contact diagenesis the effect of an intrusion on reservoir quality in the triassic sherwood sandstone group northern ireland abstract intrusion of a dolerite sill into clay bearing arkosic triassic sherwood group sandstones with moderate porosity 22 and high but anisotropic permeability mode 500 md led to the progressive transformation of precursor diagenetic minerals in the host rock locally pore filling mg rich smectite saponite quartz and dolomite existing in the rock following earlier burial diagenesis reacted to produce grain coating flakes of talc at the lowest contact temperatures 130 180 c based on equilibrium reaction path and thermal history calculations at higher temperatures 200 230 c talc reacted with calcite to produce an actinolitic amphibole close to the intrusion at temperatures of 250 c bundles of acicular needles of actinolite protruding into open pores were produced by a second reaction involving saponite hematite and calcite framework feldspar minerals mainly k feldspars played little or no part in the reactions because there were no k al rich minerals produced by contact diagenesis and because the detrital feldspar grains are essentially unaltered thus while equilibrium may have been approached on the intrapore scale 10 m it was not achieved between grains e g detrital feldspars pore water and clays in the pores total porosity has been unaffected by the intrusion and consequent mineral reactions because reactions involved recrystallization of original pore filling minerals despite the contact diagenetic changes in the rock the permeability of the sandstone remained largely unaffected by intrusion

early permian to middle jurassic rifting and sedimentation in east africa and madagascar pre drift sediments of madagascar early permian middle jurassic have been studied palynologically these studies resulted in a more precise dating of individual stratigraphic units and the recognition of minor and major breaks in the succession palynostratigraphic and physical evidence of unconformities have been used to subdivide the pre drift sediments into depositional cycles and to infer rifting events a comparison with equivalent strata of mozambique tanzania kenya ethiopia and somalia shows a general correspondence and provides additional information for the construction of a generalized framework for the east african madagascan region which demonstrates the relationships between rifting and sedimentation and elucidates the prehistory of the break up of gondwana into a western and eastern fragment during the middle jurassic the predrift succession of east africa madagascar can be subdivided into two major sequences a karoo sequence cycles 1 5 asselian early smithian and a transitional sequence cycles 6 9 ladinian early bajocian the two sequences are separeted by a late scythian to anisian hiatus which indicates extensive uplift and erosion before a major rifting event initiated the resumption of sedimentation in the ladinian this middle triassic event marks the transition from the intracratonic rift stage to the pericratonic basin stage and correlates with a significant event in the pangaean history the transition from final coalescence to initial dispersal the onset of the southward drift of madagascar is believed to have occurred about 60 ma later near the aalenian bajocian boundary contemporaneous with or immediately after the deposition of syntectonic sediments of cycle 9

phanerozoic tectonic regimes of australia reflect global events abstract phanerozoic australia was marked by three regimes uluru 570 320 ma innamincka 320 97 ma and potoroo 97 0 ma each regime a complex of uniform plate tectonic and palaeo climatic events at a similar or slowly changing latitude generated a depositional sequence of distinct facies bounded by unconformities at the margins and by stratigraphic gaps in the interior the uluru sequence in the interior is dominated by low latitude shallow water including marine carbonate deposits the innamincka sequence by high latitude non marine including glacial deposits and the potoroo sequence by increasingly lower latitude deposits confined almost wholly to the margins on the east a change from chilean to mariana type subduction marked the boundary between the innamincka and potoroo regimes the australian regimes resemble those of the other gondwanaland fragments and in particular the innamincka resembles the gondwana sequence of peninsular india the gondwanaland regimes in turn reflect those that pertained in the rest of the globe as part of two phanerozoic super cycles each ca 400 ma long the first palaeozoic early mesozoic the second late mesozoic cenozoic each reflects a cycle of mantle convection expressed through time variation in plutonism and hence in the concentration of atmospheric co 2 and in greenhouse icehouse effects in continental dispersion aggregation pangaea and eustatic sea level and in sediment type from marine platform sediment during high sea level to non marine during low sea level

