the ktb apatite fission track profiles building on a firm foundation abstract deep boreholes serve as natural laboratories for testing thermochronometers under geological conditions the kontinentale tiefbohrung ktb is an interesting candidate because the geological evidence suggests that approximate isothermal holding since the last documented exhumation in the late cretaceous to palaeocene is a reasonable assumption for the thermal histories of the ktb samples we report 30 new apatite fission track ages and 50 new mean confined track lengths determined on cores from the 4 km deep pilot hole the and external detector ages are consistent with the population ages from earlier studies and together define a clear age profile the mean track lengths from this and earlier studies reveal the effects of experimental factors the measured age and length profiles are compared with the predictions of 24 annealing models for isothermal holding there are clear discrepancies between the measured and calculated profiles down to 1 5 km depth the measured mean track lengths are shorter than the predicted the balance of methodological evidence indicates that this is due to seasoning i e a shortening of the fossil confined tracks without attendant age reduction from 2 5 to 4 0 km depth the mean track lengths are longer than the predictions this suggests that the bias model that weights the probabilities of observing tracks of different length and which is based on experiments relating surface track densities to mean track lengths is not appropriate for confined tracks experimental and methodological factors are sometimes difficult to disentangle but present a sufficient margin for there to be no need to go against the independent geological evidence unknown geological events cannot be ruled out but their existence cannot be inferred from the fission track data alone much less can the nature or magnitude of such events be specified

thin lithosphere asthenosphere boundary beneath eastern indian craton the lithosphere asthenosphere boundary lab separates the hard and rigid outer layer of the earth lithosphere and the weaker hotter and deeper part of the upper mantle asthenosphere and plays a pivotal role in plate tectonics however its definitive detection especially beneath the cratons is proving elusive one of the geophysical tools used to map the lab beneath the cratons is through magnetotelluric mt observations the resistivity at boundary falls in the range of 5 25 m and can be explained by the presence of a small amount of water in the asthenosphere possibly inducing partial melt here we report thickness of the lab in one of the oldest dated ancient cratons of india eastern indian craton eic of 3 3 gyr from mt studies the two prominent phase sensitive strike directions one each for crust and mantle and the presence of resistive continental lower crust act as a window to mantle in resolving deeper electrical conductivity structures beneath eic our results show that the lab beneath the eic is at 95 km the region is interesting as the electrical properties of the crust and mantle and the moho depth are similar to those of the slave craton canada 4 0 gyr but the depth of the lab beneath the eic is half that of the slave craton as cratonic signatures depicted by ultrapotassic rocks from gondwana coal fields close to eic are preserved at least till early cretaceous 117 ma it is likely that himalayan orogeny could have played a major role in delamination of the lithospheric roots of the eic in addition to attendant seismicity

lithospheric thinning in the eastern indian craton evidence for lithospheric delamination below the archean singhbhum craton abstract we herein present shear velocity structure extending down to 300 km depth below the archean singhbhum odisha craton soc and proterozoic chotanagpur granitic gneissic terrain cggt which has been obtained through the inversion modeling of p receiver functions we use three component broadband recordings of 200 teleseismic earthquakes 30 90 from a 15 station seismic network that has been operational in the eastern indian shield since february 2013 we obtain the thinnest crust of 35 km overlying a thin lithosphere of 78 km below the region near south singhbhum shear zone which could be attributed to the 1 6 ga plume activity associated with dalma volcanic however the thickest crust of 47 km overlying a thin lithosphere of 81 km is noticed below the region near the singhbhum granite of 3 6 ga this thinning of lithosphere could be attributed to the delamination of lithospheric root due to the himalayan orogeny with a shortening rate of 2 cm year this delamination model in soc gets further support from the densification of the lower crust which could result from repeated episodes of basaltic underplating associated with episodes related to dalma 1 6 ga and rajmahal 117 ma volcanisms this led to relatively more mafic heterogeneous and deformed crustal structure in soc as well as egmb with an average crustal vs of 4 0 km s in comparison to that in cggt with an average crustal vs of 3 9 km s as seen through our modeling results the thickest lithosphere of 100 km is observed in the southwestern soc as well as northeastern cggt we also notice that a sharp and flat moho in cggt which could be attributed to thermal reactivation and large volume melting of the mafic cratonic crust during the late archean subduction process and associated volcanism episodes this model gets further support from the estimated 169 km thick lower vs zone in the upper mantle below cggt our modeling results also support a northward subduction of archean soc under the proterozoic cggt during 1 0 1 6 ga as earlier proposed by the geological age data from the region

paleoecology of secondary tierers from western pangean tropical marine environments during the aftermath of the end permian mass extinction abstract skeletobionts that colonized organic hard parts during the early and late aftermath of the end permian mass extinction had been undescribed previously evaluation of more than 7400 skeletonized benthic invertebrates and taphonomic processes reveal a general pattern of increasing diversity and abundances of skeletozoans through the early triassic in tropical marine environments on the coast of western pangea present day western u s a griesbachian age skeletobiont assemblages are dominated by episkeletozoans while spathian ones are dominated by endoskeletozoans bivalves were the primary hard substrate for the skeletozoans in all examined strata most likely because they were the most abundant skeletonized benthic invertebrate microconchids are hypothesized to have behaved opportunistically during the immediate aftermath of the end permian mass extinction and they had a strongly preferred association with claraia this and future studies of early triassic skeletobionts will contribute to further understanding arguably one of the most evolutionary significant intervals in earth s history

a reconnaissance teleseismic study of the upper mantle and transition zone beneath the archean slave craton in nw canada abstract the objective of this study is to investigate upper mantle structure below the archean slave craton site of the oldest known rocks on earth and numerous diamondiferous kimberlites and thence to gain an understanding of early craton formation and kimberlite genesis to this aim a temporary array consisting of 13 sites equipped with broadband seismometers recorded teleseisms between november 1996 and may 1998 this data set has been augmented with recordings from the yellowknife seismic array our three most robust observations and their interpretation are 1 p wave travel time tomography reveals the oldest part of the craton the central slave basement complex to be underlain by the fastest seismic velocities indicating that this block remains distinct well into mantle depths 2 receiver function analysis requires only the moho as major s wave velocity discontinuity and points to a fairly constant crustal thickness throughout the slave province and 3 sks splitting analysis shows little variation in delay times and fast polarization directions across the array leading us to conclude that the present day plate motion of north america is the primary cause for mantle fabric beneath the entire array furthermore the data let us rule out the possibility that the mackenzie plume had any seismologically detectable effect on the slave lithosphere more speculative results of our investigation namely a possible genetic link between a low seismic velocity anomaly at depth with the overlying lac de gras kimberlite field and a possible archean origin of two shallow low velocity anomalies will require further investigation

evolution of archaean crust in the dharwar craton the nd isotope record abstract a synthesis of the available nd isotope data from the dharwar craton puts important constrains on antiquity of crust extent of basement terranes and events marking juvenile crustal addition and crustal recycling the craton is divided into two blocks namely eastern dharwar craton edc and western dharwar craton wdc nd model ages trace crust extraction as far as 3 5 ga back in both the blocks although rock record of such antiquity is yet to be found in the craton in wdc 3 35 3 0 ga is the most significant period of juvenile crustal addition as well as crustal recycling significantly depleted mantle 1 5 to 6 4 existed below the wdc as early as 3 35 ga which was probably refertilized in a later event from the resultant chondritic to slightly enriched mantle 0 3 to 0 4 juvenile mafic crust was added to the wdc during 2 9 2 6 ga a widespread crustal recycling event at 2 6 ga marks the last major event in this block in edc 3 3 3 0 ga granitoids occur as vestiges and show nd model ages higher than crystallizations ages suggesting recycling of palaeoarchaean crust during 2 7 2 5 ga extensive juvenile magmatism took place in edc from variably depleted mantle 1 4 to 5 6 which is later than the global 2 7 ga peak of crustal growth attendant crustal recycling destroyed most of the earlier crust distribution of nd model ages suggests in contrast to general believe that palaeoarchaean crust was not only abundant in the wdc but also widespread in an area extending from the wdc edc boundary to further 60 150 km east up to the hungund ramagiri kolar hrk belt this belt appears to be a major crustal boundary along which terranes of different nd isotope signatures were amalgamated during the late neoarchaean by horizontal accretion major neoarchaean crustal recycling events documented in the dharwar craton are missing from nd isotope record of the eastern block eb of the north china craton this fact does not support correlation between the two cratons as suggested by some authors

