late paleozoic glacial episodes in gondwanaland reflected in transgressive regressive depositional sequences in euramerica the late paleozoic glaciation of gondwanaland comprised two short episodes in the famennian i and visean ii confined to brazil and adjacent northwest africa and a long episode that started in the namurian iiia of eastern australia and bolivia argentina expanded to cover much of gondwanaland in the stephanian asselian iiib and collapsed in the early sakmarian iiic dropstones in eastern australia indicate that small ice centers lingered to the kazanian across the belt of low latitudes north of gondwanaland short ranging fossils in widespread shallow marine and paralic deposits indicate synchronous deposition of transgressive regressive sequences in different parts of euramerica these sequences correlate with glacial events in gondwanaland at three levels a four major regressions in euramerica in the famennian 1 visean 2 namurian 3 stephanian 4 and the tastubian transgression that preceded the sterlitamakian regression 5 also recorded in gondwanaland correlate with glacial episodes i ii and iiia iiib and iiic b the time interval of cyclothemic deposition in euramerica brigantian or latest visean to sterlitamakian correlates with that of glacial episode iii and c the dominant period of the euramerican cyclothems as estimated from the middle and late pennsylvanian deposits of the mid continent of north america and of the thickest known gondwanaland glacigenic sediment the earliest permian lyons group of western australia is 0 4 ma equivalent in turn to the long orbital eccentricity period of the quaternary ice age and the dominant period of fluctuation of the late miocene antarctic ice cap the three levels of correlations confirm wanless and shepard9s 1936 hypothesis that the late paleozoic cyclothems are controlled largely by sea level fluctuations related to the gondwanaland glaciation

a depositional record of deglaciation in a paleofjord late carboniferous pennsylvanian of san juan province argentina the role of catastrophic sedimentation the combination of high sediment supply rates and ample accommodation within fjords provides high resolution records of deglaciation ancient fjord fills provide the potential for three dimensional views of the evolution of depositional environments in response to changing sediment supply and base level through the deglacial process we describe the fill jejenes formation of a well exposed late carboniferous pennsylvanian glacial valley and its tributaries these deposits record the progressive marine flooding and infilling of topography by glacially derived sediments the geometry of the valley and its tributaries is controlled by the underlying lower paleozoic lithologies a deep valley with steep sides exists where the bedrock is massive limestones and a broader shallower valley exists where the bedrock is generally a fine grained olistostrome the valleys are locally floored with diamictites including both in situ tillites and remobilized diamictites in the trunk valley these are locally overlain by a small shallow water delta the major part of the valley fill consists of a 150 m thick mudstone dominated succession probably generated by plumes of glacial outwash containing numerous dropstones that decrease in abundance down the fjord the mudstones contain numerous thin sandstone and conglomerate turbidites that were supplied laterally via subaqueous gravel fans feeding in from the tributary valleys each of which has a distinctive clast suite related to the local subcrop the entire succession is overlain by 300 m of sandy turbidites of which the upper part includes large mass transport complexes intercalated within the succession in the trunk valley are structureless graded silty mudstones lacking dropstones but with abundant large wood fragments close to the steep western margin of the trunk valley each of these massive mudstones is underlain by a slump or debris flow locally containing meter scale blocks of ordovician limestone from the valley side we interpret these as a consequence of rockfalls from the steeper valley sides triggering debris flows on the subaqueous fjord slopes we suggest that large solitary waves were generated as the rockfalls entered the water traveling along the fjord and stripping vegetation from the shoreline large amounts of mud and silt were thrown into suspension during these events and subsequently settled from suspension to form the structureless graded beds these deposits and other mass flow deposits within the succession emphasize the potential importance of catastrophic sedimentation within deglacial successions

late devonian glaciation in south america abstract an ice age in famennian late devonian time is documented by the presence of diamictites with striated faceted and polished pebbles rhythmites with dropstones erratic boulders and striated pavements and deformed sandstones the glacigenic beds occur in three huge intracratonic basins solimoes amazonas and parnaiba and in one pericratonic basin acre in northern brazil other possible late devonian diamictites may occur elsewhere in brazil and africa which if confirmed would extend considerably the area affected by this glacial age the onset of the late devonian glaciation caused a global narrowing of the warm climatic belts sharp regression increased clastic sedimentation massive biotic extinction reduced biochemical deposition and unconformities this resulted in important facies changes in the world geological record ice centers moved from northern africa to southwestern south america from late ordovician to early silurian time from mid silurian to early late devonian time no record of glaciation is known in late late devonian time intermittent glaciation began again in central south america and from late late devonian to early late permian time ice centers migrated towards antarctica across south america and south africa the devonian and ordovician silurian glaciations together with the better known permo carboniferous glaciations may all have primarily resulted from the shifting position of the gondwana continent with respect to the south pole

origin of late paleozoic multiple glacially striated surfaces in northern parana basin brazil some implications for the dynamics of the parana glacial lobe abstract four stratigraphically repeated closely spaced striated surfaces on late paleozoic sandstone at the base of the itarare subgroup in northern parana basin were generated by subglacial erosion during advances of the grounding zone of the tidewater terminus of the parana glacial lobe on unconsolidated sand the sandstone corresponds to a channelized sheet like proglacial outwash fan accumulated sub aquatically in front of the tidewater terminus of a temperate warm based glacier at the margin of the marine flooded parana basin sandy siltstone beds intercalated with the sandstone and resting on top of the striated surfaces represent aggradational mud deposited from settling of fine debris plumes overflows erosion was mostly by abrasion wear of the sand bed under a glacier sliding over an unfrozen substratum evidence of ploughing is minimal the glacier bed is thought to have behaved rheologically as a rigid essentially undeformable substratum discontinuities in the distribution of striations on the surfaces indicate that ice may have at places decoupled from its bed the section studied documents an upward fining and deepening deglacial sequence comprising four stratigraphic cycles of accumulation of sand formation of a striated surface followed by deposition of mud cycles are correlated with short lived probably fast seasonal advances of the tidewater terminus during general retreat of the parana lobe ice advances were not associated with deposition of subglacial diamicton or lodgement of clasts but to erosion of sand probably by ice protuberances under the sliding glacier

nurse logs an ecological strategy in a late paleozoic forest from the southern andean region abstractdecaying logs on the forest oor can act as nurse logs for new seedlings helping with the regeneration of the vegetation fossil evi dence of this ecological strategy is exceptionally well preserved in the argentinean andes where an 300 m y old permineralized for est was found at 3000 m elevation in san juan province the fossil trunks some of them in life position are intercalated between volca nic rocks and sediments deposited in ooded environments probably coastal lagoons more than 100 specimens studied allow us to suggest the dominance of only one tree species in the forest the rst issue of the research was to determine the means used by the vegetation to survive in such adverse environmental conditions fossil evidence supports the hypothesis of regeneration via nurse logs little rootlets preserved inside the wood of several specimens indicate that seedlings developed on these logs important additional information provided by the fossils is the presence of aerenchymatic tissue in the rootlets aerenchyma tissue is a common feature developed in plants living in ooded environments therefore its recognition in the fossil forest helps in the ecological interpretation introduction