the paranapanema lithospheric block its importance for proterozoic rodinia gondwana supercontinent theories abstract this work considers the tectonics of the southeastern portion of the south american platform based on new geological and geophysical grounds for the last decade only three amazonic sao francisco and la plata of the many other cratonic blocks have been attributed remarked to the south america portion for most of the usual rodinia reconstitutions the possibility of the existence of other blocks has rarely been mentioned the postulation of the presence of a considerable paleoproterozoic pre brasiliano fragment as part of parana basin basement is highly probable in order to infer the basement structure of parana basin previous to the sedimentation process an isostatic modeling was applied to a large scale gravity survey looking to correlate topographic and gravity anomalies caused by sub surface loads the bouguer anomaly obtained from the gravity survey represents the crustal contribution of crystalline basement in addition to the sedimentary and volcanic layers of the basin following the isostatic modeling and the basin load stripping the residual anomaly allows observing similarities between the basement gravity signature and outcropping units besides the stress pattern of the two earlier events obtained through the back stripping analysis presents a geographically coincident maximum and a new e se high emerging for the second event suggesting continuous change of the stress field as a precursor for south american plate rotation the evident correlation between gravity highs and main attenuation suggests the presence of some pre existing suture zones the weakened lithosphere during ordovician and carboniferous provided the magma conduits to form in early cretaceous tectonic stress field pattern the resultant mosaic of gravity blocks and the main faults site give support to the presence of this cratonic proterozoic unit here on referred to as the paranapanema block which had been neglected in most of the models reported for the reconstruction of gondwana and rodinia

middle late triassic 230 5 ma singularity in the stratigraphic and magmatic history of the pangean heat anomaly the phanerozoic history of continental dispersal and coalescence contains an epoch of radical change at about the middle late triassic boundary 230 5 ma marked by 1 the final coalescence of pangea by the contact of south china and cimmeria with laurasia and terminal compressive deformation in australia and southern africa and 2 the incipient dispersal of pangea by the onset of continental rifting in eastern north america and northwest africa argentina east africa and western australia this epoch of coalescence and incipient dispersal correlates with a change from 1 an icehouse state to a greenhouse state and 2 changes from a fall to a rise in the sea level curve in the emplacement of north american granite and in the cumulative curve of reversed to normal magnetic polarity these changes are interpreted as indicating the first major loss from the heat accumulated beneath pangea now represented by the atlantic african geoid high

tectonic climatic supercycle in the billion year plate tectonic eon permian pangean icehouse alternates with cretaceous dispersed continents greenhouse abstract the earth alternates in a supercycle 400 m y long from a single continent pangea and ocean panthalassa with an icehouse climate to many continents and oceans with a greenhouse climate the supercycle is driven by the heat that accumulates beneath the insulator of pangea and the greenhouse is made by the excess co2 vented from the mantle during the faster rate of plate activity in the current supercycle a since the mid carboniferous 320 ma the growth and decay of pangean heat is observed in globally synchronous cratonic sedimentary sequences that represent in ascending order 1 a stratigraphic gap 2 sagging 3 rifting 4 fast and 5 slow seafloor spreading stages 4 and 5 of the previous supercycle b are observed back to the start of the phanerozoic in the proterozoic earlier stages of b are postulated back to 720 ma and a third supercycle c to 1100 ma the big glaciations of the latest proterozoic 700 600 ma and late palaeozoic 320 260 ma are confined to the icehouse state during stages 1 3 the sturtian 800 ma latest ordovician 440 ma and quaternary 2 0 ma glaciations fall within greenhouse states during stage 5 of slow seafloor spreading the next icehouse glaciation is expected 80 ma hence the problem of long term past and future climate change is soluble by global studies urgently needed are 1 global stock takes of a the rate of granite emplacement which serves as a proxy via plate activity for the mantle source of atmospheric co2 and b carbonate sinks and other sedimentary indicators of co2 and 2 the extension of the sea level curve back past 570 ma to the start of the plate tectonic eon 1100 ma ago from such studies environmental baselines for past climatic states can be drawn for gauging present and future background variations

