correlations of hauterivian and barremian early cretaceous stage boundaries to polarity chrons recent ammonite finds in italian maiolica limestones allow direct correlation of hauterivian and barremian ammonite zones stage boundaries to polarity chrons at laghetto and alpetto lombardy italy lower aptian ammonites occur just above polarity zone m0 and below the selli level and upper barremian ammonites occur in polarity zone m1n these correlations are consistent with the barremian aptian boundary being close to older boundary of polarity chron cm0 the uppermost hauterivian ammonite faraoni guide level has been correlated to cm4 at bosso umbria marche confirming the recent correlation of the hauterivian barremian boundary to cm4 at monte acuto umbria marche ammonites spanning the valanginian hauterivian boundary interval and the last appearance of the nannofossil t verenae occur close to the cm11 cm11n boundary the valanginian hauterivian boundary has previously been placed between the first appearance of l bollii and the last appearance of t verenae or between cm10 and cm11 the published polaveno lombardy magnetostratigraphy for the cm3 cm11 interval has now extended to cm16 this 260 m section recording the cm3 cm16 interval is the most complete single section record of cretaceous m sequence polarity chrons no diagnostic ammonites have been found in this section however the correlations of nannofossil and calpionellid events to polarity chrons are consistent with previous studies

valanginian weissert oceanic anoxic event biotic changes in nannofossils and radiolarians associated with the valanginian 1 3 c anomaly are documented at ocean drilling program hole 1149b in the pacific ocean they are coeval and similar to those previously documented in the tethys suggesting a global perturbation of marine ecosystems a marked increase in abundance of diazomatolithus absence of nannoconids and a pantanellium peak characterize the valanginian 1 3 c excursion such changes are interpreted as being due to global enhanced fertility and a biocalcification crisis under conditions of excess co 2 the occurrence of organic c rich black shales in the southern alps and in the pacific in the interval corresponding to the 1 3 c excursion suggests a valanginian oceanic anoxic event oae volcanism of the parana etendeka large igneous province ca 132 ma was presumably responsible for an increase of co 2 triggering a climate change and accelerated hydrological cycling possibly causing an indirect fertilization of the oceans widespread nutrification via introduction of biolimiting metals at spreading ridges could have significantly increased during the gondwana breakup and simultaneous tectonic events in three separate oceans there is no paleontological or 1 8 o evidence of warming during the valanginian oae on the contrary both nannofossils and oxygen isotopes record a cooling event at the climax of the 1 3 c excursion weathering of basalts and burial of organic c rich black shales were presumably responsible for co 2 drawdown and establishment of reversed greenhouse conditions

late barremian early aptian dark facies of the subbetic betic cordillera southern spain calcareous nannofossil quantitative analyses chemostratigraphy and palaeoceanographic reconstructions abstract in order to determine the driving mechanism behind the deposition of the aptian dark facies in the pelagic subbetic basin southern spain two latest barremian early aptian complementary sections embracing the oceanic anoxic event 1a were selected for a multidisciplinary study quantitative and statistical analyses of calcareous nannofossil assemblages are complemented with planktonic foraminifera radiolaria and geochemical data c and o isotopes and biomarkers the results indicate that most of the latest barremian was characterized by oligotrophic conditions with a low nutricline and neritic influence which were interrupted by short lived episodes of mesotrophic surface waters in contrast broadly meso eutrophic surface waters with a high nutricline and a probable development of water stratification are inferred for most of the early aptian it is suggested that an increased runoff as a consequence of a more humid climate in the adjacent continental area caused this fertilization neritic dwellers such as nannoconids and pentaliths experienced a drastic decrease in abundance as the result of the combined effects of a biocalcification crisis nannoconid crisis and the deepening of the basin high productivity and enhanced surface water stratification favoured low oxygen content in the bottom waters increasing organic matter preservation a reduction in surface water fertility and a shift towards generally cooler conditions occurred during the late early aptian it is postulated that a cooler and drier climate leads to a reduction in runoff and decreased nutrient flux into the basin the obtained results suggest that the formation of the aptian dark facies was mainly controlled by enhanced production of organic matter in the upper water column and not enhanced preservation

using combined ahp genetic algorithm in artificial groundwater recharge site selection of gareh bygone plain iran flood spreading is one of the suitable strategies to control and benefit from floods which in turn improve the groundwater recharge makes soil more fertile and increases nutrients in soil it is also a method for reusing sediment which is usually wasted thus selection of suitable areas for flood spreading and directing the flood water into permeable formations are amongst the most effective strategies in flood spreading projects having combined analytic hierarchy process ahp of multi criteria decision analysis and genetic algorithm ga of artificial intelligence approaches this paper addresses the problem of finding the most suitable area location for flood spreading operation in the gareh bygone plain of iran to this end the nine effective geodata layers including slope alluvium thickness geology morphology electrical conductivity land use drainage density aquifer transmissivity and elevation were prepared in geographic information system environment this stage was followed by elimination of the exclusionary areas for flood spreading while determining the potentially suitable ones having closely examined the potentially suitable areas using the proposed methodology the land suitability map for flood spreading was produced the ahp and ga were used for ranking all the alternatives and weighting the criteria involved respectively the results of the study showed that most suitable areas for the artificial groundwater recharge are located in quaternary qft2 and qsf geologic units and in morphological units of pediment and alluvial fans with slopes not exceeding 2 finally further evidence for the acceptable efficiency of the integrated ahp ga method in locating most suitable flood spreading areas have been provided by such significant spatial coincidence between the produced map and the control areas located near kowsar research station where the earlier flood spreading projects were successfully performed

