The Gzhelian (Upper Pennsylvanian) to Kungurian (Lower Permian) succession around Carlin Canyon, northern Nevada, in the Basin and Range province of the western USA is a relatively undeformed wedge of fossiliferous marine carbonate and fine-grained calcareous and cherty clastic rocks that rests with profound angular unconformity on Mississippian to mid-Pennsylvanian sedimentary rocks that had been uplifted, faulted, folded, and eroded prior to the Late Pennsylvanian transgression. This wedge of sediments, which tapers over less than 2 km from 1341 m in the west to 588 m in the east, comprises the Strathearn, Buckskin Mountain, and lower part of the Beacon Flat formations. These units form a second-order sequence within which five third-order unconformity-bounded transgressive–regressive sequences are nested. These sequences are Gzhelian, early to late Asselian, latest Asselian to late Sakmarian, latest Sakmarian to late Artinskian, and latest Artinskian to late Kungurian in age based on the determination and biostratigraphic interpretation of 26 conodont taxa, including two new species ( Adetognathus carlinensis n. sp. and Sweetognathus trexleri n. sp.). Each sequence records sedimentation on a westward-dipping ramp along which significant facies change occurs with inner-ramp coarse-grained algal and bioclastic photozoan grainstone to the east passing westward into mid- to outer-ramp heterozoan carbonate, and ultimately into deep-water fine-grained mixed clastic–carbonate facies with no fossils except sponge spicules, representing deep-water sedimentation in a basinal area that underwent repeated episodes of rapid subsidence associated with each sequence. Accommodation during sedimentation of Gzhelian–Kungurian sequences around Carlin Canyon was repeatedly created in response to flexural subsidence caused by tectonic loading west of the study area. Each sequence recorded the simultaneous foundering of the basinal area in the west and uplift of the basin margin in the east. Individual sequences overlap the underlying sequence to the east, while flexural subsidence from the Gzhelian to the earliest Artinskian led to a basin in the west that became deeper over time. A lull in tectonic activity associated with each sequence allowed carbonates to prograde from east to west, partially filling the basinal area until the early Artinskian, and completely filling it to sea level during the late Artinskian and then again in the late Kungurian. The Gzhelian–Kungurian carbonate succession of the Carlin Canyon area bears much resemblance with the coeval succession that occurs all along the northwest margin of Pangea, from Nevada in the south to the Canadian Arctic islands in the north, and down from the Barents Sea to the central Urals to the east. That broad area was affected by the same oceanographic events, the most significant of which was the earliest Sakmarian closure of the Uralian seaway, which prevented warm water from the Tethys Ocean from reaching the northwestern Pangea margin as it did before; this led to much cooler oceanic conditions all along western North America, even in the low tropical paleolatitudes where northern Nevada was located, in spite of a globally warming climate following the end of the late Paleozoic ice age.

A thick succession of upper Paleozoic carbonate rocks and minor chert crops out north of the head of Otto Fiord (northwest [NW] Ellesmere Island, Nunavut) in the Canadian Arctic Archipelago. These rocks accumulated in a tectonic subbasin—the Otto Fiord Depression (OFD)—of the Sverdrup Basin that likely originated through rifting during late Early Carboniferous (Serpukhovian). Following a long interval of passive subsidence that allowed a thick succession of Moscovian–Kasimovian carbonate rocks to fill the OFD, tectonic activity resumed during the Gzhelian (Late Pennsylvanian). This resulted in rapid collapse of the depression along its axis and simultaneous uplifts of its margins, a style of tectonism in accord with the inferred basin-wide shift to a transpressional–transtensional stress regime at that time. Late Pennsylvanian–Early Permian sedimentation in the OFD led to the development of four long-term (second-order) transgressive–regressive sequences of early Gzhelian–middle Asselian (<1200 m), late Asselian–late Sakmarian (<380 m), latest Sakmarian–late Artinskian (<160 m) and latest Artinskian–late Kungurian (<60 m) age. These ages are supported by integration of biostratigraphic data from conodonts, fusulinaceans, and small foraminifers. The development of each sequence-bounding unconformity was associated with renewed tectonism in the OFD. Each sequence recorded the development of a depositional system characterized by high energy peripheral shoreface grainstones passing basinward across a gently dipping ramp into deep-water basinal calcareous and siliceous mudstone. The ramp portion of the early Gzhelian–middle Asselian system comprises both cool-heterozoan to warmphotozoan carbonates (Nansen Formation) suggesting a relatively shallow thermocline at that time. These rocks are arranged in a series of high-order cyclothems of glacio-eustatic origin. Cyclothemic sedimentation ended at the Asselian–Sakmarian boundary, simultaneous to a major depositional system shift to cool-water heterozoan sedimentation (Raanes Formation), a change presumably brought on by the closure of the Uralian seaway linking NW Pangea with the Tethyan Ocean. This event led to the destruction of the permanent thermocline, and disappearance of photozoan carbonates by the early Sakmarian despite rising temperatures globally. Cool-water heterozoan sedimentation, associated with relatively shallow outer-ramp to midramp spiculitic chert resumed in the Artinskian and then again in the Kungurian (Great Bear Cape Formation) when the OFD was filled up. The depression ceased to exist as a separate tectonic/subsidence entity with the widespread sub-Middle Permian unconformity, above which sediments were deposited during a passive subsidence regime across most of the Sverdrup Basin. The Pennsylvanian–Lower Permian succession that accumulated in the OFD along the clastic-free northern margin of the Sverdrup Basin is essentially identical, both in terms of tectonic evolution and stratigraphic development, with the coeval succession of Raanes Peninsula, southwest (SW) Ellesmere Island, the type area of the Raanes, Trappers Cove, and Great Bear Cape formations along the clastic-influenced southern margin.

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.