quantifying extension of passive margins implications for sea level change 1 passive margins form by rifting and extension of continental crust extension of continental crust associated with subduction elsewhere decreases ocean basin volume forcing sea level to rise the amount that the continental crust has been extended can be quantified using total tectonic subsidence which is determined using sediment thickness and water depth data coupled with a model of the rifting process we calculate total tectonic subsidence the amount of extension or stretching factor and thickness of extended continental crust at a 5 min grid resolution for passive margins between 77 n and 70 s our modeled crustal thicknesses correlate well with seismic refraction data from north america and australia and can be used to estimate the change in ocean volume and the impact of extension on sea level the duration of extension is constrained by estimating the onset of rifting and the breakup age which is the time when rifting ceased and seafloor spreading began our results indicate that extension of continental crust has increased sea level by 20 8 m since the start of pangea rifting

the carnian pluvial event in western europe new data from iberia and correlation with the western neotethys and eastern north america nw africa regions abstract at the beginning of the late triassic a period of increased precipitation occurred over large tracts of central pangea the carnian pluvial event it was a short lived event 1 ma coeval with a marked sea level fall and active rifting new and classical sections of carnian age in the iberian peninsula have been studied and a new correlation scheme is proposed for the iberian domain integrating field data and subsurface electric log data this is the first time that the portuguese and spanish late triassic carnian sediments are correlated the carnian pluvial event is identified in the iberian peninsula as a continental clastic wedge manuel fm and coeval sediments in between marine evaporite formations during a marked sea level drop event its age is considered to be julian early carnian by palynological and paleogeographic considerations a new correlation of the late triassic sediments of the iberian peninsula with coeval sediments of western europe nw africa and eastern north america is proposed and a new paleogeographical map of central eastern pangea for this period is presented in order to demonstrate that the geographical extent of the siliciclastic sediments related to the carnian pluvial event was much larger than accepted before

analysis of long term variations in the geomagnetic poloidal field intensity and evaluation of their relationship with global geodynamics summary the 1167 published cooling unit cu palaeointensity estimates contained in the 400 10 ma portion of the pint global database were rigorously filtered according to accurate age determinations palaeodirectional reliability recognition of polarity and the method of palaeointensity acquisition the remaining 865 estimates group 1 were further filtered to ensure self consistency reducing the data set to 425 estimates group 2 group 1 and 2 data were clustered into temporally and or spatially distinct rock suites rs enabling each part of the record to be assessed for potential biasing by overrepresentation of palaeosecular variation psv the record was segmented according to the distribution of the data rather than using arbitrary time windows to ensure quasi consistent behaviour within each segment differences between these segments clearly indicate that a significant long timescale 10 7 and 10 8 yr variation of the mean geomagnetic poloidal field intensity gpfi occurred during the 400 10 ma period and hence that changing lowermost mantle conditions affect the capacity of the geodynamo to generate a poloidal field both the mean dipole moment and its standard deviation appear to be a function of the range of values each cu may adopt at one particular time this range is itself controlled by the variation of the maximum limit of dipole moment while the value of the minimum limit remains relatively constant tentative support is provided for the recent suggestion that psv may have been reduced during the cretaceous normal superchron cns though more data are needed in the range 120 60 ma to confirm this no conclusive evidence was found to support the suggestion that the gpfi record may be biased towards low or high values by palaeointensity determinations obtained using methods that do not adopt ptrm checks indeed offsets caused by unreliable data in well represented parts of the record are likely to be random and cancel one another out when gpfi variation is analysed at a sufficiently high resolution to allow comparisons with the geomagnetic polarity reversal frequency rf it is not possible to confirm whether the two parameters are anticorrelated decoupled or related in some more complex way however it is clear that gpfi and rf are definitely not positively correlated as has been previously suggested the present database documents sharp increases in gpfi around the onset times of the two recognized superchrons itself implying an anticorrelation the implications for geodynamo and mantle modelling of both an anticorrelation and a decoupling of the geomagnetic parameters are discussed briefly a generic geodynamic model is proposed to explain the relationship between observed longterm changes in gpfi and global geodynamic processes the model predicts that changes in gpfi result from a chain of geodynamic processes extending from crust to core beginning with plate reorganizations at the surface and culminating in increases in the vigour of outer core convection supercontinents are transient surface expressions of such geodynamic processes and provide the potential to test the generic model four time stages are proposed to describe the major long term changes in gpfi since the early devonian 400 350 350 250 250 175

