gauging the impact of glacioeustasy on a mid latitude early silurian basin margin mid wales uk the early silurian llandovery gondwanan south polar ice sheet experienced episodes of ice retreat and re advance marine base level curves constructed for the interval are widely assumed to provide a record of the associated glacioeustasy in revealing a series of progradational sequences progrades bounded by flooding surfaces recent work on the type llandovery succession in mid wales uk has provided an opportunity to test this hypothesis the grouping of these progrades into three composite sequences underpins the construction of both low order small amplitude high frequency and high order large amplitude low frequency base level movement curves revised biostratigraphical datasets for the type succession permit the accurate dating of base level events the composite sequences record progradational acmes in the acinaces lower convolutus and upper sedgwickii halli graptolite biozones a series of transgressions that postdate the hirnantian glacial maximum culminated in an upper persculptus biozone high stand maximum flooding events also occurred during the revolutus and lower sedgwickii biozones and the base of the early telychian guerichi biozone also marked the onset of a pronounced deepening a review of 62 published datasets including global and other regional base level curves records of glacial activity isotope data patterns of facies and faunal flux and putative climate models permits an evaluation of the origins of these local base level events the concept of a eustasy index is introduced and shows that the impacts of global sea level movements can only be demonstrated within narrow eustatic windows coincident with times of ice sheet collapse at other times the geometry of llandovery area progrades reflects their accumulation across a faulted basin margin where during periods of slow ice sheet advance epeirogenic processes outstripped sea level movements as the dominant forcing factors increased levels of telychian subsidence at first enhanced and then overwhelmed the influence of glacioeustasy as part of the region s response to the north european scandian deformation

geothermobarometry of high grade metapelites simultaneously operating reactions s u m m a r y experimental data on equilibria involving rock forming minerals in highgrade metapelites garnet orthopyroxene cordierite and plagioclase have been used to derive an internally consistent system of mineralogical thermometers and barometers based on component reactions and excess mixing properties of solid solutions application of these data to a granulite facies metapelite sample reveals that compositional inhomogeneity of minerals on a thin section scale is likely to be a result of several reactions opening simultaneously at the retrograde stage of metamorphic evolution the widely accepted practice of estimating pressure and temperature from separate reactions may thus lead to errors and misinterpretation of p t paths

refined timing and kinematics for baltica avalonia convergence based on the sedimentary record of a foreland basin the caledonian foreland basin of poland onlaps the sw slope of the east european craton and is elongated in a nw sw direction along the margin of the baltica palaeocontinent the base of the synorogenic clastic wedge rises in age from llandovery to ludlow between nw and se poland respectively as the initial influx of orogen derived detritus can be unequivocally identified this diachronism documents a southeastward migration of the basin depocentre parallel to the present day caledonian deformation front our best fit plate model shows an oblique collision of baltica and avalonia the latter initially indenting the baltica margin in the nw afterwards baltica was progressively underthrust beneath avalonia towards the se in response to the oblique soft mode closure of the tornquist ocean the final deformation event within the caledonian foreland took place in the earliest devonian as a far field effect of sinistral orogen parallel displacements along the iapetus suture this article is protected by copyright all rights reserved

wollastonite and scapolite in precambrian calc silicate granulites from australia and antarctica abstract scapolite wollastonite calcite diopside grossular andradite garnet and sphene occur in calc silicate rocks in the granulite terrain of the arunta block central australia this assemblage buffers the co2 activity at a low value so that any coexisting fluid phase must be h2o rich and co2 poor xco2 0 2 0 3 in contrast the h2o activity in the surrounding felsic and mafic granulites was low thus fluid activities during granulite facies metamorphism were locally buffered in various rock units and fluid flow appears to have been restricted or fluid may have been absent late retrograde rims of garnet and garnet quartz separate phases formed in the high grade stage formation of these rims would have required either an influx of water rich fluid or a decrease in pressure evidence from the surrounding granulites shows that in one locality the calc silicate rocks had undergone late isobaric hydration in another locality minor uplift had occurred soon after peak p t conditions in both scapolite had partly broken down to plagioclase calite a calc silicate rock from the granulite terrain of enderby land antarctica contains scapolite wollastonite calcite diopside quartz and sphene this assemblage also indicates low co2 activities in this rock wollastonite has broken down to calcite quartz to indicate isobaric cooling without influx of hydrous fluid

successive overprinting granulite facies metamorphic events in the anmatjira range central australia the anmatjira range and adjacent reynolds range central australia comprise early proterozoic metasediments and othogneisses that were affected by three and possibly four temporally distinct metamorphic events m1 4 and deformation events d1 4 in the period 1820 1590 ma the north western portion of the range around mt stafford preserves the effects of 1820 ma m1 d1 and shows a spectacular lateral transition from muscovite quartz bearing schists to interlayered andalusite bearing migmatites and two pyroxene granofelses that reflect extremely low pressure granulite facies conditions over a distance of less than 10 km orthopyroxene cordierite garnet k feldspar quartz bearing gneisses occur at the highest grade implying peak conditions of 750 c and 2 5 0 6 kbar an anticlockwise p t path for m1 is inferred from syn to late d1 sillimanite overprinting andalusite petrogenetic grid considerations and quantitative estimates of metamorphic conditions for inferred overprinting assemblages the effects of m1 have been variably overprinted to the south east by a c 1760 ma m2 d2 event much of the central anmatjira range around ingellina gap comprises orthogneiss deformed during d2 and metapelites that have m1 andalusite and k feldspar overprinted by m2 sillimanite and muscovite the south eastern portion of the range around mt weldon comprises metasediments and orthogneisses that were completely recrystallized during m2 d2 with metapelitic gneisses characterized by spinel sillimanite k feldspar quartz bearing assemblages that suggest peak m2 conditions of 750 c and 5 5 1 kbar overprinting parageneses in metapelitic gneisses imply that d2 occurred during essentially isobaric cooling a third granulite facies event m3 affected rocks in the reynolds range immediately to the south of the anmatjira range at c 1730 ma a possible fourth event m4 with a minimum age of c 1590 my affected both ranges but resulted in only minor overprinting of m1 3 assemblages the superimposed effects of m1 4 mapped for the entire anmatjira reynolds range area indicate that only minor or no dislocation of the regional geology occurred during any of the metamorphic and accompanying folding events although the immediate cause of each of the metamorphic events involved advection the ultimate causes were external to the metasediments and most probably external to the crust

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

icesat s new perspective on ice shelf rifts the vertical dimension 1 the small footprint 70 m and 172 m along track spacing of the geoscience laser altimeter system glas on the ice cloud and land elevation satellite icesat provides unprecedented horizontal resolution for a satellite altimeter this enables icesat to map many previously unresolved features on ice shelves such as crevasses rifts grounding zones and ice fronts we present examples of icesat derived elevation data showing topography over rifts on the amery and ross ice shelves widths of rifts and as estimates of the thickness of melange a collection of ice and snow trapped inside the rifts we show that melange thickness remains constant over the icesat data period and tends to be thicker in older rifts we validate the icesat derived melange depth estimate with an in situ measurement on the ross ice shelf

the p t deformation path for a mid proterozoic low pressure terrane the reynolds range central australia the proterozoic low pressure high temperature lpht terrane of the reynolds range occurs in a 130 km long nw trending belt in the central part of the arunta block central australia the reynolds range has been affected by two mid proterozoic tectonic cycles di and dii associated with two metamorphic events mi and mii di mi effects are restricted to the older of two sedimentary successions the lander rock beds which are separated from the younger reynolds range group by an angular unconformity the dominant structural metamorphic features formed during dii mii affected both sedimentary successions and the various granites that intruded them and reworked most di mi effects the dii deformation history can be subdivided into one prograde two peak and one retrograde stage average p t calculations in the southeastern half of the range indicate a peak metamorphic pressure of 4 1 0 3 kbar because the calculated values are derived from the same stratigraphic level corresponding to the base of the reynolds range group which is exposed throughout the area it is likely that pressures were similar in the entire range in fact however the peak metamorphic temperature shows a dramatic increase from greenschist facies c 400 c in the northwest to granulite facies 740 60 c in the southeast indicating that mii was associated with anomalously high heat flows the p t path is anticlockwise with isobaric cooling from the metamorphic peak indicated by corona textures however the evidence of a prograde increase in pressure is indirect and based on the compressional nature of the structures peak metamorphic mineral assemblages and retrograde mineral assemblages in amphibolite facies shear zones show the same metamorphic zonation suggesting they formed in response to the same thermal event if this is true the implication is that a thermal perturbation external to the crust was maintained for a considerable period of time 110 ma based on zircon dating as it is not clear whether proterozoic asthenosphere active thermal perturbations operated for this long the alternative interpretation must be considered namely that the peak metamorphic events are separate from the shear zone event associated with reheating of the area

