sedimentology and isotope geochemistry of carnian deep water marl limestone deposits from the sicani mountains sicily environmental implications and evidence for a planktonic source of lime mud abstract the upper triassic halobia bearing marl limestone deposits from the sicani mountains sicily record the sedimentary evolution of the sicanian basin through the middle and late carnian time dark marls and interbedded grey calcilutites of julian age are characterized by abundant pyrite sparse bioturbation and negative carbonate carbon 13c values they accumulated in a basin with dominantly anoxic to dysaerobic bottom waters lower tuvalian dark grey pyritic marls and calcilutites which contain carbonate minerals with relatively high mn contents and widely fluctuating 13c signatures were deposited under dysaerobic conditions middle and upper tuvalian cherty limestones show intense bioturbation and nearly invariable positive 13c values around 2 for calcite they form a thick and monotonous succession accumulated in a deeper and more oxygenated basin the halobia bearing deposits preserve some calcareous nannoplanktonic forms the nannofossils varying in size from 7 to 32 m are significantly abundant in the cherty limestones pointing to a notable role of the calcareous nannoplankton as a source of carbonate mud in the deep water basins of the southern tethys during the late triassic time

carbonate platform crisis in the carnian late triassic of hanwang sichuan basin south china insights from conodonts and stable isotope data abstract during the carnian the hanwang area in the northwestern sichuan basin south china was characterized by shallow water carbonate sedimentation that underwent an abrupt demise associated to a sudden input of terrigenous sediments this major facies change was considered to be the expression of the onset of the carnian humid episode a most remarkable environmental crisis in late triassic that is well recognized in northwestern tethys margins and coincides with a major global perturbation of the carbon stable isotope record however the lack of detailed biostratigraphic constraints have so far prevented a precise dating of the carbonate platform demise in western sichuan basin in this work the qingyan gou hwq section cropping out in hanwang was investigated for its facies and microfacies carbonate carbon and oxygen isotopes on brachiopods microbial grains and bulk matrix facies analysis shows a marine transgression from inner ramp oolitic shoal to middle ramp siliceous sponge mound then overlain by shale and calcareous siltstone with interbedded silty mudstones refined biostratigraphic data from hwq and guanyin ya hwg sections imply that the demise of sponge mounds occur in the late tuvalian or later a negative carbon isotope perturbation was found in the bulk matrix immediately below the sponge mounds demise but it was not found on the isotope record from brachiopods this suggests that the negative shift in the bulk carbonate was probably related to diagenesis given the late tuvalian last substage of carnian age attributed to the demise of the sponge mounds and the absence of a carbon isotopic excursion we infer that the carbonate platform crisis and strong terrigenous input in hanwang cannot be related to the onset of the carnian humid episode these the demise of the carbonate platform and the facies deepening trend could be rather due to the interplay between accelerating subsidence rates environmental chants and enhanced siliciclastic input related to the formation of a foreland basin during indosinian orogenesis

the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18o and 13c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuations maximum oxygen depletion and an extreme negative shift of 13corg values 34 occurred during the early falciferum zone this is explained by the recycling of 12c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

the schilfsandstein and its flora arguments for a humid mid carnian episode recently intensified research on the mid carnian episode stimulated discussions about the mid carnian climate and a supposed humid climate shift this basin scale study on the schilfsandstein the type example of the mid carnian episode applied sedimentological palynological and palaeobotanical proxies of the palaeoclimate to a large dataset of cored wells and outcrops the results demonstrate the primary control of circum tethyan eustatic cycles on the central european basin where transgressions contributed to basin scale facies shifts the palaeoclimate proxies point to a uniform arid to semi arid carnian climate with low chemical weathering and high evaporation consequently transgressions into the central european basin led to increased evaporation forcing the hydrological cycle the increased runoff from source areas resulted in high groundwater stages on lowlands characterized by hydromorphic palaeosols and intrazonal vegetation with hygrophytic elements during lowstands reduced evaporation and runoff led to increased drainage and desiccation of lowlands characterized by formation of vertisols calcisols and gypsisols and zonal vegetation with xerophytic elements the proposed model of sea level control on the hydrological cycle integrates coeval and subsequent occurrences of wet and dry lowlands hydromorphic and well drained palaeosols and intrazonal and zonal vegetations thus the schilfsandstein does not provide arguments for a humid mid carnian episode supplementary material datasets of palynomorph eco group peg and macroplant eco group meg analyses are available at https doi org 10 6084 m9 figshare c 4182593

evidence for the carnian pluvial episode in gondwana new multiproxy climate records and their bearing on early dinosaur diversification abstract the triassic hothouse world experienced dynamic changes in climate and ecosystems that set the earth s climate and biotic states for much of the mesozoic era a critical time interval was the carnian stage 237 227 ma which not only saw the first appearance of dinosaurs in the fossil record but witnessed a large igneous province eruption wrangellia lip and a sudden climate shift the carnian pluvial episode cpe compelling hypotheses suggest that the wrangellia eruptions caused the cpe which in turn set the stage for the origin and initial diversification of dinosaurs unfortunately testing these hypotheses is difficult because most relevant carnian sedimentary archives possess few if any absolute age constraints and there are little detailed paleoclimatic data for the cpe outside of the tethys region there is little existing evidence for the cpe in gondwana even though this region contains by far the best fossil record of early dinosaurs and their close relatives we present new high resolution geochronologic and paleoclimatic data from carnian aged strata in the ischigualasto villa union basin of northwest argentina which also preserves fossils of the earliest known dinosaurs new ca tims u pb zircon age of 234 47 0 44 ma from the lower los rastros formation demonstrates that most of the overlying lacustrine strata within this basin was deposited during or after the cpe including large dinosauriform footprints multiproxy paleoenvironmental data sedimentology clay mineralogy c and o stable isotopes and fossils from the same strata are the first detailed paleoclimate data for the cpe in gondwana and provide evidence that the cpe interval in western gondwana was indeed warmer and more humid than before or after these data are consistent with the interpretation of the cpe as a global event but direct linkages in gondwana and the tethys with the origin and initial diversification of dinosaurs are less clear

