variations of hydraulic properties of granular sandstones during water inrush effect of small particle migration the evaluation of the hydraulic properties evolution of granular sandstones in relation with groundwater inrush within faults is an important issue for mining engineering applications this paper presents the results of an experimental investigation of small particle migration from granular sandstone samples under different original porosities particle size compositions and water flow pressures a new rock testing system has been setup to carry out the tests based on the results it is observed that the overall permeability evolution during the tests can be divided into four different phases including i re arrangement of large rock fragments ii water inrush with substantial particle migration iii continued moderate particles seepage and iv steady state water flow the crushing of edges and corners of large rock fragments and the evolution of the fracture network has mainly been observed in the first two phases of the tests the results indicate that the migration of small particles has an essential effect on permeability and porosity increase during water inrush through fractured sandstone the samples with higher original porosity higher percentage of fine particles in their formation and under higher water flow pressures achieve higher permeability and porosity values when the test is complete furthermore using the measured data the performances of a number of empirical models for permeability evolution in fractured porous media have been studied the prediction results indicate that not all of the fractures in a sample domain contribute in small particle migration there are parts of the fracture network that are not effective in particle flow a sample with less original porosity more fine particles and under lower water pressure shows less ineffective fractures therefore using the concept of the effective porosity fracture is sufficient enough for the flow calculation

spatial variability of watermass conditions within the european epicontinental seaway during the early jurassic pliensbachian toarcian in order to constrain spatial variability in watermass conditions within the european epicontinental seaway prior to during and after the toarcian oceanic anoxic event carbon 13cbel 13ccarb and oxygen 18obel 18ocarb isotope records were obtained from three sections in the grands causses basin southern france these data were then compared with similar records along a north south transect across the european epicontinental seaway as the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite intra rostral carbon and oxygen isotope data from six belemnite specimens belonging to the genus passaloteuthis were collected intra rostral carbon isotopes are influenced by vital effects whereas oxygen isotopes reflect relative changes in temperature and salinity palaeotemperatures calculated from 18obel isotope records from the grands causses basin confirm relatively low temperatures throughout the late pliensbachian similar cool water conditions have previously been shown in germany england spain and portugal a temperature increase of up to 6 c is observed across the pliensbachian toarcian boundary a pronounced negative shift of at least 3 vienna pee dee belemnite is recorded in bulk carbonate carbon during the lower harpoceras serpentinum zone typical of the toarcian oceanic anoxic event before and after the toarcian oceanic anoxic event a good correlation between 13ccarb and 13cbel exists indicating well ventilated bottom waters and normal marine conditions instead data for the toarcian oceanic anoxic event indicate the development of a strong north south gradient in salinity stratification and surface water productivity for the western tethyan realm this study thus lends further support to a pronounced regional overprint on carbon and oxygen isotope records in epicontinental seaways

ages of sediment hosted himalayan pb zn cu ag polymetallic deposits in the lanping basin china re os geochronology of molybdenite and sm nd dating of calcite abstract the lanping basin is a significant pb zn cu ag mineralization belt of the sanjiang tethyan metallogenic province in china over 100 thrust controlled sediment hosted himalayan base metal deposits have been discovered in this basin including the largest sandstone hosted pb zn deposit in the world jinding and several cu ag co deposits baiyangping baiyangchang and jinman these deposits with total reserves of over 16 0 mt pb zn 0 6 mt cu and 7000 t ag are mainly hosted in meso cenozoic mottled clastic rocks and strictly controlled by two cenozoic thrust systems developed in the western and eastern segments of the lanping basin to define the metallogenic history of the study area we dated nine calcite samples associated with copper sulfides from the jinman cu deposit by the sm nd method and five molybdenite samples from the liancheng cu mo deposit by the re os method the calcite sm nd age for the jinman deposit 58 5 ma and the molybdenite re os age for the liancheng deposit 48 2 ma together with previously published chronological data demonstrate 1 the cu ag mineralization in the western lanping basin mainly occurred in three episodes i e 56 54 51 48 and 31 29 ma corresponding to the main and late collisional stages of the indo asian orogeny and 2 the pb zn ag cu mineralization in the eastern lanping basin lacked precise and direct dating however the apatite fission track ages of several representative deposits 21 4 ma to 32 5 ma may offer some constraints on the mineralization age

mantle derived noble gases in ore forming fluids of the granite related yaogangxian tungsten deposit southeastern china more than 90 of the tungsten resources of china are in the nanling region of south china and the yaogangxian vein deposit is the largest tungsten deposit in this region the tungsten deposits have ages of 150 160 ma and are spatially temporally and genetically related to granites which were previously believed to be produced by crustal anatexis this paper provides he and ar isotope data of fluid inclusions in pyrite and arsenopyrite from the yaogangxian w veins 3he 4he ratios range from 0 41 to 3 03 ra where ra is the 3he 4he ratio of air 1 39 10 6 and 40ar 36ar ratios from 328 to 1 191 moreover there are excellent correlations between he and ar isotopic compositions the results suggest that the ore forming fluids are a mixture between a crustal fluid containing atmospheric ar and crustal 4he and a fluid containing mantle components it is likely that the former is a low temperature meteoric fluid and the later is a fluid exsolved from the w associated granitic magma which formed by crustal melting induced by intrusion of a mantle derived magma

genesis of the jinding zn pb deposit northwest yunnan province china constraints from rare earth elements and noble gas isotopes abstract the giant sediment hosted jinding zinc lead deposit is located in the lanping basin northwestern yunnan province china the genesis of the deposit has long been debated and the sources of the ore forming fluids and metals are controversial this study presents rare earth element ree and noble gas isotope data that constrain the origins of the ore fluids and the heat source driving the hydrothermal circulation the early stage sulfides are enriched in light rees and have high ree values 30 8 94 8 ppm and weakly negative eu eu 0 85 0 89 and ce anomalies ce 0 84 0 95 suggesting that the fluids were likely derived from dissolution of upper triassic marine carbonates with input of rees from aluminosilicate rocks in the basin in contrast the late stage sulfides have irregular ree patterns generally low ree values 0 24 10 8 ppm and positive eu eu 1 22 10 9 and weakly negative ce anomalies ce 0 53 0 90 which suggest that the ore forming fluids interacted with evaporite minerals the 3 he 4 he 0 01 0 04 r a and 40 ar 36 ar values 301 340 of the ore forming fluids indicate crustal and atmospheric origins for these noble gases these findings are in agreement with the published fluid inclusion microthermometry data and the results of h o c s pb and sr isotope studies our data in combination with published results support a two stage hydrothermal mineralization model involving early stage basinal brines and late stage meteoric water that acquired metals and heat from crustal sources

diversity dynamics of early jurassic ostracods of the cordillera iberica spain and the re evaluation of the pliensbachian toarcian mass extinction the extinction and recovery of ostracoda at the pliensbachian toarcian p t boundary are analyzed based on a database of taxonomically revised pliensbachian to toarcian transition ostracod assemblages in contrast to earlier assertions the results of this study indicate that ostracod extinction rates were significant in comparison with other marine invertebrates an extinction rate of 54 has been calculated for upper pliensbachian ostracod species occurring in more than one section diversification took place in the latest pliensbachian spinatum zone and early toarcian tenuicostatum zone whereas diversity decrease occurred in the middle early toarcian strangewaysi subzone serpentinus zone this notable diversity decline in the early toarcian corresponds to a global mass extinction time whose peak has been documented in the tenuicostatum zone meanwhile the ostracod mass extinction occurred within the serpentinus zone and was followed by radiation and recovery in the succeeding bifrons zone s

landslides associated with spheroidally weathered mantle of granite porphyry induced by 2011 typhoon talas in the kii peninsula japan abstract typhoon talas brought heavy rain to the kii peninsula japan during 2 5 september 2011 causing hundreds of debris avalanches and debris flows in the southeastern part of the peninsula we undertook field investigations to understand the geological and geomorphological context of the landslides and found that the most important geological factor is spheroidal weathering of granite porphyry this granite porphyry is deeply weathered with corestones in higher elevations and forms low relief surfaces of which marginal areas were the major sources of debris avalanches corestones that failed were embedded in grus in situ or on nearby slopes of mudstone in which the granite porphyry intruded the corestones are made by spheroidal weathering from well developed columnar joints and sheeting joints sheeting joints in the source granite porphyry acted as sliding surfaces both before and during the occurrence of the 2011 debris avalanches

an attempt to constrain the age duration and eruptive history of the karoo flood basalt naude s nek section south africa we have carried out paleomagnetic sampling of a similar to 750 m sequence of the karoo large igneous province naude s nek pass south africa k ar dating cassignol gillot has been performed on four samples from the 650 m upper unit mean age 179 2 1 8 ma and a sample from the lower unit 184 8 2 6 ma a succession of two phases of volcanism is suggested the lower 25 flows 115 m thick have recorded a reversed polarity the next 23 flows 135 m thick are transitional and contribute a detailed record of the van zijl 1962 jurassic reversal the upper 38 flows 500 m thick have normal polarity directional groups dgs of lava flows with quasi identical remanence directions indicate eruption durations too short to have recorded geomagnetic secular variation and hence are interpreted as single eruptive events altogether 19 dgs and 10 sheet lobes yield a sequence of 29 distinct directions this could correspond to a total eruptive activity shorter than 3000 years less than one per mil of the total duration over which the section was emplaced we obtain a new paleomagnetic pole for south africa at similar to 180 ma lambda 75 2 degrees n phi 276 4 degrees e a 95 5 8 degrees n 19 which is consistent with earlier reports

