postapocalyptic greenhouse paleoclimate revealed by earliest triassic paleosols in the sydney basin australia the permian triassic boundary in the sydney basin of australia is coincident with a pronounced decrease in 13 c isotopic values of organic carbon the last coals anywhere in the world for all of the early triassic ca 6 m y time and extirpation of the glossopteris flora at the top of the illawarra and newcastle coal measures coal bearing paleosols of the latest permian represent extensive swamplands of the seasonally deciduous glossopteris flora in a humid cold temperate lowland southwest of an andean style volcanic arc stone rolls large ribs of floor rock up into the coal within some of the uppermost coals of the permian coal measures can be interpreted as string bogs of a kind now found in cold climates at latitudes of 68 70 which is compatible with a paleomagnetically estimated paleolatitude of 65 85 s for the sydney basin paleolatitude was not much different for earliest triassic time but paleosols of that age include inceptisols and entisols showing substantial chemical and textural weathering more like soils now forming at latitudes of 40 58 than those within polar circles this anomalous high latitude warmth set in at the permian triassic boundary sedimentation rates increased at the boundary marked by geochemically unusual acidification of clay and a dramatic carbon isotopic excursion these changes in environments and ecosystems can be explained by soil erosion following deforestation implied by the plant extinctions and abundant fungal remains at the permian triassic boundary evidence from paleosols can now be added to that from paleontological and isotopic studies showing that disruption of the carbon cycle at the permian triassic boundary resulted in a co 2 or ch 4 post apocalyptic greenhouse paleoclimate

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

changing fluvial environments across the permian triassic boundary in the karoo basin south africa and possible causes of tetrapod extinctions abstract the karoo supergroup is a 12 km thick succession of sedimentary rocks that accumulated in a large intracratonic retroarc foreland basin in southwestern gondwana the strata record 100 million years of almost continuous sediment accumulation from the permo carboniferous 300 ma through to the early jurassic 190 ma under a range of climatic regimes and within several tectonically controlled sub basins alluvial sediments dominate the succession from the late permian onwards fossils of synapsid reptiles and early dinosaurs are sufficiently common to be used in a ten fold biostratigraphic subdivision of these strata the permian triassic boundary in the karoo succession is marked by a major extinction of the herbivorous dicynodonts which co incides with a rapid change in fluvial facies this study uses field observations of the sedimentary facies palaeosols and in situ fossils of well exposed p tr boundary sequences in the southern karoo basin to provide evidence of environmental changes that may have caused the tetrapod extinctions in the main karoo basin below the p tr boundary sequence the sediments comprise drab greenish grey mudrocks with a few thick 3 12 m multistoried laterally accreted fine grained sandstone bodies the mudrocks host hydromorphic palaeosols with palustrine carbonate horizons and mostly disarticulated skeletal remains of dicynodon assemblage zone fauna above a transition zone of approximately 20 m thickness these strata change into reddish brown mudrocks with numerous thin 0 5 5 m ribbon sandstone bodies and more continuous sheet sandstones calcic palaeosols with rhizocretions nodular horizons and pervasive calcareous encrustation of articulated skeletons of lystrosaurus and associated fauna of the lystrosaurus assemblage zone within a 20 m thick interval of the transitional strata fossils of dicynodon and lystrosaurus occur together the facies transition that co incides with the latest permian dicynodont extinction is interpreted as a change in fluvial style from meandering to low sinuosity channels with general drying of the floodplain habitats and redistribution of vegetation belts the horsetails in particular became significantly reduced in areal distribution the changes in fluvial style in the karoo basin at the end of the permian were triggered by a pulse of thrusting in the southerly source area dated at 247 ma 2 ma which brought about rapid progradation of a large sandy braided fan system the katberg sandstone fm into the central parts of the basin a concomitant basinward migration of depositional environments allowed the lystrosaurus communities that were adapted to dry floodplains to colonise the entire basin to the detriment of most of the wet floodplain dicynodon fauna that lived there

multiple early triassic greenhouse crises impeded recovery from late permian mass extinction the late permian mass extinction was not only the most catastrophic known loss of biodiversity but was followed by unusually prolonged recovery through the early triassic opinion has been divided on whether delayed recovery was a legacy of especially profound ecological disruption or due to additional environmental perturbations new records from the sydney basin in southeastern australia now reveal five successive late permian and early triassic spikes of unusually high atmospheric co2 and profound chemical weathering these successive atmospheric co2 greenhouse crises coincided with unusually warm and wet paleoclimates for a paleolatitude of 61 s successive transient greenhouse crises punctuated long term cool dry and low co2 conditions and may account for the persistence of low diversity and small size in early triassic plants and animals

palaeoenvironments and faunal recovery after the end permian mass extinction abstract strata of the lower triassic werfen formation dolomites northern italy record deposition in a wide range of palaeoenvironments from peritidal to outer ramp settings this enables accurate assessment of faunal recovery following the end permian mass extinction by eliminating facies related effects extinction of the shelly taxa appears to be rapid and occurs in the latest permian tesero oolite horizon disappearance of the various trace fossil taxa appears to be more gradual following the extinction the lower and middle griesbachian are characterised by laminated sediments containing low diversity bedding plane assemblages ichnological geochemical and sedimentological data show evidence of widespread low oxygen conditions normally oxygenated waters return in the late griesbachian and there is a moderate increase in tiering above and below the surface macrofaunal and ichnofossil diversity decrease markedly during the smithian with the appearance of more terrigenous strata possibly reflecting an increased run off and more brackish conditions complete recovery begins in the basal spathian with an increase in tiering above and below the substrate crinoids and ammonoids appear for the first time in the werfen formation and the ichnogenus rhizocorallium re appears global correlation is hindered by poor biostratigraphy in the dolomites region however on a broad scale it appears as though many of the palaeoenvironmental changes are repeated worldwide current available data suggest that the re appearance of some trace fossil taxa e g diplocraterion rhizocorallium may be globally synchronous

long term cycles of triassic climate change a new δ18o record from conodont apatite jat and isw gratefully acknowledge financial support from the australian research council dp1096252 mr is grateful for financial support from progetto d ateneo 2009 cpda090175 09 and 2012 cpda 121100 and prin 2008 2008bef5z7 005

geologic interpretation of geothermal fluid movement in cerro prieto field baja california mexico a geologic model of the liquid dominated cerro prieto geothermal field was developed on the basis of geophysical and lithologic well logs the direction of subsurface geothermal fluid flow before exploitation and the geologic features controlling this movement were determined by integrating well completion and downhole temperature data with the geologic model the data show that fluid possibly heated by intrusive dikes found in wells drilled in the eastern area of the field enters the system from the east at depths 10 000 ft 3 050 m the fluid moves westward through sandstone beds and rises to shallow depths through fault zones and permeable sandy gaps in the overlying shale layers the shale layers provide local cap rocks some of the hot fluid reaches the surface west of the field in an area characterized by numerous geothermal manifestations the rest of the fluid mixes with colder ground waters west of the geothermal resource

the late holocene origin of the modern murray river course southeastern australia the modern course of the murray river flows south around the cadell tilt block in southeastern australia the avulsion that took the river in this direction formed the barmah choke a reach with an unusually straight planform this morphology has been used to argue holocene inertia of the modern river system the avulsion was initially placed at 10 ka on the basis of a single charcoal age optically stimulated luminescence osl and ams 14c dating of deposits along the barmah choke demonstrates that the murray has not been inert during this period a digitate delta deposited on the floor of a palaeolake by the avulsion is only 550 years old point bar deposition along the choke also began around this time the murray river probably followed the course of bullatale creek for most of the holocene it formed large inset meander scrolls of pleistocene kotupna type along this creek course but without source bordering dunes the persistence of kotupna type bedload along this course suggests that there wa

