origin of the breno and esino dolomites in the western southern alps italy implications for a volcanic influence the esino limestone of the western southern alps represents a differentiated ladinian lower carnian carbonate platform comprised of margin slope and peritidal inner platform facies up to 1000 m thick a major regional subaerial exposure event lead to coverage by another peritidal lower carnian carbonate platform breno formation multiphase dolomitization affected the carbonate sediments petrographic examinations identified at least three main generations of dolomites d1 d2 and d3 that occur as both replacement and fracture filling cements these phases have crystal size ranges of 3 35 m dolomicrite d1 40 600 m eu to subhedral crystals d2 and 200 m to 5 mm cavity and fracture filling anhedral to subhedral saddle dolomite d3 respectively the fabric retentive near micritic grain size coupled with low mean sr concentration 76 37 ppm and estimated 18o of the parent dolomitizing fluids of d1 suggest formation in shallow burial setting at temperature 45 50 c with possible contributions from volcanic related fluids basinal fluids circulated in volcaniclastics or related to volcanic activity which is consistent with its abnormally high fe 4438 4393 ppm and mn 1219 1418 ppm contents the larger crystal sizes homogenization temperatures d2 108 9 c d3 111 14 c of primary two phase fluid inclusions and calculated salinity estimates d2 23 2 eq wt nacl d3 20 4 eq wt nacl of d2 and d3 suggest that they formed at later stages under mid to deeper burial settings at higher temperatures from dolomitizing fluids of higher salinity which is supported by higher estimated 18o values of their parent dolomitizing fluids this is also consistent with their high fe 4462 4888 ppm and 1091 1183 ppm respectively and mn 556 289 ppm and 1091 1183 ppm contents and low sr concentrations 53 31 ppm and 57 24 ppm respectively the similarity in shale normalized sn ree patterns and ce ce ce sn and la pr pr sn anomalies of the investigated carbonates support the genetic relationship between the dolomite generations and their calcite precursor positive eu anomalies coupled with fluid inclusion gas ratios n2 ar co2 ch4 ar he high f concentration high f cl and high cl br molar ratios suggest an origin from diagenetic fluids circulated through volcanic rocks which is consistent with the co occurrence of volcaniclastic lenses in the investigated sequence

traces of carnian volcanic activity in the transdanubian range hungary the south alpine dinaridic realm was affected by igneous activity in the middle triassic the marine carbonate platforms and the adjacent basins contain highly variable intrusive volcanic assemblages we studied the petrography and determined the zircon u pb ages of the triassic volcanic products in the transdanubian range the geochemical features and thus the geodynamic context of the magmatism are badly known as the rocks experienced variable chemical alteration the exact duration of the igneous activity is also poorly constrained as the geochronological data of the former studies were obtained mostly by the weathering sensitive k ar and rb sr methods and thus some data even being younger than the age of the stratigraphic cover the presence of andesite dikes and of pebbles and cobbles 20 cm of basalt andesite rhyolite and of rhyolitic tuff in the triassic carbonate platform deposits indicates that within the transdanubian range formed a volcanic complex in triassic the major mineralogical and geochemical features of the transdanubian igneous suite are similar to the triassic formations in the southern alps however dissimilar zircon composition excludes the immediate relationship of the zircon bearing silicic formations in the two tectonic units new u pb ages show that the beginning of the volcanic activity is probably coeval with the eruption of the widespread pietra verde trachytic tuffs in the upper anisian ladinian successions but the majority of the ages are younger than those ash layers the new age constraints give a bench mark for the termination of the volcanic activity in carnian time in the transdanubian range

some constraints on geochemical features in the triassic mantle of the easternmost austroalpine southalpine domain evidence from the karawanken pluton carinthia austria

the major features of the crustal structure in north eastern venezuela from deep wide angle seismic observations and gravity modelling abstract venezuela is located on the plate boundary zone between the south american continent and the caribbean plate a relative movement of 2 cm year is accommodated by a system of strike slip faults running from the andes to the gulf of paria the interior range a moderate height mountain range separates the oriental basin from the caribbean to the south predominantly precambrian rocks are outcropping in the guayana shield south of the orinoco river results of deep wide angle seismic measurements for the region were obtained during field campaigns in 1998 ecoguay for the guayana shield and in 2001 ecco for the oriental basin the total crustal thickness decreases from 45 km beneath the guayana shield to 39 km at the orinoco river and 36 km close to el tigre in the center of the oriental basin the average crustal velocity decreases in the same sense from 6 5 to 5 95 km s detailed information was obtained on the velocity distribution within the oriental basin velocities are as low as 2 2 km s for the uppermost 2 km 4 5 km s down to 4 km in depth and a maximum depth of 13 km was derived for material with seismic velocities up to 5 9 km s interpreted as the base of the sedimentary basin a gravimetric model confirms the structures derived from the seismic data discrete increases in sedimentary thickness along the basin may be associated to extension processes during the passive margin phase in the cretaceous or during earlier extension phases