main stages of the development of the sedimentary basins of south america and their relationship with the tectonics of supercontinents abstract twelve main stages of sedimentary basins of the south american platform have been identified as follows one neoarchean seven proterozoic and four phanerozoic basin forming tectonics are related to the accretion fusion and fission of the major continental landmasses of the earth s history such as atlantica nena rodinia gondwana pannotia and pangea the first proposed stage of basin development precedes the formation of these major landmasses and was developed on mesoarchean microcontinents the last stage succeeds the fission of pangea and is still in progress

rapid earth expansion an eclectic view abstract paleobiogeography plate evolution and minor amounts of subduction require a rapidly expanding earth during post triassic time not plate tectonics an asteroid impact at the p tr boundary in the congo basin ruptured the lithosphere and together with another impact in the carnian of arizona caused earth s volume to subsequently expand the increase in volume was likely due to inner core and lower mantle transformation growth at the expense of the fluid outer core a modified pacific reconstruction is proposed that closes up the pacific basin in the triassic and allows continents to cover a 55 radius earth some serious weaknesses in the plate tectonics theory are noted and tectonics by high energy impacts is discussed

the evolution of the lorraine evaporite basin implications for the chemical and isotope composition of the triassic ocean abstract during the upper triassic times about 75 m of halite with minor anhydrite was deposited in the lorraine basin samples of halite and sulfates were systematically collected from a borehole intersecting the sequence the chemical evolution of the original brine was investigated by x ray microanalysis of primary inclusions trapped in halite the original brines were of the na mg k ca cl type being consistent with the mineral association of halite and minor anhydrite their solute content can be reproduced by evaporation of present day ocean composition in an open basin however some modifications are required the inflow of a small excess of cacl 2 into the basin 1 2 to 1 9 of the total recharge is required to explain the low so 4 values analyzed in fluid inclusions the same inflow helps to explain more satisfactorily the low na and high cl contents the back reaction of the brine with previous ca sulfate that forms polyhalite could explain the low and variable k values analyzed the excess of ca with respect to present day seawater and the formation of so 4 poor evaporite sequences is the rule rather than the exception in the geological record we have not been able to assess the ultimate origin of the ca excess in the basin nevertheless the great variation of the so 4 content within short vertical distances centimeter scale suggests that these variations are due to processes taking place within the evaporite basin rather than to changes in the composition of the ocean at a global scale the isotopic composition of sulfur and oxygen was determined using samples of sulfates from the same borehole the 34 s values of 21 samples analyzed show a narrow variation 34 s 15 5 0 4 the 18 o values of eight samples analyzed show a wider range of variation 18 o 13 0 1 1 none of the processes which modify the values such as sulfate reduction or additional sulfate sources continental recycling of sulfates from the margins were clearly identified the values of 34 s sw 15 7 to 14 5 and 18 o sw 13 7 to 12 2 for the sulfate dissolved in the triassic ocean explain the values of the sulfates interbedded in the halite of the lorraine basin and most analyses reported in the literature

magellan and comparative planetology magellan data have been widely used to provide explanations for the tectonics and volcanism on venus however it is also important to compare our understanding of these processes on venus with the earth moon and mars one essential question concerning the behavior of these bodies is how does the heat get out internal heat generation and planetary cooling are the energy sources responsible for planetary tectonics and volcanism on the earth the plates of plate tectonics are the thermal boundary layers of mantle convection cells the subduction of these cold plates at ocean trenches contributes about 75 of the mantle heat flux it is now quite clear that active plate tectonics is not occurring on venus the surface of venus is a single rigid plate as is the case for the moon mars and mercury prior to magellan the general consensus was that venus was in a near uniformatarian state with conductive heat losses through the lithosphere balancing internal heat generation and secular cooling of the planet however crater studies from magellan images provide direct evidence for a catastrophic or episodic evolution of venus one explanation is that venus died tectonically 500 m y ago plate tectonics occurred during the early evolution of the planet but ceased as the radioactive heat production decreased an alternative explanation is that venus experiences episodic global subduction events two major questions concerning the earth remain largely unanswered particularly when compared with venus 1 why does the earth have continents 2 why does the earth have plate tectonics a major difference between the earth and venus is the presence of liquid water oceans during much of the evolution of the earth it has been hypothesized that water is an essential ingredient for the silicic volcanism that produces continental rocks on the earth and the absence of well defined continental masses on venus supports this hypothesis it has long been recognized that plate tectonics cannot evolve in time without internal deformation of plates plate evolution in time results in geometrical incompatibilities that require overlaps or gaps on the earth these incompatibilities lead to broad zones of continental deformation i e the western united states and china the absence of plate tectonics on venus suggests that rheologically soft continents are necessary for plate tectonics a reasonable conclusion is that the earth is the remarkable planet in terms of tectonics and volcanism not venus