age and duration of the emeishan flood volcanism sw china geochemistry and shrimp zircon u pb dating of silicic ignimbrites post volcanic xuanwei formation and clay tuff at the chaotian section abstract the age and duration of the emeishan basalts sw china remain poorly constrained largely due to the severe thermo tectonic overprinting of the ar ar system and failure to obtain zircon separates from erupted basalts in an attempt to solve this problem geochemical analyses and shrimp zircon u pb dating have been carried out on rare felsic ignimbrite in the uppermost of the emeishan lava succession the xuanwei formation which immediately overlies the emeishan basalts and a clay tuff at the middle late permian boundary at the chaotian section clastic rocks of the lowermost xuanwei formation group 1 in eastern emeishan large igneous province lip have a geochemical affinity to the emeishan felsic volcanic rocks whereas the overlying sediments group 2 are compositionally more akin to mafic components of the emeishan traps this is the reverse of volcanic sequence of the central emeishan lip where the felsic extrusives sit above predominant mafic rocks it is likely that the clastic rocks are water transported sediments resulting from erosion of the volcanic rocks in the center of the emeishan lip this interpretation is further supported by the general agreement between the age of the lowermost xuanwei formation 257 4 ma 260 5 ma and that of the silicic ignimbrite 263 4 ma and the clay tuff at the middle late permian boundary at chaotian 260 5 ma these ages interpreted as the termination age of the emeishan volcanism are indistinguishable within error from the middle late permian boundary age 260 4 0 4 ma and the main stage 259 262 3 ma of the emeishan volcanism inferred from dating of mafic and alkaline intrusions in the emeishan lip all these suggest that the emplacement of the emeishan volcanism took place over a very short interval moreover the temporal link and geochemical analyses suggest that the chaotian clay at the middle late permian boundary was genetically related to the emeishan silicic volcanism this together with the fact at that both the emeishan basalts and the chaotian clay rest on the maokou formation leads us to infer that the emeishan basalt was emplaced at the middle late permian boundary in this sense the emeishan volcanism can be regarded as a boundary event and its age is presumed at 260 ma although more precise dating is required both stratigraphic correlation and chronologic data presented in this paper lend supports to the notion that the emeishan volcanism was one of likely causes of the end guadalupian mass extinction

sediment water interaction acidity and other water quality parameters in a subtropical setting pimpama river southeast queensland the geological setting and landuse activities of the pimpama river catchment are typical for many drainage systems in southeast queensland the river originates in coastal ranges of late paleozoic age crosses a floodplain developed during the late pleistocene holocene sea level fluctuations and flows into the southern part of the moreton bay the formation of sedimentary pyrite associated with the mid holocene transgression is an important feature of this coastal setting the oxidation and hydrolysis of pyrite and the consequent production of sulfuric acid are controlled by the amount and seasonality of rainfall and influenced locally by landuse activities the acid production and the leaching of dissolved metals from river alluvium and estuarine sediments impact substantially on land and aquatic habitats the water quality of the pimpama river and its tributaries reflects the lithology of the bedrock and can vary largely depending on season tidal regimes sediment lithology local topography and agricultural activities

last glacial to holocene evolution of semi arid rangelands in southeastern australia pollen sequences from playa lakes in the darling anabranch dunefields of southwestern new south wales record vegetation changes over the last glacial period and into the holocene this interval was one of marked taxonomic and structural reorganization with the plant communities that became established after the last glacial maximum lgm 24 18 ka distinct from those that had prevailed over the build up to full glacial conditions 70 24 ka the glacial period was characterized by a gradual reduction of woodland and tall shrubland cover recolonization of the dunefields involved a similar gradual succession from herbfields and low shrublands to tall shrublands and finally woodlands these changes are likely to have been driven by climatic change particularly fluctuations in temperature precipitation and atmospheric co2 as global climate systems entered and emerged from the last glaciation

early triassic recovery of the brachiopod faunas from the end permian mass extinction a global review abstract brachiopod faunas in lower triassic deposits from spitzbergen primorye of russia japan mangyslak of kazakhstan alpine europe the caucasus the middle east the himalaya south china new zealand and western usa are taxonomically and stratigraphically reviewed they comprise survivors of the end permian extinction and taxa originating in the early triassic origination of the mesozoic type taxa represents the recovery of early triassic brachiopods the initial recovery of brachiopod faunas began in the late griesbachian and the time interval between the end of extinction and the onset of the recovery of brachiopods is much shorter than previously suspected the early triassic recovery of brachiopod faunas is characterized by widespread brachiopod dispersal multiprovincialism and the presence of rare lazarus genera at that time taxonomic selectivity of the recovery brachiopod faunas favors the rhynchonellids the re population of post extinction brachiopods varies geographically there is a preference for regions either previously barren of latest permian taxa or regions where the pre extinction changhsingian and surviving brachiopods are very rare this unique biogeographic selectivity is probably partly responsible for the impoverished nature of brachiopod faunas in the triassic even mesozoic oceans five intervals of extinction survival survival recovery recovery dispersal and radiation are recognized based on variations in brachiopod faunas from the latest permian to the early triassic a dramatic reduction in brachiopod diversity at the end permian mass extinction is followed by several stepwise declines in diversity in the survival interval the time during which the surviving brachiopods are dominated by geographically widespread generalist faunas that adapted to a wide variety of environments the survival interval was followed by a slow re population of new lineages dominated by progenitor taxa

u pb zircon geochronology and tempo of the end permian mass extinction the mass extinction at the end of the permian was the most profound in the history of life fundamental to understanding its cause is determining the tempo and duration of the extinction uranium lead zircon data from late permian and early triassic rocks from south china place the permian triassic boundary at 251 4 0 3 million years ago biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the changhsingian pulse of the end permian extinction corresponding to the disappearance of about 85 percent of marine species lasted less than 1 million years at meishan a negative excursion in 13 c at the boundary had a duration of 165 000 years or less suggesting a catastrophic addition of light carbon

intrabasin variability of the carbon isotope record across the permian triassic transition sverdrup basin arctic canada abstract a major late paleozoic depocentre the sverdrup basin canadian high arctic has been largely left out of the latest permian extinction debate as early workers presumed middle to late permian strata were absent basin scale sequence stratigraphic and chemostratigraphic correlations indicate late permian strata are only missing on the basin margins where they were removed by sub triassic erosion whereas continuous deposition is recorded in the basin centre the varying degree of sub triassic erosion has significant impact on the carbon isotope record across the latest permian extinction event where both the apparent rate and magnitude of carbon isotope shift vary as a function of basin position the intrabasin variability in apparent 13corg shift across the event is equivalent to that observed globally in contrast to the abrupt isotope shifts recorded on the basin margin similar to many records reported globally the basin centre section shows a systematic shift associated with the latest permian extinction the earth likely underwent a prolonged period of increasing environmental stress leading up to the event

transient metazoan reefs in the aftermath of the end permian mass extinction microbes were thought to be the dominant reef constructors following the end permian mass extinction sponge microbe reef deposits formed in the early triassic from the western united states suggest that instead metazoan reef building continued immediately following the extinction wherever marine conditions allowed