reconstruction of palaeosalinity using carbon isotopes and benthic associations a comparison carbon and oxygen isotopes were determined on 40 recrystallized shells of late jurassic bivalves from the lusitanian basin of portugal in contrast with the oxygen isotopes which exhibited considerable diagenetic distortion the carbon isotopes are thought to preserve a record of the salinity of the jurassic marginal marine seas in which these bivalves lived the reconstructed palaeosalinities range from 35 o euhaline to 5 oligohaline comparing these values with the palaeosalinity reconstructed from a palaeoecological analysis of 17 stratigraphic levels within the basin the independently derived values agree in most cases strongly differing values are explained as being due to biotic factors and to diagenetic distortion of the isotopic signal they are less likely to be due to smallscale time averaging or insufficient microstratigraphic sampling on the whole the carbon isotope analyses are thought to produce reasonable palaeosalinity values although data from infaunal originally aragonitic bivalves appear to be less reliable than those from epifaunal bivalves with a predominantly or exclusively calcitic shell as diagenetic alteration of the carbon isotope signal is however unpredictable and biotic effects on the isotopic composition are insufficiently known palaeosalinity reconstructions based on stable isotope data should be supported by palaeoecological data

diagenetically enhanced bedding in argillaceous platform limestones stratified cementation and selective compaction a field and petrographic study has been made of 34 massive beds in argillaceous limestones of open marine platform facies in the u k lithologies include grainstones packstones wackestones and lime mudstones the rocks are of silurian carboniferous and jurassic ages additional information was obtained from other limestones in the u k the u s a canada and continental europe the beds are parts of sequences composed of couplets of strata fissile limestones alternating with hard limestones in the fissile limestones the effects of mechanical compaction and pressure dissolution have been concentrated whereas in the hard limestones they are minimal or absent bedding planes visible in outcrop are diagenetic in origin and lie in the middle parts of the fissile limestones where compaction has been most severe the features produced by pressure dissolution are dissolution seams and fitted fabric there are no stylolites the original carbonate sediments were bioturbated and any structures produced by flowing water were destroyed the vertical distribution of the bedding planes bears no relation to primary depositional bedding planes which are rare or absent it is inferred that the strata which were to become the hard limestones were selectively cemented before mechanical compaction had been completed thenceforth mechanical compaction and then pressure dissolution were concentrated in the less cemented strata these became the fissile limestones pressure dissolution acted late in the diagenetic history and provided only an insignificant part if any of the carbonate for cementation it is concluded that the orientation of beds couplets is parallel to successive sea floors and that the sediments that eventually became single beds accumulated synchronously similar couplets in platform limestones of the mississippian and pennsylvanian of the u s a extend over thousands of square kilometres the signal that controlled the initial selective cementation must have been widespread and synchronous and also syndepositional in its timing but otherwise cannot be further defined on the basis of the data so far collected the presumed order of events was 1 accumulation of carbonate sediment terrigenous clay and organic matter 2 hydrodynamic reworking and bioturbation the latter finally overprinting the former 3 selective cementation of the more carbonate rich strata yielding couplets each consisting of a relatively well cemented stratum and a poorly cemented stratum 4 mechanical compaction concentrated in the less cemented strata 5 pressure dissolution concentrated in the same strata

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

the role of sulphate reducing bacteria and cyanobacteria in dolomite formation in distal ephemeral lakes of the coorong region south australia abstract the dolomitic distal ephemeral lakes of the coorong region of south australia are dynamic systems in which the concentrations of solutes generally increase during late spring and summer when the rate of evaporation greatly exceeds aqueous input during late evaporation active bacterial sulphate reduction occurs in uppermost anoxic lake sediments as rising salinity and then h2s toxicity kills off the macrobiota these hypersaline lakewaters are characterised by high ph and elevated concentrations of carbonate and sulphate ions magnesium concentrated in cyanobacterial cells and sheaths is released into the strongly electrolytic alkaline lake brines from lake margin stromatolites and mats during desiccation and may explain the remarkable increase in mg levels recorded at this time continued evaporation of the lakewaters produces a halite crust overlying the dolomite sulphate free residual puddles and the absence of gypsum indicates that all sulphate is removed by sulphate reducing bacteria dolomite forms in situ as a primary precipitate from these microbially mediated lake porewaters and both the morphology and size distribution of dolomite grains is identical to bacterial cells it is not proven exactly when dolomite precipitation occurs but the submicron sized grains and multiple defects in a disordered lattice indicate that precipitation is rapid and follows bacterial removal of sulphate which is known to inhibit dolomite formation bacterial sulphate reduction and cyanobacterial degradation may thus lead to the removal of all kinetic inhibitors to dolomite formation and provide a mechanism for dolomite precipitation around bacterial cells in shallow subsurface sediments during the late stages of evaporation in adjacent non dolomitic lakes sulphate is present throughout evaporation so that other minerals principally aragonite and hydromagnesite are precipitated

dolomite formation and biogeochemical cycles in the phanerozoic summary based on present knowledge of the purely chemical controls on the kinetics of massive dolomite formation the abundance and distribution of dolomite throughout the phanerozoic remains an enigma sometimes referred to as the dolomite problem comparing dolomite abundance to secular variation in seawater chemistry indicates that some changes in seawater chemistry are more likely to have resulted from extensive dolomitization rather than to have caused it the recently formulated microbial dolomite model provides the opportunity to view the geological history of dolomite formation from a new perspective a biogeochemical approach to the dolomite problem reveals a plausible connection between phanerozoic geochemical cycles and dolomite formation in particular periods of more extensive dolomitization broadly correlate with diverse indicators of decreased oxygen levels in the atmosphere and oceans lowered oxygen levels would have fostered a more active community of anaerobic microbes including sulphate reducing bacteria which in turn could have led to more extensive dolomitization of marine carbonates

unique chronostratigraphic marker in depositional fan stratigraphy on mars evidence for ca 1 25 ma gully activity and surficial meltwater origin the origin of gullies on mars is controversial e g catastrophic groundwater release debris flows dry granular flows or meltwater from surface ice and snow and their ages are difficult to determine due to their small size we describe a gully depositional fan that contains a unique chronostratigraphic marker secondary crater clusters between episodes of gully activity during fan development this marker can be traced to its source a 7 km diameter rayed crater that we have dated as ca 1 25 ma this age links gully activity to the emplacement of dust ice mantling deposits interpreted to represent recent ice ages on mars this association together with multiple episodes of depositional fan formation favors an origin for these gullies from top down melting of snow and ice during multiple favorable spin axis and orbital variations this melting mechanism is consistent with the occurrence of gullies in unique steep sloped poleward facing insolation microenvironments that favor the melting of small amounts of surficial snow and ice