source and possible leaching process of ore metals in the uragen sandstone hosted zn pb deposit xinjiang china constraints from lead isotopes and rare earth elements geochemistry abstract the uragen world class zn pb deposit is located in the ulugqat basin in xinjiang china the deposit is characterized by low grade zn pb 3 wt and large tonnage of 4 84 mt metals in the southern ore zone and potentially 10 mt metals for the whole deposit the deposit is mainly hosted in sandstone and conglomerate of the fifth member of the lower cretaceous kezilesu group to provide better constraints on the source of ore metals systematic analyses of the pb isotopes and ree were conducted on sulfides and possible source terranes the sulfides have homogeneous pb isotopic ratios for 206pb 204pb of 18 528 18 690 for 207pb 204pb of 15 545 15 743 and for 208pb 204pb of 38 429 39 082 these ratios are different from those of the upper silurian upper devonian tangaitaer and paleocene aertashi formations the fourth member of the lower cretaceous kezilesu group and the permian granite despite partly overlapping with the values of sulfides the ratios of the proterozoic aksu metamorphic rocks are different in extent and variability however the clastic rocks of the fifth member of the lower cretaceous kezilesu group have almost the same pb isotopic compositions as the sulfides if the preferential leaching of radiogenic pb is taken into account the sulfides in the disseminated ores show lree enriched patterns with high lree hree ratios 3 50 12 06 variable changes of ce anomalies 0 67 1 22 and eu anomalies 0 52 1 33 that are also similar to those of the clastic rocks of the fifth member of the lower cretaceous kezilesu group but are significantly different from those of the basement rocks of the proterozoic aksu group and the evaporite sequences of the paleocene aertashi formation in the ce and eu anomalies petrographic observations indicate that the clastic rocks of the fifth member of the lower cretaceous kezilesu group have undergone sedimentation diagenetic reddening and bleaching reddening is related to the in situ oxidation of mafic minerals such as biotite to produce ferric iron oxide and hydroxide ioh that accompanied the liberation of ore metals from the silicate phase during subsequent crystallization of ioh to hematite preferential adsorption onto hematite could have been the main mechanism for separating zn pb from cu bleaching resulted from the dissolution of ioh during the oil gas infilling stage and based on mass balance calculations substantial amounts of leachable fe zn pb were extracted from the red clastic rocks by the ore forming fluid therefore we propose that the red clastic rocks of the fifth member of the lower cretaceous kezilesu group may be the predominant source of ore metals in the uragen deposit and that the leaching may be possibly related to the bleaching process

geology geochemistry and origin of lanuoma pb zn sb deposit in changdu area tibet the lanuoma pb zn sb polymetallic deposit is located 10 km north of jitang in changdu basin hosted by carbonate of triassic bolila group t3b the ore deposit occurs in an ore district which is considered to be a part of the sanjiang base metal ore forming belt along the lancang river it is unique in metallic composition of the ores different from the lead zinc deposits in the lanping basin and other major sedimentary rock hosted lead zinc deposits both in china and abroad the lanuoma ore deposit is characterized by mineralization of sb associated with pb zn ore composition analysis and electron microprobe analysis of ore minerals show that sb is closely associated with pb and occurs as robinsonite the ore deposit was formed at intermediate low to epithermal temperatures fluid inclusions in hydrothermal quartz and calcite veins are mainly in the two phase l v state at room temperature and are homogenized to the liquid phase between 140 and 350 their salinities w nacleq range from 2 to 10 results of bulk analysis of the fluid inclusions show that na and cl are most abundant components in liquid phase co2 and trace ch4 c2h6 were detected by bulk analysis and laser raman spectrometry in vapor phase of the fluid inclusions these data indicate that the ore forming fluid is nacl type co2 rich and hydrocarbon bearing fluid brine 13cv pdb values of hydrothermal calcite range from 3 5 to 1 8 and 18ov smow values of hydrothermal calcite range from 11 to 16 suggesting the characteristics between marine carbonate rocks and granite related fluids and the mixing of magmatic components with hydrothermal dissolution of marine carbonate the sulfide minerals have a restricted range of 34s values from 1 6 to 2 6 around zero indicating that the sulfur is of deep crustal derivation the authors hold that the mineralization was related to cenozoic magmatism associated with indo asian collision the sulfur and metals were derived mainly from igneous source or leached from crustal rocks related to tectono magmatic activity and partly from the triassic strata the fluid driven mechanism included topography driven fluid flow in cover sequences and deep magmatic heat source driving for large scale ore forming fluid flow

sanjiang tethyan metallogenesis in s w china tectonic setting metallogenic epochs and deposit types abstract tectonically the sanjiang tethyan metallogenic domain stmd is located within the eastern himalayan tibetan orogen in the sanjiang tethys southwestern china although this metallogenic domain was initiated in the early palaeozoic extensive metallogenesis occurred in the late palaeozoic late triassic and himalayan tertiary epochs corresponding tectonic settings and environments in the domain are an arc basin system related to the subduction of the palaeo tethyan oceanic slabs a post collision crustal extension setting caused by the lithospheric delamination or slab breakoff underneath the sanjiang tethys during the late triassic large scale strike slip faulting and thrusting systems due to the indo asian continent collision since the palaeocene in this metallogenic domain important gold copper base metals rare metals and tin ore belts incorporating a large number of giant deposits were developed the main types of deposits include 1 porphyry copper deposits controlled by a large scale strike slip fault system 2 vhms deposits mainly occurring in intra arc rift basins and post collision crustal extensional basins 3 shear zone type gold deposits in the ophiolitic melange zone along the thrusting shearing system 4 hydrothermal silver polymetallic deposits in the triassic intra continental rift basins and tertiary strike slip pull apart basins and 5 himalayan granite related greisen type tin and rare metallic deposits within the metallogenic epochs of the late palaeozoic to cenozoic the styles and types of the ore deposits changed from vhms types in the late palaeozoic through exhalative sedimentary type deposits in the late triassic to porphyry type copper deposits shear zone type gold deposits hydrothermal vein type silver polymetallic deposits greisen type tin and rare metal deposits in the cenozoic correspondingly ore forming metals also changed from a pb zn cu ag association through ag cu pb zn fe ag pb and ag au hg associations to ag cu pb zn cu mo au sn and li rb cs nb zr hf y ce sc associations

high resolution dynamics of early jurassic marine extinctions the case of pliensbachian toarcian ammonites cephalopoda abstract the pliensbachian toarcian interval was marked by major environmental disturbances and by a second order mass extinction here we reappraise the taxonomic spatiotemporal and selective dynamics of extinctions over the whole interval by analysing a high resolution dataset of 772 ammonite species from nw tethyan and arctic domains on average 40 65 of ammonite species disappeared during each subchronozone but higher extinction pulses reaching 70 90 prevailed from the margaritatus to the dispansum chronozone the main extinctions corresponding to the gibbosus pliensbachian toarcian boundary semicelatum bifrons variabilis and dispansum events differed in their dynamics suggesting episodes of ecological stress related to climate change regression disturbance in the carbon cycle or anoxia the multi pulsed volcanic activity in the karoo ferrar province could well have triggered these ecological changes in addition ammonites experienced a morphological bottleneck during the gibbosus event 1 ma before the early toarcian diversity collapse typically drops in richness were related both to high extinctions and to declines in origination rates this feature could result from strengthened ecological stresses related to the temporal overlap of environmental disturbances after the early toarcian crisis the recovery of ammonites was rapid 2 ma and probably influenced by a coeval marine transgression supplementary material figures showing a comparison of extinction and origination patterns based on different datasets and variations of the morphospace occupation are available at http www geolsoc org uk sup18381

diversity patterns of early jurassic brachiopod assemblages from the westernmost tethys eastern subbetic abstract a detailed faunal succession based upon 6400 brachiopods from the early jurassic in the eastern external subbetic palaeogeographical domain betic range spain is characterized and analyzed this study allows recognition of five assemblages with original biostratigraphical data in sediments where biostratigraphical markers were very scarce it also enables a sound diversity dynamics pattern to be established among the brachiopod assemblages recorded this pattern shows progressive diversification from the sinemurian to the late pliensbachian although with significant episodes during the sinemurian pliensbachian transition the first initial pulses of the disintegration of the south iberian palaeomargin played an important role in the brachiopod assemblages as a notable faunal renewal event is detected assemblage 1 to assemblage 2 maximum biodiversity and abundance were reached in the pliensbachian toarcian transition due to the partial contemporaneity of assemblages 2 and 3 and the settlement of taxa from nearby palaeogeographical basins a decrease related to the early toarcian anoxic event etoae global effect is suggested after which a slight recovery began with colonization by opportunistic taxa soaresirhynchia bouchardi but pre etoae diversity and abundance were subsequently never again reached a palaeogeographical analysis has been carried out to compare taxonomic diversity dynamics in the eastern subbetic with other representative tethyan basins this study also enables palaeobiogeographical affinities to be established for the eastern subbetic domain showing mediterranean palaeobioprovince influences until the late pliensbachian early toarcian a period when replacement occurred that shows faunal unification free connection between the sub boreal and mediterranean provinces may be inferred from the late pliensbachian early toarcian onwards