mapping 87sr 86sr variations in bedrock and water for large scale provenance studies abstract although variation in 87sr 86sr has been widely pursued as a tracer of provenance in environmental studies forensics archeology and food traceability accurate methods for mapping variations in environmental 87sr 86sr at regional scale are not available in this paper we build upon earlier efforts to model 87sr 86sr in bedrock by developing gis based models for sr isotopes in rock and water that include the combined effects of lithology and time using published data we fit lithology specific model parameters for generalized equations describing the concentration of radiogenic sr in silicate and carbonate rocks the new model explained more than 50 of the observed variance in measured sr isotope values from independent global databases of igneous metaigneous and carbonate rocks but performed more poorly explaining 33 of the variance for sedimentary and metasedimentary rocks in comparison a previously applied model formulation that did not include lithology specific parameters explained only 20 and 8 of the observed variance for igneous and sedimentary rocks respectively and exhibited an inverse relationship with measured carbonate rock values building upon the bedrock model we also developed and applied equations to predict the contribution of different rock types to 87sr 86sr variations in water as a function of their weathering rates and strontium content the resulting water model was compared to data from 68 catchments and shown to give more accurate predictions of stream water 87sr 86sr r2 0 70 than models that did not include lithological weathering parameters we applied these models to produce maps isoscapes predicting 87sr 86sr in bedrock and water across the contiguous usa and compared the mapped sr isotope distributions to data on sr isotope ratios of us marijuana crops although the maps produced here are demonstrably imperfect and leave significant scope for further refinement they provide an enhanced framework for lithology based sr isotope modeling and offer a baseline for provenance studies by constraining the 87sr 86sr in strontium sources at regional scales

dissolution rates of actinolite and chlorite from a whole rock experimental study of metabasalt dissolution from 2 ph 12 at 25 c abstract the dissolution rates of the minerals actinolite and chlorite were determined from metabasalt element release rates measured at 25 c and 2 11 86 mol m 2 s mineral dissolution rates obtained in this study are within the range of corresponding values reported in the literature this observation suggests that the dissolution rates of major constituent minerals in a multi phase rock are not affected by the presence of the other minerals this conclusion validates the common assumption that the dissolution rate of an individual mineral is equal to that of the same mineral in a dissolving multi mineralogic rock at least for major constituents

carbon cycle history through the jurassic cretaceous boundary a new global δ13c stack we present new carbon and oxygen isotope curves from sections in the bakony mts hungary constrained by biostratigraphy and magnetostratigraphy in order to evaluate whether carbon isotopes can provide a tool to help establish and correlate the last system boundary remaining undefined in the phanerozoic as well provide data to better understand the carbon cycle history and environmental drivers during the jurassic cretaceous interval we observe a gentle decrease in carbon isotope values through the late jurassic a pronounced shift to more positive carbon isotope values does not occur until the valanginian corresponding to the weissert event in order to place the newly obtained stable isotope data into a global context we compiled 31 published and stratigraphically constrained carbon isotope records from the pacific tethyan atlantic and boreal realms to produce a new global 13c stack for the late oxfordian through early hauterivian interval our new data from hungary is consistent with the global 13c stack the stack reveals a steady but slow decrease in carbon isotope values until the early valanginian in comparison the late jurassic early cretaceous 13c curve in gts 2012 shows no slope and little variation aside from the well defined valanginian positive excursion chemostratigraphic correlation durschning the jurassic cretaceous boundary interval is difficult due to relatively stable 13c values compounded by a slope which is too slight there is no clear isotopic marker event for the system boundary the long term gradual change towards more negative carbon isotope values through the jurassic cretaceous transition has previously been explained by increasingly oligotrophic condition and lessened primary production however this contradicts the reported increase in 87sr 86sr ratios suggesting intensification of weathering and a decreasing contribution of non radiogenic hydrothermal sr and presumably a concomitant rise in nutrient input into the oceans the concomitant rise of modern phytoplankton groups dinoflagellates and coccolithophores would have also led to increased primary productivity making the negative carbon isotope trend even more notable we suggest that gradual oceanographic changes more effective connections and mixing between the tethys atlantic and pacific oceans would have promoted a shift towards enhanced burial of isotopically heavy carbonate carbon and effective recycling of isotopically light organic matter these processes account for the observed long term trend interrupted only by the weissert event in the valanginian

a new chemical index of weathering for metamorphic silicate rocks in tropical regions a study from sri lanka abstract weathered and fresh samples of metamorphic rocks from sri lanka were collected from various localities and analysed for major elements by xrf method rigaku kg x system japan the content of water was determined by the ignition method the xrf results obtained from these samples form the basis of a new index of chemical weathering particularly for sri lanka which is named the silica titania index and is calculated as follows silica titania index sio 2 tio 2 sio 2 tio 2 al 2 o 3 tio 2 sio 2 al 2 o 3 100 molecular proportions the index can be used to determine the degree of weathering in chemically weathered silicate rocks of other countries in tropical regions a triangular diagram plots the position of this index the point load strengths of fresh rocksand weathered rocks with different degrees of weathering were correlated with the values of this new chemical index the relative variation in strengths of fresh rocks and weathered rocks clearly indicates its suitability and usefulness for engineering geologists

origin of red pelagic carbonates as an interplay of global climate and local basin factors insight from the lower devonian of the prague basin czech republic abstract red pelagic sediments are relatively common in the phanerozoic they are often interpreted as products of sea bottom oxidation during greenhouse climate showing a conspicuous alternation with black shales and thus carrying important palaeoceanographic information the lower devonian pragian carbonate strata of the prague basin czech republic praha formation contain a marked band of red pelagic carbonate up to 15 m thick which can be correlated for several tens of km we investigated seven sections 17 to 255 m thick of the prague basin using the methods of facies analysis outcrop gamma ray logging diffuse reflectance spectroscopy optical microscopy element geochemistry magneto mineralogy and electron microprobe analysis the aim was to find the mineral carriers of the red colour investigate the stratigraphic context of the red carbonates and evaluate the local and global prerequisites for their formation the red pigmentation represents enrichment by hematite with respect to goethite approximately 31 of the total reflectance falling in the red colour band represents a threshold for red coloration the red pigmentation is carried by submicronic hematite dispersed in argillaceous pelagic calcilutite and or inside skeletal allochems gamma ray log correlation indicates that the red carbonate band developed in stratigraphic levels with low sedimentation rates typically from 1 to 7 1 mm kyr which are comparable to the mesozoic rosso ammonitico facies the red beds and the whole praha formation pragian to early emsian are characterized by low toc values

