Asselian Sakmarian Research Articles

КОРРЕЛЯЦИЯ АССЕЛЬСКО-САКМАРСКИХ ОТЛОЖЕНИЙ БУЛКУРСКОЙ И УСТЬ-ЛЕНСКОЙ СТРУКТУРНО-ФАЦИАЛЬНЫХ ЗОН НИЗОВЬЕВ Р. ЛЕНА ПО БРАХИОПОДАМ

As a result of the monographic study of the Early Permian brachiopods from the Kubalakh and Chekurovka sections, a zonal correlation of the Asselian–Sakmarian deposits, respectively, of the Ust-Lena and Bulkur structural facies zones (SFZ) was performed. The Jakutoproductus verkhoyanicus (including layers with Jakutoproductus lenensis in the upper part of zone), Jakutoproductus insignis, Jakutoproductus terechovi, and Jakutoproductus rugosus zones are established in both SFZ (up-section). In the Kubalakh section, the Jakutoproductus verkhoyanicus Zone is present in full and conformably superposes the Upper Carboniferous Jakutoproductus protoverkhoyanicus Zone, while in the Chekurovka section, the lower part of the J. verkhoyanicus Zone unconformable overlies Upper Cambrian formations, and the lower part of this zone is probably absent in the section. In the direction from the Kubalakh section to the Chekurovka one, a significant reduction in the thickness of all established biostratigraphic units is observed, and their total thickness decreases by more than two times.

New Nautilida from the Shakhtau Asselian-Sakmarian Reef Complex (Bashkortostan)

This paper describes new nautilids from the Shakhtau Asselian–Sakmarian reef complex. Their place in the nautilid system, which is still far from being completely understood, is discussed. Two species of two genera: Omorphoceras igori gen. et sp. nov. and Stenopoceras (Leptodomatoceras) bashkiricum subgen. et sp. nov. are assigned to the subfamily Domatoceratinae Miller et Youngquist, 1949, family Grypoceratidae Hyatt, 1900. The third, Foveroceras magnum gen. et sp. nov., is included in the exotic family Permoceratidae Miller et Collinson, 1953, which was previously considered monotypic and was known only from the Early Permian of Timor Island. The classification of the family Grypoceratidae is discussed, and the validity of the subfamily Domatoceratinae is questioned. The assumed phylogenetic relationship between the families Grypoceratidae and Permoceratidae is confirmed.

The First Finds of the Most Ancient Oyster-Like Bivalves of the Genus <i>Prospondylus</i> Zimmermann (Pectinidae, Prospondylidae) in the Lower Permian of the Southern Cis-Urals (Russia)

For the first time in the Lower Permian deposits (Upper Asselian–Sakmarian stages) of the Southern Cis-Urals, the most ancient representatives of oyster-like bivalves of the genus Prospondylus Zimmermann were found, reliable findings of which were previously known only in the Lower-Middle Permian deposits of North America and the Upper Permian deposits of Germany. A description of the new species Prospondylus shakhtauensis Biakov, sp. nov. is given.

A New Species of Waagenoconcha Chao (Brachiopoda, Productida) from the Asselian–Sakmarian of the Lower Reaches of the Lena River, Northeast Russia

A New Species of Waagenoconcha Chao (Brachiopoda, Productida) from the Asselian–Sakmarian of the Lower Reaches of the Lena River, Northeast Russia

Upside-down in volcanic ash: crown reconstruction of the early Permian seed fern Medullosa stellata with attached foliated fronds.

