Tropical Pangaea Research Articles

Depositional environments and plant communities in the exceptional context of the Kungurian megacaldera of the Athesian Volcanic Group (Southern Alps, N-Italy)

We used a combined approach (lithofacies and palynology) and multivariate analyses to reconstruct the different depositional environments and changes in the plant communities throughout the middle to late Kungurian in the tropical Pangea. The late Paleozoic terrestrial biotas underwent changes under the pressure of a general aridification trend and a warming event that changed biota composition favoring drought-tolerant taxa during the Artinskian. Few studies integrate the different terrestrial ecosystem components to reconstruct palaeoenvironments and climate changes throughout the Cisuralian (early Permian). We analyzed several sedimentary successions of different stratigraphic positions intercalated in well-dated volcanic units of the megacaldera of the Athesian Volcanic Group (Southern Alps, northern Italy). The obtained palynofacies and quantitative sporomorph records with an exceptional high resolution (∼10 Ma) evidence a palaeoenvironmental/climatic change in the plant communities from the middle to the late Kungurian. The late Kungurian shows a higher diversity in the plant communities with a dominance of seed ferns and a higher relative abundance of xeromorphic-hygromorphic sporomorph taxa. This suggests the presences of more stable and putatively more humid environmental conditions in respect to the middle Kungurian. Furthermore, a direct comparison between lithofacies and all primary components of the palynofacies assemblages permits to characterize lacustrine and alluvial depositional environments since these studies are underrepresented for terrestrial environments.

First Fossil Record of Trichomanes sensu lato (Hymenophyllaceae) from the Mid-Cretaceous Kachin Amber, Myanmar.

Hymenophyllaceae (filmy ferns), with ca. 430 species, are the most species-rich family of early diverging leptosporangiate ferns but have a poor fossil record dating back to the Late Triassic period. Traditionally, Hymenophyllaceae comprise two species-rich genera or clades: Hymenophyllum (hymenophylloids) and Trichomanes sensu lato (s.l.) (trichomanoids). Unequivocal fossils of Hymenophyllum have been reported from the Early Cretaceous of central Mongolia and the early Eocene of Okanogan Highlands, Washington, USA. However, despite being a highly diversified lineage with an estimated 184 extant species, Trichomanes s.l. lack a definitive fossil record, which severely affects the reliability of the molecular dating of this group. Here, we report the first unequivocal fossil record of Trichomanes s.l. as T. angustum comb. nov. on the basis of fertile material with tubular involucres and long exserted receptacles from the mid-Cretaceous Kachin amber, Myanmar. This species was previously tentatively assigned to Hymenophyllites due to a lack of fertile evidence. Inferred to be an epiphytic fern, T. angustum further enriches the species diversity of the epiphytic palaeocommunities in the mid-Cretaceous Kachin amber, which are mainly composed of Porellalean leafy liverworts and Dicranalean and Hypnodendralean mosses. Fossil records indicate that Hymenophyllaceae probably originated in the tropical Pangea at the latest in the Triassic when all continents were coalesced into a single landmass and had already accumulated some notable diversity in low-middle latitude areas of Laurasia by the mid-Cretaceous period.

Pennsylvanian-age plant macrofossil biostratigraphy in tropical Pangaea: uniformitarianism, catastrophes and the ‘Cantabrian’ problem

Abstract Upper Carboniferous stages in terrestrial strata are consistently recognizable throughout the Euramerican Realm based on the ranges of plant macrofossils rather than named biozones. Uniformitarianism is an invaluable principle used to understand much of Earth's history. However, it has been recognized that relatively short time intervals exist when major changes occurred in the biota and sedimentation style at a non-uniformitarian time scale. Many well-defined Upper Carboniferous stage boundaries are located at such events. The Cantabrian Stage was proposed in 1969 based on the assumption that the ‘Florensprung’ (‘floral jump’) of Gothan, a dramatic change in terrestrial floras at the traditional Westphalian–Stephanian boundary, indicated that strata were missing, and the postulated ‘gap’ had to be closed by finding strata representing this ‘missing’ time elsewhere. The suggestion of a ‘gap’ or hiatus at this level reflects uniformitarian thinking, but is incorrect. As recent work has shown that a drastic climatic change reached a threshold in the tropical palaeoequatorial parts of Pangaea at the Westphalian–Stephanian (approximately the Moscovian–Kasimovian) boundary as a consequence of a drying trend, floras changed rapidly, and the traditional Westphalian–Stephanian boundary is thus one of the most easily recognizable biostratigraphic boundaries in Pennsylvanian terrestrial beds. The Cantabrian Stage, proposed to fill the non-existent gap, does not exist and cannot be recognized, either in its type area or elsewhere.