characterization of mineral surfaces using fib and tem a case study of naturally weathered alkali feldspars using a focused ion beam fib instrument electron transparent samples termed foils have been cut from the naturally weathered surfaces of perthitic alkali feldspars recovered from soils overlying the shap granite northwest england characterization of these foils by transmission electron microscopy tem has enabled determination of the crystallinity and chemical composition of near surface regions of the feldspar and an assessment of the influence of intragranular microtextures on the microtopography of grain surfaces and development of etch pits damage accompanying implantation of the 30 kv ga ions used for imaging and deposition of protective platinum prior to ion milling creates amorphous layers beneath outer grain surfaces but can be overcome by coating grains with 85 nm of gold before fib work the sidewalls of the foil and feldspar surrounding original voids are also partially amorphized during later stages of ion milling no evidence was found for the presence of amorphous or crystalline weathering products or amorphous leached layers immediately beneath outer grain surfaces the absence of a leached layer indicates that chemical weathering of feldspar in the shap soils is stoichiometric or if non stoichiometric either the layer is too thin to resolve by the tem techniques used i e similar to 2 5 nm or an insufficient proportion of ions have been leached from near surface regions so that feldspar crystallinity is maintained no evidence was found for any difference in the mechanisms of weathering where a microbial filament rests on the feldspar surface sub micrometer sized steps on the grain surface have formed where subgrains and exsolution lamellae have influenced the propagation of fractures during physical weathering whereas finer scale corrugations form due to compositional or strain related differences in dissolution rates of albite platelets and enclosing tweed orthoclase with progressive weathering etch pits that initiated at the grain surface extend into grain interiors as etch tubes by exploiting preexisting networks of nanopores that formed during the igneous history of the grain the combination of fib and tem techniques is an especially powerful way of exploring mechanisms of weathering within the internal zone beneath outer grain surfaces but results must be interpreted with caution owing to the ease with which artifacts can be created by the high energy ion and electron beams used in the preparation and characterization of the foils

bridging the gap between laboratory measurements and field estimations of silicate weathering using simple calculations weathering rates of silicate minerals observed in the laboratory are in general up to five orders of magnitude higher than those inferred from field studies simple calculations show that even if the field conditions were fully simulated in standard laboratory experiments it would be impossible to measure the slow rates of mineral dissolution that are observed in the field as it is not possible to measure the dissolution rates under typical field conditions one should extrapolate the available data to the field conditions to do this a rate law for the dissolution of plagioclase in the field was formulated by combining the far from equilibrium dissolution rate of weathered natural oligoclase at 25 c with the effect of deviation from equilibrium on dissolution rate of fresh albite at 80 c in contrast to the common view that laboratory experiments predict dissolution rates that are faster than those in the field the simulation based on this rate law indicates that laboratory dissolution experiments actually predict slower rates than those observed in the field this discrepancy is explained by the effect of precipitation of secondary minerals on the degree of saturation of the primary minerals and therefore on their dissolution rate indeed adding kaolinite precipitation to the simulation significantly enhances the dissolution rate of the plagioclase moreover a strong coupling between oligoclase dissolution and kaolinite precipitation was observed in the simulation we suggest that such a coupling must exist in the field as well therefore any attempt to predict the dissolution rate in the field requires knowledge of the rate of the secondary mineral precipitation

subsidence and sedimentation on jurassic passive continental margin southern alps italy the southern alps of italy preserve a tectonically intact array of jurassic facies that record the evolution of a part of the margin of the apulian plate from its ancestral beginnings in a complex of permian and triassic rifted continental basins through the initial stages of breakup and stepwise foundering of a carbonate platform breakup was accompanied first by the rapid accumulation of thick prisms of carbonate turbidites in newly formed fault troughs then as the new ligurian oceanic basin began to open farther west and as subsidence gradually slowed accumulation of a succession of slowly deposited biogenous pelagic sediments recorded not only the increasing depths of the seafloor but also fluctuations in oceanographic conditions of fertility carbonate dissolutio levels and the strength of bottom currents estimates of the history of seafloor depths based on a simple subsidence law of the form subsidence k age 12 provide a basis for the construction of a set of curves showing the changing depths of significant carbonate dissolution surfaces during the jurassic in this region the rapid 1 km deepening of the compensation depth for calcite during the late jurassic may be due to a change in regional oceanic vertical circulation patterns from upwelling fertile silica rich carbonate dissolving to downwelling less fertile silica poor carbonate preserving

the barremian and aptian stepwise development of the oceanic anoxic event 1a oae 1a crisis integrated benthic and planktic high resolution palaeoecology along the gorgo a cerbara stratotype section umbria marche basin italy abstract the barremian and aptian were times of global plate reconfiguration and profound changes in the ocean climate system culminating in the worldwide deposition of lower aptian black shale layers oae 1a based on high resolution lithostratigraphic and micropaleontological analyses precursor conditions and timing of the anoxia are here reconstructed along a 33 06 m thick section in the proposed barremian aptian boundary gssp stratotype at gorgo a cerbara umbria marche basin italy a non uniform history of benthic foraminiferal diversification is interrupted by the selli level oae 1a and by three turnover points for both benthic and planktic organisms each highlighted by prominent breaks in lithology and outcrop morphology the first two points at 1 1 myr and 20 50 kyr prior to the onset of the oae 1a correspond respectively to the nannoconid bathypelagic calcareous nannofossils decline and crisis events and separate a pelagic limestone chert claystone lithological cycles of the uppermost maiolica formation showing frequencies reminiscent of orbital eccentricity and containing an oligotrophic barremian benthic and planktic assemblage dominated by k selected nannoconids and rhizammina b greenish grey cherty marls of the lowermost marne a fucoidi formation associated to declining sedimentation rates and eutrophic early aptian assemblages dominated by radiolarians and lituolid benthic foraminifera and c anoxic radiolarites and shales of the carbonate free selli level high magnitude and frequency assemblage fluctuations occur between the nannoconid crisis 25 cm below the lowermost oae 1a black shale layer and the selli level base with suggestions of bottom water acidification at 800 kyr after the oae 1a end a third turnover point in the basal reddish member of the marne a fucoidi highlights middle aptian assemblages characterized by a bloom of early macroperforate planktic foraminifera hedbergella spp and appearances of new benthic species marking a shift towards better oxygenation oae 1a oxygen and pelagic carbonate factory crises are here suggested to have been step wise and linked to global warming conditions

