Cambrian Grand Cycles: A northern Appalachian perspective

Research Article| April 01, 1987 Cambrian Grand Cycles: A northern Appalachian perspective NANCY CHOW; NANCY CHOW 1Department of Earth Sciences, Memorial University of Newfoundland, St John's, Newfoundland A1B 3X5, Canada Search for other works by this author on: GSW Google Scholar NOEL P. JAMES NOEL P. JAMES 1Department of Earth Sciences, Memorial University of Newfoundland, St John's, Newfoundland A1B 3X5, Canada Search for other works by this author on: GSW Google Scholar GSA Bulletin (1987) 98 (4): 418–429. https://doi.org/10.1130/0016-7606(1987)98<418:CGCANA>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation NANCY CHOW, NOEL P. JAMES; Cambrian Grand Cycles: A northern Appalachian perspective. GSA Bulletin 1987;; 98 (4): 418–429. doi: https://doi.org/10.1130/0016-7606(1987)98<418:CGCANA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Large-scale sedimentary cycles, or Grand Cycles, are the most obvious features of the Port au Port Group in southwestern Newfoundland. Each cycle is interpreted to represent deposition in outer-platform, muddy tidal flats (lower shaly half-cycle) and ooid shoal complexes (upper carbonate half-cycle). Unpredictable metre-scale assemblages of oolite and carbonate laminite, constituting the carbonate half-cycles, are attributed to frequent migration of the shoal complexes in response to hydrographic factors such as tidal fluctuations and storms. Predictable metre-scale, shallowing-upward cycles of parted limestone and shale in the shaly half-cycles were probably controlled mainly by variable rates of carbonate sedimentation; a eustatic mechanism, however, cannot be discounted.Comparison with other North American Grand Cycles suggests a eustatic mechanism for Grand Cycle formation, possibly involving variations in the rate of sea-level rise. The interpreted sequence of formation, established on the basis of the Port au Port Group, involves (1) a rapid sea-level rise, which flooded the platform with shoreward-derived siliciclastic muds and resulted in the development of muddy tidal flats, and (2) the gradual development of ooid shoal complexes, which encroached onto the tidal flats, with decreasing rates of sea-level rise. In contrast to western North American examples, Newfoundland Grand Cycles are composed almost entirely of peritidal sediments; they are also thinner and have a smaller areal extent than do those in the west. These differences may be due to such factors as narrower shelves, slower rates of sedimentation, and lower amplitudes of sea-level rise on the present northeastern margin of the North American craton than on the western margin. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.