namurian uplift in australia and south america triggered the main gondwanan glaciation the permo carboniferous glacigenic sediment at the base of the gondwanan basins reflects the culmination1 2 of the glacial episode that started in australia and southern south america in the namurian after two local episodes in northern south america and adjacent africa in the visean and latest devonian3 fig 1 here we show that the start of each episode was associated with orogenic uplift of the bordering regions northern south america and adjacent africa in the latest devonian and visean and southern south america and eastern and central australia in the namurian all areas except southern south america in the namurian were at mid and not high latitudes thus we show that whereas the first order control of glaciation was the configuration of the continents and oceans during the closing of palaeo tethys orogenesis provided a second order control by the accumulation of ice about bordering uplifts during the three glacial episodes

creep dike intrusion and magma chamber deflation model for the 2000 miyake eruption and the izu islands earthquakes 1 analysis of global positioning system data shows shrinkage of miyake island and the widening between nijima and kozu islands during the period of the miyake island volcanic activity and the ensuing izu islands earthquakes in 2000 the estimated time evolution of a model consisting of a dike creeping faults and a mogi source suggests that a crack opening on miyake island occurred immediately after the start of the seismic activities on 26 june and ended within several days at the west coast of miyake island after the seabed eruption on 27 june magma migrated from miyake island to kozu and nijima islands within several days the estimated volume of intruded magma totals around 1 2 109 m3 associated with the magma intrusion between miyake and kozu islands left lateral and right lateral creep motions occurred in regions off the west coast of miyake island and near kozu island the accumulated moment energy is equivalent to an earthquake of mw 6 6 and 6 6 for right lateral and left lateral creeping faults respectively the estimated magma chamber continued deflation beneath the southwestern part of miyake island from 26 june totaling around 0 12 109 m3 in volume change in addition to the collapse volume of 0 6 109 m3 at the summit of mount oyama on miyake island the volume change on miyake island can be compensated by the migrated magma toward kozu island from the deflation source beneath miyake island the deflation speed of the magma chamber beneath miyake island decreased and increased before and after the eruption of 14 15 july and 18 august suggesting a change in balance of mass influx and draining out rate of the magma chamber

intensified oceanic circulation during early carboniferous cooling events evidence from carbon and nitrogen isotopes abstract the early carboniferous was a climatic transition interval from a mid paleozoic greenhouse world into the late paleozoic ice age it was marked by a long term cooling trend that was punctuated by short glaciations in the tournaisian and visean early to mid early carboniferous here we generated organic carbon and nitrogen isotope profiles for two widely separated lower carboniferous sections arrow canyon range nevada and namur dinant basin belgium in order to assess the global nature and timing of changes in the carbon nitrogen cycles linked to oceanic productivity and redox conditions during this climatic transition interval the carbon and nitrogen isotope profiles of both study sections record major perturbations during the mid tournaisian and visean a mid tournaisian event tice is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 7 0 25 2 to 23 7 and 0 6 to 8 9 respectively and namur dinant from 0 3 to 4 7 27 9 to 22 2 and 5 7 to 5 2 respectively an early visean event vice named herein is marked by increases in 13ccarb 13corg and 15nbulk at arrow canyon from 0 6 to 3 1 28 4 to 23 6 and 1 4 to 9 4 respectively and namur dinant from 2 1 to 4 3 26 7 to 25 0 and 1 4 to 3 3 respectively the positive excursions in all three isotopic records during these events are consistent with increased fractional burial of organic carbon and enhanced denitrification implying intensification of marine productivity and expansion of hypoxia in the global ocean given that each event coincided with lowering of sea surface temperatures and increased glaciation as documented from published conodont 18o and sea level records we hypothesize that global cooling led to intensified oceanic circulation and upwelling on continental margins triggering increased marine productivity and attendant redox changes within the affected upwelling zones our results provide new insights into changes in early carboniferous oceanic conditions in response to the initial stages of cooling leading into the late paleozoic ice age