orbital tuning of a lower cretaceous composite record maiolica formation central italy 1 a high resolution pelagic bulk carbonate stable isotope record from a central tethyan lower cretaceous composite section is presented three well exposed sedimentary sequences chiaserna monte acuto bosso and gorgo a cerbara sections central italy cropping out throughout the maiolica formation were correlated by a detailed magnetostratigraphy lithostratigraphy and calcareous plankton biostratigraphy in order to reconstruct a continuous composite record from the middle berriasian to the lower aptian the integrated stratigraphy of the three sequences provided an accurate time framework for the new high resolution c isotope curve which is presented in this study the composite 13c signal recorded in the depth domain was analyzed by combined lomb scargle periodogram and weighted wavelet z transform wwz weighted wavelet amplitudes wwa foster wavelet spectral methodologies both appropriate for unevenly sampled curves these tools allowed us to unravel the main frequencies modulating the record and their hypothetical shift in depth respectively the long term 400 000 and 2 400 000 years eccentricity cycles were consistently recorded throughout all the composite record once band pass filtered in these two periodicity bands and compared to the lithologic pattern cycles identified throughout the composite sequence the 13c signal was used as a valuable proxy record for a reliable construction of an orbital tuning of the early cretaceous an estimated age for all the different stratigraphic events recognized throughout the composite record was reported in particular the reestimated ages of the paleomagnetic chrons documented in the upper part of the record show differences with those reported by gradstein et al 2004 up to 2 m y the valanginian carbon shift present in the middle part of the composite sequence was estimated to be 2 3 m y long the good agreement between the estimated age of the base of this positive carbon isotope excursion 136 34 m y and the predominant volcanic phase associated to the parana etendeka large igneous province intrusion confirmed a possible cause effect link between the two events

nannofossil carbonate fluxes during the early cretaceous phytoplankton response to nutrification episodes atmospheric co2 and anoxia 1 greenhouse episodes during the valanginian and aptian correlate with major perturbations in the c cycle and in marine ecosystems carbonate crises and widespread deposition of corg rich black shales quantitative analyses of nannofossil micrite were conducted on continuous pelagic sections from the southern alps northern italy where high resolution integrated stratigraphy allows precise dating of early cretaceous geological events rock forming calcareous nannofloras were quantified in smear slides and thin sections to obtain relative and absolute abundances and paleofluxes that are interpreted as the response of calcareous phytoplankton to global changes in the ocean atmosphere system increased rates of volcanism during the formation of ontong java and manihiki plateaus and the parana etendeka large igneous province lip are proposed to have caused the geological responses associated with early aptian oceanic anoxic event oae 1a and the valanginian event respectively calcareous nannofloras reacted to the new conditions of higher pco2 and fertility by drastically reducing calcification the valanginian event is marked by a 65 reduction in nannofossil paleofluxes that would correspond to a 2 3 times increase in pco2 during formation of the parana endenteka lip a 90 reduction in nannofossil paleofluxes which occurred in a 1 5 myr long interval leading into oae1a is interpreted as the result of a 3 6 times increase in pco2 produced by emplacement of the giant ontong java and manihiki plateaus high pco2 was balanced back by an accelerated biological pump during the valanginian episode but not during oae1a suggesting persisting high levels of pco2 in the late aptian and or the inability of calcareous phytoplankton to absorb excess pco2 above threshold values

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

single crystal plagioclase feldspar dissolution rates measured by vertical scanning interferometry here we introduce a technique for simultaneous measurement of surface normal retreat rates of specific cleavage faces by vertical scanning interferometry and the bulk dissolution rate of a mineral powder a hydrothermal reactor is used to contain both a well characterized powder and oriented single crystals with a masked reference surface at elevated temperatures we show examples using both anorthite and albite reacted at temperatures between 150 and 200 c in the case of albite dissolution rates of fine grained powders are substantially enhanced compared to those prevailing on large single crystal cleavage surfaces rates developed on the 010 albite cleavage surface are also substantially faster than those on the 001 face where etch pit development was relatively modest and surface normal retreat was not detectable within the time frame of the experiment the reasons for this difference are not immediately clear but may be related to anisotropy in the distribution of al o si vs si o si bonds in the albite structure 010 twinning expressed on the 001 surface and possible disruption of kink propagation across the twin plane

calcareous nannofossils and mesozoic oceanic anoxic events abstract twenty five years ago mesozoic oceanic anoxic events oaes were documented and formalised as intervals of widespread to global deposition of organic matter the toarcian early aptian oae1a and latest cenomanian oae2 oaes are truly global in nature commonly carbonate poor and typically represented by organic carbon rich black shales in some areas these oaes are also characterised by abundant radiolarian sands and silts they are associated with negative and positive excursions in the 87sr 86sr record in addition to large global carbon isotope anomalies in carbonate and or organic matter caused by a major perturbation of the global carbon budget increased rates of volcanism during the formation of the ontong java and manihiki and caribbean plates and the karoo ferrar traps are believed to have caused the geological responses associated with oae1a oae2 and the toarcian oae respectively excess volcanogenic co2 in the atmosphere most probably turned the climate into a greenhouse mode accelerating continental weathering and increasing nutrient content in oceanic surface waters via river run off higher fertility in the global ocean was also probably triggered directly by submarine igneous events that introduced enormous quantities of biolimiting metals within hydrothermal plumes because mesozoic oaes are often represented by carbonate poor sediments quantitative studies of calcareous nannofossils have been applied to explore a the causes and effects of igneous tectonic events and climate changes relative to nannofloral increases and crises as well as b dissolution events and c diagenetic modifications characterization of calcareous nannofloras in oae intervals can improve our understanding of the marine ecosystem and biological processes such as photosynthesis biological pump and biomineralisation carbonate pump that affect the organic and inorganic carbon cycle as well as adsorption of atmospheric co2 in the oceans types and rates of nannoplankton production and evolution are interpreted to trace the impact of major palaeoceanographic and palaeoclimatic events in selected sections it has been documented that calcareous nannofloras rapidly reacted to new conditions of fertility and higher pco2 by drastically reducing calcification as in the modern oceans during oaes the increase of nutrients and atmospheric co2 induced higher abundances of nannoplankton producing small placoliths and inhibited the deep photic zone nannoconids and schizosphaerellids similarly to the nannoconid crisis preceding deposition of the early aptian oae1a black shales a schizosphaerellid crisis is detected prior to the toarcian oae both oaes are further characterised by a rapid nannofloral speciation beginning approximately 1 5 myr before the oae but without extinctions global changes during the latest cenomanian oae 2 exerted different influences on calcareous nannoplankton that experienced a turnover due to most extreme environmental conditions this event in fact was a time of extinctions followed by originations within calcareous nannofossils precise timing of the events before during and after oae1a oae2 and the toarcian oae indicates that they were intervals of enhanced oceanic productivity and that anoxia dysoxia post dated biotic changes