simultaneous horst basin formation and magmatism during late variscan transtension evidence from 40 ar 39 ar and 207 pb 206 pb geochronology in the ruhla crystalline complex ar 39ar mica and 207pb 206pb zircon dates are presented and combined with existing p t data and the sedimentary record these data indicate that the rcc was faulted into three segments which underwent different exhumation histories during the late carboniferous early permian the eastern segment shows 40ar 39ar biotite data of336 4 and 323 3 ma furthermore it is intruded by the thuringian hauptgranite dated at 337 4 ma by the 207pb 206pb single zircon method at approximately 300 ma rocks of the eastern segment were finally exposed and subsequently subsided as part of the oberhof pull apart basin filled by late carboniferous early permian molasse sediments and volcanic rocks 296 285 ma goll 1996 a similar late carboniferous evolution is inferred for the western segment since it is also overlain by upper carboniferous volcanic rocks in contrast to the eastern and western segments distinctly younger intrusion and cooling ages were recorded for the central segment of the rcc 40ar 39ar muscovite 311 3 ma 40ar 39ar biotite 293 288 3 ma that was intruded by the trusetal granite the ruhla granite and brotterode diorite 207pb 206pb single zircon 298 2 295 3 289 4 ma respectively these young data are unique in the mgcr and testify that plutonic activity and cooling of basement rocks took place simultaneously with basin formation and volcanism in the eastern and western segments overlying upper permian zechstein and triassic sediments indicate final exposure of the central segment by approximately 260 ma as a part of the ruhla schleusingen horst combination of these results with p t data from the contact aureole of the trusetal granite indicate that the central segment was unroofed by at least 8 5 km during the late carboniferous the late carboniferous early permian horst basin formation documented in the rcc is due to dextral transtensional movements along the nw trending franconian fault system it may have been enhanced by mantle upwelling widespread in central europe during the early permian that also caused intensive magmatism in the thuringian forest region

palynofacies analysis of the permian triassic transition in the amb section salt range pakistan implications for the anoxia on the south tethyan margin the uppermost chhidru formation and the lower part of the mianwali formation were sampled in the amb valley salt range pakistan for the study of the particulate organic matter pom content in order to evaluate the depositional environment during the permian triassic transition the pom content was assigned to four distinct palynofacies palynofacies a d palynofacies a recovered from siltstone within the white sandstone unit of the upper permian chhidru formation indicates a shallow marine oxic shelf setting recorded from the siltstone intercalations in the kathwai member of the basal mianwali formation the griesbachian palynofacies b is characterised by abundant acritarchs indicating a transgressive event palynofacies c recovered from the siltstone of the lowest ceratite marls middle dienerian is dominated by terrestrial organic particles and indicates shallowing of the depositional environment whereas 40 cm above palynofacies d represents transgressive oxygen depleted conditions the comparison with sections from the australian tethyan margin shows that oxygen depleted conditions occurred during the griesbachian in the perth basin while in the bonaparte basin oxygenated conditions prevailed hence oxygen depleted facies do not correspond to a single synchronous permian triassic oceanic anoxic event but depend on local geography and bathymetry

fractal dimension and its translation into a model of gold spatial proxy abstract unraveling the spatial distribution of mineral deposits is an essential part of exploration and important for developing a better understanding of ore forming processes in this study gold assay results in g t of twelve boreholes completed from mysore block and eleven boreholes completed from nabhapur north block central lode system gadag gold field ggf india were analyzed using fractal analysis both the fractal correlation integral and rescaled range analysis were used to measure the fractal dimension from the gold concentration values the fractal dimension values obtained from the fractal correlation integral were used to better constrain the possible auriferous fluid flow pathways whilst results obtained from the rescaled range analysis were used to describe the behavior of auriferous veins across the boreholes the fractal dimension values were found to vary from 0 014 to 3 0 with the higher values taken to indicate the presence of well developed interconnected fault fracture networks representing steep permeable fluid flow pathways the lower fractal dimension values were taken to indicate unfavorable fluid flow pathways in other words higher grade gold ores were deposited along the structures represented by steep fractal gradients hurst exponent h values obtained from the rescaled range analysis were found to vary from 0 50 to 0 96 satisfying the condition 0 5

geoelectric structure of the dharwar craton from magnetotelluric studies archean suture identified along the chitradurga gadag schist belt summary broad band magnetotelluric data were collected at 50 stations over a 400 km long approximately east west profile over the granite greenstone terrain of dharwar southern india the tensor decomposed data were interpreted using a 2 d inversion scheme the geoelectric model is suggestive of a suture along the chitradurga gadag schist belt formed by the thrusting of the west dharwar craton beneath its eastern counterpart with an easterly dip of 20 30 the thrust proposed here pre dates the formation of these schists which occurred during the late archean 2600 ma the accretionary wedge of the thrust and the depressed part of the west dharwar craton may have controlled the emplacement of the chitradurga gadag and shimoga dharwar schists the subsequent weathering the several episodes of tectonic activity witnessed during the precambrian and the vertical block movements caused during the passage of the indian plate over the reunion hotspot may have modified the crust leading to the present day geological configuration despite its age and several tectonothermal episodes the signature of this thrust is adequately preserved in the dharwar craton several similarities with younger sutures as is evident from the observed relics of the oceanic rocks present along the chitradurga schist belt suggest that the tectonic processes leading to this archean event may have had a close resemblance to those witnessed in recent times magnetotelluric studies also image a zone of low resistivity at a depth of 40 km beneath the west dharwar craton this seems to be a regional feature extending to the north over a distance of at least 250 km beneath the deccan volcanics the low heat flow values and the high density associated with this feature make partial melting an unlikely explanation for the low resistivity the grain boundary graphites and the sulphides deposited in the form of pyrites may have caused the low resistivity in the lithospheric mantle of the west dharwar craton although the fluids generated and trapped in the mantle during the passage of the indian plate over the reunion hotspot in the waning phase of its outburst could also be a possibility the asthenosphere is delineated at a depth of about 100 km beneath the east dharwar craton

brittle deformation events at the western border of the bohemian massif germany investigations of brittle deformation structures present within the crystalline rocks of the bavarian oberpfalz reveal a complex late to post variscan crustal evolution upper carboniferous mainly westphalian granites were emplaced into semibrittle to brittle rocks of the zev zone of erbendorf vohenstraus and the egz erbendorf greenschist unit respectively from both the alignment of the granites and the direction of granite related tension gashes a north east south west extension must be assumed for the period of magmatic activities apart from the granite intrusions rapid crustal uplift about 1 5 km my led to an increase in the geothermal gradient from 40 c km late variscan post granitic the increased geothermal gradient persisted during the succeeding reverse faulting which results from late carboniferous probably stephanian east west and northeast south west compression although not evidenced directly in the area considered strike slip faults seem to have played an important part during the late variscan crustal evolution particularly in the early permian the strike slip events indicate further crustal shortening and indentation under north south compression a similar indentation was present in cretaceous time after a weak phase of early cretaceous reverse faulting which results from north south compression strike slip faults formed under north west south east and north south compression all these faults in particular the strike slip faults seem to be related to the cretaceous and lowermost tertiary convergence of the alpine carpathian orogeny a late stage of crustal extension characterized by a radial stress tensor 2 3 is indicated through high angle normal faults which probably formed during the subsidence of the adjacent neogene eger graben

sudden and extreme hyperthermals low oxygen and sediment influx drove community phase shifts following the end permian mass extinction abstract we present a correlated record of carbon isotope geochemistry and sedimentological analysis for the lower triassic werfen formation from the italian dolomites macro and mid sized fossil diversity ecology and climate sensitivity are included to provide an integrated account of the benthic response to paleoenvironmental change novel communities developed in the wake of the mass extinction during pervasive fluctuations in environmental conditions in the sedimentary sequences of the werfen formation of the italian dolomites microbialites microconchids foraminifera and ubiquitous flat clams formed a complex community within the first 500 000 years later increased sea surface temperatures and inundation of the seafloor with siliciclastic sediments favored infaunal bivalves and microgastropods persistent trends in the environment can produce directional often irreversible community shifts defined here as phase shifts phase shifts in ecosystem structure can be driven by environmental shifts across threshold boundaries to produce an abrupt and dramatic novel community composition a phenomenon readily observed during the early triassic previously described disaster forms including flat clams microconchids foraminifera and microbialites are re envisioned as a phase shift community we hypothesize that the unique persistent and reoccurring microbialite and mid sized fauna assemblages observed during the initial recovery from the end permian mass extinction and re appearing throughout the early triassic typify a phase shift community in the smithian infaunal bivalves and microgastropods represent a second phase shift community developed in response to a persistent directional rise in sea surface temperatures and enhanced sediment influx we compare and contrast phase shifts with other models for ecosystem recovery including trophic competition and earth system succession