Our understanding of fossil floras through geological time is mainly based on various differently preserved plant parts, often found isolated under restricted taphonomic circumstances. Preservation of whole plants is exceptionally rare in the geological record but provides the most reliable proof of ancient plants, especially those lacking a nearest living relative like the late Paleozoic pteridosperms. Among them, the medullosan seed ferns represent the largest and most essential systematic group. Medullosaleans are well known from the large Euramerican tropical swamp forests of Carboniferous age, but also from seasonally dry, clastic-soil habitats of Late Pennsylvanian–early Permian intramontane basins in central Europe. An exceptional taphonomic window that offered three-dimensional preservation of early Permian plants is located in Chemnitz, eastern Germany. Here, a forest ecosystem had been buried by pyroclastic deposits in a geological instant, 291 ± 2 Ma ago. Medullosaleans are both abundant and diverse in this striking autochthonous assemblage. The upper part of a Medullosa stellata var. typica individual broke at its top resulting from the overload of volcanic ash and was buried upside-down in the basal pyroclastics. The tree crown consists of the anatomically preserved apical stem, ten attached Alethopteris schneideri foliated fronds with Myeloxylon-type petioles and rachises. Though already discovered during the scientific excavation in 2010, the remarkable find required several years of preparation work, documentation, and reconstruction. The fronds were up to 3.5 m long, bifurcating, and bore numerous bipinnately compound pinnae preserved pulvinated in life position. The apical stem vascular system consists of a cylindrical peripheral vascular segment and up to 87 central accessory strands, each surrounded by manoxylic wood and secondary phloem. The reconstructed tree is supposed to have been self-supporting and of slender stature. Its architectural model is comparable to modern tree ferns or cycads and adapted to have grown in light-deficient lower-storey (sub-) tropical forests, usually not exceeding 15 m in height. Apical meristematic growth dominated, whereas only minor secondary growth occurred during ontogenesis. The densely attached frond bases followed a 3/8 phyllotaxis and were most likely abscised shortly after becoming photosynthetically inactive. A high water-conducting potential is assumed due to the tree’s cauline, petiolar and leaf vascular anatomies. Concerning the extensive leaf surface of the densely foliated fronds, considerable transpiration is hypothesised. Alethopteris schneideri foliage is stratigraphically significant for lower Permian (Asselian–Sakmarian) continental strata of central Europe, preferring habitats of wet clastic soils in sub-humid, seasonal palaeoclimate. The new insights provide a substantial step towards the first whole-plant concept of intramontane medullosaleans.

ASSELIAN–SAKMARIAN BRACHIOPOD ZONATION OF THE LEFT BANK OF THE LOWER REACHES OF THE LENA RIVER, NORTHEAST RUSSIA

ASSELIAN–SAKMARIAN BRACHIOPOD ZONATION OF THE LEFT BANK OF THE LOWER REACHES OF THE LENA RIVER, NORTHEAST RUSSIA

A lithofacies analysis of a South Polar glaciation in the Early Permian: Pagoda Formation, Shackleton Glacier region, Antarctica

ABSTRACTThe currently favored hypothesis for Late Paleozoic Ice Age glaciations is that multiple ice centers were distributed across Gondwana and that these ice centers grew and shank asynchronously. Recent work has suggested that the Transantarctic Basin has glaciogenic deposits and erosional features from two different ice centers, one centered on the Antarctic Craton and another located over Marie Byrd Land. To work towards an understanding of LPIA glaciation that can be tied to global trends, these successions must be understood on a local level before they can be correlated to basinal, regional, or global patterns. This study evaluates the sedimentology, stratigraphy, and flow directions of the glaciogenic, Asselian–Sakmarian (Early Permian) Pagoda Formation from four localities in the Shackleton Glacier region of the Transantarctic Basin to characterize Late Paleozoic Ice Age glaciation in a South Polar, basin-marginal setting. These analyses show that the massive, sandy, clast-poor diamictites of the Pagoda Fm were deposited in a basin-marginal subaqueous setting through a variety of glaciogenic and glacially influenced mechanisms in a depositional environment with depths below normal wave base. Current-transported sands and stratified diamictites that occur at the top of the Pagoda Fm were deposited as part of grounding-line fan systems. Up to at least 100 m of topographic relief on the erosional surface underlying the Pagoda Fm strongly influenced the thickness and transport directions in the Pagoda Fm. Uniform subglacial striae orientations across 100 m of paleotopographic relief suggest that the glacier was significantly thick to “overtop” the paleotopography in the Shackleton Glacier region. This pattern suggests that the glacier was likely not alpine, but rather an ice cap or ice sheet. The greater part of the Pagoda Fm in the Shackleton Glacier region was deposited during a single retreat phase. This retreat phase is represented by a single glacial depositional sequence that is characteristic of a glacier with a temperate or mild subpolar thermal regime and significant meltwater discharge. The position of the glacier margin likely experienced minor fluctuations (readvances) during this retreat. Though the sediment in the Shackleton Glacier region was deposited during a single glacier retreat phase, evidence from this study does not preclude earlier or later glacier advance–retreat cycles preserved elsewhere in the basin. Ice flow directions indicate that the glacier responsible for this sedimentation was likely flowing off of an upland on the side of the Transantarctic Basin closer to the Panthalassan–Gondwanide margin (Marie Byrd Land), which supports the hypothesis that two different ice centers contributed glaciogenic sediments to the Transantarctic Basin. Together, these observations and interpretations provide a detailed local description of Asselian–Sakmarian glaciation in a South Polar setting that can be used to understand larger-scale patterns of regional and global climate change during the Late Paleozoic Ice Age.