geologic consequences of globe encircling equatorial currents many black shales phosphorites and cherts that formed at low paleolatitudes on the north american continent during the late paleozoic were a direct consequence of equatorial upwelling and an equatorial undercurrent in an ocean that spanned much of the globe in equatorial parts of modern oceans wind stress divergence leads to high surface productivity sinking organic matter is remineralized in the strong eastward flowing equatorial undercurrent the undercurrent thus acts as a nutrient trap that becomes progressively oxygen poor and nutrient rich as it moves eastward the late paleozoic global ocean was 60 to 80 wider than the modern pacific ocean 24 000 km total width the nutrient trapping equatorial current system of this globe encircling ocean was probably anoxic and may have been sulfate reducing nutrient rich anoxic water from the undercurrent would have had direct consequences for the genesis of black shale facies in devonian and pennsylvanian epicontinental seaways as well as possibly providing the source water for coastal upwelling in settings such as the phosphoria sea

evolution patterns of radiolaria and organic matter variations a new approach to identify sea level changes in mid cretaceous pelagic environments the relation between sea level changes plankton productivity and evolution as well as the occurrence of anoxic sediments provides an interesting avenue of paleooceanographic research in this context we examined mid cretaceous radiolarian faunas carbonate isotopic and organic matter type data of deep sea drilling project and ocean drilling program cores from the north atlantic and samples from outcrops of the western tethys from central and northern italy former studies indicate that an expansion of the oxygen minimum zone caused plankton extinctions at the cenomanian turonian boundary an expanded oxygen minimum zone would destroy deeper habitats of planktic foraminifera causing the extinction of deeper dwelling forms although this model is well established for the cenomanian turonian boundary not much is known about the causes of extinctions and radiations during the entire mid cretaceous aptian turonian we demonstrate that the dimension of the oxygen minimum zone which depends on the relative sea level and the corresponding nutrient supply causes the complex pattern of evolution and radiation of planktic protozoa and the sedimentation of black shales in the mid cretaceous this new depositional model allows correlation of micropaleontologic data and different types of black shales in the pelagic realm within a sequence stratigraphic framework

crustal deformation caused by magma migration in the northern izu islands japan intense crustal activity including earthquake swarms eruptions and a caldera formation in the northern izu islands started on june 26 2000 accompanied with large crustal deformation permanent gps data reveals the spatial pattern and time evolution of ground deformation the observations reveal shrinking and subsidence of miyakejima and extension between kouzushima and niijima we constructed a source model to explain the observed displacements during the period between june 26 and the end of august the model consists of a deflation source 0 12km beneath miyakejima tensile faults 1 04km located between miyakejima and kouzushima and several shear faults mass balance considerations suggest that a large amount of magma migrated 30km from miyakejima toward kouzushima

subsurface cyclic magma sill expansions in the 2000 miyakejima volcano eruption possibility of two phase flow oscillation 1 step like tilt changes were observed at intervals of dozens of hours during the caldera formation stage occurred during the 2000 miyakejima volcano eruption our analysis suggests that these tilt steps were caused by the cyclic expansion of a subsurface sill like magma plumbing system trending from se to nw of the volcano in the same period a caldera gradually grew at the summit area to a very large 1 6 km in diameter and 450 m in depth the source mechanism of these tilt steps is fairly well explained by a two phase flow instability called a pressure drop oscillation this model indicates that the gas phase capacity in the upper part of the conduit acts as a pump that controls the flux of two phase magma in the sill like reservoir caldera formation as well as magma uplift and descent in the conduit may reflect temporal changes in the intervals between tilt steps which are themselves proportional to the volume of this gas capacity

carbon isotopic excursions and detailed ammonoid and conodont biostratigraphies around smithian spathian boundary in the bac thuy formation vietnam abstract the smithian spathian boundary is indicated by the first occurrence of the ammonoid tirolites cf cassianus in the olenekian bac thuy formation northeastern vietnam the boundary is intercalated within organic rich dark gray mudstone that accumulated under anoxic to dysoxic conditions in the an chau and nanpanjiang basins on the south china block in lang son area three conodont zones novispathodus ex gr waageni novispathodus ex gr pingdingshanensis and icriospathodus collinsoni are recognized in the formation the smithian spathian boundary is intercalated within n ex gr pingdingshanensis conodont zone the positive excursion in 13c with values increasing from around 2 3 to 5 7 was recorded in the uppermost smithian xenoceltites variocostatus ammonoid beds and n ex gr pingdingshanensis conodont zone the 13c values decrease across the smithian spathian boundary these 13c isotopic patterns are correlated with well known positive excursions around the smithian spathian boundary globally

