Late Pennsylvanian Research Articles

Discovery of the enigmatic taeniopterid plant Ilfeldia from the lower Permian of North China and its palaeophytogeographical implications

ABSTRACT The recognition of plant biogeographic ranges over time and migration routes is crucial for understanding ancient global plate tectonic configurations. This paper deals with a new fossil plant from the uppermost part of the Taiyuan Formation (earliest Asselian) in the Wuda Coalfield, Inner Mongolia, China. It has a taeniopterid morphology comprising strap-shaped leaves with a prominent midrib and arching secondary veins, and it exhibits dimorphism between its fertile and vegetative leaves. The fertile leaf has a slightly lobed margin, with each lateral vein terminating in a marginal lobe that bears a synangium. Each synangium consists of primarily two, occasionally three, oval sporangia. Based on these distinctive characteristics it is identified as a new species of Ilfeldia. Previously, Ilfeldia had a highly restricted record in the Upper Pennsylvanian of Portugal and Germany into the lower Permian of Germany. The sedimentary and floral context suggests Ilfeldia was a xerophilous element that underwent long-distance dispersal during the Late Pennsylvanian to earliest Asselian, migrating from Gondwana (Iberia) to Cathaysia (North China) via Euramerica (Eastern Avalonia). The palaeogeographical distribution over time of Ilfeldia supports the continental model of the Wegenerian Pangaea configuration and underscores the continental connection between Euramerica and Cathaysia in the Late Pennsylvanian.

Changes in soils and terrestrial landscapes of the Appalachian Basin (Conemaugh, Monongahela, and Dunkard groups), U.S.A., at the onset of the late Paleozoic climate transition

ABSTRACT Changes in global climate from the Late Pennsylvanian to early Permian resulting from the destabilization of ice sheets in the Southern Hemisphere had important effects on terrestrial landscapes around the Paleozoic world. In the northern Appalachian Basin (U.S.A.), evidence for this transition and its effects on terrestrial systems is preserved in numerous paleosols in the Conemaugh, Monongahela, and Dunkard groups that formed in various alluvial environments. Several studies along a 50 km west–east and 40 km north–south transect through southeast Ohio and southwest West Virginia resulted in the recognition of 24 different pedotypes. An up-section shift in pedotypes from Argillisols to Vertisols and Calcisols as well as an overall upward increase in the diversity of pedotypes records a significant change in soil-forming processes and landscapes. The landscapes of the Late Pennsylvanian were largely characterized by well-developed, clay-rich Alfisols of woodland ecosystems on distal floodplains bordered by poorly developed Inceptisols of early successional or marshland ecosystems on proximal floodplains. By the early Permian, these landscapes began to experience strongly seasonal climates and increasingly prolonged dry periods, resulting in the production of pronounced shrink–swell features and well-developed carbonate horizons. These landscapes were characterized by Vertisols and Inceptisols of highly heterogeneous brakeland ecosystems, with rapid changes in sedimentation, hydrology, and vegetation over short distances. Climatic conditions were prone to fluctuations between wet and dry states during the transition, resulting in a highly heterogeneous landscape that changed significantly through time.

Anatomy of the late Pennsylvanian to early Triassic failed rift system of the Cooper Basin, eastern Australia

The onshore intracratonic Cooper Basin of central Australia developed during the Late Pennsylvanian to Middle Triassic periods at paleolatitudes of approximately 50°S within the Gondwanan sector of the Pangea. Despite the wealth of data available, including the drilling of over 4,800 boreholes, there is limited knowledge about the Cooper Basin’s origins and evolution. To better understand the basin’s geological history, legacy data sets, including composite 2D seismic sections, well logs, measured sections, and 1D burial history models from the west of the basin, are integrated to reinterpret the basin’s tectonic and sedimentary evolution. Interpretation of the seismic sections and calculated subsidence rates indicates an earlier active rift phase with grabens and half-grabens that transitioned, in the latest Permian, into a regional sag phase. The evolution of tectonic styles heavily influenced the paleogeographic evolution of the basin fill and resulting depositional architecture. The basin sediments are entirely terrestrial in nature and facies reflect a transition from glacial environments in the late Pennsylvanian to warmer and drier conditions in the early Triassic. During much of the Permian the basin was underfilled and the relative low influx of fluvial sediment did not keep pace with creation of accommodation, allowing the development of extensive mire and lake systems. Coal beds are up to 30 m thick. By contrast, the basin appears to have been overfilled during the latest Permian to Triassic with rivers flowing along the central axis of the basin. The synchroneity of commencement of rifting, termination of rifting, and commencement of a sag phase within the failed rift systems of the Cooper Basin, the East Gondwana Interior Rift, and the East Australian Rift strongly suggests a continent-wide period of extension related to significant changes in plate motions during the Late Pennsylvanian to Middle Triassic.