glaciation aridification and carbon sequestration in the permo carboniferous the isotopic record from low latitudes to evaluate the isotopic record of climate change and carbon sequestration in the late paleozoic we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from carboniferous through middle permian 359 260 ma strata we focus on the isotopic records from the u s midcontinent and the russian platform because these two regions provide well preserved marine fossils spanning a broad time interval both regions show a 18o increase at the mid carboniferous boundary ca 318 ma that roughly correlates with geologic evidence for an expansion of gondwanan glaciers only the russian platform record shows a 18o maximum during the glacial maximum in the asselian in contrast to a previous study korte c jasper t kozur h w and veizer j 2005 18o and 13c of permian brachiopods a record of seawater evolution and continental glaciation palaeogeogr palaeoclimatol palaeoecol 224 333 351 our data show no oxygen isotope evidence for glacial retreat in the early permian but instead show increasing 18o values related to aridification dissimilarity in the 18o trends for the epicontinental seas of north american and the russian platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater 18o values these results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western north america intermediate values in the midcontinent and high values in the sverdrup basin russian platform and northern spain nevertheless both u s midcontinent and russian platform records show a late serpukhovian minimum a sharp increase across the mid carboniferous boundary and a minimum centered on the kasimovian the correlative increase in brachiopod 13c and 18o values at the mid carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the permo carboniferous

permian phytogeographic patterns and climate data model comparisons abstract the most recent global icehouse hothouse climate transition in earth history began during the permian warmer polar conditions relative to today then persisted through the mesozoic and into the cenozoic we focus here on two permian stages the sakmarian 285 280 ma and the wordian 267 264 ma also known as the kazanian integrating floral with lithological data to determine their climates globally these stages postdate the permo carboniferous glaciation but retain a moderately steep equator to pole gradient judging by the level of floral and faunal differentiation floral data provide a particularly useful means of interpreting terrestrial paleoclimates often revealing information about climate gradations between dry and wet end member lithological indicators such as evaporites and coals we applied multivariate statistical analyses to the permian floral data to calibrate the nature of floral and geographical transitions as an aid to climate interpretation we then classified sakma

sequence stratigraphy of paralic coal bearing strata an overview abstract sequence stratigraphy arose in the late 1980s to fundamentally change the science of stratigraphy former practice of labeling formations and erecting stratigraphic columns gave place to a dynamic genetic stratigraphic analysis where the main concern is about understanding the history of sedimentation and to establish models able to predict facies born and mainly applied to an environment of petroleum prospecting and exploration sequence stratigraphy has gained entrance to other branches of sedimentary geology the present paper gives a short introduction to sequence stratigraphic concepts and shows an overview of its application on coal bearing strata two case studies one from the early permian coals of the parana basin brazil and one from the lower cretaceous coals of the western canada sedimentary basin illustrate the concepts

30 million years of permian volcanism recorded in the choiyoi igneous province w argentina and their source for younger ash fall deposits in the parana basin shrimp u pb zircon geochronology evidence abstract we present four shrimp u pb zircon ages for the choiyoi igneous province from the san rafael block central western argentina dated samples come from the yacimiento los reyunos formation 281 4 2 5 ma of the cochico group lower choiyoi section andesitic breccias dacitic to rhyolitic ignimbrites and continental conglomerates agua de los burros formation 264 8 2 3 ma and 264 5 3 0 ma and cerro carrizalito formation 251 9 2 7 ma upper choiyoi section rhyolitic ignimbrites and pyroclastic flows spanning the entire permian succession of the choiyoi igneous province a single zircon from the el imperial formation that is overlain unconformably by the choiyoi succession yielded an early permian age 297 2 5 3 ma while the main detrital zircon population indicated an ordovician age 453 7 8 1 ma the new data establishes a more precise permian age artinskian lopingian for the section studied spanning 30 ma of volcanic activity volcanological observations for the choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes capable of injecting enormous volumes of tephra in the troposphere stratosphere the new shrimp ages indicate contemporaneity between the choyoi succession and the upper part of the parana basin late paleozoic section from the irati up to the rio do rasto formations encompassing about 24 ma geochemical data show a general congruence in compositional and tectonic settings between the volcanics and parana basin permian ash fall derived layers of bentonites thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions thus we consider that the choiyoi igneous province was the source of ash fall deposits in the upper permian section of the parana basin data presented here allow a more consistent correlation between tectono volcanic permian events along the paleo pacific margin of southwestern gondwana and the geological evolution of neighboring paleozoic foreland basins in south america and africa

rapid onset of late paleozoic glaciation on gondwana evidence from upper mississippian strata of the midcontinent united states direct evidence of the late paleozoic glaciation of gondwana from glacial deposits suggests that geographically extensive continental glaciation began some time in the namurian late mississippian however the timing and characteristics of the onset of glaciation are poorly understood because of a lack of reliable paleontological control and reworking of initial glacial deposits by subsequent glacial advances indirect evidence of glaciation preserved in unconformity bounded low latitude ramp sequences in the illinois basin united states suggests that geographically extensive continental glaciation of gondwana actually began in the late visean an abrupt change from carbonate dominated sequences bounded by disconformities with little evidence of erosion to mixed carbonate siliciclastic sequences bounded by unconformities with deep incised valleys was likely produced by a three fold increase in the magnitude of eustatic sea level fluctuations the increase in the magnitude of sea level fluctuations was likely driven by an equally abrupt increase in ice volume and marks the onset of the geographically extensive late paleozoic glaciation of gondwana a possible explanation for the rapid onset of glaciation is the closing of the equatorial seaway between laurussia and gondwana closing of this seaway would have led to an abrupt change in oceanic and atmospheric circulation patterns that could have initiated major continental glaciation in the southern hemisphere

paleoclimatic significance of the lacustrine carboniferous deposits in northwest argentina abstract the origin and probable paleoclimatic significance of carboniferous lacustrine deposits in northwest argentina are discussed these rocks are developed extensively throughout northwestern argentina but are described in the present paper only from the region of the sistema del famatina five lithofacies have been identified a laminated siltstones and claystones b thinly interbedded mudstones and sandstones c interlayered mudstones and sandstones with sole structures flute marks and tool marks d conglomerates and fine sandstones e sandstones and diamictites these lithofacies are interpreted as lacustrine deposits formed during the final episode of the carboniferous glaciation lithofacies a originated as a suspension load deposit in the central and intermediate parts of the lake the presence of dropstones in this lithofacies suggests coeval ice rafting processes underflow currents probably formed lithofacies b and lacustrine turbidites lithofacies c lithofacies d and e were deposited in marginal environments and represent in some cases shoreline bars and small deltas the age of the lacustrine episode is deduced from paleobotanical information both palynological and megafloristic data suggest that these deposits were formed during the middle carboniferous a palynological assemblage dominated by cristatisporites like spores characterizes these sediments

bimodal character of the late paleozoic glaciations in argentina and bipolarity of climatic changes abstract the upper paleozoic sedimentary rock sequences of argentina show an outstanding record of climatic fluctuations during this interval and the complexity and rapidity of the climatic changes there were two distinct events of cooling or glacial periods the older in the middle carboniferous late visean bashkirian and the younger in the early permian asselian tastubian and these were separated by a long lasting interval of warming during the late pennsylvanian it is postulated that climatic fluctuations in the northern paleotemperate realm may have had the same causes as in argentina and that these periods of cooling and warming probably occurred at the same time in both hemispheres in western argentina and central patagonia the occurrence of the early permian glacial phase and the absence of the younger phases like those present in eastern argentina and south africa suggest that during the final deglaciation in gondwana thawing gradually progressed to the east then located closer to the paleopolar region