Middle–Late Pennsylvanian tectonosedimentary, climatic and biotic records in basins of Europe, NW Turkey and North Africa: an overview

Abstract In Europe, North Africa and Asia Minor, the remains of Pennsylvanian sedimentary basins bearing continental deposits either intimately mixed with shallow-marine strata or deposited in exclusively continental settings are preserved. Long-lasting research on these basins allowed the definition of regional stages and substages based on marine fauna and terrestrial flora, later extended by terrestrial and freshwater faunal biostratigraphies. Glacioeustatically driven marine bands provide laterally widespread correlation markers; however, where such bands are missing only biostratigraphic control exists. Resolution of biostratigraphic zonations combined with gaps in sedimentary successions and variable quality of the fossil record throughout the basin fills do not allow in all cases a precise correlation between the Pennsylvanian basins in Europe and, in turn, the timing of tectonic, climatic and biotic events, and thus an absolute complete understanding of the response of terrestrial and freshwater biota to climate changes across eastern tropical Pangaea. A helpful tool is new radioisotopic ages of intercalated volcaniclastics that reveal the partial diachroneity of some widely used biostratigraphies. We attempt to present the current state of the art to stimulate further research to mitigate gaps in our knowledge.

Significant Contribution of Paleogeography to Stratospheric Water Vapor Variations in the Past 250 Million Years

Stratospheric water vapor (SWV) variations play an important role in influencing the Earth's energy budget. Here, we investigate the SWV variations in the past 250 million years (Myr) using a fully coupled Earth System Model. It is found that both CO2 concentration and paleogeography have prominent influences on the SWV variations, while solar insolation plays a minor role. The SWV increases with surface warming and stratospheric moistening rate is accelerated during the warm periods in the past 250 Myr except for the Pangea supercontinent stage. The ratio of stratospheric moistening to surface warming is smaller in the warm Pangea supercontinent stage compared to that during the warm Cretaceous Period, which is due to the ascending and consequent cooling of the tropical tropopause layer associated with the severe surface warming over the tropical Pangea supercontinent. Our results suggest that paleogeography is an important factor in regulating SWV variations in deep-time climate.

Modes of Pangean lake level cyclicity driven by astronomical climate pacing modulated by continental position and pCO2

Orbital cyclicity is a fundamental pacemaker of Earth's climate system. The Newark-Hartford Basin (NHB) lake sediment record of eastern North America contains compelling geologic expressions of this cyclicity, reflecting variations of climatic conditions in tropical Pangea during the Late Triassic and earliest Jurassic (~233 to 199 Ma). Climate modeling enables a deeper mechanistic understanding of Earth system modulation during this unique greenhouse and supercontinent period. We link major features of the NHB record to the combined climatic effects of orbital forcing, paleogeographic changes, and atmospheric pCO[Formula: see text] variations. An ensemble of transient, orbitally driven climate simulations is assessed for nine time slices, three atmospheric pCO[Formula: see text] values, and two paleogeographic reconstructions. Climatic transitions from tropical humid to more seasonal and ultimately semiarid are associated with tectonic drift of the NHB from [Formula: see text] to [Formula: see text]. The modeled orbital modulation of the precipitation-evaporation balance is most pronounced during the 220 to 200 Ma interval, whereas it is limited by weak seasonality and increasing aridity before and after this interval. Lower pCO[Formula: see text] at around 205 Ma contributes to drier climates and could have led to the observed damping of sediment cyclicity. Eccentricity-modulated precession dominates the orbitally driven climate response in the NHB region. High obliquity further amplifies summer precipitation through the seasonal shifts in the tropical rainfall belt. Regions with other proxy records are also assessed, providing guidance toward an integrated picture of global astronomical climate forcing in the Late Triassic and ultimately of other periods in Earth history.