High-resolution chemofacies and pore system characterization of the Pennsylvanian Cline Shale, Midland Basin, Texas

The connections between the depositional environment, sediment chemistry, and pore structure of deep-water mudstones are still not completely understood. This study: 1) investigates the sediment chemistry and the depositional conditions of the Pennsylvanian Cline Shale chemofacies in the center of the Midland Basin, 2) characterizes the conditions favorable to organic matter accumulation of each mudstone chemofacies, and 3) examines the connection between the pore structure and the mudstones’ paleo-environmental and paleo-geochemical context and processes. This study uses X-ray fluorescence (XRF) and statistical methods (Isolation Forest, Principal Component Analysis, and K-means) to identify four chemofacies of 127 m of Cline Shale core from the Matthew 'D' 0906 well located in the Midland Basin depocenter in Glasscock County, Texas. In addition, petrographic and scanning electron microscopy and measurements by dual-energy computed tomography, X-ray diffraction, Rock-Eval pyrolysis, N2 isothermal adsorption tests, and mudrock reservoir properties were conducted on thin-sections, core slabs, and samples to understand the bulk geochemistry and petrophysical properties of the mudstones. Four chemofacies are identified: (1) Siliceous Mudstone with high Zr and low Ca and P, (2) Calcareous-argillaceous Mudstone I with high Ca and Zr, and low P, (3) Argillaceous Mudstone with high P and low Ca and Zr, and (4) Calcareous-argillaceous Mudstone II with high Ca and P, and low Zr. Based on elemental distribution, the first two and last two chemofacies are interpreted as low sea-level deposits and high sea-level deposits, respectively. Water stratification and P regeneration accounted for the highest total organic carbon (TOC) content, which resulted in the high porosity and pore volume of the low sea-level Siliceous Mudstone chemofacies, especially visible in the 8 nm–186 nm organic matter pores. Carbonate input hinders the development of the inorganic pore system, especially for organic lean Calcareous-argillaceous Mudstones. Nine sea-level cycles were observed in the cores and correlated to nine US mid-continent cycles attributed to the 405-kyr Milankovitch parameter (long orbital eccentricity) during the late Pennsylvanian. We hypothesize that late Pennsylvanian climate change, paced by orbital cycles, controlled the distribution and stacking pattern of mudstone chemofacies, which also controlled source rock quality and consequent pore system development.

Depositional Environment and Ecological Response of Bioconstructions: A Case Study of Southern China (Guizhou Province) in Moscovian-Gzhelian.

