comparison of dynamic flow models for the central aleutian and tonga kermadec subduction zones using three dimensional 3 d instantaneous dynamic models of the central aleutian subduction zone we show that a low viscosity low density deltarho 10 kg m3 region in the wedge is needed to match observations of topography the geoid and the stress state in the slab and overriding plate previous models of the tonga kermadec subduction zone also require a low viscosity low density deltarho 20 kg m3 region in the wedge a low viscosity region in the wedge decouples the overriding plate from the downward flow in the wedge caused by the sinking slab reducing the magnitude of negative dynamic topography on the overriding plate and changing the state of stress in the slab from down dip tension to down dip compression if the low viscosity region is large as in the tonga kermadec models then the decoupling may also cause the overriding plate to go into extension these are the first dynamic models to simultaneously match the state of stress in the slab and overriding plate and suggest that the combination of stress state within the slab and overriding plate may provide an additional constraint on the viscosity structure within subduction zones

crustal modification during subduction zone magmatism evidence from the southern salar de uyuni region 20 22 s central andes late cenozoic volcanic rocks erupted in the southern salar de uyuni region of the central andes provide evidence for recent modification of both the lower and upper continental crust during subduction zone magmatism at a given sio 2 content k 2 o and related incompatible trace element concentrations increase eastward in basaltic andesite samples and are associated with increasing sr isotopic ratios and decreasing sr concentrations these data favor a model in which basaltic andesite magmas are contaminated by lower continental crust that becomes increasingly more mafic toward the active volcanic front because of relatively recent intrusion and hybridization by primary basaltic magmas compositions of andesitic lavas continue the geochemical trends established by the basaltic andesite samples except that sr isotopic ratios of lavas erupted at the arc front are constant to slightly decreasing with increasing sio 2 contents assimilation of upper crustal rocks that also vary in composition across the strike of the arc is the most plausible mechanism to produce the distinct sr isotopic trends of the andesitic lavas at the volcanic front the magmas producing the andesitic lavas assimilated rocks within the quaternary volcanic and plutonic complex of the andean arc itself toward the east the magmas assimilated basement rocks that become progressively older with distance from the volcanic front because of diminishing modification by late cenozoic arc magmatism thus the across arc geochemical trends in the southern salar de uyuni region are consequences of spatial variations in the composition of the lower and upper continental crust and these variations appear to be linked to the subduction process itself

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

palaeobiogeography and palaeogeographical implications of permian marine bivalve faunas in northeast asia kolyma omolon and verkhoyansk okhotsk regions northeastern russia abstract the paper considers the biogeography and palaeogeographic implications of the permian marine bivalve faunas of northeast asia with a focus on the dynamic relationships between biotic similarities and palaeogeographic distance through an interval of ca 50 million years a stage by stage time series analysis of the biotic similarities between two previously recognized biochores in northeast asia the kolyma omolon and verkhoyan okhotsk provinces has been carried out using both the jaccard and dice similarity indices based on the spatio temporal distributions of 355 permian marine bivalve species in northeast asia the outcome of this analysis combined with other empirical data and previously published tectonic sedimentological and palaeontological information suggests that 1 the bivalve faunas from these two provinces were distinctive from one another as two separate biochores throughout all but the earliest asselian permian stages and 2 the biotic similarities between the verkhoyan okhotsk and kolyma omolon provinces remained consistently low since sakmarian all falling well below the minimum threshold of the jaccard index of 0 42 required for distinguishing marine biotic provinces we interpret these below threshold jaccard biotic similarities as an indication of significant palaeogeographic separation between the verkhoyan okhotsk and kolyma omolon provinces which is in turn considered to indicate rifting and sea floor spreading of the omolon microcontinent and associated terranes and island arcs away from the north asian craton at least from the sakmarian to the beginning of the late permian palaeo distance separation appears to be the primary and most significant biogeographic determinant in accounting for the differences in the spatial distribution of most permian bivalve species in northeast asia several other variables also appear to have played a significant role including regional climate conditions ocean currents and merged island chains as geographic barriers in particular the relatively high biotic similarity between the verkhoyan okhotsk and kolyma omolon provinces during the late wuchiapingian and changhsingian may have been related to the shallowing of the deep water basins oimyakon ayan yuryakh balygychan and sugoi basins that had previously separated the two provinces and the flooding submergence of the okhotsk taigonos volcanic arc system thus allowing the invasion of lower latitude warm water palaeotethyan and even gondwanan species into northeast asia

the significance of marine boreal molluscs in the early pleistocene faunas of the mediterranean area abstract repeated migration of boreal guests into the mediterranean during the early pleistocene has been considered a weak paleoclimatic oceanographic tool this attitude is partly held because the plio pleistocene boundary as defined in the mediterranean does not seem to coincide with isotopic events more important than those of the piacenzian an analysis of their present biogeographical distributions suggests that the successful migration of the boreal elements into the early pleistocene mediterranean was caused by the establishment of a climatic phase of high seasonality with winter temperatures lower than 9 10 c and summer temperatures not lower than 20 c such a situation would also have been suitable for the taxa of warm affinity that characterize the present mediterranean moroccan bioprovince this hypothesis applies mainly to the first phase of migration santernian substage which is the best known from a malacological point of view the available paleoclimatic and isotopic record seems in agreement with the hypothesis

late mesozoic bipolar bivalve faunas bipolar bivalve genera probably existed through the greater part of late mesozoic i e late jurassic late cretaceous time of the various theories put forward to account for their presence those based on some form of global climatic zonation seem most appropriate although equatorial polar temperature gradients were substantially less in late mesozoic time than at the present day high latitude regions were subjected to temperate or even cool temperate climatic regimes macro benthonic marine faunas may have been more susceptible to differentiation in response to these climatic patterns than nektonic ones this is particularly so in the late mesozoic strata of the southern hemisphere

brachiopods fusulines and palynomorphs of the mengkarang formation early permian sumatra and their palaeobiogeographical significance abstract brachiopods fusulines and palynomorphs from the lower permian mengkarang formation sumatra indonesia have been studied in order to establish the palaeogeographical position and the palaeolatitude of the west sumatra block the position of the west sumatra block within the palaeo tethys and panthalassa oceans and its relationships to their marginal landmasses in particular the gondwana supercontinent and the cathaysian palaeogeographical area currently is uncertain brachiopods fusulines and palynomorphs of the lower permian mengkarang formation were analysed to test the gondwanan versus cathaysian affinity of the west sumatra block six genera and two species of fossil brachiopods were identified neochonetes neochonetes carboniferus keyserling 1846 marginifera arenaria sp ind reticulatia sp ind stereochia aff s irianensis archbold 1981a protoanidanthus sp ind cancrinella sp ind and an undetermined genus and species of the subfamily toryniferinae multivariate analysis of the available brachiopod data including those from the mengkarang formation identified two groups the first comprising iran yukon the urals and west sumatra the second comprising south thailand baoshan central afghanistan karakoram india west and east australia indicating that lower permian brachiopods from west sumatra are best grouped with warm water taxa rather than with cold water taxa from the gondwanan perigondwanan region six fusuline species belonging to five genera were identified from six limestone samples eostaffella sp schubertella sp pseudoschwagerina cf afghanensis leven 1971 pseudoschwagerina meranginensis thompson 1936 eoparafusulina haydeni leven 1971 pseudofusulina rutschi thompson 1936 the fusuline fauna is rather poor in terms of generic composition as it is composed mainly by widespread genera but in a broad sense the lower permian west sumatra fauna is typical of palaeo tropical tethyan regions because of the common occurrence of large schwagerinids only one sample level in the mengkarang formation yielded abundant palynomorphs dominated by laevigatosporites spp indeterminate bisaccate pollen florinites florini imgrund 1960 and convolutispora sp this assemblage is very different from coeval assemblages of the gondwanan region northern palaeotethyan regions of kazakhstan and parts of western europe and the intrasudetic basin but has more affinity with the cathaysian phytogeographic province as represented in northern china turkey and northern iraq

thermal structure beneath tohoku northeast japan combined with geophysical observations and petrological considerations we have studied the thermal models of the tohoku northeast japan subduction zone the temperature of the deeper part of the mantle wedge is constrained by the petrological requirements that demand a high temperature region 1400 c beneath the volcanic zone to satisfy this condition namely to explain the arc volcanism in the tohoku subduction zone a high temperature upper mantle beneath the japan sea possibly 1400 c at the depth shallower than 100 km is required heat flow distribution which constrains the temperature structure at shallower depth shows that low heat flow values ranging from 20 to 50 mw m2 are distributed between the trench and aseismic front and consistently high heat flow values 80 120 mw m2 prevail in the area landward of the volcanic front including the japan sea recent heat flow measurements indicate that the transition from low to high heat flow occurs between the aseismic front and volcanic front this heat flow distribution restricts the form of the flow in the mantle wedge and shear stress acting at the plate boundary a rigid non moving triangular region bounded by the subducting slab and the vertical plane beneath the aseismic front is necessary to explain the low heat flow zone between the trench and aseismic front shear stress of about 500 to 1000 bar is supposed to act at the interface between the subducting slab and rigid triangular mantle we also suggest that to explain the peak of heat flow near the volcanic front 120 mw m2 magma migration rate of about 0 05 cm3 cm 2 year 1 is necessary a comparison of the thermal structure of the tohoku subduction zone with that of the central south america which was preliminary calculated by the similar scheme shows that the temperature in the mantle wedge of the central south america is probably lower than that of the tohoku subduction zone this difference may result in that of the nature of volcanic rocks

carbon isotope chemostratigraphy and implications of palaeoclimatic changes during the cisuralian early permian in the southern urals russia abstract in order to meet the requirements for potential gssps in the cisuralian series early permian isotopic chemostratigraphy from the carboniferous permian boundary to middle artinskian using bulk carbonates was investigated under high resolution biostratigraphical and new geochronologic constrains from three gssp candidate sections at usolka kondurovsky and dal ny tulkas in the southern urals russia a gradually increasing trend in carbonate carbon isotope 13 c has been observed in the interval from the base of asselian to early sakmarian which is generally consistent in timing with the increasing development of glacial iii or p1 from the latest carboniferous to early sakmarian early permian which prevailed in southern gondwana an excursion with double negative shifts in 13 c value is present around the asselian sakmarian boundary in both the usolka and kondurovsky sections which may have great potential to serve as chemostratigraphical marks for intercontinental correlation the following highly positive excursion of 13 c in early sakmarian indicates the maximium expansion of glacial iii or p1 the negative 13 c shift in the middle sakmarian is possibly related to the quick collapse of glacial iii or p1 on the gondwanaland this negative shift is largely correlative with those documented in other areas of russia the north american craton and south china but further precise biostratigraphical and geochronologic constrains are neccessary to confirm this global signal the late sakmarian is characterized by a strong oscillation stage of 13 c which probably indicates a complex climate transition marked by smaller alternating glacial interglacial transitions during glacial p2 superimposed on an overall warming trend the sharp negative 13 c shift around the sakmarian artinskian boundary at the dal ny tulkus section is difficult to interpret this is followed by long term low values 13 c values in the artinskian at the dal ny tulkas section might result regionally from the enhanced input of organic carbon after the melt out of ice sheets and the subsequent degradation and isotopic refractionation of the microbial chemosynthetic processes on the buried organic matter