Deep-scaled fish (Osteichthyes: Actinopterygii) from the lower Permian (Cisuralian) lacustrine deposits of the Parnaíba Basin, NE Brazil

The richly fossiliferous deposits of the Brazilian Pedra de Fogo Formation originated in an extensive aquatic system in tropical Pangaea, and grade from marginal lacustrine into marine deposits at the depocenter in the western part of the Parnaíba Basin. In addition to the well-known tetrapod and macrofloral records from these deposits, the Pedra de Fogo Formation yields extensive fish fossils indicating a diverse and abundant ichthyofauna. Among the actinopterygians, deep-bodied morphotypes are represented by whole fish as well as disarticulated dermal scales found at various localities in the states of Maranhão and Piauí. The gross morphology, ornamentation, and histology of some of these scales is highly distinctive, indicating the presence of a novel taxon (Piratata rogersmithii gen. et sp. nov.). The external surface of a Piratata scale is covered in multiple round-to-slightly elongated tubercles. The scale lacks a ganoin cover and is made up of cellular bone and odontocomplexes of orthodentine composing the tuberculated scale surface. The scale morphology and ornamentation most closely resemble that of Cleithrolepis granulatus from the Triassic of Australia and Cleithrolepis extoni from the Triassic Stormberg Beds of South Africa, but the new taxon differs from previously described species in several diagnostic morphological features. The use of scale characters in the taxonomy of ray-finned fishes and the palaeogeographic, palaeoenvironmental, and geochronological implications of the new taxon are discussed.

A new species of Lesleya (Spermatopsida) from the Carboniferous of Iberia and its palaeoecological and evolutionary significance

ABSTRACT Plant adaptations to environmental and climatic changes in Pangaean intramontane basins are poorly understood. Here, we document a previously unknown primitive gymnosperm species, Lesleya ceriacoi sp. nov., from the Douro Carboniferous Basin (DCB; lower Gzhelian, Upper Pennsylvanian; NW Portugal) of the Variscan Iberian Massif (Iberia). This new species is described from a 303 million-years-old fossil rediscovered at the U.Porto’s Herbarium PO, stored at the Museu de História Natural e da Ciência da Universidade do Porto (MHNC-UP; Portugal). L. ceriacoi sp. nov. displays an exquisite leaf shape with morphological traits adapted to specific ecological conditions of the DCB. These leaf morphological traits comprise toothed and dissected margins, which represent specialised adaptations to drier (xerophytic) conditions of the DCB during the Gzhelian (ca. 304–299 Ma), at the end of the Late Pennsylvanian. The xeromorphic traits of the new species represent an evolutionary novelty for the Pennsylvanian Euramerican dry-climate adapted floras, and are evidence of evolutionary adaptation to environmental and climatic change in intramontane basins like DCB within central tropical Pangaea. Such an adaptation occurred during an interval of wet to dry climate transition after the end of one late Palaeozoic Gondwana Ice Age (glaciation) in Gzhelian time.

New petrified calamitaleans from the Permian of the Parnaíba Basin, central-north Brazil, part III, with some concerns regarding anatomical features of Paleozoic petrified sphenophytes

A new petrified calamitalean is described from the Permian Motuca Formation, Parnaíba Basin, central-north Brazil. In contrast to all other three-dimensionally preserved Brazilian species, it represents a semi-self-supporting woody plant characterized by a distinctive branch system and cellular anatomy. Arthropitys buritiranensis sp. nov. is proposed to accommodate the new material. The branch architecture is composed of at least three types of branches: (i) principal woody side branches, (ii) up to three secondary woody branches per node, scattered along the stem or the principal side branches, and (iii) 8–11 leafy twigs per whorl, at every third, rarely the second node, without secondary growth. The wood is segmented into fascicular wedges and interfascicular rays, clearly visible only within the inner wood of the stem and woody branches. The tracheid walls of the secondary xylem have exclusively scalariform pits. Ray parenchyma cells have pitted horizontal walls. The new calamitalean was part of the riparian vegetation of tree ferns, calamitaleans and gymnosperms recorded in a distal fluvial plain setting. The wood shows irregular growth interruptions and, therefore, points to a seasonally dry climate that shaped even low latitude paleofloras of tropical Pangaea.