From the late Carboniferous to the early Permian, multiple pulses of glaciation and deglaciation have been caused by the LPIA. The Pennsylvanian period experienced phases of recovery, proliferation, and decline, ultimately forming a reef system distinctly different from that of the Mississippian period. During the late Bashkirian to Moscovian, the metazoan reef experienced a limited resurgence, with reef predominantly formed by chaetetid developing in the United States, northern China, and Japan. During the Kasimovian to Gzhelian, the phylloid algal reef dominated the global reef systems. In the late Pennsylvanian, bioconstruction cases and paleoenvironmental proxies in southern Guizhou Province were studied to investigate the composition, recovery, and evolutionary processes of the bioconstructions as well as their response to environmental variations during this period. Several bioconstructions have been reported in the Lumazhai section of Houchang Town, Guizhou Province, southern China, from the Moscovian to the Gzhelian. The upper Carboniferous strata are well-preserved and continuously exposed. The continuous strata, abundant fossils, and diverse bioconstructions provide excellent research materials for exploring the mutual constraints between organisms and their environment. This study identified ten microfacies, whose vertical evolution indicated significant changes in the depositional environment related to relative sea-level fluctuations. Skeletal grains are widely present in these facies. Among them, foraminifera, algae, bryozoans, crinoids, and Tubiphytes are the most common and exhibit distinct distribution characteristics in various environments. Quantitative statistics, CCA and theoretical ecospace have been utilized to examine and interpret environmental impact factors. Quantitative analysis of their relative abundance and distribution patterns provides insights into the complex interactions between organisms and environmental factors. The relative abundances of different organisms and factors controlling their bioconstructions are influenced by relative sea-level changes. CCA analysis reveal that hydrodynamic conditions are the primary influencing factor. Variation trends in average tiering and motility reveal the characteristics of biological communities during environmental changes in phylloid algae and microbial bioconstructions. These bioconstructions are not directly correlated with changes in environmental factors, and the biological communities in phylloid algae mounds and biostromes exhibit similar organism compositions and ecological niches across different environments.

Eccentricity control on fluvial sedimentation in the tropics during the Middle-Late Pennsylvanian icehouse (∼306–314 Ma, Upper Silesian Basin)

Far-field effects of the Late Paleozoic glaciation (∼340–260 Ma) recorded in well-dated stratigraphic intervals of the Pangea can be instrumental in detecting the short-term variability of icehouse climate and deconvolving the climate mechanisms. This study examines the Cracow Sandstone Series (CS), which provides a snapshot of the Middle to Late Pennsylvanian (∼306–314 Ma) fluvial sedimentation in the eastern equatorial Pangea (Upper Silesian Basin, ∼2°N paleolatitude). Spectral estimates of borehole lithological data suggest predominant ∼100-kyr eccentricity pacing of coal-bearing fluvial cycles and persistence of this pattern across the onset of Late Pennsylvanian aridification. The immediate climatic and depositional controls involve changes in seasonal precipitation along the Intertropical Convergence Zone and resulting fluctuations in sediment input. The prominence of eccentricity pacing and suppression of precession-scale variability in the fluvial environment contrasts with the frequency spectra of seasonal insolation series – an issue comparable to the “100-kyr problem” of the Late Pleistocene. The traditional explanation considers the eccentricity component being imposed as a far-field response to glaciation, analogous to the Pleistocene carbon-cycle feedback. Here we propose an alternative possibility that calls upon time-integrated insolation at the equator and the role of semi-annual wet/dry cyclicity in transferring variance from precession-scale insolation changes to the modulating eccentricity term. Autogenic processes in the fluvial system might have participated in “shredding” the precessional and semi-precessional signals. The alternative scenario is decoupled from high-latitude climate and would imply a muted climate sensitivity of the eastern equatorial Pangea to glaciation. The individual options cannot be evaluated with the Upper Silesian data alone, but offer testable hypotheses, potentially helpful in revealing the short-term structure of glaciation and climate teleconnections during the Late Paleozoic.

COMPOUND CLINOFORM MODEL FOR TIDAL-INFLUENCED DELTAS IN THE MIXED SILICICLASTIC-CARBONATE CISCO GROUP, VIRGILIAN (GZHELIAN), EASTERN SHELF OF THE PERMIAN BASIN, U.S.A.