progradation geometries of carbonate platforms examples from the triassic of the dolomites northern italy various types of progradation of triassic carbonate platforms are described from the dolomites of the southern alps the internal and external geometric relationships are exposed in spectacular natural sections and moreover their scale 500 1000 m of thickness is such that they can be compared with features found in seismic profiles the different types of progradation are controlled by a number of factors which normally interact with each other these factors include rate of basinal sedimentation rate of subsidence width of the platform depth of the surrounding basin and eustatic variations of sea level progradation is not a continuous process but episodic moments of massive debris input during which the platform advances alternate with long periods of negligible progradation during which basinal sediments accrete and onlap the toe of slope upper boundary relationships of the prograding platforms include offlap toplap and erosional truncation lower boundary relationships are horizontal climbing and descending progradations a variety of phenomena and circumstances have caused the cessation of progradation of the triassic platforms they include volcanism collapse of margins drowning rapid relative rise of sea level subaerial exposure relative fall of sea level and probably a natural decay of the system in the triassic of the dolomites two main progradation models can be put forward in the ladinian model progradation took place simultaneously with aggradation relative rise of sea level whereas the characteristic feature of the carnian model is toplap relative stillstand of sea level

mechanical and chemical compaction in fine grained shallow water limestones abstract artificial compaction of in situ cores of modern sediments from differing sedimentary environments resulted in 1 reduction of sediment thickness by 50 percent and more 2 reduction of initial porosities of 65 to 75 percent to 35 to 45 percent 3 creation of megascopic textures almost identical to many ancient lime mud and wackestones 4 creation of organic wispy stylolite like layers that in nature probably would initiate dissolution and stylolite development given burial and time 5 chemical compaction evidenced by thin sections showing quartz grains piercing mollusc shells without causing fractures and sem evidence of solutional interfitting of 1 to 4 m size aragonitic carbonate grains 6 obliteration of pellets and birdseye or fenestral voids in those sediments here early cementation was lacking pellets were preserved in slightly cemented bahama bank muds compacted to half the original thickness 7 obliteration of identifiable marine grasses and vertical root tube voids 8 mashing of sediment filled circular burrows to produce ellipsoidal structures significant mechanical compaction resulted from pressures simulating less than 1 000 ft 305 m of burial increasing loads to an equivalent of more than 10 000 ft 3 400 m did not significantly increase compaction or reduce sediment core length chemical compaction pressure dissolution was detected only in sediment cores compacted to pressures greater than 10 000 ft 3 400 m of burial these short term experiments suggest that chemical compaction would begin at much shallower depths given geologic time compaction experiments that caused chemical compaction lend support to the well established hypothesis that cement required to produce a low porosity low permeability fine grained limestone is derived internally dissolution ion diffusion and reprecipitation are considered the m st likely processes for creating significant thicknesses of dense limestones in the geologic record continuation of chemical compaction after significant porosity reduction necessitates expulsion of connate fluids possibly including hydrocarbons

deep water asymmetric cycles and progradation of carbonate platforms governed by high frequency eustatic oscillations triassic of the dolomites italy the basinal san cassiano formation triassic dolomites italy is interfingered with clinostratified megabreccia slope deposits of coeval carbonate platforms and to a large extent is composed of metre scale thickening coarsening upward cycles these asymmetrical cycles often representing bundles of five coarsening upward sequences are interpreted as platformbasin interactions governed by fourth and fifth order eustatic oscillations according to this model progradation of triassic platforms of the dolomites occurred mainly during fourthorder sea level lowstands

conodont size reduction and diversity losses during the carnian humid episode in sw china the enigmatic biotic and environmental changes during the carnian humid episode che have been investigated in south china the body size of conodonts assessed as length of p1 elements and their diversity show substantial changes in the mid carnian the well dated long chang yongyue and caizitang sections in southwestern china record a change of palaeoenvironments from shallow marine carbonate platforms to deeper euxinic basins all sections show a major loss of conodont diversity and abundance late in the julian 1 at a time of rapid warming and marine anoxia conodont size saw a reduction in maximum mean and minimum size during the julian 2 to tuvalian 2 interval caused by the short lived appearance of small species and a size decrease of the survivors conodont mean size reduction coincided with marine euxinia or anoxia and temperature fluctuations during the julian 2 to tuvalian 2 interval carnian conodonts thus follow bergmann9s rule element size is inversely correlated to the temperature climate warming with the consequential development of marine anoxia or euxinia is probably directly responsible for biotic changes at this time supplementary material conodont length data from the long chang lc yongyue nr and caizitang cz sections and data for the cross plot between estimated temperature and conodont mean size in the long chang section are available at https doi org 10 6084 m9 figshare c 4114424

triassic climates state of the art and perspectives abstract the climate of the triassic period was characterized by a non zonal pattern dictated by a strong global monsoon system with effects that are most evident in the tethys realm this strong monsoonal regime is related to the aggregation of the pangaean supercontinent which by triassic time was already completed climate oscillations existed within this framework the harsh hot house climatic conditions that characterized the late permian and perhaps precipitated the end permian mass extinction were probably maintained during the early triassic and may account for the impoverished but distinctive faunal and floral lower triassic associations although metazoan reef builders were probably the most affected group carbonate production remained high at least in the western tethys realm the middle triassic was characterized locally by humid episodes although their geographical distribution has yet to be clarified the carnian pluvial event marks an episode of increased rainfall documented worldwide was the most distinctive climate change within the triassic different hypotheses have been proposed for its causes changes of atmospheric or ocean circulation driven by plate tectonics a peak of the global monsoon due to maximum continent aggregation or triggering by the eruption of a large igneous province subsequently the late carnian and norian seem to have been climatically stable although minor climatic changes have recently been described even from this time period finally the end triassic extinction event is also associated with climate change specifically warming and increased rainfall but this evidence comes mostly from the northern parts of the central atlantic magmatic province and the global pattern of climate change at the triassic jurassic boundary has still to be resolved many facets of triassic climate are intriguing and deserve further research however palaeoclimate studies on the triassic have so far been carried out only locally with different proxies those proxies will require inter calibration in order to depict correctly the temporal and geographical patterns of triassic climate

