Evidence of a Supervolcano Eruption From Albian Cretaceous Australia

The answers are blowin' in the wind: Ultra-distal ashfall zircons, indicators of Cretaceous super-eruptions in eastern Gondwana

Authors:

Barham et al

Abstract:

An Early Cretaceous siliceous large igneous province (SLIP) that developed on the eastern margin of Gondwana produced some of the most voluminous siliceous volcaniclastic deposits known globally. We report U-Pb ages and trace-element and Hf-isotopic signatures of detrital zircons from the Madura Shelf (onshore Bight Basin), Western Australia. These zircons include a geochemically distinct 106 Ma component with age and Hf characteristics that match SLIP volcanics some 2300 km distant in eastern Australia. This young subpopulation shows limited grain abrasion, which contrasts with older detrital components that are stratigraphically persistent. Regional detrital zircon provenance demonstrates that sediment routing systems were disconnected in the eastern and western Bight Basin, negating terrestrial transport mechanisms as a possible vector of the zircons from the SLIP to their recovered position. Palynology indicates that the 106 Ma zircons are syn-depositional, and we interpret them as being significantly transported in an eruption plume. Given the grain size and distance from source, such distal zircon emplacement suggests previously undocumented 106 Ma super-eruptions. The 106 Ma zircons likely reflect Southern Hemisphere winter eruptions when tropospheric polar easterly winds would have been favored across southeastern Australia.

Abdalodon diastematicus: a new Cynodont From Upper Permian South Africa

A new taxon of cynodont from the Tropidostoma Assemblage Zone (upper Permian) of South Africa, and the early evolution of Cynodontia

Author:

Kammerer

Abstract:

A new taxon of early cynodont, Abdalodon diastematicus gen. et sp. nov., is described. The new taxon is represented by a single skull from the upper Permian Tropidostoma Assemblage Zone (AZ) of the Beaufort Group (Karoo Basin, South Africa), which was previously referred to Procynosuchus delaharpeae. Abdalodon is distinguished from Procynosuchus by the presence of only four upper and three lower incisors, fewer postcanines, a well-developed depression on the lateral surface of the maxilla posterior to the canine root, a tall mandibular symphysis forming a distinct ‘chin’, a relatively short snout, and weak or absent interdigitation of sutures in the interorbital region. These features are shared with the only other Tropidostoma AZ cynodont, Charassognathus gracilis. Abdalodon is distinguished from Charassognathus by its postcanine morphology, the presence of an expanded masseteric fossa, inset postcanine tooth rows, a broader interorbital region, and proportionally shorter temporal region. Most strikingly, Abdalodon has a lengthy diastema between the canines and postcanines on both the maxilla and the dentary. Charassognathus has a short diastema between the upper canine and postcanines, but not the lowers, and diastemata are absent from the tooth rows of Procynosuchus. Phylogenetic analysis recovers Abdalodon as the sister-taxon of Charassognathus, forming a clade (Charassognathidae fam. nov.) at the base of Cynodontia. These taxa represent a previously unrecognized radiation of small-bodied Permian cynodonts. Despite their small size, the holotypes of Abdalodon and Charassognathus probably represent adults and indicate that early evolution of cynodonts may have occurred at small body size, explaining the poor Permian fossil record of the group.

Elaphrosaurus bambergi: a Reevaluated Noasaurid Abelisauroid From Late Jurassic Tanzania

The theropod dinosaur Elaphrosaurus bambergi Janensch, 1920, from the Late Jurassic of Tendaguru, Tanzania

Authors:

Rauhaut et al

Abstract:

Theropod dinosaurs from the Late Jurassic of Gondwana are still poorly known, with Elaphrosaurus bambergi Janensch, 1920, from the late Kimmeridgian of Tendaguru, Tanzania, being the only taxon represented by more than isolated remains from Africa. Having long been considered a coelurosaurian, more specifically an ornithomimosaur, Elaphrosaurus is currently regarded as a basal ceratosaur. Here, we revise the osteology and phylogenetic position of this important taxon. Elaphrosaurus shows many unusual osteological characters, including extremely elongated and constricted cervical vertebrae, an expansive shoulder girdle with strongly modified forelimbs, a relatively small ilium, and elongate hindlimbs with a very small ascending process of the astragalus that is fused to the tibia. We found this taxon to share many derived characters with noasaurids, such as: strongly elongate cervical and dorsal vertebrae; low, rectangular neural spines in the mid-caudal vertebrae; presence of only an anterior centrodiapophyseal lamina in anterior caudal vertebrae; presence of a wide, U–shaped notch between the glenoid and the anteroventral hook in the coracoid; a laterally flared postacetabular blade of the ilium; a flat anterior side of the distal tibia; and a reduced shaft of metatarsal II. Our analysis placed Elaphrosaurus within a dichotomous Noasauridae as part of a Jurassic subclade, here termed Elaphrosaurinae, that otherwise includes taxa from eastern Asia. These results underscore the long and complex evolutionary history of abelisauroids, which is still only beginning to be understood.

The Paleobotanical Changes Across the Jurassic/Cretaceous Boundary in India

Integrated palaeobotanical and palynological analysis of subsurface Gondwana sedimentary succession (Jurassic–Cretaceous) in Jangareddygudem area, Chintalapudi Sub-basin, South India: Stratigraphical and phytogeographical implications

Authors:

Jha et al

Abstract:

Here we present an integrated palaeobotanical and palynological analysis of sub-surface terrestrial deposits of Jangareddygudem area, Chintalapudi Sub-basin, Godavari Graben, India. Plant megafossil impressions and palynomorphs were recovered in the bore core MJR-11 from Jangareddygudem area. Plant megafossils impressions: Equisetites sp., Ptilophyllum acutifolium, Pachypteris indica, Elatocladus jabalpurensis, Pagiophyllum gollapallensis, and Ptilophyllum cutchense are recorded at different depths in the bore core MJR-11. Palynological investigations carried out in these megafossil bearing beds reveal the presence of Coptospora sp., Ceratosporites equalis, Appendicisporites erdtmanii, Biretisporites spectabilis, Cicatricosisporites hughesii, Cicatricosisporites sp., Concavissimisporites sp., Contignisporites cooksoniae, C. fornicatus, C. glebulentus, C. multimuratus, C. psilatus, Converrucosisporites sp., Gleicheniidites sp., Klukisporites scaberis, Plicifera delicata, Balmeiopsis limbatus, Araucariacites australis, A. cooksonii, Callialasporites dampieri, C. monoalasporus, C. segmentatus, C. turbatus, Dacrycarpites australiensis, Podocarpidites ellipticus, Podosporites variabilis, Crybelosporites stylosus, and Foraminisporis wonthaggiensis. Very rare occurrence of monocolpate, tetracolpate and tricolpate pollen is also recorded. Both plant mega- and microfloral evidences indicate Late Jurrassic–Early Cretaceous (Tithonian–Valanginian) age for these sediments. A comparative study of present mega and microfossil assemblages with known megafloral and microfloral assemblage from the Upper Gondwana sediments of Godavari and other Indian basins has also been attempted. The floral assemblage clearly indicates the presence of Gangapur sediments in Jangareddygudem area.

Similarity of the Antarctic palynofloras with those known from Godavari and other basins on the east coast of India confirms continental reconstructions that show Lambert Graben of East Antarctica to have been contiguous with eastern India prior to Gondwana break-up. The non-marine character of the palynomorphs suggests that marine conditions in this region of the Godavari Graben did not develop until at least early Early Cretaceous time.

The Bashkirian Pennsylvanian Carboniferous was the Peak of the Late Paleozoic Ice Age

Ice volume and paleoclimate history of the late Paleozoic ice age from conodont apatite oxygen isotopes from naqing (Guizhou, China)

Authors:

Chen et al

Abstract:

A high-resolution and continuous conodont apatite oxygen isotope record spanning the late Viséan to Middle Permian is reported from South China, which is interpreted with respect to the ice volume and/or tropical sea water temperature history of the Late Paleozoic Ice Age (LPIA). The presented δ18O record shows significant fluctuations in δ18O from the late Viséan to Middle Permian with highest values observed in the Bashkirian (Early Pennsylvanian). The δ18O maximum coincides with a major eustatic sea level fall recorded in low-latitudinal successions, and postdates the significant increases in 87Sr/86Sr and δ13Ccarb measured on well-preserved brachiopod calcite, which can be interpreted as reflecting intensified weathering as consequence of the closure of Rheic Ocean as well as enhanced carbon burial. Both processes may have contributed to lower greenhouse gas levels and cooled down the Earth's surface, triggering the maximum glaciation. The high Bashkirian δ18O values are interpreted to represent the glacial maximum of the LPIA. A coeval change in faunal composition and a decreasing diversity in climate-sensitive marine invertebrates can be ascribed to icehouse cooling and/or loss of habitat. Despite inconsistenceies with earlier interpretations that the Early Permian represented the glacial maximum of the LPIA as inferred from Gondwanan glacial sediments records, the suggested Bashkirian glacial maximum agrees well with ice extent estimates based on the regional tectonic history in Gondwana, which suggests that the Bashkirian glaciation occurred during Gondwana interior uplift promoting maximum ice cover of the entire LPIA. However, maximum glaciation is only poorly represented in the depositional record because large parts of the glacial deposits were possibly removed by erosion as outlined by a major regional unconformity.

Archosauriforms From a Flood Plain in Late Triassic Argentina

Archosauriform remains from the Late Triassic of San Luis province, Argentina, Quebrada del Barro Formation, Marayes–El Carrizal Basin

Authors:

Gianechini et al

Abstract:

Here we present archosauriform remains from ‘Abra de los Colorados’, a fossiliferous locality at Sierra de Guayaguas, NW San Luis Province. Two fossiliferous levels were identified in outcrops of the Quebrada del Barro Formation (Norian), which represent the southernmost outcrops of the Marayes–El Carrizal Basin. These levels are composed by massive muddy lithofacies, interpreted as floodplain deposits. The specimens consist of one incomplete maxilla (MIC-V718), one caudal vertebra (MIC-V719), one metatarsal (MIC-V720) and one indeterminate appendicular bone (MIC-V721). The materials can be assigned to Archosauriformes but the fragmentary nature and lack of unambiguous synapomorphies preclude a more precise taxomic assignment. The maxilla is remarkably large and robust and represents the posterior process. It preserved one partially erupted tooth with ziphodont morphology. This bone shows some anatomical traits and size match with ‘rauisuchians’ and theropods. MIC-V719 corresponds to a proximal caudal vertebra. It has a high centrum, a ventral longitudinal furrow, expanded articular processes for the chevrons, a posteriorly displaced diapophysis located below the level of the prezygapophyses, and short prezygapophyses. This vertebra would be from an indeterminate archosauriform. MIC-V720 presents a cylindrical diaphysis, with a well-developed distal trochlea, which present resemblances with metatarsals of theropods, pseudosuchians, and silesaurids, although the size matches better with theropods. MIC-V721 has a slender diaphysis and a convex triangular articular surface, and corresponds to an indeterminate archosauriform. Despite being fragmentary, these materials indicate the presence of a diverse archosauriforms association from Late Triassic beds of San Luis. Thus, they add to the faunal assemblage recently reported from this basin at San Juan Province, which is much rich and diverse than the coeval paleofauna well known from Los Colorados Formation in the Ischigualasto–Villa Union Basin.

Sino-Korean Block was Located at the Northern Margin of East Gondwana Across the Ediacaran/Cambrian Boundary

Detrital zircon geochronology and Nd isotope geochemistry of the basal succession of the Taebaeksan Basin, South Korea: Implications for the Gondwana linkage of the Sino-Korean (North China) block during the Neoproterozoic–early Cambrian

Authors:

Lee et al

Abstract:

The paleogeographic configuration of continental blocks around East Gondwana during the Neoproterozoic–early Cambrian is controversial. This study reports the U–Pb ages of detrital zircons and Nd isotopic composition of the Neoproterozoic–early Cambrian succession developed on the Precambrian basement in South Korea, which formed the southeastern portion of the Sino-Korean block (SKB) in its present configuration. Three stratigraphic units are addressed in this study: the Neoproterozoic Jangsan, early Cambrian Myeonsan, and early–middle Cambrian Myobong Formations. Both the Jangsan (white to pink quartz sandstone) and Myeonsan (dark gray ilmenite-rich sandstone/shale) formations are barren and are unconformably and conformably overlain, respectively, by the dark gray, fossiliferous fine-grained Myobong Formations. The Jangsan and Myeonsan Formations contain zircons with Archean–Paleoproterozoic ages, indicative of detritus derived from the local Precambrian basement. In contrast, the Myobong Formation is dominated by Mesoproterozoic to Neoproterozoic zircons, which are not represented in the local Precambrian basement. The Sm–Nd model ages of the Myobong Formation are younger than those of the underlying strata, indicative of significant changes in provenance during the deposition of this formation. Comparison with coeval sediment having Gondwana signatures in the southern margin of the SKB and the Tethyan Himalayan terrane strongly suggests that the Myobong Formation was derived from orogens in East Gondwana. The results of this study reveal that the timing of the Myobong Formation deposition marks the onset of a sedimentation episode on the southeastern margin of the SKB, which was related to the emergence of a vast source province in East Gondwana, possibly aided by the Cambrian transgression onto the SKB. In comparison with the published literature, we argue for the paleogeographic continuity of the SKB with the northern margin of East Gondwana, possibly between northwestern Australia and northeastern India during the Neoproterozoic–early Cambrian.

How Australia and Antarctica Transitioned From Being Part of the Supercontinent Columbia to Gondwana

The Australo-Antarctic Columbia to Gondwana transition

Authors:

Aitken et al

Abstract:

From the Mesoproterozoic to Cambrian, Australo-Antarctica was characterised by tectonic reconfiguration as part of the supercontinents Columbia, Rodinia and Gondwana. New tectonic knowledge of the Wilkes Land region of Antarctica allows Australo-Antarctic tectonic linkages to be resolved through reconstruction into ca. 160 Ma Gondwana. We also resolve 330 ± 30 km of sinistral strike-slip offset on the greater than 3000 km long Mundrabilla-Frost Shear Zone and 260 ± 20 km of dextral offset on the greater than 1000 km long Aurora Fault to reconstruct the ca. 1150 Ma geometry of Australo-Antarctica. Using this revised geometry, we derive the first model of the Columbia to Gondwana reconfiguration process that is geometrically constrained to ~ 100 km scale. In this model, early Mesoproterozoic tectonics is driven by two opposing subduction systems. A dominantly west-dipping subduction zone existed at the eastern margin of Australo-Antarctica until ca. 1.55–1.50 Ga. A predominantly east-dipping subduction zone operated at the western margin of the Mawson Craton from ca. 1.70 Ga to ca. 1.42 Ga. The latter caused gradual westwards motion and clockwise rotation of the Mawson Craton relative to the West and North Australian Craton and the accretion of a series of continental ribbons now preserved in the Musgrave Province and its southern extensions. A mid-Mesoproterozoic switch to predominantly west-dipping subduction beneath the West Australian Craton brought about the final closure of the Mawson Craton with the North and West Australian Craton along the Rodona-Totten Shear Zone. Convergence was achieved prior to 1.31 Ga, but final collision may not have occurred until ca. 1.29 Ga. Post-1.29 Ga intraplate activity involved prolonged high-temperature orogenesis from 1.22 to 1.12 Ga, and significant movement on the Mundrabilla-Frost Shear Zone between 1.13 and 1.09 Ga, perhaps in response to the assembly of Rodinia at ca. 1.1 Ga. The Australo-Antarctic Craton was amalgamated with Indo-Antarctica along the Indo-Australo-Antarctic Suture (IAAS) and Kuunga Orogeny, probably in the latest Neoproterozoic to early Cambrian.

The Emu Bay Shale Cambrian Konservat-Lagerstätte

The Emu Bay Shale Konservat-Lagerstätte: a view of Cambrian life from East Gondwana

Authors:

Paterson et al

Abstract:

Recent fossil discoveries from the lower Cambrian Emu Bay Shale (EBS) on Kangaroo Island, South Australia, have provided critical insights into the tempo of the Cambrian explosion of animals, such as the origin and seemingly rapid evolution of arthropod compound eyes, as well as extending the geographical ranges of several groups to the East Gondwa-nan margin, supporting close faunal affinities with South China. The EBS also holds great potential for broadening knowl-edge on taphonomic pathways involved in the exceptional preservation of fossils in Cambrian Konservat-Lagerstätten. EBS fossils display a range of taphonomic modes for a variety of soft tissues, especially phosphatization and pyritization, in some cases recording a level of anatomical detail that is absent from most Cambrian Konservat-Lagerstätten.