Deltas in the Cisco Group contain significant volumes of potential reservoir sandstones in the Late Pennsylvanian (Virgilian/Gzhelian) mixed siliciclastic-carbonate succession in the Eastern Shelf of the Permian Basin. While early studies predominantly supported a river-dominated model for these deltas, our findings establish the presence of tide-influenced deltas characterized by the following features: (i) predominant heterolithic lithology; (ii) diagnostic structures such as flaser bedding, bidirectional ripple cross-lamination, or double-mud drapes; (iii) an abundance of interpreted fluid muds; and (iv) elongated bars on the subaqueous platform. Through analysis of 290.2 m of core, we identify six (6) facies associations related to tide-influenced deltaic systems in highstand and falling-stage intervals of the proximal Eastern Shelf: lower-delta-plain/embayed tidal flat, distributary channel and distributary mouth bar/delta front deposits on the subaerial delta; subaqueous delta platform, subaqueou s delta foreset, and prodelta deposits on the subaqueous delta. Moreover, two (2) additional facies associations, transgressive shelf deposits, and subtidal shallow-water carbonates, record continuous episodic transgressions within the deltaic packages. Well-log cross sections reveal repetitive stacking of deltas, typical of icehouse systems, and sandstone mapping suggests elongated tidal bars forming the interpreted subaqueous delta platforms. These features suggest a compound clinoform morphology of the Cisco Group deltas akin to modern tide-influenced deltas that have carbonate banks such as the Gulf of Papua. This compound clinoform morphology has implications for the elongate geometry and isolation of sandstone reservoirs, impacting fluid migration and storage. Moreover, these insights extend beyond the Cisco Group to other Pennsylvanian and Permian levels on the Eastern Shelf, as well as to other deltas in mixed siliciclastic-carbonate systems in icehouse conditions.

Wappleria tremoris gen. et sp. nov. the first representative of the insect order Caloneurodea in Spain (León, NW Spain) found in a Late Carboniferous forest

ABSTRACT We present a new genus and species of Caloneurodea from the Gzhelian (Stephanian B) of El Bierzo coalfield, in NW Iberian Peninsula (León, Spain) belonging to an uncertain family. Wappleria tremoris gen. et sp. nov. is described on the basis of a new specimen found in the Stephanian B strata of Casilda Mine, of Gzhelian age (Late Pennsylvanian, Late Carboniferous). The extinct order Caloneurodea (superorder Archaeorthoptera) is really scarce worldwide, it was previously found in the Carboniferous and Permian of Europe, North America, and Asia. This new specimen represents the first evidence of the order Caloneurodea from Spain, and the second record from the Iberian Peninsula, filling a gap in the Carboniferous palaeogeographical puzzle of this species in Europe. Little is known about the ecology and general biology of Caloneurodea. Nevertheless, Wappleria tremoris gen. et sp. nov. was found in close association with a rich palaeobotanical assemblage, dominated by pteridophytes, pteridospermatophytes, and gymnosperms, suggesting that W. tremoris could show a preference for forests under humid conditions.

Revisiting Late Pennsylvanian (Kasimovian) Corals of Egypt: New perspectives and contributions

Revisiting Late Pennsylvanian (Kasimovian) Corals of Egypt: New perspectives and contributions

Influence of Late Carboniferous–Early Permian climate change on the sedimentary evolution – a case study of the lacustrine Lower Anthracosia Shales (Intra-Sudetic Basin, SW Poland)

The Anthracosia Shales are lacustrine deposits within the volcano-sedimentary Pennsylvanian– Lower Permian succession of the Intra-Sudetic Basin. Core from the Rybnica Leśna PIG 1 borehole, which penetrated the Lower Anthracosia Shales, was analysed to explore the influence of climate on the evolution of the palaeolake, as distinct from tectonic and volcanic forcing. This reconstruction was made using mineralogical and geochemical proxies (elemental and mineralogical composition, TOC values, presence of framboidal pyrite and siderite). Based on the results, three chemically different intervals previously introduced by Wójcik-Tabol et al. (2021) are described. They represent the following stages of lake evolution: transgression (interval I), open lake (interval IIA and IIB), and termination (interval IIC and III). The initial stage of the lake (interval I) was probably related to a rise in humidity in the Late Pennsylvanian, linked to a southern Gondwana interglacial episode. Interval IIA represents the deepest facies of the Anthracosia Basin, where lake-floor anoxia prevailed. This stage was followed by a gradual lake-level fall recorded in interval IIB, with documented seasonality in humid and warm conditions. Interval IIC represents a stepwise lake regression attributed to aridification, as indicated by proxies showing a decrease in chemical weathering. Turbiditic sandy laminae in interval III reflect the terminal stage of lake infill.