Asselian–Sakmarian (Lower Permian) Brachiopod Zonation of the Verkhoyansk Region, Northeast Russia

As a result of study of new collections of brachiopods, a zonal scheme of the Asselian–Sakmarian deposits in the Verkhoyansk region based on the phylogenetic development of Jakutoproductus is elaborated. The J. verkhoyanicus Zone is distinguished in the Khorokytian Horizon; in some sections, it may be divided into the beds with J. talchanensis and beds with J. lenensis. The succession of the J. insignis, J. terechovi, and J. rugosus zones is established in the Echian Horizon and provides direct correlation with the Kolyma–Omolon region. The index species of all brachiopod zones of the Asselian–Sakmarian interval in the Verkhoyansk region are described: Jakutoproductus verkhoyanicus (Fredericks), J. insignis Abramov et Grigorjeva, J. terechovi Zavodowsky, and J. rugosus Ganelin.

Columnar ossicles of Permian crinoids, including two new genera, from the Grupera Formation (Asselian‒Sakmarian) of Chiapas, Mexico

Columnar ossicles of Permian crinoids, including two new genera, from the Grupera Formation (Asselian‒Sakmarian) of Chiapas, Mexico

Lower Permian Gastropods of Shakhtau (Asselian–Sakmarian Boundary Beds, Southern Cisuralia)

