Cyclic Sedimentation in the Middle Devonian of Southern Ontario

Abstract

<p>The Edgecliff member of the Onondaga Formation is exposed in an abandoned quarry 1.2 km west of Port Colbourne, Ontario on the north shore of Lake Erie. An investigation of the Port Colbourne Quarry has resulted in the definition of four major and three minor carbonate Facies: (1) Facies A: Biocalcarenite ( 2) Facies A-1: Biocalcarenite with in situ stromatoporoids ( 3) Facies B: Fissile biomicrite ( 4) Facies C: Cystiphyllum-rich fissile biomicrite (5) Facies B-1: Bioturbated biomicrite ( 6) Facies C-1: Packed biomicrite ( 7) Facies D: Synaptophyllum-rich sparse biomicrite.</p> <p>The facies are cyclicly arranged, and are restricted to one of three major units within the stratigraphic column.</p> <p>Typical cycles begin with the rapid deposition of a coarse grained, lensoidal biocalcarenite bed exhibiting (1) Sharp scoured bases and vertical (fining upward) size grading; (2) The abundance of abraded grains, shelter void cements and escape burrows; (3) The presence of in situ Favosites heads overlying the biocalcarenite indicating minor hiati between sporadic and violent deposition. In addition, these deposits exhibit: (1) Abundant transport and abrasion of Cystiphyllum and Favosites; (2) A general lack of in situ fauna; (3) The presence of resuspended and redeposited debris between Cystiphyllum.</p> <p>The depositional environment is deep to shallow subtidal, and a minor regression is evident towards the top of the stratigraphic column. Deposition is interpreted as being the result of sporadic, cyclic, and violent depositional events, probably storm induced.</p>