post granulite facies monazite growth and rejuvenation during permian to lower jurassic thermal and fluid events in the ivrea zone southern alps u pb analyses of single monazite grains from two granulite facies metapelites in the ivrea zone southern alps reveal the presence in both samples of at least three different ages and prove that earlier interpretations of supposedly concordant monazite data as cooling ages are unwarranted one group of monazite data defines a subconcordant discordia line with an upper intercept age of 293 4 5 8 ma and a lower intercept age of 210 14 ma the upper intercept is interpreted as the real cooling age of the monazites the lower intercept is interpreted as an episode of fluid driven pb loss indicated by the presence of internal and external corrosion structures not only of the monazites but also of the zircons in the same samples that are also rejuvenated at 210 12 ma another group of monazite data lies above the concordia the presence of excess 206pb indicates that these crystals have grown below the monazite blocking temperature thus after the granulite facies metamorphism the age of growth of the new monazite crystals is approached by their 207pb 235u ages that range between 273 and 244 ma the two groups of post cooling age post 293 4 5 8 ma monazite data correspond to two distinct late and post variscan geotectonic regimes that affected the southern alps 1 permian transtension with decompression and anatectic melting 2 upper triassic to lower jurassic rifting with geographically dispersed hydrothermal activity and alkaline magmatism

triassic latemar cycle tops subaerial exposure of platform carbonates under tropical arid climate the triassic latemar platform in the dolomites italy is the site of several ongoing controversies perhaps the most interesting debate focuses on apparent cyclic deposition within the latemar platform whose nature and duration are still open to debate further disagreement concerns the lack of meteoric diagenesis related isotope shifts at cycle tops that bear circumstantial petrographic evidence for subaerial emergence here an evaluation of the nature of latemar cycle tops is presented combining evidence from previous work and new field petrographic and geochemical data cycle tops are ranked according to increasing exposure duration and spatial extent type i surfaces lacking unequivocal evidence of prolonged supratidal conditions type ii dolomite caps formed in warm evaporitic intertidal lagoonal waters followed by exposure of perhaps intermediate duration type iii clastic rich red calcareous horizons with some showing platform wide extent representing prolonged supratidal conditions and type iv discontinuities in tepee belts genetically related to type ii and iii surfaces but likely representing shorter lived exposure stages petrographic and geochemical criteria indicate that most diagenesis occurred in the shallow marine and burial domain whilst an extensive meteoric overprint of cycle tops is lacking this is underlined by the scarcity of meteoric diagenetic fabrics such as gravitational cements that where present are here interpreted as marine vadose in origin the scarcity of carbon and oxygen isotope signatures commonly assigned to subaerial exposure stages is best explained in the context of mid triassic climate the low latitude tropical but arid setting of the latemar situated in the western extension of the tethys ocean its isolation from nearby continental areas and overall short term emergence episodes are in agreement with a limited degree of meteoric alteration of most cycle tops high amounts of aeolian clastic material beneath some cycle tops along with high fe and mn elemental abundances argue for intermittent subaerial conditions this study proposes an enhancement of the classical allan and matthews 1982 isotope model for subaerial exposure under strongly arid climates as the subaerial exposure nature of latemar cycle tops and therefore eustasy as the cause for cyclicity have been previously challenged due to the lack of meteoric induced isotopic signatures the outcome of this study is of significance for the ongoing latemar stratigraphic controversy

mg ca sr ca and u ca ratios of a porites coral from sanya bay hainan island south china sea and their relationships to sea surface temperature high resolution mg ca sr ca and u ca ratios are reported in the skeleton of porites sp collected from sanya bay on the south coast of the hainan island china using inductively coupled plasma mass spectrometry combined with isotope dilution technique icp ms id the coralline mg ca ratios covary with sea surface temperatures sst for the 10 year interval giving the relationship between mg ca and sst as t degrees c 14 13 0 31 8 846 0 068 x 10 3 mg ca with the mean square weighted deviation mswd of 9 7 using this equation we are able to reconstruct sst record with a precision better than 0 5 degrees c several sr ca and u ca ratios show poor linear relationships with the measured sst this study indicates that the growth rates of the coral do not significantly affect coralline mg ca sr ca and u ca ratios however the high meteoric precipitation in this area which may cause a heavy run off from the island may change seawater sr ca and u ca ratios and ruin the relationships between coralline sr ca or u ca ratios and sst this implies that in coastal areas like hainan coralline mg ca ratios are valid for reconstructing the sst records but sr ca and u ca ratios may be suspected c 2000 elsevier science b v all rights reserved

differential dissolution of a pleistocene reef in the ground water mixing zone of coastal yucatan mexico a geochemical explanation is provided for the extensive dissolution observed along the carbonate coast of the yucatan peninsula mexico mixing of fresh ground water with subterranean caribbean seawater generates a highly reactive geochemical zone that enhances aragonite and calcite dissolution and permits neomorphism of aragonite mixing zone dissolution caused by ground water discharge is a major geomorphic process in developing caves coves and crescent shaped beaches along the yucatan coast such dissolution has probably been a significant control on permeability and porosity distribution in carbonate rocks in the geologic record

