paleoclimatic and paleomagnetic constraints on the paleozoic reconstructions of south china north china and tarim abstract paleomagnetic and paleoclimatic data provide the most useful latitudinal constraints for plate reconstructions distributions through the paleozoic of five types of climatically sensitive sediments coals evaporites reefs dolomites and limestones for south china north china and tarim are shown on 15 maps that include 1578 reliable data points these paleoclimatic data agree reasonably well with available paleomagnetic directions although significant divergence between the two exists for the early paleozoic these data indicate the following 1 1 south china was in low latitudes during the entire paleozoic with a subtropical position in the cambrian 2 2 north china also remained near the equator in the early and late paleozoic except for the ordovian and the late permian when extensive evaporites suggest slightly higher latitudinal positions while its middle paleozoic position is uncertain due to the missing stratigraphie record 3 3 in south china local tectonics appears to have played a dominant role in determining paleogeography and therefore marine sedimentation especially after the late ordovician early silurian because the areal coverage of marine sediments through time is distinctly different from what would be expected from published global sea level curves 4 4 paleoclimatic and paleomagnetic data are compatible with biogeographic data which suggest that south china was part of eastern gondwana in the early paleozoic but was widely separated from gondwana in the late paleozoic and the split between the two probably happened in the devonian giving rise to a major break up unconformity in central south china

timing of recovery from the end permian extinction geochronologic and biostratigraphic constraints from south china four volcanic ash beds bracket the early middle triassic boundary as defined by conodont biostratigraphy in a stratigraphic section in south china high precision u pb dates of single zircons allow us to place the early to middle triassic olenekian anisian boundary at 247 2 ma magnetic reversal stratigraphy allows global correlation the new dates constrain the early triassic interval characterized by delayed biotic recovery and carbon cycle instability to 5 m y this time constraint must be considered in any model for the end permian extinction and subsequent recovery

stratigraphical and δ13c records of permo carboniferous platform carbonates south china responses to late paleozoic icehouse climate and icehouse greenhouse transition abstract little attention has been focused on the stratigraphical imprints of the late paleozoic ice age on the equatorial eastern paleo tethys an integrated study of biostratigraphy microfacies and stable carbon isotope stratigraphy was carried out on pennsylvanian middle guadalupian carbonates of the gongchuan section in the bama platform south china it records seven cooling and two warming pulses in the pre kungurian interval comparing with ice proximal stratigraphical records and far field indirect proxies in lower latitudes a kungurian negative 13 c excursion from 4 4 at the base of the kungurian to 1 6 recorded only in the subequatorial belt is documented here it is followed by a global positive 13 c trend reaching 5 3 near the cisuralian guadalupian boundary seven third order shallowing upward cycles are reported for the first time from the kungurian succession the duration of each cycle is estimated to ca 1 myr these cycles are interpreted as being of glacioeustatic origin and mainly driven by long period modulations of obliquity 1 2 myr under major p co 2 decreasing condition this interpretation is supported by recent climate ice sheet modeling and cenozoic glaciation studies which argue that astronomical forcing will be amplified by large magnitude perturbations in the carbon cycle when only localized ice centers persist our results emphasize the need for integration of sedimentological and paleoclimatological proxies in elucidating the dynamics of the deglacial phases of the late paleozoic ice age

prediction of modern bauxite occurrence implications for climate reconstruction abstract the formation of bauxite and laterite strongly depends on prevailing climate we use modern climate and bauxite distribution data to investigate quantitatively the role of climate in bauxite formation and to develop a method for testing general circulation models gcms we find that a very satisfactory prediction for potential bauxite formation can be achieved using two different sets of criteria the first requires the mean annual temperature to be greater than 22 c with annual mean precipitation greater than 1200 mm and 6 or fewer months when the rainfall is less than 60 mm the alternative model requires precipitation greater than evaporation for at least 6 months per year and monthly mean temperatures greater than 23 c for at least 8 months these proxy models are also used with simulations of the present day using a general circulation model the results show that the climate models are robust suggesting that bauxitization can be used to evaluate quantitatively such climate models for ancient times we also show that based on climate model predictions the regions favourable for bauxitization have remained stable through the holocene but with the exception of the malay peninsula bauxite formation would have ceased at the last glacial maximum

mineralogical characteristics of the karstic bauxite deposits in the xiuwen ore belt central guizhou province southwest china abstract the karstic bauxite deposits in the xiuwen ore belt of central guizhou province are hosted by the lower carboniferous jiujialu formation and show parallel unconformity with the overlying and underlying strata the ore bearing rock series that exhibits a typical coal bauxite iron structure is divided into three segments from the bottom upward namely an iron layer a bauxite layer and a coal layer based on the textural features and iron abundances the bauxite ores occurring in the middle segments are divided into three types of ores clastic compact and high iron the bauxite ores primarily comprise diaspore boehmite kaolinite illite and hematite with minor zircon pyrite rutile and feldspar the existence of rutile within diaspore lumps which were inherited from laterization suggests that diaspore was transformed from gibbsite and that karstic bauxite was transformed from laterite bauxite the results of x ray diffraction xrd scanning electron microscopy sem and electron probe x ray microanalyses epma suggest that diaspore and boehmite differ with regard to appearance and element abundance diaspore 2 10 m displays short prismatic or platy shapes and contains low sio2 abundances ranges from 0 2 to 0 51 wt whereas boehmite 0 2 5 m exhibits granular or irregular shapes and contains high contents of sio2 that vary between 2 71 and 10 4 wt the fe cu pb zn ba sulfide and sulfate mineral assemblages associated with cryptocrystalline kaolinites are discovered in the xiaoshanba deposit from the xiuwen ore belt mineralogical and geochemical studies reveal that the genesis of these assemblages is controlled by the decomposition processes of organic matter and the activities of microorganisms within the ore bearing rock series geochemical data suggest that elements rich in high organic cryptocrystalline kaolinite are produced from the adsorption effect of organic matter whereas the low concentration of these elements in pure kaolinite can be attributed to the scavenging effect during kaolinite crystallization in addition coexisting organic matter cryptocrystalline kaolinite and sulfide and sulfate minerals see sample xsb 14 indicate that the forming environment of the bauxite was hot humid tropical or subtropical climates

first report of cisuralian early permian charcoal layers within a coal bed from baode north china with reference to global wildfire distribution abstract fossil charcoal is reported for the first time from a cisuralian coal bed of the shanxi formation in the qiaotou section baode shanxi north china based on anatomical characteristics these charcoal fragments consist of coniferous or cordaitalean xylem unidentified primary xylem and cordaitalean and possible fern leaves these charcoal fragments represent the evidence of palaeowildfire taking place in tropical peat swamps during the cisuralian in cathaysia the palaeowildfire is most likely to be a surface fire and burning litter and shrubby vegetation fire frequency for this early permian peat swamp might have been on the order of 176 294 588 1429 years close to modern values compared with modern analogues the north china block during the cisuralian was probably wet in general but could be occasionally seasonally dry for short time intervals previous charcoal and inertinite records moreover indicate that palaeowildfires were globally common during the cisuralian overall more wildfire evidence was found in the artinskian kungurian than the asselian sakmarian except in the euramerican realm probably due to more suitable regional climate vegetation to fuel fires and taphonomic circumstances

microfacies and carbon isotope records of mississippian carbonates from the isolated bama platform of youjiang basin south china possible responses to climate driven upwelling changes in mississippian global paleogeography derived from the reconfiguration of the continents have been suggested to result in a change in oceanic circulation carbon cycling as well as in global cooling here integrated 13ccarb chemostratigraphy and foraminiferal biostratigraphy across the mississippian late tournaisian visean early serpukhovian mfz6 mfz16 foraminiferal biozones of the gongchuan section located in the isolated bama platform in the youjiang basin south china are presented the 13ccarb trend shows an abrupt decline during late visean asbian early brigantian mfz13 14 this decline is also observed in subequatorial western euramerica whereas coeval sections in subequatorial eastern euramerica show consistently elevated 13c values across the entire visean the 13c decline in western euramerica and the south china block eastern paleo tethys coincides with a global regression with a suggested glacioeustatic origin the onset of high frequency climate and sea level oscillations and the closure of the rheic seaway between euramerica and gondwana we propose a model explaining the divergence of 13c records resulting from the closure of the rheic seaway and development of upwelling zones in the western margin of euramerica and the eastern paleo tethys realm quantitative microfacies analysis across the mississippian succession in the gongchuan section shows facies independent disappearance of corals and increased proportion of cortoids and filter feeding organisms at the onset of the asbian 13c decline which may support an increase in nutrient level that can be expected as a result of upwelling

rise of angiosperms as a factor in long term climatic cooling by late cretaceous or early tertiary time the diversification and proliferation of angiosperm deciduous ecosystems resulted in higher rates of mineral weathering this increase in the global average weathering rate would have caused a decrease in atmospheric carbon dioxide and hence global cooling the magnitude of this decrease is quantitatively explored here by developing a formulation for global weathering which combines ecosystems that differ in their fractional global coverage and intrinsic rates of weathering incorporating this formulation into models specifically several previously developed global steady state models of the geochemical cycle of carbon between the atmosphere and carbonate rocks gives results that show signifi cant global cooling from the evolution of the angiosperm deciduous ecosystems this cooling may vary from a few degrees up to 10 c in this way deciduous ecosystems with high rates of mineral weathering could have contributed to the evolution during the past 100 m y of a cooler earth and thus were a factor in producing conditions that enhanced their global proliferation

palaeoclimate co 2 and late palaeozoic glaciation large glacial interglacial fluctuations occurred during the late palaeozoic geochemical and fossil data show these cycles were marked by coincident shifts in the carbon cycle and terrestrial biosphere

