Pennsylvanian-Permian Boundary Research Articles

Palynological analysis (biochronostratigraphy and paleoenvironments) from a fossil-Lagerstätte section within the Late Paleozoic Ice Age unit of the Paraná Basin (Itararé Group), Western Gondwana

A diverse and exceptionally preserved fossil association occurs in Campáleo Outcrop black shales of the upper Itararé Group, correlated to the Lontras Member, considered representative of the Pennsylvanian–Permian transition in the Paraná Basin, Brazil. In this paper, we present the palynological records from 20 stratigraphic horizons of these shales and related strata, which revealed 21 taxa of spores, 33 of pollen grains, two species of fungi, one species of Chlorophyceae and two species of Prasinophyceae. The section is correlated to the Vittatina costabilis Zone, due to the records of certain guide species, such as Converrucosisporites confluens, Illinites unicus and several species of Vittatina. An additional subsurface section (TC-4 core) partially correlated with the Campáleo Outcrop and comprising the passage of the Crucisaccites monoletus and Vittatina costabilis palynozones was also studied in order to support the stratigraphic positioning. Once combined with the stratigraphic positioning in the basal portion to the Lontras Shale, it allows us to consider it around the Pennsylvanian–Permian boundary, probably in the Gzhelian to age of the Campáleo Outcrop. We observed distinct palynofloristic compositions from (i) the rhythmic shale with dropstones (basal portion) and from (ii) the fossiliferous black shales (upper portion). The former presents a large dominance (about 90 %) of pollen grains (xerophylous elements) and low frequency (about 7 %) of spores (meso-hygrophylous), while the results of the latter are conversely. Marine palynormorphs were recorded herein only from the rhythmic shale. The palynological assemblages on the base of the Campáleo Outcrop demonstrated a more intense sediment supply, bringing sporomorphs from more distant regions being represented mainly by xerophylic flora, indicating the existence of regions devoid of ice cover, where forests could develop, as occur in seasonal climate regions. The upper level of the Campáleo Outcrop characterizes one of the predominance of spores (hygrophylic communities) in these palynological associations supported by the large number of insects found that indicates proximity to the coastline, little transport (spore tetrads), poor contribution of more distant continental sediments (low expressiveness of pollen grains) and low salinity water, due to the absence of marine palynomorphs, representing a reducing restricted marine environment. This data integrated with the stratigraphic context and other geological data evidenced changes in sea level due to the climatic oscillations in the course of the LPIA that influenced the sediment supply and the distance of the coastline in this region of the Paraná Basin.

A detailed stratigraphic and taphonomic reassessment of the late Paleozoic fossil flora from Promontory Butte, Arizona

A late Paleozoic, likely early Late Pennsylvanian (Missourian/early Virgilian), flora from Promontory Butte, Arizona, USA is the westernmost assemblage of this age yet described from northern Pangea. The palynological species pool is similar to that typical of more central parts of the supercontinent; in contrast, the macroflora differs by facies, reflective of original habitat differentiation. The flora is preserved in a succession that includes sandstone, siltstone, shale, and conglomerate in an upward-fining series of beds. A break between the siltstone and shale is marked by an organic-shale bed, previously described as a coal, and its underclay/paleosol. This stratigraphic unit is interpreted as an active channel fill terminating in a lake. A detailed bed-by-bed facies analysis of the macroflora, focusing on the relationship between sedimentological features and fossil-plant composition reveals that the wetland floral elements are concentrated in the upper, fine-grained beds of the fill, including the organic shale and overlying mudrock, whereas the drought-tolerant, xeromorphic plants are concentrated in siltstones and sandy siltstones below the organic-shale/underclay couplet. Palynology, in contrast, suggests a uniform flora throughout the interval, indicating that macrofloral changes within the channel-fill sequence reflect microhabitat differences resulting from local changes in soil moisture conditions rather than climate change. The palynoflora is dominated by tree ferns and compositionally suggests a Missourian (Kasimovian) age, possibly early Virgilian; rare lycospore grains, characteristic of the Middle Pennsylvanian, are likely reworked from older sediments. Earlier collecting at this site did not sort the fossils by microstratigraphy and facies types, combining all floral levels into one assemblage that indicated possible co-occurrence of wetland plants and plants tolerant of seasonal moisture stress. Furthermore, a Pennsylvanian-Permian boundary age was inferred due to the abundance of xeromorphic, drought-tolerant taxa. In light of this investigation, a late Missourian age is inferred as most likely.