An Early Permian gastropod assemblage from the reef limestones of southern Cisuralia is studied. The material was collected from the Asselian–Sakmarian interval of the Shakhtau Reef. With 91 species, this is one of the most diverse Early Permian assemblages ever described. This number of species is no more than 70% of the potential gastropod diversity in the Asselian–Sakmarian limestones of Shakhtau. Seven new generic level taxa are or have been established based on the material from Shakhtau: Perakella Mazaev, 2019, Termihabena Mazaev, 2019, Vicnigoria gen. nov., Bolicharewia gen. nov., Seleukella gen. nov., Bandelzyga gen. nov., and Monimirus gen. nov., and also 58 new species: Novlepatella uralensis sp. nov., Bellerophon shakhtauensis sp. nov., Tapinotomaria cancellata sp. nov., Peruvispira uralensis sp. nov., Ananias belaensis sp. nov., A. bashkiriensis sp. nov., Stenozone spiralis sp. nov., Globodoma magna sp. nov., Euconospira skuini sp. nov., Spiroscala elegans sp. nov., Shwedagonia pagoda sp. nov., S.korolukae sp. nov., Dictyotomaria balabanovi sp. nov., Eirlysia reticulatiformis sp. nov., Termihabena lirata Mazaev, 2019, Perakella shakhtauensis Mazaev, 2019, Baylea longispira sp. nov., Apachellarugosa sp. nov., Platyzona shikhanensis sp. nov., Callispira taosiformis sp. nov., Bellazona acuta Mazaev, 2019, Goniasma gerasimovi sp. nov., Orthonema perspicuum sp. nov., O. conspicuum sp. nov., O. nonnullum sp. nov., O. repandum sp. nov., Stegocoelia arta sp. nov., S. abscisa sp. nov., Arribazonaseleukensis sp. nov., Orecopia inopinata gen. et sp. nov., Vicnigoria monstrata gen. et sp. nov., Anomphalus glaucus sp. nov., Bolicharewia edita gen. et sp. nov., Tychonia fortis sp. nov., Anematina indiscreta sp. nov., Platyceras sagum sp. nov., Strophostylus fortuitus sp. nov., Orthonychia korotkovae sp. nov., Sallya bimaris sp. nov., S. indigena sp. nov., Trachydomia shkurkoi sp. nov., Palaeostylus confragosus sp. nov., P. nervosus sp. nov., Seleukella costata gen. et sp. nov., Pseudozygopleura applicata sp. nov., Plocezyga convexa sp. nov., P. boikoi sp. nov., P. venusta sp. nov., P. minuta sp. nov., Levizygopleura composita sp. nov., L. magna sp. nov., Bandelzyga elegans gen. et sp. nov., Stephanozyga seminuda sp. nov., Strobeus bashkiriensis sp. nov., Girtyspira oblonga sp. nov., Streptacis nalivkini sp. nov., Cristalloella (Wonwalica) permica sp. nov., and Monimirus bonus gen. et sp. nov. Two species are described in open nomenclature. Some species found in Shakhtau were previously known from Tethyan assemblages of Fergana: Bellerophonkaratshatyrensis, B. isfarensis, Permoconcha ferganica, Orthonema frequens, Amaurotoma kizilkiensis, Anomphalus planus, Yunnania romanovskyi, Pseudozygopleura knighti, P. rugosocostata, Strobeus ferganense, S. veberi; Sicily: Retispira lyelli, Naticopsis spallanzanii, and Soleniscus elegans; China: Porcellia (Porcellia) magninodosa, P. (P.) lingshuiensis, Platyzona eulkaiensis, and Stegocoelia quinquecostata. In addition, as shown in this paper, assemblages in South China contain: Bellerophon isfarensis and Baylea longispira sp. nov. It is worth mentioning that the Shakhtau assemblages contain representatives of such genera as Schwedagonia, Stenozone, Sallya, and Perakella, known from a Malaysian assemblage described by Batten (1972, 1979) (see Mazaev, 2019b). Other species found in Shakhtau had previously been known from the Pennsylvanian and Permian of North America: Globodoma spironema, Baylea gurleyi, Straparollus (Euomphalus) cornudanus, Retispira lyelli, R. modesta, Euphemites batteni,Eirlysia reticulata, and Discotomaria basisulcata. In addition, the North American assemblages contain Bellerophon isfarensis. Thus, the studied gastropod assemblage from Shakhtau unequivocally suggests that the Uralian corridor was a migration pathway between the faunas of the North America and Tethyan basins. In addition, these “relict taxa” Orecopia inopinata sp. nov. and Bellazona acuta Mazaev, 2019a, Vicnigoria monstrata gen. et sp. nov., and also “Mesozoic taxa” Cristalloella (Wonwalica) permica sp. nov. and Monimirus bonus gen. et sp. nov., which significantly expands geographical ranges and geochronological intervals of these groups.

New materials of Cisuralian (early Permian) radiolarians from western Cambodia: Paleobiogeographic implications in the Paleotethys

Radiolarians, including the new species Entactinia pailinensis Ito n. sp., were obtained from the Pailin area, western Cambodia. The radiolarians indicated an age around the Asselian–Sakmarian of the Cisuralian (early Permian). The new species is characterized by an evenly-sized-porous exosphere composed of a polygonal outer porous plate and circular inner porous plate with some radial outer spines. A previous study concluded that Entactinia Foreman rapidly expanded in the early–middle Cisuralian. Our discovery of this new species adds further occurrence data of Entactinia in the early–middle Cisuralian. In addition, another previous study highlighted the uneven distribution of Pseudotormentus De Wever and Caridroit compared with the wider distribution of Quadriremis Nazarov and Ormiston through the Permian, in particular the Guadalupian (middle Permian). Our results combined with those of previous studies indicate that the uneven distribution might extend back to the Sakmarian of the Cisuralian at least.

Detrital zircon age and provenance constraints on late Paleozoic ice-sheet growth and dynamics in Western and Central Australia

U–Pb dating and Hf-isotope provenance analysis of detrital zircons from the glaciogenic lower Permian Grant Group of the Canning Basin indicate sources principally from basement terranes in central Australia, with subordinate components from terranes to the south and north. Integrating these data with field outcrop and subsurface evidence for ice sheets, including glacial valleys and striated pavements along the southern and northern margins of the basin, suggests that continental ice sheets extended over several Precambrian upland areas of western and central Australia during the late Paleozoic ice age (LPIA). The youngest zircons constrain the maximum age for contemporaneous ice sheet development to the late Carboniferous (Kasimovian), whereas palynology provides a minimum age of early Permian (Asselian–Sakmarian). Considering the palynological age of the Grant Group within the context of regional and global climate proxies, the main phase of continental ice sheet growth was possibly in the Ghzelian–Asselian. The presence of ice sheets older than Kasimovian in western and central Australia remains difficult to prove given a regional gap in deposition possibly covering the mid-Bashkirian to early Ghzelian within the main depocentres and even larger along basin margins, and the poor evidence for older Carboniferous glacial facies. There is also no evidence for extensive glacial facies younger than mid-Sakmarian in this region as opposed to eastern Australia where the youngest regional glacial phase was Guadalupian.