changes in the global carbon cycle occurred as two episodes during the permian triassic crisis coeval records of ocean atmosphere and terrestrial change are crucial to understanding the pattern and causes of global mass extinction across the permian triassic boundary ptb however relationships among changes in different settings remain largely unclear primarily due to the challenges associated with the correlation among disparate records here we compare marine carbon isotopic records with marine and terrestrial environmental and biotic events recorded in sediments from the meishan ptb section of south china time scaled carbonate carbon isotopes exhibit two gradual major shifts across the ptb at meishan and these are duplicable elsewhere around the tethys ocean the two shifts are associated with two episodes of enhanced terrestrial weathering indicated by an increased abundance of 13 c enriched moretanes relative to hopanes and an elevated abundance of black carbon fragments key marine events previously reported for the ptb including photic zone euxinia faunal mass extinction and cyanobacterial expansion also occur as two episodes coinciding with both of the progressive shifts to negative 13 c values and enhanced weathering the temporal sequence of the duplicable events suggests that the biotic crisis was a consequence of prolonged and episodic changes in the marine and continental systems and argues against an extraterrestrial impact as the main cause

triassic climates state of the art and perspectives abstract the climate of the triassic period was characterized by a non zonal pattern dictated by a strong global monsoon system with effects that are most evident in the tethys realm this strong monsoonal regime is related to the aggregation of the pangaean supercontinent which by triassic time was already completed climate oscillations existed within this framework the harsh hot house climatic conditions that characterized the late permian and perhaps precipitated the end permian mass extinction were probably maintained during the early triassic and may account for the impoverished but distinctive faunal and floral lower triassic associations although metazoan reef builders were probably the most affected group carbonate production remained high at least in the western tethys realm the middle triassic was characterized locally by humid episodes although their geographical distribution has yet to be clarified the carnian pluvial event marks an episode of increased rainfall documented worldwide was the most distinctive climate change within the triassic different hypotheses have been proposed for its causes changes of atmospheric or ocean circulation driven by plate tectonics a peak of the global monsoon due to maximum continent aggregation or triggering by the eruption of a large igneous province subsequently the late carnian and norian seem to have been climatically stable although minor climatic changes have recently been described even from this time period finally the end triassic extinction event is also associated with climate change specifically warming and increased rainfall but this evidence comes mostly from the northern parts of the central atlantic magmatic province and the global pattern of climate change at the triassic jurassic boundary has still to be resolved many facets of triassic climate are intriguing and deserve further research however palaeoclimate studies on the triassic have so far been carried out only locally with different proxies those proxies will require inter calibration in order to depict correctly the temporal and geographical patterns of triassic climate

abundance anomalies of aromatic biomarkers in the permian triassic boundary section at meishan china evidence of end permian terrestrial ecosystem collapse several aromatic biomarkers detected in solvent extracts and kerogen pyrolysates from samples of the global stratotype section and point gssp for the permian triassic boundary at meishan china show distinctive relative abundance anomalies that may be related to the end permian biotic crisis on land enrichment of dibenzofuran homologues across the permian triassic boundary may corroborate the concept of excessive soil erosion following loss of rooted vegetation enrichment of alkylphenol entities occurs just below the main marine mass extinction horizon and prior to the characteristic end permian 13c decline the alkylphenols were probably derived from lignin and may provide a molecular record of dieback of woody vegetation highly decreased relative abundances of dibenzothiophenes could be indicative of excessive supply of fe2 it is suggested that fe2 was land derived and may have originated from soils in addition to the permian triassic boundary interval biomarker abundance anomalies also occur around the wuchiapingian changhsingian boundary in the basal part of the meishan section

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

estimation of long term diffuse groundwater discharge in the northern sahara using stable isotope profiles in soil water stable isotope profiles in soil water in the sahara have been interpreted in terms of the hydrologic processes taking place at one site where the water table is at about 10 m depth the isotope data are interpreted using the model of barnes and allison to show that the water loss by evaporation from the water table is about 2mm a 1 at another site nearby there is a net evaporative loss from the water table but the evaporation is interrupted by occasional infiltration events it is suggested that accumulation of chloride in soil water can give information about the onset of aridity in the sahara

hydrological and geochemical processes constraining groundwater salinity in wetland areas related to evaporitic karst systems a case study from southern spain abstract chemical and isotopic evolution of groundwater in an evaporite karst plateau including wetland areas and saline to hyper saline springs located at s spain was studied physicochemical parameters major ions and stable isotopes were analyzed in rain brine spring wetland and leakage water samples from which the most common mineral saturation indexes were computed and geochemical and isotopic modelling were performed results show an apparent relationship between the elevation of brine springs and their water mineralization indicating that drainage at higher altitude may be associated to gravity driven flows since brackish groundwater is isotopically fractionated due to evaporation on the other hand the lower altitude springs could drain deeper flows with longer residence time resulting in highly mineralized and warmer briny groundwater the dissolution of halite and gypsum has proved to be the main geochemical processes which are favored by the great ionic strength of groundwater calcite precipitation occurs in brackish waters draining wetlands being boosted by common ion effect when caso 4 waters are present and solute concentration caused by evaporation modelling results strongly support the hypothesis that most of the selected springs geochemically evolve in a common s n flowpath the methods used in this research contribute to a better understanding of the hydrogeological processes occurring in the studied evaporitic system but also in equivalent hydrological environments worldwide

the early triassic ammonoid recovery paleoclimatic significance of diversity gradients ammonoids recovered much faster than other marine shelly invertebrates after the end permian mass extinction based on a refined global data set at the basin level we investigate the paleobiogeographical global latitudinal and longitudinal diversity patterns in terms of climatic changes during the early triassic such analysis differs from already published qualitative or quantitative studies in that it estimates faunal patterns and endemicity at an ecologically meaningful level of spatial resolution i e at the basin level during the early triassic the global first order trend in increasing ammonoid diversity was accompanied by a progressive change from cosmopolitan to latitudinally restricted distributions this led to the emergence of a clear latitudinal diversity gradient during most of the smithian and spathian stages which entails increased steepness of the sea surface temperature gradient during the late early triassic however two brief episodes of ammonoid cosmopolitanism combined with low global diversity interrupted the first order increasing trend at the very beginning of the smithian and at its very end the longitudinal analysis of smithian distributions indicates a westward decrease of diversity within the tethys which faded away during the spathian analysis of endemicity indicates a rapid biogeographical maturing and structuring of faunas concomitant with the edification of the latitudinal diversity gradient

close up of the end permian mass extinction horizon recorded in the meishan section south china sedimentary elemental and biotic characterization and a negative shift of sulfate sulfur isotope ratio abstract the permian triassic p tr boundary beds of the meishan section south china have been re studied in detail based on complete samples across the p tr transition under the microscope the end permian mass extinction horizon is calibrated to a 12 mm stratal interval the top being 19 mm below the top of bed 24e of the changhsing formation this abrupt disappearance of skeletal fragments of major benthos characterizes the end permian extinction event suggesting a catastrophic event an abrupt decrease in the 34s 32s ratios of seawater sulfate is confirmed to coincide with the end permian event horizon the sulfur isotope event is thought to have been caused by an overturn of a stratified ocean dominated by h2s implying coincidence of the oceanic mixing and the mass extinction coincident siberian flood volcanism may have triggered a long term 103 years cooling leading an ocean mixing a presumed comet impact to the ocean could have directly caused ocean mixing and the mass extinction

