Clay Petrology of Cambro-Ordovician Continental Margin, Cow Head Klippe, Western Newfoundland

Robert K. Suchecki, Edward A. Perry Jr. and John F. Hubert
Department of Geological Sciences, University of Texas, Austin TX 78712, U.S.A.
Department of Geology/Geography, University of Massachusetts, Amherst, MA 01002, U.S.A.

Abstract: The sedimentary rocks of the Taconic Cow Head klippe contain three clay-mineral suites of progressively younger stratigraphic occurrence. An illite-14A chlorite suite is the oldest, occurring in the Middle Cambrian to early Lower Ordovician part of the 310-m Cow Head Breccia. These earliest clays were transported from the stable craton and shelf, slowly accumulating during 70 × 106 yr on the continental slope in limestone breccia, green and gray shale, and argillaceous limestone. The illite and 14A chlorite are judged to be largely detrital. An illite-expandable chlorite suite is in early to late Lower Ordovician limestone breccia, green and gray shale, and argillaceous limestone of the Cow Head Breccia. A corrensite-illite-smectite suite of late Lower to Middle Ordovician age occurs in the Cow Head Breccia and throughout the overlying 200-m ‘Red Shale’ and the more than 400-m ‘Green Sandstone’ flysch sequence of volcanogenic sandstone and gray shale. Beginning in the early Lower Ordovician, increasing amounts of Mg2+-rich volcanic detritus were rapidly transported westward from a developing volcanic island arc in central Newfoundland. During burial metamorphism, volcanic materials and their alteration products reacted to form the illite-smectite with 5–10% expandable layers plus corrensite or expandable chlorite found in the younger two clay-mineral suites.

Clays and Clay Minerals; July 1977 v. 25; no. 3; p. 163-170; DOI: 10.1346/CCMN.1977.0250301
© 1977, The Clay Minerals Society
Clay Minerals Society (www.clays.org)