very long period seismic signals and caldera formation at miyake island japan over a period of roughly 40 days starting on 8 july 2000 a caldera structure 1 7 kilometers in diameter developed by means of gradual depression and expansion of the summit crater at miyake island japan at the same time very long period vlp seismic signals were observed once or twice a day source mechanism analyses of the vlp signals show that the moment tensor solutions are smooth step functions over a time scale of 50 seconds with dominant volumetric change components we developed a model to explain the caldera and the vlp signals in which a vertical piston of solid materials in the conduit is intermittently sucked into the magma chamber by lateral magma outflow this model offers potential for making quantitative estimations of the characteristic physical properties of magma systems

aluminum dependent trace element partitioning in clinopyroxene as technical advances have dramatically increased our ability to analyze trace elements the need for more reliable data on the compositional dependence of trace element partitioning between minerals and melt has become increasingly important the late cretaceous carmacks group of south central yukon comprises a succession of primitive high mg ankaramitic lavas characterized by shoshonitic chemical affinities and containing large complexly zoned clinopyroxene phenocrysts the compositional zonation of the clinopyroxene phenocrysts is characterized by relatively fe rich mg mg mg fe 0 85 but mottled cores surrounded by mantles of cyclically zoned clinopyroxene whose mg varies repeatedly between 0 9 and 0 80 these cyclically zoned clinopyroxene mantles appear to record the repeated influx and mixing of batches of primitive with more evolved magma in a deep sub crustal 1 2 gpa magma chamber s laser ablation icp ms was used to analyze the trace element variation in these zoned clinopyroxenes the results indicate more than a threefold variation in the absolute concentrations of th zr rare earth elements ree and y within individual clinopyroxene phenocrysts with no apparent change in the degree of ree or high field strength element hfse fractionation the variation in absolute abundances of trace elements correlates closely with the major element composition of the clinopyroxene with the most enriched clinopyroxene having the lowest mg and highest al contents the problem is that the amount of crystal fractionation required to explain the major element variation 20 in these clinopyroxene phenocrysts cannot explain the increase in the abundance of the incompatible trace elements which would require more than 70 crystal fractionation if constant partition coefficients are assumed the anomalous increase in incompatible trace elements appears to reflect an increase in their partition coefficients with increasing aliv in the clinopyroxene with an increase in al2o3 from 1 5 to 4 0 wt during 20 crystal fractionation over a temperature decrease of 100 c being associated with more that a threefold increase in the partition coefficients of th zr ree and y the magnitude of these increases may indicate that the substitution of these trace elements into clinopyroxene is better modeled in some natural systems by a local charge balance model rather than the distributed charge model that better replicates the results of annealed experiments these findings indicate that the effect of al on the partition coefficients of incompatible trace elements in clinopyroxene may be under appreciated in natural magmatic systems and that the application of experimentally determined clinopyroxene partition coefficients to natural systems must be done with caution

late devonian sedimentary record of the paleotethys ocean the mae sariang section northwestern thailand abstract an 11 m thick condensed sequence of late devonian limestones in northwestern thailand exhibits faunal associations and sedimentological microfacies data which are indicative of a pelagic facies setting the entire long ranging section is completely free from clastic input similar successions are known worldwide in a few sections only the mae sariang section is characterised by low sedimentation rates as recognised by a number of hardgrounds neptunian dikes and fe mn crusts the succession comprises a number of pelagic faunal elements e g conodonts cephalopods and pelagic ostracodes the fauna records rare macrofossils and the faunal diversity is low the very condensed section ranges from the late rhenana to praesulcata conodont biozones but contains some global events as undoubtedly shown by biostratigraphical and carbon isotope results including major kellwasser and hangenberg biotic crises in terms of plate tectonics this important succession most probably belongs to the inthanon zone comprising remnants of the paleotethys ocean