isogramma meek and worthen 1870 dictyonellida brachiopoda from the upper palaeozoic of east asia implications for biogeography and evolutionary trends abstract isogramma manchoukuoensis from the upper carboniferous of northeast china is redefined based on re examination of the type specimens isogramma specimens from the middle permian of northeastern japan are reassigned to i aff paotechowensis a new family schizopleuroniidae is proposed to include schizopleuronia but excludes megapleuronia which belongs to the megapleuroniidae liao 1983 the family isogrammidae is considered to be a transitional group in the eichwaldid isogrammid schizopleuronid evolutionary lineage within the dictyonellida a review of the global distribution of isogramma species reveals that the genus has a total of 56 species ranging from the mississippian early carboniferous to the lopingian late permian isogramma diversified rapidly after its origination in the middle visean and its species diversity remained high throughout the mississippian the genus possibly suffered a severe mid carboniferous boundary mass extinction with no early carboniferous species surviving this event bashkirian isogramma species show low diversity followed by a global recovery in the moscovian during the latest carboniferous isogramma became highly diversified again at the carboniferous permian c p transition isogramma underwent another dramatic diversity drop followed by several stepwise declines in diversity during the early middle permian the wuchiapingian i sinosa is the last isogramma species ukraine was the possible centre of origin for isogramma from ukraine isogramma spread over the moscow basin of russia central europe germany austria south europe spain and west europe england ireland and scotland and migrated to the north american midcontinent and south china during the late visean early carboniferous in europe isogramma migrated to spain and eastern europe serbia in the moscovian from there it then dispersed into central asia uzbekistan and kazakhstan in the kasimovian gzhelian in the palaeo tethys isogramma migrated from south china to northeast and northwest china in the moscovian spread over the north china block during the c p transition moved to russian siberia japan and the qiangtang terrane of the palaeo tethys during the early late permian in north america isogramma spread over the midcontinent during the late carboniferous and early middle permian and migrated to south america bolivia in latest carboniferous biogeographically isogramma was confined principally to the palaeo tropical and warm to temperate zones throughout the late palaeozoic with the possible exception of the artinskian as a questionable species of the genus also occurs in the transbaikal region of southeast russia

wuchiapingian early lopingian permian global brachiopod palaeobiogeography a quantitative approach abstract a global presence absence database of 212 wuchiapingian early lopingian permian brachiopod genera from 30 stations is analysed by cluster analysis nonmetric multidimensional scaling and minimum spanning tree to document the global palaeobiogeographical patterns five core groups are revealed by the quantitative analysis and interpreted as representing five marine biotic provinces they are the cathaysian tropical western tethyan tropical himalayan warm temperate austrazean cold temperate and greenland svalbard provinces cold temperate the cathaysian province is composed of many isolated or semi isolated islands situated in the palaeotethys whereas the other four provinces occurred mainly on the continental shelves of pangea the western tethyan province along the western coast of the palaeotethys the himalayan province on the northern margin of gondwanaland the austrazean province along the southeastern margin of gondwanaland and the greenland svalbard province on the northern margin of pangea in addition nonmetric multidimensional scaling helped to identify key biogeographic determinants latitude related thermal gradient appears to have accounted for most of the variance in the data geographic distance and ocean circulation may have also played a major but subordinate role in the delineation and or enhancement of some of the provinces comparison with early and middle permian global marine provincialism indicates that marine biotic provinces had significantly reduced during the lopingian late permian in the lead up to the end permian mass extinction

dilemma of late palaeozoic mixed floras in gondwana abstract during carboniferous and permian periods the plant fossil assemblages of northern and southern hemispheres were distributed in four floral provinces and each flora had its own characteristics pteridosperms were dominant in the euramerian floras of europe and america cordaitales and equisetales along with angaridium angaropteris represent the angara flora of russia russian federation and far east provinces gigantopteris flora characterizes the cathaysian province of china japan and south east asian countries and glossopteris flora are present in southern hemispheric land masses of gondwana which includes india australia africa south america and antarctica well defined floral provinces quite often show the intermixing of different floristic elements exemplifying the presence of mixed floras the occurrence of mixed floras suggests that they have two modes of distribution one distribution pattern shows mixed floras along the marginal basins of the tethyan region during the middle and late permian another pattern is evident in the gondwana floras where glossopteris floras contain a number of extra gondwanic elements likewise some euramerian cathaysian and angaran floras show the possible presence of glossopterid related elements having comparative morphological features as part of the flora mixed floral elements of northern and southern floras have been examined in detail and it is suggested that in all probability the so called elements of the mixed floras had their ancestry or affiliation with carboniferous floras and during the early permian they duped due to severity of climatic conditions but developed again during late permian when climate became more hospitable for their development the cathaysian and euramerian forms discovered with gondwanan forms in the mixed floras of tethyan region i e hazro saudi arabia new guinea oman jordan kashmir central tibet and southern tibet belong to middle and upper permian sequences and during this time the warm humid and temperate climate helped to revive the northern hemispheric forms which had their endurance in a relatively similar climate of the late carboniferous the morphological conservatism flexibility radiation relationship and analogous features of mixed floral elements have been examined and attempts are made to sort out their disputed presence in different floral provinces

effect of three dimensional slab geometry on deformation in the mantle wedge implications for shear wave anisotropy shear wave splitting observations from many subduction zones show complex patterns of seismic anisotropy that commonly have trench parallel fast directions three dimensional flow may give rise to trench parallel stretching and provide an explanation for these patterns of seismic anisotropy along strike variations in slab geometry produce trench parallel pressure gradients and are therefore a possible mechanism for three dimensional flow in this study we quantify the effects of variable slab dip curved slabs oblique subduction and slab edges on flow geometry and finite strain in the mantle wedge of subduction zones temperature dynamic pressure velocity and strain are calculated with high resolution three dimensional finite element models these models include temperature and stress dependent rheology and parameterized slab and trench geometry thick layers 20 60 km with strong trench parallel stretching are observed in the mantle wedge when slab geometry involves a transition to slab dip less than 15 or strong curvature in the slab in these cases strong trench parallel stretching develops when flow lines have an oblique to trench normal orientation this suggests that trench parallel seismically fast directions may not indicate trench parallel flow lines in systems with large along strike variations an oblique component of stretching is confined to a 20 30 km layer above the slab in systems with oblique subduction the effects of slab edges include strong toroidal flow and focusing in the mantle near slab edges and trench parallel flow that extends 50 100 km into the core of the mantle wedge

dynamics of slab rollback and induced back arc basin formation abstract we performed a numerical study to understand the dynamical mechanisms of back arc basin formation induced by slab rollback to this end we used two dimensional numerical models of an integrated plate mantle convection system with 410 and 660 km phase transitions retrograde slab migration occurs when the slab stagnates in the transition zone or when the deep section of the slab is vertical in both cases slab rollback occurs because the deep slab section obstructs the descending motion of the shallow slab section with an inclination buoyancy of the 660 km phase boundary acts as the obstructing force in the case of stagnant slab formation and an anchoring force against the horizontal motion works similarly in the case of vertical slabs to balance the horizontal component of the obstructing force a suction force at the plate boundary pulls the overriding plate toward the ocean back arc spreading is produced by means of slab rollback when the overriding plate with a weak area is fixed to the model boundary the back arc deformation becomes compressional when the overriding plate is freely movable despite trench retreat because the wedge mantle flow viscously drags the overriding plate toward the trench this implies that forces tending to actuate the overriding plate away from the trench are necessary to generate back arc extension even when trench retreat is generated by slab rollback

faunal turnover and changing oceanography late palaeozoic warm to cool water carbonates sverdrup basin canadian arctic archipelago abstract carbonate sedimentary rocks in the fosheim hamilton sub basin at the eastern end of the sverdrup basin contain a particularly sensitive record of changing palaeoceanography and faunal turnover during the northward movement of pangaea through the late palaeozoic carboniferous and earliest permian inner ramp carbonates are a photozoan association of colonial corals fusulinids algae and ooids with sparse heterozoan elements crinoids brachiopods and bryozoans based on modern analogues these biotic components reflect warm water oligotrophic marine environments contemporaneous mid ramp and basin biotas are dominated by a heterozoan fauna solitary corals crinoids bryozoans and brachiopods that grew in cooler deeper waters that may have been beneath a thermocline initial cooling began in the latest sakmarian with an influx of cool deep water and climatic deterioration allowing cool and warm waters to mix disrupting the thermocline and producing a sub tropical marine biota whose remains were reworked by storms and re deposited as tempestites faunas are heterozoan crinoids bryozoans brachiopods and sponges with photozoan elements colonial corals and symbiont bearing fusulinids prominent only in inner ramp facies by late artinskian these photozoan components are only present in shallowest basin margin environments artinskian subtropical waters contained somewhat elevated trophic resources that together with mixing of photozoan and heterozoan elements in the subtropical inner ramp produced the greatest faunal diversity seen in the sverdrup basin the biota was completely boreal in nature and warm shallow waters with a warm refuge biota were now supplemented by cool waters derived from the panthalassa ocean profound change took place in the kungurian coincident with localised uplift during the melville disturbance and increased siliciclastic input neritic storm dominated sediments are wholly heterozoan brachiopods bryozoans crinoids and sponges with no remaining photozoan elements nutrient levels are elevated but not eutrophic as indicated by phosphate and glauconite extensive bioerosion numerous infaunal foraminifers and an impressive and diverse shelly biota that during times of high siliciclastic input was replaced by a profuse zoophycos infauna brachiopod and bryozoan faunas are distinctly boreal continued cooling relatively high nutrients as indicated by abundant glauconite and phosphate and decreased siliciclastic input eventually resulted in an abundant heterozoan biota brachiopods bryozoans crinoids and sponges with local gigantism but reduced brachiopod and bryozoan diversity these middle permian rocks may be the coolest water deposits in the sverdrup basin the faunas are still part of a boreal arctic province with strong ties to cool water faunas of uralian basin the succession ends with late permian biosiliceous spiculitic cherts containing accessory heterozoan components brachiopods bryozoans and few crinoids these sediments in part coeval with evaporites and terrestrial red beds on the eastern european platform are interpreted to reflect a combination of cool waters elevated nutrients and mid latitude storminess

geochemistry of ikaite formation at mono lake california implications for the origin of tufa mounds the mineral ikaite caco 3 6h 2 o not previously observed in lake environments precipitates seasonally along the shore of mono lake california where ca hco 3 spring water mixes with cold na co 3 lake water during the winter cold water temperatures and high concentrations of po 4 3 and organic carbon inhibit calcite precipitation allowing the metastable ikaite to form during the spring warming however ikaite decomposes to form calcium carbonate and water occasionally leaving pseudomorphs of the primary precipitate the identification of modern ikaite suggests that both pleistocene and holocene tufas in the mono basin originally precipitated as ikaite this mineral may also form in other lake environments but rapid recrystallization after warming destroys the physical chemical and isotopic evidence of formation and alters the geochemical record

stress dependent power law flow in the upper mantle following the 2002 denali alaska earthquake abstract far field continuous global positioning system gps time series data following the 2002 m7 9 denali alaska earthquake imply that mantle viscoelastic rheology is stress dependent a linear viscous mantle cannot explain fast early displacement rates at the surface that rapidly decay with time whereas a power law rheology where strain rate is proportional to stress raised to the power of 3 5 0 5 provides decay rates and spatial patterns in agreement with observations this is consistent with laboratory measurements for hot wet olivine implying a hydrated mantle and a relatively thin 60 km thick lithosphere beneath south central alaska these results suggest that the viscous strength of the lithosphere varies both spatially and temporally and that effective viscosities inferred from different loading events or observational time periods can differ by up to several orders of magnitude thus the very conditions that enable the inference of rheologic strength transient loading and unloading events significantly alter the effective viscosity

non steady state subduction and trench parallel flow induced by overriding plate structure abstract the direction of plate tectonic motion and the direction of mantle flow as inferred from observations of seismic anisotropy measurements show a good global correlation far from subduction zones however this correlation is poor near subduction zones where below the slab seismic anisotropy is aligned parallel to the trench and above the slab has a complex pattern which has not been fully explained here we present time dependent three dimensional 3d fully dynamic simulations of subduction to study the effect of overriding plate structure on the evolution of slab geometry and induced mantle flow we find that along strike variation in thermal thickness of the overriding plate causes increased hydrodynamic suction and shallower slab dip beneath the colder portion of the overriding plate the variation in slab geometry drives strong trench parallel flow beneath the slab and a complex flow pattern above the slab this new mechanism for driving trench parallel flow provides a good explanation for seismic anisotropy observations from the middle and south america subduction zones where both slab dip and overriding plate thermal state are strongly variable and correlated and thus may be an important mechanism in other subduction zones the location and strength of trench parallel flow vary with the time dependent evolution of the slab suggesting that the global variability in seismic anisotropy observations in subduction zones is in part due to the non steady state behavior of these systems