The environmental implications of upper Paleozoic plant-fossil assemblages with mixtures of wetland and drought-tolerant taxa in tropical Pangea

We evaluate the influences of elevation and climate on the spatio-temporal distribution of wetland and dryland biomes during the Pennsylvanian and early Permian in tropical Pangea. The longstanding “upland model” places drought-tolerant vegetation in elevated habitats, where slope and drainage created moisture-limited substrates under a humid climate that simultaneously promoted peat accumulation in contemporaneous lowlands. Upland plants were periodically transported to, and buried in, lowlands. Rare preservation of dryland vegetation thus reflects its general absence in basins, and taphonomic vagaries of long-distance transport. The alternative “climate model” proposes that drought-tolerant plants dominated tropical habitats when climate was seasonally dry, with wetland vegetation reduced to scattered refugia. Environmental changes attending glacial-interglacial cycles caused alternating wetter-drier conditions, and the relative abundance of wetland versus dryland biomes in basinal lowlands thus varied with climatic oscillations. The paucity of drought-tolerant plants reflects a preservational megabias against habitats with seasonal moisture deficits.The environmental signal of “mixed” plant-fossil assemblages, comprising taxa characteristic of both wetland and dryland biomes, may help resolve these debates. We review key Pennsylvanian and lower Permian mixed assemblages from tropical Euramerican Pangea, and interpret their original habitats and climatic contexts based on multidisciplinary lines of evidence, including sedimentology, taphonomy, physiology, and paleoecology. Evaluations also consider patterns of vegetational distribution and taphonomy in modern tropical environments. We suggest that even a cursory view of current tropical plant distribution exposes flaws in the upland model. Where tropical climate is sufficiently humid to support peat swamps, slopes and elevated habitats do not host drought-tolerant vegetation, but are occupied by plants similar to those in lowland settings. This occurs because equable, high precipitation strongly dampens water-table variation across entire landscapes. Furthermore, taphonomic studies indicate that most plant-fossil assemblages record vegetation living near the burial site. Fossil floras thus reflect environmental conditions near their growth site, excluding an upland origin for most occurrences of drought-tolerant taxa. Conversely, the climate model is consistent with modern tropical vegetational distribution and soundly explains late Paleozoic floristic patterns. When Pangean tropical lowlands experienced seasonally dry conditions, plants tolerant of moisture deficits dominated most habitats, whereas wetland vegetation was restricted to wetter sites with greater preservation potential. This occurred because topographic variations are magnified under seasonal precipitation regimes, creating a complex habitat mosaic with wetland patches in a landscape subject to seasonal drought. Accordingly, we propose that a macrofloral assemblage with even rare drought-tolerant taxa indicates seasonality in the broader landscape.At larger spatio-temporal scales, disagreement also persists about whether tectonic uplift or long-term climatic drying was the primary driver of changes in late Paleozoic floristic patterns and areal extent of tropical peat swamps. We argue that tectonic activity alone cannot explain the drastic reduction in peat swamps or coincident changes in dominance-diversity of wetland vegetation. Rates of plant dispersal and evolution far outpace that of mountain building, and peat-forming wetlands persisted in elevated habitats well into the Late Pennsylvanian. Therefore, progressive late Paleozoic aridification was the most probable driver of changing floral patterns and the distribution of wetland and dryland biomes in tropical Pangea.

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.

A new U–Pb zircon age and a volcanogenic model for the early Permian Chemnitz Fossil Forest