early silurian glaciation along the western margin of gondwana peru bolivia and northern argentina palaeogeographic and geodynamic setting the record of the ordovician silurian transition within the southern peru bolivia palaeozoic basin extending across peru bolivia and northern argentina is characterized by a diamictite bearing unit which overlies several different ordovician units and underlies mid silurian shales we review the lithostratigraphy sedimentology and biostratigraphy of this unit revising stratigraphic relationships and several ideas and interpretations previously proposed analysis of facies and lithofacies associations allow for a reinterpretation of sedimentary processes and environments involved during its deposition turbidite and shale interbeds within the diamictites indicate a deep marine environment with interbedded mud flows debris flows slumps and large displaced slabs providing evidence for sediment instability and resedimentation chitinozoan biostratigraphy indicates a llandovery age in contrast with previous proposals of a hirnantian age and suggests the need for more detailed sedimentologic and biostratigraphic studies and a reassessment of this diamictite unit in relation to adjacent regions in south america the resedimented character of the deposit explains some of the ordovician fauna previously described which must be considered as recycled from underlying units in situ fauna needs to be reassessed as it may be endemic diachronic and or indicative of migrations within gondwana glacially faceted and striated clasts as well as large granitoid boulders within the resedimented materials provide evidence for glaciation of the source area and are interpreted as recycled from former glacigenic deposits the evidence found in the central andes indicates a glaciomarine origin for the diamictites and corroborates glaciation of a western source area prior to the late llandovery telychian the precise age of glaciation in this part of gondwana cannot be confirmed do to a lack of true tillites tectonic deformation and the resulting relief are respectively identified as the origin for sediment instability and for local glaciation along the active margin of western gondwana during the late ordovician and early silurian the new data imply that the ordovician silurian boundary was not preserved in some areas of the basin and that an erosional hiatus disconformity with variable regional significance is present between different ordovician units and the diamictite unit late ordovician late caradoc early ashgill euxinic black shales locally present in the central altiplano and eastern cordillera of bolivia may represent the youngest ordovician unit in the region and more research should be focused on them paleogeographic reconstruction of the early silurian peru bolivia basin depicts the extension of the diamictite unit southwards into northern argentina and western paraguay connecting with the parana basin through the asuncion arch to the north it continued into northern peru and ecuador connecting with the silurian record in colombia and venezuela and to the northeast into brazil solimoes and amazonas basins the sedimentary record of glaciation in the peru bolivia basin was due to the development of local ice fields to the west of the basin related with tectonism and resulting reliefs along the active margin of gondwana and probably did not coincide with the development of the north african late ashgillian ice cap

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

a graptolite rich ordovician silurian boundary section in the south central pyrenees spain stratigraphical and palaeobiogeographical significance an ordovician silurian boundary section marked by an uninterrupted relatively high rate of black shale sedimentation and abundant diverse graptolites is described from the south central pyrenees the structurally simple estana section comprises the uppermost part of the quartzite dominated bar formation and overlying black shales of late hirnantian and early rhuddanian age which have been dated by graptolites to the upper metabolograptus persculptus and lower middle akidograptus ascensus parakidograptus acuminatus biozones due to the absence of m persculptus a metabolograptus parvulus biozone correlative with the upper part of the persculptus biozone is recognized below the lowest occurrence of akidograptids which indicate the base of the silurian system the graptolite fauna comprise 27 species including normalograptus minor n lubricus n rhizinus hirsutograptus korenograptus bifurcus k bicaudatus k lanpherei and nd shanchongensis most of which were formerly considered to be endemic to the low latitude palaeobiogeographical province of china siberia and northern north america two new species n baridaensis and n ednae are described the succession of graptolite assemblages in the estana section and occurrence of several cosmopolitan taxa in its parvulus and lower ascensus acuminatus biozones that are unknown elsewhere in peri gondwanan europe suggest that strata immediately surrounding the ordovician silurian boundary may be absent highly condensed or oxic and barren of graptolites in other sections of northwestern peri gondwana common graptolite synrhabdosomes and abnormal rhabdosomes may indicate some environmental stress in the parvulus biozone although the rather uniform black shale lithology total organic carbon content and 13 c org values suggest uninterrupted sedimentation under stable anoxic conditions

evidence for pre regional metamorphic fluid infiltration of the lower calcsilicate unit reynolds range group central australia grandite garnet rich calcsilicate rocks from the lower calcsilicate unit of the regionally metamorphosed reynolds range group central australia crop out along a strike parallel section in which a transition zone from m22 amphibolite to granulite facies rocks is exposed across this transition the grandite rich layers do not show systematic changes in mineral assemblages compositions and modes or stable isotope compositions these layers are deformed by f22 folds that are associated with the peak of regional low pressure high temperature metamorphism therefore the grandite rich layers appear to pre date regional metamorphism and to have acted as closed chemical systems during prograde m22 metamorphism mineral assemblages in the grandite rich layers are consistent with their formation through the infiltration of oxidized water rich fluids xco2 0 1 0 3 log fo2 16 to 14 the stable isotope values of calcite 13c 4 2 to 0 8 0 pdb 18o 10 5 14 0 0 v smow and bulk silicate fractions 18o 6 1 to 10 8 of the grandite rich layers are most consistent with the infiltrating fluid being from a magmatic source it is most likely that fluid infiltration occurred during the pre m22 contact metamorphism m21 that affected much of the reynolds range group the preservation of these assemblages is probably due to their high variance and little pervasive fluid rock interaction having occurred during m22 the clinopyroxene and feldspar rich calcsilicate rocks that host the grandite rich layers contain poikiloblastic grandite garnet that formed during prograde m22 metamorphism thin marbles that locally occur with the grandite rich layers contain a third garnet generation that is post or late m22 this grossular rich garnet occurs in coronas around calcite plagioclase clinopyroxene wollastonite and scapolite these coronas are consistent with cooling and or compression however because the marble assemblages are themselves overprinted by m21 grandite rich layers the development of coronal garnet does not reflect a continuous p t t path rather it more probably reflects the partial re equilibration of m21 contact metamorphic assemblages to post m22 conditions

how well established is isobaric cooling in proterozoic orogenic belts an example from the arunta inlier central australia orogenic pressure temperature paths can only be deduced from metamorphic textures if they formed during a single metamorphic event rather than recording the effects of two or more separate events erroneous tectonic models are likely to result if textures formed in several events are ascribed to one event we illustrate this problem for the arunta inlier in central australia which has been considered to be a good example of an isobarically cooled terrain rocks of the anmatjira range in the central arunta inlier which has been described in terms of isobaric cooling actually record the effects of two low pressure granulite facies metamorphic events of similar peak metamorphic grade m 1 and m 2 that are separated in time by a period of basin development and deposition of a succession of sedimentary rocks correlations of stratigraphic structural fabric and metamorphic texture data allow the effects of m 1 and m 2 to be distinguished without this fine control the textures formed by superposition of m 1 upon m 2 considered as a manifestation of one event could easily be interpreted as indicating isobaric cooling because the overprinting assemblages are of similar pressure but slightly lower temperature than the original assemblages we call this apparent isobaric cooling in fact we now recognize textures reflecting decompression that formed immediately following the peaks of both m 1 and m 2 it is now a matter for conjecture whether isobaric cooling is more apparent than real in other terrains for which it has been recorded

early silurian sea level changes global sea level fluctuated markedly during the early silurian probably as a result of the waxing and waning of ice sheets in the south american portion of gondwana the highest sea levels of the silurian are recorded by the telychian upper crispus lower griestoniensis and spiralis lower lapworthi biozones other highstands occurred in the early aeronian during the convolutus zone mid aeronian guerichi zone and late turriculatus zone early telychian and early sheinwoodian low sea levels characterized much of the argenteus and sedgwickii zones aeronian the utilis subzone late guerichi early turriculatus zones early telychian the late telychian commencing in the mid lapworthi zone and after a period of apparently only small amplitude sea level fluctuations in the late sheinwoodian and earliest homerian the mid late homerian in particular the early nassa zone facies and faunal changes in the lower silurian do not support the p and s model of jeppsson and others but are consistent with the sea level changes proposed herein mid telychian marine red beds appear to have been deposited during a minor sea level fall immediately after a period of very high sea levels rather than during a transgressive episode as previously suggested comparison of the sea level curve presented herein with those constructed in the past is hampered by the lack of precision currently possible in the correlation of early silurian deep water graptolitic and shallow water shelly sequences improving the precision of this correlation should be a priority for future research