Mixed eolian–longshore sediment transport in the late Paleozoic Arizona shelf and Pedregosa basin, U.S.A.: A case study in grain-size analysis of detrital-zircon datasets

ABSTRACT Detrital-zircon U–Pb geochronology has revolutionized sediment provenance studies over the last two decades, and zircon has been successfully analyzed from nearly all sedimentary lithologies, depositional environments, and sediment grain sizes. However, despite the ubiquity of this method and the far-reaching interpretations supported by detrital-zircon data, few studies have investigated the potential role of zircon grain size on age spectra and provenance interpretation. In this study, we investigate the connections between sample grain size, zircon grain size, U–Pb age spectra, and interpreted provenance using 18 detrital-zircon samples (4999 individual grains) collected from Pennsylvanian–Permian strata in central and southern Arizona, USA. In these samples, there is no clear correlation between sample grain size and zircon grain size and no clear correlation between sample grain size and age spectra. However, when all grains are grouped by zircon minimum long-axis dimension, the abundance of some age groups is correlated to zircon grain size. In Pennsylvanian samples, < 400 Ma grains and 2500–3000 Ma zircons are more abundant in the finer fractions, and 1400–1900 Ma zircons are more abundant in coarser fractions of both Pennsylvanian and Permian samples. In Permian samples, 500–800 Ma zircons are most abundant in the finer fractions, and 2500–3000 Ma grains are concentrated in the coarser fractions. Based on changes in abundance and grain-size distribution of 500–800 Ma grains, we interpret a change in zircon provenance across the Pennsylvanian–Permian boundary that reflects regional climate and paleogeographic changes driven in part by the northward drift of Laurentia across the equator. Specifically, we interpret the concentration of 500–800 Ma zircons in Permian samples in central and southern Arizona to indicate that these grains were: 1) sourced from Gondwana, 2) deposited in, and subsequently eroded (recycled) from, Mississippian–Pennsylvanian strata in the Arkoma, Anadarko, and Fort Worth basins at the margins of Laurentia, and 3) finally transported into the Arizona study area as loess by easterly trade winds. This study serves as a case study in the value and interpretive power of basic grain-size characterization of detrital-geochronology datasets.

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The Wabunsee (Carboniferous: Virgilian) through Sumner (Permian: Leonardian) Groups of Oklahoma preserve a record of terrestrial and nearshore marine environments during glacio-eustatic fluctuations caused by southern hemisphere glaciation. This section, with the Pennsylvanian–Permian Boundary firmly established in the Red Eagle Formation on the basis of conodonts, permitted study of vegetational change across the boundary interval. The palynology of 43 productive samples from five cores in Kay and Osage counties in Oklahoma was investigated. Palynomorphs were assigned to eight morphologic groups that also reflect climate preferences. Four distinct palynofloras are recognized. The three transitions between them—in the lower Council Grove, middle Chase and lower Sumner groups—are abrupt and, in succession, consistent with an interpretation of increasing seasonality/aridity from latest Pennsylvanian into the Early Permian. None of these floristic transitions align with the conodont-based boundary, or with any lithostratigraphic “group” boundary. These palynological data from Oklahoma are in accord with previous data from Kansas that also demonstrated no palynological shift at the boundary and increased seasonality/aridity through this period. Comparison of the palynofloras from Oklahoma, Kansas, and the boundary interval of the Pennsylvanian–Permian Boundary type section in Aidaralash Creek in Kazakhstan reveals differences in composition that suggest local to regional, including climatically induced, heterogeneities that may present an obstacle to confident palynologically based, global correlations in fully terrestrial sections.

