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.

This article utilizes over 3000 biostratigraphic reports of fusulinid taxa in the Midland Basin to produce a series of chronostratigraphic surfaces that show shelf-to-basin profiles from the end of the Atokan to the end of the Leonardian. The position of the shelf-edge break along the Eastern Shelf was geometrically reconstructed for each of the chronostratigraphic surfaces. Comparing the location of the shelf edges produced in this study to published examples resulted in significant disagreement for some time intervals, especially the Wolfcampian. These discrepancies are inferred to be predominantly the result of lithostratigraphic-based vs. biostratigraphic-based data. Assessing shelf-edge trajectory through the Pennsylvanian into the early Permian indicates that (1) tectonic and eustatic increases in shelf accommodation resulted in retrogradation of the shelf edge during the Pennsylvanian, and (2) early Permian progradation was the likely result of cessation in tectonic subsidence that allowed bypass of the shelf and passive filling of the basin center. When placed into the context of the Ancestral Rocky Mountains, subsidence analysis of the Midland Basin agrees with tectonic models that portray a synchronous start rather than an east-to-west migration of peak subsidence. Additionally, a relatively synchronous apex of tectonic subsidence occurred in the Middle to Late Pennsylvanian.

The Ancestral Rocky Mountains (ARM) represent an intraplate deformational event that resulted in a series of Precambrian-cored basement uplifts with adjacent basins that accumulated Pennsylvanian to early Permian strata. Tectonic models for the event are debated largely because of the lack of robust age control in the basin fill. In New Mexico, the ARM event resulted in a series of basins with some of the best biostratigraphic records across the orogenic province. This article utilizes published biostratigraphic and lithostratigraphic data to (1) reconcile the onset of subsidence by first accumulation of Pennsylvanian strata, (2) establish a period of peak subsidence estimated by maximum accumulation rate, (3) correlate estimated peak subsidence with the first appearance of arkose derived from the adjacent denuded Precambrian-cored block, and (4) demarcate synorogenic strata from Permian strata that are postorogenic. Results demonstrate that within New Mexico ARM basins, (1) onset was relatively synchronous, predominantly beginning in early Atokan time; (2) peak subsidence, while potentially younging southward, was relatively coeval in the Middle to Late Pennsylvanian; (3) first occurrence of arkose either predates the period of peak subsidence or is coeval with peak subsidence; and (4) early Permian strata across the study area onlap preexisting faults and folds, and/or form a buttress unconformity with Precambrian basement.

Abstract: The Permian timescale has developed over about two centuries of research to the current chronostratigraphic scale advocated by the Subcommission on Permian Stratigraphy of three series and nine stages: Cisuralian (lower Permian) – Asselian, Sakmarian, Artinskian, Kungurian; Guadalupian (middle Permian) – Roadian, Wordian, Capitanian; and Lopingian (upper Permian) – Wuchiapingian and Changhsingian. The boundaries of the Permian System are defined by global stratotype sections and points (GSSPs) and the numerical ages of those boundaries appear to be determined with a precision better than 1‰. Nevertheless, much work remains to be done to refine the Permian timescale. Precise numerical age control within the Permian is very uneven and a global polarity timescale for the Permian is far from established. Chronostratigraphic definitions of three of the nine Permian stages remain unfinished and various issues of marine biostratigraphy are still unresolved. In the non-marine Permian realm, much progress has been made in correlation, especially using palynomorphs, megafossil plants, conchostracans and both the footprints and bones of tetrapods (amphibians and reptiles), but many problems of correlation remain, especially the cross-correlation of non-marine and marine chronologies. The further development of a Permian chronostratigraphic scale faces various problems, including those of stability and priority of nomenclature and concepts, disagreements over changing taxonomy, ammonoid v. fusulinid v. conodont biostratigraphy, differences in the perceived significance of biotic events for chronostratigraphic classification and correlation problems between provinces. Future research on the Permian timescale should focus on GSSP selection for the remaining undefined stage bases, the definition and characterization of substages, and further development and integration of the Permian chronostratigraphic scale with radioisotopic, magnetostratigraphic and chemostratigraphic tools for calibration and correlation.