gravity interpretation of the dharwar greenstone gneiss granite terrain in the southern indian shield and its geological implications abstract the dharwar craton in the southern indian shield has a wide distribution of volcano sedimentary sequences surrounded by a vast gneissic complex both of which have been intruded by younger granites a gravity anomaly map of this craton compiled from all the available data is analysed here to study the structures and depths of the greenstone belts the mode of granite emplacements and the greenstone gneiss granite associations in general the anomaly map is a mosaic of well defined gravity highs and lows characterizing the dense volcano sedimentary sequences and exposed and or concealed granites respectively gravity modelling indicates that the shimoga belt has a limited depth range of only 3 4 km while the chitradurga and sandur belts have greater depths of over 10 km the structures inferred for the dharwar formations are alternating bands of synclines filled with dense schistose rocks separated by anticlinal ridges of gneisses and granites

translating the mineral systems approach into an effective exploration targeting system abstract holistic mineral systems approaches are being increasingly adopted in the study of ore deposits but application in industry has been suboptimal because of the lack of a conceptual framework to help translate the mineral system understanding to practical application a four step process is proposed for linking the conceptual mineral system with data available to support exploration targeting these steps include translation from 1 critical processes of the mineral system to 2 constituent processes of the mineral system to 3 targeting elements reflected in geology and 4 targeting criteria used to detect the targeting elements directly or by proxy this translation process is illustrated using examples from komatiite hosted ni cu pge and orogenic au mineral systems ranking of targets must be at the critical process level rather than the current practice of mixing processes elements and proxies the significance of targeting elements and their mappable criteria changes as a function of the scale at which the critical processes operate and the availability of relevant geoscience datasets this scale dependence is rarely recognised in current practice sources of uncertainty when translating the mineral system understanding into an effective exploration targeting system include 1 resolution of a mappable criterion in a dataset 2 how well the targeting criterion reflects the targeting element 3 how well the targeting element reflects the critical process and 4 whether the process being mapped is critical for the genesis of a mineral deposit the first three sources of uncertainty collectively are termed the representativeness of the targeting criteria i e how representative is a mappable criterion of the constituent process for which it is a proxy the last source of uncertainty reflects our lack of understanding of the processes that control mineralisation and highlights areas for further research

late to post variscan deformation phases and palaeostresses in the ktb pilot research well bohemian massif germany abstract brittle faults and veins are very widespread in the crystalline rocks of the northern oberpfalz particularly in the 4000 m deep kontinentale tiefbohrung ktb pilot well in the late variscan late carboniferous subvertical tension gashes were formed under ne sw extension a genetic relationship between the vein development and late phase magmatic activity of the late variscan granites is obvious subsequently but still during the late carboniferous graphite enriched reverse faults developed under e w and ne sw compression in the deeper part of the ktb pilot hole these faults were formed within the brittle ductile transition regime of the paragneisses since during the late variscan the geothermal gradient was remarkably elevated the brittle ductile regime was situated at a relatively high crustal level where cataclasis crystal plasticity and diffusion controlled deformation mechanisms were active simultaneously in post variscan time probably during the cretaceous a further generation of reverse faults developed in addition to subhorizontal tension gashes and minor strike slip faults during these events the temperature was much lower compared with the conditions during the late variscan deformations the reverse faults evolved primarily under n s compression which is probably related to the cretaceous subduction and collision events of the alpine orogeny further to the south the youngest normal faults are probably connected to the subsidence of the nearby eger graben which evolved during the neogene uplift of the investigated area the stress data derived by using faults and striations from surface outcrops and from several oriented core intervals from the ktb pilot well display weak depth dependent variations although the deformation was polyphase the inversion method has proved to be a suitable mode for determining reliable palaeostress data however if the brittle ductile transition regime or broad shear zones are reached the data become more and more invalid

mapping of tectonic corridors through hidden parts of the greater dharwar terrane southern india abstract the dharwar craton india has been divided into western and eastern domains by a tectonic boundary between the closepet granite and chitradurga schist belt it has been noted that only the central portion of the dharwar craton is exposed its northern projection is buried beneath the deccan traps and its southern margin merges with a high grade metamorphic transition of late archean age resolution of structure and extent of the greater dharwar terrane gdt beneath its northern and southern end the deccan traps metamorphic transition zone and cuddapah basin thus remains unsolved results of deep geophysical probings have been examined along with associated geological and tectonic data the analysis leads to a delineation of palaeo accretionary corridors extending under the deccan trap cover along which two damaging stable continental region earthquakes koyna and latur occurred veeraswamy and raval 2005 b it is seen that the latur earthquake seem to lies within an unsuspected tectonic corridor which bifurcates the eastern dharwar craton edc into eastern dharwar craton 1 and eastern dharwar craton 2 passing through the cuddapah basin c possibility of the palghat cauvery shear zone connecting to the 2 5 ga metamorphic karimnagar granulite belt through the interface between napier nc and rayner rc complexes of east antarctica and d the indication that the bavali moyar bhavani mettur and palghat cauvery shear zones form the southern margins of the western dharwar craton eastern dharwar craton 1 and eastern dharwar craton 2 respectively

the nature and thickness of lithosphere beneath the archean dharwar craton southern india a magnetotelluric model abstract the dharwar craton in the southern indian shield region occupies a key position in reconstructions of the earliest supercontinent ur as well as in the global neoarchean configurations of continental assembly here we synthesize the available geophysical data that include heat flow seismic tomography temperature profile derived from xenoliths and magnetotellurics mt from the dharwar craton a thickness of more than 200 km is identified for the lithosphere beneath this craton by magnetotelluric model our inference lends support to the models from recent seismological investigations that argue for the presence of a thick lithosphere as well as the upper mantle structure derived from the analysis of mantle xenoliths a synthesis of recent geophysical and geochemical data together with our magnetotelluric model indicate the existence of a thick lithospheric root beneath the dharwar craton and suggest that not much of the lithosphere has been eroded since precambrian in this region leading to the conclusion that the dharwar craton preserves an archean tectosphere an increase in the lithospheric thickness from east to west in the dharwar craton and the lithosphere asthenosphere boundary lab migration to shallower levels observed from geophysical data towards the east is interpreted as a probable reflection of the mesoproterozoic subduction erosion of the archean cratonic keel

electric lithosphere of the slave craton the archean slave craton in northwestern canada is an ideal natural laboratory for investigating lithosphere formation and evolution and has become an international focus of broad geoscientific investigation following the discovery of economic diamondiferous kimberlite pipes three deep probing magnetotelluric surveys have recently been carried out on the craton using novel acquisition procedures the magnetotelluric responses reveal an unexpected and remarkable anomaly in electrical conductivity collocated with the kimberlite field that is modeled as a spatially confined upper mantle region of low resistivity 30 m at depths of 80 100 km and is interpreted to be due to dissolved hydrogen or carbon in graphite form this geophysically anomalous upper mantle region is also spatially coincident with a geochemically defined ultradepleted harzburgitic layer the tectonic processes that emplaced this structure are possibly related to the lithospheric subduction and trapping of overlying oceanic mantle at 2630 2620 ma

inversion tectonics along the western margin of the bohemian massif abstract the block faulted southwestern margin of the bohemian massif is superimposed on a permo carboniferous graben major faults of which became repeatedly reactivated during the mesozoic and cenozoic inversion of sedimentary basins associated with this fault system occurred during the early cretaceous and again during the latest cretaceous early cenozoic

heat flow and heat generation in the archaean dharwar cratons and implications for the southern indian shield geotherm and lithospheric thickness abstract we report terrestrial heat flow density measurements from 11 new sites in the archaean eastern and western dharwar cratons of the southern indian shield the new values together with already published data have yielded a mean heat flow of 40 3 4 s d mw m 2 n 11 for the eastern dharwar craton which is a predominantly gneiss granite terrain the mean heat flow in the archaean supracrustal belts of western dharwar craton which is a granite greenstone terrain is 31 4 1 s d mw m 2 n 4 the observed difference in surface heat flow between the two cratons is ascribed to differences in radiogenic heat production in upper crustal layers inferred to be related to different crust forming processes it has been argued that low heat production appears to be an inherent characteristic of the crust similar to that of the western dharwar craton which evolved during the early archaean and suffered depletion of the lithophile elements of its lower crust prior to the late archaean radiogenic heat production measurements were carried out on borehole core samples for one heat flow site sortur and data have been compiled from the literature on three other sites and on a variety of rocks of the southern indian shield heat flow and radiogenic heat production for sortur when combined with the published data define a linear relation r 0 97 with a slope of 11 5 km and an intercept of 23 mw m 2 the thickness of the thermal lithosphere beneath the dharwar cratons is over 200 km thereby indicating beneath the cratons the existence of deep continental roots a concept which is also supported by teleseismic p wave travel time data the geothermal data has clearly demonstrated that the archaean dharwar cratons of the indian landmass are associated with low mean surface heat flow 37 7 mw m 2 reduced heat flow moho heat flux 12 17 mw m 2 and a cool and thick lithosphere all characteristics of many archaean early proterozoic terrains of other shields it is inferred that the thermal structure of the south indian lithosphere is identical with that of other cratons