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

local overprints on the global carbonate δ13c signal in devonian carboniferous boundary successions of south china abstract an integrated study of the litho bio and chemostratigraphy of the devonian carboniferous boundary at four sections qilinzhai malanbian gedongguan and long an in south china was undertaken in order to better understand paleoenvironmental changes and controls on 13 c carb variation during the hangenberg crisis sedimentological data record a major regression in the middle siphonodella praesulcata zone which coincided with the hangenberg extinction he in south china our new 13 c carb data document a negative 13 c carb shift near the base of the middle s praesulcata zone which may have been related to the he prior to and during the he respiration of organic matter contributed abundant 12 c enriched dissolved inorganic carbon dic to the restricted nanning carbonate platform resulting in a negative vertical 13 c dic gradient in the study area in the upper s praesulcata zone all four sections exhibit a positive 13 c carb shift suggesting that a vigorous biological pump existed in the aftermath of the latest devonian glaciation however peak 13 c carb values differ markedly among the study sections suggesting that local carbon cycling processes played an important role during the initial post glacial transgression

correlation of nitrate profiles with groundwater and sediment characteristics in a shallow sandy aquifer abstract sediment profiles of a shallow sandy aquifer in an agricultural area of denmark can be characterized by a new term called total reduction capacity trc quantifying the total amount of reduced compounds in the aquifer material ferrous iron reduced sulfur compounds solid organic carbon a distinct increase of trc was observed at and below the oxidation reduction front in this study the front was a zone 30 cm wide oxygen nitrate and sulfate were present above the oxidation reduction front but disappeared at the front detailed porewater profiles indicate that denitrification also takes place above the front supposedly in anaerobic microenvironments not evident in the water samples from the small wells the trc profiles showed that some reduction capacity is still present above the oxidation reduction front and is apparently able to support denitrification

onset and ending of the late palaeozoic ice age triggered by tectonically paced rock weathering the onset of the late palaeozoic ice age about 340 million years ago has been attributed to a decrease in atmospheric co2 concentrations associated with expansion of land plants as plants both enhance silicate rock weathering which consumes co2 and increase the storage of organic carbon on land however plant expansion and carbon uptake substantially predate glaciation here we use climate and carbon cycle simulations to investigate the potential effects of the uplift of the equatorial hercynian mountains and the assembly of pangaea on the late palaeozoic carbon cycle in our simulations mountain uplift during the late carboniferous caused an increase in physical weathering that removed the thick soil cover that had inhibited silicate weathering the resulting increase in chemical weathering was sufficient to cause atmospheric co2 concentrations to fall below the levels required to initiate glaciation during the permian the lowering of the mountains led to a re establishment of thick soils whilst the assembly of pangaea promoted arid conditions in continental interiors that were unfavourable for silicate weathering these changes allowed co2 concentrations to rise to levels sufficient to terminate the glacial event based on our simulations we suggest that tectonically influenced carbon cycle changes during the late palaeozoic were sufficient to initiate and terminate the late palaeozoic ice age the late palaeozoic was characterized by glacial cycles numerical simulations suggest that increased silicate weathering due to mountain uplift and soil removal caused atmospheric co2 to fall below the threshold for glaciation

eccentricity paced late paleozoic climate change abstract cyclic sedimentary deposits characterize low latitude late paleozoic successions and preserve evidence of dynamic climate change on the pangaean supercontinent although their orbitally paced glacioeustatic origins are widely accepted their climatic signatures are open to interpretation in this study we utilize the genesis general circulation model gcm coupled to dynamic ice sheet and ecosystem components to explore the response of low latitude continental climate and high latitude ice sheets to orbital and atmospheric pco2 forcing our results suggest that atmospheric pco2 concentration exerts the primary control over low latitude continental climate and high latitude glaciation our experiments constrain the atmospheric pco2 window within which late paleozoic climate was amenable to orbitally driven glacial interglacial fluctuations the results suggest that both high latitude ice sheet accumulation and ablation and low latitude climate change were paced by the eccentricity of earth s orbit periods of high eccentricity amplified precession driven changes in insolation and promoted high latitude ice sheet volume fluctuations as well as increased low latitude precipitation variability when eccentricity was low the amplification of precessionally driven insolation fluctuations was reduced which promoted high latitude continental ice sheet stability and less variable low latitude precipitation based on these modeling results we discuss the implications of eccentricity paced precessional scale climatic changes on low latitude pangaean depositional environments

controls on permo carboniferous precipitation over tropical pangaea a gcm sensitivity study abstract a series of late paleozoic climate model simulations was developed using the genesis atmospheric general circulation model to investigate the independent roles of gondwanan deglaciation atmospheric co 2 rise and regional tectonism on the long term 10 6 yr evolution of continental precipitation over tropical pangaea the model results indicate that either deglaciation or a co 2 increase from 1 to 8 present atmospheric levels could have caused substantial drying and warming at low latitudes a result that is consistent with late paleozoic proxy records yet the atmospheric processes that led to drying differ between these cases the deglaciation of gondwana reduces low latitude temperature gradients in the southern hemisphere decreasing by as much as 60 the meridional overturning in the southern hemisphere winter cell of the hadley circulation the decline in overturning reduces convective precipitation over equatorial pangaea in contrast high levels of co 2 have little effect on the large scale meridional overturning circulation but increase continental temperatures leading to high evaporation rates and reduced available soil moisture the source of convective precipitation on land in comparison to deglaciation and p co 2 regional uplift erosion of the central pangaean mountains cpms has a secondary effect on tropical precipitation in genesis and cannot explain the long term aridification and warming of western pangaea we suggest that the deglaciation of gondwana and a concomitant rise in atmospheric p co 2 could explain much of the late paleozoic climate change over low latitude pangaea

tropical laterites life on land and the history of atmospheric oxygen in the paleoproterozoic the ca 2 2 ga hekpoort paleosol of the transvaal supergroup in southern africa has been considered a type example and the youngest iron depleted paleosol formed under a reducing atmosphere in the early precambrian however the mineralogical and geochemical data on recently acquired deep drill core intersections indicate that the hekpoort paleosol represents part of an ancient lateritic weathering profile with an iron depleted pallid lower zone and an iron enriched lateritic upper zone previous studies of the paleosol took place in areas where only the lower pallid zone was preserved from erosion prior to deposition of cover beds the laterite profile is comparable to that of modern tropical laterites formed under an oxic atmosphere in the presence of abundant terrestrial biomass revised stratigraphic correlation indicates that the hekpoort laterite profile is a correlative to highly ferruginous laterite profiles of wolhaarkop in griqualand west this information indicates that the oxygen evolution curve based on loss or retention of iron in paleosols should be reexamined

climatic and hydrologic controls on upper paleozoic bauxite deposits in south china abstract the late paleozoic era was an interval of major tectonic and climatic changes including formation of the supercontinent pangea and the 60 myr long late paleozoic ice age lpia although bauxite formation declined globally from the carboniferous to the permian in conjunction with global cooling it was an interval of widespread bauxite formation in china in south china 1 the jiujialu formation bauxite deposits in central and northern guizhou zunyi area are of early middle visean age 2 the dazhuyaun formation bauxite deposits in northern guizhou wuchuan zheng an daozheng area to southern chongqing nanchuan area and southeastern guizhou fuquan kaili area are of late pennsylvanian early permian age and 3 the heshan formation bauxite deposits in western guangxi to yunnan are of middle late permian age in north china the benxi formation bauxite deposits are of late mississippian middle pennsylvanian age the contrasting trends in bauxite metallogenesis between china and the rest of the world imply different climatic patterns in the eastern tethys high annual humidity with seasonal dryness and pangea aridification this hypothesis is further supported by differences in the chemical index of alteration or cia 80 in the eastern tethys vs 50 in western pangea and in paleotemperatures mean annual temperature or mat 20 c in the eastern tethys vs 4 c in western pangea determined from permo carboniferous siliciclastic deposits permo carboniferous bauxite deposits in south china formed in coastal plain and coastal karstic depression environments in which the position of the groundwater table was related to sea level changes during the late paleozoic high frequency eustatic fluctuations caused by waxing and waning of gondwana icesheets controlled sedimentation in these coastal depositional systems leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose and phreatic type bauxite formation the results of the present study show that during interglacial stages lateritization resulted from high pco2 high sea level and groundwater table elevations low precipitation and limited vegetation cover whereas during glacial stages bauxitization of these ferralitic weathering products was promoted by low pco2 low sea level and groundwater table elevations high precipitation and more extensive vegetation cover thus a unique combination of geographic climatic and eustatic factors accounted for widespread formation of bauxite in south china during the lpia

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

greenhouse to icehouse a biostratigraphic review of latest devonian mississippian glaciations and their global effects the latest devonian mississippian interval records the long term transition from devonian greenhouse conditions into the late palaeozoic ice age lpia this transition was punctuated by three short glaciation events in the latest famennian mid tournaisian and visean stages respectively primary evidence for glaciation is based on diamictite deposits and striated pavements in south america appalachia and africa the aim of this review is to assess the primary biostratigraphic and sedimentological data constraining diamictite deposits through this transition these data are then compared to the wider record of eustasy mass extinction and isotope stratigraphy in the lower palaeolatitudes precise age determinations are vital to integrate high and low palaeolatitude datasets and to understand the glacial control on wider global changes palynological techniques currently provide the best biostratigraphic tool to date these glacial deposits and to correlate the effects of glaciation globally this review highlights a high degree of uncertainty in the known history of early lpia glaciation as much of the primary stratigraphic data are limited and or unpublished future high resolution stratigraphic studies are needed to constrain the history of glaciation both spatially and temporally through the latest devonian and mississippian

global events of the late paleozoic early devonian to middle permian a review abstract the late paleozoic early devonian to middle permian was an interval of profound changes in earth surface systems reflected in dynamic interplay among the biosphere hydrosphere atmosphere and geosphere major events transpired including the colonization of landmasses by vascular plants the assembly of the supercontinent pangea two first order mass extinctions the frasnian famennian and devonian carboniferous boundary events and the most severe icehouse climate mode of the phanerozoic the late paleozoic ice age lpia the goals of the present review are 1 to summarize major global developments in climate oceanography and paleobiology during the late paleozoic 2 to examine the roles of land plant evolution global tectonics and large igneous province magmatism in driving these developments and 3 to serve as an introduction to the 23 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology indicating how they advance our knowledge of various scientific issues related to these developments