palynological biozones and radiometric data at the carboniferous permian boundary in western gondwana absolute radiometric data obtained recently in upper paleozoic basins of south america and southern africa are available to constrain the age of some palynological biozones defined in the western gondwana some dates obtained from argentina coincide with southern africa s and are useful to constrain the palynological associations in this way the permian argentinian lueckisporites weylandites lw biozone is compared with the lueckisporites virkkiae biozone of brazil and zone 3 of south africa on the other hand the palynofloras from dwyka south africa are comparable with argentinian and brazilian associations recovered near the carboniferous permian boundary tuffaceous intervals of the dwyka group in south africa suggest the beginning of that sequence at 307 ma reaching the 290 ma at the top the available palynological paleoenvironmental and radiometric data from these three western gondwanan areas are analyzed and compared 2006 international association for gondwana research published by elsevier b v all rights reserved

the applicability of the chemical index of alteration as a paleoclimatic indicator an example from the permian of the parana basin brazil abstract the chemical index of alteration cia was expressed as cia molar to become a more sensitive measure of the degree of chemical weathering the cia molar has the value of 1 for fresh feldspars and for unweathered non peraluminous igneous rocks but increases towards infinity as chemical weathering progresses the utility of this index as a humidity indicator for both modern and ancient muds was tested a database comprising 281 entries with chemical data for modern and ancient sediments deposited under arid semi arid semi humid and humid climate was assembled from the literature and used to calibrate the relationship between humidity and cia molar values for both modern and ancient sediments the histograms display a shift towards higher values with increasing geological indicators of humidity whereas sediments deposited under conditions inferred to be arid from other geological indicators show values tightly clustered around 1 the permian of the parana basin was then used as an example of the applicability of the cia molar for paleoclimatic studies major element analyses al2o3 k2o na2o cao were performed on 55 claystones and shales from three drill cores in a stratigraphic succession spanning the early to late permian the cia molar for these rocks accorded with expectations based on sedimentologic and paleontologic evidence discriminating well between arid and humid conditions in the basin independently determined from sedimentological and paleontological indicators the use of the cia molar as a paleo humidity indicator however can be limited by the presence of carbonate rich sediments the occurrence of post depositional k addition metasomatism metamorphism diagenetic illitization as well as by inheritance of clays from sedimentary rocks in the source area nevertheless with appropriate caution the cia molar is a useful tool for the assessment of the humidity conditions in the rock record

siberian glaciation as a constraint on permian carboniferous co2 levels reconstructions of phanerozoic co2 levels have generally relied on geochemical modeling or proxy data because the uncertainty inherent in such reconstructions is large enough to be climatically significant inverse climate modeling may help to constrain paleo co2 estimates in particular we test the plausibility of this technique by focusing on the climate from 360 to 260 ma a time in which the siberian landmass was in middle to high latitudes yet had little or no permanent land ice our climate model simulations predict a lower limit for co2 the value beneath which siberia acquires excess ice simulations provide little new information for the period in which siberia was at a relatively low paleoaltitude 360 340 ma but model results imply that paleo co2 levels had to be greater than 2 4 modern values to be consistent with an apparently ice free siberia in the late permian these results for the later period in general agree with soil co2 proxies and the timing of gondwanan deglaciation thus providing support for a significant co2 increase before the end permian boundary event our technique may be applicable to other time intervals of unipolar glaciation

an upper paleozoic bio chronostratigraphic scheme for the western margin of gondwana abstract the carboniferous and permian fossiliferous sequences of the central western argentina contain abundant plant remains palynomorphs and invertebrates they include a continuous record of large distribution in the paganzo rio blanco calingasta uspallata and san rafael basins the most recent biostratigraphic schemes recognize a floristic succession represented by the biozones archaeosigillaria frenguellia af biozone frenguellia eximia nothorhacopteris kellaybelenensis cordaicarpus cesarii fnc biozone nothorhacopteris botrychiopsis ginkgophyllum nbg biozone interval biozone and gangamopteris biozone the associated palynological record is represented by the biozones reticulatisporites magnidictyus verrucosisporites quasigobbetti mq biozone raistrickia densa convolutispora muriornata dm biozone pakhapites fusus vittatina subsaccata fs biozone and lueckisporites weylandites lw biozone the precise age of the upper paleozoic western gondwanan biozones has been under discussion and remains controversial to date in some regions the main issue hampering an integrated comparison of the gondwanan biozones was its imprecise chronostratigraphic framework however new studies in some argentinian stratigraphic sections bearing floras and faunas have yielded several radiometric ages from these 206 pb 238 u zircon datings it is possible to determine the chronostratigraphic range of many fossiliferous assemblages in this sector of gondwana in this way the af and mq biozones are restricted to the late mississippian and they would be not younger than 335 ma according to radiometric ages 206 pb 238 u ages suggest that the nbg dma and dmb biozones characterize the late serpukhovian glacial deposits and persisted up to the late bashkirian beds containing the interval and dmc biozones have yielded 206 pb 238 u ages of 312 82 0 11 ma and 310 71 0 1 ma which would indicate that both zones characterize the moscovian the remains of gangamopteris biozone found in the paganzo basin overlie basalt levels ranging between 308 6 and 293 6 ma therefore the incoming of the first glossopterids was closely associated to the carboniferous permian boundary in this part of gondwana the data presented in this paper are used for establishing comparisons with other gondwanan biozones constrained by absolute ages

eolian permian deposits in west and northwest argentina abstract the sedimentary and stratigraphic characteristics of eolian permian deposits exposed in mendoza la rioja and san juan provinces west and northwest argentina are described in this paper the eolianites are fine and medium sandstones with large scale cross bedding multiple parallel truncation planes and some asymmetrical ripples three genetic types of deposits have been identified dune facies eolian sand sheet facies and mixed fluvial eolian facies fine and medium sandstones with large scale cross bedding and multiple parallel truncation planes are here interpreted as dune deposits mainly crescentic dunes and unstratified or flat bedded sandstones as eolian sand sheet deposits mixed fluvial and eolian sequences composed of sandstones mudstones and some matrix supported conglomerates represent a transitional facies between those formed in eolian and fluvial environments this considerable deposition of eolian sediments was probably brought about by the existence of an extensive medium to low latitude continent and the withdrawal of marine environments the environments with highest aridity occurred towards the south and west of the region the eolian circulation pattern was controlled by a long ensialic volcanic arc emerging towards the west of the basin

evidence of glacial abrasion in the calingasta uspallata and western paganzo basins mid carboniferous of western argentina abstract evidence of glacial abrasion is present in the basal part of the carboniferous section of the calingasta uspallata and paganzo western argentina where subglacial and proximal glacial marine diamictites with pebbly dropstone shales constitute the dominant facies association intraformational striated pavements are exposed in the hoyada verde and leoncito formations of the calingasta uspallata basin marine invertebrate fossils levispustula zone in associated shales indicate a mid carboniferous age for both units a single layer striated boulder pavement is superbly exposed in the hoyada verde formation local a axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement paleo ice flow directions have an nne ssw strike the leoncito intraformational pavement is shaped on bioturbated fine grained sandstones with plant remains glacial striations are straight and parallel with subcircular cross sections dome like features are present in the surface which is covered in turn by a sandy bouldery diamictite four striated surfaces are present in the western paganzo basin three of them pavements at the san juan river valley loma de los piojos and agua hedionda are developed on basement rocks they contain parallel to subparallel striations nailhead striations crescentic gouges impact marks and furrows the pavements are overlain by thin up to 1 5 m laterally discontinuous diamictite beds with striated clasts some of them bullet shaped paleo ice flow directions are n ne directed an intraformational pavement is also present at the san juan river valley section it is carved on the top of the basal diamictite and exhibits furrows probably caused by subglacial soft sediment grooving the dispersion of paleo ice flow directions in the calingasta uspallata and paganzo basins indicates i regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions ii glacial erosion by ice grounded below sea level and confined to the margins of the basins