middle permian brachiopods from the tumenling formation in the wuchang area southern heilongjiang ne china and their palaeobiogeographical implications abstract this paper describes nine brachiopod species in eight genera from the tumenling formation in the wuchang area southern heilongjiang northeast china the tumenling fauna is constrained to a wordian capitanian guadalupian middle permian age based on the correlation of the faunas and previously published data from the same horizons in the same area this middle permian brachiopod fauna is characterized by an admixture of elements of boreal affinity kochiproductus sp yakovlevia sp stenoscisma margaritovi gypospirifer volatilis spiriferella keilhavii spiriferella lita and alispiriferella neimongolensis with palaeoequatorial forms spinomarginifera sp vediproductus sp and leptodus nobilis the wuchang fauna as a whole is comparable to several contemporaneous faunas described from inner mongolia in northern china jilin in northeast china south primorye in eastern russia and the hida gaien belt of japan in terms of its index elements and its boreal palaeoequatorial mixture during the middle permian these areas or blocks were referred to the inner mongolia japan transition zone or the northern transition zone between the palaeoequatorial and boreal realms the overwhelming majority of the boreal elements reveal that the wuchang area was probably situated in the northern subzone of this transitional zone which belongs to the southern margin of the bureya block these east and northeast asian blocks acted as migratory stepping stones bridging faunal migration between the palaeoequatorial and boreal realms during the middle permian

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

kurosegawa terrane in southwest japan disrupted remnants of a gondwana derived terrane abstract the kurosegawa terrane is an anomalous disrupted paleozoic and mesozoic lithotectonic assemblage characterized by fragments of continent and continental margins it is located in southwest japan where it lies between two mesozoic subduction complex terranes the kurosegawa terrane is an exotic and far travelled geologic entity with respect to its present position limestones of the kurosegawa terrane formed along a continental margin yield fusulinacean fossils cancellina colania and lepidolina accordingly the kurosegawa terrane was once situated within the colania lepidolina territory in the east tethys panthalassa region at a palaeo equatorial latitude possibly close to the eastern margin of the south china and or indochina east malaya continental blocks these blocks had rifted from gondwana by late devonian they drifted northwards passing through the colania lepidolina territory in mid permian time and amalgamated with the proto asian continent during the late triassic subsequently during the cretaceous parts of the allochthonous continental blocks and their associated tectonic collage were transpressed dispersed and displaced from the southeastern periphery of asia towards the north as a result the kurosegawa terrane is formed as a disrupted allochthonous terrane characterized by a serpentinite melange zone lying between the adjoining mesozoic subduction complex terranes

island arc carbonates characterization and recognition in the ancient geologic record abstract carbonates of island arc origin that are preserved in paleozoic mesozoic terranes of the north american cordillera exhibit a distinctive suite of paleontologic and lithologic features and share a fundamental similarity with limestones forming in modern volcanic arcs this study provides the first detailed synthesis of carbonate depositional systems in island arcs and documents primary sedimentary constituents based on facies relationships and faunal communities models are developed that show patterns in the long term evolution of shallow marine organisms and the construction evolution and demise of carbonate platforms in island arcs a suite of criteria is identified that may be used to differentiate island arc carbonates from limestones that accumulated in other platform settings biogeographic isolation prolonged subsidence steep submarine slopes and tectonic instability of volcanic edifices contribute to the development of relatively high levels of species endemism impoverished normal marine faunas complex provincial affinities and relict biotas in limestones that are characterized by exceptionally thick platform and periplatform sequences fringing and barrier reefs at the shelf margin extensive lagoonal deposits and rapid lateral and vertical facies changes although destructive tectonic and geologic processes in island arcs may hinder determining the original size and extent of the carbonate platform and particular facies types may not be represented e g fringing and barrier reefs may be replaced by sand shoals at the platform margin many characteristics have potential value for identifying carbonates of island arc origin in the ancient rock record apart from being associated with calc alkaline volcanic and volcaniclastic assemblages the most valuable suite of features for recognizing island arc carbonates is marine biotas that exhibit elevated levels of endemism and mixed paleobiogeographic affinities extraordinary thicknesses of platform shallow marine and periplatform carbonates and rapid facies changes between volcanic and carbonate rocks and between shallow and deep water limestones recognizing that an ensemble of features is distinctive within island arc carbonates considerably enhances identification of volcanic arcs in the ancient geologic record and thus improves the likelihood of successfully unraveling the complex geologic history of ocean basins

the marine permian of east and northeast asia an overview of biostratigraphy palaeobiogeography and palaeogeographical implications abstract the permian marine biostratigraphy faunal successions and mutual correlations where possible throughout east and northeast asia are synthesized region by region based on both published literature and the author s field observations in certain parts of the region the correlation of the permian marine successions of ne asia with the permian international timescale and in particular with gondwanan permian marine sequences remains a major challenge due to profound marine provincialism during the permian however by employing biogeographically mixed faunas from east asia se mongolia ne china south primorye of far east russia and the south kitakami terrane of japan as biostratigraphic gateways coupled with some bipolarly and bi temperately shared permian marine taxa and faunas it has been possible to correlate with reasonable confidence some of the high palaeolatitude permian marine rock units and faunas of ne asia with those of the tethyan region and gondwana palaeobiogeographically the permian marine faunas of east and ne asia are assigned to four major provinces verkolyman sino mongolian japanese cathaysian and panthalassan provinces on the basis of their palaeogeographical distribution patterns and characteristics of faunal assemblages of these the sino mongolian japanese province has considerable significance for regional palaeogeographical plate tectonic and palaeoceanographical reconstructions during the middle permian because of its conspicuously mixed cool and warm water marine biota the origin of this biogeographically mixed marine biota is interpreted to have resulted from a combination of some key factors including the increased tectonic convergence between the bureya jiamusi terrane and the sino korean platform during the permian and the intermingling of both warm and cold water ocean currents off the eastern coastal areas of the bureya jiamusi terrane and the sino korean platform during the middle permian

solonker suture in east asia and its bearing on the final closure of the eastern segment of the palaeo asian ocean abstract the location and tectonic nature of the solonker suture in east asia and hence the late palaeozoic to early mesozoic closure of the palaeo asian ocean have notoriously been enigmatic in the past decades due to limited rock exposure and the absence of unambiguous collision related regional features several tectonic models have been proposed since but in many cases these models were derived only from single key exposures or methodologies often being over simplified or interpreted leading to questionable extrapolations on regional and global scales despite the complexity of the palaeozoic accretionary tectonic framework now the regionally consistent availability of geochronological geochemical stratigraphic and palaeo geographic data enables us to integrate these into a highly detailed and coherent palaeozoic tectonic review of the suture the region across the solonker suture can generally be subdivided into three major palaeozoic tectonic provinces e g i a sino cratonic province that resembles the active palaeozoic northern margin of the north china craton to the south of the suture ii a mongolian province that comprises the south eastern margin of the mongolian terrane to the north of the suture and iii an east asian pre pacific province in north east china that accreted with the late permian initiation of pacific plate subduction the sino cratonic province experienced episodic tectonic activity that includes the accretion of the initially ensialic bainaimiao arc onto the passive northern margin of the north china craton at 437 453 ma subsequent southward directed subduction activity beneath the amalgamated margin until at least 400 ma followed by a temporary cessation of magmatic activity accompanied by a switch from north to southward directed continental drift and finally concluded by renewed subduction activity until the final closure of the palaeo asian ocean the mongolian province is suggested to have been more closely associated with the siberian craton before the presumably late devonian opening of the mongol okhotsk ocean the east asian pre pacific province originally rifted away from the eastern margin of gondwana at 600 750 ma recorded early palaeozoic 500 ma orogenic processes along the then northern margin of the siberian craton the baolidao arc system successively developed along the present day south eastern margin of the mongolian province due to continued subduction activity throughout the palaeozoic after the middle carboniferous opening of the hegenshan back arc basin renewed subduction beneath a matured baolidao arc during carboniferous and permian times led to the obduction of the hegenshan ophiolite not earlier than 270 ma shortly after the palaeo asian ocean diachronously closed from west to east along the solonker suture in the late permian to early triassic the east asian pre pacific province re attached itself by the mid mesozoic followed by a change in the regional stress regime controlled by palaeo pacific plate subduction a divergent double sided subduction model for the closure of the palaeo asian ocean provides based on the reviewed data a tectonic model that is not only able to reasonably well explain the absence of typical collision related features in the region but also the abundance of mesozoic a type granitic magmatism in north east china

the permian antitropical fusulinoidean genus monodiexodina distribution taxonomy paleobiogeography and paleoecology all the documented occurrences with illustration of specimens of the permian fusulinoidean genus monodiexodina from a total of 33 areas in 11 regions are reviewed and their taxonomic positions are reexamined in this paper among 17 species including two subspecies of monodiexodina in the current taxonomy the following 10 species are recognized as valid m kattaensis m wanneri m caracorumensis m sutchanica m shiptoni m kumensis m wanganensis m neimongolensis m delicata and m rhaphidoformis in addition species once referred to monodiexodina but now should be excluded from the genus are also investigated in terms of their generic positions in reconstructed mid permian paleomap monodiexodina bearing areas can be restored to either northern or southern middle latitudes between high latitudinal cool cold water climatic realm and paleo tropical warm water realm these two middle latitudinal areas each corresponding to the northern and southern transitional zones respectively can be best interpreted climatologically as mesothermal warm temperate belts in both hemispheres thus suggesting the genus to be a paleobiogeographically typical antitropical fusulinoidean taxon moreover the genus is generally found in a monotypic crowded manner in sandy sediments with their shells being often aligned uni directionally this mode of occurrence of monodiexodina strongly suggests that it was adapted to shallow marine high energy environments which would probably be essentially maintained by the acquisition of highly elongated fusiform subcylindrical shells with well developed polar torsion this morphological feature is adapted to increase septal pores per unit area in polar regions thus increasing possibility to develop more pseudopodia on both sides of test it probably has a functional significance for not only locomotion but also anchoring their tests on the surface of bottom sediments in agitated water conditions the genus itself is considered to be a rather long ranging taxon from the late yakhtashian artinskian to the early midian capitanian it is therefore concluded that monodiexodina had an opportunistic character occurring repeatedly only when favorable high energy conditions such as sand shoal appeared in warm temperate climatic belts in both hemispheres monodiexodina originated in the southern transitional zone from an elongated eoparafusulina stock at late early permian around late artinskian time it flourished in southern middle latitudinal areas in latest early and early middle permian time the genus then migrated to the northern hemisphere northern transitional zone by some dispersion mechanism at around the early middle permian and prevailed there during the remaining period of the middle permian

p wave anisotropic tomography of the crust and upper mantle under hokkaido japan abstract we determined a 3 d anisotropic velocity structure beneath hokkaido in northern japan using a large number of first p wave arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our results show that low velocity zones exist beneath active arc volcanoes in the crust and in the central portion of mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images p wave anisotropy is revealed in the crust mantle wedge and the subducting pacific slab in the upper crust the anisotropy is possibly caused by microcracks and cracks in the lower crust the anisotropic structure is different from that in the upper crust and it may be affected considerably by the plastic flow deformation in the mantle wedge the fast velocity direction fvd is generally trench normal in most of the study area while it becomes trench parallel in the pacific coast areas close to the trench which agrees with the shear wave splitting results beneath the volcanic front the fvd is also trench parallel which may suggest the existence of complex 3 d mantle flow in the mantle wedge the fvd in the subducting pacific slab is nearly north south which likely keeps the original fossil anisotropy of the pacific plate formed at the mid ocean ridge or is affected by the olivine fabric transition from a type to b type fabric due to the changes in water content stress and temperature