sequence stratigraphy and onlap history of the donets basin ukraine insight into carboniferous icehouse dynamics abstract the degree to which permo carboniferous cyclothemic successions archive evidence for long term variations in ice volume during the late paleozoic ice age is insufficiently resolved here we develop the sequence stratigraphy and onlap offlap history for a 33 my interval of the carboniferous using the u pb calibrated succession of the donets basin ukraine in order to assess the relationship between sea level high latitude changes in glacial extent and climate integrated subsurface and outcrop data permit meter scale correlation of 242 biostratigraphically constrained limestones and coals and in turn individual cyclothems across 250 km of the donets basin rapid uniform subsidence and basinwide continuity of marker beds indicate pennsylvanian deposition under relatively stable tectonic conditions three scales of sequences avg durations of 140 ky 480 ky and 1 6 my are recognized on the basis of stratigraphic stacking patterns and basinwide architecture of marine to terrestrial facies assemblages the hierarchy of sequences and the geographic and stratigraphic positions of shifts in base level sensitive facies across the donets ramp permit the construction of an onlap offlap history at a sub 400 ky scale major sea level lowstands occur across the mid carboniferous boundary and during the early moscovian these lowstands coincide with glacial maxima inferred from high latitude glacigenic deposits the middle to late pennsylvanian is characterized by a stepwise onlap culminating in an earliest gzhelian highstand suggesting contraction of carboniferous ice sheets prior to the initiation of early permian glaciation the stratigraphic position of climate sensitive facies within individual donets cyclothems indicates a turnover from seasonal sub humid or semi arid climate to everwet conditions during the late lowstand and maximum ice sheet accumulation comparison of the stratigraphic and aerial distribution of coals and evaporites in the donets basin with the onlap offlap history further indicates everwet conditions during lowstands and inferred glacial maxima and drier climate during onlap and inferred ice sheet contraction at the intermediate 0 8 to 1 6 my and long 106 yr time scales taken together the relationship between inferred climate and glacioeustasy suggests a likely teleconnection between high latitude ice sheet behavior and low latitude atmospheric dynamics

middle permian u pb zircon ages of the glacial deposits of the atkan formation ayan yuryakh anticlinorium magadan province ne russia their significance for global climatic interpretations abstract the atkan formation in the ayan yuryakh anticlinorium magadan province northeastern russia is of great interest because of the occurrence of deposits of apparent dropstones and ice rafted debris that have been previously interpreted as glacial two high precision u pb zircon ages one for an intercalated volcanic tuff 262 5 0 2 ma and the other for a boulder clast 269 8 0 1 ma within a diamictite of the atkan formation constrain the age of the atkan formation as guadalupian middle permian sedimentologic study of the atkan formation casts doubt on the glacial nature of the diamictites deposition of rocks of the atkan formation temporally correlates with the capitanian interglacial event in the southern hemisphere that recently was calibrated with high precision ca tims the previously proposed climate proxy record based upon warm water foraminifera which corresponds closely to global climate fluctuations is compared with the glacial record of eastern australia and indicates that the capitanian was a time of globally warm climate the sedimentology of atkan formation the record of diversification of both fusulinids and rugosa corals global sea water temperature and sea level fluctuations agree well with high latitude paleoclimate records in northeastern russia and eastern australia major components of the atkan formation the volcanic rocks are syngenetic with the sedimentation process the volcanic activity in the nearby regions during middle late permian was quite extensive

discovery of the ree minerals and its geological significance in the quyang bauxite deposit west guangxi china most of the karstic bauxite deposits in china are enriched in ree and the ree has commonly been considered to be adsorbed on the surface of clay or diaspore minerals as ion state however occurrence of ree minerals in the bauxite deposits has not been reported by far in the quyang bauxite deposit from guangxi province we find ree minerals the minerals are parisite and churchite parisite is widely distributed in the ooids and matrix inducing positive ce anomaly of the ores whereas churchite is rare and occurred in the core of ooid the compositions of the ree minerals show the eu anomaly can change gently during the weathering and the eu anomaly analyses suggest that the ree in the ores are mostly derived from the underlying carbonates the parisite is formed in an alkaline condition while churchite in an acidic situation the co existence of the two minerals in the ores suggests the permian environment for bauxite formation is complex with great change of ph value moreover parisite is inferred to be formed earlier than the churchite

importance of hydrogeological conditions during formation of the karstic bauxite deposits central guizhou province southwest china a case study at lindai deposit abstract karstic bauxite deposits are widespread in central guizhou province sw china and high grade ores are frequently sandwiched with overlying coal and underlying iron rich layers and form a special coal bauxite iron structure the lindai deposit which is one of the most representative karstic bauxite deposits in central guizhou province was selected as a case study based on textural features and iron abundances bauxite ores in the lindai deposit are divided into three types of ores i e clastic compact and high iron the bauxite ores primarily comprise diaspore boehmite kaolinite illite and hematite with minor quartz smectite pyrite zircon rutile anatase and feldspar the al 2 o 3 53 76 8 wt is the main chemical contents of the bauxite ore samples in the lindai district followed by sio 2 fe 2 o 3 tio 2 cao mgo s and p etc our geological data on the lindai deposit indicated that the ore bearing rock series and its underlying stratum have similar rare earth elements distribution pattern and similar y ho zr hf and eu eu values additionally all ore bearing rock samples are rich in mgo range from 0 16 wt to 0 68 wt and the plots of the dolomites and laterites lie almost on or close to the weathering line fit by the al bearing rocks in zr vs hf and nb vs ta diagrams suggesting that the underlying middle cambrian shilengshui formation dolomite is the parent rock of bauxite resources in the lindai district simulated weathering experiments on the modern laterite from the shilengshui formation dolomite in the lindai bauxite deposit show that hydrogeological conditions are important for karstic bauxite formation si is most likely to migrate its migration rate is several magnitudes higher than those of al and fe under natural conditions the reducing inorganic acid condition is the most conducive to al enrichment and si removal fe does not migrate easily in groundwater al enrichment and fe removal can occur only in acidic and reducing conditions with the presence of organic matter the geological and experimental studies show that coal bauxite iron structure in lindai deposit is formed under certain hydrogeological conditions i e since lateritic bauxite or al rich laterite deposited upon the semi closed karst depressions si can be continuously removed out under neutral acidic groundwater conditions the coal carbonaceous rock overlying the bauxitic materials were easily oxidized to produce acidic h 2 s h 2 so 4 etc and reductant groundwater with organic materials that percolated downward resulting in enrichment of al in underlying bauxite it also reduced fe 3 to its easily migrating form fe 2 moving downward to near the basal carbonate culminated in precipitating of ferruginous fes 2 feco 3 etc strata of the coal bauxite iron structure thus the bauxitic materials experienced al enrichment and si and fe removal under above certain hydrogeological conditions forming the high quality bauxite

reevaluation of the timing and extent of late paleozoic glaciation in gondwana role of the transantarctic mountains evidence from antarctica indicates that a 2000 km long section of the transantarctic mountains including victoria land the darwin glacier region and the central transantarctic mountains was not located near the center of an enormous car boniferous to early permian ice sheet as depicted in many paleo geographic reconstructions weathering profiles and soft sediment deformation immediately below the preglacial pre permian un conformity suggest an absence of ice cover during the carbonif erous otherwise multiple glacial cycles would have destroyed these features the occurrence of glaciotectonite massive and strat ified diamictite thrust sheets sandstones containing dewatering structures and lonestone bearing shales in southern victoria land and the darwin glacier region indicate that permian sedimenta tion occurred in ice marginal periglacial and or glaciomarine set tings no evidence was found that indicates the transantarctic mountains were near a glacial spreading center during the late paleozoic although these findings do not negate carboniferous glaciation in antarctica they do indicate that gondwanan glacia tion was less widespread and therefore that glacially driven changes to other earth systems i e glacioeustatic fluctuations cli mate were much smaller than previously hypothesized

genesis of ree minerals in the karstic bauxite in western guangxi china and its constraints on the deposit formation conditions abstract karstic bauxites in western guangxi china comprise two subtypes permian bauxite and quaternary bauxite the quaternary bauxite originated from the breaking up rolling and accumulating of permian bauxite in karstic depressions in quaternary various types of rare earth element ree minerals were discovered during the formation of the permian and quaternary bauxites from the xinxu longhe and tianyang bauxite deposits in this study five types of ree minerals including bastnasite parisite cerianite rhabdophane and churchite were identified bastnasite and parisite are the most abundant and they are widely developed in the permian ore and also present in the quaternary ore obvious variations in bastnasite and parisite ree compositions were observed which is ascribed to distinctions in the source materials in the primary weathering profile from different areas the mode of occurrence of bastnasite and parisite suggests they were mainly precipitated under alkaline and reducing conditions during the permian bauxite forming stage and underwent intensive corrosion in the quaternary churchite was formed during the permian weathering stage under acidic condition both cerianite and rhabdophane occur in fractures within the permian bauxite ore indicating that both formed during the quaternary weathering stage it is considered that the rhabdophane enriched in ce have formed locally in the process of that the ce3 released from bastnasite rapidly entered the rhabdophane lattice before being oxidized to ce4 cerianite was mainly found in association with mn al hydroxides suggesting that the released ce3 was oxidized into ce4 and precipitated cerianite in fractures within the permian bauxite ore mass balance equations reveal a depletion in nearly all rees during the transformation from the permian to the quaternary bauxite ore mainly caused by the dissolution of bastnasite and parisite the genesis of the ree minerals together with the occurrence of other minerals indicates that intensively acidic and oxidizing conditions developed before the formation of the permian bauxite ore towards the end of the permian the conditions became reducing and alkaline favorable for the large scale bauxitization the quaternary bauxite forming stage was characterized by variable ph and eh conditions with acidic ph 4 6 and oxidizing eh 2 conditions at the surface of the exposed permian bauxite ore