40ar 39ar dating of hydrothermal activity biota and gold mineralization in the rhynie hot spring system aberdeenshire scotland this study presents a new high precision 40ar 39ar age for the devonian hot spring system at rhynie hydrothermal k feldspar sampled from two veins that represent feeder conduits and a hydrothermally altered andesite wall rock date the hydrothermal activity the fossilised biota and syn k feldspar gold mineralization at 403 9 2 1 ma 2 oxygen isotope data for the parent fluid 4 to 2 show that the k feldspar was precipitated from a dominantly meteoric fluid which mixed with magmatic fluids from a degassing magma chamber the 40ar 39ar age 403 9 2 1 ma 2 when recalculated 407 1 2 2 ma 2 with respect to the astronomically tuned age for fish canyon sanidine 28 201 0 023 ma 1 also provides a robust marker for the polygonalis emsiensis spore assemblage biozone within the pragian earliest emsian furthermore the age identifies the devonian pull apart volcano sedimentary basins of the british and irish caledonides and their root zones as specific targets for future gold exploration

early jurassic mass extinction a global long term event the end pliensbachian extinction event 187 ma has been interpreted either as one of 10 global periodically recurring mass extinctions of the past 250 m y or as a minor localized european event elevated levels of family extinction spanned five ammonite zones during the late pliensbachian and the early toarcian an interval of 7 5 m y and were distributed unequally in the boreal tethyan and austral realms detailed sampling of invertebrate macrofaunas through complete expanded sequences in northwest europe shows that most species extinctions occurred in the early toarcian following a regional anoxic event the early jurassic mass extinction event took place over a long time scale and it was global in extent

mantle fluids in the karakoram fault helium isotope evidence abstract the karakoram fault kkf is the 1000 km long strike slip fault separating the western himalaya from the tibetan plateau from geologic and geodetic data the kkf is argued either to be a lithospheric scale fault with hundreds of km of offset at several cm a or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper crustal localization of distributed deformation at depth here we show 3he 4he ratios in geothermal springs along a 500 km segment of the kkf are 3 100 times the normal ratio in continental crust providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle mantle enrichment is absent along the indus yarlung suture zone isz just 35 km southwest of the kkf suggesting that the mantle fluids flow only within the kkf within the last few ma the kkf must have accessed tectonically active tibetan mantle northeast of the mantle suture which we therefore locate vertically beneath the kkf very close to the surface trace of the isz hence in southwestern tibet indian crust may not now be underthrusting substantially north of the isz even though miocene underthrusting may have placed indian crust north of the isz in the lower half of the tibetan plateau crust this is in significant contrast to central and eastern tibet where underthrust indian material not only forms the lower half of the tibetan crust but is also currently underthrusting for 200 km north of the isz our new constraint on kkf penetration to the mantle allows an improved description of the continuously evolving karakoram fault as a tectonically significant yet perhaps geologically ephemeral lithospheric structure

tracing element sources of hydrothermal mineral deposits ree and y distribution and sr nd pb isotopes in fluorite from mvt deposits in the pennine orefield england fluorite from mississippi valley type mvt deposits in the south pennine orefield england displays significantly different distributions of rare earths and yttrium rey compared to fluorite from similar mvt deposits in the north pennine orefield samples from the south pennine orefield display negative ce and positive gd and y anomalies but lack any eu anomaly indicating that the rey were mobilized from relatively pure marine sedimentary carbonates in marked contrast fluorite from the north pennine orefield lacks any ce and gd anomalies but shows a pronounced positive eu anomaly suggesting that the rey were provided by different source rock s that the mineralizing hydrothermal fluid had experienced higher temperatures prior to fluorite precipitation and that it was derived from deeper crustal levels in the north compared to the south the isotopic composition of sr in blue john fluorite from the south pennine orefield suggests that sr was mobilized from lower carboniferous tournaisian limestones whereas pb isotopes suggest that in contrast to rey and sr pb was derived from aluminosilicate rocks neither nd nor sr or pb isotopes can be used to radiometrically date the formation of blue john fluorite all isotope systems studied indicate that the limestone host rock of this fluorite mineralization did not contribute to the trace element budget of the hydrothermal fluid our results show that different solutes in a natural water hydrothermal fluid groundwater etc may be derived from different sources and that the study of a small set of elements or isotope ratios may not provide full insight into the genesis or history of a mineralization or a hydrothermal fluid our data provide evidence for the uncoupling of sr nd and pb during fluid rock interaction and fluid migration and show that the use of plots such as 87sr 86sr vs end to learn about mixing relationships as is commonly done in igneous geochemistry is unreliable when applied to natural waters and their precipitates

numerical evaluation of mechanisms driving early jurassic changes in global carbon cycling the early jurassic early toarcian ca 183 ma carbon cycle perturbation is characterized by aabout 5 parts per thousand delta sup 13 c excursion in the exogenic carbon reservoirs a 1000 ppm rise in atmospheric co sub 2 and a 6 7 degrees warming two proposed explanations for this presumed global carbon cycle perturbation are the liberation of massive amounts of isotopically light ch4 from 1 gondwanan coals by heating during the intrusive eruption of the karoo ferrar large igneous province lip or 2 the thermal dissociation of gas hydrates carbon cycle modeling indicates that the release of ch4 from gondwanan coals synchronous with the eruption of the karoo ferrar lip fails to reproduce the magnitude or timing of the co sub 2 and delta sup 13 c excursions however sensitivity analyses constrained by a marine cyclostratigraphically dated delta sup 13 c record indicate that both features of geologic record can be explained with the huge input of about 15 340 24 750 gt c over about 220 k y a result possibly pointing to the involvement of hydrothermal vent complexes in the karoo basin the simulated release of 6000 gt c from gas hydrates also reproduces aspects of the early toarcian rock record but the large mass involved raises fundamental questionsmore about its formation storage and release less

countermeasures of water and mud inrush disaster in completely weathered granite tunnels a case study this paper presents a case study of the countermeasures of water and mud inrush disasters in the junchang tunnel in guangxi china this tunnel was constructed in a weathered granite formation and four serious water and mud inrush disasters occurred during construction the geological and hydrological conditions are first reviewed to understand their effects on the water and mud inrush disasters four potential causes of the serious water and mud inrush disasters in the junchang tunnel were proposed including the poor stability of the completely weathered granite the high groundwater level and large groundwater flow rate insufficient pre reinforcement of the surrounding rock and the disturbances caused by tunnel construction water sealing and ground reinforcement measures were suggested before excavation to improve the stability of the surrounding rock and plug the water outflow channels and full face curtain grouting was considered as the first choice furthermore several improvements including the combined utilization of various grouting materials supplementary grouting with steel pipes in collapsed boreholes and dynamically optimized grouting methods were implemented to solve the serious water inflow and collapse problems experienced during the drilling and grouting work a detailed curtain grouting scheme was proposed and applied in practice a comprehensive evaluation based on inspection borehole investigations and p q t analysis indicated that the curtain grouting method yielded satisfactory performance in water sealing and ground reinforcement in addition the groundwater level and settlement data collected in the field validated the effectiveness of the proposed countermeasures

the pliensbachian and tithonian extinction events the claim by raup and sepkoski1 that an approximately 26 myr mass extinction periodicity can be recognized on a global scale at family level over the past 250 myr has excited much attention and provoked speculation about an ultimate extraterrestrial cause2 10 while the purported periodicity can be challenged on grounds of both the inaccuracy of the geological timescale11 and the method of extinction analysis12 there can be no doubting the reality of at least some of the 12 proposed extinction events such as those at or near the end of the permian triassic and cretaceous others are less widely acknowledged further analysis by raup and sepkoski13 confirms the importance of two of these events within the jurassic at the end of the pliensbachian and tithonian stages i demonstrate here that marine invertebrate mass extinctions at approximately these times occurred on a regional not a global scale they can be related to severe reductions in habitat area provoked either by regression of epicontinental sea or by widespread anoxia