a temporal link between the emeishan large igneous province sw china and the end guadalupian mass extinction abstract previous studies have suggested that there were two mass extinction events in the late permian one that occurred at the permo triassic p t boundary 251 ma and a second smaller mass extinction that occurred 5 8 myr earlier at the end of the guadalupian many workers have argued that there is a causal relationship between large scale volcanic activity and mass extinctions the major mass extinction event at the p t boundary coincides with the outpouring of huge quantities of lava that formed the siberian flood basalt province in russia courtillot et al earth planet sci lett 166 1999 177 195 and wignall earth sci rev 53 2001 1 33 suggested that the earlier late permian mass extinction coincided with the eruption of the lavas that formed the emeishan flood basalt efb province in sw china however the age of eruption of the efb lavas is poorly constrained using the sensitive high resolution ion microprobe to analyze zircons we have established the age of the xinjie intrusion believed to be a feeder to the main phase of efb volcanism to be 259 3 ma hence the formation of the efb is coincident with a proposed extinction event at 256 259 ma this result supports a temporal link between the emeishan large igneous province and the end guadalupian mass extinction

a new u pb zircon age dating and palynological data from a lower permian section of the southernmost parana basin brazil biochronostratigraphical and geochronological implications for gondwanan correlations abstract index species useful for correlations with the international stratigraphical column are rare or absent in the pennsylvanian permian strata of the parana basin in brazil preventing accuracy in geochronologic assignments besides absolute datings are very scarce in comparison with other gondwana basins this paper presents palynological data from an outcrop on the surroundings of the candiota coal mine southmost brazil from several levels of the rio bonito and palermo formations the presence of certain index species of spore pollen allowed the recognition of two permian palynozones the vittatina costabilis and the lueckisporites virkkiae zones furthermore u pb in zircons from a volcaniclastic level interbedded in the coal strata of the former unit was analyzed through la mc icp ms method providing a new absolute age dating of 281 4 3 4 ma cisuralian early permian this dating is assumed as the oldest occurrence of the l virkkiae zone in parana basin which contains index species that are widespread in other gondwana basins a well distributed surface boundary occurs in this section also allowing local and regional correlations these new biostratigraphical and geochronological data are integrated in order to offer a deep analysis on the stratigraphical significance for correlations across the occidental gondwana

patterns of late palaeozoic deglaciation in the parana basin brazil abstract the itarare subgroup middle carboniferous early permian of the parana basin of southeastern brazil contains the thickest most extensive and one of the longest records of late palaeozoic glaciation in all of the gondwana supercontinent glacially controlled deposition started as early as the middle carboniferous when lobate termini of ice streams from the windhoek ice sheet wis and rio grande do sul and asuncion ice caps moved into the parana basin lobes reached sea level and advanced grounded at least as far as 200 km into the basin stabilizing as tidal intertidal margins glaciation and glacial sedimentation occurred penecontemporaneously with the transgressive phase of the late palaeozoic tectonic cycle of the parana basin while gondwana was gradually moving away from the south pole evolution involved complex interaction of tectonic palaeogeographic and palaeoclimatic factors initial flooding of the basin by an epicontinental sea in the middle carboniferous may have provided moisture necessary for the growth of glaciers conversely episodes of sea level rise probably affected the stability of marine glaciers the palaeoclimatic setting for the wis and other ice masses at the margins of the parana basin was mostly temperate multiple ice advances are evidenced by subglacial tillites resting on striated and or glaciotectonized basement and deformed glacigenic sediments identified at different stratigraphic levels in the itarare subgroup glaciation reached its maximum expansion sometime between the late carboniferous and early permian gradually diminishing and vanishing in the late early permian the reconstructed palaeogeographic evolution favors a model of irregular melt back of ice masses particularly along the eastern margin of the parana basin in analogy with the deglacial pattern of the pleistocene laurentide ice sheet in north america retreat of marine glaciers was mostly associated with relatively simple accumulations or complex build ups of ice contact proglacial facies associations in glacial estuarine embayments fast retreat was mainly controlled by decoupling associated with sea level rise and intense calving in the terrestrial environment more fragmentary evidence shows that retreat may have involved several mechanisms including downwasting of stagnant inactive ice margins and destabilization by surging of glaciers moving over deformable sediments highstand sea level following ice wastage is often marked by widespread deposition of relatively thin marine beds at least four stratigraphically different basinwide marine horizons are recognized isostatic rebound of deglaciated margins of the parana basin is recorded by transition from deep marine beds to shallowing coarsening upward prograding sequences of littoral fluvio deltaic facies basinwards sourced from raised basin margins eventually upon emersion these constituted platforms for interglacial and postglacial peat development although glaciation lasted for a long time glacial sedimentation alternated with relatively long periods of intense and widespread subaerial and subaquatic submarine reworking of previously deposited glacigenic sediments and deposition of normal non glacial sediments that comprise the bulk of the itarare subgroup sequence thin coal beds which locally rest on fossil soils denote climatic amelioration during these interglacial phases

ichnological signatures of shallow freshwater lakes in the glacial itarare group mafra formation upper carboniferous lower permian of parana basin s brazil abstract the upper carboniferous lower permian glacigenic deposits of the itarare group parana basin are widely known and cover an extensive area in the southern brazil these deposits consist of different arrangements of massive shales diamictites rhythmites and fine to medium grained sandstones with trough cross stratification five genetically distinct thickening locally coarsening upward successions of regular rhythmites can be distinguished in the mafra rio negro region santa catarina and parana states southern brazil representing the landward portion of an incised valley filled during deglaciation a low diversity invertebrate ichnofauna composed of a freshwater shallow burrow dominated suite and trackway dominated suite occurs in these rhythmites the freshwater shallow burrow dominated suite is composed of cochlichnus anguineus cruziana cf problematica gordia arcuata gordia marina hormosiroidea meandrica rusophycus cf carbonarius and treptichnus pollardi as well as undichnia consulca and intermittent rusophiciform traces it represents a mermia ichnocoenosis and occurs in the rhythmites of the upper sets commonly overlapped by d gouldi and d biformis in palimpsest preservation d gouldi and d biformis compose the trackway dominated suite which occur in all ichnofossiliferous paired mudstone siltstone of the basal sets of the rhythmite succession and in almost all of the upper sets it represents an atypical scoyenia ichnocoenosis and is generally preserved over microbially induced wrinkle structures the rhythmic deposition suggests distal underwater gravity flow deposits filling shallow lakes or ponds in depressed areas the siltstones deposited by melting currents and the mudstones by sediment fall out after the flux ceased the abundant wrinkle structures suggest quiet waters the overlying deposits bearing a brackish water ichnofauna and marine fossils suggest a coastal setting connected with the sea although atypical the occurrence of a scoyenia ichnocoenosis in almost all ichnofossiliferous rhythmite couplets preserved over wrinkle structures or overlapping mermia ichnocoenosis suggests that these shallow lakes were episodically dried up at least partially the present data allow interpreting the regular ichnofossiliferous rhythmites of the mafra formation as deposited in shallow lakes or ponds developed in outwash plains at the landward side of a fjord embayment during deglaciation