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

permian palaeogeographic evolution of the jiangnan basin south china abstract the most striking geographic feature of the permian of south china is the jiangnan basin which intimately reflects the interplay between the yangtze and cathaysia blocks geographic and sedimentological evolution suggests that the jiangnan basin superposed on a precambrian collisonial megasuture and a folded early paleozoic deep basin was an extensional intracratonic basin it opened in the longlinian and became more passive and restricted in the latest maokouan the remarkably similar geographic patterns of the jiangnan basin in the early and late palaeozoic suggest that the yangtze and cathaysia blocks were coherent during the paleozoic

sequence stratigraphic distribution of coaly rocks fundamental controls and paralic examples significant volumes of terrigenous organic matter can be preserved to form coals only when and where the overall increase in accommodation approximately equals the production rate of peat accommodation is a function of subsidence and base level for mires base level is very specifically the groundwater table in paralic settings the groundwater table is strongly controlled by sea level and the precipitation evaporation ratio peat accumulates over a range of rates but always with a definite maximum rate set by original organic productivity and space available below depositional base level groundwater table below a threshold accommodation rate nonzero no continuous peats accumulate due to falling or low groundwater table sedimentary bypass and extensive erosion by fluvial channels this is typical of upper highstand lowstand fan and basal lowstand wedge systems tracts higher accommodation rates provide relatively stable conditions with rising groundwater tables mires initiate and copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received september 7 1995 revised manuscript received november 25 1996 final acceptance may 5 1997 2exxon production research company 3120 buffalo speedway houston texas 77096 3exxon production research company 3120 buffalo speedway houston texas 77096 present address conoco inc p o box 2197 houston texas 77252 we benefited from the input and assistance of many people of special assistance were the teams involved in collaborative studies with esso australia and esso malaysia p moore m sloan j emmett b burns a partridge s creaney hanif hussein r hill r lovell and m feeley we also thank the rock springs team r beauboeuf p mclaughlin w devlin a carroll y y chen g grabowski jr k miskell gerhardt m farley r webster and j schwalbach group members d curry and j yeakel were always helpful we also enjoyed and profited from many discussions of these concepts with our colleagues outside exxon c diessel r boyd k shanley b zaitlin p mccabe m hendricks a cohen and m kirschbaum we thank the reviewers of company reports whose careful comments on several generations of this work improved it s creaney m feeley j van wagoner f wehr j yeakel and a young f weber and j zullig provided extensive management support k linke translated our sketches into the fine figures herein we value all the help

global continental weathering trends across the early permian glacial to postglacial transition correlating high and low paleolatitude sedimentary records time equivalent early permian sedimentary successions from high latitude gondwana basins and from equatorial accumulations in north china covering the glacial to postglacial transition display correlatable trends in continental weathering intensity based on chemical index of alteration cia values the successions display a pattern of cia values that varies with latitude similar to modern estuarine suspended sediments based on the modern day cia temperature correlation the glacial early permian low to high latitude land surface temperature gradient is estimated as 20 c slightly higher than the calculated values for the contemporaneous sea surface temperature gradient

coal in a carbonate sequence stratigraphic framework the upper permian heshan formation in central guangxi southern china microfacies and sedimentological analyses of the upper permian coal bearing heshan formation in the heshan coalfield of central guangxi suggest that these coal measures formed in a marine carbonate platform setting low volatile bituminous coals with very high organic sulphur overlie either palaeosols or locally developed cherts the petrography and geochemistry of the coals suggest formation in low lying mires in which marine influence increased upwards in the heshan and overlying dalong formations four third order sequences are described based on the recognition of four sequence boundaries higher order sequences within each of these third order sequences are also documented and within sequence iii coal seams are developed above higher order transgressive surfaces representing the deposits formed during the lag time between initial flooding of the platform and the onset of carbonate production in the heshan formation the coals with greatest thickness occur immediately above third order transgressive surfaces it is argued that in some coal bearing siliciclastic free marine carbonate platform settings accommodation creation rates and peat accumulation rates are balanced hence greater coal accumulation can be achieved at the transgressive surface rather than at the maximum flooding surface

permian diamictites in northeastern asia their significance concerning the bipolarity of the late paleozoic ice age despite a lack of detailed sedimentologic analyses diamictites in the middle permian atkan formation were previously interpreted as glaciomarine and glacially influenced marine deposits this interpretation allowed this unit to play a prominent role in paleoclimatic and biogeographical reconstructions associated with presumed bipolar glaciation during the late paleozoic ice age lpia in this sense the lpia is considered to be a close analog to bipolar glaciation and climate change during the cenozoic here results are presented that challenge the glacigenic interpretation for these strata and negate interpretations of the bipolar nature of the lpia the 400 to 1500 m thick atkan formation was deposited in back arc basins associated with activity of the okhotsk taigonos volcanic arc along the leading edge of pangea as it drifted across the north polar circle the occurrence of tuffs volcanic clasts and glass shards indicate derivation from a nearby arc cooling and solidification of some clasts during sedimentation is suggested by the occurrence of clasts with embayments and protrusions that extend into the surrounding matrix clasts with columnar like jointing and alteration of the matrix surrounding some clasts ca tims dating of tuff zircons indicate a late capitanian age which is consistent with fossils within the strata bedded diamictites deposited as debrites dominate these diamictites which occur as tens of m thick downlapping packages that thicken then thin upward were deposited as prograding and abandoning sediment gravity flow fans chaotic and folded strata formed as slumps graded sandstones and conglomerates were deposited as turbidites and mudstones were deposited as mudflows low density turbidites and hemipelagic deposits striated clasts and outsized clasts piercing bedding were not observed in the study area strata above and below the atkan formation contain abundant graded beds and deep water trace fossils indicating deposition as turbidites the combination of debrites turbidites slumps volcanic grains clasts glass and tuffs and an absence of glacigenic indicators suggest that atkan strata were deposited in deep water basins associated with the development of the volcanic arc rather than due to glacial activity these findings are significant as they require reconsideration of current views of lpia glaciation and suggest that ice sheets were limited to gondwana

genesis of the guangou karstic bauxite deposit in western henan china abstract the guangou bauxite deposit in western henan china is located in the north china block and to the north of the north qinling orogenic belt the orebody is hosted within the lower member of the carboniferous benxi formation which overlies unconformably upon the ordovician majiagou formation in the lower member of the benxi formation the bauxite orebody with a diaspore illite anatase mineral assemblage is sandwiched between underlying ferric clay illite hematite goethite and overlying top clay kaolinite quartz goethite according to field observations and geochemical evidence including trace and rare earth element ree compositions especially zr hf ratios the ferric clays were weathered from the underlying argillaceous limestones in the majiagou formation during this weathering process trace elements s zn ni cr v sc f ba and be are depleted li rb and b are enriched and zr hf bi ta ga nb and th are relatively immobile rees exhibit evident differentiation with enrichment of la ce pr and nd and depletion of gd tb dy ho er tm yb and lu the bauxite formed in weak reducing slightly basic water conditions according to the geneses of coexisting diaspore and anatase and it was altered during the epigenetic and second exposure periods forming kaolinite and goethite respectively interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and rees in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements for instance zircon rutile and anatase contain zr hf nb ta w and u based on geochemical evidence together with age data and chemical compositions of the detrital minerals both distant igneous rocks in the plate margin and paleozoic carbonates and precambrian rocks inside north china block provide the miscellaneous material for the bauxite ore and the top clay

early wuchiapingian cooling linked to emeishan basaltic weathering abstract the last glaciation during the late paleozoic ice age commenced at around the guadalupian lopingian g l boundary and is synchronous with the emplacement of the emeishan large igneous province using ca tims zircon u pb dating we obtained an age of 259 51 0 21 ma for the uppermost tuff from the puan volcanic sequence in the eastern emeishan large igneous province constraining the timing of emeishan volcanism and providing another candidate age for the g l boundary in addition we determined an age of 259 69 0 72 ma for a basal claystone in the immediately overlying longtan formation from a drill core section in southwest south china these ages along with source weathering trends of mudstones from the lower longtan formation and compiled paleotemperature records indicate an earliest wuchiapingian cooling coinciding with the onset of the last permian glaciation this global cooling is associated with positive shifts in both organic and carbonate carbon isotopic records and likely a decrease in atmospheric pco2 a hypothesised causal linkage is proposed in which the rapid post eruptive basaltic weathering of the emeishan province in an equatorial humid belt may accelerate the atmospheric co2 consumption and lead to climate cooling our work supports the long term climate cooling effects of large igneous provinces

earliest laterites and possible evidence for terrestrial vegetation in the early proterozoic paleosols preserve information about the composition of the atmosphere and paleoclimatic conditions here we report the discovery of the first pisolitic laterites of precambrian age the laterites are immediately above the regional unconformity at the base of the early proterozoic gamagara formation in paleokarst depressions on the campbellrand dolomite transvaal supergroup south africa the paleosol profiles are very well preserved and show zoning relict soil textures and chemical composition virtually identical to those of modern laterites the pisolitic laterites provide not only evidence for a highly oxygenated atmosphere and possible hot and humid climatic conditions in early proterozoic time but also indicate the presence of terrestrial life on the kaapvaal craton 2 0 2 2 b y ago

the coal bauxite iron structure in the ore bearing rock series as a prospecting indicator for southeastern guizhou bauxite mines bauxite deposits in southeastern guizhou occur in the lower permian liangshan formation the rock series bearing the sedimentary bauxite exhibit a typical coal bauxite iron structure in which the lower part consists of bauxitic shale intercalated with siderite concretions the middle part consists of bauxitic rock intercalated with multilayer lenticular or earthy bauxite and the upper part consists of carbonaceous shales and sandstones intercalated with coal seams the paralic coastal and paludal depositional environments at one time had a stable tectonic setting by studying the elemental geochemistry of the ore bearing rock series it can be seen that the common presence of the coal bauxite iron structure has resulted from 1 the extensive desilication and iron depletion during the formation of the sedimentary bauxite due to the varying physical and chemical environment and 2 the sufficient supply of organic matter by the external environment such geological anomalies that resulted from the physical and chemical changes during the formation of the layered structure in the ore bearing rock series can serve as a mineralization indicator in prospecting for new deposits