hot fingers in the mantle wedge new insights into magma genesis in subduction zones abstract quaternary volcanoes in the northeast japan arc can be grouped into 10 volcanic clusters striking transverse to the arc these have an average width of 50 km and are separated by parallel gaps 30 75 km wide this clustering of volcanic centres topographic profiles low velocity regions in the mantle wedge and local negative bouguer gravity anomalies along the japan sea side of the volcanic arc are closely correlated all these observations may be related to locally developed hot regions within the mantle wedge that have the form of inclined 50 km wide fingers each of the 10 fingers recognised extends from deep mantle 150 km below the back arc region towards the shallower mantle 50 km beneath the volcanic front quaternary volcanoes are built immediately above the hot mantle fingers the volcanic basement along the fingers has been uplifted by repeated injection of magmas into the crust accompanied by quaternary volcanic activity at the surface although volcanic activity is rare along the japan sea coast tomographic results show that hot low velocity mantle fingers exist within the mantle wedge the negative bouguer anomalies at the rear of the volcanic arc could be caused by magmas supplied from the hot mantle fingers these have not yet been erupted but have accumulated at the moho discontinuity

the permian fusulinoidean faunas of the sibumasu and baoshan blocks their implications for the paleogeographic and paleoclimatologic reconstruction of the cimmerian continent abstract permian fusulinoidean faunas occur in mainly four stratigraphic levels in the baoshan block of west yunnan and the sibumasu block of southeast asia which constituted part of the eastern cimmerian continent the oldest fauna from the upper part of the dingjiazhai formation in the baoshan block consists of pseudofusulina eoparafusulina and a new boultoniid genus and is assignable to the yakhtashian artinskian the second one which occurs in the basal part of the ratburi limestone and its equivalent strata in the sibumasu block is represented by monodiexodina and is probably referable to the bolorian kungurian the third fauna composed of eopolydiexodina rugososchwagerina yangchienia chusenella jinzhangia and several other genera is dated to the murgabian wordian and occurs in the lower part of the shazipo and daaozi formations in the baoshan block and the main part of the ratburi limestone in the sibumasu block the youngest fauna of probably dzhulfian wuchiapingian age is found in the upper part of the ratburi limestone and contains nanlingella reichelina codonofusiella and a few staffellid genera a smaller foraminiferal genus shanita found from the upper part of the ratburi limestone and the upper part of the shazipo formation is also an important element of the foraminiferal assemblage near the midian dzhulfian capitanian wuchiapingian boundary in the baoshan and sibumasu blocks in the eastern cimmerian continent low generic diversity throughout the permian and the paucity of tethys characterizing neoschwagerinid and verbeekinid genera during middle permian time are two remarkable features of the permian fusulinoidean faunas in the cimmerian continent the generic diversity of permian fusulinoidean faunas in space and time gradually increases from the early permian to late middle permian as well as from the eastern cimmerian areas to western ones the temporal increase of the generic diversity can be explained by the northward drift of the cimmerian continent during permian time in contrast the lower generic diversity of the eastern cimmerian permian fusulinoidean faunas against western ones is possibly due to an oblique arrangement of the continent to paleolatitude thus the western cimmerian continent was more proximal to the tropical tethyan domain than its eastern part in addition the middle permian cimmerian paleobiogeographic region is likely to be subdivided into two subregions the western tethyan cimmerian and the eastern gondwanan cimmerian based on the distribution pattern of verbeekinid and neoschwagerinid fusulinoideans and overall generic diversity the scarce occurrence or total absence of these essentially tethys indicating fusulinoideans in the baoshan and sibumasu blocks suggests that the eastern cimmerian continent was still far from the equatoro tropical cathaysian domain and was probably in a warm temperate or subtropical zone until the end of the permian the eastern cimmerian areas finally migrated into a tropical zone by the late triassic judging from well developed carnian sponge coral buildups in the chaiburi formation in the sibumasu block

stress and flow beneath island arcs summary the flow pattern stress distribution topography and gravity anomalies were computed from numerical models having density and viscosity distributions resemblant to the aleutian arc the results were compatible with the hypothesis that the excess density of the slab drives its descent and that hydrodynamic forces are responsible for topographic and gravity highs over the outer rise seaward of the trench and the frontal arc and lows over the trench in models with simple distributions of rheological parameters the force from the slab was transmitted directly upward producing a negative gravity anomaly over the arc material with low resistance to flow was needed along the fault plane above the slab or within the crust of the frontal arc and within the wedge of asthenosphere above the slab to reduce that force and to allow the horizontal lithosphere to move with the slab models with the resistance to flow thus reduced had outer rises deep trenches horizontal tension seaward of the trench horizontal compression under the trench and downdip tension in the slab free air gravity anomalies which are the sum of between deflections of the free surface due to hydrodynamic forces and direct attractions from the masses driving the flow were not fit excellently by any of the models in part because the coarse grid used precluded accurate representation of the fault zone above the slab and the frontal arc an alternate to the hypothesis that about 5 kb of stress on the fault plane is needed to produce an outer rise is offered by these models shear stress between the slab and the island arc was always below 700 bars in the more successful models if the density distribution was scaled to match the topography of the trench this is much less than the 2000 bars stresses needed if frictional heating causes island arc volcanism

a biogeographically mixed late guadalupian late middle permian brachiopod fauna from an exotic limestone block at xiukang in lhaze county tibet a total of 17 brachiopod species belonging to 15 genera are recorded from a limestone block of about 3 4 km2 in the indus tsangbo suture zone at xiukang in lhaze county of tibet the brachiopod fauna generally indicates a late guadalupian age late wordian capitanian late middle permian based on its association with the timorites bearing ammonoid fauna and the presence of the brachiopod urushtenoidea crenulata palaeobiogeographically the fauna exhibits transitional mixed characters between the warm water cathaysian and cold to temperate gondwanan faunas and may have developed on a carbonate build up or seamount on the oceanic crust

the margins of laurussia in central and southeast europe and southwest asia the continuation of the laurussian margin into central and southeast europe and southwest asia is defined by the rheic suture which becomes harder to trace to the southeast because of complex post variscan strike slip displacements and tectonic stacking linked to the cimmerian and alpine cycles the uncertain extent of the neoproterozoic baikalian orogeny fringing baltica ambiguous early paleozoic paleobiogeographic data and strike slip activity complicate the distinction of the tornquist suture from the transeuropean suture zone there is growing evidence for the incorporation of the brunovistulian malopolska and west moesian terranes into the late neoproterozoic cambrian baltican margin the istanbul zonguldak terrane along with the bitesh and east moesia terranes may have been part of the avalonian terrane assemblage although an arabian nubian shield or baltica provenance cannot be excluded the terranes of the armorica terrane assemblage bordering the rheic suture include the outer carpathian tatra getic and balkan terranes in southeast europe and sakarya and the anatolide tauride terrane in turkey further east the rheic suture may be present in the caucasus in all probability between the greater caucasus and the scythian platform or alternatively between the greater caucasus and transcaucasia alborz in northern iran is interpreted as a distal part of transcaucasia the location of the rheic suture in the southeast part of the turan domain of central asia is poorly constrained

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

effects of oblique subduction on the 3 d pattern of small scale convection within the mantle wedge 1 we have developed a 3 d numerical model of obliquely subducting slab and mantle flow above using this model we explore the effects of oblique subduction on the small scale convection within the mantle wedge we find that the spatial pattern and time dependent characteristics of oblique subduction are similar to those of non oblique cases whose subduction speed is the same as the subduction velocity component normal to the strike of subducting slab this also implies that the axes of rolls of small scale convection are nearly normal to the plate boundary assuming that the plate boundary represents the strike of subducting plate only when the back arc lithosphere overlying the small scale convection moves along the strike of subduction a significant change of the orientation of roll axes is observed

early permian cisuralian global brachiopod palaeobiogeography abstract palaeobiogeography of four consecutive early permian cisuralian stages is quantitatively analyzed based on a global database of brachiopods consisting of 9131 occurrences 3003 species of 515 genera of brachiopods from 2757 localities all over the world our analyses reveal three distinct largely palaeolatitude related palaeobiogeographical realms developed during the cisuralian like the other stages of the permian six distinct provinces are distinguished during the asselian the asselian brachiopod faunas from gondwanaland and its surrounding areas in general are not well differentiated at the provincial level and characterized an indoralian province a large transitional zone southern transitional zone stz between the palaeoequatorial and gondwanan realms and another distinct austrazean province in the eastern margin of gondwanaland were formed from sakmarian contemporaneous with the largest peak of the late palaeozoic ice age in contrast to the stz the palaeogeographical stations in the northern temperate transitional zone are not differentiated before kungurian instead they are grouped with the stations in the palaeoequatorial region thus collectively constituting a large asymmetrical cathaysian province stretching from south china iran in the western palaeotethys to the mongolian continent in the north the northeast european province mainly consisting of the stations in the ural fold belt and eastern and northeastern parts of the european platform shows a closer palaeobiogeographical relationship with the cathaysian province when the ural seaway opened to the palaeotethys in the southern end before the kungurian but became more distinguished during the kungurian after the closure of the ural seaway and showed a relationship with the faunas of the boreal realm and the northern transitional zone ntz the stations in texas western north america constitute a distinct grandian province based on the high diversity brachiopod faunas with abundant endemic taxa and became distinguishable even at the realm level during the kungurian three high latitude provinces the verkolyman province with characteristic boreal brachiopod faunas the paratinan province with some bipolar and cosmopolitan genera in south america and the austrazean province in eastern australia and new zealand were present from the sakmarian further principal co ordinate analysis pco and minimum spanning tree mst analysis suggest that palaeolatitude related thermal gradient was the major controlling determinant for the cisuralian provincialism and brachiopod distribution in addition geographic barriers and regional eustatic changes also played some roles in the brachiopod distribution and cisuralian marine palaeobiogeography the transition from an icehouse to greenhouse stage led to a steady increase in brachiopod diversity and provincialism during the cisuralian and guadalupian

distribution and characteristics of mixed transitional mid permian late artinskian ufimian marine faunas in asia and their palaeogeographical implications abstract the permian marine biogeography of the asian region is characterised by the development of three broad realms boreal tethyan and gondwanan in the early early permian asselian to early artinskian there seems to have existed sharp biogeographical boundaries with no transitional zones between the realms presumably due to the effect of gondwanan glaciation and sharp climatic zonation the mid permian late artinskian to ufimian of the asian region is distinguished by the rise of two broad transitional zones in which mixed marine faunas flourished the northern transitional zone north and northeast china sikhote alin central and northeast japan is characterised by an admixture of both warm water cathaysian and cold temperate boreal genera the southern transitional zone arabian peninsula iran afghanistan the karakorum southeast and central pamir salt range central and northwest tibet shan thai terrane timor and western irian jaya on the other hand is distinguished by incorporating faunal elements of both gondwanan and cathaysian origin the mixed faunas of both transitional zones share several antitropically distributed genera e g monodiexodina lytvolasma and spiriferella and are succeeded by palaeotropical tethyan faunas of late permian age it has been postulated that the mixed mid permian fauna of the northern transitional zone was probably formed in an epicontinental sea which was connected to both the asian tethys and the arctic which facilitated the migration of cathaysian and boreal forms into the epicontinental sea and subsequent faunal mixing the formation of the mixed faunas of the southern transitional zone on the other hand is probably related to the breaking off of the cimmerian blocks from northern gondwana and subsequent drifting into a lower latitudinal zone with geographical proximity to both gondwana and cathaysia during the mid permian