conodonts across the devonian carboniferous boundary a review and implication for the redefinition of the boundary and a proposal for an updated conodont zonation this paper is a contribution to the redefinition of the base of carboniferous system at present the criterion for the definition of the devonian carboniferous boundary is the first occurrence of a conodont species in order to evaluate the stratigraphic potential for new criteria for the definition of the devonian carboniferous boundary the distribution of conodont species of bispathodus branmehla palmatolepis polygnathus protognathodus pseudopolygnathus and siphonodella across the boundary is presented and discussed an updated biozonation scheme across the boundary based on the first appearance of bispathodus ac aculeatus bispathodus costatus bispathodus ultimus protognathodus kockeli siphonodella bransoni and siphonodella duplicata is proposed and it is suggested that the new criterion for the definition of the base of the carboniferous system be the first appearance datum of pr kockeli or si bransoni

middle to late famennian successions at ain jemaa moroccan meseta implications for regional correlation event stratigraphy and synsedimentary tectonics of nw gondwana

climate controlled mass extinctions facies and sea level changes around the devonian carboniferous boundary in the eastern anti atlas se morocco abstract detailed sedimentological and biostratigraphical studies of successions in the eastern anti atlas se morocco focused on changing depositional environments and reconstructions of sea level changes during the late famennian to middle tournaisian the investigations cover a transect from the central maider to the easternmost and southern tafilalt regions near the moroccan algerian border the moroccan data are compared with the standard succession of the german rhenish massif and with the regional and global stratigraphic record the results testify to high frequency sea level changes including two global transgressive and anoxic events the main hangenberg event hangenberg black shale level at the top of the wocklumeria zone upper devonian vi e and the lower alum shale event at the lower middle tournaisian lower carboniferous i ii boundary regionally both anoxic intervals coincided with mass extinctions followed by rapid radiation especially of pelagic biota a significant shallowing and regression occurred just below the devonian carboniferous boundary at the northern margin of gondwana and caused the sudden n nw progradation of a large deltaic complex over 300 500 km thick siliciclastic successions filled fast subsiding synsedimentary troughs of the maider and amessoui syncline southern tafilalt correlation with the glacial phases of southern gondwana south america south africa indicates a glacial eustatic origin of sea level changes and a major sea level fall in the scale of 100 m or more coinciding with the main regressive phase of the extended hangenberg crisis interval the new results are in accord with the hypothesis of an episode of cool humid climate at the end of the devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of nw africa

earliest known carboniferous shallow water reefs gudman formation tn1b queensland australia implications for late devonian reef collapse and recovery the phanerozoic history of reefs extensively has been considered a direct reflection of the history of skeletal reef building organisms however such a relationship does not characterize global mid paleozoic reef history the extinction of most reef building stromatoporoids and corals at the frasnian famennian boundary correlates with the collapse of north american and european stromatoporoid dominated reefs but western australian russian and chinese reefs were much less severely affected until the late famennian when algae calcimicrobes and nonskeletal microbialites i e stromatolites thrombolites declined globally additionally reef recovery was more rapid than previously thought small early tournaisian tn1b shallow water reefs in the gudman formation of eastern central queensland substantially reduce the duration of the reefless lag time following late devonian reef decline essentially confining it to the strunian gudman reefs are dominated by microbialite but contain a diverse although volumetrically insignificant skeletal fauna and flora including large colonial corals bryozoans crinoids brachiopods and calcareous algae hence mid paleozoic reef collapse and recovery reflect an amalgam of more or less independent histories of skeletal organisms calcimicrobes and nonskeletal microbialites in response to regional and global environmental parameters a better understanding of mid paleozoic reef history will require detailed local and regional scale studies to isolate global from nonglobal signals