The uppermost Carboniferous (Gzhelian)–Lower Permian (Asselian–Sakmarian) stratigraphy and smaller foraminifers of the Ozbak‐Kuh region (Tabas Block, east central Iran)

The uppermost Carboniferous (Gzhelian)–Lower Permian (Asselian to Sakmarian) Anarak Group of the Zaladou section in central Iran is more than 180‐m thick and includes thick units of shale, calcareous sandstone, fusulinid limestone, sandy limestone, and dolomite. The Zaladou and Tigh‐e‐Madanu formations of this group were dated as Gzhelian to Sakmarian. A review of the smaller foraminifers of the Zaladou section is presented. Five foraminiferal subzones grouped in three biozones are proposed in this work: The first assemblage zone (I) is Gzhelian; the second zone (II) corresponds to the Gzhelian–Asselian boundary interval, and the third biozone (III) is Asselian in age. Biozone I is subdivided informally into two subzones: the Hemigordius spirilliniformis‐Bradyina cf. samarica subzone IA (probably early Gzhelian in age) and the Raphconilia modificata and Globivalvulina spp. subzone IB (middle to late Gzhelian); biozone II is the Nodosinelloides spp. zone; biozone III is subdivided informally into two subzones: IIIA with Pseudoacutella partoazari‐Bradyina lucida and IIIB with Planoendothyra persica n. sp.‐Rectogordius sp. The studied assemblages are correlated with those from the Carnic Alps (Austria–Italy), East European Platform of Russia, the Urals (Russia), Darvas (Uzbekistan), the northern and central Pamirs (Tajikistan), northern Iran (Alborz), northern Afghanistan, and other classical regions of the Tethyan realm. The genera Raphconilia and Planoendothyra are revised, and Planoendothyra persica n. sp. is described.

First record of fossil basidiomycete clamp connections in cordaitalean stems from the Asselian–Sakmarian (lower Permian) of Shanxi Province, North China

Fungi today occur in great diversity on virtually every plant part, living and dead. Cordaitalean gymnosperms were important components of floral element in the late Palaeozoic palaeotropical floras. However, fungi associated with the stems of these plants are rarely documented. Basidiomycetes are one of the major groups of extant fungi, and may have played an important role in ancient continental ecosystems, but are rarely discovered in the upper Palaeozoic. A stem of the fossil cordaite Shanxioxylon sp. containing abundant ramifying and septate hyphae with clamp connections is preserved in the upper Taiyuan Formation (Cisuralian, lower Permian) in Shanxi Province, North China. The fungal remains described here are the first evidence of fungi associated with Permian cordaitalean stems from Cathaysia. Their association with Cathaysian cordaites expands knowledge of the ecology and plant substrates of basidiomycetous fungi in the Permian.

Permian oolitic carbonates from the Baoshan Block in western Yunnan, China, and their paleoclimatic and paleogeographic significance

Marine carbonate ooids are environment-sensitive and hence valuable for paleoclimatic and paleogeographic reconstructions. This paper describes Permian ooids from the Baoshan Block in western Yunnan, China, in order to offer a new means to refine the uncertain paleogeographic details of this Gondwana-derived block. Four major types of ooids (micritic ooids, compound ooids, leached ooids and half-moon ooids) are documented from the Hewanjie Formation in the northern and the Shazipo Formation in the southern Baoshan Block. These ooids are dated via biostratigraphic analysis to be Wordian–early Wuchiapingian and signify an ameliorated shallow-marine temperature for the Guadalupian strata of the Baoshan Block. Results of this study, coupled with literature data, reveal diachronous debut of Permian ooids among the Gondwana-derived blocks: mostly Sakmarian in Central Taurides of Turkey, Central Iran, Central Pamir and Karakorum Block versus Wordian–Capitanian in Baoshan Block, Peninsular Thailand and South Qiangtang. In contrast, Asselian–Sakmarian strata of Baoshan Block as well as Peninsular Thailand and South Qiangtang are characterized by glaciomarine diamictites. These observations suggest that the Baoshan Block was probably situated at a considerably higher paleolatitude under distinct influence of Gondwana glaciation during the Asselian–Sakmarian than those blocks yielding Sakmarian ooids. Moreover, marine ooids are virtually absent nearby the equator within the Permian Tethys, similar to the modern situation. The Baoshan Block is accordingly interpreted to drift to warm-water southern mid-latitudes during the Wordian–Capitanian and remain to the south of Central Iran, Karakorum Block and South China, which were equatorially located in the Capitanian.