paleozoic terranes of eastern australia and the drift history of gondwana abstract critical assessment of paleozoic paleomagnetic results from australia shows that paleopoles from locations on the main craton and in the various terranes of the tasman fold belt of eastern australia follow the same path since 400 ma for the lachlan and thomson superterranes but not until 250 ma or younger for the new england superterrane most of the paleopoles from the tasman fold belt are derived from the lolworth ravenswood terrane of the thomson superterrane and the molong monaro terrane of the lachlan superterrane consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic australia by the late early devonian the lolworth ravenswood terrane is interpreted to have undergone a 90 clockwise rotation between 425 and 380 ma although the tamworth terrane of the western new england superterrane is thought to have amalgamated with the lachlan superterrane by the late carboniferous geological syntheses suggest that movements between these regions may have persisted until the middle triassic this view is supported by the available paleomagnetic data with these constraints an apparent polar wander path for gondwana during the paleozoic has been constructed after review of the gondwana paleomagnetic data the drift history of gondwana with respect to laurentia and baltica during the paleozoic is shown in a series of paleogeographic maps

the flora of early permian coal measures from the parana basin in brazil a review abstract this paper presents an updated overview integrating both previous and newly published data on the most important floras found associated with early permian coal seams in the parana basin brazil these floras occur within the rio bonito formation and correspond to the gondwana glossopteris flora for this review five floras are selected in ascending stratigraphic order the sao joao do triunfo figueira quiteria morro do papaleo and irapua bed floras they are the best known floras of the basin in terms of taxonomic composition paleoecology and environments of deposition an early mid sakmarian to earliest artinskian age is indicated for the rio bonito formation based on absolute radiometric and relative biostratigraphic ages integration of available information about the selected floras allows evaluation of taphonomic and paleoecological factors to provide a more comprehensive understanding of the early permian floral record in the parana basin the variation observed in both the taxonomic composition of individual floras and in the frequency of occurrence of different plant groups is due to the broad range of environmental edaphic conditions that prevailed in the many different depositional settings represented in the rio bonito formation a more precise age determination obtained for the plant bearing deposits permits the establishment of a more confident correlation between the early permian floral succession in the parana basin and other early permian floral successions in other basins the sakmarian global warming favored the appearance of pecopterid and sphenopterid ferns amongst the spore producing plants and the glossopterids amongst the pollen producing plants

thin bedded diamictites in the glaciomarine hoyada verde formation carboniferous calingasta uspallata basin western argentina a discussion on the emplacement condition of subaqueous cohesive debris flows abstract thin bedded 0 5 20 cm diamictites are present in the glaciomarine sequence of the hoyoda verde formation carboniferous of the calingasta uspallata basin the sharp non erosive contacts the high mud content and the wide range in clast size suggest that the thin bedded diamictites have been deposited as subaqueous debris flows bed thickness bth versus maximum clast size mcs plots show a strong positive correlation 0 95 proving that the flows had a close balance between capacity and competence and were laminar the cohesive factor also deduced from the bth mcs plots indicates that the flows can be interpreted as cohesive debris flows the widespread presence of inversely graded or massive beds and low bth mcs values mean bth mcs 2 71 standard deviation 0 33 suggest relatively concentrated competent debris flows with minor water intake in contrast to other more frequent examples of more dilute water rich subaqueous debris flows with lower competence relative to flow thickness

late paleozoic paleoclimatology of central west argentina abstract based on sedimentologic and paleontological characteristics present in the sedimentary record of the calingasta uspallata and paganzo basins a model of paleoclimatic evolution for the late paleozoic of central west argentina is proposed additional evidence is also provided by data from other basins of southern san rafael and tepuel basins and northern tarija basin west argentina five paleoclimatic stages have been defined paleoclimatic stage i tournalism visean early carboniferous is characterized by temperature and humid preglacial conditions as evidencedin the el raton and maliman formations calingasta uspallata basin plant remains of archeosigillaria and lepidodendropsis zone are present in both units the paleoclimatic stage ii namurian early westphalian middle carboniferous comprises widespread glacial deposits including glaciomarine sequence in the westernmost basins calingasta uspallata western paganzo san rafael and tepuel and terrestrial tillites and glaciolacustrine fine clastics in some areas of the paganzo basin fossils of the levipustula fauna are distinctive in the glaciomarine deposits of this stage and in the overlying postglacial fine clastics of the basal portion of stage iii substage iiia the paleoclimatic stage iii of middle carboniferous late westphalian age corresponds to postglacial transgressions that flooded the previously glaciated shelves in the calingasta uspallata and tepuel basins terminal glaciolacustrine deposits substage iiia indicate of the demise of glacial conditions and coal measures of fluvial affinity in the paganzo basin substage iiib probably this postglacial stage was characterized by high humidity and moderate temperatures this stage is paleobiologi defined by a floral assemblage known as nbg nothorhacopteris botrychiopsis and ginkgophyllum the paleoclimatic stage iv late carboniferous stephanian early permian corresponds to a time interval characterized by seasonally dry climates and a progressive amelioration in humidity clear evidence of these climatic conditions is present in several localities in the paganzo basin the first astherothecae and glossopteris leaves are found finally paleoclimatic stage v middle late permian is dominated by red beds thick eolian sequences and saline lake facies deposited under arid to semi arid conditions coeval volcanism derived from the west is expressed by interbedded tuffs and agglomerates calingasta uspallata paganzo and san rafael basins

complex effective depth of the ocean bottom the effective depth approximation is extended to allow for energy loss on reflection at an attenuating low shear speed solid ocean bottom the resulting complex effective depth leads to a novel and efficient algorithm for finding the exact complex eigenvalues for the normal modes in isovelocity water over an attenuating fluid or solid bottom while avoiding numerical searches the method gives rapid normal mode solutions for shallow water propagation including the effects of leaky modes

lower permian oncolites from south china implications for equatorial sea level responses to late palaeozoic gondwanan glaciation the oncoid bearing chuanshan formation is a regionally extensive carbonate deposit of predominantly asselian to early sakmarian early permian age in south china occupying an area of some 500 000 km2 throughout south china the oncoid bearing horizons are generally stable and broadly comparable in lithology fossil content and the morphology of the oncoid grains four types of microfacies are recognized from the oncolite succession and overall they suggest a moderate to high energy wave agitated shallow marine carbonate platform environment an analysis of the stratigraphic distribution of oncoid grain size density thickness and the bedding structures of the oncolite beds and the number of coating laminae indicate the presence of metre scale cyclothems suggestive of possible high frequency cycles of sea level fluctuation compared to carbonate successions above and below that lack oncolites and in conjunction with evidence from sequence stratigraphic and isotopic geochemical analyses of coeval carbonate deposits in south china and elsewhere the origin of the chuanshan oncolites is linked to a drastic drop in global sea level at the pennsylvanian permian boundary that can be correlated closely in timing with the zenith of the late palaeozoic gondwanan glaciation it is further suggested that the eustatic changes apparent from the deposition of the chuanshan oncolites and similar coeval deposits in lower palaeolatitudes were coupled with and influenced by the contemporaneous high latitude gondwanan glaciation the largest and longest known such event in phanerozoic earth history

