| The Late Llandovery Chicotte Formation consists predominantly of crinoidal grainstones interspersed with reefs, deposited in a tropical foreland basin, open marine setting. A diverse and well preserved tabulate and rugose coral fauna grew in reefal and peri-reefal settings. Growth periodicity in 12 species was measured from internal and external skeletal features preserved as pristine primary calcite. Annual cycles were exhibited by internal skeletal features as couplets of high- and low-density bands. High-density bands, considered as storm or monsoonal season growth, generally consisted of closely spaced tabulae or tabellae, greater abundance and/or thickening of septa, development of septal crests on dissepiments or tabulae, and thickening of corallite walls. In contrast, low-density bands have relatively widely spaced tabulae and sparse to rare septa, or featured zoning of cysts in coenenchyme or dissepimentaria. Periodic external skeletal structures in colonial rugosans included fine growth ridges and higher-order rugae. (Abstract shortened by UMI.)... |
