A GLASS RAMP: LATE PERMIAN SPICULITES, SVERDRUP BASIN, ARCTIC CANADA

The ramp motif is a recurring theme in both siliciclastic and carbonate depositional environments. Recent studies indicate that biosiliceous spiculitic depositional systems are not limited to deep-water settings, but also develop a ramp-like facies disposition when forming in shallow marine environments. One such ramp is of Capitanian to Lopingian age (the Degerböls and Lindstrom formations) on Hvitland and Svartfjeld peninsulas of northwestern Ellesmere Island, Nunavut. Eight different lithofacies occur within this succession, and can be placed in an inner ramp to distally-steepened slope setting. Inner ramp facies include fossiliferous carbonate grainstone, brachiopod-rich spiculitic chert, and light spiculitic chert. Trace fossils on the inner ramp include Planolites and local Skolithos, and excellent examples of hummocky cross-stratification are contained within the light spiculitic chert facies. Burrow-mottled spiculitic chert and dark spiculitic chert typify the mid ramp facies. Ubiquitous burrows such as Planolites and Zoophycos, together with hummocky cross-stratification and wave ripple cross-lamination characterize these mid ramp spiculites. Poorly bioturbated, finely-laminated spiculitic siltstone, ankeritic siltstone and fissile shale occur in the outer ramp to proximal basinal settings. While the geometry of this biosiliceous depositional system is similar to both siliciclastic and carbonate ramp settings, major differences exist. Limited facies within the biosiliceous ramp environment result from a low diversity biosiliceous sediment factory that produces a limited number of grain types. Accumulation rates in this environment are very low, on the order of 1-3 cm/ky, but comparable to Tertiary temperate carbonate ramps.