Cambrian Grand Cycles: A northern Appalachian perspective

摘要: Large-scale sedimentary cycles, or Grand Cycles, are the most obvious features of Port au Group in southwestern Newfoundland. Each cycle is interpreted to represent deposition outer-platform, muddy tidal flats (lower shaly half-cycle) and ooid shoal complexes (upper carbonate half-cycle). Unpredictable metre-scale assemblages oolite laminite, constituting half-cycles, attributed frequent migration response hydrographic factors such as fluctuations storms. Predictable metre-scale, shallowing-upward cycles parted limestone shale half-cycles were probably controlled mainly by variable rates sedimentation; a eustatic mechanism, however, cannot be discounted. Comparison with other North American Cycles suggests mechanism for Cycle formation, possibly involving variations rate sea-level rise. The sequence established on basis Group, involves (1) rapid rise, which flooded platform shoreward-derived siliciclastic muds resulted development flats, (2) gradual complexes, encroached onto decreasing In contrast western examples, Newfoundland composed almost entirely peritidal sediments; they also thinner have smaller areal extent than do those west. These differences may due narrower shelves, slower sedimentation, lower amplitudes rise present northeastern margin craton margin.