Continuous Neoproterozoic to Ordovician Sedimentation in Victoria Land, Antarctica

Continuous Neoproterozoic to Ordovician sedimentation at the East Gondwana margin – implications from detrital zircons of the Ross Orogen in northern Victoria Land, Antarctica

Authors:

Estrada et al

Abstract:

The Ross-Delamerian orogenic belt was formed along the eastern side of the Australian-East Antarctic continent during west-directed subduction of the Palaeo-Pacific Ocean in the early Palaeozoic. Northern Victoria Land (NVL) in Antarctica was located at a central position of the Ross-Delamerian system. Its metamorphic basement is formed by three lithotectonic units formerly interpreted as terranes: the Wilson, Bowers and Robertson Bay terranes (from west to east). Dating of detrital zircons from 14 metasedimentary samples of these terranes combined with petrographical and whole-rock geochemical studies give new insights into the stratigraphic and tectonic evolution of NVL. All samples show very similar zircon age spectra with two main intervals, a Ross/Pan-African-age interval (470–700 Ma) and a Grenville-age interval (900–1300 Ma), as well as subordinate craton-related ages dispersed over the range of ca. 1600–3500 Ma. The Ross/Pan-African-age zircon population tends to get more dominant from the Priestley Formation of the Wilson Terrane to the Molar Formation of the Bowers Terrane, and finally to the Robertson Bay Group, whereas the number of craton-related ages diminishes in this direction. A common East Antarctic source area is indicated for all analyzed samples. The Priestley Formation was deposited on the Palaeo-Pacific passive continental margin of East Gondwana in the late Neoproterozoic after Rodinia breakup. The sequence was subsequently metamorphosed and intruded by the Granite Harbour Intrusives during the Ross Orogeny. The Molar Formation of the Bowers Terrane is interpreted as a turbiditic sequence deposited in an accretionary setting on the active continental margin in the Late Cambrian during and after accretion of the Glasgow island arc allochthon. The thick, homogeneous sequence of the Robertson Bay Group resulted from continuous turbiditic sedimentation in an accretionary wedge in front of the Ross Orogen after docking and imbrication of the Glasgow island arc in the Early Ordovician.

A New Cisuralian Permian Fauna From Tropical Gondwana

New Permian fauna from tropical Gondwana

Authors:

Cisneros et al

Abstract:

Terrestrial vertebrates are first known to colonize high-latitude regions during the middle Permian (Guadalupian) about 270 million years ago, following the Pennsylvanian Gondwanan continental glaciation. However, despite over 150 years of study in these areas, the biogeographic origins of these rich communities of land-dwelling vertebrates remain obscure. Here we report on a new early Permian continental tetrapod fauna from South America in tropical Western Gondwana that sheds new light on patterns of tetrapod distribution. Northeastern Brazil hosted an extensive lacustrine system inhabited by a unique community of temnospondyl amphibians and reptiles that considerably expand the known temporal and geographic ranges of key subgroups. Our findings demonstrate that tetrapod groups common in later Permian and Triassic temperate communities were already present in tropical Gondwana by the early Permian (Cisuralian). This new fauna constitutes a new biogeographic province with North American affinities and clearly demonstrates that tetrapod dispersal into Gondwana was already underway at the beginning of the Permian.

pop sci write up.

Chilesaurus diegosuarezi: A Bizarre new Herbivorous Theropod From Tithonian Jurassic Chile

An enigmatic plant-eating theropod from the Late Jurassic period of Chile

Authors:

Novas et al

Abstract:

Theropod dinosaurs were the dominant predators in most Mesozoic era terrestrial ecosystems. Early theropod evolution is currently interpreted as the diversification of various carnivorous and cursorial taxa, whereas the acquisition of herbivorism, together with the secondary loss of cursorial adaptations, occurred much later among advanced coelurosaurian theropods. new, bizarre herbivorous basal tetanuran from the Upper Jurassic of Chile challenges this conception. The new dinosaur was discovered at Aysén, a fossil locality in the Upper Jurassic Toqui Formation of southern Chile (General Carrera Lake). The site yielded abundant and exquisitely preserved three-dimensional skeletons of small archosaurs. Several articulated individuals of Chilesaurus at different ontogenetic stages have been collected, as well as less abundant basal crocodyliforms, and fragmentary remains of sauropod dinosaurs (diplodocids and titanosaurians).