The Chemnitz Fossil Forest depicts one of the most completely preserved forest ecosystems in late Paleozoic Northern Hemisphere of tropical Pangaea. Fossil biota was preserved as a T0 taphocoenosis resulting from the instantaneous entombment by volcanic ashes of the Zeisigwald Tuff. The eruption depicts one of the late magmatic events of post-variscan rhyolitic volcanism in Central Europe. This study represents a multi-method evaluation of the pyroclastic ejecta encompassing sedimentological and (isotope) geochemical approaches to shed light on magmatic and volcanic processes, and their role in preserving the fossil assemblage. The Zeisigwald Tuff pyroclastics (ZTP) reveal a radiometric age of 291 ± 2 Ma, pointing to a late Sakmarian/early Artinskian (early Permian) stratigraphic position for the Chemnitz Fossil Forest. The initial eruption was of phreatomagmatic style producing deposits of cool, wet ashes, which deposited from pyroclastic fall out and density currents. Culmination of the eruption is reflected by massive hot and dry ignimbrites. Whole-rock geochemistry and zircon grain analysis show that pyroclastic deposits originated from a felsic, highly specialised magma, which underwent advanced fractionation, and is probably related to post-Carboniferous magmatism in the Western Erzgebirge. The ascending magma recycled old cadomic crust of the Saxo-thuringian zone, likely induced by a mantle-derived heat flow during a phase of post-variscan crustal delamination. Geochemical trends within the succession of the basal pyroclastic horizons reflect inverse zonation of the magma chamber and provide evidence for the continuous eruption and thus a simultaneous burial of the diverse ecosystem.

Paleosols of the upper Paleozoic Sangre de Cristo Formation, north-central New Mexico: Record of early Permian palaeoclimate in tropical Pangaea

The lower Permian (Wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial plain. Locally, mudstones display a variety of pedogenic features. Common mudstone fabrics vary from platy to prismatic; some beds display prominent pedogenic slickensides. Drab-colored root traces are common throughout the section, as are calcareous nodules, which vary from small bodies with diffuse boundaries to vertically stacked, discrete, cm-scale nodules (rhizocretions), and less commonly form coalescing horizons. Vertisols occur only in the lower portion of the ca. 90-m measured section. Most of the mudstone beds contain calcretes that are immature (calcic Protosols to calcic Argillisols), but the lower to middle portion of the section also contains mature calcrete horizons (argillic Calcisols and Calcisols).Intercalated micritic limestone beds with sharp contacts containing root traces, are of laterally variable thickness and grade to nodular calcretes. These are interpreted as floodplain pond carbonates that have undergone pedogenic alteration (palustrine limestones), indicating long periods of exposure under strongly seasonal climatic conditions. The isotopic composition of the pedogenic carbonate displays a substantial range of values, but most of the range of variation in isotopic composition is accounted for by isotopically heavier carbonate (both carbon and oxygen) precipitated in shallow ponds subject to intense pedogenic reworking (palustrine carbonate).During the early Permian, northern New Mexico was situated in a near equatorial position (ca. 4° N). The overall character of the paleosols suggests a persistent warm, semi-humid, seasonal climate throughout most of the interval of deposition during the Wolfcampian, but with episodically increased aridity during formation of the more mature calcretes. No long-term trend of climate change is evident in the stratigraphic section examined for this study.

A 25 million year macrofloral record (Carboniferous–Permian) in the Czech part of the Intra-Sudetic Basin; biostratigraphy, plant diversity and vegetation patterns

The Intra-Sudetic Basin is essentially a post-orogenic (Variscan) continental basin with a depositional history that ranges from the late Viséan to the Triassic. The fossil record in the Czech part of the basin, although discontinuous, spans the interval from the late Viséan to the Asselian. Middle Baskhirian (late Namurian) to Asselian adpression floras collected from boreholes, coal mines and outcrops permit reconstruction of the stratigraphic ranges of individual species in considerable detail, and reveal changes in plant diversity and vegetation patterns throughout this ~25Myr interval at high resolution, even to the scale of individual coal-bearing cycles. Species diversity recorded in the rock record throughout the studied interval mainly was controlled by climatically-driven potential for preservation of plant material, which was highest in poorly drained/waterlogged habitats (wetlands, lakes) concentrated in basinal lowlands and representing major windows of preservation. Low fossilization potential is typical for well-drained fluvial habitats, now represented by red beds deposited under drier (seasonal) climate. Diversity in major windows of preservation was highest during the late Langsettian and Duckmantian (>50 species), lower in the Late Pennsylvanian (25–40 species) and the lowest in the Asselian (~20 species). The diversity in red bed intervals with poor preservation potential varies between 11 and 21 species. The two distinct habitat types, with high and low preservation potential, were dominated by different plant groups. Wetland habitats flourishing during the (per)humid to slightly seasonal intervals were colonized mainly by cryptogamic plants and some early gymnosperms, mainly pteridosperms and cordaitaleans. Habitats represented by red beds were dominated by cordaitaleans; from late Asturian time walchian conifers also occurred in these plant assemblages. However, conifers only became common in red beds in the Cantabrian. In the Saberian, conifers are rarely found in discrete beds associated with coal-bearing strata, however, their common occurrences start in lacustrine rocks of Asselian age. Temporal changes in vegetation patterns that show an increasing proportion of gymnosperms, in both wetland and dryland habitats are in agreement with the well known aridification trend in late Paleozoic tropical Pangea. Delays between the first appearance of walchian conifers in red beds (late Asturian) versus coal-bearing deposits (Saberian) supports the hypothesis that evolutionary innovations took place outside the windows of preservation, i.e. in well-drained, moisture-deficient areas.