pacing of the toarcian oceanic anoxic event early jurassic from astronomical correlation of marine sections abstract the early toarcian oceanic anoxic event oae in the early jurassic period is associated with a major negative carbon isotope excursion cie mass extinction marine transgression and global warming the toarcian oae is thought to have been caused by flood basalt magmatism and may have been a trigger for mass extinction however these proposed causes of the toarcian oae and associated biotic crisis are not adequately resolved by a precise chronology the duration of the toarcian oae has been estimated to be anywhere from 0 12 to 0 9 myr most recently 0 74 to 3 26 myr from u pb dating the cie associated with the toarcian oae has a similar pattern at numerous localities and there is evidence that the marine carbon isotope variations recorded astronomical forcing signals here we estimate a duration of 620 kyr for the main negative cie 860 kyr for the polymorphum zone and 1 58 myr for the levisoni zone based on 405 kyr astronomical eccentricity tuning of the marine section at peniche portugal this 405 kyr tuned series provides a 2 5 myr continuous high resolution chronology through the early toarcian there are 6 or possibly 7 short eccentricity cycles in the main cie interval at peniche to confirm this astronomically based estimate we analyzed three other sections at yorkshire uk dotternhausen germany and valdorbia italy from marine carbon isotopic series these four stratigraphic sections from early jurassic western tethys record the toarcian oae with 6 prominent carbon isotope cycles in the cie that span a 600 100 kyr duration the peniche 405 kyr tuned series indicates that the pre and post cie intervals experienced strong precession eccentricity forced climate change whereas the cie interval is marked by dominant obliquity forcing these dramatic and abrupt changes in astronomical response in the carbon isotopes point to fundamental shifting in the early toarcian paleoclimate system that was directly linked to the global carbon cycle

biosedimentology of the early jurassic post extinction carbonate depositional system central high atlas rift basin morocco this study documents a liassic example of the long ranging effects of mass extinction on carbonate systems biohistoric constraints inherent in the liassic carbonate depositional system are deciphered from normal marine sub tidal deposits of the central high atlas rift basin morocco through hettangian sinemurian to early toarcian times the integration of results from the analysis of lithofacies depositional geometries microfacies macrobenthos carbonate build ups carbon and oxygen stable isotopes and rare earth element yttrium distribution patterns allows the intrinsic or biohistoric control on the central high atlas deposits to be separated from extrinsic factors such as basin development and palaeoclimate the survival interval in the aftermath of the end triassic mass extinction persisted until the early sinemurian indicated by a severely depleted carbonate system impoverished in skeletal organisms a tectonic pulse at the early to late sinemurian boundary interval caused a basin widening with immigration of a marine fauna however until the latest sinemurian macdonelli subzone of the raricostatum zone the deposits were dominated by filter feeding benthic heterotrophs sponges brachiopods polychaetes and crinoids during this stage primary production within the enlarged basin must have been largely planktonic and there was a net flux of organic matter to the sea floor oxygen minimum zone a regional radiation of organic walled phytoplankton is inferred to explain the selective success of the filter feeding community and the occurrence of sponge mounds thus significant effects of the end triassic mass extinction are still present during the late sinemurian through almost the entire pliensbachian a highly productive shoal rimmed carbonate platform existed it developed subsequent to tectonic reorganization and a marine recirculation event radiolarian facies 13c 1 1 strongly negative ce anomaly photosymbiotic sediment producers mainly large bivalves now state the success of specialists and environmental equilibrium conditions in the latest pliensbachian the climax stage was reached with the development of a coralgal reef rimmed carbonate platform the liassic carbonate depositional system experienced a terminal multicausal early toarcian drowning event during which most of the large bivalves became extinct

diversity and morphological evolution of jurassic belemnites from south germany abstract belemnites are extinct cephalopods whose evolutionary history is representative of successful adaptive radiations during the mesozoic nevertheless a detailed understanding of the dynamics and palaeoenvironmental drivers of this evolution is still lacking in order to fill this gap we analyze the diversity and morphological disparity of jurassic rostra from south germany and compare these patterns with other euro boreal trends we show that after an early apparition of few dissimilar groups during the hettangian sinemurian interval belemnites experienced four periods of diversification i e early pliensbachian middle late toarcian early bajocian and oxfordian marked by morphological disparifications of rostra towards forms potentially optimized for different hydrodynamic properties these adaptive radiations were interrupted at regional scale by four biological crises corresponding to morphological bottlenecks i e pliensbachian toarcian aalenian late bajocian and kimmeridgian most of them were morphoselective except the aalenian extinction which could be related to a prominent sea level fall by comparing our results to palaeoenvironmental data we show that warm temperate seawater temperatures might have favoured the diversification of belemnites potentially by accelerating their metabolic rates the population turnovers and the evolutionary rates on the long term conversely cooling or hyperthermal events correspond with biological crises migrations towards refuge areas located in the arctic and mediterranean domains could have been key factors for rapid post crisis recoveries finally the available data suggest a trend towards increased streamlining of the rostrum through the jurassic

early jurassic schizosphaerellid crisis in cantabria spain implications for calcification rates and phytoplankton evolution across the toarcian oceanic anoxic event 1 the toarcian oceanic anoxic event 183 myr ago represents a global perturbation marked by increasing organic carbon burial and a general decrease in calcium carbonate production likely triggered by elevated carbon dioxide levels in the atmosphere here we present quantitative analyses of calcareous nannofossil diversity and abundance from the castillo de pedroso section in cantabria northern spain we compare these data with geochemical data c and o isotopes obtained from biogenic and bulk carbonate records in order to highlight the response of calcareous phytoplankton to major climatic and paleoceanographic changes the pliensbachian toarcian boundary is characterized by an abrupt decrease in abundance of schizosphaerella punctulata the most important lithogenic contributor to hemi pelagic carbonates in the early jurassic the early toarcian nannofloral assemblages show an increase in abundance of mitrolithus jansae and small sized r selected taxa and a progressive decrease in s punctulata percentages the deep dwellers m jansae and s punctulata experienced a major crisis slightly prior to the deposition of the toarcian black shales that are characterized by high abundances of eutrophic taxa such as lotharingius spp and biscutum spp the return of s punctulata associated with lower percentages of eutrophic taxa was observed just above the toarcian black shales the toarcian episode reveals that high co2 levels and increasing primary productivity probably triggered a shift in abundance from highly calcified nannoliths such as s punctulata and m jansae to small sized r selected coccoliths that overall record a biocalcification crisis at the onset and during the toarcian episode

spatial temporal evolution of ore forming fluids and related mineralization in the western lanping basin yunnan province china abstract the lanping basin is a significant pb zn cu ag mineralization belt in the sanjiang tethyan metallogenic province a series of sediment hosted himalayan cu ag pb zn polymetallic deposits have been discovered in the western part of the basin controlled by a thrust nappe system in the thrust nappe system the cu orebodies mainly occur in the western and relatively deep part of the mineralization system the root zone whereas the pb zn ag cu orebodies occur in the eastern and relatively shallow part of the system the front zone both as vein type mineralization in this paper we present new data combined with existing data on fluid inclusions isotopes and geologic characteristics of representative deposits to provide the first study that contrasts mineralizing fluids in the cu ag mo and pb zn ag cu polymetallic deposits fluid inclusion and isotope studies show that the cu ag mo mineralization in the root zone formed predominantly from deep crustal fluids with the participation of basinal brines the deep crustal fluids are marked by high co2 content relatively high temperatures 280 to 340 c and low salinities 1 to 4 wt nacl equivalent whereas the basinal brine shows relatively low temperatures 160 c to 220 c and high salinities 12 to 22 wt nacl equivalent containing almost no co2 in comparison hydrothermal activity associated with the pb zn ag cu deposits in the front zone is characterized by basinal brine with relatively low temperatures 130 c to 180 c high salinities 9 to 24 wt nacl equivalent and low co2 concentrations although evolved meteoric waters have predominantly been proposed as the source for deep crustal fluids magmatic and metamorphic components cannot be completely excluded the basinal brine was predominantly derived from meteoric water the 34s values of sulfides from the cu ag mo deposits and pb zn ag cu deposits range from 17 9 to 16 3 and from 2 5 to 11 2 respectively these ranges may relate to variations in physicochemical conditions or compositional variation of the sources lead isotope compositions indicate that the ore forming metals were predominantly derived from sedimentary rocks of the lanping basin

periodicity in extinction and the problem of catastrophism in the history of life the hypothesis that extinction events have recurred periodically over the last quarter billion years is greatly strengthened by new data on the stratigraphic ranges of marine animal genera in the interval from the permian to recent these data encompass some 13 000 generic extinctions providing a more sensitive indicator of species level extinctions than previously used familial data extinction time series computed from the generic data display nine strong peaks that are nearly uniformly spaced at 26 ma intervals over the last 270 ma most of these peaks correspond to extinction events recognized in more detailed if limited biostratigraphic studies these new data weaken or negate most arguments against periodicity which have involved criticisms of the taxonomic data base sampling intervals chronometric time scales and statistical methods used in previous analyses the criticisms are reviewed in some detail and various new calculations and simulations including one assessing the effects of paraphyletic taxa are presented although the new data strengthen the case for periodicity they offer little new insight into the driving mechanism behind the pattern however they do suggest that many of the periodic events may not have been catastrophic occurring instead over several stratigraphic stages or substages