No word whether it preferred red or green.   Obviously it was a Hatched variety.

Reconstructing the Evolving PaleoEcology of Mesozoic Gondwana

Gondwanan Mesozoic biotas and bioevents

Authors:

McLoughlin et al

Abstract:

This special issue draws together presentations and related studies arising from both the symposium on “Mesozoic bioevents and Gondwanan biotas” at the 34th International Geological Congress in Brisbane, 2012, and the “Southern Hemisphere floras: unique insights into the biology and ecology of Southern Hemisphere ecosystems” meeting of the joint 13th International Palynological Congress and 9th Palaeobotanical Conference held in Tokyo, 2012. The theme also builds upon recent specialist compilations of similar works on Mesozoic biotas from the Northern and Southern hemispheres (Vajda and Turner, 2009; McLoughlin and Kear, 2010), and emphasizes the continuing high level of interest in events and processes that shaped the world’s faunas and floras between two of the greatest mass extinctions in Earth’s history.

The Mesozoic (251–66 Ma) is arguably one of the most spectacular intervals of biotic evolution in the Phanerozoic. The era began in the depths of Earth's most severe biotic crisis – the end-Permian extinction event, which was followed by prolonged and climatically harsh hothouse conditions of the Early Triassic (Retallack, 2013; Metcalfe et al., 2013). New radiometric data are now providing a precise means of calibrating the individual stages of decline and recovery associated with this mass extinction event (Metcalfe et al. in press). The slow recuperation of biotic diversity through the Middle and Late Triassic saw the rise of two animal groups that would compete for dominance of the terrestrial faunas for the remainder of the Phanerozoic –dinosaurs and mammals. Further mass extinctions and marine anoxia events at the end of the Triassic and in the Toarcian punctuated the evolution of life through the mid-Mesozoic (Hesselbo et al., 2002; Huang and Hesselbo, 2014). The Jurassic was also marked by episodic asteroid impacts, regionally intensive volcanism and the early stages of continental rifting (Vajda and Wigforss-Lange, 2009). Nevertheless, the mild, equable climates and broad connections between landmasses in the Jurassic saw the development of relatively cosmopolitan floras and faunas during the dinosaurian ‘heyday’ (Meyen, 1987; Novas, 2009). The subsequent, Late Jurassic–Cretaceous fragmentation of Pangaea and of Gondwana (Chatterjee et al., 2013; Torsvik and Cocks, 2013) saw progressive isolation of biotas, particularly in the Southern Hemisphere, and had a major influence on endemism and overall levels of biodiversity (Lloyd et al., 2008). Accompanying this fragmentation, new groups of vertebrates evolved to take advantage of niches arising through the constantly changing environmental pressures. These changes are evident not only on land, where new groups of dinosaurs (including birds), squamates, and mammals thrived, but also in the oceans where there were major radiations amongst coccolithophorids, dinoflagellates and centric diatoms, where modern lamniform sharks and teleosts rose to the fore, and gigantic mosasaurid lizards ultimately claimed dominance as the ocean’s apex predators (Cloudsley-Thompson, 2005).

Within the terrestrial flora, one insignificant and possibly aquatic group – the flowering plants – made their first appearance in the Early Cretaceous. These opportunistic colonizers possessed seeds protected in ovaries, and in many cases developed showy appendages to encourage a special relationship with insects as pollination vectors. During their rapid diversification and rise to dominance through the mid-Cretaceous, the flowering plants evolved a bewildering array of forms, from minute single-leafed floating plants to some of the world's tallest trees. By the end of the Cretaceous, these formerly obscure plants had claimed dominance of the vegetation and had transformed the face of the landscape (Friis et al., 2011). In turn, the new vegetation types, including closed damp forests, offered opportunities for other plant lineages, such as polypodialean ferns, to undergo evolutionary radiations of their own (Pryer et al., 2004).