High-resolution late Paleozoic cyclostratigraphy and tectonic evolution of the Keeler Basin, California, southwest Laurentia

Abstract Cyclic strata exposed in the Inyo Mountains of eastern California contain a continuous 6 m.y. record of deep marine deposition that spans the Pennsylvanian–Permian boundary. To better understand the geologic evolution of southwest Laurentia and the role of glacially driven eustasy in upper Paleozoic stratigraphy, we measured two detailed ∼600 m composite stratigraphic sections of the Keeler Canyon Formation and collected a handheld spectral gamma ray log. Post-depositional deformation complicates field relationships, but 1:5000 scale mapping of faults and folds permits assembly of two continuous sections. Measured strata alternate at the 5–20 m scale between intervals of fine-grained laminated marlstone and intervals of mixed carbonate and siliciclastic turbidites and debrites. Based on facies characteristics and a prominent marker horizon, we reassign the Pennsylvanian-Permian age upper Salt Tram unit of the upper Keeler Canyon Formation to a new Estelle Member. We estimate sediment accumulation rates within the Keeler Canyon Formation using published conodont biostratigraphy and correlative U-Pb geochronology from Eastern Europe combined with spectral analysis and timescale optimization using the Astrochron R package. Evolutive harmonic analysis of gamma ray-derived element concentrations reveals prominent bundled periodicities that are consistent with both long and short eccentricity cycles. Average sediment accumulation rates calculated using the time scale optimization function of Astrochron suggest a gradual increase from 40–60 m/m.y. to ∼120 m/m.y. during the late Pennsylvanian and then a minima of ∼50 m/m.y. near the Pennsylvanian–Permian boundary, which is followed by an increase to ∼175 m/m.y. into the Early Permian. This trend in sediment accumulation rates and subsequent Permian contractile deformation are compatible with flexural subsidence in a SW-migrating foreland basin related to the southern part of the late Antler orogenic system.

Response of Soils and Soil Ecosystems to the Pennsylvanian–Permian Climate Transition in the Upper Fluvial Plain of the Dunkard Basin, Southeastern Ohio, USA

Direct exposure of paleosols to the atmosphere during formation make them ideal for reconstructing paleoclimate. Paleosol and ichnofossil properties are dependently linked making it important to study them in tandem, to avoid errors in interpretation. Small scale studies (<1 km) yield high resolution data that can be used to assess allogenic processes through comparison of spatial and temporal trends. This study used field and laboratory analyses to gather data from Late Pennsylvanian to Early Permian Upper Monongahela and Lower Dunkard group paleosols on Ohio Route 33 in Meigs County, OH, USA. The physical and geochemical properties of the paleosols from the field sites indicate that channel migration was the primary control on paleosol formation in the study area, however, a clear climate signal was observed. The change in paleosol type and calculated mean annual precipitation (MAP) values indicate that the climate became more strongly seasonal and drier over the course of the Pennsylvanian–Permian transition with a temporary excursion to a more ever-wet climate with higher MAP, marked by the occurrence of the Waynesburg Coal at the Pennsylvanian–Permian boundary.

Pedogenic record of climate change across the Pennsylvanian-Permian boundary in red-bed strata of the Cutler Group, northern New Mexico, USA

The Upper Pennsylvanian to lowermost Permian El Cobre Canyon and Arroyo del Agua formations are well exposed in a 250+ m section in the Chama Basin in northern New Mexico. This is one of the few known successions of fossiliferous red-bed siliciclastic sediments encompassing the Pennsylvanian-Permian boundary in the American Southwest and thus may inform questions regarding changing paleoclimate in tropical Pangea across the Pennsylvanian-Permian boundary. The section consists mainly of silty mudstones and sandstones with sheet-like to ribbon geometry and very minor limestones and records an upward transition from mainly braided stream deposition in the El Cobre Canyon Formation to anastomosing stream deposition in the Arroyo del Agua Formation.We recognized multiple paleosol types within these strata, including calcic Protosols, calcic Argillisols, argillic Calcisols and Calcisols, all generally consistent with the interpretation of a seasonal sub-humid to semi-arid climate. The calcretes in these paleosols occur primarily as truncated profiles. Although Calcisols occur in both formations, we note that Protosols are more common in the El Cobre Canyon Formation, and Argillisols dominate in the Arroyo del Agua Formation. Also, we find that the calcretes in the Arroyo del Agua Formation are generally thicker than those in the underlying El Cobre Canyon Formation. The difference in calcrete maturity could be explained by changes in source-area relief and sedimentation rate. However, stable isotope analyses of pedogenic carbonate indicate that a significant enrichment of δ18O occurs near the transition between the two formations, which approximates the Virgilian-Wolfcampian (equals Gzhelian-Asselian) boundary. Although the δ13C data suggest that pCO2 remained stable during the interval of deposition, the δ18O data are consistent with the interpretation of climate aridification across the Pennsylvanian-Permian transition, potentially related to the onset of Gondwanan glaciation in the earliest Permian.