the karnataka late cretaceous dykes as products of the marion hot spot at the madagascar india breakup event evidence from 40ar 39ar geochronology and geochemistry two late cretaceous mafic dykes with an ene strike that is orthogonal to the west coast of india and located nearly 200 km inland around huliyardurga karnataka state yield 40ar 39ar plateau ages of 90 0 1 0 and 87 5 0 9 ma these fe ti enriched tholeiites are essentially co eval with at least four other igneous suites widely scattered in southern india namely the south and north kerala dykes the agali anaikatti dykes of central kerala tamil nadu and lavas of st mary islands off the west coast of india the karnataka cretaceous dykes are also co eval and compositionally very similar to the fe ti enriched tholeiitic lavas and dykes around mananjary a major phase of late cretaceous magmatism along the eastern rifted margin of madagascar which are believed to be products of the marion hot spot that extruded at 88 ma synchronous with the india madagascar break up event the age and compositional similarities between these late cretaceous magmatic rocks from india and madagascar constitute a clear evidence for extension of the thermal manifestations deep into the indian peninsula

comment on the paper of gierlowski kordesch and cassle the spirorbis problem revisited sedimentology and biology of microconchids in marine nonmarine transitions earth science reviews 148 2015 209 227 abstract gierlowski kordesch and cassle 2015 earth science reviews 148 209 227 interpreted microconchids extinct tentaculitoid encrusters as strictly marine rejecting the previous conclusions that these organisms occupied a variety of habitats ranging from marine to non marine we argue that due to misunderstanding of previous statements concerning the affinity of microconchids the authors used an actualistic approach and incorrectly compared microconchids with modern phoronids which led to oversimplifications and misinterpretations also their idea that microconchids as supposedly strictly marine organisms were preserved in non marine settings only because of transport by storm surges and tsunamis is unsupported on paleontological grounds these errors led to mistaken conclusions about microconchid paleoecology that must be discussed in order to avoid an erroneous interpretation of microconchid paleoenvironments

constraining long term denudation and faulting history in intraplate regions by multisystem thermochronology an example of the sudetic marginal fault bohemian massif central europe 1 the rychlebske hory mountain region in the sudetes ne bohemian massif provides a natural laboratory for studies of postorogenic landscape evolution this work reveals both the exhumation history of the region and the paleoactivity along the sudetic marginal fault smf using zircon u th he zhe apatite fission track aft and apatite u th he ahe dating of crystalline basement and postorogenic sedimentary samples most significantly and in direct contradiction of traditional paleogeographic reconstructions this work has found evidence of a large cretaceous sea and regional burial to 6 5 km of the carboniferous permian basement in the late cretaceous 95 80 ma during the burial by sediments of the bohemian cretaceous basin system the smf acted as a normal fault as documented by offset zhe ages across the fault at 85 70 ma the basin was inverted cretaceous strata eroded and basement blocks were exhumed to the near surface at a rate of 300 m ma as evidenced by late cretaceous paleocene aft ages and thermal modeling results there is no appreciable difference in aft and ahe ages across the fault suggesting that the smf acted as a reverse fault during exhumation in the late eocene oligocene the basement was locally heated to 70 c by magmatic activity related to opening of the eger rift system neogene or younger thermal activity was not recorded in the thermochronological data confirming that late cenozoic uplift and erosion of the basement blocks was limited to less than 1 5 km in the study area

on the calibration of fission track annealing models to obtain thermal histories from fission track length data the rates at which track lengths are reduced must be estimated the usual method is to use empirical equations calibrated via laboratory analogues a major concern is the extrapolation of the equations to predict temperatures on the geological time scale which is far outside the range of the calibration data using objective statistical criteria it is shown that the inclusion of geological data from age standards and deep boreholes is an important measure to ensure that model predictions of geological annealing rates are at least close to being correct it is shown that high temperature geological data should be the preferential target in the search for new field evidence a discussion on the use and limitations of geological data and their consequences is presented

microconchid dominated cobbles from the upper devonian of russia opportunism and dominance in a restricted environment following the frasnian famennian biotic crisis abstract carbonate cobbles from the lower famennian crepida conodont zone brachiopod shell beds of the russkiy brod quarry central devonian field russia have been investigated with respect to paleoecology and paleoenvironment the cobbles composed of similar shell bioclasts as the host deposits were eroded from lithified shell beds during intervals of non deposition the smooth surfaces and the presence of borings and encrustations on all sides suggest that the cobbles were periodically transported and overturned the fact that all the bioerosion traces are encrusted and none of the encrusters were bioeroded indicates that the first colonizers of the cobbles were worm like suspension feeders leaving long cylindrical borings trypanites the encrusting organisms are dominated by spirally coiled microconchid tubeworms followed by cornulitids productid brachiopods hederelloids foraminifera enigmatic ascodictyon and trepostome bryozoans the high abundance but low diversity brachiopod fauna and general rarity of such stenohaline taxa as echinoderms in the shell beds or bryozoans on the cobbles suggest that the salinity fluctuated the presence of dolomite crystals in both the host deposit and cobbles suggests that salinity increased from normal marine to a higher salinity level during colonization of the cobbles in fact as shown by the facies and palynofacies data the cobble bearing deposits represent near shore restricted environments created during the first phases of transgression of the early famennian that followed the regional regression at the frasnian famennian transition in such shallow restricted settings a higher salinity could have appeared seasonally during a hot and dry climate as with the microconchids from the aftermath of the end permian mass extinction those from the post crisis early famennian interval of russia were also dominant due to unstable environmental conditions here at least in the case of the russkiy brod the periodic higher salinity episodes may have discouraged other encrusters and thus promoted the settlement of the opportunistic microconchids

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

environmental controls on the post permian recovery of benthic tropical marine ecosystems in western palaeotethys aggtelek karst hungary climate warming during the late permian is associated with the most severe mass extinction event of the phanerozoic and the expansion of hypoxic and anoxic conditions in shallow shelf settings it has been hypothesised that wave aeration provided a habitable zone in the shallowest environments that allowed the survival and rapid recovery of benthic invertebrates during the early triassic we test this hypothesis by studying the rock and fossil records of the aggtelek karst hungary nearshore settings recorded in the bodvaszilas sandstone formation and units a and d of the szin marl formation are characterised by taxonomically homogenous fossil assemblages of low diversity and low evenness ecological and taxonomic recovery in this environmental setting was hampered by persistent environmental stress this stress is attributed to increased runoff related to climate warming during the early triassic that resulted in large salinity fluctuations increased sedimentation rates and eutrophication that led to seasonal hypoxia and an environment only favourable for opportunistic taxa in contrast shoal and mid ramp settings further offshore are characterised by high diversity faunas with a greater functional complexity prior to the late spathian tirolites carniolicus zone the shelly fossils and trace fossils are limited to settings aerated by wave activity which supports the habitable zone hypothesis in the tirolites carniolicus zone however the oxygen minimum zone retreats offshore and the habitable deeper shelf settings are rapidly colonised by shallow water taxa evidenced by the highest levels of diversity and bioturbation recorded in the study locally full recovery of marine ecosystems is not recorded until the illyrian with the establishment of a sponge reef complex

late variscan strike slip tectonics between the tepla barrandian and moldanubian terranes czech bohemian massif petrostructural evidence in the variscan bohemian massif czech republic no agreement has been reached on the nature of the relationship between the tepla barrandian and the moldanubian terranes however the tepla barrandian is interpreted as a central segment separating the moldanubian and saxothuringian terranes and its position is therefore essential for any reconstruction of this part of the variscan belt our petrological and structural study in the domazlice klatovy region spans the boundary between the tepla barrandian and moldanubian terranes there is no conformity of ductile structures in both domains near their interface and their p t evolution is separate in time the development of major structures and associated metamorphism in the southwestern part of the barrandian was accompanied by syntectonic intrusions of granitoid and diorite bodies dated at about 520 ma the moldanubian migmatites are characterized by a lp ht metamorphism that possibly took place at about 320 ma the metamorphic record of the barrandian rocks shows no influence of the moldanubian partial melting the contacts are marked by semi brittle to brittle structures sinistral strike slip faulting developed in the central bohemian shear zone whereas the west bohemian shear zone acted as a semi brittle normal fault with a dextral component both shear zones may be nearly contemporaneous accommodating a bulk n s compression the central bohemian shear zone was later reactivated in a dextral regime although timing is uncertain the juxtaposition of both terranes took place probably in the waning stages of the variscan orogeny earlier than the late stephanian we argue that the late orogenic semi brittle strike slip tectonics modified considerably the face of the bohemian massif and the geodynamic models of the bohemian massif have to be reviewed with reference to this essential point