significance of early scapolite in greenschist facies marbles from the reynolds range group central australia marbles from the upper calcsilicate unit of the reynolds range group central australia experienced regional proterozoic greenschist facies metamorphism but preserve relicts of an earlier higher temperature assemblage the earlier assemblage is typified by intermediate scapolite that predates regional metamorphic fabrics and it is pseudomorphed by assemblages that were stable during regional greenschist facies metamorphism the scapolite was formed at temperatures in excess of 540 575 c far higher than the regional metamorphic temperatures 400 450 oc marbles and associated pelites display variable but lower i8 o values than are typical of greenschist facies metasediments scapolitization and lowering of isotope ratios probably resulted from pre regional metamorphic contact metamorphism around early granites

u mo ratios and δ98 95mo as local and global redox proxies during mass extinction events abstract when used in conjunction with trace metal redox proxies the use of u mo ratios and 98 95 mo values can considerably enhance the interpretation of ocean oxygenation trends both locally and globally this is illustrated with studies from two biogenic chert dominated records of mass extinction the ordovician silurian boundary and the late permian in sections from the yangtze block in south china the latest ordovician mass extinction is well known to coincide with oxygenation episode in the hirnantian stage here revealed by trace metal proxies v v ni v cr ni co that show it sandwiched between anoxic euxinic black shales the predominantly anoxic euxinic ordovician silurian strata provide a record of seawater 98 95 mo values that are seen to gradually rise during the interval from 0 5 to 1 0 the exception to the 98 95 mo stability is the datum of the slight negatively 98 95 mo associated with decreasing of v cr and v v ni ratio suggesting the hirnantian oxygenation event the upper permian chert succession at shangsi reveals an overall better ventilated record in which the best oxygenated strata show the highest u mo values that is interpreted as relative enrichment of u in suboxic conditions at a few levels anoxic euxinic conditions show the 98 95 mo values to be 2 close to modern values implying that latest permian oceans were as well ventilated as those today the well known end permian oceanic anoxic event is therefore suggested to only develop at the end of this period

isotopic and petrological evidence for the infiltration of water rich fluids during the miocene m2 metamorphism on naxos greece abstract a detailed carbon and oxygen isotopic study in conjunction with petrological work has been carried out across calcite dolomite marble layers in the high grade metamorphic sequence on the island of naxos greece the purpose of this study is to examine fluid flow during the miocene barrovian metamorphic event individual marble bands show two dominant styles of isotopic alteration from core values of 22 to 29 in 18o and 1 to 3 in 13c firstly contacts between the marble bands and surrounding pelitic rocks have altered isotopic ratios across a metre wide boundary layer the isotopic values of the marble along the contacts drop to 15 to 17 in 18o and 1 to 5 in 13c secondly there is a drop in the isotopic composition of the marbles along vein networks associated with the development of calc silicates the isotopic compositions in these veins drop to 14 to 16 in 18o and 3 to 4 in 13c cross cutting relationships observed between these two alterations allow the relative timing of infiltration to be determined the development of boundary layers is shown to result from the infiltration of fluids with isotopic signatures of 12 to 16 in 18o and 3 to 12 in 13c and an xco2 less than 0 3 these fluids are derived from dehydration of graphite bearing pelites during the prograde metamorphism these conclusions are at odds with those of previous workers who suggested that the prograde metamorphism was a result of the pervasive influx of mantle derived fluids with xco2 greater than 0 5 the alteration associated with vein networks results from peak to post peak infiltration of fluids which drive decarbonation reactions at least some of these fluids have an xco2 less than 0 05 but this is obscured by the production of co2 during the decarbonation reactions these fluids were most probably produced from the crystallising partial melts formed during the prograde metamorphism these infiltrating fluids are thought to have 18 o 10 and 13c of 5 to 7

fluid evolution and transport during metamorphism evidence from the llano uplift texas a field petrologic and stable isotopic investigation of the marbles and calc silicates of the 1 15 b y valley spring gneiss documents the dilution of internally evolved co2 rich fluids by externally derived aqueous fluids introduced along channelways reaction textures within calcsilicates record the evolution through time of initially co2 rich fluids toward increasingly more aqueous compositions assemblage zonations within calc silicates require equilibration within local gradients of the mole fraction of co2 in the fluid and suggest that the infiltration of aqueous fluids was largely channelized along more permeable lithologies localized depletions in 13c and 18o corroborate petrologic evidence for channelized infiltration isotopic compositions reflect both devolatilization and the introduction of low 18o fluids estimated minimum oxygen equivalent fluid to rock ratios are near unity both mineralogical and stable isotopic systematics document the essential role of infiltration in driving decarbonation reactions during calc silicate formation the calc silicate assemblages which equilibrated with fluids of the lowest mole fraction of co2 record isotopic exchange equilibrium with fluids of 18o typical of those derived from normal granites as do the granitic aplites and pegmatites which transect most calcsilicate occurrences thus the infiltrating fluids are believed to be genetically linked to the intrusion of a suite of granitic plutons emplaced after the peak of regional metamorphism

fluid heterogeneity during granulite facies metamorphism in the adirondacks stable isotope evidence the preservation of premetamorphic whole rock oxygen isotope ratios in adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived hot co2 h2o fluids during granulite facies metamorphism this conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations the data suggest that these rocks were not an open system during metamorphism that fluid rock ratios were in many instances between 0 0 and 0 1 that externally derived fluids as well as fluids derived by metamorphic volatilization rose along localized channels and were not pervasive and thus that no single generalization can be applied to metamorphic fluid conditions in the adirondacks

grounding line basal melt rates determined using radar derived internal stratigraphy we use ice penetrating radar data across grounding lines of siple dome and roosevelt island antarctica to measure the spatial pattern magnitude and duration of sub ice shelf melting at these locations stratigraphic layers across the grounding line show in places a large amplitude downwarp at or slightly downstream of the grounding line due to sub ice shelf basal melting localized downwarping indicates that melting is transient melt rates or the grounding line position have changed within a few hundred years in order to produce the observed stratigraphy elsewhere no melt related stratigraphic signature is preserved in part heterogeneity in the amount of sub ice shelf melt is due to regional circulation patterns in the sub shelf cavity but local on the order of tens of kilometers heterogeneity in the melt pattern may reflect small differences in the shape of the ice shelf base at the grounding line we find that all of the grounding lines crossed have been in place for at most 400 years

the influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic napperby gneiss central australia in the napperby gneiss central australia a distinctive group of elongate leucosomes occurs along the axial planes of mesoscopic crenulations that have harmonic two dimensional kink band like geometries the leucosomes truncate a fabric defined by biotite quartz k feldspar plagioclase sillimanite and are chiefly composed of k feldspar and quartz with or without plagioclase they are characterized by accessory garnet or aggregates of intergrown ilmenite and magnetite produced during the melting reactions bi plag q sill g ksp melt and bi plag q ru ilm mt ksp melt the absence of garnet and intergrown ilmenitemagnetite aggregates in the gneiss surrounding the crenulation zones indicates that these melting reactions preferentially occurred in the deformation zones in spite of a homogeneous distribution of reactant phases in the gneiss this means that strain partitioning and partial melting are coupled processes in which the garnet and ilmenite magnetite producing melt reactions initially occurred in high strain zones where the melting reaction activation energy was first overstepped this was a consequence of an additional strain induced matrix free energy component on top of the temperature effect once reaction product nucleation had occurred the deformation zones became the sites for continued melting which was energetically favoured over nucleating garnet and ilmenite magnetite elsewhere the melt reactions producing garnet and ilmenite magnetite resulted in the formation of grain supported leucosomes with a higher melt component than the surrounding gneiss and the leucosomes were therefore relatively incompetent in a differential stress field diffusional processes will cause elongation of the leucosome in a plane normal to 1 parallel to the axial planes of folds if sufficient melting has occurred an interconnected leucosome network will result creating a potentially important buoyancy driven melt drainage system in the napperby gneiss interconnected leucosome bearing crenulation zones are mostly vertical which is an ideal orientation for buoyancy driven diffusive melt migration however melt segregations remained small due to a melt impermeable lithological boundary overlying the gneiss