early pliocene increase in thermohaline overturning a precondition for the development of the modern equatorial pacific cold tongue unraveling the processes responsible for earth s climate transition from an el nino like state during the warm early pliocene into a modern like la nina dominated state currently challenges the scientific community recently the pliocene climate switch has been linked to oceanic thermocline shoaling at 3 million years ago along with earth s final transition into a bipolar icehouse world here we present pliocene proxy data and climate model results which suggest an earlier timing of the pliocene climate switch and a different chain of forcing mechanisms we show that the increase in north atlantic meridional overturning circulation between 4 8 and 4 0 million years ago initiated by the progressive closure of the central american seaway triggered overall shoaling of the tropical thermocline this preconditioned the turnaround from a warm eastern equatorial pacific to the modern equatorial cold tongue state about 1 million years earlier than previously assumed since 3 6 3 5 million years ago the intensification of northern hemisphere glaciation resulted in a strengthening of the trade winds thereby amplifying upwelling and biogenic productivity at low latitudes

devonian carboniferous transition containing a hangenberg black shale equivalent in the pho han formation on cat ba island northeastern vietnam abstract on cat ba island in northeastern vietnam the devonian to carboniferous d c transition consists mainly of ramp carbonates intercalated with black shale beds beds 1 to 176 in the pho han formation and is one of the few records of the d c transition of the eastern paleotethys the three main facies of the sequence are facies 1 alternations of whitish gray to gray limestone and marl facies 2 calcirudite bed 115b and facies 3 alternations of dark gray limestone and organic carbon rich black shale beds 115c 120 and 126 129 the latest famennian siphonodella praesulcata subzone conodont assemblage of s praesulcata palmatolepis gracilis palmatolepis sigmoidalis and rhodalepis polylophodontiformis was recognized in beds 113 115c beds 105 112 commonly contain palmatolepis expansa p gracilis and p sigmoidalis bed 119 yielded a basal carboniferous index conodont siphonodella sulcata in beds 116 118 solenoporids such as pseudochaetetes elliotti and parachaetetes sp were characteristic species in organic carbon rich dark gray limestone facies 1 is characterized by bioclastic peloidal and intraclastic grainstone and packstone containing massive normal grading and cross laminations and is interpreted to represent deep ramp carbonates above storm wave base facies 2 is represented by typical lag deposits overlying a transgressive surface facies 3 comprises organic carbon rich black shale and minor scour filling bioclastic peloidal and intraclastic packstone and may represent a marginal basin plain environment surrounding a carbonate ramp the alternations of organic carbon rich black shale and dark gray packstone facies 3 show no evidence of bioturbation and have high toc contents 0 18 5 73 wt a minor succession within the transgressive lag deposits from bed 115b of facies 2 to beds 115c 120 in the lower part of facies 3 is equivalent to the hangenberg black shale s l in the middle part of the siphonodella praesulcata to siphonodella sulcata zones because beds 115b 120 characterized by no evidence of bioturbation and high toc contents are interpreted to be accumulated in anoxic to dysoxic conditions

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

mechanisms of step like tilt changes and very long period seismic signals during the 2000 miyakejima eruption insights from kinematic gps during the 2000 eruption of the miyakejima volcano in japan step like tilt changes tc generally accompanied by very long period vlp seismic signals with a pulse like shape and widths of 50 s were repeatedly observed tc vlp events kinematic gps time series for miyakejima were investigated in order to detect displacements associated with these events we found that the kinematic gps time series could be interpreted as the superposition of the following features 1 displacement associated with the tc vlp events the source of which possibly corresponded to a shallow magma chamber represented by an almost vertical ellipsoidal cavity elongated ne sw at a depth of 2 3 km 2 displacement following tc vlp events that may have been caused by exponential type volume decreases of the same magma chamber with a decay constant of approximately half a day and 3 displacements that may be caused by continuous volume decreases of the same magma chamber these features broadly support the piston model of vlp seismic signals in which a vertical piston of solid conduit material intermittently sinks into a magma chamber located a few kilometer beneath the edifice following deflation caused by continuous outflux of magma the volume increase of the magma chamber associated with the tc vlp events was found to be much smaller than that of the collapsed caldera suggesting that most of the mass in the conduit sank into the magma chamber without generating vlp seismic waves or step like tc