New species of Jakutoproductus from the Lower Permian of Verkhoyansk Region

Two new brachiopod species of Jakutoproductus, J. lenensis sp. nov. and J. talchanensis sp. nov., are described. J. lenensis occurs in the upper part of the J. verkhoyanicus Zone of the Khorokytian Horizon (Asselian–Sakmarian deposits) of the lower reaches of the Lena River and in the Sobolokh-Mayan and Allara-Khadaryn’ya river basins. J. talchanensis is identified from the Khorokytian Horizon of the Talchan River (Baraiy River basin). A new subzone, the J. lenensis Subzone, is proposed for the upper part of the J. verkhoyanicus Zone of the Khorokytian Horizon of the Verkhoyansk Region.

New occurrences of tetrapod ichnotaxa from the Permian Orobic Basin (Northern Italy) and critical discussion of the age of the ichnoassociation

AbstractThe late Cisuralian (Artinskian–Kungurian) is a key time interval for Permian tetrapod evolution. In all the main low‐latitude Pangean sites, the fossil footprint record clearly shows a diversification and dispersal of non‐synapsid amniote tracks compared to the early Cisuralian (Asselian–Sakmarian). However, data on latest Cisuralian (i.e. late Kungurian) sites are quite fragmentary. A new ichnotaxonomic study was carried out in the central part of the Orobic Basin, where the highly‐fossiliferous Pizzo del Diavolo formation crops out and can potentially cover this gap in knowledge. The following tetrapod ichnogenera were identified: Amphisauropus, Batrachichnus, cf. Dimetropus, Dromopus, Erpetopus, Hyloidichnus, Limnopus, cf. Merifontichnus and Varanopus; they can be attributed to seymouriamorph and temnospondyl amphibians; pelycosaur synapsids; and diapsid, parareptile and captorhinid reptiles. Dimetropus and Merifontichnus are identified for the first time in the Permian of Italy. The ichnoassociation, in agreement with the radiometric dating of the underlying Cabianca formation, suggests a late Kungurian (latest Cisuralian) age for the Pizzo del Diavolo formation. It includes the youngest and most diverse non‐synapsid amniote ichnofauna of the Cisuralian with five different ichnogenera and possibly six ichnospecies, and thus constitutes a key area for the study of eureptile and parareptile dispersal at low latitudes of Pangaea in the time span that immediately pre‐dates the first therapsid synapsid radiation.

Larval cases of caddisfly (Insecta: Trichoptera) affinity in Early Permian marine environments of Gondwana

Caddisflies (Trichoptera) are small, cosmopolitan insects closely related to the Lepidoptera (moths and butterflies). Most caddisflies construct protective cases during their larval development. Although the earliest recognisable caddisflies date back to the early Mesozoic (Early and Middle Triassic), being particularly numerous and diverse during the Late Jurassic and Early Cretaceous, the first records of their larval case constructions are known exclusively from much younger, Early to Middle Jurassic non-marine deposits in the northern hemisphere. Here we present fossils from the Early Permian (Asselian–Sakmarian) marine deposits of Brazil which have strong morphological and compositional similarity to larval cases of caddisflies. If they are, which is very probable, these finds not only push back the fossil record of true caddisflies, but also indicate that their larvae constructed cases at the very beginning of their evolution in marine environments. Since modern caddisflies that construct larval cases in marine environments are only known from eastern Australia and New Zealand, we suggest that this marine ecology may have first evolved in western Gondwana during the Early Permian and later spread across southern Pangea.