mesozoic and early tertiary evolution of the alpine foreland in upper austria and salzburg austria abstract the cenozoic molasse basin of upper austria and salzburg is part of the alpine foredeep its substratum is formed by the crystalline basement of the bohemian massif and its mesozoic sedimentary cover this autochthonous complex extends for a considerable but unquantifiable distance beneath the alpine nappes the area occupied by upper austria and salzburg started to subside during the middle jurassic and by late jurassic time it was covered by an extensive carbonate platform early cretaceous wrench deformations related to rifting activity in northwestern europe were accompanied by a major erosional phase during the late cretaceous 750 to 1000 m of shallow marine shales and elastics accumulated in the area whereby the clastic influx from the bohemian massif increased during the late senonian at the transition from the cretaceous to the tertiary dextral transpressional deformation induced partial basin inversion this deformation phase may be related to the collision of the north european craton with the alpine orogenic system following an erosional phase during the palaeocene and early eocene the area subsided again and became part of the alpine foredeep

teleseismic tomographic evidence for contrasting crust and upper mantles in south indian archaean terrains abstract we compare the velocity structure of the crust and upper mantle of the archaen granulite terrain of southernmost india with that of the archaean granite greenstone dharwar craton terrain just to the north through p wave teleseismic travel time measurements the teleseismic rays recorded by a coarse network of 11 portable seismic stations show an anomalous pattern of late arrivals delays over the granulite terrain in contrast to fast arrivals on the dharwar craton such a pattern of time residuals amongst these archaean terrains which have remained inert in the last 2 ga may indicate the presence of compositional heterogeneity within the crust and upper mantle beneath them three dimensional p wave velocity tomography using teleseismic rays from a variety of azimuths indicates the existence of contrasting p wave crust and upper mantle velocity patterns 1 in the crust 0 40 km the western dharwar craton and the granulite terrain have lower velocity up to 3 compared with the higher velocity 1 3 observed over the eastern dharwar craton and 2 in the upper mantle 40 177 km there is 2 3 lower velocity beneath the granulite terrain compared with the western dharwar craton the existence of such lateral velocity variation in the crust and upper mantle and its preservation since late archaean times points to the presence of possibly thick and chemically distinct lithospheres that did not participate in mantle convection

evolution of the molasse basin germany switzerland abstract in the molasse basin 500 1000 m thick mesozoic sediments overlie the variscan basement and locally permo carboniferous grabens containing a largely unknown thickness of clastic sediments the vindelician basement high extended southwestward from the bohemian massif and separated the southern part of the german basin from the tethys shelf triassic early and middle jurassic sediments progressively transgressed over this high which became fully inundated during the late jurassic following a temporary regression sedimentation resumed in the early cretaceous and after another hiatus in the late aptian to campanian during the latest cretaceous to earliest tertiary the area of southern germany became uplifted resulting in a progressive northwestward truncation of cretaceous strata and the late jurassic carbonates at the same time the bohemian massif became upthrusted along northwest striking wrench faults similar faults controlled the upthrusting of the landshut neuoetting high over which some 1 000 m of mesozoic sediments were eroded these wrench and thrust tectonics are part of an extensive compressional deformation in central europe that is supposed to be caused by the latest cretaceous earliest tertiary collision of the adriatic african and european plates during the alpine orogeny the area subsided again during the late eocene and developed into the molasse basin proper in which oligocene to miocene elastics reach a thickness of some 5 000 m near the alpine thrust front subduction and flexuring of the foreland caused numerous essentially basin parallel synthetic and antithetic normal faults the latter form the primary traps for oil and gas accumulations in the molasse basin

paleoecology and sedimentary environment of the late devonian coral biostrome from the central devonian field russia the upper frasnian coral biostrome well exposed in the russkiy brod quarry central devonian field russia has been studied in detail with respect to paleoecology and sedimentary environment the biostrome formed by auloporid tabulates and solitary and colonial rugose corals originated in an offshore environment characterized by calmer periods with slow or halted sedimentation and more energetic periods when sedimentation rate increased the episodic higher sediment influx and stronger hydrodynamic regime are not only well expressed in the microfacies but also in the variability of colony integration of the rugose corals observed even within single coralla distinct development of constrictions rejuvenescences and deflection of growth directions in rugose corallites may also indicate unstable sedimentary conditions the latter features however may have in part also resulted from syn vivo biotic interaction with the associated auloporids both the facies and paleontological observations suggest that the biostrome originated by the colonization of deposited bioclasts by pioneering auloporids creating the framework for settlement of later generations of auloporids and rugose corals apart from abundant auloporids representing a single species and associated rugose corals the other encrusters are not numerous and poorly diversified represented by dominating foraminifers followed by single species of productid brachiopods stromatoporoids microconchids and cornulitids the coral associated macrobenthos has similarly a low diversity being represented by single species of spiriferid and rhynchonellid brachiopods and gastropods being developed in an offshore carbonate sedimentary system devoid of any organic rich deposits and characterized by extremely low abundance and diversity of suspension feeding organisms the biostrome is considered to have originated in a low productivity oligotrophic environment strictly dominated by heterozoan coral communities its development in a well oxygenated oligotrophic environment during the time when organic rich black kellwasser facies developed elsewhere additionally attests for multi causal scenarios for the frasnian famennian event during which other factors were responsible in different paleogeographic and facies settings

gastropod evidence against the early triassic lilliput effect comment brayard et al 2010 1 assert that their study of late early triassic gastropods provides evidence against the post extinction lilliput effect regrettably their data provide no such evidence the lilliput effect as defined by urbanek 1993 2 is a quantifiable temporary decrease in the

precambrian continental crust of india and its evolution the indian precambrian continental crust exhibits a variety of geological features fashioned at different times by different geotectonic processes the bulk of this crust was formed prior to 2600 m y ago and remobilized at least twice between 2600 2000 m y ago early proterozoic mobile belt epmb and 2000 1500 m y ago middle proterozoic mobile belt mpmb three early precambrian nucleii karnataka kn jeypore bastar jbn and singhbhum sn appear to have survived in the craton and are characterized by low grade supracrustals and tonalitic trondhjemite gneisses formed 3800 2600 m y ago the epmb event involved sedimentation amphibolite granulite facies metamorphism and co 2 k metasomatism and produced amphibolite facies rocks and k granites in the north and charnockite and other granulite facies rocks in the south gold sporadically distributed in the supracrustal rocks of the craton was remobilized during the epmb event k granites form a garland around the central dharwar craton sugg

magnetotelluric evidence on the southward extension of the eastern ghats mobile belt from ongole india abstract there has been a longstanding and scientifically contentious issue concerning whether or not the eastern ghats mobile belt egmb extends southward beyond ongole in the state of andhra pradesh in south india various geological and geophysical investigations carried out in different campaigns could not conclusively address this important issue some argued that the egmb that originates near mahanadi in the northeast of india and extends along the eastern continental boundary is abruptly cut near ongole in the south swerves eastward towards the bay of bengal and joins the erstwhile east antarctica boundary others opined differently and debated about its southward extension beyond ongole in the present study we provide a conclusive evidence for the first time on this perplexing issue by determining the deep earth electrical resistivity structure of the egmb region through broad band magnetotelluric mt investigations carried out along two different profiles laid out one near the ongole region profile aa of 35 km length and the other near the nellore region profile bb of 52 km length the latter is located at a distance of about 125 km south of the former the lengths of both these profiles are sufficiently far from the influences of the electrical nature of the subsurface of the adjoining geological terrains namely the east dharwar craton the cuddappah basin and the southern granulite terrain this enables to determine the electrical nature of the egmb alone and examine whether or not it extends south of ongole two dimensional inversion of mt data of both the profiles revealed a very thin top conductive layer of about 1 10 m with an average thickness of about 500 m representing the alluvium this layer is underlain by very high resistive subsurface with resistivity of about 107 m extending up to about 30 km and probably further beyond not shown in the present study since the major rock types in the study area namely khondalites calc granulites charnockites and granitic gneisses of archaean age have large overlapping resistivities mt data could not explicitly discern the nature of the multilayered crust beneath the egmb as a result the subsurface beneath both the regions shows up as a very thick single layer of very high resistivity the high grade rocks of the ongole domain and supracrustals of nellore schist belt nsb which lies south of ongole domain have undergone synchronous tectonic activity at ca 1 6 by this is evident by the kanigiri and kandra ophiolites within nsb that signify the proterozoic subduction of the egmb this geological evidence together with the similar nature of the high electrical resistivity of the subsurface observed at ongole and nellore regions confirm the southward extension of the egmb beyond ongole