Temporal and spatial distribution of ostracodes across the Pennsylvanian–Permian boundary interval in eastern North America

Ostracodes recovered from eastern North American coal measures in the Appalachian, Illinois, and Maritimes Basins have the potential to resolve the temporal and spatial relationships of the strata deposited during the Pennsylvanian–Permian boundary interval. The ostracode associations include: (1) a Pennsylvanian (Virgilian; Gzhelian) marine association dominated Hollinella cushmani with abundant brachiopods and foraminifera exclusive to the GIL 30 Core in Kentucky (Illinois Basin); (2) a latest Pennsylvanian (Virgilian; Gzhelian) brackish association dominated by Geisina upsoni (Kellet), Cavellina nebrascensis (Geintz), and Velatomorpha fittsi (Kellet) exclusive to the GIL 30 Core in Kentucky (Illinois Basin); and (3) an uppermost Permian (Asselian/Sakmarian) association of nonmarine taxa dominated by Whipplella cuneiformis (Holland), Whipplella parvula (Holland), Paleodarwinula hollandi (Scott), and Haworthina bulleta (Harris and Lalicker) that occurs in the uppermost continental facies of both the Illinois and Dunkard Basins. A comparable nonmarine association of Paleodarwinula hollandi and Whipplella bretonensis (Copeland) occurs in the Bolsovian to Cantabrian (Moscovian to Kasimovian) coal measures of the Maritimes Basin of Atlantic Canada. The data presented herein provides new information about the withdrawal of marine waters from several major Late Paleozoic basins in eastern North America. Mid-continental marine influence persisted into the latest Pennsylvanian to earliest Permian during deposition in the eastern Illinois Basin on the western Appalachian coastal plain. The uppermost nonmarine association of nonmarine Ostracoda in both the Illinois Basin and Dunkard Basin indicates a synchronous development of aquatic freshwater faunas during Lower Permian times. With increasing geographic isolation of the eastern North American basins, the dispersal and radiation of Ostracoda in these basins was apparently facilitated by brood rearing as demonstrated by the dominance of the Platycopina and Darwinulocopina.

Callipterid peltasperms of the Dunkard Group, Central Appalachian Basin

The Dunkard Group is the youngest late Paleozoic rock unit in the Central Appalachian Basin. Its age, however, remains controversial. In its southern and western two-thirds the Dunkard is comprised largely of red beds, sandstone and siltstone channel deposits and paleosols. In its thickest, most northerly exposures, in southwestern Pennsylvania, northern West Virginia, and east-central Ohio, much of the lower part of the unit is composed of coals, non-marine limestones and gray, often calcareous, paleosols. Age dating is confounded by the non-marine nature of the deposit and by the lack of dateable volcanic ash beds. Dunkard fossils include plants, vertebrates, and both aquatic and terrestrial invertebrates. Most of the fossil groups point to an age very close to, if not including, the Pennsylvanian–Permian boundary, though the exact position of that boundary is uncertain. Callipterids make their first appearance in the Dunkard flora in the middle of the Washington Formation and continue into the Greene Formation, but in different beds from those containing wetland floral elements. Publication of these plants in the “Permian Flora” of Fontaine and White (1880) created an immediate controversy about the age of the unit because Callipteris conferta (now Autunia conferta) was, at the time, considered to be an index fossil for the base of the Permian. Subsequent collecting has revealed these callipterds to comprise four species: A. conferta, Autunia naumannii, Lodevia oxydata and Rhachiphyllum schenkii. Callipterids – and the conifers with which they are sometimes associated – are typically found in seasonally dry equatorial environments and most likely constitute an environmentally controlled biofacies. This biofacies is not well known, resulting in limited biostratigraphic utility.