the response of two tethyan carbonate platforms to the early toarcian jurassic oceanic anoxic event environmental change and differential subsidence chemostratigraphic analyses 87 sr 86 sr d 13 ccarb of limestones from two jurassic platform carbonate sequences in italy trento and campania lucania platforms illustrate previously established trends found in pelagic sediments and skeletal carbonates from biostratigraphically well calibrated sections elsewhere in europe chemostratigraphic correlations between the platform carbonate successions and appropriate intervals from well dated reference sections allow the application of high resolution stratigraphy to these shallow water peritidal carbonates and furthermore elucidate the facies response to the early toarcian oceanic anoxic event oae lower jurassic toarcian levels of the western trento platform southern alps northern italy contain spiculitic cherts that appear where rising carbon isotope values characterize the onset of the oae a palaeoceanographic phenomenon interpreted as driven by increased nutrient levels in near surface waters there is a facies change to more clay rich facies at the level of the abrupt negative carbon isotope excursion also characteristic of the oae higher in the section the campania lucania platform southern apennines southern italy records a change to more clay rich facies where carbon isotope values begin to rise at the beginning of the oae but the negative excursion higher in the section occurs within oolitic facies although in both examples the early toarcian oae can be recognized by a change to more clay rich lithologies this facies development is diachronous and in neither case did the platform drown although the trento platform in the south west sector studied here was adversely affected by the oae it did not drown definitively until late aalenian time the campania lucania platform persisted throughout the jurassic and cretaceous differential subsidence rates which can be calculated using comparative chemostratigraphy are identified as a crucial factor in the divergent behaviour of these two carbonate platforms relatively fast in the case of the trento platform relatively slow in the case of the campania lucania platform it is proposed that where water depths remained as shallow as a few metres during the oae campania lucania platform dissolved oxygen levels remained high nutrient levels relatively low and conditions for carbonate secretion and precipitation remained relatively favourable whereas more poorly ventilated and or more nutrient rich waters trento platform adversely

the search for the origin of the planktic foraminifera planktic foraminifera are an extremely abundant important and successful group of marine protists they are particularly useful in reconstructing past environments and for biostratigraphic dating despite their importance the origin of the group is uncertain previous work has suggested that they evolved from a benthic ancestor during the triassic or perhaps the mid jurassic bajocian but a reason for their origination has remained unclear here we present evidence from the toarcian early jurassic of nw europe that the origin of the planktic foraminifera may have been one of the results of the early toarcian oceanic anoxic event this event appears to have been associated with a massive dissociation of gas hydrates and other perhaps related water chemistry changes

rare earth element geochemistry of hydrothermal deposits from the active tag mound 26 n mid atlantic ridge the rare earth element ree geochemistry of various phases from the active tag hydrothermal mound has been examined and related to their mineralogy and fluid chemistry the mound deposits range from black and white smoker chimneys massive anhydrite sulphide mixtures oxides and ochres all phases except black smoker chimney anhydrite demonstrate a positive eu anomaly when normalised to chondrite ree values ree substitution into sulphide and sulphate phases appears to be strongly influenced by crystallographic control for all ree other than eu precipitation of anhydrite within the tag mound is the major mechanism for removal of ree during mound circulation and 0 15 0 35 g anhydrite is inferred to precipitate from every kg of fluid venting from the white smoker chimneys oxides from the mound fall into three different categories with distinct ree patterns oxide rims on sulphides atacamite bearing oxides and silica rich fe oxides and ochres the oxide rim phases contain sulphide and seawater derived rees whereas the atacamite bearing oxides and the ochreous material exhibit no seawater signature which suggests precipitation from or alteration by a modified hydrothermal fluid

metallogenesis in tibetan collisional orogenic belt ii mineralization in late collisional transformation setting the collisional processes established many paleo mountain belts are commonly divided by many geologists into two simple but distinct stages i e syn collisional and post collisional periods as the transition from late to post collisional is not clear and the definition of post and late collisions also is blurring however the tectonic evolution of the tibetan orogen underwent a complicate history which is divided into 1 syn collisional 65 41 ma 2 late collisional 40 26 ma and 3 post collisional 25 0 ma periods the orogeny during the late collisional period generally happened in a compressional regime resulted from successional convergence between indian and asian continents and is characterized by intra continental subduction underthrust crustal shortening large scale thrusting and strike slip faulting systems developed in the margins of the tibetan plateau which resulted in the development of potassic porphyry stocks and carbonatite alkalic complexes in the eastern tibet and potassic ultrapotassic volcanic rocks in the northern tibet at least four significant metallogenic events associated with the late collsional orogeny have been recognized in the eastern margin of the tibetan plateau a tectonic transformation belt they are 1 the porphyry cu mo au mineralization related to large scale strike slip faults system which controlled the localization of the yulong porphyry cu belt 40 36 ma in east tibet 2 the ree mineralization associated with carbonatite alkalic complexes formed the mianning dechang ree belt 40 27 ma in the western sichuan 3 the pb zn ag mineralization controlled by thrust faulting systems formed at least two large sized pb zn ag deposits 40 30 ma in the lanping strike slip pull apart basin western yunnan and 4 the au mineralization related to large scale shearing which produced the ailaoshan au belts composed of numerous shear type or orogenic type au deposits in the western sichuan and yunnan these data indicate that the late collisional metallogensis in the tibetan orogen were mainly developed in an intra continental transformation orogenic sdetting characterized by a series of large scale strike slip faulting thrusting and shearing systems developed in the late collisional period available data suggest that the metallogensis is probably controlled by a shared deep lithospheric process most likely related to upwelling of the asthenosphere triggered by face to face subduction of the yangtze and lhasa blocks continental slabs in the eastern margin of the tibetan plateau during the late collisional period

yttrium and rare earth elements in fluids from various deep sea hydrothermal systems rare earth element ree and yttrium y concentrations were measured in fluids collected from deep sea hydrothermal systems including the mid atlantic ridge mar i e menez gwen lucky strike tag and snakepit the east pacific rise epr i e 13 n and 17 19 s and the lau vai lili and manus vienna woods pacmanus desmos back arc basins bab in the south west pacific in most fluids y is trivalent and behaves like ho chondrite normalized y ree y reen concentrations of fluids from mar epr and two bab sites i e vai lili and vienna woods showed common patterns with lree enrichment and positive eu anomalies ree analysis of plagioclase collected at lucky strike strengthens the idea that fluid ree contents are controlled by plagioclase phenocrysts other processes however such as ree complexation by ligands cl f so42 secondary phase precipitation and phase separation modify ree distributions in deep sea hydrothermal fluids ree speciation calculations suggest that aqueous ree are mainly complexed by cl ions in hot acidic fluids from deep sea hydrothermal systems ree concentrations in the fluid phases are therefore influenced by temperature ph and duration of rock fluid interaction unusual y reen patterns found in the pacmanus fluids are characterized by depleted lree and a positive eu anomaly the demos fluid sample shows a flat y reen pattern which increases regularly from lree to hree with no eu anomaly these manus basin fluids also have an unusual major element chemistry with relatively high mg so4 h2s and f contents which may be due to the incorporation of magmatic fluids into heated seawater during hydrothermal circulation ree distribution in pacmanus fluids may stem from a subseafloor barite precipitation and the ree in demos fluids are likely influenced by the presence of sulfate ions

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

early jurassic south american pectinaceans and circum pacific palaeobiogeography abstract in the light of new data from south america high latitude southern bivalve faunas are now recognized for the early jurassic it is proposed that an austral realm was in continuous existence throughout jurassic times some bivalve genera palmoxytoma kolymonectes radulonectites agerchlamys n gen and groups of species of plicatula harpax show a bipolar distribution suggesting climatic control in the early jurassic a distinctive group of high latitude bivalves included monotidae kalenteridae oxytomidae and some pectinidae and plicatulidae based on the pectinacean s l bivalves the east west faunal differentiation was weaker than the latitudinal one in the early jurassic pacific the southern andes were situated in a transitional area between the tethyan and austral realms as shown by the mixed influence of the local bivalve faunas

uranium metallogenesis in south china and its relationship to crustal extension during the cretaceous to tertiary south china is rich in vein type hydrothermal uranium deposits hosted in granitic volcanic and carbonaceous and siliceous pelitic sedimentary rocks the uranium deposits are spatially associated with extensional structures and or mantle derived mafic dikes both the uranium deposits and mafic dikes are cretaceous to tertiary in age temporally coincident with the crustal extension carbon isotope analyses of calcite deposited in the main stage mineralization in the veins from 12 representative uranium deposits yield 13c values of ore forming fluids mainly from 4 to 8 per mil which are permissive of a mantle origin for the co2 in the ore forming fluids a mantle origin is consistent with the association of the deposits with mafic dikes and the 3he 4he ratios of ore forming fluids e g 0 10 2 02 ra for the volcanic hosted xiangshan uranium deposit isotopic compositions of h and o demonstrate that water in the ore forming fluids is predominantly meteoric in origin ore forming temperatures ranged approximately from 150 to 250 c uranium rich crustal rocks in south china may have been the sources for the uranium crustal extension and associated mafic magmatism are considered to have heated the rocks and allowed co2 possibly from mantle sources to migrate upward and to mix with co2 poor meteoric water the co2 rich hydrothermal fluids mobilized uranium from the source rocks and then the uranium was deposited in various host rocks to form the uranium deposits