the paleogeography of paleozoic and mesozoic storm depositional systems present day hurricane belts are confined to 5 45 latitude along the western edges of oceans whereas winter storms occur ubiquitously above 25 latitude both hurricanes and winter storms occur between 25 and 45 latitude in some areas storm zones can be identified on global paleogeographic maps with the assumption that this latitudinal zonation of storm systems existed in the geological past evaluation of 69 previously recognized paleozoic and mesozoic storm depositional systems on such maps showed that only 70 of them occur in ancient hurricane mixed hurricane and winter storm and winter storm belts the remainder occur on the western sides of continents and or at low paleolatitudes and therefore well may be of different origin mesozoic storm depositional systems containing hummocky stratification tend to occur in counterpart paleo winter storm belts whereas hummocky stratification in suggested paleozoic examples occur in both winter storm and hurricane belts and in paleolatitudes where we in

silicic magmas from the emeishan large igneous province southwest china petrogenesis and their link with the end guadalupian biological crisis abstract the emeishan large igneous province in sw china comprises a bimodal mafic silicic suite with the silicic rocks occurring at the uppermost part of the thick lava sequence the silicic rocks have an age of 257 263 ma and are thus roughly coeval with the guadalupian loping g l boundary event most silicic rocks trachyte and rhyolite from the emeishan province have rather uniform e nd values 1 to 2 9 that are comparable with the uncontaminated high ti basalts this fact and the remarkably narrow ranges of incompatible element ratios e g zr nb of the basalt silicic suite indicate a genetic relationship between basalt and silicic members the significant difference between the emeishan rocks and the experimental melts of hydrated basaltic crust suggests the fractional crystallization of basaltic magma rather than crustal melting as the major petrogenetic process for the formation of silicic rocks indeed their major and trace element trends can be modeled by fractionation of the observed mineral phases feldspar clinopyroxene fe ti oxide and apatite in contrast to the virtually closed system differentiation processes associated with trachytes the rhyolites may have experienced interaction with upper crustal material during ascent the geochemical characteristics and recent assessment of timing of the emeishan volcanism suggest the emeishan rhyolites as the potential source of the widespread clay bed at the g l boundary in south china this enhanced the causal link between the emeishan eruption and the end guadalupian biological crisis

paleocurrent evidence for lateral displacement of the pliocene colorado river delta by the san andreas fault system southeastern california more than 600 paleocurrent measurements from fluvial paleochannels of the early colorado river delta plain preserved in the palm spring formation in the fish creek vallecito fcv section of southern california indicate that the fcv section was on the gulf of california southeastern flank of the delta plain as recently as 2 8 ma these measurements imply 130 km of tectonic translation to the northwest since 2 8 ma which can be accounted for by the displacement histories of baja california and component faults of the san andreas system stratigraphic data from the fcv section and other neogene localities when plotted on a palinspastic base indicate 1 marine transgression of a narrow gulf of california rift basin and bouse embayment site of modern lower colorado river by 5 5 ma and 2 uplift of the bouse embayment initiation of the lower colorado river and southward progradation of the delta to essentially its present position by 4 ma

altered river morphology in south africa related to the permian triassic extinction the permian triassic transition in the karoo basin of south africa was characterized by a rapid and apparently basin wide change from meandering to braided river systems as evidenced by preserved sedimentary facies this radical changeover in river morphology is consistent with geomorphic consequences stemming from a rapid and major die off of rooted plant life in the basin evidence from correlative nonmarine strata elsewhere in the world containing fluvial permian triassic boundary sections suggests that a catastrophic terrestrial die off of vegetation was a global event producing a marked increase in sediment yield as well as contributing to the global 13 c excursion across the permian triassic boundary

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

rainfall patterns and the distribution of coals and evaporites in the mesozoic and cenozoic abstract paleoclimatologists have adequately demonstrated over the last twenty years that the distribution of climatically sensitive sediments can be related to present day climatic zones that are roughly parallel to latitude for example coals were deposited at paleolatitudes that correspond to the present day rainy zones at the equator and at about 55 n and 55 s indicating that those zones were present in the past from this it can be concluded that atmospheric circulation has not been radically different from its present configuration despite some apparently great differences in some climatic parameters such as the equator to pole temperature gradient nevertheless the zonal model for predicting the distribution of climatically sensitive sediments is not wholly adequate although general atmospheric circulation may not have been radically altered from its present pattern it would have differed in some respects because the paleogeography was different from the present geography therefore we have constructed what we believe are more realistic maps of the distribution of rainfall through time these maps are based on maps of atmospheric circulation that have been successfully used to predict the distribution of some petroleum source beds and phosphorites we have compared the predicted distribution of rainfall to the distribution of coals and evaporites for each of seven geologic stages the circulation rainfall maps were more successful than the zonal model for predicting the distribution of evaporites and coals for times when the paleogeography would have maximized the development of a monsoonal circulation which most effectively disrupts the general zonal pattern for times when a monsoonal circulation would not have been important the zonal model adequately predicted the distribution of these rocks

detailed correlation and age of continental late changhsingian and earliest triassic beds implications for the role of the siberian trap in the permian triassic biotic crisis abstract conchostracan rich beds between the siberian trap flood basalts and within the thick underlying hungtukun tuffs of the tunguska basin can be closely correlated with conchostracan faunas of dalongkou nw china and the germanic basin the germanic basin faunas in turn can be closely correlated with the marine international stratigraphic time scale and the accuracy of the biostratigraphic correlation of the permian triassic boundary ptb is confirmed by a minimum in 13ccarb values at this level these high resolution correlations demonstrate conclusively that the ptb is located within the temporally brief but thick siberian trap flood basalt sequence the ptb lies slightly above the level of the main permo triassic extinction event in low latitude marine beds which occurred at the base of the c meishanensis h praeparvus conodont zone and correlates with the beginning of the siberian trap flood basalt event the main end permian continental extinction event was somewhat earlier within the middle of the c changxingensis c deflecta conodont zone this horizon marks a mass extinction that devastated a diverse conchostracan fauna and left only low diversity faunas at low and high latitudes this continental extinction event horizon lies within the middle of the hungtukun tuffs of the tunguska basin and 107 m above the base of the guodikeng formation at dalongkou nw china a triassic type pioneer flora with numerous lycopod spores appears immediately above this level severe high northern and southern latitude marine extinctions occurred concurrently with this continental event but low latitude marine biota was not then affected this earlier event is best explained by global warming the main low latitude extinction event in marine warm water faunas occurred somewhat later and left no signature in high latitude marine faunas or in continental faunas but it does coincide with a rapid collapse of tropical rain forest environments disappearance of the highly diverse gigantopteris flora this collapse likely was caused by global cooling due to a volcanic winter event

rapid and synchronous collapse of marine and terrestrial ecosystems during the end permian biotic crisis a newly studied permian triassic p tr boundary section in jameson land east greenland contains an abundant and well preserved marine fauna as well as terrestrial palynomorphs for the first time it is possible to compare the biotic crises of the marine and terrestrial realms using the same samples from the same section the sediments record a negative excursion in 13 c carb values of 8 9 and in 13 c org values of 10 11 the presence of the conodont hindeodus parvus combined with the 13 c carb record enables correlation with the proposed global stratotype section at meishan this shows that the greenland section is the most expanded p tr section known collapse of the marine and terrestrial ecosystems took between 10 and 60 k y it took a further few hundred thousand years for the final disappearance of permian floral elements collapse of the terrestrial and marine ecosystems began at the same stratigraphic level and preceded the sharp negative excursion in the 13 c record