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

voluminous silicic eruptions during late permian emeishan igneous province and link to climate cooling abstract silicic eruptive units can constitute a substantive component in flood basalts dominated large igneous provinces but usually constitute only a small proportion of the preserved volume due to poor preservation thus their environmental impact can be underestimated or ignored establishing the original volume and potential climate sensitive gas emissions of silicic eruptions is generally lacking for most large igneous provinces we present a case study for the 260 ma emeishan province where silicic volcanic rocks are a very minor component of the preserved rock archive due to extensive erosion during the late permian modal and geochemical data from late permian sandstones derived from the province suggest that silicic volcanic rocks constituted some 30 by volume of the total eroded emeishan volcanic source rocks this volume corresponds to 3 10 4 km 3 on the basis of two independent estimate methods detrital zircon trace element and hf isotopic data require the silicic source rocks to be formed mainly by fractional crystallization from associated basaltic magmas based on experimental and theoretical calculations these basalt derived 104 km3 silicic eruptions released 1017 g sulfur gases into the higher atmosphere and contribute to the contemporaneous climate cooling at the capitanian wuchiapingian transition 260 ma this study highlights the potentially important impact on climate of silicic eruptions associated with large igneous province volcanism

reconstructing early permian tropical climates from chemical weathering indices this study was financially supported by the national natural science foundation of china grants 41302083 41572078 the national basic research program of china grant 2011cb808800 and the fundamental research funds for the central universities grant cugl140402 china university of geosciences wuhan p a cawood acknowledges support from nerc grant ne j021822 1

the history of south american tropical precipitation for the past 25 000 years long sediment cores recovered from the deep portions of lake titicaca are used to reconstruct the precipitation history of tropical south america for the past 25 000 years lake titicaca was a deep fresh and continuously overflowing lake during the last glacial stage from before 25 000 to 15 000 calibrated years before the present cal yr b p signifying that during the last glacial maximum lgm the altiplano of bolivia and peru and much of the amazon basin were wetter than today the lgm in this part of the andes is dated at 21 000 cal yr b p approximately coincident with the global lgm maximum aridity and lowest lake level occurred in the early and middle holocene 8000 to 5500 cal yr b p during a time of low summer insolation today rising levels of lake titicaca and wet conditions in amazonia are correlated with anomalously cold sea surface temperatures in the northern equatorial atlantic likewise during the deglacial and holocene periods there were several millennial scale wet phases on the altiplano and in amazonia that coincided with anomalously cold periods in the equatorial and high latitude north atlantic such as the younger dryas

paleomagnetism of carboniferous sediments in the hexi corridor its origin and tectonic implications we report paleomagnetic results for carboniferous rocks from the eastern part of the hexi corridor which we have demonstrated to be the western extension of the north china block ncb the characteristic high temperature remanence component b component exhibits predominantly reverse polarity and is generally separable by thermal demagnetization temperature steps between 350 and 580 c this b component can also be isolated by alternating fields afs cleaning at a peak value of 20 30 mt using a hybrid thermal af demagnetization method the b component shows a positive fold test at the 95 confidence level indicating that it was acquired before late triassic to early jurassic folding we interpret the b component to be of primary origin acquired during the carboniferous the corresponding pole positions are at 14 0 e 10 5 n 95 6 2 for the early middle carboniferous late visean to namurian and at 10 2 e 33 3 n 95 16 7 for the late carboniferous stephanian the preliminary late carboniferous pole is in agreement with that for the ncb supporting earlier claims that the hexi corridor has been the western extension of the ncb since the ordovician on the other hand these two carboniferous paleopoles are distinct from the coeval ones for inner mongolia outer mongolia south china tarim and stable europe at greater than 95 confidence suggesting that these continental blocks could not have been connected in their present configuration during carboniferous time the significant difference in paleolatitude between the ncb and australian part of gondwanaland according to the two new hexi corridor poles indicates that they had drifted apart by the late visean

mineralogy and geochemistry of claystones from the guadalupian lopingian boundary at penglaitan south china insights into the pre lopingian geological events abstract the guadalupian lopingian g l boundary at a stratigraphically well documented outcrop in penglaitan guangxi autonomous region south china has been approved as the global stratotype section and point gssp several volcanic ashes or tuffs occur at this boundary but their mineralogy and geochemistry are not available yet and no reliable age for this boundary has been obtained a combined study of mineralogy geochemistry and geochronology has been carried out in this study on six layers of claystones collected below group 1 and above group 2 the g l boundary at the penglaitan section both group 1 and group 2 claystones are likely clastic in origin rather than volcanic ashes as previously thought thus the penglaitan claystones are not suitable for age determination of the g l boundary they are significantly different in terms of mineralogy and geochemistry specifically group 1 claystones are likely derived from a mafic source which is genetically related to the emeishan large igneous province therefore providing additional evidence for the synchroneity between the g l boundary mass extinction and the emeishan volcanism group 2 samples were derived from a felsic source of which zircons yield an age spectrum peaked at 262 3 ma undistinguishable within the uncertainty from the currently accepted g l boundary age 260 4 0 4 ma nevertheless group 2 samples are not related to emeishan volcanism because their negative zircon ehf t values differ significantly from those of emeishan magmas and trace element compositions of zircons are indicative of an arc source rather than a within plate source in consideration of paleogeographic reconstruction we propose that the group 2 claystones may have been derived from continental arcs during the palaeo tethys evolution this is the first sedimentary evidence for permian continental arc in the northern margin of palaeo tethys

a review of dendrogeomorphological research applied to flood risk analysis in spain over the last forty years applying dendrogeomorphology to palaeoflood analysis has improved estimates of the frequency and magnitude of past floods worldwide this paper reviews the main results obtained by applying dendrogeomorphology to flood research in several case studies in central spain these dendrogeomorphological studies focused on the following topics 1 anatomical analysis to understand the physiological response of trees to flood damage and improve sampling efficiency 2 compiling robust flood chronologies in ungauged mountain streams 3 determining flow depth and estimating flood discharge using two dimensional hydraulic modelling and comparing them with other palaeostage indicators 4 calibrating hydraulic model parameters i e manning roughness and 5 implementing stochastic based cost benefit analysis to select optimal mitigation measures the progress made in these areas is presented with suggestions for further research to improve the applicability of dendrogeochronology to palaeoflood studies further developments will include new methods for better identification of the causes of specific types of flood damage to trees e g tilted trees or stable isotope analysis of tree rings to identify the climatic conditions associated with periods of increasing flood magnitude or frequency

genetic relationship between the emeishan plume and the bauxite deposits in western guangxi china constraints from u pb and lu hf isotopes of the detrital zircons in bauxite ores abstract the formation processes and alumina sources of the large and super large bauxite deposits that have developed in west guangxi in the yangtze block have been debated for a long time shrimp zircon u pb dates combined with in situ hf isotopic data of the detrital zircons from permian bauxite ores in the western guangxi province china provide new constraints on the genesis of the bauxites in west guangxi u pb dating ages of the detrital zircons cluster around 256 ma and 261 ma this is consistent with the emplacement age of the emeishan plume thus it has been determined that the detrital zircons come from magmatic rocks related to the emeishan plume and that the emeishan plume has significant control on the formation of bauxites in addition this work presents new evidence for the evolution of the emeishan plume most of the e hf t values of the zircons around 256 ma and 261 ma are negative varying widely from 1 3 to 16 1 this data indicates the melting of yangtze block basement rocks and the mixing of magmas generated both from the mantle and from the crust occurred at the periphery of the plume in the main phase of emeishan lip magmatism this study verified that the plume induced uplift exposed carbonates as well as the mafic and felsic rocks generated by the emeishan plume to long periods of intense weathering under humid tropical conditions the weathering remnants of the high alumina magmatic rocks and carbonates were deposited on or transported to the paleokarst surface and converted to bauxites

the tice event perturbation of carbon nitrogen cycles during the mid tournaisian early carboniferous greenhouse icehouse transition abstract carbonate carbon 13ccarb and bulk nitrogen 15n isotopic variation during the mid tournaisian was analyzed in the malanbian and long an sections of south china their c isotope profiles document a large positive excursion herein termed the mid tournaisian carbon isotope excursion tice during the siphonodella isosticha conodont zone although its magnitude differed between the two sections 6 at malanbian versus 3 at long an the tice event coincided with sedimentologic and oxygen isotopic evidence of climatic cooling and glaciation during the mid tournaisian it was probably triggered by an increase in organic carbon burial rates linked to changes in global ocean circulation the study sections also document a large positive shift in 15n from 1 7 to 4 2 at malanbian and from 1 5 to 3 8 at long an the n isotope shift shows no termination within the study sections and is likely to mark the onset of an extended interval of 15n enriched marine nitrate that lasted for the duration of the late paleozoic ice age its initiation coincided with tice and thus may have been linked to ocean circulation changes that resulted in intensified upwelling and an increase in water column denitrification the continuation of the n isotope shift over millions of years may have been linked to glacio eustatic fall and a long term shift in the locus of denitrification from continental shelf sediments to continent margin oxygen minimum zones the tice event thus marks the onset of sustained continental glaciation during the late paleozoic ice age

deglaciation sequences in the permo carboniferous karoo and kalahari basins of southern africa a tool in the analysis of cyclic glaciomarine basin fills the late westphalian to artinskian glaciomarine deposits of the karoo and kalahari basins of southern africa consist of massive and stratified diamictite mudrock with ice rafted material sandstone silty rhythmite shale and subordinate conglomerate forming a cyclic succession recognizable across both basins a complete cycle comprises a resistant basal unit of apparently massive diamictite overlain by softer bedded stratified diamictite sandstone and mudrock with a total thickness of as much as 350 m four major cycles are observed each separated by bounding surfaces lateral facies changes are present in some cycles the massive diamictites formed as aprons and fans in front of the ice grounding line whereas the stratified diamictites represent more distal debris flow fans the sandstones originated in different environments as turbidite sands small subaqueous outwash channel sands and delta front sands the rhythmites and mudrock represent blanket deposits derived from turbid meltwater plumes cycles represent deglaciation sequences which formed during ice retreat phases caused by eustatic changes in the karoo and kalahari basins evidence for shorter term fluctuation of the ice margin is present within the major advance retreat cycles hardly any sediment was deposited during lowstand ice sheet expansion whereas a deglaciation sequence was laid down during a sea level rise and ice margin retreat with the volume of meltwater and sediment input depending on temporary stillstands of the ice margin during the retreat phase the duration of the cycles is between 9 and 11 ma suggesting major global tectono eustatic events smaller cycles probably linked to orbital forcing were superimposed on the longer term events a sequence stratigraphic approach using the stacking of deglaciation sequences with the ice margin advance phases forming bounding surfaces can be a tool in the framework analysis of ancient glaciomarine basin fills