intermediate steps of southwards faunal shifts testified by last glacial submerged thanatocoenoses in the atlantic ocean several southwards faunal shifts sfs of boreal species bgs boreal guests of authors are known to have occurred in the colder periods of the e atlantic pleistocene the latest invasion of bgs took place during the last glacial 75 000 10 000 yr b p and is recorded all over the mediterranean by a number of submerged thanatocoenoses containing sublittoral to bathyal faunas on the other hand these sfs are quite poorly documented within the atlantic ocean pre modern quaternary thanatocoenoses have been discovered at many sites along the eastern atlantic margin between ca 35 and 48 n these assemblages contain typical bgs modiolus modiolus chlamys islandica pseudamussium septemradiatum arctica islandica trichotropis borealis buccinum undatum and or scleractinian corals lophelia pertusa madrepora oculata caryophyllia smithi samples of representative species were radiocarbon dated showing four age clusters cluster 1 ca 27 000 yr b p is relative to the pleniglacial and is documented by c islandica assemblages in the bay of biscay and by coral thanatocoenoses in the ibero moroccan gulf cluster 2 ca 12 000 13 500 yr b p represents latest glacial faunas containing bg assemblages of milder climatic significance m modiolus and corals dredged in the ibero moroccan gulf cluster 3 7500 10 000 yr b p may represent retreating time delayed and or postglacial acclimatization of mild bgs p septemradiatum in the ibero moroccan gulf finally cluster 4 is relative to quite recent assemblages late holocene containing potential bgs b humphreysianum the paleoclimatic significance of which has to be revised our results show that intermediate steps missing links of sfs during the quaternary between the ne atlantic bg reservoir and the mediterranean are more frequent than previously supposed calling for their careful survey in order to shed light on expansion and contraction of cold faunas during the last glacial

permian gondwana boreal antitropicality with special reference to brachiopod faunas in a reconstructed global permian marine biogeographic framework antitropicality is defined as a biogeographic phenomenon whereby a taxon occurs only in the boreal and gondwanan realms and is lacking completely or nearly so in the intervening palaeoequatorial realm we recognise three types of antitropical distributions bipolar high latitude generally 50 latitude in each hemisphere bitemperate approximately between 30 and 50 latitudes in each hemisphere and a combination of both evidence of permian antitropicality has been reported from almost all major marine invertebrate groups both pelagic or benthic forms and is best known at the generic level although an increasing number of antitropical species have also been recognised antitropicality appears to have occurred throughout most of the permian but its strength varied from stage to stage judging by the number of brachiopod genera shared between the two hemispheres the phenomenon manifests itself most strongly from the sakmarian to the kazanian wordian suggesting a prolonged interval of enhanced biotic interchanges between the gondwanan and boreal realms possible migration pathways and mechanisms are reviewed and discussed among a number of existing scenarios invoked to explain the origin of both modern and geological antitropicality we here present data particularly supporting 1 a south to north stepping stone migratory mechanism via island terranes scattered in the eastern palaeotethys 2 a vicariance model exemplified by the spatio temporal distribution of tomiopsis and 3 a shelf north to south migration along the western coast of the palaeotethys as suggested by sowerbina in addition we also consider dispersal along the western coast of pangea facilitated at times by upwelling systems as an additional migration pathway for intercontinental biotic exchanges during the permian although corroborating data are required at present

provenance of the sedimentary rakaia sub terrane torlesse terrane south island new zealand the use of igneous clast compositions to define the source abstract the permian to late triassic rakaia sub terrane part of the torlesse superterrane of the new zealand eastern province is an accretionary complex that comprises an enormous volume of quartzofeldspathic sandstones and mudstones with subsidiary conglomerates plus minor oceanic assemblages the field of provenance analysis has undergone a revolution with the development of single crystal isotope dating techniques using mainly silt to sand sized single mineral grains fine sand and mud may be transported over thousands of kilometres with potential problems for provenance studies reinforcing the need for caution when interpreting provenance evidence from single heavy mineral grains this study focuses on coarser grained rocks notably conglomerates which involve much shorter transport distances and therefore may be used to trace proximal sources a detailed rock sampling programme and geochronological geochemical and sr nd isotope analysis of igneous clasts from four conglomerates boundary creek te moana mckenzie pass and lake hill have broadly characterised the igneous source for the rakaia sub terrane shrimp u pb zircon ages of rakaia sub terrane igneous clasts define three distinct periods of magmatic crystallisation the first period ranges in age from 292 to 243 ma permian to middle triassic with two clusters recognisable a minor early permian one ranging in age from 292 to 277 ma and a major late permian to middle triassic one from 258 to 243 ma all these clasts are confined to the kazanian permian te moana the dorashamian permian mckenzie pass and the carnian late triassic lake hill conglomerates the clasts which are subduction related calc alkaline to high k calc alkaline and metaluminous to peraluminous range in lithology from andesite to rhyolite and their plutonic equivalents many clasts at lake hill have chemical compositions characteristic of partial melts of a source of basaltic composition in equilibrium with amphibole pyroxene garnet adakites indicative of a thick crust in the clast source area the second period comprises carboniferous calc alkaline metaluminous to weakly peraluminous clasts of the permian boundary creek conglomerate ranging in age from 356 to 325 ma the third group consists of two cambrian clasts a monzogranite from te moana c 497 8 ma and a dacite from lake hill c 517 ma geochronology geochemistry and sr nd isotopes of rakaia igneous clasts correlate broadly with those of permian to triassic plutons and volcanics from the amundsen and ross provinces of marie byrd land thus the antarctic sector of the panthalassan margin of gondwana is the probable source for the rakaia sub terranes as opposed to the other postulated sources in eastern australia

a simple semi dynamic model of the subduction zone effects of a moving plate boundary on the small scale convection under the island arc summary a simple semi dynamic numerical model of the subduction zone which incorporates the plate velocity and a moving plate boundary as a priori constraints has been developed this model may be useful for studying specific subduction zones where a history of kinematic movements of plates is well constrained as an application of this model the effects of a moving plate boundary on the nature of the small scale convection in the mantle wedge were studied under the restriction of given relative velocity between two converging plates the absolute velocity of each plate was changed and i found that the characteristics of small scale convection are not significantly affected by the movement of the plate boundary at least within the parameter range used in this study i also found a small systematic change which may be related to the difference of the heat supply to the mantle wedge caused by the moving plate boundary thus the model with a fixed continental plate and moving oceanic plate with a given relative velocity may be sufficient for studying the present subject this model can be extended into a simple 3d subduction zone model

why is the north america cordillera high hot backarcs thermal isostasy and mountain belts global mountain belts are commonly concluded to be a consequence of crustal thickening resulting from continental collision with high elevations supported by crustal roots however accumulating seismic structure data indicate that many mountain belts have no crustal root most of the north american cordillera has a 30 35 km crust in contrast to 40 45 km for the lower elevation craton and other stable areas it has been shown previously that most such mountain belts are in present or recent backarcs that are uniformly hot from thermal constraints we predict a uniform 1600 m elevation support of the cordillera by thermal expansion compared to stable areas over most of the cordillera relative to stable areas the elevations after correction for variable crustal thickness and density are in excellent agreement when subduction and shallow backarc convection stop the lithosphere may cool and the elevations of mountain belts subside over 300 m y

olivine fabric transitions and shear wave anisotropy in the ryukyu subduction system recent shear wave splitting measurements from the fore arc region of the ryukyu subduction system show large magnitude 0 3 1 6 s trenchparallel splitting in both local and teleseismic phases the similarity of splitting parameters associated with shallow local s and teleseismic phases suggests that the source of anisotropy is located in the fore arc mantle one explanation for this pattern of shear wave splitting involves a transition from commonly observed high temperature olivine fabrics with flow parallel seismically fast directions to a flow normal b type olivine fabric in the cold fore arc mantle of the ryukyu wedge we test the b type fabric hypothesis by comparing observed splitting parameters to those predicted from geodynamic models that incorporate olivine fabric development the distribution of olivine fabric is calculated with high resolution thermomechanical models of the ryukyu subduction zone that include realistic slab geometry and an experimentally based wet olivine rheology we conclude that b type fabric can explain the magnitude and trench parallel orientation of deep local s phases that sample the core of the forearc mantle however our calculations show that b type fabric alone cannot account for large magnitude trench parallel splitting associated with teleseismic phases that sample the shallow tip of the fore arc mantle alternative models for trench parallel teleseismic splitting in the shallow tip of the fore arc mantle involve the addition of crustal or slab anisotropy and highly anisotropic foliated antigorite serpentinite 2008 elsevier b v all rights reserved

abrupt environmental and climatic change during the deposition of the early permian haushi limestone oman during the late sakmarian early permian the haushi limestone was deposited in a shallow embayment of the neotethys ocean covering what is now north oman and parts of southeast saudi arabia the sea persisted through the late sakmarian but by the time of the deposition of the artinskian middle gharif member limestone deposition had ceased and generally arid fluvial and minor lacustrine palaeonvironments in a low accommodation space setting had become established analysis of three subsurface cored boreholes and other surface sections of the haushi limestone shows an upward change in microfacies from bryonoderm to molechfor associations reflecting the passage from heterozoan to photozoan communities the biotic turnover indicates cooler climate and eutrophy in the lower parts of the unit and an upward trend towards warmer climate and more oligotrophic conditions in the upper part common autochthonous algal palynomorphs and high 13corg in the lower part suggest that high nutrient levels were due to greater fluvial runoff while allochthonous pollen assemblages indicate that the climate of the hinterland became more arid through the deposition of the unit causing upward increasing seawater trends in 18ocarb several extraneous factors are likely to have contributed to this palaeoenvironmental change which was more abrupt than in other parts of post glacial early permian gondwana first the haushi sea being an embayment partially isolated by hawasina rift shoulder uplift was more vulnerable to changes in rainfall and runoff than an open sea second continued post glacial global warming and small northward movement of gondwana may have contributed to temperature increase aridity may have been caused by the onset of monsoons and the influence of rift shoulders to the northeast and southeast

global brachiopod palaeobiogeographical evolution from changhsingian late permian to rhaetian late triassic abstract previous studies suggest that the end permian mass extinction caused a dramatic drop of marine biodiversity near the permian triassic boundary however it is unclear how profoundly this severe extinction might have changed the global provincialism and how global provincialism responded to the protracted process of this extinction and subsequent recovery through the triassic in this paper we carried out quantitative time series analyses of global brachiopod palaeobiogeography over a timespan of nine consecutive stages substages from the latest permian changhsingian to the latest triassic rhaetian based on a global brachiopod database of 483 genera and 2459 species from 1425 localities our results suggest that the extinction resulted in a global biogeographical eclipse in the ensuing early triassic griesbachian and dienerian times in that neither biogeographic realm nor province could be recognized it was characterized by an extreme low diversity mostly dwarfed and nearly globally distributed brachiopod fauna coupled with persistently high sea surface temperature and a flattened global latitudinal thermal gradient global provincialization emerged again during the olenekian at province level and reached its peak stage during the carnian when three realms and six provinces were clearly recognized global provincialism became weakened again in the latest triassic rhaetian marked by three general realms but no province distinguished our analyses suggest that both palaeolatitude related thermal gradient and the presence of pangea a profound geographic barrier were most effective in explaining the spatial patterns in addition oceanic currents along the northwestern coast of pangea also played an important albeit regional role in linking southern north and central america brachiopod faunas with those of the boreal realm this study also revealed that the brachiopod biodiversity center moved northwards over the studied interval accompanied and hence accountable for by the northward drift of a large number of tectonic blocks in the palaeotethys and neotethys during the triassic