The end of the Cretaceous saw another of Earth's great catastrophes – the impact of an asteroid in the Yucatan Peninsula region. This event witnessed the demise of the great (non-feathered) dinosaurs and radically altered life in both the seas and the terrestrial forests, thus bringing the final chapter of the Mesozoic to an abrupt close (Schulte et al., 2010).

Evidence of Continental Rifting of Supercontinent Rodinia From Ediacaran China

The 600–580 Ma continental rift basalts in North Qilian Shan, northwest China: Links between the Qilian-Qaidam block and SE Australia, and the reconstruction of East Gondwana

Authors:

Xu et al

Abstract:

We report a sequence of thick, well-preserved basaltic lavas interlayered with shallow marine dolomitic carbonates, mudstones and siltstones of the Zhulongguan Group, in the western segment of the North Qilian orogen, northwest China. Two new zircon SIMS ages show that this sequence formed at ∼600–580 Ma. The mafic volcanics can be subdivided into tholeiitic and alkaline basalts, and have compositions similar to present-day ocean island basalt (OIB) or continental flood basalts. The occurrence, geochemical features and age data suggest that the Zhulongguan basalts originated at a continental rift setting in the latest Neoproterozoic, within the north margin of the Qilian-Qaidam block. This volcanic-sedimentary formation exhibits close affinity to the passive continental margin in southeastern Australia. Our observations favor a link of the Qilian-Qaidam block with SE Australia (also south China) during the breakup of Rodinia, thereby filling a void in existing reconstructions of the region.

Examining the Height and end of the Permian Ice Age in Australia

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

Authors:

Frank et al

Abstract:

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.

Evidence of a Campanian Cretaceous Wildfire From Antarctica

The first report of a Campanian palaeo-wildfire in the West Antarctic Peninsula

Authors:

Manfroi et al

Abstract:

The analysis of palaeofloras and the related palaeoecological conditions is of great importance for the understanding of past environmental and palaeoclimatic events in Antarctica. At the end of the Cretaceous, subtropical forests developed there because of wet and temperate climate conditions. On the Antarctic Peninsula, which is geologically characterized by a forearc context, volcanic activity caused by tectonics favours the ignition of vegetation fires. In the present study, the occurrence of palaeo-wildfires during the Upper Cretaceous is demonstrated for the Rip Point outcrop on Nelson Island, South Shetland Islands. During Brazilian expeditions to the area, macroscopic charcoal was collected and subsequently analysed under a stereomicroscope and scanning electron microscope (SEM). The charred wood remains were identified as belonging to conifers, which were important components of the Antarctic palaeoflora during the Cretaceous. A review of the data published thus far regarding palaeo-wildfires in the Southern Hemisphere confirms that the charcoal remains analysed here are the first to verify the occurrence of palaeo-wildfires in the upper Campanian levels of the West Antarctic Peninsula.

Early Seed Plants From Tournaisian Mississipian Carboniferous Argentina

Early seed plants from Western Gondwana: Paleobiogeographical and ecological implications based on Tournaisian (Lower Carboniferous) records from Argentina

Authors:

Prestianni et al

Abstract:

The oldest seed occurrences in Western Gondwana have been recognized in a new stratigraphic section located in Western Argentina (Precordillera Basin). Palynological evidence indicates an Early Mississippian (probably Tournaisian) age for this new succession. The two identified early seeds generas, Pseudosporogonites cf. hallei and Warsteinia sancheziae n. sp. were up to now considered as restricted to the Devonian of Laurussia. This finding suggests a dispersal of earliest spermatophytes between Laurussia and Gondwana during Devonian/Tournaisian times, thus accounting for the Rheic Ocean as a surmountable biogeographic barrier for continental biotas. Alternatively, contrasting biogeographic hypotheses dealing with early spermatophytes rising in paleotropics and then displacing herbaceous communities of non-spermatophytes typical from cool high latitudinal regions, are explored for explaining the recognized paleobiogeographical pattern. The new information supports a weak impact of the Devonian/Carboniferous biotic crisis on earliest seed plant diversity. Based on preliminary evidences of niches differentiation and ecological dynamics probably affected by wildfires, Tournaisian Gondwanan plant communities from high latitudes are interpreted as being more complex than previously thought, and more similar to those reported from Laurussia. In addition, their discovery in a sedimentary environment associated to glacigenic deposits, show that this new record might be linked to the coeval glacial age widely recorded elsewhere in Gondwana.