permo carboniferous paleogeography and coal accumulation and their tectonic control in the north and south china continental plates abstract permo carboniferous strata in north china and south china were essentially controlled by paleogeography paleoclimate and plate tectonics during that time north china and south china were separate microcontinents located on opposite sides of the equator thus the characteristics of their coal deposits differ substantially in north china the coal seams were initially deposited on a north sloping epicontinental basin during the middle carboniferous by the middle of the late permian the locus of coal formation had shifted from the north to the south as a result of the uplift of the northern margin due to continental collision with the siberian plate as the paleoplate was situated in the low northern latitudes moist tropical climate and favorable geographic setting allowed the extensive development of late carboniferous and earliest permian peat swamps on the northern alluvial fluvial plain and central paralic regimes more significantly two thick coal sequences were formed in the transition belt between the alluvial apron and fluvial plain and the shoreline area where high groundwatertable fed by both rainwater and groundwater favored the formation of thick peat in swamps with northward drift the paleoplate entered the subtropic semiarid and arid climatic belt between the late early permian and early late permian coal formation was restricted to the paralic delta plain where locally oceanic wet climate and high groundwatertable prevailed following this the subduction of the paleo tethys beneath the southern margin of north china led to the upwarp of the southern margin and kept the delta system growing vertically for a considerable period so that it kept pace with shoreline fluctuations on the southern area the result was that multicycle deltaic coals were well developed at this stage in south china coal was formed in the coastal zone of an epeiric and shelf sea which connected the marinal basins the basins were frequently influenced by plate marginal tectonic movements and continental rifting related to back arc extension as a result coal formation was often interrupted by sea level fluctuations early carboniferous coal was deposited during the short regressions during the widespread transgression mainly on the restricted marine paralic plain where clastic deposition was active in the middle and late carboniferous no coal was formed because the paleoplate had drifted into a subtropic arid belt early permian coal accumulated at first in the northeast and later in the southwest due to tectonic influences in the late permian relatively thick and extensive coal was formed even though it was during a transgressive period in both the western and eastern margins under the equatorial hot humid conditions in general the seam geometry and quality particularly ash and sulfur of the coal was directly controlled by the geography and the changes in the depositional environments however the fluctuation in coal formation and the migration of thicker coal zones was indirectly controlled by paleoclimate and the sea level fluctuations in response to plate tectonic influences

mineralogical characteristics of the superlarge quaternary bauxite deposits in jingxi and debao counties western guangxi china abstract in recent decades more than 0 5 billion tons of ores scattered in the quaternary laterite in western guangxi china have been explored the ores were derived from a bauxite horizon in permian via physical break up and re sediment process utilizing various test methods i e xrd dta tg dtg sem eds and epma the mineralogical characteristics of the quaternary bauxite ores in jingxi and debao counties were investigated xrd was used together with tg dtg to obtain relatively accurate ore mineral abundance diaspore is the major phase whereas hematite kaolinite anatase chamosite gibbsite goethite illite and rutile are minor diaspore is characterized by a small particle size low degrees of crystallinity and complex chemical composition both gibbsite and goethite have a varied particle size and goethite crystals contain high al substitution and si it is clarified that diaspore chamosite and anatase were formed in a mildly reduced and alkaline depositional environment in permian while gibbsite hematite goethite and part kaolinite were precipitated from al 3 si 4 and fe 3 enriched solutions within an quaternary oxidized environment the ions al 3 si 4 and fe 3 are mostly released from chamosite in its dissolution process the different physicochemical conditions between the permian depositional and the quaternary weathering periods resulted in a complex mineral assemblage in the quaternary bauxite

climate pco2 and terrestrial carbon cycle linkages during late palaeozoic glacial interglacial cycles the late palaeozoic was marked by a series of glacial interglacial cycles geochemical and fossil data suggest a role for terrestrial vegetation carbon cycle feedbacks in the climate response to orbital forcing

the guadalupian lopingian boundary mudstones at chaotian sw china are clastic rocks rather than acidic tuffs implication for a temporal coincidence between the end guadalupian mass extinction and the emeishan volcanism abstract previous studies on the temporal link between the end guadalupian mass extinction event and emeishan flood volcanism were mainly based on geochronological and bio and chemostratigraphic correlation techniques wignall et al 2009 the absence of material based hard evidence that directly links the extinction with the emeishan volcanism remains a major obstacle regardless of the indication of coincidence in timing isozaki et al 2007 the emeishan basalts overlie permian platform carbonates that may contain a record of the end guadalupian mass extinction and erosional product of this province this paper presents mineralogy and geochemistry of mudstones from the guadalupian lopingian boundary g lb at chaotian sw china results indicate that these g lb mudstones are not air fall acidic tuff as previously thought but likely represent clastic rocks derived from erosional deposits of the emeishan large igneous province elip mudstones of the lower part group 1 have a geochemical affinity to the emeishan felsic volcanic rocks whereas mudstones of the upper part group 2 are compositionally akin to mafic components of the emeishan traps this chemostratigraphic sequence resembles the xuanwei formation which sits on the emeishan basalts he et al 2007 these data therefore indicate that the lower part of the mudstones at the chaotian g lb section the lowermost part of xuanwei and longtan formations and the emeishan felsic extrusives broadly constitute an isochron horizon throughout the elip and adjacent region suggesting a short duration for the emeishan volcanism a temporal coincidence between emeishan volcanism and the end guadalupian mass extinction are therefore inferred thus providing support for a cause and effect relationship

transformation from permian to quaternary bauxite in southwestern south china block driven by superimposed orogeny a case study from sanhe ore deposit abstract permian karstic bauxite and its quaternary derivative in western guangxi southwestern south china block possess a total tonnage greater than 0 5 billion tons the primary late permian karstic bauxite formed in reduced environment in the background of tethyan accretionary orogenesis and as one consequence of cenozoic convergence of the indian and eurasia continents the primary orebody was uplifted eroded and re sedimented within quaternary laterite the geochemical variation and its controls during the ore transformation from permian to quaternary remain poorly understood quaternary ore blocks comprise an inner zone of fresh ore and then it gradually transited through a middle zone to a margin with extensive weathering one such bauxite block was selected and further subdivided into twenty three samples for geochemical and mineralogical analysis the inner and middle zones contain similar mineralogical compositions dominated by diaspore and amesite with minor illite anatase goethite pyrite zircon and rutile the margin is composed of diaspore with small amounts of amesite boehmite illite goethite anatase kaolinite zircon rutile and barite bauxite in all three zones is composed of mainly al si fe and ti and high contents of zr cr li f s zn v sr nb ba and ree variations in fe2 and fe3 between the three zones were observed the elements si al fe2 mg ba cr f li ni zn and ree decrease from the core of the ore block outwards corresponding to an increase in s and fe3 depletions in si al fe2 mg ba and cr were caused by the dissolution of amesite most of the al and si in amesite were lost during the weathering and minor retained to form kaolinite depletions in li ni and zn resulted from changes in the depositional environment between the late permian and quaternary dissolution of ree bearing fluorocarbonates resulted in depletions of ree and f the enrichment of fe3 and s was related to the precipitation of goethite hematite and barite in an oxidizing environment while local enrichment of ce resulted from the redox change of ce3 ce4 under the same condition this shows that the chemical composition of laterite enwrapping the bauxite also took part in quaternary bauxite transformation this study shows that the elements migrations during bauxite transformation were influenced by multiple independent factors except for the elemental attributes

a model based evaluation of tropical climate in pangaea during the late palaeozoic icehouse abstract the late palaeozoic ice age lpia is the earth s penultimate icehouse climate geological proxies for tropical pangaean climate during the lpia are significantly modulated on 100 400 kyr and sub 100 kyr scales in addition some geological proxies suggest that equatorial continental areas may have been colder and more arid during lpia glacial intervals than during late cenozoic glacial intervals furthermore the relationship between polar and tropical climate variability remains controversial the climate dynamics underlying these phenomena are only partly understood nevertheless past modeling of lpia climate has suggested that precipitation near the equator was modulated by monsoonal circulation that itself was modulated by orbital variability here the earth s climate during asselian sakmarian time 299 284 ma was simulated with the community climate system model version 3 ccsm3 these simulations address model climate sensitivity to direct and indirect effects of glaciation as well as variability in the earth s orbit the results of these simulations suggest that sea level and orbitally forced monsoon variability were the primary controls on tropical precipitation when ice sheets were confined to polar latitudes any impact of orbital forcing on glaciation therefore could have led to aliasing between glacial and monsoonal effects in particular regions perhaps explaining contrasting geologically based interpretations of how tropical climate responded to glaciation glaciation of the central pangaean mountains would have led to widespread cold and aridity in equatorial pangaea but forming these glaciers would have required an unknown additional climate forcing with an unknown impact on tropical precipitation

late devonian glacial deposits from the eastern united states signal an end of the mid paleozoic warm period abstract a late devonian polymictic diamictite extends for more than 400 km from northeastern pennsylvania across western maryland and into east central west virginia the matrix supported unbedded locally sheared diamictite contains subangular to rounded clasts up to 2 m in diameter the mostly rounded clasts are both locally derived and exotic some exhibit striations faceting and polish the diamictite commonly is overlain by laminated siltstone mudstone facies associations laminites the laminites contain isolated clasts ranging in size from sand and pebbles to boulders some of which are striated the diamictite laminite sequence is capped by massive coarse grained pebbly sandstone that is trough cross bedded a stratigraphic change from red calcic paleo vertisols in strata below the diamictite to non calcic paleo spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite the diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the late devonian of the appalachian basin these deposits record a late devonian episode of climatic cooling so extreme that it produced glaciation in the appalachian basin evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite overlain by glaciolacustrine varves containing dropstones and capped by sandstone interpreted as braided stream outwash the appalachian glacigenic deposits are contemporaneous with glacial deposits in south america and suggest that late devonian climatic cooling was global this period of dramatic global cooling may represent the end of the mid paleozoic warm interval that began in the middle silurian

whole rock geochemistry of upper paleozoic loessite western pangaea implications for paleo atmospheric circulation abstract average bulk major and trace element chemical composition of upper paleozoic loessite lithified loess from several widely scattered sites in western equatorial pangaea western north america approximates upper continental crust ucc but is more similar to the bulk composition of precambrian basement coring uplifts of the ancestral rocky mountains however distinct compositional signatures occur among the various loessite deposits controlled primarily by differences in al 2 o 3 mgo na 2 o k 2 o and rb furthermore values of the chemical index of alteration cia of these loessites are low 55 63 skewed toward lower values closely matching values for north american loess and precambrian basement although diagenesis can account for some of the compositional differences e g local sio 2 or k 2 o enrichment it fails to explain the major differences among the sites rather these differences are best explained as a result of variations in regional basement that sourced the loess coupled with transport wind pathways which varied from zonal easterlies to monsoonal westerlies in this region of tropical pangaea from late carboniferous to early permian time the low cia values generally reflect first cycle derivation from regional basement uplifts of the arm and for younger deposits a variable contribution from the suture zone uplifts and volcanism of the appalachian ouachita marathon collisional belt the variations in bulk chemical composition of the loessite coupled with previously collected detrital zircon geochronology suggest that these low latitude loessites are not simply the result of deflation of mid latitude erg deposits or coastal alluvial plain sediments these data represent a first attempt at geochemical characterization of pre quaternary loess and demonstrate the utility of loess geochemistry as a proxy for paleoatmospheric circulation in earth s deep time past