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.

The late Serpukhovian-earliest Moscovian flora from westernmost Gondwana

Late Serpukhovian-earliest Moscovian floras are well represented in central-western Argentina by the Nothorhacopteris-Botrychiopsis-Ginkgophyllum (NBG) Biozone. These diverse plant remains have been recognised since the end of the last century from glacial and postglacial deposits of the Paganzo Group. However, the palaeoflora composed of at least thirty-two fossil species has not been fully documented until today, including reproductive structures of significant taxonomic value. Radiometric U–Pb ages of 319.57 ± 0.09 Ma and 312.82 ± 0.11 Ma constrain the stratigraphic interval where these assemblages flourished, making them one of the best-known Gondwanan palaeofloristic records of the late Palaeozoic Ice Age. This vegetation was replaced, with the incoming of common ferns and conifers, by the Krauselcladus-Asterotheca Biozone during the late Pennsylvanian. Recognising arborescent and subarborescent lycophytes, delicate fronds, permineralised stems, and abundant palynofloras enables vegetation reconstruction in this Gondwana region.

The Late Paleozoic Ice Age in western equatorial Pangea: Context for complex interactions among aeolian, alluvial, and shoreface sedimentary environments during the Late Pennsylvanian – early Permian

The evolution of depositional environments in the Late Pennsylvanian-early Permian of the Paradox Basin in Utah, USA, is investigated through detailed sedimentological and high-resolution sequence stratigraphic analyses, in order to define a model of landscape evolution, to discuss the stratigraphic model, and to evaluate the significance of the cyclicity in the paleoclimatic context. Forty high-resolution cycles integrated in 15 minor and two major cycles are observed for the first time throughout the Late Pennsylvanian-early Permian units. A-three steps landscape evolution is recognized. First, the lower Cutler beds, mainly corresponded to a marine environment, with longshore bar, subtidal, tidal, mouth-bar, and with locally fluvial deposits. The upper part of the lower Cutler beds also contains an aeolian dune. Second, the Cedar Mesa Sandstone, corresponded to broad erg deposits which are present across the entire study area, whereas longshore bar, subtidal, mouth-bar, and some fluvial deposits are mainly preserved in the northern part of the studied area. Third, the Organ Rock Formation records decreasing aeolian dune field preservation. To the south, the aeolian environments are interbedded with shoreface deposits, whereas to the north, fluvial deposits with some mouth-bars are more developed. Semi-arid climatic conditions persisted, as indicated by the presence of calcretes. Everywhere in these three steps, root traces within sandstone bars indicate that a soil was once present above the sand dunes. This new model of landscape evolution documents complex interactions between aeolian, fluvial and marine environments within the entire Permian succession of the Paradox Basin. High-resolution stratigraphic analyses allow to discuss the significance of the cyclicity in a scenario that take into consideration sea-level variation in the Late Paleozoic Ice Age paleoclimatic context. This Late Pennsylvanian to early Permian succession reflects both relative sea-level fluctuations and the variability of sediment supply.

A multistage model of preservation in fossil plants from the Llewellyn Formation (Pennsylvanian), St. Clair, Pennsylvania, U.S.A

Exceptionally preserved plant fossils from St. Clair, Pennsylvania, have long been part of museum and private collections. Fossil leaf fragments and stems from the underclay of the Buck Mountain Coal (Reading Anthracite Company quarry), lowest Llewellyn Formation (late Pennsylvanian, Virgilian), combine outer layers of coalified organic material (phytoleim) with strikingly white kaolinite, quartz, and the low-grade metamorphic mineral pyrophyllite in the interior. The surficial dark, coalified material appears to preserve the dense outer layers (cuticle, epidermis, and palisade layer) and some cells of the spongy mesophyll in the fossilized leaves. XRD spectra of separated phytoleim contain graphite peaks. Raman spectra with peaks near 1600 and 1320 cm−1 indicate that the phytoleim is composed of disordered graphitic material. ID/IG ratios from ca. 0.3 to 0.45 are consistent with greenschist facies metamorphic conditions forming the anthracite coal. The interior pyrophyllite is highly crystalline, with large crystals often oriented perpendicular to leaf surfaces. Hydrothermal formation of pyrophyllite requires relatively limited groundwater flow conditions and temperatures between ca. 275 and 350 °C. Although many fossil leaves are compressed, some are near their original thickness. We infer that the remains were replaced prior to significant burial and compression of the sediment by an early-forming mineral phase, possibly pyrite, which was in turn replaced by kaolinite and then pyrophyllite at higher temperature and pressure. Woody structures such as cuticle and veins, which had resisted replacement by the initial low temperature phase, were coalified at higher temperatures.