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

a low viscosity wedge in subduction zones geochemical petrologic and seismological observations indicate that there may be high concentrations of water in the region above a subducting slab the mantle wedge which could decrease the viscosity of the mantle locally by several orders of magnitude using numerical models we demonstrate that a low viscosity wedge has a dramatic influence on the force balance in a subduction zone and leads to an observable signal in the topography gravity and geoid a regional dynamic model of the tonga kermadec subduction zone shows that the viscosity of the wedge is at least a factor of 10 smaller than surrounding mantle lithosphere and asthenosphere consistent with estimates from seismic dissipation and deformation experiments

permian higher latitude bryozoan biogeography abstract bryozoans from gondwana and northern eurasia are within the higher latitude gondwana and boreal realms respectively and display a clear antitropical faunal distribution with lower diversity than tropical realms within these realms however faunas at highest latitudes are the least diverse and dominated by cosmopolitan genera further separate geological and oceanographic developmental histories of the boreal and gondwanan regions have resulted in the boreal realm showing much higher diversity than its southern counterpart gondwana was in a high latitude position during the permian experiencing the polar climatic conditions of the late palaeozoic ice age and the distribution of bryozoans show a distinct diversity decrease towards cold water high latitudes where the eurytopic fenestrates and trepostomes were the dominant groups the eastern australian margin with the least diverse faunas of the gondwanan realm is oriented north south as a narrow shelf hindering the migration of taxa into the southern coldest environments in contrast northern hemisphere mid to high latitude basins experienced cooling through the permian as pangaea moved northward and tectonics altered oceanographic circulation however glaciomarine deposits were not widespread even at highest latitudes the marine shelf of the northern eurasian margin was broad and oriented west east allowing establishment of widespread stable faunas in waters that became increasingly nutrient fed through the permian from cool water upwelling from the panthalassa ocean in the west this cool water mid latitude setting west east shelf and nutrient enrichment resulted in a boreal realm bryozoan fauna of over 100 genera more diverse than the gondwanan realm with only 61 genera antitropical taxa restricted to boreal and gondwanan realms only include diploporaria lyropora and metelipora however a number of other genera are more abundant outside the tropics even if they occur in all realms these genera include alternifenestella rectifenestella polypora polyporella shulgapora dyscritella stenopora streblascopora pinegopora maychella maychellina ramipora tabulipora and hexagonella the wide nutrient fed mid latitude shelf of the boreal realm also allowed development of a number of endemic taxa or taxa that are rare elsewhere including permoheloclema timanodictya permofenestella lyrocladia wjatkella parafenestralia triznella and gilmouropora in southern gondwana endemic taxa are limited to crockfordia and paramaychella however there is an abundance of evactinostella etherella and liguloclema that are distinctive of western australia

global distribution of permian conulariids and palaeobiogeographical implications previously minimal work has been carried out on conulariids due to their rare occurrences and resultant biostratigraphical limitations the palaeobiogeographical distribution of permian conulariids suggests that they have a marked preference for cold to cool water regions that they are significant indicators for migration patterns and that they can potentially provide information on the palaeogeographical configuration and movement of terranes permian conulariids are found in australia india new zealand pakistan iran afghanistan kashmir china japan russia germany canada united states of america and bolivia the diversity of permian conulariids is markedly higher in the polar regions than in the palaeoequatorial region permian conulariid genera include notoconularia thomas 1969 gondaconularia waterhouse 1986 cheliconularia waterhouse 1986 neoconularia sugiyama 1942 calloconularia sinclair 1952 diconularia sinclair 1952 paraconularia sinclair 1940 mesoconularia boucek 1939 and conularia sowerby 1821 this paper describes two new species of conulariids diconularia meadepeakensis sp nov from the phosphoria formation guadalupian idaho usa and paraconularia kazanensis sp nov from the sokian horizon roadian volga region russia

provenance and geochemistry of lower to middle permian strata in the southern junggar and turpan basins a terrestrial record from mid latitude ne pangea abstract the lower to middle permian terrestrial successions in the southern junggar and turpan basins provide a wealth of information regarding the paleoclimatic and paleogeographic evolution of mid latitude ne pangea two sections namely the xiaolongkou section in the southern junggar basin and the southwest sw tarlong section in the turpan basin were systematically studied using detrital zircon geochronology and whole rock geochemical analysis stratigraphic studies suggest that in both sections the lucaogou and hongyanchi formations are dominated by lacustrine deposits while the quanzijie formation represents mixed fluvial lacustrine and loess environments the lucaogou formation displays low cia chemical index of alteration values and th u ratios suggesting semiarid to arid conditions in both sections the hongyanchi formation shows low to intermittently moderate cia values and th u ratios indicating variably semiarid arid conditions alternating with subhumid semiarid episodes the lower part of the quanzijie formation reflects subhumid semiarid to semiarid arid conditions while the upper part of the quanzijie formation mainly records semiarid arid and shifts into subhumid conditions toward the top detrital zircon and element data indicate that within each section all three formations display similar zircon age distributions and geochemical characteristics suggesting no significant changes in provenance during deposition however the provenance characteristics of the two sections differ from each other the xiaolongkou section is rich in felsic material with two detrital zircon age peaks while the sw tarlong section contains more mafic components with a single peak in detrital zircon age spectrum this suggests that the greater junggar turpan basin was highly partitioned with several independent provenance systems active during the early middle permian the abrupt change in depositional environments in both sections may have resulted from uplift of the north tian shan which induced rapid regression of the lakeshore and uplift of sediment source and catchment areas

capitanian late guadalupian permian global brachiopod palaeobiogeography and latitudinal diversity pattern a global database containing 3365 occurrences 821 species and 251 genera of the capitanian late guadalupian permian brachiopod faunas from 24 stations has been analyzed by cluster analysis using the jaccard and otsuka coefficients and the probabilistic index of similarity nonmetric multidimensional scaling and minimum spanning tree two supergroups three groups and six subgroups are revealed and interpreted as representing respectively two biotic realms the palaeoequatorial and gondwanan realms two regions and six provinces an additional realm the boreal realm based on the fauna from spitsbergen also appears recognizable although it also shows considerable similarities with southwestern north america and the northern margin of gondwana as revealed by the statistical analysis the palaeoequatorial realm can be further subdivided into the north america region and the asian tethyan region the six biotic provinces are the cathaysian province in the palaeotethys and mesotethys the greenland svalbard province in the arctic region the austrazean province in eastern australia and new zealand the grandian province in western north america and the two transitional zones the himalayan province in the southern temperate zone and the sino mongolian japanese province in the northern temperate zone polynomial regression analysis and rarefaction analysis indicate that the generic diversities of brachiopod faunas during the capitanian peaked in the palaeoequatorial cathaysian province and the two transitional zones himalayan province and sino mongolian japanese province but fell dramatically in the polar regions the generic diversity of the palaeoequatorial grandian province is apparently lower than in the two transitional zones of temperate palaeolatitudes suggesting that the generic diversity of capitanian brachiopod faunas does not exhibit a strict negative correlation with palaeolatitudes this in turn would suggest that biogeographical determinants such as geographical barriers inhabitable area and ocean currents other than latitude related temperature control may also have played an important role in the dispersal of some brachiopods and the characterization of some local provinces and high diversities the capitanian global brachiopod palaeobiogeography is generally comparable with those in the wuchiapingian and changhsingian but with some notable differences these include 1 that the grandian province of the capitanian in western north america vanished after the end guadalupian regression 2 that the western tethyan province of the lopingian could not be distinguished in the capitanian and 3 that the austrazean province was larger in area than either in the wuchiapingian or in the changhsingian

global review of permian muir wood and cooper 1960 brachiopoda morphology palaeobiogeographical and palaeogeographical implications a global review of the stratigraphical and geographical distribution of tyloplecta reveals that the genus ranges in age from kungurian to changhsingian middle to late permian tyloplecta first evolved in south china in the kungurian late early permian the genus went through its first diversification in the guadalupian suffered a major extinction at the end of the guadalupian and re diversified in the wuchiapingian t yangtzeensis persisted into the changhsingian as the only survivor of the genus involved in the end permian mass extinction palaeogeographically south china is not only the centre of origin for the genus but also an area of diversification and evolution in addition to south china tyloplecta has also been recorded from the far east russia japan central thailand laos cambodia qiangtang terrane of tibet salt range iran armenia hungary yugoslavia and slovenia this geographic spread suggests that tyloplecta was primarily restricted to the palaeotethys and is indicative of warm water palaeoequatorial conditions its presence in some of the northeast asian terranes e g parts of japan and far east russia and in the salt range pakistan and central and north iran part of the cimmerian microcontinents demonstrate that the genus invaded the middle palaeolatitudinal regions in both hemispheres during the late middle permian in response to increased shallow marine biotic communications between cathaysia in the eastern palaeotethys and southern angaraland and between cathaysia and peri gondwanaland the invasion of tyloplecta and some other taxa into the southern shore waters of angaraland may be explained by assuming ocean surface current connections and close palaeogeographical proximities between the south china sino korea and bureya blocks in comparison the invasion of tyloplecta into the peri gondwanaland region is more likely a result of reduced palaeogeographical distance between south china and peri gondwanaland and the appearance of the cimmerian microcontinents as migratory stepping stones

distinct regional differences in crustal thickness along the axis of the mariana trough inferred from gravity anomalies we have compiled extensive gravity and bathymetry data for the whole mariana trough which were collected during several japanese scientific cruises over the last few years this study aims to clarify the lateral distribution of the local differences in geochemical signatures which have been observed locally in the mariana trough shipboard free air gravity anomaly data from eight japan agency for marine earth science and technology jamstec cruises were compiled with those crossover errors of 2 85 mgal mantle bouguer anomalies mba were calculated by subtracting the predictable gravity signal due to the seawater crust and crust mantle density boundaries the crustal thickness variation along the spreading axis was estimated from the mba different features in crustal thickness its variation and segment length for each segment allow us to identify four distinct regional differences in magmatic activity along the spreading axis of the mariana trough segment in region a to the north of 20 35 n shows the largest sectional dimensions of crust along the axis and it is probably affected by an additional supply from island arc magma sources a variety of crustal thickness values and of along axis crustal thickness variations in region b between 15 38 n and 20 35 n suggests two types of segments one is similar to a slow spreading ridge segment that has a plume like mantle upwelling under the spreading axis and the other is a magma starved segment region c between 14 22 n and 15 38 n is a less magmatic region individual crustal thickness averages of 3 4 4 1 km region d to the south of 14 22 n has higher individual crustal thickness averages of 5 9 6 9 km suggesting higher magmatic activity with a sheet like mantle upwelling under the spreading axis different features in the mba for off axis areas suggest that these four regions have existed since the mariana trough started spreading moreover comparison between our results of crustal thickness and previous geochemical results indicates that less magmatic spreading segments with thin crust which are locally distributed in both regions b and c probably result from mantle source depleted of water and incompatible elements this suggests that lateral compositional variation of water and incompatible elements exists on a segment scale in the mantle source beneath the spreading axis of the mariana trough

convection beneath young oceanic lithosphere implications for thermal structure and gravity small scale convection under the oceanic lithosphere which begins in the first 5 m y of cooling can produce a gravity signal with the amplitude and wavelength observed for large areas of the central pacific and southern indian oceans using seasat altimeter data the trend of the observed anomalies is parallel to the direction of plate motion as might be expected if they were produced by small scale convection models predict that the wavelengths of gravity anomalies increase more rapidly with age than is observed the persistence of short relatively uniform wavelength anomalies 200 km to crustal ages of 50 ma may indicate that they were produced when the lithosphere was very young and thin and were frozen in as cooling thickened the elastic lithosphere small scale convection which begins under very young lithosphere does not violate other geophysical data such as the rate of seafloor subsidence and variations of geoid height with age after convection has begun the subsidence due to thermal contraction within the lithosphere varies linearly with age in the absence of mantle heat sources although the rate of change of these quantities is affected by convection much of the variation of the geoid height across fracture zones can be fit by a model which includes small scale convection