warming driven mass extinction in the early toarcian early jurassic of northern and central spain correlation with other time equivalent european sections abstract causes of the major mass extinction recorded during the early toarcian early jurassic are controversial many authors have concluded that the mass extinction is caused by the widespread oceanic anoxia derived from a postulated early toarcian oceanic anoxic event etoae supposedly synchronous in all basins and global in extent another group of papers links the mass extinction with a major climate change that occurred synchronously with the mass extinction the results of the study of five sections of the uppermost pliensbachian and lower middle toarcian deposits located in northern and central spain are presented detailed ammonite based biostratigraphy coupled with stable isotope analysis of belemnite calcite and bulk carbonates as well as total organic carbon toc analyses have been performed in all sections records of the vertical distribution of mainly benthic fossils have been compiled in four of the studied sections results obtained in the spanish outcrops have been compared and correlated with other european sections the excellent mutual relation between the patterns of the early toarcian progressive warming and the concomitant progressive losses of species evidences a cause and effect relationship between the increase of temperature and the mass extinction from an uppermost pliensbachian cooling interval warming started at the lower toarcian tenuicostatum zone increase of average seawater palaeotemperature is associated with a progressive and substantial drawdown in the number of species of nektonic planktonic and benthic organisms representing the extinction interval a prominent increase in seawater temperature occurred around the lower toarcian tenuicostatum serpentinum zonal boundary average temperatures at the serpentinum zone increased about 7 c marking the extinction boundary the high temperatures continued during the middle toarcian bifrons chronozone representing the repopulation interval the anoxia linked to the postulated etoae cannot be the responsible for the mass extinction because it has been synchronously recorded in the oxygenated environments of many european and northern african platforms deposition of laminated organic rich black shale facies above 5 wt toc indicating anoxic environments was mostly confined geographically to the western europe euxinic basin and mainly deposited after the extinction event during the interval of faunal recovery

foraminiferal assemblages extinctions and appearances associated with the early toarcian oceanic anoxic event in the llanbedr mochras farm borehole cardigan bay basin united kingdom abstract the uppermost pliensbachian lower toarcian sediments recovered from llanbedr mochras farm borehole north wales uk were deposited in the cardigan bay basin and mainly consist of alternating marls and marly limestones the current study analyses the foraminiferal assemblages from the cored interval 143 m that has been assigned to the spinatum zone upper pliensbachian to the lower part of the bifrons zone middle toarcian the foraminiferal assemblages are dominated by the suborders lagenina and robertinina four main ecostratigraphic intervals have been identified based on changes in the foraminiferal assemblages that occurred before during and after the toarcian oceanic anoxic event t oae ecostratigraphic interval i upper part of the spinatum zone is characterized by a diverse assemblage with specialist opportunist and intermediate forms this assemblage is interpreted to represent a phase that pre dates the biotic crisis the ecostratigraphic interval ii tenuicostatum zone shows an abrupt increase in opportunist forms such as the genus reinholdella and a facultative opportunist such as paralingulina tenera which was tolerant to oxygen depleted conditions this second interval represents the initial biotic crisis phase in response to decreasing oxygenation the ecostratigraphic interval iii is considered the peak of the biotic crisis coincident with the negative carbon isotopic excursion at the base of the serpentinum zone and characterized by the dominance of the opportunist reinholdella 87 97 of the assemblage and low diversity the ecostratigraphic interval iv upper part of serpentinum zone and lower part of bifrons zone is characterized by an increase of diversity and an abrupt decrease in reinholdella this assemblage is interpreted to reflect the increased availability of oxygen from deep infaunal to epifaunal microhabitats and the return to normal conditions at the sea bottom ecostratigraphic fluctuations in the mochras foraminiferal assemblages across the t oae event are comparable with those from other parts of the uk the lusitanian basin portugal the umbria marche basin italy and the atlassic basin north africa in addition a foraminiferal turnover is evident across the pliensbachian toarcian boundary and the t oae and reflects the effects of the early jurassic biotic crisis on benthic foraminifera controlling factors of the biotic crisis are discussed regarding that anoxic conditions do not necessarily have a lethal effect on all foraminiferal species and other oceanographic and environmental factors need consideration fragmentation of epicontinental platforms sea level changes crisis of carbonate productivity and temperature changes

alteration characteristics of granite contact zone and treatment measures for inrush hazards during tunnel construction a case study abstract several large scale mud and water inrush events occurred during excavation of the denghuazhai tunnel at a depth of 175 m in the contact zone between geodic granite and tuff by analyzing the inrush process the characteristics of the inrush hazards such as high pressure abundant water high mud and sand content and strong destructive power were revealed in addition the inrush hazards were intermittent uncertain and sudden an intrusive contact zone between geodic granite and tuff was revealed by regional geological investigation large scale alteration occurred both in geodic granite and tuff near the contact zone petrographic analyses indicated that alteration to albite sericite and kaolinite occurred in geodic granite and alteration to quartz and montmorillonite took place in tuff gradually toward the contact zone furthermore the changes were gradational within and between various alteration grades the closer to the contact zone the higher degree of alteration the less the primary minerals including quartz k feldspar and plagioclase the more the secondary minerals such as sericite and clay minerals tests on porosity saturated water content and uniaxial compressive strength indicated that alteration led to significant deterioration of physical and mechanical properties of rocks except for silicified tuff especially for the zonal clay in the central area of contact zone the physical and mechanical properties were poor and obvious swelling disintegration and argillation were observed tunnel excavation triggered swelling disintegration and argillation of clay leading to several large scale inrush events in terms of treatment of inrush hazards first of all a comprehensive exploration method based on petrographic analyses geophysical detection and borehole drilling was established according to the alteration characteristics so as to identify the scale and composition of the altered zone the principle of consolidation before removal was adopted to deal with the inrush deposits for breach sealing and reinforcement energy release and stress reduction during tunnel construction and regular drainage during operation were achieved by dewatering measures namely drainage supplemented by sealing water drainage and solids remaining reinforcement measures including full face curtain grouting and double layer pipe sheds were adopted to reinforce and seal the highly disturbed rock and soil in advance finally technical measures including bench excavation enhancement of support stiffness and timely installation of secondary support were employed to effectively prevent large deformation in disturbed rock masses with the above measures the left and right tunnels of the denghuozhai tunnel have passed through the altered zone successfully

a carbon isotope perturbation at the pliensbachian toarcian boundary evidence from the lias group ne england a perturbation in the carbon isotope record at the time of the pliensbachian toarcian boundary 184 ma in the early jurassic is reported based on new data from yorkshire england two sharp 13 c org negative excursions each with a magnitude of 2 5 and reaching minimum values of 28 5 are recorded in the bulk organic matter record in sediments of latest pliensbachian to earliest toarcian age a similar pattern of negative carbon isotope excursions has been observed at the stage boundary in the sw european section at peniche portugal in 13 c carbonate 13 c wood and 13 c brachiopod records the isotopic excursion is of interest when considering the genesis and development of the later toarcian oceanic anoxic event oae as well as the second order global extinction event that spans the stage boundary furthermore the isotope excursion potentially provides a chemostratigraphic marker for recognition of the stage boundary which is currently achieved on the basis of different ammonite faunas in the nw european and tethyan realms

helium isotopes as tracers of trapped hydrothermal fluids in ocean floor sulfides helium isotopes have been measured in fluids trapped in minerals from three mid ocean ridge hydrothermal systems at bare rock sites and at the sediment covered site at middle valley northern juan de fuca ridge fluid inclusion 3 he 4 he ratios from the bare rock sites are indistinguishable from those of the vent fluids and are close to the local basalt values values for 34 s of the host sulfide are consistent with variable contributions of seawater sulfate s to the basalt derived s in the hydrothermal fluids this does not affect inclusion hosted 3 he 4 he because of the high he concentration of the hydrothermal fluids relative to seawater fluid inclusion 3 he 4 he ratios from middle valley are a mixture of basalt derived he and radiogenic he acquired from pore fluids in the overlying pleistocene turbidite sediments after seawater basalt interaction the radiogenic he accompanies isotopicalty heavy s demonstrating that he isotopes may be used to distinguish pore fluids from seawater in hydrothermal systems