Reply to the comment on “Chronostratigraphy and paleoclimatology of the Lodève Basin, France: Evidence for a pan-tropical aridification event across the Carboniferous–Permian boundary” by Michel et al., (2015). Palaeogeography, Palaeoclimatology, Palaeoecology 430, 118–131

Michel et al. (2015) present new radioisotopic age estimates coupled with paleosol data from the Lodève basin, France that indicate a Pennsylvanian–Permian trend toward aridity that is similar to trends seen in other western equatorial basins across tropical Pangaea. In their comment, Pochat and Van Den Driessche (2015) call into question these newly published U-Pb zircon chemical-abrasion isotope dilution thermal ionization mass spectrometry (CA-IDTIMS) age estimates from volcanic ash layers preserved within the Lodève Basin. Furthermore, Pochat and Van Den Driessche (2015) reject our assertion that the rates of sediment accumulation for the Carboniferous–Permian strata in the Lodève basin are in need of recalculation as a result of the new geochronological dates. Finally, Pochat and Van Den Driessche (2015) suggest that the paleosol data presented in Michel et al. (2015) do not provide meaningful proxies of paleoclimate change, and reassert the position presented in Pochat and Van Den Driessche (2011) that sedimentary strata are not strongly affected by paleoclimatic change compared with the influence of tectonic processes of the Lodève basin.

Early Pennsylvanian (Langsettian) fish assemblages from the Joggins Formation, Canada, and their implications for palaeoecology and palaeogeography

AbstractA review of all available specimens of fossil fishes from the classic Pennsylvanian Joggins locality of Nova Scotia, Canada, reveals the existence of a diverse community of chondrichthyans (xenacanthids, ctenacanthids and the enigmatic Ageleodus), acanthodians (gyracanthids), sarcopterygians (rhizodontids, megalichthyids, rhizodopsids and dipnoans) and actinopterygians (haplolepids). Reassessment of supposed endemic species (Ctenoptychius cristatus, Sagenodus plicatus, Gyracanthus duplicatus) indicates they are invalid, and overall, the assemblage comprises cosmopolitan taxa that were widespread around the coasts of tropical Pangaea. Strontium isotope analysis of fish remains and a critical study of their facies context suggest that these fish communities occupied bodies of water with salinities across the marine–freshwater spectrum. This preponderance of euryhaline forms implies a community structure quite distinct from that of today and might represent a transitory phase prior to the establishment of fully freshwater fish communities. Interpretation of fish ecology provides further evidence that the Joggins Formation was deposited in a paralic setting, and the recognition of one previously undetected brackish incursion strengthens the link between sedimentary cycles at Joggins and Milankovitch‐induced glacio‐eustatic change. Furthermore, interregional correlation of these marine transgressions supports palynostratigraphical arguments for an early Langsettian age for the Joggins Formation. This places tighter constraints on the age of the earliest known crown amniote, Hylonomus lyelli, an important calibration point used in phylogenomic studies.