paleoenvironmental changes during the valanginian new insights from variations in phosphorus contents and bulk and clay mineralogies in the western tethys paleoenvironmental and paleoclimatic changes during the valanginian carbon isotopic excursion cie have been investigated in the western tethys for this purpose bulk rock and clay mineralogies as well as phosphorus p contents were evaluated in a selection of five sections located in the vocontian basin angles se france alvier e switzerland malleval e france and the lombardian basin capriolo n italy breggia s switzerland within the cie interval bulk rock and clay mineralogies are inferred to reflect mostly climate change the onset of the cie busnardoites campylotoxus ammonite zone is characterized by higher detrital index di sum of the detrital minerals divided by calcite contents values and the presence of kaolinite in their clay mineral assemblages in the late valanginian from the saynoceras verrucosum zone up to the end of the valanginian the samples show relatively variable di and lower values or the absence of kaolinite the variation in the mineralogical composition is interpreted as reflecting a change from a climate characterized by optimal weathering conditions associated with an increase in terrigenous input on the southern european margin during the cie towards an overall unstable climate associated with drier conditions in the late valanginian this is contrasted by a dissymmetry proximal vs distal along the studied transect the northern tethyan margin being more sensitive to changes in continental input compared to the distal environments p accumulation rates par present similar features in the vocontian basin p content variations are associated with changes in terrigenous influx whereas in the lombardian basin i e capriolo and breggia par values are less well correlated this is mainly because the deeper part of the tethys was less sensitive to changes in continental inputs the onset of the cie top of the b campylotoxus zone records a general increase in par suggesting an increase in marine nutrient levels this is linked to higher continental weathering rates and the enhanced influx of nutrients into the ocean in the period corresponding to the shift itself p contents show a dissymmetry between the vocontian and lombardian basins proximal vs distal for the sections of malleval alvier and angles a decrease in p concentrations associated to a decrease in detrital input is observed in capriolo and breggia par show maximum values during the plateau indicating a more complex interaction between different p sources the time interval including the top of s verrucosum zone up to the end of the valanginian is characterized by variable par values suggesting variable nutrient influxes these changes are in agreement with an evolution towards seasonally contrasted conditions in the late valanginian

al si order in albite and its effect on albite dissolution processes a monte carlo study the role of al si disorder in the kinetics of albite dissolution is explored through parameterized monte carlo methods two dissolution mechanisms multilayer leaching and single layer retreat were tested on 48 albite test configurations in simulations involving multilayer leaching dissolution rates increased with decreasing long range order lro we observed a fivefold maximum increase in dissolution rate tied to al si disordering roughly equivalent to that accompanying a decrease of 1 4 ph units at ph 1 5 this increase in rate due to disordering in albite is similar to that observed from compositional variation in plagioclase feldspars an47 vs an at low ph in contrast al si disordering had no discernible effect during the simulations involving the single layer retreat mechanism these results suggest that the effect of al si disorder on albite dissolution rate is mechanism dependent

evidence for a complex valanginian nannoconid decline in the vocontian basin south east france the early cretaceous is punctuated by widespread biocalcification crises these are characterized by decrease in the carbonate platform growth and in the pelagic realm by a decline in nannoconus relative abundance in the calcareous nannofossil assemblages the valanginian nannoconus decline started before the positive 13c excursion characterizing the weissert event the nannoconid decline is investigated in two sections of the vocontian basin la charce and vergol which are biostratigraphically well constrained and contain wellpreserved calcareous nannofossils absolute and relative abundances of nannoconus show a polyphased decline with a first decrease in the interval from the campylotoxus to the verrucosum ammonite subzones before the positive 13c shift and a second decrease from the end of the peregrinus to the base of the radiatus ammonite zones concomitant with the long term decrease in 13c these two declines are separated by an important increase in the nannoconus abundance from the verrucosum to the peregrinus ammonite subzones concomitant with a slight short term decrease of 13c biometric analysis shows size changes of n steinmannii and n kamptneri along the nannoconid decline the patterns of abundances and size changes seem to be related to paleoenvironmental changes mainly characterized by a temperature decrease and variable nutrient supply the described valanginian nannoconid recovery seems to occur during the most intense phase of the cooling event and is recorded in the vocontian basin as well as in the atlantic and tethys oceans these spatial correlations suggest a supra regional character for the valanginian nannoconid recovery event best recorded in the vocontian basin and at low latitudes

magnetostratigraphic calibration of the late valanginian carbon isotope event in pelagic limestones from northern italy and switzerland abstract magnetostratigraphic biostratigraphic and carbon isotope data are presented from five lower cretaceous pelagic limestone sections in the southern alps a positive carbon isotope event is recorded in bulk carbonate from the upper valanginian of all five sections and the magnetostratigraphy and biostratigraphy provide the age model the record of the isotope event in absolute time is closely replicated in all five sections as the sections are located in two paleogeographic basins and are separated by up to 300 km the synchronous isotope event cannot be interpreted as an artifact of diagenesis a reduction in magnetization intensity coincident with the 13 c peak may be due to diagenetic magnetite dissolution enhanced by increased organic carbon burial according to the age model which uses gts89 timescale 1 background 13 c values of 1 5 are recorded from 145 to 137 ma between 137 and 136 ma 13 c increases to a maximum value of about 3 values begin to decrease from 136 ma and reach background values at about 132 ma the rate of change of 13 c for the onset of the event about 1 5 m y is greater than for the decay about 0 5 m y suggesting an abrupt perturbation of the carbon system from equilibrium followed by a more gradual return to background values