About this title - Ice Ages, Climate Dynamics and Biotic Events: the Late Pennsylvanian World

The Middle through Late Pennsylvanian was a time of ice ages, climate dynamics and a turning point in terrestrial biotic evolution. This provides a laboratory for studying changes in a glacial world. This book focuses on a dynamic Late Pennsylvanian world that bears close comparison to the late Cenozoic world.

GEOBOTANICAL ANALYSIS OF PLANT FOSSIL ASSEMBLAGES FROM THE UPPER PENNSYLVANIAN LIMNIC DEPOSITS OF THE NORTHERN CAUCASUS

Analysis of plant fossil assemblages from the Upper Pennsylvanian deposits of the Northern Caucasus was carried out within the intervals, which are compared with the megafloral zones of the Stephanian of the Western European scale. The identification of the taxonomic composition and the interpretation of environments of the Late Pennsylvanian plant communities showed that the Northern Caucasus vegetation was represented by wetland and seasonally dry forests of river valleys. The wetland forests were composed of the calamitalean-fern and calamitalean-fern-pteridosperm communities of the shores of floodplain lakes and the lycopsid-calamitalean-fern-pteridosperm communities of floodplains. Throughout the Late Pennsylvanian (Stephanian and early Autunian), the most widespread taxa of wetland forests were lycophytes Subsigillaria brardii, calamitaleans with the stems of Calamites suckowii and the foliage of Annularia sphenophylloides, A. spinulosa, ferns Acitheca polymorpha, Cyathocarpus arboreus, C. cyatheus, ‘Pecopteris’ bredovii, Nemejcopteris feminaeformis, Diplazites unitus and pteridosperms Odontopteris brardii, Callipteridium gigas, C. pteridium, Pseudomariopteris cordato-ovata, Dicksonites sterzelii. The seasonally dry vegetation was widespread in the middle Stephanian (Stephanian B) and the late Stephanian–early Autunian (Stephanian C–early Autunian) and composed of the pteridosperm-conifer communities of river valley slopes. In the middle Stephanian, the drought-tolerant plants were represented by pteridosperms Odontopteris subcrenulata, Sphenopteridium cf. germanicum, Taeniopteris jejunata, cordaitaleans Cordaites sp. and conifers Walchia piniformis, Culmitzschia frondosa. In the late Stephanian–early Autunian, the seasonally dry vegetation of the river valley slopes included pteridosperms Autunia conferta, Dichophyllum flabelliferum, Sphenopteridium germanicum, Taeniopteris jejunata, conifers Walchia piniformis, Otovicia hypnoides and cordaitaleans Cordaites sp.

Chemotaxonomy, biomechanics, and paleophysiology of Alethopteris ambigua and Neuropteris ovata var. simonii (Late Pennsylvanian, Canada). A chemometric approach