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

carboniferous permian carbon isotope stratigraphy of successions from china yangtze platform usa kansas and russia moscow basin and urals abstract the pennsylvanian and early permian were times of extreme sea level changes of 100 to perhaps up to 200 m for example glacio eustatic sea level changes are well documented from the us midcontinent moscow basin and yangtze platform where more than 100 stacked subtidal to supratidal sequences have been described in contrast carbonates developed in the ural mountains and south guizhou of the yangtze platform were deposited in ramp and slope settings 13c values of whole rock samples from the us midcontinent and moscow basin were intensively affected by diagenesis only well preserved brachiopod shells maintained their original carbon isotope ratios in contrast limestones deposited in the deeper water slope environments were not affected by meteoric diagenesis and are interpreted to have mainly retained their carbon isotope ratios mean 13c values of slope carbonates of the yangtze platform increase from about 3 during the visean and serpukhovian to 5 at the carboniferous permian boundary and decrease to values around 2 in the early kungurian this positive 13c excursion coincides with low 13c values in the yangtze platform successions which were reset by meteoric diagenesis the highest 13c values recorded in the slope succession coincide with the inferred maximum glaciation that caused pronounced sea level lowstands short lived but significant negative 13c excursions in the chinese slope succession are interpreted to reflect changes in ocean circulation due to sea level rises which caused enhanced production and or preservation of organic matter which influenced the subsequent early diagenetic cementation

cool climate or warm spike lateritic bauxites at high latitudes abstractlaterites and bauxites and their associated ultisols and oxisols are widespread in warm wet climates today and their spread to high latitudes has been attributed to episodes of past global warming bauxitic paleosols from the early eocene monaro volcanics of southeastern australia have been claimed as exceptions formed in a cool wet climate reexamination and chemical analysis of a sequence of intrabasaltic paleosols in the bega no 7 core of radiometrically dated monaro volcanics now show highly variable paleotemperature and precipitation the core includes 53 successive paleosols mostly nonbauxitic but bauxitic paleosols reveal local spikes in warmth and precipitation coincident with early eocene 55 52 51 and 48 ma global spikes of warmth precipitation and high atmospheric co2 these bauxitic paleosols thus formed in warm wet not cool dry climates and their poleward spread coincided with global greenhouse spikes

a latest carboniferous warming spike recorded by a fusulinid rich bioherm in timor leste implications for east gondwana deglaciation abstract during the late paleozoic and early mesozoic timor lay in the northern part of the north south east gondwana rift system along which the western margin of australia later developed discovery of a latest gzhelian bioherm in the central highlands of timor leste has implications for latest carboniferous earliest permian climate history and deglaciation in basins further south in the rift system limestone outcrop of the maubisse formation near the village of kulau is recognized as a bioherm with a massive lower unit including reef framework at the base and a bedded grainstone upper unit the bioherm developed on a basalt substrate in warm shallow water as indicated by photozoan assemblages in the massive lower unit foraminifera belonging to 17 genera are recorded from the bioherm these include representatives of the families biseriamminidae biwaellidae bradyinidae cornuspiridae lasiodiscidae palaeotextulariidae pseudotaxidae ozawainellidae schubertellidae schwagerinidae staffellidae and textrataxidae twenty one species have been referred to known types and 12 species are left in open nomenclature the assemblage probably belongs within the uppermost gzhelian schwagerina robusta ultradaixina bosbytauensis zone although a possible lowest asselian correlation cannot be excluded the bioherm is the oldest carbonate unit so far recorded from the maubisse formation and the oldest sedimentary unit biostratigraphically dated in timor the dominantly heterozoan composition of the skeletal component of the limestone except for the basal photozoan assemblage and the taxonomic diversity of the larger foraminifera suggest a subtropical environment consistent with a paleolatitude of about 40 s the late pennsylvanian was a time of glaciation that in australia is represented by a significant stratigraphic hiatus in basins to the south of timor in the east gondwana rift system the development of the kulau bioherm during the latest gzhelian may have coincided with a global warming spike that led to rapid melting of continental ice sheets and a substantial influx of glacigene sediment alternating diamictite and mudstone in the southern basins

orebody vertical structure and implications for ore forming processes in the xinxu bauxite deposit western guangxi china abstract the xinxu bauxite orebodies which are contained in quaternary depressions overlying strata of permian to devonian age were formed through the break up oxidation and re sedimentation of a pre existing permian bauxite horizon with progressive karsitification the underlying strata of the quaternary orebodies were eroded out downwards in sequence gradually transiting from permian to devonian thus an older underlying stratum generally infers a higher degree of weathering a total of 47 exploration wells sampled each meter were chosen from several orebodies to evaluate the vertical distribution of four major components al 2 o 3 fe 2 o 3 sio 2 and loss on ignition in the ores the vertical evenness is quantified via a box gliding multifractal model the small width of the multifractal spectrum suggests that the vertical ore quality is even overall indicating an intertwining break up and mixing up processes during evolution of the quaternary orebody although the four components show complex spatial distributions topographic elevation displays a positive relationship with the mean fe 2 o 3 content and a negative correlation with the vertical unevenness of al 2 o 3 and fe 2 o 3 in the wells this is taken to reflect the more uniform oxidizing environment in the higher depressions which facilitates a homogeneous and greater increase of fe 2 o 3 content throughout the orebody in contrast the redox conditions in lower depressions are less oxidizing and varied in space inducing great variation in degree of fe 2 o 3 increase in the ores this study also demonstrates that in the xinxu deposit the ore forming redox environment has more impact on the ore quality than the degree of weathering as the contents show irregular vertical changes in the lower depressions it follows that it is the ancient redox environment rather than the modern conditions which affect the orebody vertical structure this clarifies the fact that the vertical structure of the orebody is jointly constrained by the physical melange accumulation of ores and the differences between the ancient redox environments in the higher and lower locations these factors should be the primary factors affecting the vertical structure of karst bauxite deposits

palaeozoic uplands and unconformity in the north china block constraints from zircon la icp ms dating and geochemical analysis of bauxite the problem of location of the north china block ncb during the palaeozoic and its history of uplift and erosion have not been established satisfactorily a regional unconformity was developed in the ncb between the upper ordovician and the middle upper carboniferous zircon grains in the samples collected for isotopic age dating from the unconformable surface in central north china show two main clusters of ages around c 444 and c 313 ma and a scatter of ages between c 2500 and c 550 ma silurian and devonian ages were not observed similarities between the zircon rare earth element and trace elements show that the c 444 and c 313 ma zircon grains were derived from rocks in the active margins of the ncb geological and isotopic evidence suggests that between c 444 and 312 ma north china was uplifted and that there was a long gap in sedimentation this major change in the environment of north china from marine to continental upland occurred at the same time as the separation of north china from northern gondwana the closure of the northern palaeotethys along the altai inner mongolia zone and the collision between gondwana and laurasia

paleokarst on the top of the maokou formation further evidence for domal crustal uplift prior to the emeishan flood volcanism abstract the 260 ma emeishan large igneous province elip in southwest china has previously been demonstrated to provide compelling evidence for pre volcanic crustal doming in support of the mantle plume hypothesis however this has been questioned by ukstins peate and bryan 2008 by showing hydrothermal magmatic activity at the daqiao section to solve this argument a detailed characterization of the contact between the emeishan basalts and the maokou formation was carried out the contact is shown to be an unconformity which is characterized by paleokarst on top of the maokou formation including paleokarst relief sinkholes caves tower karst and its corresponding rocks such as kaolinite bauxite and ferruginous duricrust and collapsed breccias etc this paleokarst unconformity was in turn covered or infilled by the emeishan basalts and tuffs suggesting that uplift and erosion occurred prior to the eruption of the elip the extent of erosion of the maokou formation indicates the elip can be divided into three roughly concentric zones the inner intermediate and outer zones the paleokarst features on the top of maokou formation vary across the elip in the inner zone a likely sinkhole and an incision valley with 450 m relief in height are found in the intermediate zone various paleokarst landforms such as karst relief sinkholes and tower karsts are well developed some sinkholes that developed in the qixia formation below the maokou formation imply that the paleorelief is more than 350 m in height in the outer zone the paleokarstic surface is a paleo weathering layer with minor karstification and development of caves at 10 50 m this spatial variation of the paleokarst reflects variation of uplift height across the elip the extent of minimal uplift is estimated to be at least 450 m in the inner zone 350 m in the intermediate zone whereas uplift is minor tens 50 m in the outer zone the magnitude and shape of the uplift is roughly consistent with that predicted by mantle plume models the paleokarst was formed after the deposition of the maokou formation and the eruption of the emeishan basalts at the end guadalupian and indicates a short duration of uplift thus this study lends further support to domal uplift prior to the emeishan flood volcanism but also to the mantle plume initiation model for the generation of the elip

late cretaceous coal overlying karstic bauxite deposits in the parnassus ghiona unit central greece coal characteristics and depositional environment abstract the pera lakkos coal located on top of bauxite deposits in the ghiona mining district central greece is the only known mesozoic late cretaceous coal in the country it was derived from herbaceous plants and algae growing in mildly brackish mires that formed behind a barrier system during a regression of the sea on a karstified limestone partly filled in with bauxitic detritus petrological mineralogical and geochemical data point to the predominance of reducing conditions and intense organic matter degradation in the palaeomires o c vs h c and oi vs hi plots based on elemental analysis and rock eval data characterize kerogen types i ii this reflects the relatively high liptinite content of the coal besides kerogen composition o c vs h c plot for the pera lakkos coals is in accordance with a catagenesis stage of maturation in contrast with vitrinite reflectance and t max from rock eval pyrolysis which indicate the onset of oil window maturation stage suppression of vitrinite reflectance should be considered and the high liptinite content corroborates this hypothesis despite some favourable aspects for petroleum generation presented by the pera lakkos coal its maximum thickness up to 50 cm points to a restricted potential for petroleum generation coal oxidation took place either during the late stage of peat formation due to wave action accompanying the subsequent marine transgression or epigenetically after the emergence of the whole sequence due to percolation of drainage waters both options are also supported by the ree shale normalized profiles which demonstrate an upwards depletion in the coal layer oxidation also affected pyrite included in the coal this led to the formation of acidic sulfate rich solutions which percolated downwards resulting in bleaching of the upper part of the underlying bauxite