halogen rich scapolite and biotite implications for metamorphic fluid rock interaction abundant cl rich scapolite and biotite indicate high cl activities during greenschistthrough amphibolite facies regional metamorphism of metasedimentary rocks northwest of the idaho batholith biotite zone granofels contain up to 40 modal percent cl rich scapolite the strict stratigraphic control on the occurrence ofscapolite and the fine scale interlayering of cl rich and cl poor metasedimentary rocks suggest that scapolite was formed during regional metamorphism by reaction of plagioclase with calcite and halite mass balance constraints on the formation of scapolite show that prior to metamorphism sedimentary units containing l0 modal percent halite along restricted sedimentary horizons 0 5 to 20 cm thick would have been sufficient to form the most scapolite rich layers the abundance ofcl rich phases decreases abruptly with the appearance ofzoisite bearing assemblages in the metasedimentary rocks suggesting infiltration of low cl hro at higher grades scapolite compositions range from 32 to 62 equivalent anorthite eqan and 0 7 6 to 0 06 xo there is a general increase in eqan and decrease in x with increasing metamorphic grade however local variations in scapolite composition suggest hat metamorphic fluid compositions were heterogeneous and internally bufered biotites coexisting with scapolite contain up to 0 51 wto o cl biotite grade and 2 58 wto o f kyanite sillimanite grade biotite compositions indicate significant differences inlogffir fr values of fluids in equilibrium with low grade biotiteand carbonate rich granofels differences in the inferred metamorphic fluid compositions are observed in some cases down t o a s c a l e o f l c m cl is strongly partitioned into an aqueous fluid relative to solid phases and is removed by metamorphic devolatilization and infiltration by dilute fluids therefore the occurrence of bufered activity gradients in cl as indicated by scapolite and biotite compositions suggests that metamorphic fluid flow was highly channelized and aqueous fluid rock interaction was limited high and variable cl activities were not smoothed out by aqueous fluid rock interaction through two regional metamorphic events

proterozoic granulite facies metamorphism in the southeastern reynolds range central australia geological context p t path and overprinting relationships in the southeastern reynolds range central australia a low p granulite facies metamorphism affected two sedimentary sequences the lander rock beds and the reynolds range group in the context of the whole of the reynolds range and the adjacent anmatjira range this metamorphism is m3 in a sequence m1 4 that occurred over a period of 250 ma in particular m1 affected the lander rock beds prior to the deposition of the reynolds group m3 has an areally restricted high grade area in the southeastern reynolds range affecting both the reynolds range group and the underlying lander rock beds the effects of m3 are characterized by spinel quartz bearing peak metamorphic assemblages in metapelites which imply peak conditions of 750 c and 4 5 1 kbar and involved isobaric cooling or compression with cooling it is concluded that one of a series of thermal perturbations caused by thinning of mantle lithosphere contemporaneous with crustal thickening was responsible for m3 in the southeastern reynolds range evidence of both the unconformity between the two rock groups and previous metamorphism deformation has been completely erased by recrystallization during m3 d3

the late ordovician mass extinction abstract near the end of the late ordovician in the first of five mass extinctions in the phanerozoic about 85 of marine species died the cause was a brief glacial interval that produced two pulses of extinction the first pulse was at the beginning of the glaciation when sea level decline drained epicontinental seaways produced a harsh climate in low and mid latitudes and initiated active deep oceanic currents that aerated the deep oceans and brought nutrients and possibly toxic material up from oceanic depths following that initial pulse of extinction surviving faunas adapted to the new ecologic setting the glaciation ended suddenly and as sea level rose the climate moderated and oceanic circulation stagnated another pulse of extinction occurred the second extinction marked the end of a long interval of ecologic stasis an ecologic evolutionary unit recovery from the event took several million years but the resulting fauna had ecologic patterns similar to the fauna that had become e

ephemeral grounding as a signal of ice shelf change interferometric synthetic aperture radar insar observations of ice shelf tidal deformation reveal the wide transition between grounded and floating ice as well as local areas where the ice shelf is only grounded at low tide a condition that we call ephemeral grounding ephemeral grounding creates a subtle local disturbance on the vertical motion field of the ice shelf surface in response to changes in occanic tide which is detected with millimetric precision using insar these ice shelf features are however not expected to produce a noticeable disturbance on the ice shelf velocity field to illustrate the influence of ephemeral grounding on ice shelf creep flow we use a finite element model in which ephemeral grounding is incorporated through a variable basal friction coefficient the results show that while ice rises permanently grounded areas have a pronounced influence on the ice shelf velocity field areas of ephemeral grounding have a vanishingly small influence what is thus of most interest is the capacity for observations of ephemeral grounding to reveal subtle changes in ice shelf thickness over time we discuss an example in the thwaites glacier area west antarctica where multi year data show how ice rises become ephemeral grounding and subsequently disappear this result is consistent with the grounding line retreat and ice thinning of thwaites glacier

an ice shelf model test based on the ross ice shelf a standard numerical experiment featuring the ross ice shelf antarctica is presented as a test package for the development and intercomparison of ice shelfmodels the emphasis of this package is solution of stress equilibrium equations for an ice shelf velocity consistent with present observations as ademonstration we compare five independently developed ice shelf models based on finite difference and finite element methods our results suggest thatthere is little difference between finite element and finite difference methods in capturing the basic large scale flow features of the ice shelf we additionallyshow that the fit between model and observed velocity depends strongly on the ice shelf temperature field for which there is presently little observationalcontrol the main differences between model results are due to the equations being solved the boundary conditions at the ice front and the discretisationmethod finite element vs finite difference

trace element budgets in the ohio sunbury shales of kentucky constraints on ocean circulation and primary productivity in the devonian mississippian appalachian basin abstract the hydrography of the appalachian basin in late devonian early mississippian time is modeled based on the geochemistry of black shales and constrained by others paleogeographic reconstructions the model supports a robust exchange of basin bottom water with the open ocean with residence times of less than forty years during deposition of the cleveland shale member of the ohio shale this is counter to previous interpretations of these carbon rich units having accumulated under a stratified and stagnant water column i e with a strongly restricted bottom bottom water circulation a robust circulation of bottom waters is further consistent with the palaeoclimatology whereby eastern trade winds drove upwelling and arid conditions limited terrestrial inputs of siliciclastic sediment fresh waters and riverine nutrients the model suggests that primary productivity was high 2 g c m 2 d 1 although no higher than in select locations in the ocean today the flux of organic carbon settling through the water column and its deposition on the sea floor was similar to fluxes found in modern marine environments calculations based on the average accumulation rate of the marine fraction of ni suggest the flux of organic carbon settling out of the water column was approximately 9 of primary productivity versus an accumulation rate burial of organic carbon of 0 5 of primary productivity trace element ratios of v mo and cr mo in the marine sediment fraction indicate that bottom waters shifted from predominantly anoxic sulfate reducing during deposition of the huron shale member of the ohio shale to predominantly suboxic nitrate reducing during deposition of the cleveland shale member and the sunbury shale but with anoxic conditions occurring intermittently throughout this period

interactions of wind transported snow with a rift in the ross ice shelf antarctica 1 rifts in ice shelves accumulate a melange of snow and firn from above and marine ice from below material that has been postulated to negatively influence iceberg calving from measurements and modeling we show that a 100 m wide rift near the front of the ross ice shelf captures all wind transported snow traveling in saltation and a substantial fraction of the snow blowing in suspension across the rift moderate winds and snow transport appear sufficient to fill the rift in several years whereas the melange surface profile remains relatively constant within the 30 m deep rift observed subsidence and ocean temperatures in the rift suggest that net basal melting dissolves the melange from below limiting its effectiveness as an anti calving agent near ice fronts

high temperature metamorphic imprint on calc silicate granulites of rayagada eastern ghats india implication for the isobaric cooling path calc silicate granulites from rayagada north central sector of eastern ghats granulite belt show a wide range of mineral assemblages and chemical compositions which can be grouped as gr i grossular rich garnet wollastonite scapolite calcite clinopyroxene gr ii andradite rich garnet scapolite calcite clinopyr oxene and gr iii scapolite calcite clinopyroxene plagioclase assemblages petrographic features suggest the following several reactions in the cao al2o3 sio2 vapor system mei 4wo cal 3grs qtz 2co2 mei 3wo 2cal 3grs co2 mei 3an cal wo co2 cal qtz mei 5wo 3grs 2qtz co2 an wo grs qtz mei 5cal 3qtz 3grs 6co2 and the following reactions in the cao feo mgo al2o3 sio2 vapor system cpxss scp wo grtss qtz co2 4hd 2cal o2 2adr 2qtz 2co2 cpxss scp grtss cal qtz these reactions have been used to estimate peak t xco2 condition for these granulites a maximum temperature of 920 c has been calculated at an estimated pressure of 9 kbar a t xco2 diagram shows an isobaric cooling from 920 c to 815 c a range of xco2 0 50 at 920 c to 0 25 at 815 c has been observed for gr i calc silicate granulites based on the reaction sequences including coronal garnet forming reactions this sequence is suggestive of internal fluid buffering rather than external fluid influx and the differences in xco2 conditions has been thought to be due to local buffering of fluid phases group ii and gr iii calc silicate granulites on the other hand exhibit relatively lower temperature conditions