crustal thermal regime prior to during and after rifting a geochronological and modeling study of the mesozoic south alpine rifted margin an approximately 15 km thick segment of the mesozoic passive continental margin of adria was involved in alpine shortening and is now exposed in the lake como lake lugano area southern alps northern italy and southern swit zerland the segment comprises the monte generoso basin a deep 9 km extensional basin controlled by the activity of the lugano val grande normal fault the paleosurface and mesozoic geometric relations are well preserved so that the kinematics of fault blocks prior to during and after extension are well constrained rb sr 4oar 39ar and zircon fission track data from basement rocks underlying at various the generoso basin depths provide independent estimates on the thermal evolution of the crustal segment during and after rifting most rb sr and 4oar 39ar ages are contemporaneous with the initial stages of rifting late triassic to early jurassic documenting 1 strongly altered thermal conditions before the onset of ex tension and 2 cooling throughout rifting thermal gradients decreased from 60oc km at the onset of extension to 20oc km 4 shortly after breakup zircon fission track ages are juras sic to early cretaceous providing evidence for continued cooling until the beginning of alpine shortening thermoki nematic numerical modeling of the considered crustal segment provides a full two dimensional description of synrift and postrift evolution synthetic time versus temperature curves are extracted from the model and compared with those derived from absolute ages

permian 87sr 86sr chemostratigraphy from carbonate sequences in south china abstract a continuous strontium isotope profile with high resolution sampling is desirable to calibrate multiple global events realize temporal correlation among different continents and understand tectonic history of the permian period in this paper we analyzed 90 micritic limestone samples from south china and 7 samples from iran with the aim to gain new 87sr 86sr data and obtain a curve of sr isotopes for the permian the concentrations of mg fe mn and sr are used to discriminate possible diagenesis of the samples a comparison of those 87sr 86sr values between south china and southern urals confirms that sr isotope proxy has the potential to be used for time calibration and correlation in regions where biostratigraphic or radiometric markers are not available the 87sr 86sr curve obtained in this study shows a trend comparable with the locally weighted scatterplot smoothing lowess regression curve from the previous studies a continuous decline trend from the latest carboniferous to late guadalupian was shown and the lowest 87sr 86sr values in the late capitanian was constrained within the interval from the conodont jinogondolella shannoni j altudaensis to j xuanhanensis zones it is followed by an increasing trend to more radiogenic values in the lopingian with a minor fluctuation in the early wuchiapingian we consider that mid ocean ridge spreading and increasing continental weathering during the transition from convergence to the breakup of pangea as the dominant factors driving the changes of the seawater sr isotope ratios