Late Pennsylvanian–Early Permian vegetational transition in Oklahoma: Palynological record

The Wabunsee (Carboniferous: Virgilian) through Sumner (Permian: Leonardian) Groups of Oklahoma preserve a record of terrestrial and nearshore marine environments during glacio-eustatic fluctuations caused by southern hemisphere glaciation. This section, with the Pennsylvanian–Permian Boundary firmly established in the Red Eagle Formation on the basis of conodonts, permitted study of vegetational change across the boundary interval. The palynology of 43 productive samples from five cores in Kay and Osage counties in Oklahoma was investigated. Palynomorphs were assigned to eight morphologic groups that also reflect climate preferences. Four distinct palynofloras are recognized. The three transitions between them—in the lower Council Grove, middle Chase and lower Sumner groups—are abrupt and, in succession, consistent with an interpretation of increasing seasonality/aridity from latest Pennsylvanian into the Early Permian. None of these floristic transitions align with the conodont-based boundary, or with any lithostratigraphic “group” boundary. These palynological data from Oklahoma are in accord with previous data from Kansas that also demonstrated no palynological shift at the boundary and increased seasonality/aridity through this period. Comparison of the palynofloras from Oklahoma, Kansas, and the boundary interval of the Pennsylvanian–Permian Boundary type section in Aidaralash Creek in Kazakhstan reveals differences in composition that suggest local to regional, including climatically induced, heterogeneities that may present an obstacle to confident palynologically based, global correlations in fully terrestrial sections.

Vertebrate biostratigraphy and biochronology of the upper Paleozoic Dunkard Group, Pennsylvania–West Virginia–Ohio, USA

The Dunkard Group is ~343m of mostly clastic rocks exposed in Pennsylvania, Ohio and West Virginia, USA. Correlation of the Dunkard Group to the Pennsylvanian–Permian boundary has long been debated. Fossil vertebrates from the Dunkard Group include paleoniscoids, dipnoans, a rhipidistian crossopterygian, selachians, lepospondyl and temnospondyl amphibians, diadectomorphs, primitive amniotes, eureptiles and eupelycosaurs. These vertebrates represent two biostratigraphically distinct assemblages, one from the Waynesburg and Washington formations and the other from the overlying Greene Formation. Comparison of the Dunkard vertebrate biostratigraphy to a vertebrate biostratigraphy and biochronology developed in New Mexico–Texas allows correlation to the Coyotean (= latest Virgilian–middle Wolfcampian) and Seymouran (late Wolfcampian–early Leonardian) land-vertebrate faunachrons. Tetrapod taxa from the Waynesburg and Washington formations include Edops and Protorothyris, Coyotean index taxa, as well as the characteristic Coyotean taxa Trimerorhachis, Diadectes, Edaphosaurus and Dimetrodon. Significantly, these Dunkard taxa are best known from the Archer City Formation in Texas, which is late Coyotean (=middle Wolfcampian). The Greene Formation contains the eupelycosaur Ctenospondylus, an index taxon of the Seymouran land-vertebrate faunachron. Dunkard xenacanth selachians support the tetrapod-based correlations. Vertebrate biochronology thus indicates that the Waynesburg and Washington formations are late Coyotean, whereas the Greene Formation is Seymouran. Therefore, vertebrate biostratigraphy and biochronology indicate that the entire Dunkard Group is Early Permian and likely straddles the Wolfcampian–Leonardian boundary.

Pennsylvanian to Lower Permian (Desmoinesian-Wolfcampian) fusulinid biostratigraphy of Midcontinent North America