Chronostratigraphy and Paleoclimatology of the Lodève Basin, France: Evidence for a pan-tropical aridification event across the Carboniferous–Permian boundary

Paleosols preserved within the Carboniferous–Permian succession of the Lodève Basin, Massif Central, France change stratigraphically from Histosols to calcic Vertisols and Calcisols to gypsic Vertisols and ultimately back to calcic Vertisols and Calcisols. New high-precision U–Pb zircon ages (CA-IDTIMS) for tuff beds within the Lodève and adjacent Graissessac basins significantly revise the chronostratigraphy of these and correlated Permian terrestrial basins of eastern Euramerica. Under the newly revised chronostratigraphy presented here these stratigraphic changes in morphology indicate a substantial drying of paleoenvironments across the Carboniferous–Permian boundary with a trend toward progressively more arid and seasonal climates through most of the early Permian. This newly-realized chronology provides a paleoenvironmental and paleoclimatic timeline for eastern tropical Pangea that is contemporaneous with similar records in western Pangea and suggests pan-tropical, progressive climate change toward aridity and seasonality occurred from the Late Carboniferous through early Permian. • New chronometric dates significantly revise the ages of the Lodève Basin strata. • Stratigraphy suggests an aridification trend near Carboniferous–Permian boundary. • This paleoclimate change in the basin agrees with trends from other equatorial basins. • The combined observations across Pangea suggest a global climate transition.

Acme and demise of the late Palaeozoic ice age: A view from the southeastern margin of Gondwana

Palaeoenvironmental reconstructions from across the globe indicate that the climatic and oceanographic changes that accompanied the Permian transition from deep icehouse to greenhouse conditions were uneven and asynchronous. Because of a paucity of well-constrained data, environmental changes in Gondwana remain poorly understood relative to tropical Pangaea. In this regard, the Permian System of eastern Australia provides a unique record of this transition along a high-latitude, open marine shelf. Not only was glaciation protracted here relative to other regions of Gondwana, but the record also spans temperate to polar palaeolatitudes, providing an opportunity to examine environmental changes along a latitudinal transect. We integrate proxies for δ18Oseawater, palaeotemperature, pCO2, and depositional environment to assess the evolution of nearshore conditions through the Permian. Glaciation was not continuous, but rather focused into four discrete, glacial epochs (P1–P4), each several million years in length, which alternated with nonglacial intervals of similar duration. During the Asselian–mid-Artinskian (P1–P2 time), uniform conditions along the full extent of the margin were maintained by a cold boundary current coupled with oceanic upwelling. Increased spatiotemporal variability is evident at the end of glacial P2 (mid-Artinskian), perhaps due to tectonic changes that impacted the palaeogeography of the margin. Although glaciers had disappeared by this time elsewhere in Gondwana, eastern Australia saw two additional periods of glaciation, P3 (Roadian–earliest Captianian) and P4 (early Wuchiagingian). Continued, albeit intermittent, glaciation was facilitated by drift toward higher palaeolatitudes, orogenic activity that led to the development of areas of high elevation that could serve as nucleation points for glaciers, and transient drops in atmospheric pCO2. Variations in meltwater input exerted a strong effect on local δ18Oseawater values, complicating attempts to reconstruct latitudinal gradients in palaeotemperature. Results point to atmospheric CO2 as the primary driver responsible for the dynamic climate variations evident in the record.

Upland Glaciation in Tropical Pangaea: Geologic Evidence and Implications for Late Paleozoic Climate Modeling

The late Paleozoic archives a prolonged icehouse, long recognized by means of Gondwanan continental glaciation. In contrast, the paleotropics have long been considered warm. Here we present the hypothesis of upland glaciation in the Ancestral Rocky Mountains (ARM) of western equatorial Pangaea, a region located within 11° of the paleoequator. The data to support this hypothesis include (a) a Permo-Pennsylvanian valley with glacial attributes and diamictite exhibiting rare striated clasts; (b) coarse-grained lacustrine strata onlapping the valley and preserving lonestones in Gilbert-type deltaic deposits proximally, along with (c) coarse-grained fluvial siliciclastic strata with microstriae and evidence for widespread flood deposition; (d) polygonally cracked paleosurfaces inferred to reflect frozen ground; and (e) voluminous paleoloess. Tropical glaciation occurs today at altitudes >4500 m and descended to 2100–3000 m at the last glacial maximum (LGM). However, ARM depositional systems terminating at sea level and emanating from inferred ice-contact facies indicate that ice-terminus elevations were lower (<1200–1600 m) than those of the LGM. If valid, tropical temperatures were ∼15°C cooler than today during intervals recording hypothesized tropical glacial conditions. This implies at least episodic cold within western tropical Pangaea, which conflicts with inferences from oxygen isotope paleothermometry. Furthermore, climate models for the late Paleozoic cannot reproduce tropical upland glaciation except under prohibitively low Pco2, implying the need to consider other forcings, such as cloud and aerosol behavior. Upland glaciation in the Permo-Pennsylvanian tropics was potentially widespread, given the global orogenesis accompanying Pangaean assembly. However, testing this hypothesis requires identification of pro- and periglacial indicators, owing to widespread erosion of upland (glaciated) regions. Midlatitude glaciation in both hemispheres also was likely, challenging climate models and paleogeographic consensus for this period.