neogene marine climate trends implications for biogeography and evolution of the shallow sea biota a host of data on the biodistribution diversity and taxonomic age patterns of neogene shallow sea faunas can be accommodated within a climatic model which assumes that oceans in the late paleogene were significantly cooler in low latitudes and wanner in high latitudes than at present these climatic assumptions seem compatible with the state of the art in paleotemperature interpretation if the model holds it will effectively eliminate hypotheses of species diversity regulation that depend on the age of climates and will explain the relative youth of genera and families in the tropics

laboratory convection experiments effect of lateral cooling and generation of instabilities in the horizontal boundary layers convection experiments are carried out in a tank with two isothermal heat sinks the top plate and one of the sidewalls heating is supplied either by an isothermal bottom plate or by generation within the fluid this situation is similar to that of the earth s subcontinental mantle in the presence of a neighboring subducting oceanic lithosphere there the mantle material loses heat not only to the base of the continental lithosphere but also to the cold dipping oceanic slab the thermal structure of the convective fluid is observed by a variety of techniques including differential interferometry and strioscopy two parameters characterize the observations the usual vertical rayleigh number and a newly defined lateral rayleigh number the lateral cooling induces a large roll with axis parallel to the cold wall the variation of its width relative to the values of the two rayleigh numbers has been determined an application to the earth s upper mantle would predict rolls 5 times wider than high the circulation in the large roll remains two dimensional for rayleigh numbers up to about 3 104 beyond this value boundary layer instabilities are observed within the persisting large roll their period has been determined the interferometric method is shown to be very useful for visualizing other time dependent processes such as the growth of the induced large rolls this growth is rapid enough to allow us to propose the existence of such large rolls in the earth and argue that their action could have led to continental break up

oxygen isotope values from high latitudes clues for permian sea surface temperature gradients and late palaeozoic deglaciation abstract the permian was a period of waning large scale continental glaciations in the southern hemisphere the waning of these ice sheets during the early permian led to discharge of 18o depleted ice melt water into the oceans this coupled with rising seawater temperatures resulted in a concomitant decline of about 2 5 in the 18o of seawater as recorded by brachiopod shells from low latitude

facies and allostratigraphy of high latitude glacially influenced marine strata of the early permian southern sydney basin australia the sydney basin of new south wales australia is a foreland basin containing a thick up to 10 km permo triassic succession the southern margin of the basin exposes strata deposited during late palaeozoic glaciation of south eastern gondwana the early permian wasp head pebbley beach snapper point formations and wandrawandian siltstone were deposited between 277 and 258 ma on a polar glacially influenced continental margin adjacent to ice sheets located over east antarctica and eastern australia sedimentary facies together with related ichnofacies and fauna can be grouped into six facies associations that record marine sub environments ranging from high energy storm dominated inner shelf to turbidite dominated upper slope settings cold marine conditions with near freezing bottom water temperatures are recorded by glendonites ice rafted debris most likely deposited by icebergs occurs in almost all facies associations an allostratigraphic approach emphasizing the recognition of bounding discontinuities i e erosion surfaces and marine flooding surfaces is used to subdivide the early permian stratigraphy into facies successions three types of succession can be identified and record changes in the relative influence of allocyclic controls such as basin tectonics sediment supply and glacio eustatic sea level variation together sedimentological and allostratigraphic data allow reconstruction of the depositional history of the south western margin of the sydney basin initial marine sedimentation characterized by sediment gravity flows and storm deposited sandstones of the lower wasp head formation occurred adjacent to a faulted basin margin overlying successions within the upper wasp head pebbley beach and snapper point formations record aggradation in inner to outer shelf settings along a storm and glacially influenced continental margin tectonic subsidence and basin flooding is recorded by deeper water turbidites of the wandrawandian siltstone

paleopositions of some northern eurasian tectonic blocks paleomagnetic and paleobiologic constraints abstract northern eurasia consists of several large tectonic elements which have amalgamated during phanerozoic time namely the baltic shield russian platform siberian platform kazakhstan block chukotka block verkhoyansk belt and omolon massif amur block sikhote alin sino korean block north china block yangtze paraplatform japan arc west spitsbergen and numerous smaller units not treated in this paper accretion phases of these elements to each other are discussed in terms of their paleomagnetic signatures paleolatitudinal distributions and paleobiological constraints and a plate tectonic cladogram has been constructed for the mostly mesozoic amalgamation of the asian elements

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

multiscale dynamics of the tonga kermadec subduction zone our understanding of mantle convection and the motion of plates depends intimately on our understanding of the viscosity structure of the mantle while geoid and gravity observations have provided fundamental constraints on the radial viscosity structure of the mantle the influence of short wavelength variations in viscosity is still poorly understood we present 2 d and 3 d finite element models of mantle flow including strong lateral viscosity variations and local sources of buoyancy owing to both thermal and compositional effects we first use generic 2 d models of a subduction zone to investigate how different observations depend on various aspects of the viscosity structure in particular the slab and lower mantle viscosity and the presence of a low viscosity region in the mantle wedge above the slab we find that 1 the strain rate provides a strong constraint on the absolute viscosity of the slab 10 23 pa s 2 stress orientation within the slab is sensitive to the relative viscosity of the slab lower mantle and the wedge and 3 the stress state and topography of the overriding plate depend on the wedge viscosity and local sources of buoyancy in particular the state of stress in the overriding plate changes from compression to extension with the addition of a low viscosity wedge we then use observations of strain rate stress orientation dynamic topography and the geoid for the tonga kermadec subduction zone as simultaneous constraints on the viscosity and buoyancy in a 3 d regional dynamic model together these observations are used to develop a self consistent model of the viscosity and buoyancy by taking advantage of the sensitivity of each observation to different aspects of the dynamics over a broad range of length scales the presence of a low viscosity wedge makes it possible to match observations of shallow dynamic topography and horizontal extension within the backarc and down dip compression in the shallow portion of the slab these results suggest that a low viscosity wedge plays an important role in controlling the presence of backarc spreading however for a model with a low viscosity and low density region that provides a good fit to the observed topography we find that a reduction of the slab density by a factor of 1 3 relative to the reference density model is required to match the observed geoid these results suggest that compensation of the slab by dynamic topography may be a much smaller effect at short to intermediate wavelengths than predicted by long wavelength modelling of the geoid

earliest permian brachiopod faunas of west central argentina defining the pennsylvanian permian boundary in gondwana abstract late palaeozoic marine successions in the west central argentinian basins have one of the most complete stratigraphic records of the earliest permian in gondwana two brachiopod faunal assemblages characterize this interval the tivertonia jachalensis streptorhynchus inaequiornatus fauna widely documented in the rio blanco and western paganzo basins and the costatumulus amosi fauna identified in the earliest permian successions of the southern calingasta uspallata basin this study reviews the composition and biostratigraphy of these two brachiopod faunas with special reference to their global significance for defining the carboniferous permian boundary in gondwana and deciphering the early permian climate change in western gondwana

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

permian brachiopods from new localities in northeast thailand implications for paleobiogeographic analysis abstract a small permian brachiopod fauna is described from new localities in northeastern thailand brachiopods were collected from early permian asselian limestones of the nam maholan formation and middle permian murgabian sandstones of the nam duk formation and limestones of the khao khwang formation analyses of taxa confirm preliminary hypotheses of cathaysian affinities for brachiopods and fusulinids found in this part of thailand fossils found in sandstones of the nam duk molasse facies however also show possible gondwanan relationships with brachiopod taxa described in australia this has to be further tested with ongoing research in a better understanding of the paleobiogeography of this part of southeast asia

coevolution of brachiopod boreal realm and pangea abstract the boreal realm originated in the early carboniferous the realm became more firmly established during the late carboniferous and early permian and peaked in the middle permian before decaying in the late permian in the early carboniferous the geographic distribution of the boreal realm was latitudinally narrow and many brachiopod genera of the realm were also common in the tethys realm the boreal realm faunas were however also characterized by many geographically and temporally restricted genera the boreal realm was well developed in the late carboniferous as represented by the continued expansion of the geographical ranges and numbers of occurrences of many permian characteristic boreal realm genera in the early permian the geographic distribution of the boreal realm expanded further as did the distribution of characteristic boreal realm genera in the middle permian the geographic distributions of the boreal realm had expanded to their greatest extent and the characteristic boreal realm genera were most abundant and diverse in the late permian the cool water characteristic genera which flourished during the carboniferous to middle permian disappeared in these areas and resulted in the decay of boreal realm the development of the boreal realm was closely related to events leading to the formation of pangea in which a variety of plates laurussian siberian etc were continuously drifting northwards some plates blocks entered middle and high latitudinal regions and were located in cool climatic environments during the evolution of pangea the siberian kazakhstan and eastern european plates were continuously located in the center of the boreal realm the barents ocean developed to the west and the paleo asian ocean developed to the east of these plates this configuration of oceans and continents differentiated the eastern central asia region and the western barents region in the paleo asian ocean tectonic domain the northern branch of the paleo asian ocean was surrounded by the siberian plate the kazakhstan plate and the jiamusi mongolia block and named the mongolia okhotsk ocean the mongolia okhotsk brachiopod fauna developed on the southern margin of the mongolia okhotsk ocean i e the northeastern margins of the siberian and kazakhstan plates and the northern margin of the jiamusi mongolia block thus forming the mongolia okhotsk province during the middle permian the xar moron ocean was enclosed by the jiamusi mongolia block and the kazakhstan tarim and south china plates on the southern margin of the xar moron ocean i e the southern margin of the jiamusi mongolia block the zhesi brachiopod fauna developed and the inner mongolia province was formed during the carboniferous permian the kolyma chukchi block siberian plate and north american plate comprised the barents ocean tectonic domain the verkhoyansk brachiopod fauna developed on the northern margin of the barents ocean i e on verkhoyansk and the southwestern margin of the siberian plate thus forming the verkhoyansk taymyr province starting in the late carboniferous a cool water brachiopod fauna developed on the southern margin of the barents ocean i e the northern margin of the north american plate and the northern margin of the eastern european plate thus forming the yukon pechora province the geographical range of which extended continuously with time

first report of coupled early permian paleomagnetic and geochronologic data from the dunhuang block nw china and implications for the tectonic evolution of the paleo asian ocean abstract in order to better understand the tectonic relationship between the dunhuang block dhb and its adjacent blocks and to constrain the timing of the closure of the paleo asian ocean a combined geochronologic and paleomagnetic investigation has been undertaken on early permian tuff basalt flows and sandstones from the shuangbaotang formation in the northwestern part of the dhb u pb zircon dating indicates that the age of the strata is between 280 6 2 9 ma and 291 4 2 6 ma thermal demagnetization of a three component isothermal remanent magnetization irm and curie point experiment suggest that magnetite dominates in the rock samples analyzed in addition there is a minor amount of hematite in some sandstones stepwise thermal demagnetization successfully isolated stable characteristic remanent magnetization chrm from 11 tuff layers two lava flows and nine sandstone beds two components were isolated from all samples a lower temperature component ltc and a higher temperature component htc the ltc is near the direction of the present day geomagnetic field and produced a negative fold test indicating it is a viscous remanent magnetization in the present day geomagnetic field most of the htc are reverse polarity normal 4 reverse 158 which is in accordance with the kiaman reversed superchron that spans the late carboniferous permian interval in addition the htc of all studied sites passed the fold and reverse tests suggesting that they likely represent primary remanent magnetization the tilt corrected mean direction from all sites tuff basalts and sandstones is ds 1 7 is 43 1 ks 403 95 1 5 n 22 the mean paleopole of the site mean direction corresponded vgps lies at 74 5 n 268 5 e with a95 1 6 considering the consistent inclination values recorded among the studied tuff basalts and sandstones and the low degrees of anisotropy within all samples we suggest that there is no significant inclination shallowing caused by depositional compaction in the sedimentary layers of the studied section taking into account the results from this study as well as previous late paleozoic paleomagentic studies from adjacent tectonic blocks we conclude that the dhb formed part of the amalgamated dunhuang north china alxa qaidam mega block during the early permian but was separated from the tarim block by a small ocean here named the qiemo xingxingxia paleo ocean at this time a comparison of the early permian paleolatitudes of these and other adjacent blocks suggest that the paleo asian ocean sensu lato was still open at this time combined with other geological evidence a paleogeographic reconstruction of the paleo asian ocean has been reconstructed for the early permian