the sandstone memory of the evolution of a triassic volcanic arc in the southern alps italy the erosion of a southern volcanic belt provided the bulk of the fine grained and moderately sorted siliciclastic detritus in the whole deltaic to lagoonal carnian upper triassic sequence of the bergamasc alps volcanic input began in the early carnian calcare metallifero bergamasco and became prominent in early middle val sabbia sandstone and late carnian times s giovanni bianco fm after an intervening period of diminished supply gorno fm the mineralogical and chemical composition of the sandstones compares closely with that of siliciclastics derived from modern pacific type magmatic arcs and it testifies to an evolution of the source rocks from andesites and dacites during the deposition of the val sabbia sandstone towards rhyodacitic ignimbrites for the s giovanni bianco fm the marked reduction in feldspars at the top of the sequence contrasts with the classical trend from undissected to dissected magmatic arc provenance and is ascribed to the progressive deepening of erosion into middle triassic felsic volcanics an increase in undulatory and polycrystalline quartz grains in the late carnian shows that the erosion did reach deeper into the crystalline roots of the arc although non volcanic detritus never exceeded 10 after a terminal pyroclastic event in middle late carnian times suggested by the sudden appearance of pumiceous vitric clasts at the top of the val sabbia sandstone the mid triassic orogenic magmatism ended and was followed by the tensional stage which led to the birth of neotethys

pre alpine and alpine evolution of the south alpine basement of the orobic alps new k ar age determinations on the gneisses and schists of the south alpine basement of the orobic alps and their separated minerals have been carried out to supplement and support the previous study ofbocchio et al 1981

high fluxes of radium and barium from the mouth of the ganges brahmaputra river during low river discharge suggest a large groundwater source the annual flux of sediment from the ganges brahmaputra river is among the highest in the world the desorption of226ra and ba from this sediment produces a major point source of226ra and ba input to the ocean highest226ra and ba fluxes are expected to occur during high river flow june september when most of the sediment is discharged surprisingly during low discharge of the ganges brahmaputra river fluxes of226ra and ba to the northern bay of bengal are comparable to expected river derived fluxes during peak river discharge a large non riverine source of ra and ba is required to explain the high fluxes during low river discharge i suggest that this source is submarine discharge of groundwater containing high concentrations of226ra and ba total annual fluxes of226ra and ba to the ocean from this system are significantly greater than estimated previously

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

syntectonic sedimentation in a middle triassic rift northern apennines italy abstract the anatomy of the sedimentary and volcanic fill of a middle triassic continental rift at the western margin of the tethys is illustrated by the study of a 250 m thick sequence on the tyrrhenian coasts of the northern apennines this sequence contains two cycles of sedimentation 1 a the lower cycle comprises a basal transgressive sequence from continental alluvial fans to shallow marine carbonates and an upper sequence which correspond to an increasing tectonic activity submarine syntectonic facies assemblage the lower part of the last assemblage is characterized by a thick 22 m rapidly deposited sequence of coarse carbonate breccias with minor calcareous sandy turbidites this is overlain by channelized red beds of submarine fans composed of close interstratification and juxtaposition of carbonate breccias with red clastic matrix and red sandy quartz pebble conglomerates and silty sands interbedded alkaline pillow lava record penecontemporaneous submarine eruptions the lavas are capped by thin red cherty diaspri crusts the lower cycle of sedimentation ends with a karstic surface on relatively deep marine carbonate layers this suggests a rapid emersion due to the arrest and reversal of the downsinking of the initial aborted or failed rift 2 b the upper cycle of sedimentation starts with more mature fluvial red beds and changes upward into shallow marine sands and carbonates this upper cycle represents an early stage of evolution of a new major rift this second major rift led in jurassic times to the opening of an oceanic area between europe and western italy

using multiple geochemical tracers to characterize the hydrogeology of the submarine spring off crescent beach florida abstract a spectacular submarine spring is located about 4 km east of crescent beach fl in the atlantic ocean the single vent feature of crescent beach spring provides a unique opportunity to examine onshore offshore hydrogeologic processes as well as point source submarine ground water discharge the floridan aquifer system in northeastern florida consists of tertiary interspersed limestone and dolomite strata impermeable beds confine the water bearing zones under artesian pressure miocene and younger confining strata have been eroded away at the vent feature enabling direct hydrologic communication of eocene ground water with coastal bottom waters the spring water had a salinity of 6 02 which was immediately diluted by ambient seawater during advection mixing the concentration of major solutes in spring water and onshore well waters confirm a generalized easterly flow direction of artesian ground water nutrient concentrations were generally low in the reducing vent samples and the majority of the total nitrogen species existed as nh 3 the submarine ground water tracers rn 222 1174 dpm l 1 dpm methane 232 nm and barium 294 5 nm were all highly enriched in the spring water relative to ambient seawater the concentrations of the reverse redox elements u v and mo were expectedly low in the submarine waters the strontium isotope ratio of the vent water 87 sr 86 sr 0 70798 suggests that the spring water contain an integrated signature indicative of floridan aquifer system ground water additional sr isotopic ratios from a series of surficial and lower floridan well samples suggest dynamic ground water mixing and do not provide clear evidence for a single hydrogeologic water source at the spring vent in this karst dominated aquifer such energetic mixing at the vent feature is expected and would be facilitated by conduit and fractured flow radium isotope activities were utilized to estimate flow path trajectories and to provide information on potential travel times between an onshore well and the spring using either 223 ra and 224 ra or 228 ra and qualifying this approach with several key assumptions estimates of water mass travel times from an upper floridan well in crescent beach to the submarine vent feature distance 4050 m are in the order of 0 01 0 1 m min 1

