the limestone of Parafavreina, an anomuran crab coprolite fossil, suggests a probable Mesozoic age for the rock. The occurrence of this shallow-water Mesozoic limestone would confirm previous suggestions that a non-spreading crustal block exists at the Vema offset zone.