the influence of regional factors in the expression of oceanic anoxic event 1a oae1a in the semi restricted organya basin south central pyrenees spain abstract the global occurrence of oxygen deprived conditions in the ocean characterizes the early aptian hence the hallmark of that time interval is the accumulation of organic rich sediments during an episode of severe oxygen deficiency known as oceanic anoxic event 1a oae1a as seen elsewhere in the tethyan domain an overall change in facies marked by increased input of terrigenous material distinguishes the lower aptian in the study area but the nature of the lithologies associated with the organic carbon rich deposits remain dominated by carbonate sediments and are expressed differently with respect to other areas where the occurrence of black shales characterizes oae1a this comparison indicates that significant spatial heterogeneity occurred in sub tethyan basins coeval with the global oceanic event the present work provides a high resolution multi proxy study petrography total inorganic carbon tic total organic carbon toc carbon isotope 13corg clay mineralogy and biomarkers of the upper 155 m of the el pui section organya basin including the record of oae1a the results reveal that oxygenic conditions fluctuated throughout the studied interval with episodes of oxygen depletion that concurred with toc values 1 however petrographic observations molecular biomarkers and redox sensitive trace elements rstes indicate that full anoxia was not achieved the results also provide the first high resolution 13corg profile for the el pui section that replicates in greater detail the carbon isotopic signature reported for the tethyan domain the upper 155 m of the el pui section include expanded and well defined trends of the carbon isotope segments c2 upper part c3 c4 c5 and c6 partial which correlate with other tethyan sections and allow for the recognition of the lower aptian oae1a in the uppermost 40 m of the section such improved high resolution chemostratigraphic curve could contribute to a more precise chronostratigraphic correlation of aptian events in a broader scale

calcareous nannofossil response to the weissert episode early cretaceous implications for palaeoecological and palaeoceanographic reconstructions abstract the causal link between changes in calcareous nannofossil abundances their size and the palaeoenvironmental conditions in the tethyan realm across the valanginian weissert episode was examined through high resolution quantitative analyses of the genera nannoconus and micrantholithus from the angles section vocontian basin se france a set of published mineralogical micropalaeontological and geochemical data from numerous european localities including nannofossil data from italy france and romania and from the atlantic and pacific oceans allows us to propose a coherent palaeoecological and palaeoceanographic model and to discuss the possible forcing factors behind the palaeoenvironmental changes that occurred during the valanginian in the vocontian basin the genus nannoconus appears to be particularly sensitive to global fertility conditions and local continental input while micrantholithus is clearly associated with salinity levels during the first phase of the weissert episode a global increase in nutrients together with a breakdown of the upper water column stratification explains the nannoconid decline elevated freshwater fluxes into the vocontian basin under warmer and more humid conditions account for pentalith decreases low resolution data on pco 2 and ocean ca 2 concentrations cannot highlight large magnitude rapid fluctuations in pco 2 and oceanic ca 2 if they exist however relatively low pco 2 levels and high oceanic ca 2 concentrations probably helped the recovery of nannoconus and micrantholithus from the aftermath of the weissert episode to the early hauterivian the long term changes observed in the valanginian nannolith distribution are consistent with increased hydrothermal activity that influenced fertility levels low to mid latitudinal monsoonal circulation probably contributed to their short term changes by the way of rapid changes in the chemical weathering pattern that triggered significant fluctuations in turbidity fertility and salinity conditions

magnetostratigraphy nannofossil stratigraphy and apparent polar wander for adria africa in the jurassic cretaceous boundary interval article i nfo existing correlations of early cretaceous nannofossil events to polarity zones in italian pelagic limestones are the basis for correlation of polarity chrons to geologic stages and hence calibration of the early cretaceous geomagnetic polarity timescale here we present correlations of nannofossil events to polarity chrons for the late jurassic and jurassic cretaceous boundary interval from the southern alps making the case for revisions of current geologic timescales in this interval the jurassic cretaceous and kimmeridgian tithonian boundaries can be usefully defined at the onsets of polarity chrons cm18r and cm22r respectively the oxfordian kimmeridgian boundary can be assigned to cm25 an apparent polar wander path apwp for the southern alps derived from and time calibrated by bio magnetostratigraphic data is similar to and provides a proxy for the african apwp in the absence of adequate african data of this age the southern alpine apwp is characterized by a cusp hairpin at 30 n 270 e at a time close to the oxfordian kimmeridgian boundary polarity chron cm25 154 ma rapid apwp from high latitude n60 n in the preceding middle jurassic bajocian oxfordian interval coincident with the onset of central atlantic ligurian oceanic rifting and a return to high latitudes during the cretaceous early jurassic poles at high latitudes n60 n are evident for sinemurian to toarcian aalenian time 175 195 ma an apwp for this time interval with this level of temporal calibration cannot be constructed using data from africa itself or from other atlantic bordering continents by rotation to african coordinates

experimental determination of plagioclase dissolution rates as a function of its composition and ph at 22 c abstract the steady state far from equilibrium dissolution rates of nine distinct plagioclases ranging in composition from an2 to an89 were measured in mixed flow reactors at 22 2 c and ph from 2 to 11 the dissolution rates of all plagioclases based on silica release show a common u shaped behaviour as a function of ph where rates decrease with increasing ph at acid condition but rise with increasing ph at alkaline conditions consistent with literature findings constant ph plagioclase dissolution rates increase with increasing anorthite content at acidic conditions measured anorthite dissolution rates are 2 5 orders of magnitude faster than those of albite at ph 2 perhaps more significantly rates are independent of plagioclase composition at alkaline conditions interpretation and data fitting suggests that plagioclase dissolution rates are consistent with their control by the detachment of si rich activated complexes formed by the removal of al from the mineral framework taking account of this mechanism and transition state theory yields equations describing plagioclase dissolution rates r as a function of both the mineral and aqueous fluid compositions found in natural earth surface systems for ph 6 rates are consistent with log r mol cm 2 s 0 35 log a h 3 a al 3 11 53 and for ph log r mol cm 2 s n acid log a h 3 a al 3 0 033 an 14 77 where an represents the percent anorthite in the plagioclase solid solution ai corresponds to the activity of the ith aqueous species and nacid is given by n acid 0 004 an 0 05

biostratigraphic correlation of mesozoic polarity chrons cm1 to cm23 at capriolo and xausa southern alps italy abstract two pelagic limestone sections in the southern alps spanning the kimmeridgian late jurassic to barremian early cretaceous interval yield magnetostratigraphies which can be correlated to oceanic magnetic anomalies m1 m3 and m8 m23 this includes the interval m11 m13 which has not previously been correlated to a sedimentary section detailed investigations of nanofossils and calpionellids in these sequences allow precise correlation of polarity chrons to biostratigraphic events and these results compare favorably to those of previous studies the close correspondence in polarity pattern between that interpreted from the m8 to m15 interval in the hawaiian lineations and that recorded at the capriolo section suggests that sedimentation rates in this sequence and spreading rates in the hawaiian lineations were rather constant during this interval in contrast the sedimentation rate at the xausa section appears to increase up section with the facies transition from the rosso ammonitico to the maiolica formation