shrimp u pb zircon triassic intrusion age of the finero mafic complex ivrea verbano zone western alps and its geodynamic implications interstitial subhedral slightly pink zircons have been separated from a diorite of the external gabbro unit of the finero mafic complex which crops out in the northernmost tip of the ivrea verbano zone ivz southern alps they are characterized by oscillatory zoning under cathodoluminescence cl a highth u ratio 0 9 0 4 and associated high u th pb rare earth element ree ta nb li and p contents consistent with a magmatic origin the mean of the single concordant ages is 232 3 ma which is here proposed to constrain the timing of intrusion of the finero mafic complex most of these magmatic zircons exhibit an outer rim up to 50 mm thick with a bright emission with transgressive and or sub concordant contacts to the internal oscillatory zoned domains in which the th u ratio is decreased as are the u th pb ree ta and nb contents these rims give younger slightly discordant pb u ages between 219 3 ma and 205 3 ma which are interpreted to highlight a fluid assisted recrystallization event the gabbros also have an interstitial zircon population consisting of rounded small colourless bright to milky crystals with blurred zoning patterns in cl these zircons have low u th pb nb and ta contents and lowth u ratio down to 0 08 the overall metamorphic character together with field evidence of the presence of blocks of paragneiss belonging to the crystalline basement at the roof of the external gabbro unit indicates that these zircons are inherited from local crustal rocks they have u and pb isotopic compositions that are strongly altered and discordant showing an upper limit of the timing of recrystallization consistent with the middletriassic emplacement age obtained from the magmatic zircons it is concluded that the finero mafic complex can no longer be considered as a part of the huge permian mafic complex of the central ivz it follows that the intrusive record preserved in the ivz allows us to look at the interplay between the continental crust and mantle melts through time i e permian totriassic in this scenario the modest crustal assimilation shown by the finero mafic complex can be interpreted in the first instance as the consequence of the limited volume of intruded melt less than 2 km in thickness however the possible role played by the decreased fertility of the metamorphic country rocks owing to a inferred permian magmatic event must be better constrained the intrusion of the finero mafic complex may represent the deep crustal counterparts of the ladinian volcanism that is widespread throughout the southern alps the geodynamic

post variscan verrucano like deposits in italy and the onset of the alpine tectono sedimentary cycle abstract in the italian regions the stratigraphic successions of the verrucano s l consist essentially of continental alluvial plain to coastal neritic siliciclastic redbeds deposited at different times in the alps mid late permian the northern apennines mid late triassic p p locally in southern tuscany also followed by the jurassic pseudoverrucano complex and the calabro peloritani arc mid late triassic exceptionally reaching earliest jurassic whereas in sardinia the recognition of the verrucano succession is still a topic of discussion the most typical metamorphic lithofacies in the pisan mts of tuscany is represented by the verrucano s s conglomerates and breccias including quartz clasts and minor metamorphic and volcanic lithics grading laterally and vertically to quartzitic sandstones and pelites in the pisa symposium the term verrucano was suggested only for those detrital deposits laid down in the alpine mediterranean areas after the final act of the variscan orogeny and also to use local geographical names consequently the typical terms verrucano toscano the verrucano lombardo the verrucano brianconnais and other similar deposits being linked to the variscan belt were generally accepted the ages of these verrucanos since they are devoid of fossils can only be interpreted indirectly the verrucano lombardo of central southern alps was recently ascribed to a mid late permian interval late guadalupian lopingian p p taking into account that the connected val gardena sandstones of the nearby venetian region are interdigitated with the late permian bellerophon fm the verrucano brianconnais of the maritime alps is again mostly related to late permian being covered by the lower triassic alluvial deltaic quartzites in the easternmost ligurian apennines near la spezia the mesozoic section of punta bianca which begins with a fluvial conglomerate transgressive and unconformable on a metamorphosed paleozoic variscan basement is composed of two main cycles of which the upper one correlates to the typical pisan verrucano s s and the overlying mt serra quartzites the latter yielding carnian pelecypods and vertebrate footprints the verrucano from the mid tuscan ridge to mt leoni and in the argentario promontory is delimited above by the tocchi formation and presumably developed from middle late ladinian up to late triassic carnian times in contrast in calabria e g the longobucco unit of sila grande and in sicily e g the taormina longi unit of peloritani mts the so called pseudo verrucano deposits pertain to mid late triassic and are capped by a basal jurassic succession determined by the discovery of an early hettangian palynoflora all over their distribution areas the above mentioned alpine verrucanos rest through an unconformity marked by a gap of varying and imprecise duration on late paleozoic volcanic sedimentary successions or directly on the underlying variscan metamorphic basement schematically the post variscan succession in italy can be subdivided into three main tectono sedimentary megacycles the first generally ranges from the late carboniferous to or slightly above the early permian the second from mid late permian to middle triassic while the third cycle begins with the mid late triassic p p attaining the jurassic in some parts of southern tuscany and the calabro peloritani arc after the late carboniferous and early permian transtensional tectonics represented by many strike slip continental basins cycle i widespread middle permian geodynamic reorganization mid permian episode auctt led to the development of a dominant extensional regime and the birth of tectonic plates and oceans neotethys meliata maliak etc between africa and europe the erosion of the variscan relief was followed by ingression from s e sectors of shallow marine branches of neotethys cycle ii the major rifting events that led to the jurassic birth of the ligurian piedmont ocean started during the middle late triassic and were related to the eastern opening of the atlantic ocean these rifting events gave rise to the development of the adria and europe corsica sardinia conjugate passive margins characterized by an asymmetric structural and sedimentary evolution in this geological context the verrucano like deposits of italy can be interpreted as a discontinuous and asynchronous tectofacies that marks the final dismantling of the se border of the variscan chain