lithospheric electrical imaging of the deccan trap covered region of western india 1 we present here the results of magnetotelluric mt studies carried out along a 330 km long ne sw trending traverse from daulatabad at the northeastern end to koyna on the southwestern end across the deccan volcanic province dvp in western india the 2 d mt modeling results obtained along this traverse together with those from other mt traverses in this area are examined and integrated with the results from deep seismic sounding 3 d teleseismic tomography and heat flow studies the deep geoelectric section as deduced from mt models point out to a two layered lithospheric mantle structures with an upper very high resistive layer several thousands of ohm m and a bottom relatively conductive one a few tens of ohm m to a few hundred ohm m the lithospheric electrical structure is inferred to be linked to compositional changes associated with a depleted lithospheric upper mantle in the dharwar craton an impressive feature that the study has brought out is the presence of a well defined lithospheric upper mantle conductor in the depth range of 80 120 km limited to the middle segment of the mt traverse from sangole to partur over the dvp the electrical characterization of the region including the presence of upper mantle conductor shows close similarities with that of other similar cratonic regions like the slave and superior cratons in northwestern canada

positioning the titanite fission track partial annealing zone abstract as part of the ktb kontinentale tiefbohrung programme in germany titanite sphene fission track data were acquired for samples to a depth of 9000 m where the host rock temperature is 265 c at this depth age and confined track length information suggest that the partial annealing zone for the fission tracks in titanite was not reached by reconstructing the thermal history and backstacking of an uplifted partial annealing zone it is suggested that the in situ partial annealing zone is likely to be found in the region 265 310 c this value is more precise than previous estimates of the titanite partial annealing zone and it is also higher than previous estimates microprobe analysis indicates that the chemical composition of the titanites is rather homogeneous throughout the whole drilled section

subduction related tectonic evolution of the neoarchean eastern dharwar craton southern india new geochemical and isotopic constraints the neoarchean eastern dharwar craton edc is distinct from the mesoarchean western dharwar craton wdc in many aspects of its geology the important distinguishing features of the edc are the predominance of younger granitoids abundance of gold mineralization and the exposure at lower crustal depths no consensus exists on evolutionary models for edc mutually exclusive plume and subduction derived tectonic models have been proposed geochemical and radiogenic isotopic studies on the granitoids and volcanic rocks of three greenstone belts along a cross section in the northern part of edc are presented herein the evolved nd isotopic signatures radiogenic pb isotopic ratios and arc like geochemical signatures are suggestive of a subduction regime and the involvement of recycled older crust in the derivation of these rocks the proposed petrogenetic mechanism involves multi stage processes in a supra subduction regime involving slab dehydration formation of hydrous basaltic melts and re melting and interaction with sub arc basaltic crust at low pressures where amphibole plagioclase is the dominant residual phase there is a notable systematic decrease in the extent of older crustal involvement from west to east in the edc this is in concurrence with the younging of dharwar craton from west to east and eastward subduction the proposed petrogenetic model can efficiently explain the variations in older crustal involvement which is very common in other archean cratons c 2012 elsevier b v all rights reserved

co and postseismic characteristics of indian sub continent in response to the 2004 sumatra earthquake abstract the m w 9 3 sumatra earthquake of december 26 2004 caused extensive coseismic displacements globally measurements of which were made essentially using modern geodetic techniques this earthquake induced considerable perturbation in stress distribution as far as 8000 km away from the epicenteral region which is tending to relax to its normal rates as seen from postseismic transient deformation the monitoring of crustal displacements from strategically located sites using gps provides coseismic as well as postseismic deformation that facilitates the understanding of the fault geometry elastic thickness postseismic relaxation mechanisms rheology and earthquake recurrence time interval we investigated coseismic and postseismic gps derived displacements in indian region together with the gps data collected from andaman and sumatra region it is found that while ew displacements are significantly large in peninsular india those in the region to the north of central india tectonic zone citz are relatively small we could delineate the postseismic transients from position time series and interpreted them in terms of viscoelastic relaxation it is inferred that the postseismic deformation is characterized by a power law viscoelastic flow in the mantle in indian peninsula region the timescale parameter of the exponential decay 250 days would require an extremely low viscosity for the upper mantle relying on the prevailing coseismic and postseismic displacement fields the present study also reflects upon the contemporary litho tectonics of the indian sub continent

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

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

anoxia as a cause of the permian triassic mass extinction facies evidence from northern italy and the western united states facies faunal and geochemical evidence from the permian triassic boundary sediments of the dolomites and idaho indicates a major anoxic event in the earliest triassic in both regions the basal beds consist of finely laminated micrites with common syngenetic pyrite the only fauna consists of occasional bedding plane assemblages of lingula or clacaria a typical lower dysaerobic assemblage this is a level where previous studies have shown a major negative carbon isotope excursion and a cerium anomaly in the dolomites the pyritic micrite directly overlies strata containing a diverse and typically permian marine fauna of algae foraminifers including fusulinids and articulate brachiopods implying an abrupt extinction in contradiction to many previous views sequence stratigraphic analysis of the dolomite boundary sediments reveals a minor sequence boundary in the late permian followed by extremely rapid transgression leading to the development of the relatively deep water pyritic micrite a maximum flooding surface at the permo triassic boundary a further pulsed deepening in the lower griesbachian recorded in both the dolomites and idaho lead to the widespread establishment of dysaerobic facies it is clear that most of the extinctions occurred at the erathem boundary although the subsequent failure of the marine benthos to fill the empty ecospace in the ensuing griesbachian may have been due to the widespread development of dysaerobic conditions

convergent morphology in small spiral worm tubes spirorbis and its palaeoenvironmental implications calcareous tube worms generally identified as spirorbis range from ordovician to recent often profusely encrusting shells and other substrates whereas recent spirorbis is a polychaete annelid details of tube structure in pre cretaceous spirorbis suggest affinities with the microconchida an extinct order of possible lophophorates although characteristically palaeozoic microconchid tube worms survived the permian mass extinction before being replaced in late mesozoic ecosystems by true spirorbis recent spirorbis is stenohaline but spirorbiform microconchids also colonized freshwater brackish and hypersaline environments during the devonian triassic anomalies in the palaeoenvironmental distributions of fossil spirorbis are explained with the recognition of this striking convergence between microconchids and true spirorbis

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

environmental controls on marine ecosystem recovery following mass extinctions with an example from the early triassic abstract the recovery of marine ecosystems following a mass extinction event involves an extended interval of increasing biotic diversity and ecosystem complexity the pace of recovery may be controlled by intrinsic ecosystem or extrinsic environmental factors here we present an analysis of changes in marine conditions following the end permian mass extinction with the objective of evaluating the role of environmental factors in the protracted 5 myr long recovery of marine ecosystems during the early triassic specifically our study examines changes in weathering productivity and redox proxies in three sections in south china chaohu daxiakou and zuodeng and one in northern india mud our results reveal 1 recurrent environmental perturbations during the early triassic 2 a general pattern of high terrestrial weathering rates and more intensely reducing marine redox conditions during the early griesbachian late griesbachian mid smithian and more weakly the mid spathian 3 increases in marine productivity during the aforementioned intervals except for the early griesbachian and 4 stronger and more temporally discrete intervals of environmental change in deepwater sections chaohu and daxiakou relative to shallow and intermediate sections zuodeng and mud our analysis reveals a close relationship between episodes of marine environmental deterioration and a slowing or reversal of ecosystem recovery based on metrics of biodiversity within community alpha diversity infaunal burrowing and ecosystem tiering we infer that the pattern and pace of marine ecosystem recovery was strongly modulated by recurrent environmental perturbations during the early triassic these perturbations were associated with elevated weathering and productivity fluxes implying that nutrient and energy flows were key influences on recovery more regular secular variation in deepwater relative to shallow water environmental conditions implies that perturbations originated at depth i e within the oceanic thermocline and influenced the ocean surface layer irregularly finally we compared patterns of environmental disturbance and ecosystem recovery following the other four big five phanerozoic mass extinctions to evaluate whether commonalities exist in general the pace of ecosystem recovery depends on the degree of stability of the post crisis marine environment