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

lower silurian hot shales in north africa and arabia regional distribution and depositional model abstract lowermost silurian organic rich hot shales are the origin of 80 90 of palaeozoic sourced hydrocarbons in north africa and also played a major role in petroleum generation on the arabian peninsula in most cases the shales were deposited directly above upper ordovician peri glacial sandstones during the initial early silurian transgression that was a result of the melting of the late ordovician icecap deposition of the main organic rich shale unit in the north african arabian region was restricted to the earliest silurian rhuddanian stage acuminatus atavus and probably early cyphus graptolite biozones during this short period 1 2 m y a favourable combination of factors existed which led to the development of exceptionally strong oxygen deficiency in the area in most countries of the study area the post rhuddanian silurian shales are organically lean and have not contributed to petroleum generation the distribution and thickness of the basal silurian hot shales have been mapped in detail for the whole north african region using logs from some 300 exploration wells in libya tunisia algeria and morocco in addition all relevant accessible published and unpublished surface and subsurface data of the lower silurian shales in north africa and arabia have been reviewed including sedimentological biostratigraphic and organic geochemical data the lowermost silurian hot shales of northern gondwana are laterally discontinuous and their distribution and thickness were controlled by the early silurian palaeorelief which was shaped mainly by glacial processes of the late ordovician ice age and by pan african and infracambrian compressional and extensional tectonism the thickest and areally most extensive basal silurian organic rich shales in north africa occur in algeria tunisia and western libya while on the arabian peninsula they are most prolific in saudi arabia oman jordan and iraq the hot shales were not deposited in egypt which was a large palaeohigh at that time the depositional model presented may help in better understanding the source potential of the basal silurian shales in less explored regions of north africa and arabia including morocco northern niger and the kufra basin in southeast libya

end ordovician extinctions a coincidence of causes the end ordovician hirnantian extinction was the first of the five big phanerozoic extinction events and the first that involved metazoan based communities it comprised two discrete pulses both linked in different ways to an intense but short lived glaciation at the south pole the first occurring at or just below the normalograptus extraordinarius graptolite biozone mainly affected nektonic and planktonic species together with those living on the shallow shelf and in deeper water whereas the second within the n persculptus graptolite biozone was less focused eradicating faunas across a range of water depths in all about 85 of marine species were removed proposed kill mechanisms for the first phase have included glacially induced cooling falling sea level and chemical recycling in the oceans but a general consensus is lacking the second phase is more clearly linked to near global anoxia associated with a marked transgression during the late hirnantian most recently however new drivers for the extinctions have been proposed including widespread euxinia together with habitat destruction caused by plate tectonic movements suggesting that the end ordovician mass extinctions were a product of the coincidence of a number of contributing factors moreover when the deteriorating climate intensified causing widespread glaciation a tipping point was reached resulting in catastrophe

orbital control on cyclical primary productivity and benthic anoxia astronomical tuning of the telychian stage early silurian abstract the identification of milankovitch cycles and the establishment of a high resolution astronomical time scale for the palaeozoic represent a research frontier in cyclostratigraphy and astrochronology a continuous core drilled through the telychian stage llandovery silurian of the paslek formation in the baltic basin poland is characterized by repetitive centimetre scale alternations of homogeneous greenish grey mudstones and faintly laminated dark grey to black mudstones such lithological rhythmicity reflects a cyclical variation in redox conditions at the sediment water interface and therefore was used to construct a floating astronomical time scale ats for the telychian stage the cyclostratigraphic analysis was performed on a 5 mm resolution greyscale scan based upon photographs of the slabbed core with lower values associated with greenish grey mudstones and higher values related to dark grey to black mudstone facies spectral density estimation by means of the multitaper method mtm reveals significant peaks rising above the 95 red noise confidence level that we interpret as the 405 kyr long eccentricity short eccentricity obliquity and precession components the mtm evolutive power spectral analysis epsa shows a gradual increase in the velocity of sedimentation from 5 03 m myr in the lowermost interval to 5 48 m myr towards the uppermost part of the studied sequence we postulate that the observed cycles reflect orbitally driven climatic variations from stable wet conditions to monsoon like high seasonal contrasts that affected weathering intensity runoff and nutrient supply these cyclical variations led to rhythmic variations in organic matter fluxes and benthic anoxic conditions in the analysed record orbital precession influenced the deposition of the greenish grey mudstone and dark grey to black mudstone couplets occurring on average every 10 cm furthermore long eccentricity modulation of precession controlled the relative depositional predominance of one facies over the other observed periodicities resemble those of cenozoic and mesozoic orbitally controlled records thus suggesting that during the silurian the orbital eccentricity forcing on the carbon flux acted in the same way as in the cenozoic and mesozoic the orbital tuning of the studied interval calibrated by means of accurate acritarch biostratigraphy allowed for the estimation of an astronomically calibrated duration for the telychian stage of about 5 46 myr

channelled fluid infiltration and variation in permeability in reynolds range marbles australia strike parallel flow of h 2 o rich fluids through reynolds range marbles formed wollastonite bearing assemblages wollastonite abundance varies on a millimetre de from 10 to 66 modal the mineralogy of unmetasomatized marbles suggests that the formation of more than c 19 wollastonite requires silica metasomatism comparison with advective transport models suggests that the variable wollastonite contents may be explained by time integrated fluid fluxes and intrinsic permeability varying by up to two orders of magnitude on a millimetre scale fluids were probably focused through the marble within microfractures and the variations in intrinsic permeability may reflect variable fracture density

sapphirine kornerupine rocks from the reynolds range central australia constraints on the uplift history of a proterozoic low pressure terrain sapphirine kornerupine bearing rocks from the reynolds range northern territory australia preserve spectacular metamorphic reaction textures that provide valuable insights into the regional metamorphic uplift history the rocks occur in pods that are several meters in diameter within high temperature low pressure 750 to 800 c and 4 to 5 kbar granulite facies exposures of the early proterozoic lander rock beds a laterally extensive sequence of folded pelitic and quartzose metasediments the pods are not associated with large volumes of partial melts and are likely to have formed by metasomatism near the peak of m2 metamorphism the rocks in the pods consist of high temperature mg and al rich minerals such as boron free korneurpine and are coarse grained 0 5 to 15 cm non foliated and locally nearly monomineralic the growth of the coarse minerals in the pods largely post dated the high grade regional metamorphic d2 fabric and completely reconstructed the precursor rocks the retrograde metamorphic reaction textures show that the early retrogression from the m2 granulite facies conditions was characterized not by isobaric cooling as previously proposed but by nearly isthermal decompression these data imply that the reynolds range did not follow a simple anticlockwise p t t path because rocks such as these preserve information from a only restricted portion of the metamorphic history and can preserve evidence of decompression reactions more clearly than many more ordinary lithologies they can be especially important for discerning metamorphic p t t paths

the origin of pyrite mineralization implications for late cambrian geology of the holy cross mountains south central poland abstract this paper presents results of a petrographic mineralogical and geochemical study of ore gangue and rock forming minerals that occur within the upper cambrian furongian age siliciclastic rocks of the wi niowka massif western part of the main range holy cross mountains south central poland this area is characterized by the presence of ubiquitous pyrite that makes up two stratiform mineralization zones assigned to the early and middle late cambrian giving rise to acid mine drainage the oldest zone comprises additionally sedimentary breccias with intraclast supported pyrite cement the predominant microscopic colloform and partly framboidal pyrite typically shows high concentrations of as up to 8 23 wt and a distinct enrichment in the light sulfur isotope 34s from 41 4 to 23 6 the occurrences of large amounts of as rich pyrite showing strongly negative 34s values are rather uncommon in paleozoic sedimentary formations worldwide that exhibit distinctly smaller amounts of as and mostly enrichments in heavier sulfur isotope 34s up to 63 another specific feature of the wi niowka rock series is the presence of ree bearing aluminophosphate and phosphate minerals that occur primarily in clayey silty shales and bentonites based on the results obtained a sequence of hydrothermal index minerals was discriminated including pyrite whose grains are usually made of alternating arsenic rich and arsenic poor bands as well as paragenetic assemblages of dickite nacrite xenotime and the crandallite series of aluminum phosphate sulfate minerals both mineral composition and specific microtextures are indicative of multistage hydrothermal activity that took place in the wi niowka depositional basin during the late cambrian time this is in distinct contrast to the remaining part of the main range which is devoid of the hydrothermal pyrite imprint moreover the results of this study give insight into the complex sedimentary and early diagenetic history of the southwestern passive margin of the baltica craton this currently makes up a part of the ysogory block terrane that borders on the trans european suture zone separating the precambrian east european craton from the paleozoic platform of central europe this study is important because we still lack the full knowledge about the hydrothermal processes that took place in early paleozoic depositional basins