Midcontinent North American Middle Pennsylvanian-Lower Permian (Desmoinesian-Wolfcampian) fusulinid foraminiferal species range charts were plotted and new fusulinid zones were defined. The species range charts were plotted together with lithostratigraphic columns and cyclothemic sea level curves in order to compare biostratigraphic, lithostratigraphic, and glacio-eustatic patterns. The fusulinids Beedeina and Wedekindellina appeared during widespread early Desmoinesian transgressions and characterized that interval. The mid-Desmoinesian extinction of Wedekindellina and turnover of Beedeina species coincided with a lowstand followed by a widespread transgression, generally higher sea levels, and changing paleoclimatic patterns. Beedeina went to extinction near the Desmoinesian-Missourian sequence boundary. The earliest Missourian is barren of fusulinids in the Midcontinent, followed by a thin zone of Eowaeringella, and then the appearance of Triticites, which dominated fusulinid faunas through the remainder of the Upper Pennsylvanian. Lower and Middle Missourian Triticites have relatively small tests and plane septa. In the Upper Missourian, Triticites became medium-sized with more complex septal fluting, and Kansanella appeared. In the uppermost Missourian and lower Virgilian, most Triticites are medium-sized and evenly biconvex, and have weak septal fluting. Kansanella gradually declined through the lower Virgilian and disappeared in the lowest middle Virgilian. The middle Virgilian is dominated by medium to large Triticites with complex septal fluting, and Dunbarinella appeared and became locally common. The upper Virgilian has mostly large inflated Triticites and the first Leptotriticites. The uppermost Virgilian (‘Bursumian’) has large Triticites, diverse Leptotriticites, and the first primitive elongate Schwagerina. That fauna extends across the new conodont-based Pennsylvanian-Permian (Virgilian-Wolfcampian) boundary, and the first definitive Wolfcampian (Lower Permian) fusulinids did not appear until the Neva Limestone, which is a couple cycles above the new systemic boundary. Most significant fusulinid biostratigraphic changes correlate with major glacio-eustatic cyclothem boundaries, but not all major cyclothem boundaries have significant faunal turnovers. Fusulinid zonal boundaries that were based on only fusulinid species ranges were found to closely approximate maximum sea level lowstands. Most new genera and species appear in the regressive phases of the next cyclothem, probably because faunal migrations occurred during maximum flooding events, and subsequent highstand system tracts had more paleoenvironmental diversity and thus more niches to fill.

The Carboniferous-Permian boundary at Carrizo Arroyo, Central New Mexico, USA

At Carrizo Arroyo southwest of Albuquerque, New Mexico,USA, an approximately 105-m-thick section of upper Paleozoic clastic and carbonate rocks yields extensive fossil assemblages of marine and nonmarine origin. Most of the section at Carrizo Arroyo belongs to the Red Tanks Member of the Bursum Formation, ~ 100m thick and mostly variegated shale, mudstone and siltstone of nonmarine origin, intercalated with some beds of limestone and shale of marine origin. Red Tanks Member fossils include palynomorphs, charophytes, plant megafossils, non-fusulinid foraminifers, fusulinids, bryozoans, brachiopods, gastropods, bivalves, nautiloids, eurypterids, ostracods, syncarid crustaceans, conchostracans, insects and some other arthropods, echinoids, crinoids, conodonts, fish ichthyoliths and bones of amphibians and reptiles. At stratigraphic levels 43m and 68m above the base of the section are Lagerstätten of plants, insects, crustaceans, eurypterids and other fossils that form unique Late Paleozoic nearshore arthropod assemblages. Most of the fossil groups from the Red Tanks Member have been used to support diverse placements of the Pennsylvanian-Permian boundary at Carrizo Arroyo. We review previous placement of the Pennsylvanian-Permian boundary in the Carrizo Arroyo section and present newly collected insect and conodont data. The insects indicate that the two Lagerstätten in the Red Tanks Member are of early Asselian age. The new conodont data include the presence of Streptognathodus virgilicus in the uppermost part of the Atrasado Formation, which constrains its age to the middle to upper part of the Virgilian and to a comparable position in the Gzhelian. The only biostratigraphically-significant conodont assemblage in the Red Tanks Member comes from a marine horizon near the middle of the member, and the assemblage is probably equivalent in age to the Midcontinent Streptognathodus nevaensis Zone, of early to middle Asselian in age. Asignificant amount of latest Pennsylvanian to earliest Permian time apparently is not represented by rock record at the Carrizo Arroyo section, most likely at a major disconformity at the top of the Atrasado Formation and smaller ones at the bases of depositional sequences in the lower part of the Red Tanks Member. Conodont biostratigraphy provides compelling evidence that Bursum Formation deposition was not simply driven by glacio-eustatic cyclicity, but in this area it was partly overprinted by local tectonics.