evolutionary models in the early triassic marine realm abstract the relative influences of extrinsic compared to intrinsic drivers of evolutionary change have long been theorized and debated in the fossil record ecological recoveries from mass extinction events present records in which to examine these contrasts competition in a low diversity world reproductive strategy reconstruction of trophic systems and ecological specialization represent possible intrinsic controls on diversification feedback between diversity and abundance shifts of marine organisms with biogeochemical cycling and environmental conditions act as extrinsic controls on recovery process and rate disentangling these evolutionary pressures is a major challenge for understanding evolutionary recovery from mass extinction the end permian mass extinction 251 88 ma represents the largest mass extinction in earth history and led to an extended recovery interval which lasted the duration of the early triassic 4 8 myr and beyond recent analyses suggest that the survivors of the mass extinction were biased toward organisms with higher metabolic rates that were more resilient against the volatile environmental changes that pervaded the early triassic including extreme temperature events low ph and low oxygen conditions we use the early triassic recovery of gastropods echinoids and ammonoids to examine the processes of taxonomic and ecological evolution in response to or in spite of extrinsic environmental perturbations the case studies of benthic gastropods and echinoids when compared to pelagic ammonoids reflect similarities and differences in recovery following the end permian mass extinction gastropods and echinoids exhibit evidence of strong extrinsic environmental limitations which implicate the availability of refugia as a control on recovery low initial taxonomic diversity of survivors may have also limited the evolutionary recovery of both clades abundant and diverse microgastropod assemblages are interpreted as an adaptation to extreme environmental conditions the morphological diversity of disarticulated echinoid spines and plates described in the southwestern united states and examination of phylogenetic ghost lineages hints at a significant hidden diversity of early triassic echinoids ammonoids experienced taxonomic resets but are shown to be resilient to repeated environmental perturbations in the boreal ocean over the duration of the early triassic ammonoids may have adapted to persistent latitudinal temperature gradients and oxygen minimum zones that developed in the early triassic ocean basins

mesozoic and tertiary evolution of the alpine carpathian foreland in eastern austria abstract the bohemian massif partly covered by mesozoic sediments extends southward some 50 km under the alpine carpathian nappe complex a major basement spur devoid of mesozoic sediments and referred to as the south bohemian basement spur separates the jurassic cretaceous upper austrian basin from the lower austrian basin the latter came into evidence during the middle jurassic under a tensional setting late jurassic shelf carbonates and basinal shales were deposited under a tectonically quiet regime early cretaceous uplift of the south bohemian basement spur induced the truncation of jurassic strata along its margins transgressive late cretaceous elastics overlap the truncated jurassic series and locally onlap on basement upper austria latest cretaceous to paleocene foreland deformations may have caused a renewed uplift of the south bohemian basement spur the eocene to late miocene evolution of the molasse foredeep went hand in hand with the emplacement of the alpine carpathian nappe system differential movements between the eastern alpine nappes and the carpathian nappes combined with tensional stresses in the basement caused the subsidence of the vienna basin

magnetotelluric images of paleoproterozoic accretion and mesoproterozoic to neoproterozoic reworking processes in the northern sao francisco craton central eastern brazil abstract broadband and long period magnetotelluric mt data were collected along an east west oriented 580 km long profile across the northern sao francisco craton where extensive proterozoic and phanerozoic sedimentary cover and lack of deep probing geophysical surveys have prevented to establish unequivocally the cratonic character of the archean paleoproterozoic lithosphere following dimensionality analyses the mt dataset was interpreted using both 2 d and 3 d inversion procedures the near surface structure is better resolved in the 2 d model due to its finer resolution a huge upper crustal conductor is found all along the shallow early neoproterozoic irece basin in the central domain of the craton extending laterally for approximately 150 km and restricting signal propagation below the basin its high conductance is explained by a combination of high porosity and high fluid salinity in the sedimentary package another upper crustal conductor is observed on the west side of the profile interpreted as fractured metasedimentary rocks of the rio preto belt thrusted on top of the craton basement during neoproterozoic marginal collision the 3 d model explains significantly better the measured data related to deep structure contrary to what is expected for a stable cratonic block the geoelectric model shows pronounced electrical complexity and heterogeneity an indication that the cratonic lithosphere was multiply reworked in the past by tectonothermal events different lithospheric resistive blocks bounded by major conductive zones are identified constrained by geochemical and isotopic data these vertical conductive interfaces are interpreted as cryptic suture zones due to large scale amalgamation of continents and microcontinents leading to the assembly of the sao francisco craton in the paleoproterozoic the conductivity enhancement is more likely explained by emplacement of sulfides along previous suture zones during mafic magmatism at upper mantle depths high conductivity observed below most of the profile indicates that metasomatism or refertilization processes with incompatible elements caused by the paleoproterozoic subducting slabs and mesoproterozoic to neoproterozoic upwelling of deep fluids and melts reworked this portion of the craton mantle

shallow marine sedimentary facies in the earliest triassic griesbachian cordilleran miogeocline u s a abstract permian history in the cordilleran miogeocline u s a ended with an erosional interval of 1 to 22 million years previous studies of this event focused on unrepresented time faunal extinction regional truncation or physical evidence in local areas another way to view this unconformity is to examine the nature of shallow marine sediments deposited on the erosional surface during the earliest triassic griesbachian transgression as part of this study the rate of the initial mesozoic flood was estimated by determining the extent of the oldest triassic conodont biozone within the study area the calculated rate of transgression over 194 000 km2 occupied by this biozone within the 270 000 km2 depositional area of the earliest triassic dinwoody formation is orders of magnitude greater than those suggested for eustatic sea level change related to glaciation or plate tectonic processes the rapidity of transgression paucity of reworked material at the base of the triassic a general lack of local relief and nearly conformable relations of permian and triassic rocks throughout the region suggest that the triassic sea advanced across a featureless plain the earliest triassic sediments described in this study are restricted to the basal 2 m of the dinwoody formation the generalized geographic distribution of facies within the depositional basin follows evaporites are restricted to the northeast lingula bearing dolomite characterizes the north central sandstone is locally present in the northwest and central areas the southern part is dominated by shaly bedded siltstone with some thin limestone interbeds and calcareous silty shale is present in the west toward the basin center the similarity of basalmost triassic depositional environments to those of the earlier permian documents tectonic rejuvenation of a previous paleogeographic regime that strongly controlled early triassic sedimentation

catastrophic soil erosion during the end permian biotic crisis organic geochemical analyses of sedimentary organic matter from a marine permian triassic transition sequence in northeastern italy reveal a significant influx of land derived diagenetic products of polysaccharides this unique event reflects massive soil erosion resulting from destruction of land vegetation due to volcanogenic disturbance of atmospheric chemistry the excessive supply of soil materials to the oceans provides a direct link between terrestrial and marine ecological crises suggesting that ecosystem collapse on land could have contributed to the end permian marine extinctions

structural pattern in the dharwar craton high grade and low grade supracrustal belts sargur and dharwar set in a matrix of gneisses dotted with granitic plutons of different ages make up the dharwar craton the overall structural pattern is one of subparallel linear belts and stringers whose regional trend changes from nw se in the northern part to n s in the south both the high grade and low grade belts show three principal episodes of folding however the correlation between the deformation episodes in the sargur and the dharwar rocks is controversial and the structural relations between them are not unequivocally established parallelism of the first phase structures in the sargur and the dharwar rocks can be interpreted either as synchronous development or rotation of the earlier sargur structures into parallelism with the younger dharwar structures during later deformation the extension of the supracrustal belts is parallel to the f 2 axial traces of the second deformation granite diapirism and basement uplift further modified

magnetotelluric study to characterize kachchh mainland fault kmf and katrol hill fault khf in the western part of kachchh region of gujarat india abstract the kachchh mainland fault kmf is a major e w trending fault in the kachchh region of gujarat extending 150 km from lakhpat village in the west to the bhachau town in the east the katrol hill fault khf is an e w trending intrabasinal fault located in the central region of kachchh basin and the south of kmf the western parts of both of the faults are characterized and the sediment thickness has been estimated in the region using a magnetotelluric mt survey at 17 sites along a 55 km long north south profile with a site spacing of 2 3 km the analysis reveals that the maximum sediment thickness is 2 3 km quaternary tertiary and mesozoic in the region out of which the mesozoic sediments feature a maximum thickness of 2 km the estimated sediment thickness is found consistent with the thickness suggested by a deep borehole depth approx 2 5 km drilled by oil and natural gas corporation ongc at nirona northern part of the study area from 2 d inversion of the mt data three conductive zones are identified from north to south the first conductive zone is dipping nearly vertical down to 7 8 km depth it becomes north dipping below 8 km depth and is inferred as kmf the second conductive zone is found steeply dipping into the southern limbs near manjal village 28 km south of nirona which is inferred as the khf a vertical dipping down to 20 km depth conductive zone has also been observed near ulat village located 16 km north of manjal village and 12 km south of nirona village this conductive zone becomes listric north dipping beyond 20 km depth it is reported first time by a geophysical survey in the region