analysis of marine environmental conditions based onmolybdenum uranium covariation applications to mesozoic paleoceanography article i nfo article history accepted 13 september 2011 available online 17 september 2011 patterns of uranium molybdenum covariation in marine sediments have the potential to provide insights re garding depositional conditions and processes in paleoceanographic systems specifically such patterns can be used to assess bottom water redox conditions the operation of metal oxyhydroxide particulate shuttles in the water column and the degree of water mass restriction the utility of this paleoenvironmental proxy is due to the differential geochemical behavior of u and mo 1 uptake of authigenic u by marine sediments begins at the fe ii fe iii redox boundary i e suboxic conditions whereas authigenic mo enrichment re quires the presence of h2s i e euxinic conditions and 2 transfer of aqueous mo to the sediment may be enhanced through particulate shuttles whereas aqueous u is unaffected by this process in the present study we examine u mo covariation in organic rich sediments deposited mostly in the western tethyan region during oceanic anoxic events oaes of early jurassic to late cretaceous age our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regard ing water mass restriction and the operation of particulate shuttles in depositional systems these insights will help to address contentious issues pertaining to the character and origin of mesozoic oaes such as the degree to which regional paleoceanographic factors controlled the development of the oaes

discrete proterozoic structural terranes associated with low p high t metamorphism anmatjira range arunta inlier central australia tectonic implications structural overprinting relationships indicate that two discrete terranes mt stafford and weldon occur in the anmatjira range northern arunta inlier central australia in the mt stafford terrane early recumbent structures associated with d1a 1b deformation are restricted to areas of granulite facies metamorphism and are overprinted by upright km scale folds f1c which extend into areas of lower metamorphic grade structural relationships are simple in the low grade rocks but complex and variable in higher grade equivalents the three deformation events in the mt stafford terrane constitute the first tectonic cycle d1 d2 deformation in the weldon terrane comprises the second tectonic cycle the earliest foliation s2a was largely obliterated by the dominant reclined to recumbent mylonitic foliation s2b produced during progressive non coaxial deformation with local sheath folds and w to sw directed thrusts locally d2d tectonites have been rotated by n s trending upright f2c folds but the regional upright fold event f2d also evident in the adjacent reynolds range rotated earlier surfaces into shallow plunging nw se trending folds that dominate the regional outcrop pattern the terranes can be separated on structural metamorphic and isotopic criteria a high strain d2 mylonite zone produced during w to sw directed thrusting separates the weldon and mt stafford terranes 1820 ma megacrystic granites in the mt stafford terrane intruded high grade metamorphic rocks that had undergone d1a and d1b deformation but in turn were deformed by s1c which provides a minimum age limit for the first structural metamorphic event 1760 ma charnockites in the weldon terrane were emplaced post d2a and metamorphosed under granulite facies conditions during d2b constraining the second tectonic cycle to this period each terrane is associated with low p high t metamorphism characterized by anticlockwise p t t paths with the thermal peaks occurring before or very early in the tectonic cycle these relations are not compatible with continental style collision nor with extensional tectonics as the deformation was compressional the preferred model involves thickening of previously thinned lithosphere at a stage significantly after 50 ma the early extensional event compression was driven by external forces such as plate convergence but deformation was largely confined to and around composite granitoid sheets in the mid crust the sheets comprise up to 80 of the terranes and induced low p high t metamorphism including migmatization thereby markedly reducing the yield strength and accelerating deformation of the country rocks mid crustal ductile shearing and reclined to recumbent folding resulted followed by upright folding that extended beyond the thermal anomaly thus thermal softening induced by heat focusing is capable of generating discrete structural terranes characterized by subhorizontal ductile shear in the mid crust localized around large granitoid intrusions

late neoproterozoic to early palaeozoic palaoegeography of the holy cross mountains central europe an integrated approach study of geochemistry examination of isotope ages of detrital minerals palaeomagnetic analysis and a study of the trilobites were performed to provide constraints on the palaeogeographical position of the holy cross mountains in late ediacaran early palaeozoic time the geochemical results indicate an active continental margin or continental island arc provenance of the ediacaran sediments sediments from a passive continental margin were deposited here during the cambrian and ordovician the palaeomagnetic pole isolated from cambrian rocks of the malopolska region of the holy cross mountains corresponds to the cambrian segment of the baltic apparent polar wander path isotope age estimations indicate that cambrian sediments of the malopolska region contain detritus not only from a latest neoproterozoic source but also from sources with ages of c 0 8 0 9 ga 1 5 ga and 1 8 ga the malopolska brunosilesia dobrugea and moesia terranes which originally developed near the present southern edge of baltica and were partly involved in the cadomian orogen were dextrally relocated along its trans european suture zone margin the first stage of this movement took place as early as latest ediacaran time while baltica rotated anticlockwise anticlockwise rotation of baltica at the cambrian ordovician boundary implies further dextral movement of the malopolska block

black shale deposition in an upper ordovician silurian permanently stratified peri glacial basin southern jordan abstract the lower palaeozoic upper ordovician silurian succession of north africa contains one of the world s most prolific black shale source rocks yet the origin of these rocks remains contentious the black shale of the batra formation in jordan was deposited at high palaeolatitude during rapid hirnantian to early silurian deglaciation here we report geological and organic geochemical results that provide evidence for an increase in photic zone primary productivity during ice melting the decay of this organic matter through oxidative respiration resulted in euxinia which enhanced the potential for organic matter preservation the occurrence of isorenieratane in all samples indicates euxinia extended from the photic zone to the sediment water interface the stratified basins and fjords of east antarctica provide a likely modern analogue

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

the middle rhuddanian lower silurian hot shale of north africa and arabia an atypical hydrocarbon source rock an important hydrocarbon source rock a hot shale has been identified from the middle rhuddanian llandovery lower silurian of a number of localities in north africa and arabia it is unusual in having been deposited during a eustatic fall in sea level evidence for this sea level fall in libya and jordan is manifested in a wide variety of palynological proxy data including reduced acritarch and chitinozoan total abundance reduced acritarch diversity and changes in the relative abundances of various environmentally sensitive acritarch morphogroups and from the presence of a minor positive 13corg excursion at the same stratigraphical level as the hot shale the environment of deposition was anoxic before during and after deposition of the hot shale except for some very brief incursions of more oxygenated water that enabled the development of a very limited burrowing benthos and graptolite preservation as three dimensional pyrite internal moulds these incursions occurred just before and during deposition of the hot shale and are interpreted as resulting from the influx of sediment laden oxygenated currents from shallower water environments enhanced organic matter preservation within the hot shale is attributed to greater productivity resulting from increased nutrient input particularly from wind blown dust more rapid descent through the water column of organic matter in post bloom marine snow macroaggregates development of geochemically sealing microbial mats at the sea floor and more rapid burial of organic material than had occurred earlier in the rhuddanian

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

the geological evolution of the reynolds range central australia evidence for three distinct structural metamorphic cycles the reynolds range is affected by three distinct structural metamorphic cycles di mi dii mii anddiii miii which represent the local expressions of a series of orogenic events that affected large sections of the arunta block central australia the tectonic cycles recognized in the reynolds range correlate extremely well with similar events in the nearby anmatjira range di mi took place around 1820 ma and only affected the nw reynolds range dii mii occurred between 1760 and 1650 ma and involved ne sw shortening with identical timing relationships between the deformations and metamorphism along the entire reynolds range dii commenced with the formation of a fabric sii1 preserved as inclusion trails in porphyroblasts sii1 formed early during a progressive event dii1 2 which involved the formation and tightening of upright nw se trending isoclinal folds a penetrative subvertical nw se trending fabric sii2 developed axial planar to these folds the general symmetry of dii2 microstructures suggests that fii2 folds were formed during progressive coaxial deformation under plane strain conditions dii3 structures are associated with conjugate sets of crenulation bands within the macroscopic crenulation bands large sections of earlier folds and fabrics are rotated to a near recumbent position the dominant set of crenulation bands is upright and trends ene wsw while the conjugate to this set trends nw se no penetrative fabric formed during dii3 dii4 is associated with a system of amphibolite grade ne dipping thrusts interconnected by numerous smaller shear zones the sense of movement is ne over sw during dii essentially penetrative coaxial deformation dii2 evolved into essentially localized non coaxial deformation dii3 dii4 dii deformation occurred concomitant with a low pressure granulite facies metamorphic event mii 1730 ma peak metamorphic sillimanite cordierite orthopyroxene ilmenite spinel garnet k feldspar quartz assemblages define sii2 oriented sillimanite biotite assemblages that formed early during dii3 and unoriented andalusite chlorite muscovite assemblages that formed late during dii3 indicate that cooling of mii was initially isobaric during dii4 thrusting staurolite garnet biotite quartz and biotite kyanite quartz assemblages defining the mylonitic fabric overprint the late dii3 andalusite assemblages dii4 shear movement is therefore accompanied by a slight rise in pressure dii4 shear zones gradually increase in grade eastward along the reynolds range this trend coincides with the variation in peak metamorphic grade attained during mii indicating that the rocks had not yet fully cooled when dii4 thrusting commenced diii miii is late devonian to carboniferous in age and caused minor differential movement 100 m and retrogression along dii4 shear zones