Lithostratigraphy, Paleontology, Biostratigraphy, and Age of the Upper Paleozoic Abo Formation Near Jemez Springs, Northern New Mexico, USA

In the Jemez Springs area of Sandoval County, northern New Mexico, siliciclastic red beds of the upper Paleozoic Abo Formation are well exposed and yield fossil plants and vertebrates. The local Abo Formation section is more than 190 m thick and rests disconformably on the Upper Pennsylvanian Guadalupe Box Formation and is conformably overlain by the Lower Permian DeChelly Sandstone (Yeso Group). Abo sandstone sheets are low sinuosity river deposits, and intercalated sandstone beds and lenses represent sheet splays and minor channel fills that formed during overbank flooding. The dominant Abo lithofacies is mudstone, which represents floodplain deposits, many with calcareous paleosols. Fossils are present in three stratigraphie intervals of the lower to middle Abo Formation. All three intervals yield eupelycosaur-dominated vertebrate fossil assemblages of Coyotean age (Coyotean = late Virgilian-Wolfcampian on the North American provincial marine timescale: Lucas 2006). The lowest interval also yields the Spanish Queen Mine paleoflora of pteridosperms and conifers. Strata of the Guadalupe Box Formation disconformably below the Abo Formation contain late Virgilian fusulinids. We correlate the Abo Formation fossil assemblages in the Jemez Springs area to the Coyotean-age fossil assemblages in the upper part of the El Cobre Canyon Formation in the Arroyo del Agua area and in the Canon del Cobre in the Chama basin of northern New Mexico. This suggests a middle Wolfcampian age for the Jemez Springs area fossil assemblages, an age very close to the Pennsylvanian-Permian boundary.

The Pennsylvanian–Permian transition in the low-latitude carbonate record and the onset of major Gondwanan glaciation

Recent studies suggest a marked expansion of glacial ice across much of Gondwana beginning in the earliest Permian. Because expansion of glacial ice results in a lowering of sea level, the imprint of ice expansion should be evident worldwide as significant exposure event, hiatuses, or other evidence for sea level drop at or near the Pennsylvanian–Permian boundary. This literature review investigates the signature of an Early Permian expansion of Gondwanan ice through examination of stratigraphic records from eight carbonate-dominated, palaeotropical regions across Pangaea. Tropical carbonate environments are used because most form in tectonically quiescent regions and are sensitive indicators of eustatic change. Correlation between stratigraphic sections is achieved using the most current biostratigraphic and absolute time constraints available. All studied sections show a sequence boundary or basinward shift in facies at or near the Pennsylvanian–Permian boundary, supporting the hypothesis of a significant expansion of glacial ice and global eustatic lowstand beginning in the Early Permian. By contrast, a series of mid-Sakmarian–Kungurian transgression events in the palaeotropics are interpreted to reflect the asynchronous deglaciation of Gondwana. The stratigraphic framework developed herein will allow for better correlations among stratigraphic records from Gondwana and northern Pangaea, which will ultimately improve the understanding of how carbonate systems respond to global icehouse conditions, such as during the late Palaeozoic.

Earliest Permian brachiopod faunas of west-central Argentina: Defining the Pennsylvanian–Permian boundary in Gondwana

Late Palaeozoic marine successions in the west-central Argentinian basins have one of the most complete stratigraphic records of the earliest Permian in Gondwana. Two brachiopod faunal assemblages characterize this interval: the Tivertonia jachalensis– Streptorhynchus inaequiornatus fauna, widely documented in the Río Blanco and western Paganzo basins; and the Costatumulus amosi fauna identified in the earliest Permian successions of the southern Calingasta–Uspallata Basin. This study reviews the composition and biostratigraphy of these two brachiopod faunas with special reference to their global significance for defining the Carboniferous–Permian boundary in Gondwana and deciphering the Early Permian climate change in western Gondwana.

Lower Permian oncolites from South China: Implications for equatorial sea-level responses to Late Palaeozoic Gondwanan glaciation

The oncoid-bearing Chuanshan Formation is a regionally extensive carbonate deposit of predominantly Asselian to early Sakmarian (Early Permian) age in South China, occupying an area of some 500,000 km 2. Throughout South China, the oncoid-bearing horizons are generally stable and broadly comparable in lithology, fossil content and the morphology of the oncoid grains. Four types of microfacies are recognized from the oncolite succession and overall they suggest a moderate- to high-energy, wave-agitated shallow marine carbonate platform environment. An analysis of the stratigraphic distribution of oncoid grain size, density, thickness and the bedding structures of the oncolite beds and the number of coating laminae indicate the presence of metre-scale cyclothems, suggestive of possible high-frequency cycles of sea-level fluctuation. Compared to carbonate successions above and below that lack oncolites, and in conjunction with evidence from sequence stratigraphic and isotopic geochemical analyses of coeval carbonate deposits in South China and elsewhere, the origin of the Chuanshan oncolites is linked to a drastic drop in global sea-level at the Pennsylvanian–Permian boundary, that can be correlated closely in timing with the zenith of the Late Palaeozoic Gondwanan glaciation. It is further suggested that the eustatic changes apparent from the deposition of the Chuanshan oncolites and similar coeval deposits in lower palaeolatitudes were coupled with, and influenced by, the contemporaneous high-latitude Gondwanan glaciation, the largest and longest known such event in Phanerozoic Earth history.