non river flood barium signals in the skeletons of corals from coastal queensland australia abstract two corals from coastal queensland cow and calf islands and orpheus island have been analysed for a suite of trace elements by laser ablation icp ms la icp ms barium signals in these two corals are anomalous in comparison with ba behaviour seen in other near shore corals from this region the two corals display large sharp peaks in spring which do not correlate with markers of river discharge y ca and fluorescence this ba pattern contrasts with normal behaviour characterised here by the patterns previously published for two other coastal queensland corals king reef and pandora reef which display ba peaks in summer associated with flooding of nearby rivers 1 d j sinclair m t mcculloch corals record low mobile barium concentrations in the burdekin river during the 1974 flood evidence for limited ba supply to rivers palaeogeogr palaeoclimatol palaeoecol 214 1 2 2004 155 174 similarities are observed between the anomalous ba in the queensland corals and other published patterns of ba behaviour in corals from south africa and the arabian sea this non river flood ba behaviour is characterized by large sharp spikes of ba which are resistant to oxidative cleaning and form a continuous horizon within the coral curiously not all corals from a region display anomalous ba behaviour despite being in similar environments the timing of anomalous ba is consistent within a coral but may vary from one location to the next anomalous ba spikes are too large to be caused by ba rich upwelling and no single environmental forcing function seems to be able to account for their timing this combination of observations argues against an exogenous abiotic source for the anomalous ba signal instead it may result from a biological event triggered by a combination of environmental parameters three hypotheses are presented and critically tested against the observations barite inclusion following phytoplankton blooms decaying blooms of the blue green algae trichodesmium and physiological perturbations associated coral mass spawning none of the three hypotheses are fully consistent with all of the observations and it is concluded that no satisfactory explanation currently exists for the anomalous ba spikes

high temporal resolution mg ca and ba ca records in modern porites lobata corals 1 secondary ion mass spectrometry sims was used to determine mg ca and ba ca variations across two skeletal structures the fasciculi and the centers of calcification cocs in two porites lobata corals of different linear extension rates from oahu hawaii both corals exhibit large mg and ba heterogeneity which is not related to sea surface temperature sst or composition higher concentrations of ba occur in the fasciculi and higher mg in the cocs of the slowly extending coral compared to the fast growing coral mg and ba concentrations are significantly higher in the cocs of both corals compared to the fasciculi trace element variations may reflect changes in the calcifying fluid composition or changes in skeletal trace element incorporation regressions between mg ba and sr reported in a prior publication indicate that the skeletal incorporation of each element is affected by a different factor or combination of factors smoothed sims records of ba ca variations across the fasciculi of the fast growing coral follow the seasonal trend predicted from sst and expected seawater chemistry variations smoothed sims mg ca records do not correlate with sst indicating that sims mg ca records cannot be used to estimate past ssts

the middle triassic magmatic tectonic arc development in the southern alps abstract the geodynamic meaning of the middle triassic magmatic and tectonic events in the southern alps is still uncertain the main problem is the significance of the compressional tectonic structures recognized in the central dolomites in fact these structures are incompatible with the extensional geodynamic interpretation crustal rifting assumed by several authors therefore the compressional tectonic elements of the dolomites have been mostly ignored or not seriously taken into account or considered as local phenomena due to the volcanic tectonic interplay other more modern interpretations are founded on regional transcurrent and or transpressive tectonics recent discovery of a middle triassic thrust system located in the piave river area some tens of kilometres east of the central dolomites lends more credence to the compressional middle triassic event the magmatic series of volcanic and plutonic middle triassic rocks display an orogenic character with typical calc alkaline trends recognized across the whole southern alps as well as in the dinaric and hellenic domains such a character is rather uncommon in the crustal evolution by rifting but is more in accord with a compressional geodynamic setting furthermore the time space distribution of the south alpine magmatic rocks coupled with their petrochemical affinity are close to the modern volcanic arcs nevertheless the general geodynamic context of the southern alps owing to their pronounced ensialic character does not fit the oceanic model