grouting for water and mud inrush control in weathered granite tunnel a case study abstract this paper presents a case study of curtain grouting to prevent water and mud inrush disasters for a weathered granite tunnel in guangxi china first the basic information of the junchang tunnel is given including ground conditions water and mud inrush disasters and the subsequent prevention countermeasures then we present the original grouting design and procedure and the field operation of 25 grouting cycles and excavations for the evaluation of the grouting effect and suggestion for future grouting work based on the field investigation the values of the major grouting parameters are suggested including grouting thickness of 5 8 m grouting length of 15 18 m 3 3 6 times of thickness and per meter grouting volume of 34 2 m3 furthermore the guidelines for composite materials selection are proposed for the various flowing water environments moreover the space positions and water quality of the inspection boreholes and the original water richness of the ground should be taken into consideration in the grouting evaluation criteria the optimized grouting parameters materials selection and evaluation criteria provide important references for disasters prevention in similar projects

improved compound support system for coal mine tunnels in densely faulted zones a case study of china s huainan coal field abstract when tunnelling in densely faulted zones of coal mines serious deformation often occurs due to adverse geological conditions such as extremely broken and weak rock mass high tectonic stress fissure water to investigate a more efficient support strategy for tunnels passing through densely faulted zones a tunnel in china s huainan mining area is taken as an experimental site to study an improved support method some key factors associated with the stability of tunnels in the densely faulted zone are analysed based on the analysis of failure characteristics of a previously excavated tunnel a detailed procedure for the improved support method is proposed in which a long pipe pre grouting method together with a new kind of grouting cable are applied finally the improved support strategy is implemented in the experimental tunnel the monitoring results suggest that serious deformation is avoided and the improved compound support method is feasible for tunnels in densely faulted zones

lithiotis bivalvia bioherms in the lower jurassic of east central oregon u s a abstract the epifaunal rudist like bivalve lithiotis formed extensive bioherms during the pliensbachian and toarcian ages of the early jurassic the best developed bioherms in north america occur in the pliensbachian robertson formation of east central oregon a unit deposited in a shallow sea transgressing across the suplee shelf a typical bioherm consists of three biofacies that coexisted laterally and replaced each other vertically the reef flank assemblage is the most diverse consisting of nerinea gastropods terebratulid brachiopods and lithiotis debris in a calcarenite or calcilutite matrix the death assemblage consists of tightly packed current aligned lithiotis valves with gastropods and brachiopods much reduced in numbers the core of the reef is built almost exclusively of in situ lithiotis forming a bafflestone with a calcilutite matrix lithiotis inhabited a stressful environment inimical to most invertebrates since diversity is very low and there is no evidence of bioerosion during the pliensbachian lithiotis formed an endemic centre encompassing western north america and the tethyan ocean linked through central america and the central atlantic by the hispanic corridor by the close of the pliensbachian it had disappeared from north america but in the toarcian made its first appearance in south america by the end of the toarcian lithiotis was extinct

the smooth brachiopods of the mediterranean jurassic refugees or invaders the jurassic brachiopod fauna of the alpine mediterranean region is dominated by smooth rhynchonellids and spiriferinids and sulcate or perforate terebratulids in contrast to the typical coarsely ribbed brachiopods of the contemporaneous european and african epicontinental areas the best studied example of the mediterranean brachiopod province is the pliensbachian fauna of the bakony mountains hungary there the five most abundant genera are all smooth linguithyris securithyris apringia bakonyithyris pisirhynchia these smooth genera represent different morphological types sulcate axiniform uniplicate phylogenetically related forms are known from several evolutionary lineages of discontinuous record ranging from the triassic to the recent the triassic jurassic and the neogene recent parts of these evolutionary lineages are represented by several genera while in the late cretaceous paleogene interval they seemingly disappear at least they have no record the recent relatives of the above pliensbachian genera live mostly in the deep sea three are shallow bathyal 200 400 m three deep bathyal 800 1200 m and three abyssal 2000 4500 m the abyssal genera occur mainly in the east pacific the geographical distribution of the bathyal genera shows peculiar features they are more or less confined to the western sides of the great ocean basins west pacific west indian ocean caribbean region and they are thalassobathyal i e they are living on submarine plateaus seamounts or island aprons and not on the continental slopes this pattern extrapolated to the past shows good analogy with the jurassic palaeogeographical model developed for the western part of the tethys ocean it is hypothesized that smooth mainly sulcate articulate brachiopods flourished in the bathyal or even abyssal zones during the palaeozoic they were not refugees but formed well adapted communities this stable conservative fauna may have survived the crises manifested in the shelf seas and in cases of appropriate palaeogeographical situations may have implanted its descendants to the shallow bathyal or even sublittoral regions of the western margins of the ocean basins the mediterranean microcontinent system at the western part of the jurassic tethys might have been such an invaded region correlation between plate tectonic changes of ocean continent configurations the presence of ocean basins closed on the west and the occurrence of smooth articulate brachiopod groups in shallow bathyal to sublittoral settings collectively suggest that the deep water forms invaded the shallow environments of the western tethys in early mesozoic times and the w pacific and w indian oceans in the neogene they stayed in the deep sea reservoir when a circum equatorial ocean existed in the late mesozoic

rb sr isotopic age s pb sr isotopic compositions and genesis of the ca 200 ma yunluheba pb zn deposit in nw guizhou province sw china abstract over 400 carbonate hosted pb zn deposits in the western yangtze block constitute the giant sichuan yunnan guizhou syg pb zn metallogenic province the majority of pb zn deposits hosted in devonian carbonates are characterized by low 34s values causing debates on their ore genesis to address this issue the yunluheba pb zn deposit is chosen as a case study ore bodies of this deposit are hosted in middle devonian carbonates ore minerals are sphalerite galena and pyrite sphalerite rb sr dating yields an isochron age of 206 2 4 9 ma consistent with ages of most pb zn deposits in the syg province arguing for a regional intensive pb zn mineralization event during the late indosinian orogeny sulfides have pb isotopic compositions that form a linear trend above the average crustal pb growth curve in the 207pb 204pb vs 206pb 204pb plot moreover pb isotopic ratios are consistent with the devonian to permian carbonates age corrected pb isotopic ratios suggesting mixed crustal pb sources with the majority of pb derived from country rocks combined with initial 87sr 86sr ratios of sphalerite approximately equal to 87sr 86sr200ma ratios of the d p carbonates ore forming metals are considered to have been derived mainly from ore hosting rocks sulfides 34scdt values range mainly from 2 0 to 2 9 interpreted to be a result of mixing by syn sedimentary pyrite originated biogenic s and thermochemically reduced s we conclude that the yunluheba deposit and other pb zn deposits in the syg province should belong to mississippi valley type deposits

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

characteristics of dewatering induced drawdown curve under blocking effect of retaining wall in aquifer summary for deep excavation pits that require the pumping of confined groundwater a combination of a retaining wall and dewatering with large diameter wells is usually adopted during excavation to improve safety since a retaining wall has a much lower hydraulic conductivity than the surrounding material in the aquifer blocking of seepage to prolong the seepage path of the groundwater outside of the pit is effective the retaining walls used during excavation dewatering cause hydraulic head drawdown inside the pit much faster than outside the pit thus difference in hydraulic head between inside and outside of the pit increases to investigate the mechanism of the blocking effect numerical simulation using the finite difference method fdm was conducted to analyze the effects of pumping in the pit the fdm results show that drawdown varies along the depth of the confined aquifer the influence factors of drawdown inside and outside the pit include insertion depth of retaining walls anisotropy of a confined aquifer and screen length of pumping wells in addition fdm results also show that the drawdown time curve can be divided into four stages in stage i drawdown inside the pit is very small and outside the pit it is almost zero in stage ii drawdown increases quickly with time in stage iii the drawdown curve is parallel to the cooper jacob curve on semi log axes and in stage iv the drawdown becomes constant these characteristics of the drawdown curve under the blocking effect of a retaining wall in an aquifer provide a way of estimating hydrogeological parameters according to pumping test results

sedimentary organic matter and early toarcian environmental changes in the lusitanian basin portugal abstract the objective of this study is to investigate the relationship between early toarcian climatic events and the composition of kerogen assemblages in the lusitanian basin portugal in particular we aim to understand how the pliensbachian toarcian event pl toa event and toarcian oceanic anoxic event toae affected the continental areas of the western iberian margin and how possible variations in continental sources of organic matter om were expressed in marginal marine and hemipelagic depositional environments during the early toarcian we present here a characterisation total organic carbon toc total sulphur ts 13c in kerogen concentrate 13ckerogen and palynofacies of kerogen assemblages from several uppermost pliensbachian emaciatum ammonite zone lower toarcian sections in the lusitanian basin western iberian margin including the peniche section which contains the toarcian gssp in all sections toc concentration is low average 0 4 wt with the highest values reaching up to 2 1 wt in a discrete level located approximately 10 5 m above the base of the levisoni zone at peniche the toae negative carbon isotope excursion is observed in kerogen concentrate at the base of the levisoni zone throughout the basin palynofacies analysis demonstrates that the kerogen assemblages are mostly of terrestrial affinity with the dominance of the phytoclast group and terrestrial palynomorphs and with punctual increases in amorphous organic matter freshwater e g botryococcus sp and marine microplankton dinoflagellate cysts acritarchs and prasinophyte algae in specific stratigraphic intervals a change in palynofacies assemblages associated with the toae is observed around the base of levisoni zone although with slight differences between sections the toae interval records an increase in non opaque translucent phytoclasts nop and cuticle fragments and is also associated with an increased contribution of terrestrial palynomorphs increase in sporomorphs and classopollis in tetrads and agglomerates and decrease in marine palynomorphs the increases in nop and terrestrial palynomorphs support the postulated enhancement of the hydrological cycle and increased export of terrestrial om into marine environments during the early toarcian especially during the toae in the western iberian margin understanding the impact of the early toarcian climatic events on land based ecosystems may provide important insights into current climate change