Medullosales was a highly diverse and ecologically differentiated group of plants that flourished in the Late Carboniferous and Early Permian tropical wetlands of Euramerica and China. Although the Medullosales have been extensively studied, some aspects of their life habits are still not fully understood. This study focuses on the relationships between chemical composition and biomechanical /physiological characteristics of the two largest-known frond segments of Alethopteris ambigua (45 cm long) and Neuropteris ovata var. simonii (65 cm long) from the Late Pennsylvanian of the Sydney Coalfield, Canada. Additionally, this study provides new data obtained from Fourier transform infrared spectroscopy (FTIR) analysis that, in conjunction with morphological features, could be used to efficiently distinguish species and genera of fossil plants. The density of the different frond parts is calculated using a 3D multivariate model derived from FTIR data. Tensile strength, tensile modulus of elasticity, flexural stiffness, and leaf mass per area for the different frond parts are estimated using trait relationships linking density and structural properties established for modern plant-leaf tissues. Key results include the cognition of continuous variation of geomacromolecular compounds throughout the different-order rachises and pinnules from proximal to distal frond sections. In the proposed, theoretical fronds, these diagenetically-modified biomacromolecules would represent tannin-, lignin-, and resin-related compounds. Overall, pinnules and rachises of A. ambigua are characterized by high contents of aliphatic-rich structures, whereas those of N. ovata are mostly aromatic in composition. The chemical composition of the two fronds is hierarchically partitioned, indicating density dependence on the frond parts. This is reflected in the metabolic construction costs that, in the two species, differ significantly among pinnules and rachises. These results indicate “flexibility” of resource allocation, resulting into two different, architectural frond designs. The costs of building harder, stiffer, and more expensive pinnules in the N. ovata frond are compensated for by the metabolically inexpensive rachises. The opposite holds for the A. ambigua frond, i.e., relatively cheaper pinnules and more expensive rachises. This reveals the complexity of the biomechanical and physiological strategies employed by these two taxa to construct mechanically resistant and physiologically efficient, longer-lived fronds. Results suggest that these plants were likely stress-tolerant and opportunistic colonizers that dominated eutrophic habitats, which were typical of some tropical ecosystems of the Late Pennsylvanian.

High-precision U-Pb geochronology and Bayesian age-depth modeling of the glacial-postglacial transition of the southern Paraná Basin: Detailing the terminal phase of the Late Paleozoic Ice Age on Gondwana

The timing of the terminal deglaciation of the Late Paleozoic Ice Age – LPIA in the Paraná Basin has been under investigation. However, the low availability of high-precision radioisotopic ages prevents the construction of a detailed chronostratigraphic framework necessary to constrain the demise of the glaciation and perform correlation with contemporaneous records across neighboring basins and within the extensive Paraná Basin. This study aims to contribute to the chronostratigraphic detailing of the Carboniferous-Permian succession of the southern Paraná Basin, interval preserving LPIA glacial-postglacial transition. Therefore, we document new high-precision U-Pb radioisotopic ages and reexamine previously published samples through single crystal chemical abrasion, isotope dilution-thermal ionization mass spectrometry (CA-IDTIMS). We integrate all high-precision radioisotopic ages into the first Bayesian age-depth models for the late Carboniferous-early Permian succession recorded in the southern Paraná Basin. Age-depth models were performed on DU-08-RS and HN-120-RS drill cores, located in the Capané and Candiota paleovalleys, respectively. The weighted mean 206Pb/238U date for the Rio Bonito Formation are 297.914 ± 0.10 (T6), 297.495 ± 0.11 (HN), 296.796 ± 0.114 (T1), 296.293 ± 0.098 (T1.5), 296.252 ± 0.117 (T2), and 296.148 ± 0.136 Ma (RB). For the Itararé Group sample, the weighted mean date is 301.809 ± 0.224 Ma (ITA). T1 and T2 high-precision ages turned out to be older than LA-ICP-MS ages published before (Cagliari et al., 2014), and RB and ITA ages younger (Cagliari et al., 2016). Age-depth models constraints the Rio Bonito Formation between Gzhelian and Sakmarian stages, encompassing ~6.9 and ~1.6 Myr in cores DU-08-RS and HN-120-RS, respectively. The results demonstrate that the successions of the Rio Bonito Formation recorded in Capané and Candiota paleovalleys are contemporaneous. They also corroborate to assign the final glaciation to the early Gzhelian (Late Pennsylvanian) and to place the Carboniferous-Permian boundary within the Rio Bonito Formation, in the study area.

