ABSTRACT We have identified 57 large-magnitude, sequence boundaries in the Phanerozoic succession of the Canadian High Arctic. The characteristics of the boundaries, which include angular unconformities and significant changes in depositional and tectonic regimes across the boundaries, indicate that they were primarily generated by tectonics rather than by eustasy. Boundary frequency averages 10 million years throughout the Phanerozoic and there is no notable variation in this frequency. It is interpreted that each boundary was generated during a tectonic episode that lasted two million years or less. Each episode began with uplift of the basin margins and pronounced regression. This was followed by a rapid subsidence and the flooding of the basin margins. Each tectonic episode was terminated by a return to slow, long-term subsidence related to basin forming mechanisms such as thermal decay. The tectonic episodes were separated by longer intervals of tectonic quiescence characterized by slow subsidence and basin filling. The tectonic episodes are interpreted to be the product of changes in lithospheric stress fields with uplift being related to increased, compressional horizontal stress and the following time of rapid subsidence reflecting a decrease in such stresses or an increase in tensional stresses. Conversely, the longer intervals of tectonic quiescence would reflect relatively stable, horizontal stress fields. The episodic changes in stress fields affecting the Canadian High Arctic throughout the Phanerozoic may be a product of intermittent, plate tectonic reorganizations that involved changes in the speed and directions of plate movements. The longer intervals of tectonic quiescence would occur during times of quasi-equilibrium in the plate tectonic mosaic. The tectonic episodes that generated the sequence boundaries were governed by nonlinear dynamics and chaotic behavior, and there is a one-in-10-million chance that a tectonic episode will be initiated in the Canadian High Arctic in any given year. Thus, the major transgression associated with each episode can be referred to as a “10-million-year flood.”

Abstract Pennsylvanian-Early Permian carbonate factories of the Sverdrup Basin, Arctic Canada, and their adjoining slopes were under warm-tropical conditions in the Bashkirian-Asselian and cool-water warm-temperate conditions in the Artinskian-Kungurian. All other factors being the same, the Sverdrup Basin is a unique laboratory where these two types of slope development can be compared and contrasted. Key differences include high carbonate production, widespread boundstone margin development, shelf-margin storm protection, and early lithification for warm margins, and the lack thereof for cool margins. In addition, slope sedimentation below a shallow lysocline during the cool interval led to extensive carbonate dissolution. As a result, Artinskian-Kungurian middle and lower slopes are dominated by spiculitic chert. The Pennsylvanian-Early Permian succession consists of four third-order unconformity-bounded transgressive-regressive (T-R) sequences driven by episodic tectonics. The regressive systems tracts of each sequence recorded progradation of an accretionary margin at a time of tectonic quiescence. The warm-water accretionary margins had slopes that were either planar or exponential. Steep upper slopes formed the downward extension of a lithified boundstone margin. Strike-discontinuous erosion of that margin led to the shedding of channelized debris in the proximal middle slopes. Grainflows and proximal turbidites accumulated between areas of debris deposition. Distal turbidites forming large strike-continuous aprons were deposited in the distal part of the middle slope. This part of the slope also contains high-amplitude truncation surfaces and slump folds. The lower slope was composed of distal turbidites interstratified with hemipelagic material. The cool-water accretionary margins had sigmoidal slopes. Upper slopes formed the downward extension of a high-energy open shelf. Gravity-aided grain-dominated tempestites were deposited in the upper slope, locally associated with mud mounds. The steeper part of the sigmoidal slope was the middle slope, where key processes included slope failure and extensive sponge spicule production. Grainflow and proximal turbidites accumulated in the proximal portion of the middle slope. Mud-dominated siliceous distal turbidites associated with large-scale truncation surfaces accumulated in the distal part of the middle slope. Distal turbidites interfinger with hemipelagic siliceous shale and fine siltstone in the lower slope.

Abstract 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.

Abstract: A vast area of northwest Pangea, extending from the Sverdrup Basin (Canadian Arctic) to the Barents Sea (Norwegian and Russian Arctic) was affected by a significant climatic cooling in Permian time. Warm tropical-like conditions prevailed during the Asselian and Sakmarian interval, cool to cold temperate-like conditions occurred during the Artinskian to Kazanian interval, and very cold, polar-like conditions were established during latest Permian time (undetermined Kazanian-Tatarian). This climatic deterioration led to a significant shift in the composition of biogenic sedjments. Asselian and Sakmarian shallow-water carbonates comprise abundant aragonite-secreted skeletal and non-skeletal elements (ooid, cement) dominated by abundant green algae and foraminifers, associated with a great variety of microfloral and invertebrate elements (Chloroforam Assemblage). These elements combine to form hjgji- to low- energy facies including various buildups that range from small patch reefs to barrier-like structures extending for lens of kilometers. Submarine cements formed widely in both reefal and non-reefal carbonates. Evidence of meteoric-pedogenic diagenesis is pervasive in subaerially exposed carbonates. Artinskian to Kazanian shallow-water carbonates, which are poorly- lo non-cemented by submarine phases, are dominated by bryozoans, echinoderms and brachiopods (Bryonodcrm assemblage). Fusulinaceans and colonial rugose corals locally occur in Artinskian strata (Bryonoderm-extended assemblage). Small patch reefs and larger reef-mounds are locally developed in Artinskian deposits. No reefs have been encountered in Kungurian and younger strata. There is linle evidence of meteoric-pedogenic diagenesis in subaerially exposed Artinskian carbonates and none in post-Artinskian sediments. Artinskian and younger shallow-water Bryonoderm carbonates are thoroughly cemented by clear sparry calcite of shallow and relatively early burial origin. Latest Permiaji (undetermined Kazanian-Tatarian) shallow-water sediments are dominated by spic- ulitic chert (Hyalosponge assemblage) with rrujnor lenses and patches of variably silicified Bryonoderm carbonates.

The biotic succession of the Sverdrup Basin, Canadian Arctic, records a significant Permian climatic cooling trend. Highly diversified, tropicallike associations dominated by calcareous alga and foraminifer (Chloroforam) prevailed during the Asselian and Sakmarian, whereas poorly diversified, temperatelike associations, dominated by bryozoan, echinoderm, and brachiopod, characterized the Artinskian (Bryonoderm-extended) to Kazanian (Bryonoderm) interval. Polarlike, siliceous sponge–dominated biota (Hyalosponge) prevailed during the latest Permian. The climatic gradient suggested by this trend, and by other climatic indicators (ooid, oncoid, evaporite, reef, submarine cement, dropstone, red bed, caliche, coal), is far greater than that expected from the 10 to 15° of northerly migration inferred for Pangea during the Permian. The cooling trend, the causes of which are unknown, is evidence for a dramatic climatic deterioration in northern Pangea at the end of the Paleozoic.