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.

The stratal architecture of the upper Ely Limestone and Mormon Gap Formation (Pennsylvanian–Lower Permian) in west-central Utah reflects the interaction of icehouse sea-level change and tectonic activity in the distal Antler–Sonoma foreland basin. Nineteen stratigraphic sections correlated by physical and biostratigraphic means provide a basis for tracing Carboniferous–Permian boundary strata over a north–south distance of 60 km. These formations can be subdivided into 14 unconformity-bounded, third-order depositional sequences of differing internal architecture and regional extent. Conodonts and fusulinids provide ages for selected sequences and parasequences, permitting correlation with tectonostratigraphic units in the proximal foreland in north-central Nevada and with selected Midcontinent cyclothems. The 14 third-order sequences stack into three second-order supersequences characterized by distinctive differences in facies and facies stacking patterns, regional continuity of cycles, relative abundance of dolomite and limestone, calculated rock accumulation rates, and the frequency and inferred duration of sequence-bounding hiatuses. These reflect the effect of high-frequency sea-level change on an intermittently subsiding distal foreland shelf. Sediment accommodation was relatively high during the Bashkirian through middle Moscovian (upper part of Lower Absaroka I supersequence) and again during the late Sakmarian and Artinskian (lower part of Lower Absaroka III supersequence) as a function of continuous subsidence and high-amplitude sea-level change. During the late Moscovian through upper Sakmarian (Lower Absaroka II supersequence), however, subsidence slowed or ceased in response to tectonic activity in north-central Nevada, with concomitant development of the West-Central Utah Highlands (forebulge). During this episode of reduced subsidence, intermittent sedimentation was driven by second- and third-order eustatic fluctuations in sea level. Constituent strata form a wedge of onlapping, northward-thinning sequences and parasequences deposited during selected third-order highstands of the Lower Absaroka II second-order sea-level event. Depositional sequences in the distal foreland are bounded by low-relief disconformities of variable duration, in contrast to the angular unconformities and intensely deformed tectonostratigraphic domains that characterize the proximal foreland basin in north-central Nevada.

The end-Permian mass extinction was associated with the onset of anoxia in widespread marine environments; however, the extent of this anoxia remains controversial. Proposed models range from near-universal “superanoxia” in the Panthalassic Basin to a more limited expansion of anoxia in the upper water column in response to enhanced primary productivity. The Peck Creek and Ursula Creek sections of northern British Columbia were deposited at ~200 m water depth in the Ishbel Trough, on the margin of cratonic North America. This trough was generally contiguous with the Slide Mountain Ocean, and thus with the broader Panthalassic Ocean, though it may have been partially separated by structural highs at various times during the Permian. Both sections include continuous Wordian to Changhsingian sedimentary successions, which span the end-Permian mass extinction boundary and continue into the earliest Triassic. The extinction is recognizable as the disappearance of biogenic silica from the environment, which defines the contact between the Fantasque Formation and overlying Grayling Formation. This surface also corresponds with the onset of anoxia, and the accumulation of redox-sensitive trace metals. The covariation trends in these metals, and in other isotopic proxies, can be used as tools to trace the degree of communication between the Ishbel Trough–Slide Mountain Ocean and the broader Panthalassic Basin. Molybdenum-uranium covariation trends indicate that the northern Slide Mountain Ocean and Ishbel Trough remained in communication with the larger global ocean throughout this interval, suggesting inversion of the Wordian structural high to form a depositional subbasin by the Changhsingian. This is in contrast to the Opal Creek section of southern Alberta, which shows evidence for some degree of restriction, suggesting that the Slide Mountain Ocean may have maintained a north–south gradient in water chemistry. Several lines of evidence suggest that this onset of anoxia was not related to expansion of an upwelling-driven oxygen minimum zone. No clear changes in primary productivity, as recorded by organic carbon or authigenic phosphorus and barium, are observed across the extinction horizon. Changhsingian nitrogen isotope values are generally in the 2 to 3‰ range, suggesting minimal denitrification at thermocline water depths, and these values decreased in the earliest Triassic, likely in response to enhanced nitrogen fixation. This suggests that anoxia was driven by shoaling of a chemocline that developed due to stratification of the Slide Mountain Ocean, rather than western-boundary upwelling effects.