timing of canyon fed turbidite deposition in a rifted basin the early cretaceous turbidite complex of the cerrajon formation subbetic southern spain abstract the subbetic cerrajon formation of latest hauterivian earliest late albian age is made up of turbidite sandstones and calcarenites intercalated in marly limestones and marls it can be defined as a turbidite complex with three distinct intervals where turbidites are recorded latest hauterivian barremian p p late aptian p p and middle to middle late albian age the distribution of four biochronostratigraphic units of these ages throughout the studied outcrops is shown the main hiatuses latest barremian early late aptian and latest aptian early late albian mainly the latter have been identified in many other outcrops of the southern tethys and are related to tectonics and associated palaeogeographic and palaeoceanographic changes platform environments as the source area of the clastics the feeding submarine canyon base of slope channels and related basinal lobes or sheet systems have been identified and can be traced laterally along more than 80 km of discontinuous outcrops aligned in a downcurrent direction the system could have extended more than 150 km in length the mean palaeocurrent direction fits well with the present alignment of the outcrops and after corrections for tectonics rotation with the current palaeogeographic model of the southern iberian continental palaeomargin sicp this conclusion largely supports previous interpretations of a longitudinal pattern for the distribution of clastics during the cretaceous in that part of the sicp the ages of the main cretaceous events deduced from the study of the cerrajon formation correlate quite well with the sequence sets and subsidence history of the prebetic zone where the cretaceous platform environments adjacent to the turbidite basin are recorded moreover the main unconformities dated such as the onset and the end of turbidite sedimentation show good correlation with the sequence boundaries described for the european basins the analysis in time and space of the turbidite distribution and its correlation with the prebetic carbonate platforms enables us to outline some interesting conclusion that might be a suitable subject for future research

the impact of calcareous nannofossils on the pelagic carbonate accumulation across the jurassic cretaceous boundary abstract calcareous nannofossils were important producers of pelagic carbonates in mesozoic oceans in order to better understand the origin of mesozoic pelagic carbonates we studied upper jurassic to lower cretaceous sediments in the central atlantic ocean dsdp sites 105 367 534a with respect to their content of calcareous nannofossils the interval under investigation is characterized by a significant increase in the deposition of carbonate rich sediments a trend that goes along with the rapid radiation of calcareous nannofossils the assemblage composition and the size variation of common taxa were analyzed and subsequently the contribution of this phytoplankton group to the pelagic carbonate accumulation was calculated results reveal two long term changes of the nannofossil assemblage composition 1 the early tithonian coccolith assemblages are of low diversity watznaueria spp cyclagelosphaera spp zeugrhabdotus spp whilst the mid to late tithonian assemblage is dominated by nannoliths conusphaera mexicana polycostella beckmannii nannoconus spp and large sized watznaueria 2 the early berriasian is characterized by a shift from the late tithonian nannolith rich assemblage to a highly diverse coccolith assemblage morphometric studies of the placolith genus watznaueria show for all three dsdp sites large sized forms of this genus in the mid and late tithonian followed by a decrease of up to 2 m for the mean size in the earliest berriasian at dsdp site 105 the studied nannolith taxa show an increase in size during the mid tithonian to berriasian interval the records of both nannofossil carbonate estimates and the measured bulk rock carbonate reveal two periods of increase in the nannofossil carbonate record of dsdp site 105 a first significant increase of the carbonate accumulation is observed in the mid and late tithonian probably caused by mass occurrences of strongly calcified taxa c mexicana p beckmannii nannoconus spp watznaueria cf manivitae this interval is here named nannofossil calcification event nce the second carbonate maximum in the late berriasian is related to a rise in absolute abundances of nannofossils this peak is amplified by an overall increase of the sedimentation rate the calculated accumulation rates of nannofossils nannofossil carbonate and bulk rock carbonate for the late berriasian are on the same scale as values from recent ocean surface sediments a comparison of nannofossil carbonate values with the bulk rock carbonate content shows that on average only 27 of the total carbonate can be explained by our nannofossil carbonate estimates this discrepancy is most likely caused by the high amount of unidentifiable micrite and fragments of calcareous nannofossils other factors contributing to the error are possible inaccuracies in the determination of absolute abundances and nannofossil volume calculations the nce occurs during a long term sea level fall dry climate and presumed low pco 2 levels a decline in abundance of strongly calcified nannofossils coincides with the opening of the pacific atlantic seaway via central america which may have had a substantial impact on the palaeoceanographic situation in the central atlantic ocean these changes are here considered to have at least partly caused the shifts in abundance size and assemblage composition of calcareous nannofossils observed across the jurassic cretaceous boundary interval

early cretaceous magnetic stratigraphy in the apticore drill core and adjacent outcrop at cismon southern alps italy and correlation to the proposed barremian aptian boundary stratotype lower cretaceous mainly white and or gray pelagic cherty limestones have been sampled in the apticore drill core and in the adjacent outcrop at cismon southern alps italy magnetic polarity stratigraphy of the drill core indicates that the top of the section is in the cretaceous long normal polarity interval 26 m above the reverse polarity zone correlative to polarity chron cm0 the base of the drilled section at a stratigraphic depth of 116 71 m is in a reverse polarity zone correlative to cm9 the coeval stratigraphic interval has been sampled in the adjacent outcrop in order to tie the drill core record to the outcrop the correlation of polarity zones to polarity chrons is aided by the known correlation of nannofossil events to polarity chrons in other italian land sections new magnetostratigraphic sampling of the proposed barremian aptian boundary stratotype section at gorgo a cerbara umbria italy improves the definition of cm0 in this section and facilitates correlation to cismon revised nannofossil biostratigraphy based on quantitative analyses greatly increases the stratigraphic resolution of the barremian aptian boundary interval both at the proposed boundary stratotype gorgo a cerbara and at cismon