geochemical indicators of depositional and early diagenetic facies in holocene carbonate muds and their preservation potential during stabilisation holocene carbonate muds 63 m fraction and macro organic matter were collected from marine subtidal mudbanks and supralittoral mud islands of florida bay and freshwater marshes of the florida everglades u s a geochemistry sedimentology and mineralogy were used to determine whether carbonate mud formation in specific marine and freshwater environments was geochemically distinct and to assess the importance of early diagenetic reactions on mud chemistry and mineralogy significant variations were found in the relative amounts of carbonate minerals not just between the marine and freshwater environments but also within florida bay in particular mg calcite is enriched in crane key muds by 10 relative to nearby cross bank the mg calcite appears to precipitate in the surface living cyanobacterial mats of the key and seems to be linked to mg chelation by the cyanobacterial organic matter this mg calcite has a distinct 13c around 4 6 lighter than mg calcite derived from thalassia epibionts in the cross bank muds dolomite was found just below the cyanobacterial mats forming in the only part of the core where reactive organic carbon has been completely removed by sulphate reducing bacteria the 13c values of this dolomite at least 4 are consistent with previously published 13c values of dissolved inorganic carbon in pore waters at this horizon which support dolomite formation in situ mg supply for dolomite formation may be from dissolution of the overlying cyanobacterial mat mg calcite the various types of organic matter have distinctive 13c values ranging from 25 mangrove and sawgrass to 10 cyanobacterial mats and 8 thalassia seagrass values intermediate between these end members record mixing of the organic matter types which shows particularly the time when the bank muds became dominated by thalassia organic matter i e were relatively removed from mangrove vegetation five holocene mud suites bank key cyanobacterial mats mangrove swamp and freshwater everglades swamp show distinct chemical signatures in their mean 13c 18o mgco3 and sr values na distinguishes between seawater and non seawater influenced environments but fe mn and p are mainly controlled by non carbonate materials comparison with published stable isotope and elemental data for pleistocene limestones in the south florida area suggests that only the facies diagnostic signatures of 13c and mg will be resolvable once the muds have been stabilised to micrite alteration of the 18o and sr values during stabilisation will probably be more severe to the extent that original facies variations are destroyed

palaeoenvironmental controls on the clay mineralogy of carnian sections from the transdanubian range hungary abstract the upper triassic sediments both in nw europe and in the mediterranean region imply a generally arid climate regime in the carnian however a humid phase with a high input of siliciclastics is assumed carnian pluvial event but its causes are still highly controversial the carnian marine succession of the transdanubian range tr hungary also shows a significant change in sedimentation pelagic carbonate deposition fured limestone formation was followed by the formation of marly sediments veszprem marl and sandorhegy formations in order to understand the environmental changes the clay mineralogy of 240 carnian samples determined by x ray diffraction is discussed in the present paper additionally this set of clay mineral data from four boreholes from the bakony hills bakonysz cs bszu 1 balaton highland balatonfured bfu 1 mencshely met 1 and zsambek basin zsambek zs 14 allows us to test the reliability of clay minerals as palaeoclimatic proxies for the carnian late triassic by reconstructing spatial and temporal variations the first increase in clay content of the studied carnian succession can be detected in the limestone marl couplets of the cordevolian fured limestone its clay fraction is dominated by illite mixed layer illite smectite is and chlorite without kaolinite a good indicator of landmasses with a hot climate and constant humidity thus this compositional change probably related to a sea level drop subsequently the clay mineral assemblages of the veszprem marl sections in the bakony hills and the balaton highland are composed of illite poorly ordered r 0 is with 60 70 expandable component chlorite and kaolinite on the other hand the clay fraction of the samples from the zsambek basin is composed of illite is with an average of 40 50 expandable component and a transitional r 0 to r 1 type of ordering and kaolinite chlorite does not occur in the early julian kaolinite enrichments 10 20 in the clay fraction can be regarded as a manifestation of the climate shift from the prevailing aridity to the more seasonal climate with enhanced humid season the overall presence of abundant illite and accompanying chlorite can indicate a high rate of erosion of moderately weathered rocks while the large amount of smectitic clay transformed to is could be partly derived from transport of weathering products from a distant source area and subordinately from diagenetic alteration of intermediate to basic volcanic rocks spatial variation in the expandability and ordering of the is at least partially could be caused by different degree of the diagenetic overprint

drill hole convergence and a quantitative analysis of drill holes in mollusks and brachiopods from the triassic of italy and poland abstract the history of predation is recorded primarily from drilling in cenozoic invertebrates quantitative data are uncommon from the triassic a period before the appearance and radiation of many known drill hole producers such as various gastropod families and octopods we present quantitative evidence of drilling from the late triassic carnian cassian formation of italy and the middle triassic anisian lower muschelkalk of poland documenting the first drill holes in triassic brachiopods a single brachiopod with a cylindrical complete drill hole was found in a brachiopod sample from of poland drilling percentage 0 3 n 365 the cassian formation yielded drill holes in gastropods bivalves and brachiopods indicating that more species are drilled than was known previously the minimum drilling percentage exclusive of incomplete drill holes of a sample from the stuores wiesen cassian formation is 1 7 n 116 5 prey selectivity is evident complete drill holes are primarily present in one gastropod species polygyrina lommeli 11 8 of specimens with a complete drill hole whereas other common species were not drilled single drill holes in brachiopods are cylindrical and complete and may be predatory in origin multiple drill holes in mollusks are common and drill holes are parabolic and often incomplete with a central boss resembling the shape of drill holes produced by extant naticid gastropods a survey of the paleozoic literature showed that such drill holes are also present in devonian and carboniferous brachiopods however naticids did not evolve until the cretaceous so we propose the term drill hole convergence for similar shaped drill holes produced by different organisms the triassic parabolic drill holes are not caused by domicile seeking or boring organisms instead we favor a predatory origin of these drill holes but we cannot entirely rule out parasitism surveying other triassic invertebrate assemblages should yield more evidence of drilling

multiple negative carbon isotope excursions during the carnian pluvial episode late triassic abstract the carnian pluvial episode was a phase of global climatic change and biotic turnover that occurred during the early late triassic in marine sedimentary basins the arrival of huge amounts of siliciclastic sediments the establishment of anoxic conditions and a sudden change of the carbonate factory on platforms marked the carnian pluvial episode the sedimentary changes are closely associated with abrupt biological turnover among marine and terrestrial groups as for example an extinction among ammonoids and conodonts in the ocean and a turnover of the vertebrate fauna and the flora on land multiple negative carbon isotope excursions were recorded during the carnian pluvial episode in both organic matter and marine carbonates suggesting repeated injection of 13c depleted co2 into the ocean atmosphere system but their temporal and causal links with the sedimentological and palaeontological changes are poorly understood we here review the existing carbon isotope records and present new data on the carbon isotope composition of organic carbon in selected sections of the western tethys realm that record the entire carnian pluvial episode new ammonoid conodont and sporomorph biostratigraphic data were collected and coupled to an extensive review of the existing biostratigraphy to constrain the age of the sampled sections the results provide biostratigraphically constrained composite organic carbon isotope curves for the carnian which sheds light on the temporal and causal links between the main carbon isotope perturbations and the distinct environmental and biotic changes that mark the carnian pluvial episode the carbon isotope records suggest that a series of carbon cycle perturbations possibly recording multiple phases of volcanic activity during the emplacement of the wrangellia large igneous province disrupted carnian environments and ecosystems repeatedly over a remarkably long time interval of about 1 million years