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

age and tectonostratigraphic significance of the upper carboniferous series in the basement of the andean frontal cordillera geodynamic implications the age and tectonosedimentary environment of the palaeozoic sediments on the frontal cordillera is not well known and earlier studies have been unable to satisfactorily explain the geological history of the basement of the andes in the vicinity of the old castano viejo mine crop out various levels of partially metamorphosed microbialite limestones which alternate with thin marly lutitic interstrata these levels contain abundant palynomorph remains which allow the series to be dated as silurian devonian these data together with the presence of warm climate fossils lend support to the hypothesis of a major allochtony of the chilenia terrane of which the frontal cordillera formed part relative to the cuyania terrane which included the precordillera prior to their amalgamation upper carboniferous palynomorphs found during this study occur in association with resedimented palynomorphs and chitinozoa of possible devonian age this demonstrates the equivalence of both fossiliferous series and their location within the upper part of the upper carboniferous agua negra fm the silurian devonian elements deformed during a phase prior to the gondwanic orogeny were eroded and transported to the foreland basin during the upper carboniferous the palynomorph associations found in all samples correspond to the ancistrospora palynological zone and to the raistrickia densa convolutispora muriornata biozone which are indicative of upper carboniferous times characteristic forms such as ancistrospora verrucosa and c muriornata both indicative of an upper carboniferous age were found in samples from the castano viejo area

tuffs tectonism and glacially related sea level changes carboniferous permian southern namibia abstract the carboniferous permian glacigene dwyka group in southern africa has been widely regarded as amagmatic only in the higher parts of the permian and subsequent younger strata has evidence of magmatism been recognised particularly in the form of pyroclastic fallout ash beds the source of these tuffs has been suggested to be patagonia and west antarctica forming part of an extensive volcanic arc which lay some 1500 to 2000 km to the south and west in their pre break up gondwana positions rhyolitic dacitic and basaltic andesitic tuff beds within the glaciomarine sediments of the dwyka group in namibia reveal new evidence for an early onset of proximal bimodal volcanic activity in southern africa contemporaneous tectonism is recorded by type 1 unconformities and systematic thickness changes across nw se trending extensional normal faults we suggest that this tectonomagmatic period marks initial extensional events in southern namibia and the carboniferous permian volcanic trend appears to coincide with the position of the eventual namibian continental margin significantly the stratigraphic positions of the tuff beds show a distinct association with enclosing marine transgressive depositional sequences most of them coincide with sharply defined flooding surfaces within relatively thick shaly successions reflecting their multiple transgressive nature widening the study context to the latest early permian in southern africa the main karoo basin of southern africa exhibits a similar coincidence of marine transgressions and extrusion of volcanics the relationship between tuff beds and transgressive depositional sequences is not only the result of enhanced preservational potential during transgression but of a genetic coupling between magmatism extensional tectonics and basin subsidence the latter accelerating a rise in relative sea level this interaction is significant not only for understanding potential controls on relative sea level change but also for understanding the early geodynamic evolution of the southern south atlantic continental margin

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

extreme freshwater release during the late paleozoic gondwana deglaciation and its impact on coastal ecosystems abstractstrata in the paganzo tarija and parana basins of argentina and brazil provideevidence for reconstructing the effects of late paleozoic glacial retreat the depositionalenvironment of the transgressive and early highstand ne grained deposits has been con troversial with interpretations ranging from normal marine shelves to estuaries to lakes whereas their counterparts from shallow marine settings not in uenced by glaciation hostdiverse fully marine ichnofaunas these ne grained postglacial deposits are dominatedby nonspecialized grazing trails simple feeding traces arthropod trackways and shtrails they are typical of freshwater environments and represent examples of the mermia and scoyenia ichnofacies however the local presence of acritarchs indicates sporadicmarine in uence these observations suggest a new interpretation that freshwater con ditions in fjordlike settings across south america were widespread because gondwananbasins were overwhelmed by strong meltwater discharge issuing from melting of the con tinental ice masses keywords

structural setting of the neoarchean terrains in the commonwealth bay area 143 145 e terre adelie craton east antarctica lithological and structural maps from the east commonwealth bay unit ecb terre adelie and georges v land antarctica are presented with a summary of the main structural and metamorphic data obtained in the area the ecb unit is structured during the late archean lower proterozoic at 2 4 2 5 ga with i granulite metamorphism at 9 6 kbar and 850 50 c of lower mid crust and amphibolite metamorphism p 5 kbar t 750 c of the upper crustal levels ii the lower crustal granulites are uplifted and suffered local partial melting and then retrogression into the amphibolite facies at 550 50 c 5 kbar granulites are extruded in the core of a crustal scale anticlinal fold granulites being retrogressed only on the rims of the anticline crustal scale folding along with other structural features results from intense ne sw shortening that prevailed during the late archean orogenic cycle strike slip and extensive motions are only minor in that process iii top to the east thrusting and nappe piling has at least locally occurred under lower amphibolite to greenschist facies conditions finally it seems that iv the paleoproterozoic 1 7 ga structural imprint may have only affected the rims of the archean units the tectonic context observed in the 1 7 ga cape hunter phyllites features mainly e w shortening component and vertical extrusion the eastern mertz and western port martin parts of the archean block were reactivated by localized dextral shearing

facies and architecture of a carboniferous grounding line system from the guandacol formation paganzo basin northwestern argentina abstract new outcrops of middle carboniferous glacigenic deposits found in the guandacol formation western paganzo basin are described in this paper the study locality of los pozuelos creek northwestern argentina includes coarse grained diamictites rhythmites laminated pebbly mudstones and shales that represent an expanded column of the gondwanic glaciation in this region thirteen lithofacies recorded at the measured section have been grouped into three facies associations facies association i is composed of coarse grained massive and stratified diamictites lithofacies dmm dms dmg dcs laminated siltstones with dropstones fld and interstratified sandstones and mudstones fl sr these rocks represent both tillites and resedimented diamictites closely associated to small water bodies where laminated siltstones with dropstones and stratified sandstones and mudstones were deposited facies association ii comprises couplets of matrix supported thinly bedded diamictites dmld and laminated mudstones with dropstones fld this facies association results from the combination of three different processes subaqueous cohesionless debris flows coeval rainout of ice rafted debris and settling of fine grained particles from supension finally facies association iii is made up of laminated mudstones without dropstones thin marl levels and scarce fine to very fine grained sandstones this assemblage clearly suggests sedimentation in a deep marine environment below the wave base the architecture of the glacigenic deposits has been investigated using photomosaic panels the geometry of the depositional bodies and facies suggest that los pozuelos creek outcrops exhibit a well preserved three dimensional example of a grounding line system in particular three different subenvironments of a morainal bank were interpreted a bank front a bank core and a bank back the bank front assemblage is characterized by coarse grained mainly resedimented diamictites grading laterally to prograding clinoforms composed of interbedded matrix supported thinly bedded diamictite and mudstones the bank core assemblage is formed by a stacking of coarse grained diamictites where at least five major erosional surfaces bounding four multistory diamictite bodies can be recognized finally the bank back assemblage corresponds to discontinuous intervals of striated lodgement till and coarse grained resedimented diamictites showing important post depositional deformation the retrogradational stacking of the morainal banks indicate an overall glacial retreat and a glacioeustatic sea level rise erosional surfaces at the base of each morainal bank suggest intervening short term episodes of ice advance the new data presented here confirm the existence of true tillites in western paganzo basin and suggest several at least four pulses of glacial advance and retreat during the namurian glaciation in the region and permit a more refined interpretation of the glacial deposits in the huaco area