stratigraphy and morphotectonics of karoo deposits of the northern selous basin tanzania late permian karoo deposits of the northern selous basin in south central tanzania comprise conglomerates and diamictitic boulder beds of alluvial and scarp foot fan origin these merge with grey to greenish sandstones siltstones and black shales of deltaic and lacustrine environments microflora assemblages indicate a late permian age lateral changes and interfingering of various lithofacies units are common depositional development was controlled by syndepositional faulting and variations of gradients resulting from fault movements the position of the fault scarp separating the basin area from the elevated basement horst to the west roughly corresponded with the present boundary between the selous basin and the precambrian metamorphics of the uluguru mountains the late permian karoo succession of this part of the selous basin apparently overlaps older karoo deposits contained in the north northeast trending narrow graben structures it is therefore regarded as a new depositional event which was initiated by renewed tensional tectonism in late permian time during this tectonic episode the narrow early karoo graben structures were expanded into much broader rift basins material eroded from the rift shoulders and associated highlands was literally dumped across the fault scarps forming debris aprons and scarp foot fans rivers emanating from the highlands formed large alluvial fans and further afield deltas issued into freshwater lakes some of these late permian faults were rejuvenated by late cretaceous to early tertiary tectonism thermal waters circulating along fractures converted feldspars biotites and hornblendes to prehnite further tectonic adjustments in mid tertiary time led to the present day morphology

analcimic zones in the tertiary of anatolia and their geological positions abstract the anatolian tertiary and especially the neogene have some geological series with analcime as the principal rock forming mineral sedimentation basins receiving material in suspension and in solution permit the authigenesis of analcime dolomite calcite and opal c t analcimes formed by hydrothermal alteration on the ocean floor after the pillow lava and diabasic dyke complexes of ophiolites can form a source of detrital analcime when they are on the continental medium continental alteration of the pillow lavas and diabasic dykes permits the formation of solutions suitable in composition for analcime authigenesis analcimes formed in these environments are particularly related to the silica content of these media principal clay minerals formed with analcimic formations are smectites and 14 s 14 c mixed layers illite chlorite and corrensite are also present in smaller quantities

comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the mesozoic of nw europe this paper reviews the opportunities and pitfalls associated with using clay mineralogical analysis in palaeoclimatic reconstructions following this conjunctive methods of improving the reliability of clay mineralogical analysis are reviewed the mesozoic succession of nw europe is employed as a case study this demonstrates the relationship between clay mineralogy and palaeoclimate proxy analyses may be integrated with clay mineralogical analysis to provide an assessment of aridity humidity contrasts in the hinterland climate as an example the abundance of kaolinite through the mesozoic shows that while interpretations may be difficult the mesozoic climate of nw europe was subject to great changes in rates of continental precipitation we may compare sedimentological facies mineralogy geochemistry indicators of palaeoprecipitation with palaeotemperature estimates the integration of clay mineralogical analyses with other sedimentological proxy indicators of palaeoclimate allows differentiation of palaeoclimatic effects from those of sea level and tectonic change we may also observe how widespread palaeoclimate changes were whether they were diachronous or synchronous how climate sea level and tectonics interact to control sedimentary facies and what palaeoclimate indicators are reliable

episodic burial and exhumation of the southern baltic shield epeirogenic uplifts during and after break up of pangaea cratons are conventionally assumed to be areas of long term stability however whereas precambrian basement crops out across most of the baltic shield palaeozoic and mesozoic sediments rest on basement in southern sweden and thus testify to a complex history of exhumation and burial our synthesis of published stratigraphic landscape analysis and new apatite fission track analysis data reveals a history involving five steps after formation of the extremely flat sub cambrian peneplain 1 cambrian to lower triassic rocks accumulated on the peneplain interrupted by late carboniferous uplift and exhumation 2 middle triassic uplift removed the palaeozoic cover along the south western margin of the shield leading to formation of a triassic peneplain with a predominantly flat relief followed by deposition of upper triassic to lower jurassic rocks 3 uplift that began during the middle jurassic to earliest cretaceous caused denudation leading to deep weathering that shaped an undulating hilly relief that was buried below upper cretaceous to oligocene sediments 4 early miocene uplift and erosion produced the south smaland peneplain with scattered hills 5 early pliocene uplift raised the miocene peneplain to its present elevation leading to reexposure of the sub cretaceous hilly relief near the coast our results thus provide constraints on the magnitude and timing of episodes of deposition and removal of significant volumes of phanerozoic rocks across the southern portion of the baltic shield late carboniferous middle triassic and mid jurassic events of uplift and exhumation affected wide areas beyond the baltic shield and we interpret them as epeirogenic uplifts accompanying fragmentation of pangaea caused by accumulation of mantle heat beneath the supercontinent early miocene uplift affected north west europe but not east greenland and thus likely resulted from compressive stresses from an orogeny on the eurasian plate early pliocene uplift related to changes in mantle convection and plate motion affected wide areas beyond north east atlantic margins

