Early Permian Buildups (Tolkien Reefs) Associated With Subaqueous Evaporites, Canadian Arctic: A Record of Syn-Tectonic to Post-Tectonic Reciprocal Uplift and Subsidence
Benoit Beauchamp, Beata Olchowy, 2003. "Early Permian Buildups (Tolkien Reefs) Associated With Subaqueous Evaporites, Canadian Arctic: A Record of Syn-Tectonic to Post-Tectonic Reciprocal Uplift and Subsidence", Permo-Carboniferous Carbonate Platforms and Reefs, Wayne M. Ahr, Paul M. (Mitch) Harris, William A. Morgan, Ian D. Somerville
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Twenty-six reef-mounds of Early Permian (Middle or Late Asselian) age crop out along the north shore of Greely Fiord on west-central Ellesmere Island, Canadian Arctic Archipelago. Each reef was attributed the name of a character from J.R.R. Tolkien’s “The Lord of the Rings”. The reefs interfinger with evaporites in the upper part of the Mount Bayley Formation, immediately below the Tanquary Formation. The reefs grew at the northern margin of a large depression of the Sverdrup Basin referred to as the Fosheim-Hamilton sub-basin, which is separated from the main Sverdrup Basin by the Elmerson high, an elongated structure of probable compressional origin. The Tolkien reefs range from 50 m to over 130 m in thickness and between 50 m and 500 m in width and length. The buildups have a massive core around which are wrapped a series of well-defined, variably steep beds (flanks), many of which display a sharp erosional base. Facies of the core and inner flank comprise: bryozoan-Tubiphytes-stromatactoid (sponge) boundstone; bryozoan cementstone; bryozoan mudstone-wackestone; and bryozoan (fusulinacean) packstone-grainstone. Facies of the outer flank include: algal boundstone; and fusulinid-algal grainstone-rudstone. Facies that occur both in the inner and outer flanks include carbonate breccia and moldic dolomicrite.
The Tolkien Reefs of west-central Ellesmere Island recorded the transition from an evaporite-dominated succession (Mount Bayley Formation) to an evaporite-free succession (Tanquary Formation). The reefs grew south of a major structural element—the Elmerson high—through the complex interplay between high-order to low-order relative sea-level fluctuations driven by tectonics, glacio-eustasy, and evaporative drawdown. The Tolkien Reefs recorded the rapid transition between a long episode of differential, and in part fault-controlled, syntectonic subsidence and a long period of slower, regional post-tectonic passive subsidence. While the former can be associated with a pulse of compressional tectonics that affected many areas of the Sverdrup Basin, the latter represents a phase of tectonic quiescence.