paleogeographic implications of high latitude and middle latitude affinities of the ammonoid uraloceras the ammonoid genus uraloceras characterized a lower permian boreal paleogeographic realm reported lower permian pangaean uraloceras occurrences have a boreal or high latitude distribution additional lower permian occurrences in alaska dominated by boreal species are compatible with and reinforce the boreal distribution of the genus in contrast a new uraloceras species from nevada and from the yukon as well as representatives of the genus form nei monggol inhabited regions of lower latitudes the latter ammonoid faunas geographically and paleoecologically transitional between boreal and equatorial realms include the genus uraloceras as well as abundant other ammonoid taxa and representatives of equatorial perinitid ammonoids the lower assemblage of wrangellia terrane in eastern alaska consisting of the lower permian mankomen group slana spur and eagle creek formations contains abundant uraloceras and paragastrioceras of high latitude affinities published paleomagnetic data indicate that the nikolai greenstone is of equatorial origin with paleolatitudes 10 to 17 degree the nikolai greenstone seems to have a far traveled history incompatible with ammonoid evidence suggesting cool water setting on the pangaean continental shelf a reinterpretation for the origin of wrangellia or its magnetic signature may be in order alternative hypotheses suggest that the eagle creek uraloceras paragastrioceras boreal fauna was scraped off the craton atmore higher latitudes possible 30 45 degree and carried with wrangellia to its present location less

application of the fujita ziegler paleoclimate model early permian and late cretaceous examples abstract the fujita ziegler model is a new semi quantitative technique for reconstructing atmospheric circulation and resulting rainfall patterns of the geological past using uniformitarian assumptions in this paper we evaluate the performance of the model when applied to geographic and climatic conditions that were significantly different from the recent a late cretaceous maastrichtian reconstruction permits a test of the performance of the technique during a time that apparently lacked polar ice caps and steep latitudinal temperature gradients an early permian sakmarian reconstruction is used to evaluate the performance of the technique when the equator to pole temperature gradient was steep more like today but all major land masses had merged to form one large supercontinent pangea for both the maastrichtian and sakmarian the model produced more detailed retrodictions of surface air pressure and precipitation continuity than previously published paleoclimate reconstructions the results compare favorably with the known distribution of climatically sensitive sediments such as coals evaporites and phosphorites although the model considers complex relationships among land and sea distribution air pressure surface winds ocean currents and specific precipitation mechanisms it is still relatively simple and easy to apply therefore it is an excellent learning tool for the student of paleoclimate and should be an important technique to complement other methods of paleoclimate reconstruction

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

effects of strongly temperature dependent viscosity on time dependent three dimensional models of mantle convection numerical simulations of thermal convection in a wide 8 8 1 cartesian box heated from below with temperature dependent viscosity contrasts of 1000 and rayleigh number 105 show that boundary conditions and aspect ratio have an enormous effect on the preferred flow pattern with rigid upper and lower boundaries spoke pattern flow with small diameter 1 5 cells is obtained consistent with laboratory experiments and previous numerical results however with the arguably more realistic stress free boundaries the flow chooses the largest possible wavelength forming a single square cell of aspect ratio 8 with one huge cylindrical downwelling surrounded by upwelling sheets the addition of stress dependence to the rheology weakens the stiff upper boundary layer resulting in smaller cells though still with upwelling sheets and downwelling plumes

possible existence of small scale convection under the back arc 1 we discuss a possible existence of small scale convection under the back arc which may be a cause of recently proposed along arc variation of thermal structure under northeastern japan based on numerical simulations we find that under the situation of opening of japan sea a possible existence of low viscosity layer lvl below the back arc makes the existence of small scale convection be likely a shear produced by the movement of subducting slab aligns the axes of convection roll perpendicular to the arc to explain the observed wavelength of along arc variation 50 to 80 km our preferred model requires a similar thickness of the lvl whose viscosity is two orders of magnitude less than that of surrounding another notable feature is the upward movement of the mantle associated with the small scale convection we discuss the water released from the subducting crust as a possible origin of the lvl

small scale convection under the back arc occurring in the low viscosity wedge abstract water released from subducting slabs through a dehydration reaction may lower the viscosity of the mantle significantly thus we may expect a low viscosity wedge lvw above the subducting slabs the lvw coupled with a large scale flow induced by the subducting slabs may allow the existence of roll like small scale convection whose axis is normal to the strike of the plate boundary such a roll structure may explain the origin of along arc variations of mantle temperature proposed recently in northeast japan we study this possibility using both 2d and 3d models with without pressure and temperature dependent viscosity 2d models without pressure and temperature dependence of viscosity show that with a reasonable geometry of the lvw and subduction speed small scale convection is likely to occur when the viscosity of the lvw is less than 10 19 pa s corresponding 3d model studies reveal that the wavelength of rolls depends on the depth of the lvw the inclusion of temperature dependent viscosity requires the existence of further low viscosity in the lvw since temperature dependence suppresses the instability of the cold thermal boundary layer pressure i e depth dependence coupled with temperature dependence of the viscosity promotes short wavelength instabilities the model which shows a relatively moderate viscosity decrease in the lvw most of the lvw viscosity is 10 18 10 19 pa s and a wavelength of roll 80 km has a rather small activation energy and volume 130 kj mol and 4 cm 3 mol of the viscosity this small activation energy and volume may be possible if we regard them as an effective viscosity of non linear rheology

survival strategies of brachiopod faunas from the end permian mass extinction abstract global reviews reveal that 102 brachiopod species including 40 indeterminate species belonging to 43 genera within 27 families survived the end permian mass extinction in south china the himalayan regions southern tibet nepal salt range and kashmir southern alps italy arctic canada western usa and western australia of these the surviving brachiopods are most abundant and widespread in south china where they occur in 32 of the 42 permian triassic p t boundary sections around the world brachiopod faunas are the most abundant and diverse post extinction survivors and their appearance above the end permian mass extinction horizon somewhat masks recognition of the end permian extinction these surviving brachiopods occur in three stratal intervals corresponding to the mixed fauna beds mfb hereafter 1 3 of the p t boundary beds a sharp drop in diversity of the brachiopod faunas coincides with the widely accepted end permian mass extinction horizon the post extinction brachiopods were also affected by a subsequent crisis corresponding to the boundary between mfb 2 and mfb 3 so that most survivors were extinct approximately 0 7 ma after the end permian mass extinction the surviving brachiopods were mainly productida followed by spiriferida in particular small chonetids chonetid like productellids and smooth thin shelled ambocollid spiriferids are most abundant lingula is extraordinarily abundant and widespread approximately 0 7 ma after the greatest extinction when many regions became devoid of articulate brachiopods widespread broadly adapted and small sized taxa preferentially survived frequent intrageneric speciation of widespread widely adapted generalist genera enabled survival brachiopods to occupy rapidly and efficiently vacant ecospace in the aftermath of the end permian extinction the ecological habitats of the post extinction brachiopods are subdivided into nearshore epeiric sea restricted carbonate platform open carbonate platform ramp and outer shelf environments of these the survival brachiopods are most diverse in the open platform environments the nearshore zone provided ideal habitats for the nonarticulated brachiopods to occupy whereas the survivors in the outer shelf are predominantly chonetids and chonetid like productellids the most successful survivors the productid brachiopods are widely distributed in six types of ecological habitats and thus have no apparent preference for specific environments the end permian extinction resulted in the movement of biogeographical provinces towards the palaeo equator the brachiopods survived mostly in the palaeo equatorial provinces and along the southern margins of the palaeo tethys ocean

a consistent model for fluid distribution viscosity distribution and flow thermal structure in subduction zone water plays crucial roles in the subduction zone dynamics affecting the thermal flow structure through the fluid processes we aim to understand what controls the dynamics and construct a model to solve consistently fluid generation fluid transport its reaction with the solid and resultant viscosity and thermal flow structure we highlight the effect of mechanical weakening of rocks associated with hydration the viscosity of serpentinite serp in subduction zones critically controls the flow thermal structure via extent of mechanical coupling between the subducting slab and overlying mantle wedge when serp is greater than 1021 pa s the thermal flow structure reaches a steady state beneath the volcanic zone and the melting region expands until cin initial water content in the subducting oceanic crust reaches 3 wt and it does not expand from 3 wt on the other hand when serp is less than 1019 pa s the greater water dependence of viscosity expressed by a larger fv confines a hot material to a narrower channel intruding into the wedge corner from a deeper part of the back arc region consequently the overall heat flux becomes less for a larger fv when ageba age of back arc basin as a rifted lithosphere 7 5 ma the increase in fv weakens but shifts the melting region toward the trench side because of the narrow channel flow intruding into the wedge corner where as it shuts down melting when ageba 20 ma several model cases particularly those with serp 1020 to 1021 pa s and a relatively large fv for cin 2 to 3 wt broadly account for the observations in the northeast japan arc i e location and width of volcanic chain extent of serpentinite surface heat flow and seismic tomography although the large variability of surface heat flow and seismic tomographic images does not allow us to constrain the parameter range tightly

effect of a shallow low viscosity zone on small scale instabilities under the cooling oceanic plates we have studied the role of a low viscosity zone in the uppermost mantle on convective instabilities in the cooling oceanic plates the upper mantle is represented by three layers in a finite element model a conducting lid overlies a low viscosity zone which in turn overlies a layer of constant viscosity extending to the base of the upper mantle at 675 km in depth the viscosity contrast the rayleigh number the relative fluid layer thicknesses and the conducting lid thickness are varied if the rayleigh number of the low viscosity zone exceeds a critical value then convection will be confined to the low viscosity zone for a period which depends on the viscosity contrast and the rayleigh number however the scale of the convection will eventually grow and extend throughout the upper mantle we compare our model to the small scale geoid and topography anomalies observed in the central pacific which are 50 80 cm in geoid and 250 m in topography 10 40 m y after plate formation and whose wavelength 150 500 km increases with age the magnitude early onset time and lifetime of the anomalies suggest a viscosity contrast of greater than 2 orders of magnitude the increase in wavelength with time also suggests a high rayleigh number 106 and the initial 150 250 km wavelength indicates a low viscosity zone thickness of 75 125 km small scale convection does not alter the slope of the depth age curve but does elevate the depth age curve by 250 m it is not until the onset of long wavelength convection that the depth age curve departs from age predicted by a cooling half space these results agree with the depth age behavior observed in the pacific where the depth age curve is elevated in the region of small scale anomalies and departs from age at 70 m y the models also predict heat flow values on old ocean floor which are higher than the plate model 50 55 mw m2 but which are in agreement with heat flow measurements in the atlantic and pacific

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

permian of myanmar abstract permo triassic carbonates with minor basal clastics cover extensive tracts of the shan plateau in the eastern part of myanmar these carbonates are grouped into the permian thitsipin limestone formation and the late permian early triassic nwabangyi dolomite formation the thitsipin formation occurs as isolated masses in many places faulted against older rocks it is now known that there is a regional unconformity between the thitsipin limestone formation and the underlying silici carbonates of devonian age in shan state and between the thitsipin limestone formation and carboniferous meta siliciclastics in kayah state mon state kayin state and tanintharyi division some of the thitsipin limestone is dolomitized and passes transitionally upward into the nwabangyi dolomite formation permian shelf carbonates occur within two different sequences the silici carbonate sequence of the shan thai block and the meta siliciclastic sequence of the mergui terrane suggesting that the permian limestones were deposited after the emplacement of the mergui terrane onto the southern margin of the shan thai block this event occurred when the shan thai block was in the southern hemisphere