late early triassic microbial reefs of the western united states a description and model for their deposition in the aftermath of the end permian mass extinction abstract research in the western united states to reinvestigate and characterize the previously reported stromatolites of the latest early triassic spathian virgin limestone member of the moenkopi formation has shown that these microbial build ups formed patch reef mounds detailed field analysis of these reef mounds and the surrounding beds has established that they attained 1 2 m of topographic relief above the seafloor a petrographic study of these microbial mounds illustrates that they consisted of microbial fabrics as well as voids with early marine cements and formed in the absence of in situ metazoans these reef mounds formed during the aftermath of the end permian mass extinction that spanned the early triassic due to the devastation of marine metazoans at this extinction the early triassic has often been deemed a reef gap because no metazoan reefs are found at this time whereas colonial metazoan reefs are globally absent from lower triassic strata microbial build ups similar to these described from the western united states have been found in south china armenia southern turkey and greenland a regional early permian to late early triassic unconformity exists in the study region however analysis of these microbial reefs within a global context suggests that conditions favouring microbial reef development must have existed as long as 4 8 m y after the end permian mass extinction a depositional model of these microbial mounds indicates that flooding of the shelf with anoxic and or co2 rich deep waters may have fostered their occurrence

δ13c depth profiles from paleosols across the permian triassic boundary evidence for methane release stable carbon isotopic analyses of organic carbon 13 c in individual paleosol profiles from permian triassic sequences of antarctica reveal systematic isotopic variations with profile depth these variations are in many cases analogous to those in modern soils which are functions of redox conditions soil development and degree and type of microbial decay in modern soils these isotopic depth functions develop independently from vegetation changes c 3 versus c 4 vegetation and can be diagnostic of soil orders this study shows that soil intrinsic functions can be preserved in the 13 c values of paleosols as old as 260 ma and constitute valuable data for paleoecological interpretations a large carbon isotopic offset of as much as 10 in whole paleosol profiles across the permian triassic boundary indicates significant changes in the soil biogeochemistry and the soil atmosphere system early triassic paleosols are distinctive in their extremely low 13 c values to 42 and often show an anomalous 13 c depth distribution compared to both permian paleosols and modern soils highly depleted 13 c values as the ones in early triassic paleosols are suggested to be associated with microbial methane oxidation methanotrophy this hypothesis implies increased methane concentrations in the early triassic soil atmosphere system increased atmospheric methane was probably partly responsible for the global carbon isotopic shift documented in marine and terrestrial sediments across the permian triassic boundary

hydrogeochemistry and pollution assessment of quaternary tertiary aquifer in the liwa area united arab emirates this study presents the data on the hydrochemical characteristics and isotope chemistry of liwa aquifer which could be useful to clarify the hydrochemical facies and hydrogeological regime in the study area electric conductivity and total dissolved solid values show that the investigated water is slightly brackish due to the effect of evaporation and the occurrences of evaporite rocks in the adjacent sabkhas of abu dhabi major cations and anions arranged according to their decreasing concentrations are na ca 2 k mg 2 and cl hco3 so4 2 respectively as sodium is the dominate cation and chloride is the prevailing anion hydrochemically the groundwater of liwa can be classified as na cl rich predominantly chloridic ion concentrations increase towards the northeast and presumably coincide with the lithological sources of ions factors affecting the hydrochemistry of the groundwater of the investigated area include the effect of weathering of soil and rocks evaporation and agricultural activities stable isotopes of oxygen and hydrogen show that the shallow aquifers contain a single water type that originated in a distinct climatic regime this water type deviates from the local meteoric water line as well as from the eastern mediterranean meteoric water line suggesting potential evaporation of recharged water prior to infiltration the waters are poor in tritium and thus can be considered generally as indication for recharge prior to 1952 the degradation of groundwater quality can be attributed to evaporation and agricultural practices in most cases

catastrophic dispersion of coal fly ash into oceans during the latest permian extinction the eruption of the siberian trap flood basalts resulted in the heating and combustion of coals and organic rich sediments at the time of the permian mass extinction the presence of char in distant lake sediments linked to the eruption suggests that fly ash could have been generated by the coal combustion and then dispersed globally creating toxic marine conditions

groundwater geochemistry of the chihuahua city region in the rio conchos basin northern mexico and implications for water resources management the chihuahua city region located in the semiarid arid northern highlands of mexico has experienced intensive groundwater abstraction during the last 40 years to meet water demands in the region a geochemical survey was carried out to investigate the evolution from baseline to modern conditions of a 130 km flow path including the el sauz chihuahua aldama san diego de alcala regions the research approach included the use of major chemical elements chlorofluorocarbons and environmental isotope 18o 2h 13c and 14c tracers stable isotopes indicate that groundwater evolves from the evaporation of local rainfall and surface water groundwater located at the lower end of the flow section is up to 6000 years old and older groundwater in the order of 9000 years bp was found in a deep well located in the upper part of the flow system implying contribution from a neighbour basin the background groundwater chemistry upstream of chihuahua city results from feldspar weathering beyond chihuahua city the chemical conditions are strongly modified owing to disposal of sewage from public and industrial water supplies into the rio chuviscar subsequent allocation of this water to agricultural irrigation areas and direct infiltration under the river bed as a consequence anions like chloride and sulphate are mainly related to surface sources nitrate is controlled in part by sewage from public supply and industry and in part by agricultural practices arsenic and fluoride are related to weathering of rock formations of local mineralized ranges and subsequent enrichment of the basin fill by magmatic processes the results of this study have implications for groundwater management in an arid region that depends entirely on groundwater for domestic industrial and agricultural water consumption copyright 2008 john wiley sons ltd

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

stable isotopes of carbon from basaltic rocks and their possible relation to atmospheric isotope excursions abstract repeated short time negative excursions from the general trend of organic carbon isotopes occur at and shortly after the permo triassic and cretaceous tertiary mass extinctions the cause of these excursions is unexplained since an extinction event can only explain one excursion at each boundary at the p t boundary one negative excursion occurs shortly before the boundary proper followed by one at the boundary followed by several excursions that can be correlated in both marine and terrestrial environments over larger geographical distances also at the k t boundary negative excursions in organic carbon which can be correlated occur after the boundary in both marine and terrestrial settings as both mass extinctions occurred contemporaneously with major continental flood basalts the present study focuses on the possible effect of eruption of flood basalts on the atmospheric carbon isotopic budget the carbon isotopic compositions of forty different basalts from the time span of albian to the recent and predominantly continental flood were measured the isotopic composition of the co2 gas released by basalts is generally accepted as being rather heavy 5 pdb based on observations from hawaii this is in strong contrast to the observed values in this study which showed that the gas released had an average isotopic value of around 23 pdb acid digestion by hf left a residue of elemental carbon with isotopic values in the range of 24 to almost 28 pdb this corresponds to the carbon released during stepped heating experiments in the temperature range from 200 to 600 c since basalt in a molten state has a temperature of 600 c and since the most negative carbon i e the elemental carbon is released below that temperature it suggests that the most isotopically negative component is not present as elemental carbon above temperatures of 600 c in view of the recorded isotopic composition of 24 for gas collected at a temperature between 700 and 800 c from mauna loa it seems that the generally assumed 5 is unrepresentative for flood basalts it is therefore possible that high intensity volcanic episodes have caused the repeated negative excursions it is further suggested that the short time non secular isotopic variation pattern of organic carbon through time may be a record of volcanic activity the episodic nature of volcanism precludes it from being causally related to the secular variations elemental carbon from four different kimberlites yielded carbon isotopic values similar to those from basalts it is suggested that the boudouard reaction 2co c co2 may be responsible for the formation of the elemental carbon