A model-based evaluation of tropical climate in Pangaea during the late Palaeozoic icehouse

Abstract The late Palaeozoic ice age (LPIA) is the Earth's penultimate “icehouse climate.” Geological proxies for tropical Pangaean climate during the LPIA are significantly modulated on 100–400 kyr and sub-100 kyr scales. In addition, some geological proxies suggest that equatorial continental areas may have been colder and more arid during LPIA glacial intervals than during late Cenozoic glacial intervals. Furthermore, the relationship between polar and tropical climate variability remains controversial. The climate dynamics underlying these phenomena are only partly understood. Nevertheless, past modeling of LPIA climate has suggested that precipitation near the Equator was modulated by monsoonal circulation that itself was modulated by orbital variability. Here, the Earth's climate during Asselian–Sakmarian time (299–284 Ma) was simulated with the Community Climate System Model version 3 (CCSM3). These simulations address model climate sensitivity to direct and indirect effects of glaciation as well as variability in the Earth's orbit. The results of these simulations suggest that sea level and orbitally forced monsoon variability were the primary controls on tropical precipitation when ice sheets were confined to polar latitudes. Any impact of orbital forcing on glaciation therefore could have led to aliasing between glacial and monsoonal effects in particular regions, perhaps explaining contrasting geologically-based interpretations of how tropical climate responded to glaciation. Glaciation of the Central Pangaean Mountains would have led to widespread cold and aridity in equatorial Pangaea, but forming these glaciers would have required an unknown additional climate forcing with an unknown impact on tropical precipitation.

Permian and Triassic microfloral assemblages from the Blue Nile Basin, central Ethiopia

Palynological investigation was carried out on surface samples from up to 400m thick continental siliciclastic sediments, here referred to as “Fincha Sandstone”, in the Blue Nile Basin, central Ethiopia. One hundred sixty species were identified from 15 productive samples collected along a continuous road-cut exposure. Six informal palynological assemblage zones have been identified. These assemblage zones, in ascending order, are: “Central Ethiopian Permian Assemblage Zone – CEPAZ I”, earliest Permian (Asselian–Sakmarian); “CEPAZ II”, late Early Permian (Artinskian–Kungurian); CEPAZ III – Late Permian (Kazanian–Tatarian); “CETAZ IV”, Lower Triassic (Olenekian Induan); “CETAZ V”, Middle Triassic (Anisian Ladinian); “CETAZ VI”, Late Triassic (Carnian Norian). Tentative age ranges proposed herein are compared with faunally calibrated palynological zones in Gondwana. The overall composition and vertical distribution of miospores throughout the studied section reveals a wide variation both qualitatively and quantitatively. The high frequency of monosaccate pollen in CEPAZ I may reflect a Glossopterid-dominated upland flora in the earliest Permian. The succeeding zone is dominated by straite/taeniate disaccate pollen and polyplicates, suggesting a notable increase in diversity of glossopterids. The decline in the diversity of taeniate disaccate pollen and the concomitant rise in abundance of non-taeniate disaccates in CEPAZ III may suggest the decline in Glossopteris diversity, though no additional evidence is available to equate this change with End-Permian extinction. More diverse and dominant non-taeniate, disaccate, seed fern pollen assignable to FalcisporitesAlisporites in CETAZ IV may represent an earliest Triassic recovery flora. The introduction of new disaccate forms with thick, rigid sacci, such as Staurosaccites and Cuneatisporites, in CETAZ V and VI may indicate the emergence of new gymnospermous plants that might have favourably adapted to coastal plain wetland environments with the return of humid conditions in the Middle to early Late Triassic. The present data constitute the first paleontologically substantiated record for the existence of Permian strata in the Blue Nile Basin. The new results allow for the first time a reliable biostratigraphic subdivision of the central Ethiopia Karoo and its correlation with coeval strata of adjacent regions in Gondwana. From a phytogeographic point of view, the overall microfloral evidence is in support of the position of central Ethiopia occupying the northern part of the southern Gondwana palynofloral province. In view of palaeoecological and paleoclimatic conditions, the microfloral change from the base to the top of the studied section may indicate a response to shifting climatic belts from warm- and cool-temparate climate in the earliest Permian to progressively drier seasonal conditions at successively higher palaeolatitudes during the Late Permian to Middle Triassic.