mineralogical and geochemical studies of boron rich bauxite ore deposits in the songqi region sw henan china the songqi region sw henan is an important bauxite province in china the bauxite ore deposits occur unconformably on the top of middle ordovician argillaceous carbonates the bauxite ores from the songqi region are characterized by unusually high boron contents in this paper we report the mineralogical and chemical compositions of selected bauxite ores from the region these new data together with existing geochemical data of soils in the region are used to evaluate the origin of boron enrichment in the bauxite ores the compositional characteristics of tourmaline in the bauxite ores suggests that this mineral was likely derived from a meta sedimentary protolith mass balance calculation reveals that tourmaline only accounts for a small portion of boron in the bauxite ores the majority of boron in the ores must occur in other forms possibly by ion absorption on the surfaces of diaspore and clay minerals in the songqi region the precambrian meta sedimentary rocks are known to contain abundant tourmalines whereas the cambrian ordovician argillaceous carbonates and the upper proterozoic shales are all enriched in boron in free ion state we suggest that these rocks provided tourmaline and boron ion to the bauxite deposits in the region most known bauxite deposits in the songqi region occur at the margins of boron rich soil domains suggesting that boron in soils is a potential exploration indicator for unknown bauxite deposits in this region

the magnitude of late paleozoic glacioeustatic fluctuations a synthesis a comprehensive literature review shows that the magnitude of eustatic fluctuations varied throughout the carboniferous and permian and that at least eight distinct phases can be recognized facies juxtapositions in carbonate successions and erosional relief in clastic successions indicate that glacioeustatic fluctuations of 20 25 m and occasionally as much as 60 m took place throughout the early mississippian tournaisian a widely recognized glacial period middle mississippian mid chadian through holkerian shallow marine carbonate and clastic successions indicate that eustatic fluctuations were 10 25 m a decrease that matches well with the paucity of coeval glacial deposits late visean asbian through mid brigantian glacioeustatic fluctuations of 10 50 m record the initial phases of ice accumulation in advance of the widespread mid carboniferous glacial event the latest mississippian earliest pennsylvanian mid brigantian through langsettian was a time of widespread glaciation and strata of this age commonly exhibit evidence of glacioeustatic fluctuations of as much as 40 100 m although middle pennsylvanian duckmantian through asturian glacial deposits are present in eastern australia paleovalley depths suggest that coeval glacioeustatic fluctuations were less than 40 m glacioeustatic fluctuations of as much as 100 120 m have been widely reported from late pennsylvanian earliest permian stephanian through mid sakmarian successions in north america an increase that corresponds to the growth of large ice sheets across much of gondwana and the accumulation of ice in the northern hemisphere incision and facies juxtaposition in early middle permian mid sakmarian through kungurian successions in eastern australia indicate that glacioeustatic fluctuations of 30 70 m occurred during the waning stages of major glaciation erosional relief in paleoequatorial carbonates and the presence of coeval glacial deposits in australia suggests that eustatic fluctuations of 10 60 m occurred during the final stages of glaciation in the middle to late permian roadian through capitanian but the modest size of most of these fluctuations makes it difficult to isolate the glacioeustatic signature this review demonstrates that far field cyclic successions record changing glacial conditions in gondwana that the magnitude of glacioeustatic fluctuations was directly related to the volume of glacial ice that carboniferous permian glacioeustasy was more variable than previously recognized and that generalizations from short temporal intervals are probably not representative of the late paleozoic ice age as a whole although any attempt to quantify the magnitude of ancient eustatic changes is based on caveats and assumptions this review incorporates the results of over 100 published papers on the topic in an attempt to minimize the errors inherent in any one study

postglacial early permian late sakmarian early artinskian shallow marine carbonate deposition along a 2000 km transect from timor to west australia abstract late sakmarian to early artinskian early permian carbonate deposition was widespread in the marine intracratonic rift basins that extended into the interior of eastern gondwana from timor in the north to the northern perth basin in the south these basins spanned about 20 of paleolatitude approximately 35 s to 55 s this study describes the type section of the maubisse limestone in timor leste and compares this unit with carbonate sections in the canning basin nura nura member of the poole sandstone the southern carnarvon basin callytharra formation and the northern perth basin fossil cliff member of the holmwood shale the carbonate units have no glacial influence and formed part of a major depositional cycle that in the southern basins overlies glacially influenced strata and lies a short distance below mudstone containing marine fossils and scattered dropstones perhaps indicative of sea ice in the south marine conditions became more restricted and were replaced by coal measures at the top of the depositional sequence in the north the carbonate deposits are possibly bryozoan crinoidal mounds whereas in the southern basins they form laterally continuous relatively thin beds deposited on a very low gradient seafloor at the tops of shale limestone parasequences that thicken upward in parasequence sets all marine deposition within the sequence took place under very shallow inner neritic conditions and the limestones have similar grain composition bryozoan and crinoidal debris dominate the grain assemblages and brachiopod shell fragments foraminifera and ostracod valves are usually common tubiphytes ranged as far south as the southern carnarvon basin albeit rarely but is more common to the north gastropod and bivalve shell debris echinoid spines solitary rugose corals and trilobite carapace elements are rare the uniformity of the grain assemblage and the lack of tropical elements such as larger fusulinid foraminifera colonial corals or dasycladacean algae indicate temperate marine conditions with only a small increase in temperature to the north the depositional cycle containing the studied carbonate deposits represents a warmer phase than the preceding glacially influenced asselian to early sakmarian interval and the subsequent cool phase of the mid artinskian that is followed by significant warming during the late artinskian early kungurian the timing of cooler and warmer intervals in the west australian basins seems out of phase with the eastern australian succession but this may be a problem of chronostratigraphic miscorrelation due to endemic faunas and palynofloras

lateritization and bauxitization events laterites and bauxites are produced in tropical soils by weathering which enriches iron of laterites and alu mina of bauxites as well as trace elements such as nickel gold phosphorus and niobium to ore grade la terites and bauxites can be redeposited into sedimentary sequences and remain as ores if not transported far and diluted with other materials the age of redeposited laterites and bauxites and of bauxitic and lateritic pa leosols can be established from the geologic age of overlying rocks an approach especially effective in pale osols within sequences of isotopically datable volcanic rocks lateritic profiles can also be dated by paleomag netic inclination in special cases in which land masses such as in australia and india drifted long distances northward during cenozoic time in addition cryptomelane and other k mn oxides can be dated by k ar and 40ar 39ar techniques to obtain multiple ages from different crystals in a single relict paleosol compilation of new and more accurate laterite and bauxite ages reveals unusually widespread and intense laterite and bauxite formation during events of less than 100 k y duration at 2 12 16 35 48 55 65 and 100 ma such events can also be inferred at times older than 100 ma from paleolatitudinal distribution of laterites and bauxites but these are poorly sampled laterite and bauxite peaks were coeval with times of global high warmth and pre cipitation elevated atmospheric carbon dioxide oceanic anoxia exceptional fossil preservation and mass ex tinction these co2 greenhouse events and attendant titration of carbonic acid with soils are interpreted as transient fluctuations in the atmosphere produced by meteorite impact flood basalt volcanism and methane outbursts concentration of bauxite and laterite resources in particular stratigraphic horizons formed during greenhouse crises suggests the usefulness of an event stratigraphic approach to exploration and exploitation of these and related ores

genesis of the permian karstic pingguo bauxite deposit western guangxi china more than 0 5 billion tons of late permian bauxite overlies the karstic topography of the maokou formation of western guangxi in china here we provide new mineralogical geochemical sr nd pb isotopic and pyrite s isotope and trace element compositional data for the pingguo bauxite deposit aiming to further our understanding of the genesis of permian bauxite the pingguo bauxite contains three distinct layers a lower layer dominated by ferric clay or weathered iron ore a middle layer of cryptocrystalline and oolitic bauxite ore and an upper layer dominated by argillaceous bauxite the bauxite ore is mainly diaspore pyrite chamosite and anatase whereas the argillaceous bauxite contains diaspore kaolinite pyrophyllite pyrite and anatase two types of pyrite have been identified within the bauxite fine grained and framboidal pyrite py1 occurring in aggregates and coarse grained and euhedral pyrite py2 py1 is enriched in trace elements and is thought to have a diagenetic origin whereas py2 is deficient in trace elements and is considered to have formed by later recrystallization the s isotopic composition of pyrite 34 11 to 18 91 and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation the sr nd pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the emeishan large igneous province lip and limestones of the maokou formation microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near surface conditions

provenance of late carboniferous bauxite deposits in the north china craton new constraints on marginal arc construction and accretion processes abstract the north china craton ncc is bounded by two paleozoic accretionary arc terranes the north qinling terrane to the south and the bainaimiao terrane to the north the timing of arc accretion to the ncc and the architecture of the bainaimiao arc remain unclear during the building and accretion of the arcs along its margins the ncc experienced a long sedimentary hiatus since the ordovician which ended with the deposition of bauxite bearing sediments in the late carboniferous in this paper we report the u pb and hf isotopes of detrital zircons from the late carboniferous bauxite layer and use these data to constrain the tectonic evolution of the margin of the ncc the detrital zircons yield a minimum u pb age of ca 310 ma and a prominent age peak at ca 450 ma zircon crystals with ages of ca 330 ma and ca 1900 ma are more common in the bauxite samples from the northern part of the ncc than in those from the central part the ehf t values of the ca 450 ma detrital zircon crystals of the bauxite samples from the ncc are similar to those of the contemporaneous detrital zircon crystals from the north qinling arc terrane to the south but different from those of the contemporaneous detrital zircon crystals from the bainaimiao arc terrane to the north the ca 450 ma detrital zircon crystals in the ca 310 ma bauxite deposits are therefore interpreted to have been derived from the north qinling arc terrane the source of the ca 330 ma detrital zircon crystals of the bauxite deposits is interpreted to be the northern margin of the ncc where intermediate felsic plutons formed at ca 330 ma are common the results from this study support the interpretation that the paleozoic continental arc terranes and their concomitant back arc basins were developed along the margins of the ncc before ca 450 ma and the arc complexes were subsequently accreted to the craton in the late carboniferous this was then followed by the formation of a walled continental basin within the ncc