determination of flow characteristics in the aquifer of the northwestern peninsula of yucatan mexico abstract flow characteristics were studied in the northwestern peninsula of yucatan mexico the yucatan aquifer is a mature karst system influenced by the ring of cenotes sinkholes this zone of aligned sinkholes is a high permeability zone with respect to its surroundings the aquifer is unconfined within the study area water level measurements at 48 locations were made in june and october 1994 they were measured up to four times in october water levels in a limited group of wells showed variations up to 60 during october 1994 whereas others had variations of the order of 5 in the same period by studying the resulting equipotential regimes a highly variable zone hvz was identified drain characteristics are significantly different from the rest of the study area which leads to the hypothesis that the hvz represents an independent subsystem of interconnected fractures to determine directions of high permeability within the study area azimuthal resistivity surveys were conducted at 22 locations resistivity curves particularly in the hvz show two or more peaks each indicating a direction of high permeability directions of high permeability are interpreted to be preferential directions of aligned fractures comparison with the two different equipotential regimes in october 1994 shows that in the majority of the cases the direction of the hydraulic gradient coincides with the direction of one fracture system the hydraulic gradient can be considered to be the major control in the dissolution process at least in the hvz resulting in the selective opening of the fractures peaks in the resistivity curves are of the same order of magnitude this shows that both regimes of equipotential lines and the corresponding changes of the hydraulic gradients are sufficiently frequent to be able to create different fracture systems with a comparable fracture density the variations of the equipotential regime in time may have severe consequences in terms of the risk of aquifer contamination in the highly variable zone contaminants generated mainly in the city of merida are generally believed to flow towards the north coast of the peninsula however reversals in the hydraulic gradient may allow contaminants to flow towards the southeast of the city at least for limited periods in the year

triassic volcanogenic sediments from the southern alps italy austria yugoslavia a contribution to the pietra verde problem abstract during the middle triassic anisian and ladinian volcanogenic sediments of silicic explosive volcanism have been deposited throughout the southern alps these sediments show an insignificant variation in mineralogical composition and contain various amounts of shards and pumice fragments individual deposits are 1 cm to 150 m thick and are interbedded between basinal or rare shallow water limestones sedimentary structures often clearly exhibit redeposition and primary settings neither in palaeogeography including basins and reefs nor in field evidence can we find an indication where eruption sites had been located scanning electron microscope sem studies of shards and pumice fragments elucidate primary textures and alteration processes alteration and or diagenesis caused the mobility of main elements so primary chemical composition is camouflaged sizes and shapes of shards and pumice fragments infer an alkali trachytic source for deposits of the eastern part of the southern alps

reconciling plate tectonic reconstructions of alpine tethys with the geological geophysical record of spreading and subduction in the alps article a new reconstruction of alpine tethys combines plate kinematic modelling with a wealth of geological data and seismic tomography to shed light on its evolution from sea floor spreading through subduction to collision in the alps unlike previous models which relate the fate of alpine tethys solely to relative motions of africa iberia and europe during opening of the atlantic our reconstruction additionally invokes independent microplates whose motions are constrained primarily by the geological record the motions of these microplates adria iberia alcapia alkapecia and tiszia relative to both africa and europe during late cretaceous to cenozoic time involved the subduction of remnant tethyan basins during the following three stages that are characterized by contrasting plate motions and driving forces 1 131 84 ma intra oceanic subduction of the ligurian part of alpine tethys attached to iberia coincided with eo alpine orogenesis in the alcapia microplate north of africa these events were triggered primarily by foundering of the older 170 131 ma neotethyan subduction slab along the ne margin of the composite african adriatic plate subduction was linked by a sinistral transform system to e w opening of the valais part of alpine tethys 2 84 35 ma subduction of primarily the piemont and valais parts of alpine tethys which were then attached to the european plate beneath the overriding african and later adriatic plates nw translation of adria with respect to africa was accommodated primarily by slow widening of the ionian sea 3 35 ma recent rollback subduction of the ligurian part of alpine tethys coincided with western alpine orogenesis and involved the formation of the gibraltar and calabrian arcs rapid subduction and arc formation were driven primarily by the pull of the gravitationally unstable retreating adriatic and african slabs during slow convergence of africa and europe the upper european iberian plate stretched to accommodate this slab retreat in a very mobile fashion while the continental core of the adriatic microplate acted as a rigid indenter within the alpine collisional zone the subducted lithosphere in this reconstruction can be correlated with slab material imaged by seismic tomography beneath the alps and apennines as well as beneath parts of the pannonian basin the adriatic sea the ligurian sea and the western mediterranean the predicted amount of subducted lithosphere exceeds the estimated volume of slab material residing at depth by some 10 30 indicating that parts of slabs may be superposed within the mantle transition zone and or that some of this subducted lithosphere became seismically transparent