sequence stratigraphy after the demise of a high relief carbonate platform carnian of the dolomites sea level and climate disentangled abstract sedimentary facies analysis aided by quantitative 3d georeferenced field data is applied to constrain the sequence stratigraphy of a complex stratigraphic interval in the late triassic of the dolomites this multidisciplinary approach was the key to disentangle the timing of climatic change vs sea level fluctuation and their effects on shallow water carbonate depositional systems the carnian pluvial event a global episode of climate change worldwide documented at low latitudes involved increased rainfall and possibly global warming this climatic event begins before a drop of sea level and caused the demise of microbial dominated high relief carbonate platforms that dominated the dolomites region and was followed by a period of coexistence of small microbial carbonate mounds and arenaceous skeletal oolitic grainstones a subsequent sea level fall brought to the definitive disappearance of microbialites and shallow water carbonates switched to ramps dominated by oolitic bioclastic grainstones the crisis of early carnian shallow water carbonate systems of the dolomites generated a geological surface similar to a drowning unconformity although no transgression occurred as the high relief microbial carbonate systems characterized by steep slopes switched to gently inclined oolitic skeletal siliciclastic ramps basins were rapidly filled the change of carbonate depositional systems was associated with an increase in siliciclastic input in turn triggered by the onset of a humid climatic event and only later to a sea level drop this evolution of carbonate systems cannot be interpreted in the light of sea level changes only climate change and consequent ecological changes in the main carbonate producing biotas induced significant modifications in depositional geometries this case study may serve as a conceptual model for the sedimentary evolution of carbonate systems subject to ecological crisis that do not evolve in platform drowning because despite a drop in shallow water carbonate production a combination of low subsidence and or sea level drop maintains the platform top at shallow depth

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

palynological correlation of carnian humid pulses throughout western tethys abstract the carnian pluvial event is an upper triassic swing toward increased rainfall best documented in the tethys tropical belt and mainly recognized on its effects on sedimentary systems as the demise of carbonate platforms and the enhanced siliciclastic supply in some portions of western tethys and particularly in the raibler schichten of the northern calcareous alps and in the dolomites the carnian pluvial event is recorded by four discrete siliciclastic pulses in the raibler schichten three siliciclastic intervals are documented and take the name of first second and third shale in order to correlate these pulses at the basinal scale the study of the palynological assemblages in a section of the raibler schichten near rubland austria and of the classical succession of the lunz nappe have been carried out more than eighty palynomorph species are recorded most of them correspond to typical carnian morphospecies of the carnian pluvial event in europe on the base of their stratigraphic distribution three different palynomorph assemblages are described aulisporites astigmosus assemblage lagenella martinii assemblage and granuloperculatipollis rudis assemblage a fourth older assemblage is also informally defined a palynostratigraphic correlation between the nca the germanic basin and the dolomites has been obtained the four siliciclastic pulses recognized in the raibler schichten and lunz are also found in the dolomites and yield the same palynological associations the base of the schilfsandstein that record the carnian pluvial event in the germanic basin is correlated to the second or third siliciclastic pulse first or second shale of the raibler schichten siliciclastic pulses are thus correlated throughout western tethys and can thus be interpreted as short lived humid climate wiggles within the carnian pluvial event a quantitative analysis of the carnian successions of the nca highlights a shift toward hygrophytic elements in the uppermost julian and an abrupt return to xerophytic associations in the lower tuvalian the palynological hygrophytic associations that characterize the aulisporites astigmosus and lagenella martinii assemblages are present in many other parts of europe and middle east suggesting that the carnian pluvial event determined a humid climate perturbation in a wide area of the northern hemisphere spanning from tropical to high latitudes

reef expansion during the triassic spread of photosymbiosis balancing climatic cooling the paleoreefs database indicates that reef abundance increased profoundly during the triassic period from a pronounced low in the early triassic to a major peak in the norian this expansion is also evident when standardizing for sampling corresponding to the reef expansion is a relative increase of scleractinian corals as reef builders whereas the contribution of hypercalcifying sponges and microbes decreased during the triassic the numerical expansion of corals is paralleled by a proportional increase of morphological features that are suggestive of photosymbiosis such that the norian reef boom might be explained by the spread of photosymbiosis in corals the geographical expansion of reefs was far less pronounced especially concerning palaeolatitude late triassic reef growth was limited to more or less the same latitudinal range as modern reefs as oxygen isotope data and new modeling results indicate declining temperatures and co2 concentrations during the late triassic the lack of latitudinal expansion might be attributed to global cooling reef development during the triassic can thus be explained by the evolutionary spread of photosymbiosis balancing the effects of climatic cooling

termination of carbonate slope progradation an example from the carnian of the dolomites northern italy abstract the demise of carbonate platforms during carnian time is a widespread phenomenon of the western tethys but the controlling factors are not well understood the dolomites of the southern alps northern italy are well known for their large scale ladinian and carnian prograding carbonate platforms platform growth stopped during the early carnian and both platforms and basinal areas were subsequently covered by mixed carbonate siliciclastic sediments raibl group we present a carbonate platform whose slope progradation came to a halt prior to draping by the siliciclastic sediments judging from the height of the clinoforms a platform to basin relief of at least 100 m existed during the final stage of progradation this paleo slope was colonized by coral patches draped by skeletal packstones to microbial bindstones forming typically lens shaped mounds on the steep slope the formation of mounds on the platform flank was only possible because the downslope transport of detritus from the platform and or upper slope was stopped the sedimentary evolution in the adjacent basin indicates a poorly oxygenated environment with abundant brackish water ostracods of low diversity based on the inherited platform to basin relief and the lithofacies of the basin fill a local sea level drop in the order of 60 80 m is postulated with rising sea level the accommodation space between former basin and platform became filled by shallow marine mixed carbonate siliciclastic sediments the abundance of epibenthic suspension feeders of the basin fill such as megalodonts suggests increased nutrient supply the termination of slope progradation was a multiphased process triggered by a stagnation of the regional subsidence a reduction of water circulation followed by a sea level drop the influx of freshwater and the input of siliciclastics fluctuating salinity caused intermittently a biotically stressed environment