mid carboniferous deglaciation of the protoprecordillera argentina recorded in the agua de jaguel palaeovalley abstract the agua de jaguel formation near uspallata mendoza province argentina was deposited within a palaeovalley along the southeastern margin of the calingasta uspallata basin adjacent to the protoprecordillera the basal glacigenic sequence of the formation was deposited in the serpukhovian early bashkirian near the beginning of the late palaeozoic ice age the sequence is composed of diamictite conglomerate sandstone and mudrock and records four depositional stages within a palaeofjord 1 morainal bank deposition by a wet based tidewater glacier 2 glacial retreat succession where ice retreated up the fjord out of the immediate area allowing iceberg deposition of dropstones and dump deposits 3 continued glacial retreat with ice receding onto land allowing a shoreface to develop within the palaeovalley and 4 transgression across the shoreface and resumption of iceberg deposition the thickness and facies of this succession are similar to deposits within modern alaskan fjords housing temperate tidewater glaciers comparison of the agua de jaguel formation with alaskan fjords indicates that sequence stratigraphy used for low latitude deposits must be applied with caution as glacimarine ice retreat within a fjord produces strata surfaces that are easily misidentified as flooding surfaces resulting from changes in water depth likewise the transgression during stage 4 is significant as it indicates a rise in sea level that occurred during glaciation of the protoprecordillera thus suggesting that the transgression between stages 3 and 4 was not driven by input of glacial meltwater additionally the sediment geochemistry suggests that the bottom waters of the palaeovalley were anoxic which may help explain the absence of bioturbation in the sequence as well as in other ancient glacimarine palaeovalleys the deglaciation succession and transgression are also recorded in the nearby hoyada verde and tramojo formations so it is proposed that all three formations record one glacial event in the protoprecordillera overlying fluvial and shallow marine strata in the agua de jaguel hoyada verde and tramojo formations show no indication of continued glaciation in the protoprecordillera following stage 4 and equivalent strata the deglaciation succession of the agua de jaguel formation affirms the emerging concept that the late palaeozoic ice age was characterized by alpine glaciers ice caps and small ice sheets that were not massive enough to have driven eustatic fluctuations of 100 m as previously understood and that ice never covered westernmost gondwana during later lpia events

u pb dating of tonstein layers from a coal succession of the southern parana basin brazil a new geochronological approach abstract this paper presents new radiometric dating of zircons idtims u pb from tonsteins interbedded with coal seams from the candiota coalfield rio grande do sul state the ages obtained 296 9 1 65 ma and 296 4 2 ma are consistent within error and are quite different from a previously published age of 267 1 3 4 ma calibrations of palynostratigraphic data with numerical ages showed that the candiota coals from the southern parana basin related to the protohaploxypinus goraiensis subzone are constrained to the asselian consequently the basal part of the gondwana sequence in the southern part of the basin must belong to the carboniferous permian boundary and not to the sakmarian as it was previously considered the new results have far reaching significance for correlations of the parana basin with sequences of the argentinian paganzo basin 302 6 ma and 288 7 ma and also with the karoo basin with the top of the dwyka tillite 302 3 ma and 299 2 3 2 ma and with the lowermost ecca group 288 3 ma and 289 6 3 8 ma this new evidence supports the presence of an active and widespread upper carboniferous volcanism in western gondwana

late palaeozoic global changes affecting high latitude environments and biotas an introduction abstract the late palaeozoic ice age lpia spanning approximately from 320 ma serpukhovian late mississippian to 290 ma mid sakmarian early permian represents the vegetated earth s largest and most long lasting regime of severe and multiple glaciations involving processes and patterns probably comparable to those of the last ice age accompanying the lpia occurred a number of broadly synchronous global environmental and biotic changes these global changes as briefly reviewed and summarized in this introductory paper comprised but are not limited to the following massive continental reorganization in the lead up to the final assembly of pangea resulting in profound changes in global palaeogeography palaeoceanography and palaeobiogeogarphy substantially lowered global atmospheric carbon dioxide concentrations p co 2 coupled with an unprecedented increase in atmospheric oxygen concentrations reaching earth s all time high in its last 600 million year history sharp global temperature and sea level drops albeit with considerable spatial and temporal variability throughout the ice age and apparently a prolonged period of global sluggish macro evolution with both low extinction and origination rates compared to other times in the aftermath of the lpia the world s climate entered into a transitional climate phase through the late early to middle permian before its transformation into a greenhouse state towards the end permian in recent years considerable amount of data and interpretations have been published concerning the physical evidence in support of the lpia its broad timeframe and eustatic and ecosystem responses from the lower latitudes but relatively less attention has been drawn to the impact of the ice age on late palaeozoic high latitude environments and biotas it is with this mission in mind that we have organized this special issue with the central focus on late palaeozoic high latitude regions of both hemispheres that is gondwana and northern eurasia our aim is to gather a set of papers that not only document the physical environmental changes that had occurred in the polar regions of gondwana and northern eurasia during the lpia but also review on the biotic responses at different taxonomic ecological and spatial scales to these physical changes in a refined chronological timeframe this introductory paper is designed to provide a global context for the special issue with a brief review of key late palaeozoic global environmental changes including changes in global land sea configurations atmospheric chemistry global climate regimes global ocean circulation patterns and sea levels and large scale biotic biogeographic and evolutionary responses followed by a summary of what we see as unresolved scientific issues and various working hypotheses concerning late palaeozoic global changes and in particular the lpia as a possible reference to future research

a paleoclimatic review of southern south america during the late paleozoic a record from icehouse to extreme greenhouse conditions abstract this paper provides a review of the late mississippian to permian paleoclimatic history for southern south america based on lithologic indicators biostratigraphic information and chronostratigraphic data the region is divided into three major types of basins 1 eastern intraplate basins e g parana basin 2 western retroarc basins e g paganzo basin and 3 western arc related basins e g rio blanco basin four major types of paleoclimatic stages are recognized in these basins 1 glacial late visean early bashkirian 2 terminal glacial bashkirian earliest cisuralian 3 postglacial cisuralian early guadalupian and 4 semiarid arid late guadalupian lopingian the glacial stage began in the late visean and continued until the latest serpukhovian or early bashkirian in almost all of the basins in southern south america during the bashkirian earliest cisuralian terminal glacial stage glacial deposits disappeared almost completely in the western retroarc basins e g paganzo basin but glaciation persisted in the eastern basins e g parana and sauce grande basins a gradual climatic amelioration postglacial stage began to occur during the earliest permian when glacial deposits completely disappeared across all of south america during this interval glacial diamictites were replaced by thick coal beds in the parana basin while north south climatic belts began to be delineated in the western basins which were likely controlled by the distribution of mountain belts along the panthalassan margin of south america towards the late permian climatic belts became less evident and semiarid or arid conditions dominated in the southern south america basins eolian dunes playa lake deposits and mixed eolian fluvial sequences occur in the parana basin and in the western retroarc basins volcanism and volcaniclastic sedimentation dominated along the western margin of south america at that time the stratigraphic record obtained in southern south america supports a long duration transition from icehouse to extreme greenhouse conditions