a high resolution sr ca and δ18o coral record from the great barrier reef australia and the 1982 1983 el nino abstract a high resolution near weekly sr ca and oxygen isotopic record is presented for a coral from the pandora reef in the great barrier reef gbr of australia during the period 1978 to 1984 the records are well correlated except for periods of high rainfall when river runoff has significantly modified the 18o value of seawater using the sr ca temperature calibration of de villiers et al 1994 the sr ca records exhibit seasonally controlled cyclical sst sea surface temperature variations of from 21 to 28 c during the very strong el nino of 1982 1983 the sr ca systematics indicate a sharp drop in the winter sst to 18 5 c this represents a temperature anomaly of 3 c which is approximately twice that given by the 18o variations suggesting an 2 amplification of the anomaly by the sr ca system possibly due to the increasing dominance of inorganically controlled aragoniteseawater fractionation the oxygen isotopic systematics show the combined effects of both temperature and changing seawater 18o values the latter reflecting the influx of 18o depleted runoff during periods of high rainfall due to the extremely low 10 3 sr and ca contents of river run off relative to seawater it is possible to use the sr ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the 18o value of seawater using this approach it is possible to quantitatively reproduce the volume of runoff from the burdekin river during the periods of major flooding that occurred in early 1979 and 1981 the results of this study demonstrate that the combined use of high resolution sr ca and 18o systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate

siderite deposits in northern italy early permian to early triassic hydrothermalism in the southern alps abstract we present a minero petrographic geochemical and geochronological study of siderite orebodies from different localities of the southern alps northern italy siderite occurs as veins cutting the variscan basement and the overlying lower permian volcano sedimentary cover collio fm and as both veins and conformable stratabound orebodies in the upper permian verrucano lombardo and bellerophon fms and lower triassic servino and werfen fms sedimentary sequences of the lombardian and the venetian alps all types of deposits show similar major and rare earth ree element patterns suggesting a common iron mineralizing event the compositions of coexisting siderite fe rich dolomite and calcite suggest formation from hydrothermal fluids at relatively high temperature conditions 250 c geochemical modelling supported by ree analyses and by literature and new 1 3 c and 18 o isotopic data suggests that fluids responsible for the formation of siderite in the variscan basement and in the overlying lower permian cover were derived from dominant fresh water which leached fe and c from volcanic rocks mainly rhyolites rhyodacites and organic carbon bearing continental sediments on the basis of u th pb microchemical dating of uraninite associated with siderite in the val vedello and novazza deposits lombardian alps the onset of hydrothermalism is constrained to 275 13 ma early mid permian i e it was virtually contemporaneous to the plutonism and the volcanic sedimentary cycle reported in the same area orobic basin the youngest iron mineralizing event is represented by siderite veins and conformable orebodies hosted in lower triassic shallow marine carbonatic successions in this case the siderite forming fluids contained a seawater component interacted with the underlying permian successions and eventually replaced the marine carbonates at temperatures of 250 c the absence of siderite in younger rocks suggests an early triassic upper limit for the iron pulse in the southern alps which would thus predate the middle triassic magmatism based on the overlap between hydrothermalism extensional tectonics and in part magmatism the genesis of siderite in the southern alps may be related to plutonic activity and or magmatic underplating occurring since the permian in a geodynamic scenario preluding the opening of the neo tethys

emplacement modes of the ladinian plutonic rocks of the dolomites insights from anisotropy of magnetic susceptibility abstract in the dolomites eastern southern alps italy a diffuse middle triassic igneous activity is now present mostly as lava flow and pyroclastic successions with rare shallow depth intrusive bodies cropping out at predazzo monzoni and cima pape areas in this work the emplacement modes of the predazzo and monzoni bodies were investigated by means of petrographic and anisotropy of magnetic susceptibility ams data coupled with a field geological study the presence of intrusive rocks in between these two bodies and the continuity of the metamorphic aureola from west of the predazzo to east of the monzoni body suggest that they are parts of a 20 km wide sw ne oriented continuous pluton sub parallel to ladinian strike slip faults ams and petrographic data from the predazzo body are consistent with a multistage ring dyke emplacement mode with areas of upward flow of the magma located in the nw and ese part of the intrusion whereas in the southern sector of the pluton our data suggest prevalently horizontal flows in general the predazzo sheets indicate either upward magma flow or along strike lateral magma transport and the round shape suggests no influence of ladinian tectonic structures on the contrary the ene wsw elongated shape of the monzoni body was controlled by the occurrence of strike slip faults associated with ladinian tectonics the feeder being likely located at the ne edge of the body however the absence of deformation at the field and micro scale is consistent with a post ladinian tectonics timing of emplacement as for the predazzo pluton

corals at their latitudinal limits laser ablation trace element systematics in porites from shirigai bay japan the rapid analytical technique of laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure the trace elements b mg sr ba and u in a high latitude coral colony porites lobata taken from shirigai bay japan 32 n a wide range of sea surface temperatures ssts 14 5 28 c and upwelling events influenced this coral cold winter ssts caused a decrease and or cessation of skeletal extension measurements of u ca and sr ca indicate an approximately linear response to ssts above 18 c and a non linear response below 18 c mg ca and b ca measurements both showed annual cycles broadly consistent with sst variations but also exhibited intra annual fluctuations not associated with temperature suggesting that the incorporation of mg and b into the coral skeleton was not simply regulated by temperature it is shown that ba ca ratios provide a proxy for wind induced seasonal upwelling this is inferred from the strong correlations between the strength of zonal winds 1 month prior to the sst minimum and the ba ca maximum secondary upwelling events occurred during the summers of 1982 1987 1991 and 1992 these summers were cooler than average and were associated with el nino southern oscillation events