synchroneity of climatic change and extinctions in the late triassic although the late triassic was a time of widespread aridity evidence exists for a significant increase in rainfall during the middle to late carnian upper triassic playa lake sediments were interrupted by late carnian fluviatile sandstones with erosive bases and high kao linite illite ratios there was also an increase in the clastic component of marine sequences during this interval middle and upper carnian marine carbonates show an extreme depletion in 13 c values consistent with increased fresh water influx large scale karstic phenomena in limestone areas subaerially exposed during the late triassic are a further indication of increased rainfall important faunal and floral changes occurred during the carnian norian interval marine invertebrate turnover was greatest at the lower middle carnian boundary and terrestrial extinctions were concentrated at the carnian norian boundary the cause of this carnian pluvial episode may have been related to the rifting of pangea through disruption of atmospheric and oceanic circulation patterns eustatic changes or the effects of volcanism associated with rifting a change in surface ocean temperature salinity or ph or habitat loss may have caused the decline of many shallow marine invertebrates at the start of the middle carnian a return to arid conditions at the carnian norian boundary would account for the turnover among terrestrial vertebrates and plants

the start up of the dolomia principale hauptdolomit carbonate platform upper triassic in the eastern southern alps wide carbonate platform environments developed on the western passive margin of the tethys during the late triassic after a major climate change carnian pluvial episode that produced a crisis of high relief microbial carbonate platforms the peritidal succession of this epicontinental platform dolomia principale hauptdolomit dachstein limestone is widespread in the mediterranean region however the start up stage is not fully understood the original platform to basin depositional geometries of the system have been studied in the north eastern southern alps close to the italian slovenian boundary where they are exceptionally preserved sedimentological features have been investigated in detail by measuring several stratigraphic sections cropping out along an ideal depositional profile the analysis of the facies architecture allowed reconstruction of the paleoenvironments of the dolomia principale platform during its start up and early growth stages in the late carnian the carbonate platform was characterized by an outer platform area connected northward to steep slopes facing a relatively deep basin southward the outer platform was connected to inner sheltered environments by a narrow often emerged shelf crest behind this zone carbonate sedimentation occurred in shallow lagoons and tidal flats passing inward to a siliciclastic mudflat the dolomia principale platform was initially aggrading and able to keep pace with a concomitant sea level rise and then prograding during the late carnian this stratigraphic interval was correlated to the tuvalian succession of the dolomites allowing depiction of the depositional system on a wide scale of hundreds of kilometrew this large scale depositional system presents features in common with some palaeozoic and mesozoic carbonate buildups fo example the permian capitan reef complex anisian latemar platform both in terms of architecture and prevailing carbonate producers a microbial dominated carbonate factory is testified in the outer platform and upper slope the recovery of high relief microbial carbonate platforms marks the end of the carnian pluvial episode in the tuvalian of tethys this article is protected by copyright all rights reserved

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

the changing climate framework and depositional dynamics of triassic carbonate platforms from the dolomites abstract the triassic of the dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms the reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological palaeobotanical pedological and geochemical proxies the triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts during the triassic the dolomites were placed at an intertropical northern latitude of about 16 18 and were generally dominated by dry climate and elevated temperature at least five pulses toward moister climate are however documented dated to early olenekian middle anisian late ladinian middle carnian and late norian times within this variable climatic scenario the carbonate systems record a global evolutionary trend from late permian early triassic regional shelves rich in loose micrites and bio calcarenites to anisian ladinian synsedimentary cemented steep sided 35 40 high relief platforms and back to carnian low angle ramps moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms probably because of the reduced space competition by syndepositional cementation structures the permo triassic boundary extinction dramatically impacted on the calcified organism communities but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary the early triassic and earliest anisian were commonly associated with hyperhaline sometimes evaporitic conditions intervals of moister climate and efficient river discharge are however documented by earliest induan and early olenekian sediments the latter terrigenous deposits matched a crisis in the carbonate production after a return to arid conditions during the anisian a fluctuation toward moister climate developed associated to a massive continental vegetation cover the anisian tectonic activation of the region fragmented the previous carbonate shelf triggering the development of three generations of fast prograding but globally backstepping isolated platforms recording an increasing role of the synsedimentary cementation a dry climate dominated the late anisian and early ladinian interval at the time a fast subsidence pulse was associated with platform drowning and basinal anoxia only a few aggrading pinnacles were able to survive providing the nuclei for larger prograding platforms during a dry climate interval massive syndepositional cementation generated a major source of carbonate carbonate production stayed active through the ladinian magmatic phase but the onset of volcanism was associated with a large modification in the platform carbonate facies which became dominated by automicrites moist climate phases are well documented again during the late ladinian followed by a return to dry conditions the late ladinian early carnian platforms prograded toward the eastern dolomites depocentre eventually infilling almost the whole of the accommodation space the middle portion of the carnian recorded renewed sharply moist phases associated with the demise of the rimmed platforms and with the return to loose sediment ramps at least four separated humid fluctuations can be identified in this carnian interval alone climate then returned to persistent aridity until the late norian moist phase

a continental record of the carnian pluvial episode cpe from the mercia mudstone group uk palynology and climatic implications the generally arid late triassic climate was interrupted by a wet phase during the mid carnian termed the carnian pluvial episode cpe quantitative palynological data from the mercia mudstone group in the wessex basin uk reveal vegetation changes and palaeoclimate trends palynostratigraphy and bulk organic carbon isotope data allow correlation to other carnian successions the palynostratigraphy indicates that the dunscombe mudstone is julian and the lowest part of the overlying branscombe mudstone formation is tuvalian the aulisporites acme characterizing the cpe in tethyan successions and the germanic basin is missing in the uk the quantitative palynological record suggests the predominance of xerophyte floral elements with a few horizons of increased hygrophytes a humidity signal is not seen owing to the dry climate in central pangea also the signal might be masked by the overrepresentation of xerophyte regional pollen and the predominance of xerophyte hinterland flora the bias towards regional pollen rain is enhanced by the potential increase in continental runoff related to seasonally humid conditions and differences in pollen production rates and transport mechanisms the vegetation of british cpe successions suggests a more complex climate history during the carnian indicating that the cpe is not recognized by the same changes everywhere supplementary material a detailed lithological log of the strangman9s cove devon outcrop with the description of the mercia mudstone group lithostratigraphical units a description of the laboratory techniques seven photoplates with selected spores and pollen grains a list of all identified palynomorphs excel sheets with the palynological and palynofacies counts bulk organic carbon isotope ratios and total organic carbon values of the strangman9s cove outcrop are available at https doi org 10 6084 m9 figshare c 4138085