resolving mantle and crustal contributions to ancient hydrothermal fluids hear isotopes in fluid inclusions from dae hwa wmo mineralisation south korea abstract helium and argon isotopes from fluid inclusions in individual colour zones b c d and e of a large scheelite crystal from the 88 ma dae hwa w mo deposit south korea trace the source and history of the ore fluids a gradual decrease of the fluid 3 he 4 he 3 he 36 ar and 40 ar 36 ar from the core to the edge of the scheelite reflects the progressive dilution of a magmatic fluid by meteoric water and is consistent with the previously observed decrease of 18oh2o and fluid inclusion homogenisation temperatures th shelton et al 1987 the covariation of fluid inclusion he ar isotope systematics with 18o and th defines a magmatic component with 3 he 4 he 1 2 10 6 3 he 36 ar 0 01 and 40 ar 36 ar 1000 anomalously high helium and argon isotope ratios in zone d fluids represents undiluted magmatic noble gases this may reflect local variation in the magmatic gas flux or gas loss due to boiling of the hydrothermal fluids prior to mixing with magmatic gas helium and argon isotope systematics constrain mantle and crustal components in the hydrothermal fluids 40 ar 3 he 4 5 104 are close to the mid ocean ridge basalt value implying that 40ar is mantle in origin radiogenic isotope ratios of the mantle endmember 40 ar 4 he 0 69 0 06 are similar to contemporary geothermal fluids the coincidence of mantle derived he and ar in the fluids is strong evidence that mantle melting during late cretaceous subduction triggered the crystal melting responsible for granite formation 40 ar 4 he of the meteoric fluid 0 007 0 001 is far lower than the crystal production ratio 0 2 implying an origin in crust below 200 c

the world class jinding zn pb deposit ore formation in an evaporite dome lanping basin yunnan china the jinding zn pb sediment hosted deposit in western yunnan china is the fourth largest zn deposit in asia based on field observations of the ore textures breccias and the sandstone host rocks the ores formed in a dome that was created by the diapiric migration of evaporites in the lanping basin during paleogene deformation and thrust loading most of the ore occurs in sandstones that are interpreted to be a former evaporite glacier containing a melange of extruded diapiric material including breccias fluidized sand and evaporites that mixed with sediment from a fluvial sandstone system a pre ore hydrocarbon and reduced sulfur reservoir formed in the evaporite glacier that became the chemical sink for zn and pb in a crustal derived metalliferous fluid in stark contrast to previous models the jinding deposit does not define a unique class of ore deposits rather it should be classified as mvt sub type hosted in a diapiric environment given that jinding is a world class ore body this new interpretation elevates the exploration potential for zn pb deposit in other diapir regions in the world

globally enhanced mercury deposition during the end pliensbachian extinction and toarcian oae a link to the karoo ferrar large igneous province the mesozoic era featured emplacement of a number of large igneous provinces lips formed by the outpouring of millions of cubic kilometres of basaltic magma the radiometric ages of several mesozoic lips coincide with the dates of oceanic anoxic events oaes as a result of these coincidences a causal link has been suggested but never conclusively proven this study explores the use of mercury as a possible direct link between the karoo ferrar lip and the coeval toarcian oae t oae mercury is emitted to the atmosphere as a trace constituent of volcanic gas and may be distributed globally before being deposited in sediments modern marine deposits show a strong linear correlation between mercury and organic matter content results presented here indicate departures from such a simple linear relationship in sediments deposited during the t oae and also during the pliensbachian toarcian transition an event that saw elevated benthic extinctions and carbon cycle perturbations prior to the t oae a number of depositional settings illustrate an increased mercury concentration in sediments that record one or both events suggesting a rise in the depositional flux of this element complications to this relationship may arise from very organic rich sediments potentially overprinting any hg toc signal whereas environments preserving negligible organic matter may leave no record of mercury deposition however the global distribution of coevally elevated hg rich levels suggests enhanced atmospheric mercury availability during the early toarcian potentially aided by the apparent affinity of hg for terrestrial organic matter although the relative importance of aquatic vs terrestrial fixation of hg in governing these enrichments remains uncertain a perturbation in atmospheric hg is most easily explained by enhanced volcanic output it is suggested that extrusive igneous activity caused increased mercury flux to the early toarcian sedimentary realm supporting the potential of this element as a proxy for ancient volcanism this interpretation is consistent with a relationship between lip formation and a perturbed carbon cycle during the pliensbachian toarcian transition and t oae the recording of these two distinct hg excursions may also indicate that the karoo ferrar lip released volatiles in temporally distinct episodes due either to multiple phases of magmatic emplacement or sporadic release of thermogenic gaseous products from intrusion of igneous material into volatile rich lithologies

the early toarcian early jurassic ostracod extinction events in the iberian range the effect of temperature changes and prolonged exposure to low dissolved oxygen concentrations abstract the early toarcian extinction event once regarded as spanning in the late pliensbachian early toarcian boundary period actually occurred in two distinct phases in the early toarcian of the iberian range the first episode occurred in the mirabile subzone tenuicostatum zone and is characterised by the disappearance of about 12 of ostracod species and one suborder the metacopina superfamily healdioidea this study shows that this suborder disappears during stratigraphical intervals that are considered to be representative of low oxygen conditions in the iberian range the collapse of marine ecosystems affecting up to 40 of ostracod species in the elegantulum subzone serpentinum zone was most likely triggered by a sudden and widespread lethal increase in seawater temperature these combined processes of oxygenation and temperature change are considered to be responsible for the profound changes in marine environments that resulted in the early toarcian ostracod extinction in the iberian range

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

palaeogeography physiography palaeoenvironments and brachiopod communities example of the liassic brachiopods in the western tethys abstract within the western different and characteristic brachiopod communities as well as other benthic and necto benthic faunas have evolved in various palaeoenvironments resulting from the differentiation of a highly controlled submarine topography this physiography depends on palaeogeographical conditions which were induced by eustatic changes exaggerated or lessened by local tectonic movements the characteristics of brachiopod communities their location in the tectono sedimentary context the reconstruction of biotooe conditions from the study of sediments allow us to propose a pattern in which the relationships between the various characteristic brachiopod communities and the different palaeoenvironments are established these environmental settings include 1 inner carbonate platforms 2 protected carbonate ramps and mud flats 3 hinge zones between mud flats and basins 4 low energy outer platforms and gentle slopes 5 medium to high energy outer platforms 6 episodically waved and winnowed outer platforms and shoal borders 7 slopes transitional to basin 8 umbilicus and narrow troughs 9 epioceanic basins then according to this model the recognition and the distribution through time and space of these different brachiopod communities makes it possible to reconstruct the palaeogeographical evolution and to give a more accurate of the tectonic framework buried antithetic faults when the palaeogeographical evolution is mainly due to tilted blocks tectonic example of the portuguese lias

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation

terrane boundary and spatio temporal distribution of ore deposits in the sanjiang tethyan orogen insights from zircon hf isotopic mapping abstract the sanjiang tethyan orogen sjto of the eastern tethyan tectonic belt in china records a transition from late paleozoic tethys realm to cenozoic continental collision associated with the formation of large metallic mineral deposits this contribution combines geological and hf isotopic data for igneous rocks from the sjto together with the salient features associated with mineralization to gain insights into the crustal architecture and metallogeny integrating the available information from tectonic events sedimentary successions paleobiogeography and paleolatitude based on paleomagnetic data the hf isotopic maps that we construct highlight the changning menglian suture as an important tectonic boundary between the gondwana and cathaysian continents the changning menglian suture separates two distinct hf isotopic domains with an old reworked crustal block to the southwestern part of the sjto and a juvenile crustal block with significant mantle derived components to the northeastern part of the orogen the hf isotopic mapping of the sjto also provides important indications on the location of different deposits the jinshajiang ailaoshan suture appears to have exerted a first order control on the localisation of cenozoic magmatism and intrusion related mineral systems the magmatic source for intrusions in the eastern high ehf low tdmc domain is dominated by mantle components and gave rise to porphyry and porphyry skarn cu mo mineralization in contrast the magma sources for intrusions in the low ehf high tdmc domains contain an old and reworked crustal component and gave rise to granite related sn w mineralization those for the intrusions characterized by variable ehf and tdmc are dominantly reworked older crustal components together with subordinate juvenile material which generated the granite related pb zn cu ag mineralization