middle triassic paleosols and paleoclimate of antarctica abstract the lashly formation in the allan hills of southern victoria land antarctica is now at a latitude of 76 s and during the middle triassic was at least 70 s the combined evidence of fossil roots and soils indicates a paleoclimate unusual for such a high latitude temperate paleotemperature is indicated by roots logs and leaves of woody plants and the degree of chemical weathering and clay formation within the paleosols paleosols of the lashly formation are more like soils of southern sweden than those of either finland or southern europe silt infiltration structures around root traces and in cracks within the paleosols are evidence for a seasonally snowy climate but there is no evidence of ice wedges or other permafrost features in the paleosols other evidence of climatic seasonality includes well defined growth rings in fossil wood and abscission scars at the base of fossil leaves diverse broadleaf plants and noncalcareous paleosols indicate a humid climate with mean annual precipitation of about 1200 mm such a wet climate is anomalous for the interior of the supercontinent of pangea and such a warm and mildly seasonal climate is anomalous for such high latitudes this paleoclimatic anomaly may be a lingering effect of global greenhouse initiated at the permian triassic boundary paleoclimatic variables calculated here may be useful for recalibrating global paleoclimatic models for the middle triassic

time interval between volcanism and burial metamorphism and rate of basin subsidence in a cretaceous andean extensional setting 40ar 39ar ages were obtained from basaltic flows belonging to a 9 km thick sequence generated in an extensional ensialic setting of an arc back arc basin type during the early cretaceous and presently exposed along the coastal range of central chile the basalts have been affected by very low to low grade burial metamorphism mostly under prehnite pumpellyite facies age values obtained from primary volcanic and secondary metamorphic minerals permit to quantify the time interval between volcanism and burial metamorphism a plateau age of 119 1 2 ma from primary plagioclase represents the best estimation of the age of the volcanism whereas adularia in low variance assemblages contained in amygdules gave a plateau age of 93 1 0 3 ma which is interpreted as the age of the metamorphism considering the p t conditions estimated for this metamorphic event the c 25 ma time interval between volcanic emplacement and prehnite pumpellyite facies metamorphism the rate of basin subsidence in this extensional geodynamic setting would be comprised in the interval 150 180 m ma

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

episodic behavior of gondwanide deformation in eastern australia insights from the gympie terrane the mechanisms that drove permian triassic orogenesis in australia and throughout the cordilleran type gondwanan margin is a subject of debate here we present field based results on the structural evolution of the gympie terrane eastern australia with the aim of evaluating its possible role in triggering widespread orogenesis we document several deformation events d d in the gympie terrane and show that the earliest deformation d occurred only during the final pulse of orogenesis 235 230 ma within the broader gondwanide orogeny in addition we found no evidence for a crustal suture suggesting that terrane accretion was not the main mechanism behind deformation rather the similar spatiotemporal evolution of permian triassic orogenic belts in australia antarctica south africa and south america suggest that the gondwanide orogeny was more likely linked to large scale tectonic processes such as plate reorganization in the context of previous work our results highlight a number of spatial and temporal variations in pulses of deformation in eastern australia suggesting that shorter cycles of deformation occurred at a regional scale within the broader episode of the gondwanide orogeny similarly to the cenozoic evolution of the central and southern andes we suggest that plate coupling and orogenic cycles in the late paleozoic to early mesozoic gondwanide orogeny have resulted from the superposition of mechanisms acting at a range of scales perhaps contributing to the observed variations in the intensity timing and duration of deformation phases within the orogenic belt