geochemical and geochronological data on triassic volcanism of the southern alps of lombardy italy genetic implications a widespread volcanism mainly consisting of pyroclastic products and lava flows is found in the southern alps of lombardy the volcanics are interbedded with anisian ladinian carbonatic sequences and continental terrigenous or transitional deposits of ladinian carnian age the petrographic and geochemical data for this volcanism indicate a calc alkaline affinity with characters similar to those of convergent continental margins in this sector of the alps the geological evidences show that in the middle triassic general extensional movements were the dominant deformation event and do not support the existence of a subduction zone during this period the apparent contrast between the tectonic environment and the type of magmas erupted in the anisian carnian is tentatively explained by partial melting during the early stage of rifting of an upper mantle deeply modified during the previous hercynian orogenesis and contaminated by crustal material this hypothesis is in agreement with the preliminary sr isotopic ratios 0 705 and 0 709 k ar and rb sr ages on biotites date the beginning of the volcanism at around 225 m y

coral ba ca molar ratios as a proxy of precipitation in the northern yucatan peninsula mexico the yucatan peninsula consists of a karstic terrain that allows the aquifer to directly recharge from rainfall due to the various dissolution precipitation reactions occurring during groundwater flow the groundwater discharge in the coastal zone becomes a source of trace elements including ba the aim of this study was to use the coralline ba ca record as a proxy of precipitation under the consideration that rainfall rates vary at inter annual time scales annual ba ca ratios both the total content ba catc and the ca substitutive fraction ba cacaf were quantified in a 52 a old coral colony of montastraea annularis from the punta nizuc reef mexican caribbean average ba catc 5 90 0 56 lmol mol was 20 higher than ba cacaf 4 85 0 33 lmol mol indicating that ba is also incorporated in other fractions correlation between annual precipitation and ba catc time series is significant r 0 77 p 0 05 allowing the use of the ba catc ratio as a proxy of precipitation and hence enabling the reconstruction of precipitation patterns through time likewise the ba cacaf ratio can be used for the reconstruction of dissolved ba in coastal seawater 2012 elsevier ltd all rights reserved

tracking an upper limit of the carnian crisis and or carnian stage in the western carpathians slovakia the late triassic timescale especially the carnian norian boundary is poorly constrained mainly due to a paucity of high precision radio isotopic ages that can be related accurately to contradictions between the biostratigraphic and magnetostratigraphic correlations la icp ms dating of detrital zircons from five samples of the lunz formation the upper triassic siliciclastic sediments from the western carpathians slovakia provided a wide spectrum of ages that vary from late archaean ca 2582 ma to triassic ca 216 ma these marine delta sediments represent a typical product of the carnian crisis a major climate change and biotic turnover that occurred during the carnian stage in the tethys ocean within the carbonate shelf and intrashelf basins in the northern calcareous alps and the western carpathians the supply of clastic material in the studied lunz formation was derived from several sources especially i from the recycled variscan orogen ii from the remote east european platform and iii from the contemporaneous triassic volcanic sources syn sedimentary volcanic zircons with a concordia age of 221 2 1 6 ma calculated from 12 single analyses represent the maximum age of deposition of the lunz formation and demonstrate that the upper limit of the carnian crisis and or the carnian stage in the alpine carpathians realm is younger than the current age of the carnian norian boundary at ca 227 ma listed on the international chronostratigraphic chart international commission on stratigraphy 2016 12 edition

high resolution upb dating of middle triassic volcaniclastics time scale calibration and verification of tuning parameters for carbonate sedimentation abstract we report high resolution single zircon u pb age data for middle triassic volcaniclastic intercalations in biostratigraphically calibrated pelagic successions of the southern alps the results require a redefinition of the chronometric scale for the middle triassic moreover they do not support current models relating cyclic sedimentation in platform carbonates of the dolomites to orbital tuning tight concordant age clusters were obtained for five volcaniclastic layers in three ammonoid biozones of late anisian to early ladinian age two layers in the nevadites secedensis zone yielded identical mean 206 pb 238 u ages of 241 2 0 8 0 8 ma and 241 2 0 8 0 6 ma errors given at the 95 confidence level a layer in the gredleri zone is dated at 238 8 0 5 0 2 ma and two horizons in the archelaus zone yield similar ages of 237 9 1 0 0 7 ma and 238 0 0 4 0 7 ma these results are significantly older than the age values of 233 235 ma assigned to the anisian ladinian boundary by several current time scales 1 4 moreover our estimate of 240 7 241 3 ma depending on biostratigraphic collocation for the anisian ladinian boundary casts doubts on the reliability of age values of 245 250 ma proposed by most time scales for the permian triassic boundary the occurrence of pelagic fossils in basinal sediments as well as in age equivalent shallow marine middle triassic platform carbonates in the dolomites allows the sedimentary sequences of both environments to be correlated the 800 m thick latemar platform western dolomites is characterized by cyclic stacking patterns which have been interpreted as results of milankovitch type high frequency low amplitude sea level fluctuations the 12 m y interval of platform growth postulated from the assignment of orbital periodicities to the platform carbonate cycles 5 6 is in conflict with a maximum time span of 4 7 m y allowed by the present zircon data