Abrupt and high-magnitude changes in atmospheric circulation recorded in the Permian Maroon Formation, tropical Pangaea

Geochemical, magnetic, sedimentologic, and U-Pb detrital zircon data from loessitepaleosol couplets within the Maroon Formation of Colorado (western U.S.) record abrupt and high-magnitude changes in atmospheric circulation in western tropical Pangaea during Early Permian (Wolfcampian) time. The relative quartz grain size increases by 50%–100% in loessite compared to superjacent paleo sols. Quartz grain size correlates inversely with bulk magnetic susceptibility (r 2 = 0.89); susceptibility values from paleosols are two times higher than from underlying loessite. This pattern is interpreted to refl ect high-frequency shifts in dust-transporting wind intensity. Loessite represents semi-arid times when dusttransporting winds were stronger, depositing coarser sediment, whereas paleosols record accumulation of fisediment marked by pedogenic enhancement of magnetic susceptibility within a wetter, less windy climate. Both major- and trace-element geochemistry differ between the loessite and superjacent paleosols. The paleosols are more phyllosilicate rich, likely tied to differences in grain size. However, a multivariate analysis of log-transformed trace-element data suggests that the thicker loessite units exhibit a shift in provenance compared to paleosols and thinner loessite units. U-Pb ages of detrital zircons also differ between loessite and paleosols. Four couplets were analyzed; all loessite samples contain at least one grain with U-Pb ages (1) <300 Ma and (2) 760–940 Ma, whereas no paleosol sample contains these ages. The fi rst population refl ects coeval arcs fringing western Pangaea and eastward transport in a westerly wind regime. The second population is more enigmatic but may refl ect erosion of Proterozoic rift-related volcanics, located along the western edge of Pangaea or located in northern Canada. In addition, the loessite samples contain a lower ratio (0.69) of Neoproterozoic grains (760–570 Ma) to Paleozoic grains (500–300 Ma) compared to paleosols (1.32). Both loessite and paleosol samples contain zircons with U-Pb ages between 1360–925 Ma and 1800–1610 Ma. The Neoproterozoic, Paleozoic, and 1360–925 Ma (Mesoproterozoic) grains were sourced from the Appalachian-Ouachita orogen to the east to southeast, whereas the 1800–1610 Ma (Paleo proterozoic) grains refl ect local basement uplifts (Ancestral Rocky Mountains). Overall, the combined geochemical and detrital zircon data indicate changes in provenance tied to abrupt and repeated changes in the direction of dust-transporting winds. The loessite-paleosol pairs exhibit a nested stratigraphy with a thick paleosol capping a thick loessite followed by thinner loessites grading into thinner, and less well-developed, paleosols. Our data suggest that thick loessite intervals accumulated in a monsoonal climate with strong, seasonal westerly winds coupled with semi-arid conditions, whereas the superjacent thick paleosol records more humid climate and a provenance derived primarily from the east. The muted sedimentologic, magnetic, and geochemical differences exhibited in the series of thinner loessitepaleosol couplets likely refl ect muted climate change. In this model, the thick loessitepaleosol couplet represents a period of major glaciation and the subsequent interglacial, respectively, in which a more elliptical Earth orbit accentuates climatic extremes. The thinner couplets likely represent more circular Earth orbits during times of advancing glacial conditions when climatic extremes were muted. The inferred depositional duration of the Maroon Formation indicates these