Early jointing in coal and black shale: Evidence for an Appalachian-wide stress field as a prelude to the Alleghanian orogeny

Early ENE-striking joints (present coordinates) within both Pennsylvanian coal and Devonian black shale of the Central and Southern Appalachians reflect an approximately rectilinear stress field with a dimension > 1500 km. This Appalachian-wide stress field (AWSF) dates from the time of joint propagation, when both the coal and shale were buried to the oil window during the 10-15 m.y. period straddling the Pennsylvanian-Permian boundary. The AWSF was generated during the final assembly of Pangea as a consequence of plate-boundary tractions arising from late-stage oblique convergence, where maximum horizontal stress, S-H, of the AWSF was parallel to the direction of closure between Gondwana and Laurentia. After closure, the AWSF persisted during dextral slip of peri-Gondwanan microcontinents, when SH appears to have crosscut plate-scale trans-current faults at around 30{sup o}. Following > 10 m.y. of dextral slip during tightening of Gondwana against Laurentia, the AWSF was disrupted by local stress fields associated with thrusting on master basement decollements to produce the local orocline-shaped Alleghanian map pattern seen today.

From Cyclothems to Sequences: The Record of Eustasy and Climate on an Icehouse Epeiric Platform (Pennsylvanian-Permian, North American Midcontinent)

The stratigraphic succession of the North American Midcontinent contains a high-resolution (< 100,000 year) record of sea level and climate change spanning the Pennsylvanian-Permian boundary. Outcrop-based sequence stratigraphic analysis on the upper Wabaunsee, Admire, and lower Council Grove groups in Kansas and Nebraska reveals a hierarchy of fifty-one fifth-order meter-scale cycles grouped into five fourth-order composite sequences. Fifth-order cycles are bounded by subaerial unconformities in nearshore settings and correlative conformities in offshore settings, and are therefore very thin depositional sequences. Lowstand systems tracts, observed only in nearshore deposits, are expressed as sandy, incised-valley fills in these meter-scale cycles. Transgressive systems tracts, which are dominated by carbonate deposition, include coastal evaporites indicating arid climatic conditions. Highstand systems tracts, which are dominated by siliciclastic deposition, include thin but persistent coals in muddy coastal successions indicating humid climatic conditions. Paleosols at sequence boundaries evolve from vertic to calcic, indicating climate change from relatively humid to relatively arid conditions during subaerial exposure. This indicates that relatively arid climate coincided with eustatic lows while relatively humid climate coincided with eustatic highs on this low-latitude platform. Composite sequences are bounded by subaerial, angular unconformities and display a transgressive-regressive stacking pattern of meter-scale cycles. The high-resolution stratigraphic record of the Midcontinent helps constrain the rate and magnitude of environmental change in ancient icehouse conditions and can serve as a baseline of environmental change for comparison with other coeval successions.

Discovery of radiolaria and conodonts in the Carboniferous–Permian of San Salvador Patlanoaya (Puebla, Mexico); biostratigraphic implications

New identifications of radiolaria and conodonts allow clarifying the biostratigraphy of the Pennsylvanian and Permian deposits in San Salvador Patlanoaya (Puebla State, Mexico). The radiolaria are sometimes relatively common in the series, but weakly diversified and endemic. Among the conodonts, Streptognathodus bellus is characteristic of the Late ‘Virgilian’ sensu Baars, probably coeval with the Early Wolfcampian sensu Thompson or Wilde, the Bursumian of Ross & Ross or the Orenburgian–Asselian stage or substage of Russia (sensu Davydov). San Salvador Patlanoaya is a key-section for the Pennsylvanian–Permian boundary in Mexico.