growth and demise of permian biogenic chert along northwest pangea evidence for end permian collapse of thermohaline circulation abstract the permian chert event pce was a 30 ma long episode of unusual chert accumulation along the northwest margin of pangea and possibly worldwide the onset of the pce occurred at about the sakmarian artinskian boundary in the sverdrup basin canadian arctic where it coincides with a maximum flooding event the ending of high frequency high amplitude shelf cyclicity the onset of massive biogenic chert deposition in deep water distal areas and a long term shift from warm to cool water carbonate sedimentation in shallow water proximal areas a similar and coeval shift is observed from the barents sea to the northwestern usa a landward and southward expansion of silica factories occurred during the middle and late permian at which time warm water carbonate producers disappeared completely from the northwest margin of pangea biotically impoverished and increasingly narrow cold water carbonate factories characterised by non cemented bioclasts of sponges bryozoans echinoderms and brachiopods were then progressively replaced by silica factories by late permian time little carbonate sediments accumulated in the barents sea and in the sverdrup basin where the deep to shallow water sedimentary spectrum was occupied by siliceous sponge spicules by that time biogenic silica sedimentation was common throughout the world silica factories collapsed in the late permian abruptly bringing the pce to an end in northwest pangea the end permian collapse of the pce was associated with a major transgression and with a return to much warmer oceanic and continental climatic conditions chert deposition resumed in the distal oceanic areas during the early middle triassic anisian after a 8 10 ma interruption early triassic chert gap the conditions necessary for the onset expansion and zenith of the pce were provided by the thermohaline circulation of nutrient rich cold waters along the northwestern and western margin of pangea and possibly throughout the world oceans these conditions provided an efficient transportation mechanism that constantly replenished the supply of silica in the area created a nutrient and oxygen rich environment favouring siliceous biogenic productivity established cold sea floor conditions hindering silica dissolution while increasing calcium carbonate solubility and provided conditions adverse to organic and inorganic carbonate production the northwest margin of pangea was for nearly 30 ma bathed by cold waters presumably derived from the seasonal melting of northern sea ice the assumed engine for thermohaline circulation this process started near the sakmarian artinskian boundary intensified throughout middle and late permian time and ceased suddenly in latest permian time it led to oceanic conditions much colder than normally expected from the palaeolatitudes and the influence of cold northerly derived water was felt as far south southern nevada the demise of silica factories was caused by the rapid breakdown of these conditions and the establishment of a much warmer marine environment accompanied by sluggish circulation and perhaps a reduced input of dissolved silica to the ocean complete thawing of northern sea ice would have ended thermohaline circulation and led to warm and sluggish oceanic conditions inimical to the production accumulation and preservation of biogenic silica

triassic environments climates and reptile evolution abstract a consideration of all the available data on triassic vertebrate faunas and their stratigraphic location reveals a relatively sudden extinction event among the last of the mammal like reptiles and the herbivorous rhynchosaurs in the norian of the upper triassic this event was apparently quickly followed by the radiation of the dinosaurs also in the norian this conclusion suggests that competition was not the main factor in the initial success of the dinosaurs but opportunistic radiation following the extinction of major reptile groups a global review of triassic sedimentary facies shows that there were climatic and floral changes towards the end of the triassic it is envisaged that increasing aridity in the later triassic resulting from plate motions and particularly affecting gondwanaland and southwestern laurasia brought about floral changes and then the reptile extinctions with the rapid evolution of new floras of conifers and bennettitaleans the dinosaurs came to dominate all terrestrial faunas within the space of only a few million years

early triassic terrestrial tetrapod fauna a review abstract the permian triassic mass extinction ptme ca 252 mya was one of the most severe biotic crises of the phanerozoic eliminating 90 of marine and terrestrial species this was followed by a long period of recovery in the early and middle triassic which revolutionised the structure of both marine and terrestrial ecosystems triggering the new ecosystem structure of the mesozoic and cenozoic entire new clades emerged after the mass extinction including decapods and marine reptiles in the oceans and new tetrapods on land in both marine and terrestrial ecosystems the recovery is interpreted as stepwise and slow from a combination of continuing environmental perturbations and complex multilevel interaction between species in the new environments as ecosystems reconstructed themselves here we present a review of early triassic terrestrial tetrapod faunas geological formations and outcrops around the world and provide a semi quantitative analysis of a data set of early triassic terrestrial tetrapods we identify a marked regionalisation of early triassic terrestrial tetrapods with faunas varying in both taxonomic composition and relative abundance according to palaeolatitudinal belt we reject the alleged uniformity of faunas around pangaea suggested in the literature as a result of the hot house climate in addition we can restrict the tetrapod gap of terrestrial life in the early triassic to palaeolatitudes between 15 n and about 31 s in contrast to the earlier suggestion of total absence of tetrapod taxa between 30 n and 40 s there was fairly strong provincialism following the ptme according to cluster analysis of a taxon presence matrix entirely consistent with early triassic palaeobiogeography unexpectedly the overall pattern for early triassic terrestrial tetrapod faunas largely reflects that of the late permian suggesting that the recovery faunas in the early triassic retained some kind of imprint of tetrapod distributions according to palaeogeography and palaeoclimate despite the near total extinction of life through the ptme

lilliput effect in freshwater ostracods during the permian triassic extinction abstract the lilliput effect following the permian triassic mass extinction and its aftermath has been documented in a variety of marine animal groups but it is less known in terrestrial and freshwater invertebrates here we present new investigations of the size variations of terrestrial ostracods of the genus darwinula based on fossil records from a permian triassic section on the northern limb of the dalongkou anticline section in northwest china quantitative analyses reveal that ostracod test sizes decreased sharply through the terrestrial permian triassic mass extinction interval the lilliput effect in terrestrial ostracods is characterized by the extinction of large taxa and the rise of small sized and elongate new forms coupled with the dramatic loss of conchostracans charophytes and the blooming of lycopod spores the size decrease in terrestrial ostracods following the biotic crisis through the permian triassic interval was probably triggered by several interacting events including global warming anoxia and enhanced sediment input following acid rain and wildfire

an ecologic explanation for the permo triassic carbon and sulfur isotope shifts the boundary between late permian and early triassic stratigraphic sequences is characterized by the onset of a marked shift in the isotopic composition of both marine carbonates and sulfates the abrupt 3 decrease in the carbon isotope ratio of carbonates and the more gradual 5 increase in the sulfur isotope ratio of sulfates can be explained by changes in the nature of the earth s ecosystems induced by the massive permo triassic extinctions we propose that the continental ecosystem responsible for the preservation and burial of organic matter during permian time was disrupted and that the relatively efficient marine food web of permian time was replaced by a less efficient system which allowed for a greater fraction of the marine organic matter to reach the seafloor these changes were reflected by a major shift in the depositional environment for the reduced component of material accumulating in sediments during the permian organic carbon burial on the continents dominated whereas during the triassic deposition of organic carbon on the seafloor dominated allowing sulfides to become an important component of the reduced phase