the nature of the crust in southern india implications for precambrian crustal evolution 1 we present crustal thickness and poisson s ratio determinations from receiver function analyzes at 32 sites on the archaean and proterozoic terrains of south india the crustal thickness in the late archaean 2 5 ga eastern dharwar craton varies from 34 39 km similar crustal thickness is observed beneath the deccan volcanic province and the cuddapah basin the most unexpected result is the anomalous present day crustal thickness of 42 51 km beneath the mid archaean 3 4 3 0 ga segment of the western dharwar craton since the amphibolite grade metamorphic mineral assemblages 5 7 kbar paleopressures in this part of western dharwar craton equilibrated at the depths of 15 20 km our observations suggest the existence of an exceptionally thick 57 70 km crust 3 0 ga ago beneath the exhumed granulite terrain in southernmost india the crustal thickness varies between 42 60 km the poisson s ratio ranges between 0 24 0 28 beneath the precambrian terrains indicating the presence of intermediate rock type in the lower crust these observations of thickened crust suggest significant crustal shortening in south india during the archaean

the transition from thick skinned to thin skinned tectonics in the basque cantabrian pyrenees the burgalesa platform and surroundings interpretation of seismic data in the margins of the burgalesa platform in the basque cantabrian pyrenees has allowed proposition of a new structural model that combines different modes of deformation during oblique tectonic inversion conditioned by the distribution of triassic salts deformation was decoupled by the presence of the salt horizon between basement involved thrusts inverting formerly triassic and late jurassic early cretaceous extensional faults and a detached thrust system involving the upper triassic to neogene sedimentary package structural units experiencing different styles of deformation are not only stacked vertically above and below the salt but most importantly they change from one to the other along strike across the transversal edges of the triassic salts the burgalesa platform detached thrust system was confined between the basement involved structures of the cantabrian mountains westward and the nw tip of the iberian basement involved structures san pedro southward this together with the obliquity between the pyrenean shortening direction and the strike of the previous extensional faults mostly during the late stages of deformation determined the strike slip reactivation of the basement involved inverted faults and the lateral extrusion of the burgalesa platform detached mesozoic successions above the salt towards the se to form a prominent thrust salient oblique to the main pyrenean trend the proposed model combines thick skinned with thin skinned structural styles during oblique tectonic inversion and is consistent with the surface data including the fracture system the available subsurface data and the mechanical stratigraphy

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

superposition of burial and hydrothermal events post variscan thermal evolution of the erzgebirge germany the post variscan thermal history of the erzgebirge germany is the result of periods of sedimentary burial exhumation and superimposed hydrothermal activity the timing and degree of thermal overprint have been analysed by zircon and apatite u th he and apatite fission track thermochronology the present day surface of the erzgebirge was exhumed to a near surface position after the variscan orogeny thermal modelling reveals permo mesozoic burial to temperatures of up to 80 100 c although the sedimentary cover thins out towards the north resulting in maximum burial temperatures of less than 40 c this thermal pattern was locally modified by cretaceous hydrothermal activity that reset the zircon u th he thermochronometer along ore veins the thermal models show no significant regional exhumation during cenozoic times indicating that the peneplain like morphology of the basement is a late cretaceous feature

40ar 39ar thermochronometry of k feldspar from the ktb borehole germany abstract the great depth and relatively steep geothermal gradient 29 c km of the ktb deep crustal borehole located in the bavarian region of germany provides the basis for our study of diffusive argon loss in k feldspar the observed borehole temperature at 9 km is 265 c which reaches well into the argon closure interval for k feldspar 125 350 c four microcline and two adularia samples distributed relatively evenly down the 9 1 km deep borehole were analyzed by the 40ar 39ar method the thermal histories of the shallow samples are consistent with existing thermochronologic data from the borehole after correction for chlorine correlated excess 40ar the deepest two samples result in age spectra that record zero apparent ages over the first few percent of 39ar released which is predicted by diffusion theory where a range of diffusion volumes are present inverse modeling of the argon kinetics of these two deep samples reveals that the present elevated geothermal gradient in the borehole has existed for only the last approximately one million years recent volcanism within 30 km of the borehole is likely the source of this present day thermal pulse

middle triassic anisian ladinian tejra red beds and late triassic carnian carbonate sedimentary records of southern tunisia saharan platform biostratigraphy sedimentology and implication on regional stratigraphic correlations abstract the red beds of the triassic succession outcropping at tejra medenine southern tunisia saharan platform have yielded rich fossil assemblages of both freshwater and brackish marine invertebrates and vertebrates the new discovered fauna indicates an anisian lower ladinian age for the tejra section its lowermost part is considered as equivalent of ouled chebbi formation while the medium and upper parts are considered as equivalent of the kirchaou formation both sedimentological characteristics and fossil assemblages indicate the increasing marine influences within the middle part of the section and the migration of brackish and freshwater fauna into the lacustrine playa environment at the top the marine fauna rich interval of the tejra section correlates well with the well known myophoria rich carbonate stratigraphic marker confirming the middle triassic ladinian major transgression well recorded eastward in the tunisian jeffara basin and in libya the use of this ladinian stratigraphic event in addition to the carnian carbonate transgressive events of the jeffara escarpment outcrops was of great help for regional lithostratigraphic correlations between the triassic outcropping series and those currently buried in ghadames and berkine basins the age of the sandstones of trias argilo greseux inferieur tagi which forms the main oil and gas reservoir in the saharan domain is attributed to the anisian carnian and considered as coeval of ouled chebbi and kirchaou formations of the dahar escarpment an updated synthetic stratigraphic chart is proposed for the triassic of saharan platform domain on the basis of the compilation of the new obtained results and the subsurface data taken from published literature

early triassic gulliver gastropods spatio temporal distribution and significance for biotic recovery after the end permian mass extinction a reduction in body size lilliput effect has been repeatedly proposed for many marine organisms in the aftermath of the permian triassic pt mass extinction specifically reduced maximum sizes of benthic marine invertebrates have been proposed for the entire early triassic this concept was originally based on observations on early triassic gastropods from the western usa basin and the dolomites n italy and it stimulated subsequent studies on other taxonomic groups however only a few studies have tested the validity of the lilliput effect in gastropods to determine whether the paucity of large sized gastropods is a genuine signal or the result of a poor fossil record and insufficient sampling in combination with a review of the literature we document numerous new abundant large sized gastropods from the griesbachian outcrops of greenland and from the smithian early spathian interval in the southwestern usa we show that large sized gulliver gastropods i were present soon after the pt mass extinction ii occurred in various basins sedimentary facies and environmental contexts from shallow to deeper settings and iii belong to diverse higher rank taxa focusing on the western usa basin we investigate areas from which microgastropod shell beds were previously presented as being typical however we show that gulliver gastropods do occur in the very same areas insufficient sampling effort is probably the main reason for the rarity of reports of large early triassic gastropods which is supported by preliminary rarefaction based simulations finally it appears that the recently documented middle to late smithian climate shifts and the severe end smithian extinction of nekto pelagic faunas did not reduce maximum shell sizes of gastropods

aftermath of the permian triassic mass extinction event paleoecology of lower triassic carbonates in the western usa paleoecologic study of invertebrate faunas from three successive early triassic seaways reveals that biotic recovery from the end permian mass extinction event was slow and that full recovery did not occur until after the early triassic simple cosmopolitan opportunistic generalists and low diversity low complexity paleocommunities were characteristic of the entire early triassic in the western usa an increase in guild and taxonomic diversity was observed with the addition of several new higher taxa in the late early triassic spathian to the almost exclusively molluscan faunas of the earlier early triassic nammalian potential disaster forms the inarticulate brachiopod lingula and the paper pecten claraia dominated the earliest early triassic faunas griesbachian and even occurred in the late early triassic normal marine stromatolites comparison with data on faunas from the permian and triassic suggests that even the most diverse early triassic faunas in the spathian were rather low in guild diversity and species richness these characteristics of genera and paleocommunities in the early triassic may be typical of mass extinction aftermaths

a magnetotelluric study from over dharwar cratonic nucleus into billigiri rangan charnockitic massif india abstract the electrical resistivity structure of the crust beneath the dharwar craton in southern india was investigated by magnetotelluric method in the present study a northwest southeast oriented 220 km long profile of 18 stations with a station spacing of 10 15 km is used the profile extends from dharwar cratonic nucleus in the north to billigiri rangan charnockitic massifs in the south time series data are processed to get the apparent resistivity and phase the dominant geoelectric strike direction 75 was calculated in a period range of 0 01 1000 s the data are rotated to 75 strike direction two dimensional inversion is carried out by using the non linear conjugate gradient scheme for both apparent resistivity and phase our inversion results show a conductor in the northern side of the profile and two distinct prominent conductors in southern part of the profile the mid lower crust in southern part of the profile shows less resistive 2 flushed terranes regional scale carbonation occurred in late archaean is associated with chitradurga shear zone and in late proterozoic is associated with salem attur shear zone the co 2 rich fluids derived during that time might have exhausted in dehydration reactions later events such as the indian plate passing over several hotspots and the metasomatized fluids associated with the cretaceous tertiary magmatism in the region is the reason for observed low resistivity near billigiri rangan massif and surrounding regions in the south