Microbioherms of the Waldron Shale (Silurian, Indiana); implications for organic framework in Silurian reefs of the Great Lakes area

biogenic structures Cnidaria Crinozoa Echinodermata Bryozoa Anthozoa isotopes C-13/C-12 Lower Silurian carbon Invertebrata Porifera bioherms Indiana sedimentary structures Middle Silurian paleoecology reefs Silurian Waldron Shale stable isotopes Wenlock Paleozoic sedimentary petrology United States