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

jurassic epithermal au ag deposits of patagonia argentina abstract important precious metal deposits have been discovered during the last 10 years in the deseado massif region of patagonia argentina this region is a plateau consisting of middle to upper jurassic volcanic rocks that host fracture controlled epithermal au ag mineralization these mineral deposits represent low sulfidation type hydrothermal systems and formed following the main period of volcanism probably during the late jurassic period the presence of silica sinters and veins interpreted to be feeder structures indicates that the tops of some deposits have been preserved with erosion of younger sedimentary and volcanic rocks now exposing these systems these deposits represent diverse erosional levels ranging from sinter formed at the paleosurface to intermediate au ag rich quartz veins to base metal bearing au ag veins that represent deeper levels of the epithermal systems the best known deposits are in the cerro vanguardia district where vein systems occur over a 350 km 2 area and veins can be traced for more than 14 km geological mapping of the district has resulted in the definition of over 140 km of veins current reserves are over 3 2 million ounces au equivalent with grades of 10 g t au and 120 g t ag the geologic characteristics of the region and the presence of major au ag deposits provide targets for continuing exploration in the deseado massif

late paleozoic glaciotectonic structures in northern parana basin brazil abstract fluviatile deltaic sediments containing thin coal layers and glaciofluvial sediments of the itarare subgroup late paleozoic cropping out near cerquilho northern parana basin exhibit post depositional deformation such as recumbent and drag folds shear fractures faults and shear lamination the deformation occurs in an interval of 3 4 m thick and is confined between horizontal strata the deformed strata are directly overlain along a horizontal erosional tectonic contact surface by a silty sandy massive 1 m thick clast poor tillite deformation shows a consistent geometry indicating a predominant vergence toward the ssw having been developed under a horizontal stress oriented from nne to ssw the deformation is interpreted to be of glaciotectonic origin associated with an ice readvance in the area the glacier moved toward the ssw on relatively soft deformable sediments depositing the subglacial till on top of them the tillite shows parallel upglacier dipping shear fractures at its base and wedge like intrusions into the underlying sandstone probably formed during its subglacial deposition the tillite is overlain by cyclic braided stream fluviatile sandstone beds the top of these shows deformations small recumbent folds and reverse faults below another clast poor silty sandy tillite this could represent another glacial readvance with subglacial deposition of till occurrence of glaciotectonic deformation overlain by subglacially deposited tillites in the cerquilho area indicates glacier readvances and permanence of the glacial influence in the upper part of the itarare subgroup absence of incorporated material from the underlying deformed sediments in the tillite and the style of the deformations suggest an unfrozen water saturated mostly unconsolidated substratum these conditions may have generated instability and fast ice flow of the glacier they also suggest that the sediment may have most likely failed in this manner under rapidly applied stresses associated with a surging behavior of the retreating glacier

radiometric age determination of tonsteins and stratigraphic constraints for the lower permian coal succession in southern parana basin brazil abstract ion microprobe shrimp ii dating of zircons from tonsteins interbedded with coal seams from the candiota and faxinal coalfields early permian rio bonito formation parana basin brazil is presented the mean ages obtained 290 6 1 5 ma are more precise than previously published intervals calibrations of chronostratigraphic data with radiometric ages show that the main coal succession from the southern basin is constrained to the middle sakmarian the 2 ma time interval of deposition supports the hypothesis that the coal generating process was quite rapid in terms of geological time in a general context faxinal and candiota coals are assigned into the protohaploxypinus goraiensis subzone besides some paleocological differences evidenced by palynological studies this bio interval does not correspond to a consistent palynostratigraphic tool and more accurate biostratigraphic zonation for the carboniferous permian interval must be delineated the new results have far reaching significance for correlations of the basin with sequences of the argentinian paganzo basin 302 6 ma and 288 7 ma and also with the karoo basin with the lowermost ecca group 288 3 ma and 289 6 3 8 ma this new evidence supports the presence of an active and widespread lower permian explosive volcanic event in western gondwana which is interpreted as the same volcanism which produced the choiyoi group in western argentina according to this correlation the ash fall source is located about 1400 km to the southwest of their area of deposition

late paleozoic tropical climate response to gondwanan deglaciation coupled climate biome model simulations of the late paleozoic were developed to determine the response of pangean tropical climate to gondwanan deglaciation the model simulations predict substantial changes over equatorial pangea including continental drying a reversal of equatorial winds warming heavier 18 o values of meteoric precipitation and the expansion of deserts and the contraction of forests the magnitude of these tropical responses is sensi tive to the extent of gondwana continental ice and the deglacial rise in atmospheric pco 2 boundary conditions that are not well known for the late paleozoic nonetheless the model predictions are consistent with climatic and environmental trends determined from terrestrial proxy data implying that the deglaciation of gondwana was a transformational climate event in tropical pangea

shrimp u pb zircon dating and palynology of bentonitic layers from the permian irati formation parana basin brazil abstract this paper presents the first shrimp zircon age data from bentonitic ash fall layers intercalated with the irati sedimentary rocks as well as palynofossils retrieved from the petrobras six mine parana state southern brazil the permian irati formation is one the most important oil source horizons within the parana basin and consists mainly of siltstones gray claystones as well as organic rich claystones intercalated with limestones zircon morphology based on cathodoluminescence images includes two different populations a dominant population of euhedral prismatic elongate to acicular grains which are most likely related to an ash fall volcanism and a population of rounded to large prismatic grains that were interpreted as detrital grains shrimp analysis performed on the euhedral and prismatic grains revealed an age of ca 278 4 2 2 ma 7 points with 95 confidence interpreted as the crystallization age of the volcanic eruption based on this new dating the irati formation should be placed on the lower permian cisuralian artinskian in age modifying substantially the traditional ages previously attributed to this unit the palynofossils from this level include key species of the lueckisporites virkkiae zone such as l virkkiae l densicorpus l stenotaeniatus weylandites lucifer alisporites splendens typical species of this zone also occur in african and other south american argentina permian strata allowing stratigraphical correlations the origin of the ash falls is not clearly defined it may be related either to calc alkaline arc magmatism associated to the sanrafaelica orogeny 275 and 250 ma or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern gondwana at ca 278 my the dating of this unit is significative to calibrate biostratigraphic schemes along the parana basin as well as equivalent zones in gondwana areas mainly in its occidental portion

absolute dating of permian ash fall in the rio bonito formation parana basin brazil abstract the rio bonito formation in southern parana basin contains a set of tonsteins interbedded with coal seams these tonsteins are composed mainly of kaolinite with zircon apatite and beta quartz paramorphs as accessory minerals and were interpreted as volcanic ashes deposited by ash falls over pits protected by barrier islands in a barrier lagoon system a u pb dating of zircons in the tonstein a which furnished an age of 267 1 3 4 ma early permian confirming previous age dates based on palynology and correlating them with one of the main periods of volcanic activity in the gondwana the source of the pyroclastic material was attributed to the early permian choiyoi magmatic arc in argentina developed during the sanrafaelic orogeny and with a main peak of volcanic activity between 260 and 272 ma

evolution in a cold climate abstract a brief appraisal of marine fossils from high latitudes and episodically cold climate especially in east australia and new zealand during late palaeozoic and early mesozoic times shows patterns of evolution and survival that differ from those adduced for the palaeotropics and northern hemisphere examples taken from amongst phyla scyphozoa bryozoa brachiopoda and classes bivalvia and class cephalopoda suggest these attributes 1 evolution and demise of species and genera proceeded at a rate close to that known for palaeotropical and northern hemisphere macro invertebrates but involved fewer families and orders 2 possibly intraspecific variation was greater amongst southern palaeohemisphere permian species than in those of the permian palaeotropics 3 there was no proven diminution of life at the end of the guadalupian middle permian at southern high latitudes where however the fossil record is meagre for this interval younger wuchiapingian and changhsingian faunas were moderately diverse 4 there is no evidence for a high latitude southern hemisphere anoxic event in the early triassic despite claims of a world wide anoxic interval nor has any substantial volcanic eruption or bolide impact left any marked traces in the sedimentary record 5 as a consequence some major groups such as bryozoa and conulariida staurozoa survived the end permian extinction shock in the southern hemisphere 6 other major groups appear to have survived better in the south than in the north notably mollusc bivalvia and cephalopoda it therefore appears likely that triassic seas were restocked substantially from the southern hemisphere and that the permian extinction shock was asymmetric with respect to latitudes in its distribution and affect