glacial interglacial changes in dust deposition on the chinese loess plateau the chinese loess plateau clp contains an extensive record of aeolian deposition through multiple glacial interglacial cycles independent chronologies based on pedostratigraphy magnetic susceptibility radiocarbon and luminescence dating were developed for 79 sites and used to estimate aeolian mass accumulation rates mars for marine isotope stages 1 5 the regional median value of mar for stage 2 is 310 g m2 yr compared to an estimate of 65 g m2 yr for stage 5 estimated mars from individual sites for stage 2 are approximately 4 3 times greater than mars for stage 5 and 2 1 times greater than for stage 1 mar values at individual sites are consistently highest in the northwest and lowest in the southwest of the clp during all marine isotope stages mars estimated on sections through loess terraces are consistently higher than mar estimates at other sites indicating that local recycling of loess material from exposed river valley deposits has been significant throughout the last 130 kyr although the spatial and temporal patterns in mar are robust there are uncertainties about the magnitude of these changes due to a lack of bulk density measurements and uncertainties in the chronologies for individual sites b site and chronological biases in the sampling used to derive regional estimates and c the unquantified nature of human impact on accumulation rates during the late holocene nevertheless the records from the clp pose a number of challenges which could be addressed by numerical models of the palaeo dust cycle

climatic and biotic change in the late triassic generally arid conditions that pervaded much of europe and north america during the late triassic were interrupted by a wet monsoonal climatic phase during middle and late carnian times extensive fluviatile sandstones deposited at this time throughout the region occur within a thick sequence of playa lake mudstones the sandstones occasionally contain kaolinite suggesting a humid climate an extreme 13 c depletion in a shallow marine sequence of this age in israel has been interpreted as evidence for an influx of freshwater a widespread change from carbonates to clastics in marine sequences at this time may also be climate related water course cave systems in limestone areas exposed during the late triassic indicate high levels of runoff during the middle and late carnian the marine invertebrate fauna shows a significant turnover at the end of the early carnian the terrestrial fauna and flora were relatively unaffected at this time but subsequently diversified prior to a major biotic turnover at the carnian norian boundary these periods of biotic change appear to be synchronous with the onset and cessation of a carnian humid phase the change to a monsoonal climate during this interval has been documented over more than 90 of longitude between 5 and 50 north of the triassic equator it may have been caused by rising atmospheric co 2 levels due to volcanism associated with the incipient dispersal of pangaea

strontium isotope evolution of late permian and triassic seawater the 87sr 86sr values based on brachiopods and conodonts define a nearly continuous record for the late permian and triassic intervals minor gaps in measurements exist only for the uppermost brahmanian lower part of the upper olenekian and middle norian and only sparse data are available for the late permian these 219 measurements include 67 brachiopods and 114 conodont samples from the tethyan realm as well as 37 brachiopods and one conodont sample from the mid european middle triassic muschelkalk sea the late permian lower triassic interval is characterized by a steep 1 3 10 3 rise from 0 7070 at the base of the dzhulfian to 0 7082 in the late olenekian a rate of change comparable to that in the cenozoic in the mid triassic anisian and ladinian the isotope values fall to 0 7075 followed again by a rise to 0 7081 in the middle late norian the 87sr 86sr values decline again in the late norian sevatian and rhaetian to 0 7076 the sharp rise in the 87sr 86sr values during the late permian early triassic was coincident with widespread clastic sedimentation because of the paucity of tectonic uplifts the enhanced erosion may have been due to intermittent humid phases during mainly an arid interval coupled with the absence of a dense protective land plant cover following the mass extinction during the latest permian the apex of the 87sr 86sr curve at the olenekian anisian boundary coincides with cessation of the large scale clastic sedimentation and also marks the final recovery of land vegetation as indicated by the renewed onset of coal formation in the middle triassic the rising 87sr 86sr values from the middle carnian to the late norian coincide with the uplift and erosion of the cimmeride indosinian orogens marking the closure of the palaeotethys the subsequent rhaetian decline that continues into jurassic pliensbachian toarcian boundary on the other hand coincides with the opening of the vardar ocean and its eastern continuation in the izmir ankara ophiolitic belt samples from the upper muschelkalk are more radiogenic than the global trend this may reflect separation of the basin from the open ocean due to strong meteoric influx from a large land mass in the north the germanic basin became increasing brackish up section in the north and east but because of the high evaporation rates the salt content was not much reduced in the southern and central basin where a rich but increasingly endemic marine fauna survived