strain in the ice sheet deduced from the crystal orientation fabrics from bare icefields adjacent to the sor rondane mountains dronning maud land east antarctica

pyrite framboid study of marine permian triassic boundary sections a complex anoxic event and its relationship to contemporaneous mass extinction size analysis of pyrite framboids has been undertaken on epicontinental permian triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia mid paleolatitude sections from the margins of the boreal spitsbergen greenland and neotethyan oceans western australia reveal intense anoxia throughout the permian triassic boundary interval with euxinic conditions frequently developing and dysoxia encountered even in relatively shallow water settings above storm wave base at equatorial paleolatitudes weakly oxygenated dysoxic conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition although euxinia was rare western and eastern tethyan locations re veal a complex and unstable redox history anoxia in the hindeodus praeparvus zone was replaced by oxygenated facies in the permian triassic boundary interval h changxingensis to h parvus zones oxygen poor deposition returned during the succeeding isarcicella isarcica zone the more persistent and intense development of oxygen restriction in cooler water mid paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of permian triassic bound ary anoxia in higher paleolatitudes the ben thic invertebrate extinctions occurred during a prolonged phase of oxygen poor deposition while in equatorial tethyan locations benthic losses occurred at the end of the fi rst anoxic phase in the late h praeparvus zone

granulite facies metasomatism zoned calc silicate boudins from the rauer group east antarctica calc silicate boudins from the rauer group east antarctica were metamorphosed under granulite facies conditions during late proterozoic ca 1 000 ma m3 metamorphism boudin cores contain low to moderate aco2 assemblages including wollastonite grossularandradite grandite garnet clinopyroxene scapolite plagioclase quartz calcite petrological and stable isotopic evidence suggests that these core assemblages resulted from pre peak m3 infiltration of water rich fluids there is no evidence for a pervasive fluid phase under peak m3 conditions the boudins are separated from the surrounding fe rich pelites and semi pelites by a series of concentric high variance reaction zones developed under peak m3 conditions variations in mineral assemblage mineral composition and whole rock composition across these zones suggest that they formed by diffusional masstransfer controlled principally by a chemical potential gradient in ca across the original calc silicate paragneiss lithological boundary as a consequence of the nearcomplete decarbonation of the calc silicatesbefore the m3 peak development of the diffusion controlled reaction zones did not liberate significant co2 during granulite facies metamorphism similar calcite poor low aco2 calc silicate horizons in other granulite facies terrains are unlikely to have been important local fluid sources during deep crustal metamorphism

lower wenlock black shales in the northern holy cross mountains poland sedimentary and geochemical controls on the ireviken event in a deep marine setting the stratigraphic variability and geochemistry of llandovery wenlock l w series boundary sediments in poland reveals that hemipelagic sedimentation under an anoxic euxinic water column was interrupted by low density bottom currents or detached diluted turbid layers that resulted in intermittent seafloor oxygenation total organic carbon values and inorganic proxies throughout the wilkow 1 borehole section suggest variable redox conditions u mo ratios 1 throughout much of the aeronian and telychian stages together with an absence of pyrite framboids suggest oxygenated conditions prevailed however elevated total organic carbon near the aeronian telychian boundary together with increased u th and v v ni ratios and populations of small pyrite framboids are consistent with the development of dysoxic anoxic conditions at that time u th v cr and v v ni ratios as well as u authig and mo concentrations suggest that during the ireviken black shale deposition bottom water conditions deteriorated from oxic during telychian time to mostly suboxic anoxic immediately prior to the l w boundary before a brief reoxygenation at the end of the ireviken black shale sedimentation in the sheinwoodian stage rapid fluctuations in u mo during the ireviken event are characteristic of fluctuating redox conditions that culminated in an anoxic euxinic seafloor in sheinwoodian time following ireviken black shale deposition conditions once again became oxygen deficient with the development of a euxinic zone in the water column the aeronian to sheinwoodian deep water redox history was unstable and rapid fluctuations of the chemocline across the l w series boundary probably contributed to the ireviken event extinctions which affected mainly pelagic and hemipelagic fauna

llandovery green grey and black mudrock facies of the northern holy cross mountains poland and their relation to early silurian sea level changes and benthic oxygen level abstract the llandovery mudrock facies in the northern holy cross mountains reveal lithological variability allowing their interpretation in the context of post ordovician climate and sea level changes in the caledonian foredeep basin developed along the present sw margin of baltica they form a succession up to 50 m thick made up of grey and greenish clayey mudstones interrupted by black shales the sedimentary and geochemical data total organic carbon pyrite framboids and trace metals clearly show that the black shales document periods of the significant sediment starvation and oxygen deficient conditions their occurrence is confined to the persculptus acuminatus vesiculosus cyphus convolutus sedgwickii turriculatus crispus crenulata and spiralis graptolite biozones and they can be correlated with post glacial transgressions in contrast the grey and greenish mudstones are interpreted as lithofacies reflecting permanent benthic oxygenation driven by deep water ventilation during the aeronian and telychian regressions supported by sedimentary and geochemical studies and diameters of pyrite framboids

a sulfidic driver for the end ordovician mass extinction the end ordovician extinction consisted of two discrete pulses both linked in various ways to glaciation at the south pole the first phase starting just below the normalograptus extraordinarius zone particularly affected nektonic and planktonic species while the second pulse associated with the normalograptus persculptus zone was less selective glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end ordovician extinction but a general consensus is lacking we have used geochemical redox indicators such as iron speciation molybdenum concentrations pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key hirnantian sections these indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end ordovician extinction and that these conditions expanded towards the second pulse even though the n extraordinarius zone appears to have been a time of oxygenated deposition pyrite is significantly enriched in 34s in our sections as well as in sections reported from south china this suggests a widespread reduction in marine sulfate concentrations which we attribute to an increase in pyrite burial during the early hirnantian the s isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well we argue that euxinic conditions prevailed and intensified in the early hirnantian oceans and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites in the n persculptus zone an interval associated with a major sea level rise our redox indicators suggests that euxinic conditions and ferruginous in some places encroached onto the continental shelves in our model the expansion of euxinic conditions during the n extraordinarius zone was generated by a reorganization of nutrient cycling during sea level fall and we argue overall that these dynamics in ocean chemistry played an important role for the end ordovician mass extinction during the first pulse of the extinction euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep water benthic and nektonic organisms during the second pulse the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

comparison of ice shelf creep flow simulations with ice front motion of filchner ronne ice shelf antarctica detected by sar interferometry comparison between numerical model ice shelf flow simulations and synthetic aperture radar sar interferograms is used to study the dynamics at the hemmen ice rise hir and lassiter coast lc corners of the iceberg calving front of the filchner ronne ice shelf fris

heterogeneity characterization of the lower silurian longmaxi marine shale in the pengshui area south china abstract the heterogeneity of shale is significant for the evaluation and sweet spot prediction of a shale gas reservoir core observations thin sections field emission scanning electron microscopy fe sem nitrogen gas adsorption n2ga and geochemical analyses were performed on shale samples from the lower longmaxi formation in the pengshui area of south china in this study the macroscopic and microscopic heterogeneities of the longmaxi shale are revealed and their origins and inner link are also discussed the results show that three systems tracts were developed in the lower longmaxi formation a transgressive systems tract tst early highstand systems tract ehst and late highstand systems tract lhst from tst to lhst toc total organic carbon siliceous minerals quartz feldspar and pyrite show an upward decreasing trend in weight content while the clay minerals and carbonate contents increase upward hence the tst ehst and lhst shales are generally characterized by organic rich shale lithofacies organic moderate shale lithofacies and organic lean shale lithofacies respectively the in situ gas content decreases from tst to lhst and primarily depends on toc content the sedimentary environment of the tst shale is an anoxic environment with high paleoproductivity which then evolves to a dysoxic oxic environment in the ehst shale and an oxic environment in the lhst shale with relatively low paleoproductivity organic matter pores are the primary contributors to the total pore volume in the tst shale and then the pore content and role in porosity decrease upward from ehst to lhst however the proportions of clay related pores and brittle mineral related pores gradually elevate from the tst shale to the lhst shale the sedimentary environment including water depth redox conditions paleoproductivity terrigenous input and hydrodynamics etc control the development of organic matter mineral composition lithofacies association color bedding and palaeobios in the lower longmaxi shales which constitute the macroscopic heterogeneity nevertheless the microscopic heterogeneity of shale originates from diagenesis catagenesis specifically shales are primarily composed of interparticle pores and clay related pores during deposition and the porosity is reduced primarily under mechanical compaction and chemical cementation as the burial depth and diagenetic degree increase a large number of organic matter pores and dissolution pores begin to appear which are associated with the hydrocarbon generation process moreover macroscopic shale composition plays a crucial role in development levels of microscopic shale pores