Abstract: In 1841, Murchison coined the term Permian for strata in the Russian Urals. Recognition of the Permian outside of Russia and central Europe soon followed, but it took about a century for the Permian to be accepted globally as a distinct geological system. The work of the Subcommission on Permian Stratigraphy began in the 1970s and resulted in current recognition of nine Permian stages in three series: the Cisuralian (lower Permian) – Asselian, Sakmarian, Artinskian and Kungurian; the Guadalupian (middle Permian) – Roadian, Wordian and Capitanian; and the Lopingian (upper Permian) – Wuchiapingian and Changhsingian. The 1990s saw the rise of Permian conodont biostratigraphy, so that all Permian Global Stratigraphic Sections and Points (GSSPs) use conodont evolutionary events as the primary signal for correlation. Issues in the development of a Permian chronostratigraphic scale include those of stability and priority of nomenclature and concepts, disagreements over changing taxonomy, ammonoid v. fusulinid v. conodont biostratigraphy, differences in the perceived significance of biotic events for chronostratigraphic classification, and correlation problems between provinces. Further development of the Permian chronostratigraphic scale should focus on GSSP selection for the remaining, undefined stage bases, definition and characterization of substages, and further integration of the Permian chronostratigraphic scale with radioisotopic, magnetostratigraphic and chemostratigraphic tools for calibration and correlation.

Abstract: The reverse polarity Kiaman Superchron has strong evidence for at least three, or probably four, normal magnetochrons during the early Permian. Normal magnetochrons are during the early Asselian (base CI1r.1n at 297.94±0.33 Ma), late Artinskian (CI2n at 281.24±2.3 Ma), mid-Kungurian (CI3n at 275.86±2.0 Ma) and Roa"dian (CI3r.an at 269.54±1.6 Ma). The mixed-polarity Illawarra Superchron begins in the early Wordian at 266.66±0.76 Ma. The Wordian–Capitanian interval is biased to normal polarity, but the basal Wuchiapingian begins the beginning of a significant reverse polarity magnetochron LP0r, with an overlying mixed-polarity interval through the later Lopingian. No significant magnetostratigraphic data gaps exist in the Permian geomagnetic polarity record. The early Cisuralian magnetochrons are calibrated to a succession of fusulinid zones, the later Cisuralian and Guadalupian to a conodont and fusulinid biostratigraphy, and Lopingian magnetochrons to conodont zonations. Age calibration of the magnetochrons is obtained through a Bayesian approach using 35 radiometric dates, and 95% confidence intervals on the ages and chron durations are obtained. The dating control points are most numerous in the Gzhelian–Asselian, Wordian and Changhsingian intervals. This significant advance should provide a framework for better correlation and dating of the marine and non-marine Permian.

Abstract: A review of Permian fusuline biostratigraphy is made in this paper in order to improve the correlation of Permian strata globally. Permian fusuline biostratigraphy in the Tethyan and Panthalassan regions can be correlated roughly because the fusulines had good faunal communications between these two regions. However, fusuline faunas from the North American Craton region were devoid of almost all neoschwagerinids and dominated exclusively by schwagerinids during the Guadalupian (Middle Permian) because of the blockage caused by the vast Pangaea supercontinent. This renders the correlation of Middle Permian biostratigraphy and chronostratigraphy between the Tethyan region and North American region challenging. Significant evolutionary key points in fusulines include the first occurrence of Pseudoschwagerina or Sphaeroschwagerina during the earliest Permian, first occurrence of Pamirina and Misellina during the Yakhtashian and Bolorian, and the extinction of all schwagerinids and neoschwagerinids by the end of the Midian.