Deserts in Southwest Gondwana During Moscovian Pennsylvannian Carboniferous

Late Pennsylvanian aridification on the southwestern margin of Gondwana (Paganzo Basin, NW Argentina): A regional expression of a global climate perturbation
Authors:

Gulbranson et al

Abstract:

Paleosols of the Paganzo Group preserve a shift from the cool climate of the glaciated high-latitudes of Gondwana to a long-term aridification punctuated by shorter-term fluctuations in moisture regime in the late Carboniferous. A quantitative reconstruction of paleoclimate inferred from the major element chemistry of paleosol horizons and the stable isotope geochemistry of soil-formed minerals and organic matter indicates that the climate varied substantially during deglaciation along the southwestern margin of Gondwana in the Middle Pennsylvanian including two geologically abrupt shifts to notably drier conditions. This dynamic climate terminates in a dry subhumid moisture regime characterized by steppe/dry scrub floral provinces. Quantitative estimates of net primary production during the post-glacial interval inferred from paleosol major element geochemistry are consistent with a mesic soil temperature regime, in agreement with paleotemperatures inferred from pedogenic goethite δD and δ18O. Contemporaneous aridification is well expressed in paleotropical continental records with Middle to Late Pennsylvanian aridification coincident with an abrupt evolutionary change in many marine and terrestrial species. The synchrony of aridification between the high and low paleo-latitudes and concomitant major restructuring of some ecosystems suggests that a paleoclimate change of global nature occurred during the Moscovian and Kasimovian.

Middle Cretaceous Dinosaur Assemblages From northern Brazil and Africa

Middle Cretaceous dinosaur assemblages from northern Brazil and northern Africa and their implications for northern Gondwanan composition

Author:

Candeiro

Abstract:

Dinosaurs are one of the most dominant groups in Cretaceous reptilian faunas. A summary of their record in northern Brazil and northern Africa during the middle of the Cretaceous Period (Aptian-Cenomanian) is presented here. Dinosaurs are represented by 32 species (three ornithischians, six sauropods and 23 theropods) from Brazil, Egypt, Lybia, Morocco, Niger, Sudan and Tunisia. These dinosaur assemblages provide fundamental data about distribution and composition of sauropods and theropods in northern Gondwana during the middle of the Cretaceous Period and confirm these assemblages to be among the most important dinosaur faunas in the north Gondwana areas.

Evidence of Gondwana's Assembly During Cryogenian/Ediacaran NeoProterozoic

U-Pb age of the coesite-bearing eclogite from NW Borborema Province, NE Brazil: Implications for western Gondwana assembly

Authors:

Saraiva dos Santos et al

Abstract:

The Late Neoproterozoic assembly of western Gondwana played an important role in the subduction of oceanic and continental lithosphere. Such event was also source of arc magmatism, reworking of cratonic margins and development of ultra-high pressure (UHP) suture zones. In the Borborema province, NE Brazil, we have described for the first time UHP rocks enclosed within gneiss migmatite and calc-silicate rocks. They bear coesite included in atoll-type garnet from metamafic rocks, identified by petrographic study and Raman microspectroscopy analysis. U-Pb zircon dating of the leucosome of the migmatites and the calc-silicate rocks displays, concordant ages of 639 ± 10 Ma and 649.7 ± 5 Ma, respectively, here interpreted as the minimum age of the eclogitization event in the region. U-Pb zircon dating of the coesite-bearing rock defined a concordia age of 614. 9 ± 7.9 Ma that comprised the retrograde eclogitic conditions to amphibolite facies. The UHP rocks, mostly retrograded to garnet amphibolites, occur enclosed in the Paleoproterozoic continental block composed of calc-silicate rocks, migmatized sillimanite gneiss, mylonitic augen gneiss and granitic and tonalitic gneiss along a narrow N-S oriented belt between the Santa Quitéria magmatic arc and the Transbrasiliano lineament. This block was involved in the subduction to UHP eclogite depths, and was retrogressed to amphibolite during its exhumation and thrusting. Our data indicate an important Neoproterozoic transcontinental suture zone connecting the Pharusian belt with Borborema Province, and probably with the Brasília belt in central Brazil.