seismic model of a progradational carbonate platform picco di vallandro the dolomites northern italy we present a seismic model of a well exposed carbonate platform to basin transition from the triassic succession at picco di vallandro the dolomites northern italy the core of this model is a detailed lithologic cross section that represents 1500 m of stratigraphic section over a distance of 3 5 km the cross section is based on detailed measured sections photo interpretation and careful projection of surface mapping into the plane of section samples from the measured sections provide control on velocity and density distribution and these data were used to generate an impedance model from the cross section the impedance model was convolved with a zero phase 25 hz peak frequency wavelet to produce the seismic model the results illustrate how the platform to basin transition might be imaged by conventional seismic reflection data how the reflections relate to the distribution of lithology and through going geological surfaces and how constructive and destructive interference and seismic resolution combine to produce individual reflections the picco di vallandro section displays several scales of progradation and retrogradation ranging from stacked buildups that are several hundreds of meters thick to the interfingering of individual beds the seismic model displays this complexity with varying degrees of success the individual buildups are well imaged but as expected smaller features are not as clearly reproduced by the model intermediate scale sections that represent platform retrogradation are shown as surfaces of onlap in the seismic model but field work shows that the platform was still shedding sediment while retreating and that no simple onlap surface exists in the outcropping section a similar lack of stratigraphic resolution is shown by the model at the downlapping clinoforms which do not correspond to iscrete stratal surfaces but to the toe of slope position where major bedding units thin below seismic resolution smaller features such as the position of downslope terminations of carbonate breccia wedges are not resolved by the model toe of slope packages of limestone turbidites are represented only by reflection segments of higher amplitude the decreasing seismic resolution is caused by limited seismic bandwidths and by the effects of constructive and destructive interference interference has the largest effects at the complexly interfingering buildup to basin transition or at the most detailed part of our model an understanding of these types of seismic limitations and their controls is important as we try to extract more and more stratigraphic information from seismic data p

unraveling the origin of carbonate platform cyclothems in the upper triassic durrenstein formation dolomites italy abstract facies analysis of the durrenstein formation central eastern dolomites northern italy indicates that this unit was deposited on a carbonate ramp as evidenced by the lack of a shelf break slope facies or a reef margin together with the occurrence of a molechfor biological association its deposition following the accumulation of rimmed carbonate platforms during the ladinian and early carnian marks a major shift in growth mode of the triassic shallow marine carbonates in the dolomites the durrenstein formation is characterized by a hierarchical cyclicity with elements strongly suggestive of an allocyclic origin including a subaerial exposure features directly above subtidal facies within meter scale cyclothems b purely subtidal carbonate cyclothems c symmetric peritidal carbonate cyclothems and d continuity of cyclothems of different orders through facies boundaries the durrenstein cyclothems are usually defined by transgressive and regressive successions and so most of them probably originated from sea level oscillations their allocyclic origin allows their use for high resolution correlations over distances up to 30 km a stratigraphic section in the tre cime di lavaredo area encompassing the upper part of the durrenstein formation and the lower part of the overlying raibl formation upper carnian was studied using time frequency analysis a strong milankovitch signal appeared when interference arising from a variable sedimentation rate was estimated and removed by tuning the short precession line in a spectrogram all of the principal periodicities related to the precession index and eccentricity calculated for 220 ma are present p1 21 9 ky p2 17 8 ky e1 400 ky e2 95 ky and e3 125 ky along with a peak at a frequency double that of the precession which is a predicted feature of orbitally forced insolation at the equator components possibly related to earth s obliquity at ca 35 ky and ca 46 ky are present as well the recovery of milankovitch periodicities allows reconstruction of a high resolution timescale that is in good agreement with published durations of the carnian based on radiometric ages the recognition of a milankovitch signal in the durrenstein and lower raibl formations as well as in other mesozoic carbonate platforms strongly supports a deterministic and predictable rather than stochastic control on the formation of carbonate platforms carbonate platforms might thus be used in the future for the construction of an astronomical time scale for the mesozoic

seasonal climatic fluctuations in the late triassic tropics high resolution oxygen isotope records from aragonitic bivalve shells cassian formation northern italy abstract three megalodontoid bivalves from the upper triassic cassian formation n italy dolomites were sampled for 13 c and 18 o sclerochronology n 270 with more than 1000 described invertebrate species the cassian formation has one of the best records of an early mesozoic tropical fauna in addition the cassian formation is one of the very few triassic occurrences with original aragonite preservation with all studied shells consisting of pristine aragonite the presence of aragonite and crossed lamellar as well as fibrous prismatic shell microstructures shown for the first time for triassic megalodontoids suggests absence or minimal impact of diagenetic alteration the 13 c values range from 3 6 to 5 8 and show a distinct cyclicity in two studied shells whereas a third shell shows no obvious cyclicity in one bivalve specimen the cycles are somewhat offset from 18 o cycles and in the other specimen 18 o and 13 c curves are inversely correlated seasonal variation in freshwater runoff including nutrient input and subsequent changes in plankton productivity during dry and wet seasons may explain 13 c cyclicity 18 o values show a pronounced cyclicity within each of the studied shells varying from 3 6 to 1 4 the variations in 18 o suggest a pronounced seasonality in late triassic tropical shallow waters of the western tethys with inferred seasonal temperature changes ranging from 24 to 32 c influx of fresh water during the rainy seasons mega monsoon or upwelling might also explain part of the variation in 18 o the presented data suggest that the diverse cassian fauna lived under conditions characterized by warm sea surface waters with a pronounced seasonality similar conditions are reported for some modern tropical settings

global carbon cycle perturbations triggered by volatile volcanism and ecosystem responses during the carnian pluvial episode late triassic abstract the carnian pluvial episode cpe was a dramatic climatic event during the early late triassic the cpe has been recognized worldwide and is marked by the termination of carbonate platform successions and by pronounced negative 13c excursions denoted as the cpe excursion the onset of the cpe has been proposed to be linked with the volatile eruption of the wrangellia large igneous province w lip however this extreme climatic event remains disputed in terms of its precise global correlation timing of onset duration and global magnitude we compiled a database of 13 conodont biozone controlled stable isotope reference sections throughout the tethyan region after a reexamination of previously published conodont taxonomy from each section the statistics on the conodont assemblages zones yield a global set of 17 high resolution conodont unitary association zones uazs spanning the entire carnian successions a set of age tie points placed an age model on this global uaz scale we added paired 13ccarb and 13corg data from two sections in south china to other records in this global database and then normalized all carbon isotope datasets a pronounced negative 13ccarb excursion with a magnitude of 2 0 5 from an average of 3 to 1 is evident in these normalized trends and is recognized around the entire tethys realm the cpe excursion coincides with conodont uaz 4 234 ma through uaz 8 within the mazzaella carnica and paragondolella praelindae zones julian2 and has a duration of ca 1 5 myr we note that an apparent delayed onset of the cpe excursion in south china relative to elsewhere in the tethys as suggested by previous studies may have been an artifact caused by incomplete conodont stratigraphic records and or irregularities in taxonomic identification a carbon and phosphorus cycle model highlight the strong relationship between the eruption of the w lip and cpe excursion however the estimated amount of co2volatiles released by the w lip would directly account for only 25 of the total amount of light carbon required to explain the combined magnitude and duration of the global cpe excursion