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

the relative permeabilities of quartzites and schists during active metamorphism at mid crustal levels the hot spot near bristol new hampshire was an area of high fluid flow during metamorphism in order to determine the mechanisms of fluid flow through the area we made a detailed study of the 18o values of quartz from an outcrop of interlayered quartzites and schists results indicate that the permeability of the quartzite was very low in comparison to that of the schist the 18qtz values from schist layers are remarkably homogenous 15 5 15 8 in contrast to the 18qtz values of schist units outside of the hot spot which vary widely quartz veins that cut the quartzites and pinch out in the schists have the same 18o values 15 7 as quartz from the schists in the quartzites 18qtz values immediately adjacent to the veins and schists are similar to those in the veins and schists but decrease by 1 permil in the centers of the layer we interpret these results to indicate that fluid flow in the hot spot was mainly through the schists and fractures in the quartzites the oxygen isotope exchange fronts in the quartzites prove that there was some flow from the the schists and the fractures into the quartzites comparisons of the shapes of these exchange fronts with exchange fronts predicted by two different models of fluid flow in rocks indicate that fluid transport in the quartzite was predominantly by advection and that the kinetic rates of isotope exchange were fast relative to the advective velocity of the fluid infiltrating the system considering the slow rate of oxygen isotope exchange between quartz and a fluid this implies that fluid flow from the schist and vein fracture into the quartzite was extremely limited

upper ordovician and silurian ash beds in the holy cross mountains poland preservation in mudrock facies and relation to atmospheric circulation in the southern hemisphere numerous volcanic ash beds k bentonite are recognized globally in ordovician to early devonian sedimentary successions and are important for regional stratigraphic correlations relatively little however is understood of the origin and transport of these ash deposits here we examine ash beds preserved in the upper ordovician and silurian dark shales and mudstones of the holy cross mountains poland and discuss their origin in the context of contemporaneous tectonic configurations the ordovician ash beds occur in the upper sandbian and katian mudrock succession whereas the silurian k bentonites form prominent beds in the upper wenlock and lower ludlow graptolite shales their various thickness and irregular distribution reflect fluctuation of volcanic activity and contribution of physical and biogenic factors in their preservation deposition under dysoxic or anoxic conditions and relatively rapid burial by muddy sediment seem to be dominant factors preventing physical and biological reworking and mixing of the volcanic ash the upper ordovician ash beds in the holy cross mountains as well as the baltoscandian k bentonites appear to be accumulated from pyroclastic material delivered by westerlies of the southern hemisphere from the avalonian volcanoes in the silurian the distribution of pyroclastic material was controlled by se trade winds and therefore the source area for the wenlock and ludlow k bentonites in the holy cross mountains appears to have been an active subduction zone developed close to the southeastern side of baltica however the delivery of volcanic ash to the central part of baltica might have been strongly affected by climatically driven latitudinal migration of the intertropical convergence zone

paleomagnetism and integrated stratigraphy of the upper berriasian hemipelagic succession in the barlya section western balkan bulgaria implications for lithogenic input and paleoredox variations abstract a continuous late berriasian sedimentary and stratigraphic record is here presented from a hemipelagic succession from the western balkan barlya section bulgaria the section 39 m thick was stratigraphically calibrated using a variety of methods biostratigraphy calpionellids calcareous nannofossils and calcareous dinocysts magnetostratigraphy and carbon isotope stratigraphy additionally chemostratigraphy and rock magnetic stratigraphy were applied in order to identify major paleoenvironmental changes lithogenic input and paleoredox variations polarity zones from m17r to m14r were identified from the uppermost lower berriasian up to the berriasian valanginian boundary elliptica to darderi calpionellid subzones and nk 1 to nk 3 nannofossil zones late berriasian calcareous dinocyst zones of stomiosphaerina proxima stomiosphaera wanneri and colomisphaera conferta were correlated with magnetostratigraphy for the first time a carbon isotope profile correlates very well with the 13 c records from se france and the western atlantic documenting some well resolved minima and maxima in a generally decreasing trend magnetic susceptibility ms reveals a very good positive correlation with lithogenic elements e g al ti zr th and others and is regarded as a reliable proxy of detrital input influx of fine grained terrigenous material increases in the upper berriasian up to the berriasian valanginian boundary a prominent ms increase takes place in the lowermost part of polarity zone m16n close to the simplex oblonga subzonal boundary the ms event can be traced in the central carpathian apennine and se france sections exactly in the same stratigraphic position it is coeval with an important climatic turnover in western tethys however it might have been strengthened by a general regression and regional tectonic events in the carpatho balkan area two oxygen deficient intervals were documented the first in the lower berriasian m17r to m16r the second one in the uppermost upper berriasian up to the boundary with valanginian m15r to m14r both intervals correlate with an elevated sea level in the western tethys

isobaric cooling of proterozoic high temperature metamorphites in the northern arunta block central australia implications for tectonic evolution abstract protoliths of metamorphites in the proterozoic reynolds range region northern arunta block central australia included mafic and felsic igneous rocks pelites calcareous rocks and quartzites metamorphism began with an early high t low p facies stage followed by early rehydration in higher grade areas isobaric cooling and late high t low p facies hydration in and near shear zones metamorphic grade increases southeastwards shown by the change from andalusite in metapelites in the northwest to sillimanite in the southeast and by the incoming of cordierite cordierite biotite cordierite k feldspar sillimanite and cordierite garnet migmatites kornerupine quartz spinel and orthopyroxene k feldspar assemblages occur in the highest grade rocks downwarping at near peak temperatures is shown by garnet sillimanite replacing cordierite and by sillimanite pseudomorphing andalusite early in the near isobaric cooling that followed peak temperatures freezing of partial melts released water and biotite formed the hydrated retrograde assemblages formed after temperatures had fallen considerably are also zoned from northwest to southeast with andalusite sillimanite or kyanite bearing assemblages developed in appropriate bulk compositions the early high t metamorphism is best explained by tectonic models based on extension crustal delamination and underplating the hydration and deformation were caused by processes unrelated to the early history occurring at least 200 ma later possibly as late as the mid palaeozoic

analysis of coseismic surface displacement gradients using radar interferometryc new insights into the landers earthquake the map of the coseismic displacement field generated by interferometric processing of synthetic aperture radar lsarr images taken before and after the june 28 1992 landers earthquake sequence brings new insights into the nature of deformation caused by these earthquakes we use the interferometric map generated by massonnet et al l1993r to analyze the surface displacement field in the vicinity of the fault trace complexities in the fringe pattern near the fault reflect shorthwavelength variations of the surface rupture and slip distribution and attest to large displacement gradients along two sections of the fault characteristic fringe patterns can be recognized contrasting in density and direction with patterns observed away from the rupture in order to understand the observed fringe patterns we compute synthetic interferograms in three simple cases l1r rigidhbody rotations about a vertical axis l2r about a horizontal axis ltiltr and l3r distributed simple shear the orientation and spatial separation of interferometric fringes predicted by these models help constrain nearhfield deformation and rupture parameters where the kickapoo fault connects with the homestead valley fault the interferogram shows a clear pattern of parallel n20 w fringes separated by about 160 m this pattern and vertical offsets measured along the kickapoo fault suggest that the block between this fault and the johnson valley fault may have been tilted down to the west a 5hkm block lifted by l m on one side would be tilted by an angle of 0 01 l190 radr producing fringes separated by about 160 m parallel to the tilt axis such a tilt parallel to a n20 w direction would account for the gradual northward increase of the vertical slip component observed along the kickapoo fault this tilt may also explain the 1 m of reverse slip observed along the slip gap section of the homestead valley break between the southern end of the johnson valley fault and the eureka peak fault where no surface rupture has been mapped the dense pattern of fringes implies distributed shear probably resulting from fault slip at depth the density and direction of the fringes in the gap are consistent with a righthlateral slip of 1 2 3 8 m on a blind fault locked above the depth of 1 5 2 km such observations of small wavelength features in the sar interferogram bring new insights into the nearhfield displacement gradient and thus on response of the uppermost crust to seismic rupture

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

glaciological advances made with interferometric synthetic aperture radar spaceborne interferometric synthetic aperture radar insar techniques for measuring ice flow velocity and topography have developed rapidly over the last decade and a half revolutionizing the study of ice dynamics spaceborne interferometry has contributed to major progress in many areas of glaciological study by providing the first comprehensive measurements of ice stream flow velocity over the major outlets of greenland and antarctica revealing that ice stream and outlet glacier flow can change rapidly months to years improving understanding of several ice sheet and ice shelf processes providing velocity for flux gate based mass balance assessment mapping flow of mountain glaciers and capturing the geomorphic traces of past ice flow we review the basic technique development the measurement characteristics and the extensive set of results yielded by these measurements