Orientation of corals and stromatoporoids in some Pleistocene, Devonian, and Silurian reef facies

Abstract

A quantitative study was made of the orientation of corals and stromatoporoids in reef core, flank, and interreef rocks representing three geological periods at eight sites, including the Florida Keys (Pleistocene), Ridgemount, Ontario (Devonian), and Pekin, New York, Maumee and Rockford, Ohio, and Bluffton and Delphi, Indiana (Silurian). Orientation, width, and height were measured for each fossil as seen in outcrop.Fossils in Pleistocene and Silurian reef core facies have pronounced upward orientation, suggesting that most fossils are in growth location, or that the reefs were moved to their present location without appreciable tilting. Silurian distal flank facies have approximately random coral orientations, while the proximal (near-core) Silurian flank facies at Rockford has coral orientations with some upward bias. Coral width is greater than or equal to coral height (on outcrop) for 79% of the corals at all flank sites, and for 80% of the corals at the interreef site, an indicator of transport when taken with orientation data. This study permits reef facies differentiation and illustrates that fossil orientation is a useful technique for studying reefs.