A glass ramp: shallow-water Permian spiculitic chert sedimentation, Sverdrup Basin, Arctic Canada

摘要

Thick, widespread spiculitic chert and subordinate carbonate of the upper Permian (late Guadalupian to Lopingian) Degerboels and Lindstrom formation record deposition during a third-order, late Palaeozoic sea level cycle. The succession is interpreted to have accumulated as a ramp in a mid-latitude, relative low-energy setting that was periodically perturbed by storms, one of the few such occurrences of neritic spiculitic chert in the geological record. Sediments comprise seven lithofacies that can be placed in inner ramp to basinal paleoenvironments. Inner ramp facies range from fossiliferous glauconite-rich carbonate grainstone, to light spiculitic chert. The mid-ramp is typified by dark spiculitic chert containing few other fossils but typically textured by hummocky cross-stratification. Sediments in both environments are burrowed, with particularly conspicuous Zoophycos and Planotites. Dark, finely laminated spiculitic siltstone and shale characterize outer-ramp and basinal settings. The elevated trophic resources and abundant silica necessary for such sedimentation are interpreted to have resulted from upwelling.