Redefinition of the Petersburg batholith and implications for crustal inheritance in the Dinwiddie terrane, Virginia, USA

Field relations as well as geochemical and petrologic studies of meta-igneous rocks assigned to the Pennsylvanian–Permian Petersburg batholith identify at least two distinct rock types: foliated metagranitoid gneiss and massive to porphyritic granite. Foliated metagranitoid gneiss of mostly granodioritic composition is geochemically distinct from associated massive and porphyritic granitic rocks. These gneissic rocks yield radiometric ages from ca. 425 Ma to ca. 403 Ma and document that many of the rocks assigned to the late Paleozoic Petersburg batholith are 100 m.y. older than the youngest portions of the composite batholith and are part of an earlier infrastructural terrane. Two samples of massive equigranular granite southwest of Petersburg, Virginia, yield ages of ca. 321 Ma and ca. 317 Ma, which are 15–20 m.y. older than ca. 300 Ma ages for porphyritic granite, massive granite, and monzodiorite near Richmond, Virginia. Geologic mapping shows that the Early Pennsylvanian granite southwest of Petersburg is separated from Late Pennsylvanian to early Permian granite near Richmond by a map-scale septum of Silurian–Devonian foliated metagranitoid gneiss, referred to herein as the informal Pocoshock Creek gneiss. Laser ablation–inductively coupled plasma–mass spectrometry data from one sample of a quartz-muscovite felsic schist xenolith show a peak age mode of ca. 529 Ma that we interpret to be the maximum depositional age. Inherited zircons from foliated metagranitoid gneiss and massive equigranular granite range from ca. 631 Ma to ca. 376 Ma, but many are Cambrian. Neoproterozoic–Cambrian quartz-muscovite felsic schist and amphibolite, Silurian–Devonian Pocoshock Creek gneiss, and Pennsylvanian–Permian granite comprise a fault-bounded terrane referred to herein as the Dinwiddie terrane. Ages of inherited cores in zircon from igneous rocks and limited detrital zircon geochronology suggest the terrane is of peri-Gondwanan affinity. U/Pb ages of healed fractures in zircon grains from foliated metagranitoid gneiss indicate low-grade deformation of the gneiss at ca. 378–376 Ma, while ca. 320–280 Ma rims on many grains record intrusion of late Paleozoic granite. The temperature-time-deformation history of the Dinwiddie terrane is distinct from the adjacent Goochland and Roanoke Rapids terranes. Orogen-scale dextral transpression likely translated the Dinwiddie terrane southward during the Alleghanian orogeny, at which time they were intruded by Pennsylvanian to Permian granite.

Tectonic and stratigraphic evolution of the late Paleozoic Darwin Basin, eastern California, USA, and implications for the onset of subduction along the southwestern Cordilleran margin of Laurentia

The Darwin Basin, eastern California, USA, represents a key sedimentary record of tectonics along the southwestern margin of Laurentia for the late Pennsylvanian and Cisuralian (Early Permian). The basin formed when the subsidence rate of the southwestern margin of the Bird Spring Shelf abruptly increased, resulting in the deposition of deep-water facies in areas that had been shelf or littoral environments since the Neoproterozoic. We present new sedimentologic, stratigraphic, conodont biostratigraphic, and subsidence analyses of Darwin Basin strata that document the Pennsylvanian−Permian evolution of the Darwin Basin. We argue that the Darwin Basin evolved in two phases: (1) a Pennsylvanian to mid-Cisuralian foreland basin phase that co-occurred with transpressional deformation of the southwestern margin of Laurentia and was characterized by unconformity development, deposition of coarse-grained carbonate slope-apron facies, syndepositional deformation, and the development of complex basin-floor bathymetry; and (2) a mid-Cisuralian to Guadalupian (middle Permian) phase that preceded and co-occurred with the onset of arc magmatism outboard of the Darwin Basin and is characterized by rapid, uniform subsidence of the entire basin, burial of paleobathymetric highs, and the end of syndepositional deformation. We propose that the transition between these phases may represent a local response to the initiation of the North American Cordilleran subduction zone to the west of the Darwin Basin. We argue that the onset of rapid mid-Cisuralian subsidence documented within the Darwin Basin provides an estimated date of subduction zone initiation that is consistent with previous estimates of the timing of this event, the arc magmatic record, and Cenozoic subduction zone analogs.