quantitative mineralogy of sandstones by x ray diffractometry and normative analysis abstract quantitative x ray diffraction normative calculation and whole rock chemical analysis have been compared for permo triassic quartz lithic to litho feldspathic sandstones from eastern australia the quantitative xrd technique provides mineralogical percentages that correlate well with the chemical composition of the sandstones and also with most of the mineral percentages derived from normative calculation the need for assumptions on potassium distribution between minerals provides a limitation on estimates of k feldspar and illite using the normative technique although these can be improved on a sample specific basis if necessary using complementary thin section observations or qualitative x ray diffractograms quantitative xrd analysis possibly indicates a small proportion of amorphous material in some of the sandstones especially materials with abundant lithic fragments or clay minerals but the proportion of any amorphous material overall is probably negligible both quantitative xrd and normative calculation avoid problems associated with sample heterogeneity or operator inconsistency that may affect point counting of thin sections they can also be used to provide quantitative information on sediments with abundant rock fragments or matrix components the actual mineralogy of which is not resolvable in conventional microscope investigations

the aftermath of the carnian carbonate platform demise a basinal perspective dolomites southern alps in the dolomites of northernmost italy the carbonate platform growth came to a standstill late in the early carnian late triassic the response to this shutdown of shallow water carbonate production in the interplatform basins is largely unknown because erosion has removed most of the soft basinal sediments giving rise to today s scenic landscape of the dolomites mapping in the central part of the dolomites and newly available core material has recently revealed a wellpreserved succession of basinal rocks within the heiligkreuz hospiz basin ital ospizio di santa croce basin in this paper the regional depositional nature of arrested carbonate platform production is reconstructed by tracing its sedimentological record across the slope and into the basin the uppermost st cassian formation the time equivalent basinal rocks to the prograding carbonate platforms is overlain by the heiligkreuz formation whose basal succession was deposited in a restricted and oxygen depleted environment immediately post dating the platform demise the succession consists mainly of mudrocks marlstones and peloidal packstones with abundant low diversity ostracod and pelecypod fauna and early diagenetic dolomite c and o isotope values of the basal heiligkreuz formation post dating platform demise average 2 ae4 and 2ae4 respectively and largely overlap the isotopic composition of st cassian carbonates a shift toward slightly lower d 13 c values in the heiligkreuz formation may reflect incorporation of isotopically depleted c released during bacterial sulphate reduction in the heiligkreuz sediments sedimentological palaeobiological and geochemical indices suggest that nearnormal marine conditions persisted long after the shutdown of shallow water carbonate platform growth although there are clear indications of severely reduced oxygen levels in the restricted heiligkreuz hospiz interplatform basin the early carnian platform demise induced a distinct switch in the locus of carbonate production from the shallow water platform and slope to the basin floor and a decrease in the availability of dissolved oxygen in the basinal waters it is inferred that anoxia extended at least temporarily to the top of the carbonate slope as indicated by the onlap of normal marine mounds by dark marlstones of the basal heiligkreuz formation

a tethys wide mid carnian upper triassic carbonate productivity crisis evidence for the alpine reingraben event from spiti indian himalaya abstract a significant mid carnian lithological change from carbonatic to siliciclastic sedimentation is described from the spiti himalaya n india the recorded sudden increase of terrigenous influx occurs at the boundary from the chomule to the rama formation it is dated within the late lower carnian uppermost aonoides zone and isochronous all over the tethys himalaya bio and chemostratigraphic data point to a synchrony with changes in carbonate productivity known from on area of wide extent along the nw tethys the reingraben event of the northern calcareous alps austria defines a regional decline in carbonate productivity related to both a platform demise and enhanced siliciclastic input laminated shales found in a distal part of the spiti basin document the onset of anoxic conditions within the deeper shelf synchronous to the reingraben event in austria high resolution biostratigraphy and identical 13ccarb curves are therefore in support of a direct link between the change in spiti and the reingraben event our data combined with a comprehensive review of previously postulated scenarios regarding the reingraben event suggest linking of climatic change with siliciclastic input and a carbonate productivity crisis initiated by onset of a relatively humid megamonsoonal late lower carnian atmospheric system that affected both the southern and northwestern tethys and point to a supra regional trigger of the alpine reingraben event

numerical modelling of aeolian erosion over rough surfaces the presence of non erodible roughness elements on erodible surfaces has the effect of absorbing part of the wind shear stress and thus protecting the erodible surface from wind erosion this paper examines the shear stress distribution over roughness arrays of varying density representing the progress of erosion on a bed of erodible and non erodible particles three dimensional numerical simulations simulating wind flow over a bed of particles covered by roughness elements were conducted in order to investigate the effect of roughness elements on the shear stress near the surface the results of these simulations confirm that the erosion of soil by wind is strongly attenuated by the presence of roughness elements on the surface and depends on the geometric properties of the roughness elements based on the new numerical results obtained a refinement of existing theoretical approaches is developed to describe the dependence of the friction velocity upon roughness frontal area and real exposed cover rate the new formulation proposed will allow a more accurate evaluation of shear stress partitioning as a function of topographic changes copyright 2010 john wiley sons ltd

perturbations in the carbon cycle during the carnian humid episode carbonate carbon isotope records from southwestern china and northern oman the carnian humid episode is an interval of prominent climatic changes in the late triassic we studied the carbon isotope 13c geochemistry of carbonates from sections in southwestern china and northern oman 13c records from the yongyue section western guizhou south china show a progressive positive shift from 1 4 to 2 8 in the early to middle julian 1 substage this positive trend is followed by a swift negative shift of c 4 2 from 2 8 to 1 4 in the julian 2 substage 13c from the wadi mayhah section northern oman shows a positive shift from 2 2 to 2 8 in the julian 1 substage followed by a negative shift of c 3 2 from 2 8 to 0 3 in the julian 2 substage the 13c records from the two study sections generally correlate well with each other as well as with published records pointing to a considerable input of isotopically light carbon starting in the late julian 1 substage such a large amount of light carbon probably derived from direct degassing and the sediment sill contact metamorphism of the panthalassan wrangellia large igneous province and contemporary tethyan volcanism the voluminous volcanogenic greenhouse gases probably contributed to the warming pulse in the middle carnian thus the dry wet climatic transition during the carnian humid episode is best interpreted as a warm climate driven intensification of the activities of the atmospheric circulation and hydrological cycle