brachiopod miniaturization and its possible causes during the permian triassic crisis in deep water environments south china abstract brachiopod miniaturization is both the reduction in size of individuals of a species over time and where one brachiopod fauna dominated by larger individuals was replaced by a brachiopod fauna dominated by smaller individuals over time this paper investigates this phenomenon prior to and during the end permian crisis in a deep water setting in south china based on precise measurements of brachiopod body size and on the abundance and diversity of brachiopod species the process of miniaturization near the permian triassic boundary in deep water environments is characterized by 1 larger species including martinia sp costatumulus dongpanensis and anidanthus mucronata reduced in average body size and abundance over time towards the end permian brachiopod extinction event 2 small species including attenuatella mengi and spinomarginifera semicircridge showed a mixed response with either no size change or a reduction in average body size while these species increased in abundance over time indicating they were less sensitive to the stressed environmental setting 3 both the total abundance and the diversity of this brachiopod fauna decreased over time towards the end permian crisis regression an increased input of terrestrial material and productivity decline are considered to all have contributed to brachiopod miniaturization based on the biotic replacement and changes in sea water chemistry among these factors the fall in sea level is perhaps the primary factor and led to a decline in productivity and an increased input of terrestrial material into the marine setting

the geochemistry and isotope hydrology of the southern mexicali valley in the area of the cerro prieto baja california mexico geothermal field abstract groundwaters from the phreatic aquifer within and surrounding of the cerro prieto geothermal field were analyzed geochemically and isotopically in order to establish a hydrodynamic model of the study zone which is located in the mexicali valley between 655 000 685 000 m e w and 3 605 000 3 576 000 m n s relative to utm coordinates based on their chemical composition three types of water were recognized chloride sulfate and bicarbonate however four groups of water were identified on a statistical multi variable method of cluster analysis a d the average temperature is 25 c with a few exceptions in the south where temperature can be as high as 47 c stable isotope ratios for some waters plot close to the world meteoric line corresponding to the original unaltered waters of the zone the hydrogeochemistry varies in relation to three principal processes evaporation infiltration of water used in agriculture and rock interaction by reaction with evaporitic deposits major quartz calcite and plagioclase and minor smectite kaolinite halite sylvite and gypsum were identified by x ray diffraction in lacustrine sediments of the central part of the zone chemical modeling indicates saturation with respect to calcite and undersaturation with respect to gypsum by incorporating chemical and isotope data into geological and isopotential well information a hydrodynamic model has been postulated in this hydrodynamic model the water a enters the study zone from the east and it is originally of the old colorado river water the water samples on which the model is based were draw from agricultural wells that intersected two aquifers a shallow and a deep one representing the recharge to the zone the salinity of the deep aquifer water b is lower than that of the shallow aquifer water c and so is the stable isotope ratio the difference is though to be due to dissolution of evaporates evaporation and possible infiltration of spent agriculture water both waters then pass through lacustrine sediments and gain in salinity and become isotopically heavier mainly by evaporation in a stagnate flow they eventually emerge as a saline water d in the central part of the study zone this saline water is the one that mixes with thermal fluid discharges from the geothermal reservoir in the south

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

consequences of siberian traps volcanism m k reichow et al 40ar 39ar dates from the west siberian basin siberian flood basalt province doubled reports 7 june p 1846 1 report that the areal extent and volume of the siberian traps volcanism of 250 million years ago were much greater than previously thought traps volcanism

lacustrine fluvial interactions in australia s riverine plains climatic forcing of fluvial systems has been a pre occupation of geomorphological studies in australia since the 1940s in the riverine plain southeastern australia the stable tectonic setting and absence of glaciation have combined to produce sediment loads that are amongst the lowest in the world surficial sediments and landforms exceed 140 000 yr in age and geomorphological change recorded in the fluvial fluvio lacustrine and aeolian features have provided a well studied record of quaternary environmental change over the last glacial cycle the region includes the willandra lakes whose distinctive lunette lakes preserve a history of water level variations and ecological change that is the cornerstone of australian quaternary chronostratigraphy the lunette sediments also contain an ancient record of human occupation that includes the earliest human fossils yet found on the australian continent to date the lake level and palaeochannel records in the lachlan willandra system have not been fully integrated making it difficult to establish the regional significance of hydrological change here we compare the willandra lakes environmental record with the morphology and location of fluvial systems in the lower lachlan an ancient channel belt of the lachlan willandra creek acted as the main feeder channel to willandra lakes before channel avulsion caused the lakes to dry out in the late pleistocene electromagnetic surveys geomorphological and sedimentary evidence are used to reconstruct the evolution of the first new channel belt following the avulsion single grain optical dating of floodplain sediments indicates that sedimentation in the new middle billabong palaeochannel had commenced before 18 4 1 1 ka a second avulsion shifted its upper reaches to the location of the present lachlan river by 16 2 0 9 ka the timing of these events is consistent with palaeohydrological records reconstructed from willandra lakes and with the record of palaeochannels on the lachlan river upstream willandra lakes shows high inflows during the last glacial maximum 22 ka but their subsequent drying between 20 5 ka and 19 ka was caused by river avulsion rather than regional aridity this case study highlights the benefits of combining fluvial with lacustrine archives to build complementary records of hydrological change in lowland riverine plains

downstream hydrogeomorphic changes along the macquarie river southeastern australia leading to channel breakdown and floodplain wetlands abstract floodplain wetlands and floodouts in the macquarie marshes are fed by numerous anastomosing and distributary channels on the lower reaches of the macquarie river southeastern australia river discharge is seasonally and annually variable and is affected by both interannual and interdecadal climatic trends related to enso and ipo a downstream comparison of hydrologic data shows that flows decrease significantly in magnitude and stream power along the allogenic lower macquarie river as distributary outflows are not matched by tributary inputs intrinsic hydrologic and geomorphic thresholds along the lower macquarie river lead to the breakdown of the trunk stream into smaller distributaries with disintegration of channelised flows and development of extensive wetlands on the low gradient dryland alluvial floodplain fan cross sectional analysis shows that the morphology and morphometry of the trunk stream change accordingly with adjustments in planform and cross sectional shape and marked downstream reductions in channel capacity and bed width despite monotonic declines in river discharge gross stream power and channel cross sectional area there is a threshold change in the geomorphic response channel width to depth ratio decreases in the middle reaches and then increases while channel sinuosity increases until immediately upstream of the core wetlands and then rapidly declines as straight channels enter areas of extensive channel breakdown floodplain width is greatest on the alluvial plain allowing a broader area of floodplain wetlands to develop that are characterised by fine cohesive sediments floodplain connection is greatest where floodouts and wetlands form in the marshes channel breakdown and floodplain wetland formation along the lower macquarie river and in the macquarie marshes are distinct examples of a nonequilibrium response to downstream declining discharge and stream power which is an inherent condition in many dryland australian rivers during the holocene

two pulses of extinction during the permian triassic crisis over 90 of marine species were lost during the end permian extinction fossil data show that the crisis in china was marked by two distinct phases of marine extinction separated by a 180 000 year recovery period

episodic fluvial activity of inland rivers in southeastern australia palaeochannel systems and terraces of the lachlan river inland rivers in southeastern australia preserve a long record of surface palaeochannels accompanied by alluvial terraces that reflect changes in water and sediment discharges from the southeastern highlands through much of the last glacial cycle a compilation of ages on rivers of the southern murray darling basin together with new dates from the lachlan river suggest that the fluvial response to climate change has been regionally consistent and responsive to climate change on timescales 10 ka for much of the last glacial cycle inland rivers were mixed load sinuous single and anabranching channels that carried bankfull discharges of between 3 and 11 times present day rivers incision of the upper alluvial plains and valleys occurred in the lead up to the coldest part of the last glacial cycle this was followed at 34 ka by the synchronous development of large meandering channels that may have been associated with lower evapotranspiration from alpine highland catchments accompanied by higher precipitation smaller channels and declining lateral channel sedimentation suggests arid climates during the last glacial maximum and late glacial period with seasonally large actively migrating channels being maintained in rivers dominated by snowmelt runoff from the australian alps during the holocene sensitivity to recorded changes in precipitation amounts and variability differed between catchments with some rivers constructing larger or more actively migrating channels in the early to mid holocene

newly discovered fish faunas from the early triassic karoo basin south africa and their correlative implications recent collecting in exposures of the lowermost burgersdorp formation beaufort group of the karoo basin of south africa has revealed a previously unknown fish fauna from the early triassic scythian lowermost cynognathus assemblage zone caz which forms an important component of the total vertebrate assemblage the newly discovered fish material includes lungfish saurichthyids and a large microfauna that includes numerous isolated chondrichthyan teeth two fin spine fragments and actinopterygian scales and teeth the latest fish finds together with the lowermost cynognathus assemblage zone vertebrate faunas make this karoo basin assemblage zone one of the most diverse early triassic faunal assemblages comparable in faunal diversity to those from the czatkowice formation poland and the arcadia formation australia the presence of the lungfish ptychoceratodus phillipsi in the early middle triassic cynognathus assemblage zone subzone b and in the underlying latest early triassic cynognathus assemblage zone subzone a indicates that these lungfish could serve as range index fossils within the caz and thus are potentially useful biostratigraphic markers across the early middle triassic boundary furthermore the new fish fauna provides a vital marine realm link in particular with the faunas of madagascar and australia that is unavailable using the tetrapod faunal elements of the lower caz

the permian triassic boundary in western slovenia idrijca valley section magnetostratigraphy stable isotopes and elemental variations stable isotope analyses of carbonate 13ccarb and total organic carbon toc 13corg together with geochemical analyses of 54 major minor and trace elements and magnetic susceptibility measurements were carried out on whole rock samples of the undisturbed permian triassic p tr limestone boundary sequence in the idrijca valley w slovenia at the p tr boundary there is a 0 8 cm thick clayey marl layer ptb showing a characteristic magnetic susceptibility pulse and considerable enrichment in most major minor and trace elements the p tr transition is characterized by 1 an abrupt decrease in sedimentation rate from 32 to 5 cm 100 ka 2 a well known prominent negative excursion of 13ccarb and 13corg reflecting global perturbations in the carbon cycle and 3 the drastic disappearance of typically upper permian marine fauna although the shape of the 13ccarb curve indicates gradual long term change across the p tr boundary the sharp negative 13corg anomaly within an interval from 30 cm below to 6 cm above the boundary suggests an interruption of those gradual processes our observations for selected redox sensitive elements mo u v and zn abundances for organic carbon and sulphur and the rare earth elements ree distribution in the boundary sequence as well as the shape of the ce ce curve suggest that oceanic anoxia was typical of the upper permian and that the transition to oxygenated conditions occurred at the p tr boundary oxygenation at the p tr transition is coincidental with the terminal phase of the upper permian marine regression the shape of the ce ce curve indicates that the redox environmental conditions changed again in the earliest triassic resulting once more in oxygen deficient conditions

the holocene history of mediterraneantype plant communities little desert national park victoria australia this paper begins to identify the relative roles of climate change people and fire as factors in the late pleistocene and holocene evolution of one of the most diverse terrestrial ecosystems in southern australia our research illustrates that pollen from mediterranean type heathlands can be recognized from sediments taken from small basins in semi arid ecosystems the use of pollen and carbonized panicle analyses from sediment cores in conjunction with ecological research on plant fire relationships establishes a role for palaeoecological techniques in the interpretation of long term processes in semi arid heathlands in australia radiocarbon dates indicate that the treeless structure at our study site in the little desert of western victoria has existed since at least the early holocene pollen evidence indicates an increase in plant diversity especially in proteaceae and fire ephemerals and a decrease in fire sensitive taxa e g callitris spp allocasuarina muelleriana type over the last 4000 years this decline occurs in conjunction with increases in the frequency of carbonized particles

pre pliocene extension around the gulf of california and the transfer of baja california to the pacific plate late miocene 12 5 ma extension around the edges of the gulf of california has been alternatively attributed to basin and range extension back arc extension or development of the pacific north america plate boundary this extension was ene directed and similar in structural style to extension in the basin and range province timing constraints permit nearly synchronous onset of this deformation in a belt extending sse from northernmost baja california to the mouth of the gulf where this extensional faulting continued through pliocene time to the present synchronous with motion on the modern transform plate boundary in the gulf of california no change in direction of extension can be resolved revised constraints on pacific north america plate motion support the development of this late miocene extension as a component of pacific north america displacement that could not be accommodated by strike slip displacement along the existing plate boundary west of the baja california peninsula this scenario implies that transfer of baja california from the north america plate to the pacific plate was a gradual process beginning about 12 10 ma when motion of the pacific plate relative to north america was partitioned into separate regimes of strike slip and dip slip displacement on opposite sides of baja california

tethyan uppermost permian dzhulfian and dorashamian foraminiferal faunas and their paleogeographic and tectonic implications abstract the foraminiferal faunas and biostratigraphic correlation of the tethyan uppermost permian dzhulfian and dorashamian provide important paleogeographic and tectonic data for the interpretation of the palaeofusulina bearing terranes in east and southeast asia these interpretations have a significant bearing on understanding japanese pre cretaceous tectonostratigraphic and micropaleontologic data as well as the geodynamic evolution of the japanese palaeofusulina bearing terranes the tethyan foraminiferal fauna in the uppermost permian is characterized by the occurrence of provincial and endemic schubertellid genera and the absence of neoschwagerinids and verbeekinids which had characterized the rapidly evolving middle permian tethyan marine faunas until their extinction at the end of the midian difficulties in world wide correlation of the uppermost permian have resulted because of different geographic faunal compositions and the geographic patterns of extinction of permian marine faunas the palaeofusulina fauna is one of the most reliable indicators of the uppermost permian its presence or absence serves as paleogeographic constraints on east and southeast asian terranes for example the absence of palaeofusulina fauna and the presence of late midian lepidolina multiseptata faunas in the lhasa terrane in tibet and the wolya terrane in sumatra the third continental sliver north of gondwana are important particularly for identifying the rift drift collision process of the gondwana affinity terranes they suggest a late permian separation of the two terranes from gondwana tethyan palaeofusulina occur in the latest permian tropical to subtropical latitudinal belt and along with other geologic data assist in paleogeographic reconstructions and in interpreting the possible movement and emplacement of the palaeofusulina bearing terranes such as the maizuru south kitakami kurosegawa and chichibu terranes in japan they reveal that 1 the upper permian maizuru group was deposited on the eastern continental margin of south china 2 the occurrence of the lower permian cathaysian flora and a number of geologic data in the south kitakami kurosegawa suggest an arc trench system setting and the late permian deposition in a shallow open marine environment in proximity to south china 3 foraminiferal biogeograpic data and the reconstructed oceanic plate stratigraphy in the chichibu terrane constrain the location of the chichibu seamount chains to the western part of the panthalassan domain as they moved westwards against the cathaysian continent until their jurassic accretion