sedimentation in the tethyan pelagic realm during the cenomanian monotonous settling or active redistribution sea bottom processes of the pelagic realm are still not completely understood and represent an intriguing subject this paper focuses on the relationships between normal settling processes redistribution of sediments and oceanographic parameters in a pelagic setting during the cenomanian five key tethyian localities in the cenomanian umbria marche and belluno basins have been studied in order to understand the interplay among sea bottom processes that acted on the sea floor the dataset consists of the mm scale sedimentological description of the sections complemented by microfacies analysis on selected samples different sedimentological indications such as presence of intraclasts lined forams pervasive plane parallel lamination suggest a continuous reworking under action of bottom currents with varying intensity and direction all the identified facies are here illustrated in detail and organized in a comprehensive schematic facies framework the facies matrix that leads to recognize two depositional facies suites the settling dominated and the traction current dominated under different oxygenation conditions our results suggest that settling of biogenic and inorganic particles represents the main source of pelagic sediments but not the unique depositional process under the action of sea bottom currents of different intensity sediments are continuously redistributed on the sea floor all the collected evidences contribute to the proposal of a comprehensive depositional model for these reworked and redistributed fine grained sediments that represent true calcareous pelagic contourites the model suggests that the identified traction related facies can be used as a proxy for bottom current intensity and indirectly as an indicator of changing ventilation regimes at the sea floor through time

calcareous nannofossils of the barremian aptian interval from the southeastern tethys zagros basin west iran and their paleoceanographic implications a record of oceanic anoxic event 1a abstract calcareous nannofossils and stable isotope data 13ccarb from a pelagic section of the zagros basin west iran were used for an integrated oceanographic analysis of the barremian aptian interval the study aims at analyzing various oceanographic shifts recorded from this period including the oceanic anoxic event 1a oae 1a in an expanded carbonate rich mudstone sequence of the eastern tethys the extreme thickness 510 m of the succession allows us to study the environmental changes known from the barremian and aptian interval in much more detail than previously done by looking at closely spaced samples it is possible to better understand the onset the course and the aftermath of the oae 1a event calcareous nannofossils suggest an early barremian nannofossil zone cc5 nc5c to late aptian age nannofossil zone cc7b nc7b for the studied sequence the biostratigraphic zonation is based on the last occurrence of calcicalathina oblongata the first occurrences of rucinolithus irregularis and eprolithus floralis and the last occurrence of micrantholithus hoschulzii a total of 98 species has been encountered in the studied interval with good to moderate in few cases poor preservation based on the calcareous nannofossil assemblages signals for a warming event in the mid barremian are characterized by high relative abundances of warm water specie e g rhagodiscus asper along with neritic taxa micrantholithus spp nannoconus spp the oae 1a was identified via calcareous nannofossil biostratigraphy in combination with the 13ccarb record for the oae 1a early aptian warm and eutroph conditions were likely as suggested by high relative abundances of r asper diazomatolithus lehmanii small zeugrhabdotus spp and lithraphidites carniolensis the late aptian is characterized by cool surface water conditions

theoretical approach to evaluating plagioclase dissolution mechanisms abstract the more rapid dissolution of ca rich feldspars relative to na k rich feldspars has been attributed to the preferential leaching of al deep within the feldspar structure evidence from surface microanalysis e g hellmann et al 2003 however shows that preferential dissolution of al is confined to the top layers of the feldspar lattice and that the amorphous surface layer most likely results from precipitation versus dissolution it is thus critical to examine the extent of preferential al removal here we present a theoretical study of plagioclase dissolution behavior using parameterized monte carlo simulations two different dissolution mechanisms a mechanism involving preferential leaching of al and an interfacial dissolution reprecipitation mechanism are tested using compositions representing the entire plagioclase solid solution series our modeling results indicate that under the control of the preferential al leaching mechanism the influence of al si disorder on the dissolution rate is significant at a fixed composition an increase in the degree of al si disorder yields an increased dissolution rate with an 8 fold increase in dissolution rate observed for highly disordered albite an 0 compared to low albite increasing anorthite content tends to decrease the variation in the dissolution rate due to disorder the difference in the dissolution rate of 293 tested oligoclase configurations with a composition of an 20 is 3 fold and the difference is reduced to 2 fold among 107 andesine configurations of an 30 furthermore feldspar configurations with completely disordered al si distributions yield a consistent log linear dependence of dissolution rate on the anorthite content an while other feldspar configurations with modest degrees of al si disorder exhibit rates less than this trend in contrast when al removal is confined to the top surface layers a variety of feldspar configurations with different al si disorder but a single fixed composition have similar dissolution rates and the dissolution rate of ca rich feldspars departs positively from its log linear relationship with anorthite content this departure occurs around an 80 and is in good agreement with previous experimental studies subsequent modeling results of aluminum inhibition g dependence and formation of altered surface layers in the framework of the interfacial dissolution reprecipitation mechanism are all comparable with experimental investigations and these results suggest that an interfacial dissolution reprecipitation mechanism governs the dissolution of plagioclase feldspars

organic facies variations in the valanginian mid hauterivian interval of the agrio formation chos malal area neuquen argentina local significance and global context

size scales over which ordinary chondrites and their parent asteroids are homogeneous in oxidation state and oxygen isotopic composition abstract literature data demonstrate that on a global asteroid wide scale plausibly on the order of 100 km ordinary chondrites oc have heterogeneous oxidation states and o isotopic compositions represented respectively by the mean olivine fa and bulk 17 o compositions of equilibrated samples samples analyzed here include a two h5 chondrite antarctic finds alha79046 and til 82415 that have the same cosmic ray exposure age 7 6 ma and were probably within 1 km of each other when they were excavated from the h chondrite parent body b different individual stones from the holbrook l ll6 fall that were probably within 1 m of each other when their parent meteoroid penetrated the earth s atmosphere and c drill cores from a large slab of the estacado h6 find located within a few tens of centimeters of each other our results indicate that oc are heterogeneous in their bulk oxidation state and o isotopic composition on 100 km size scales but homogeneous on meter decimeter and centimeter size scales on kilometer size scales oxidation state is heterogeneous but o isotopes appear to be homogeneous the asteroid wide heterogeneity in oxidation state and o isotopic composition was inherited from the solar nebula the homogeneity on small size scales was probably caused in part by fluid assisted metamorphism and mainly by impact gardening processes which are most effective at mixing target materials on scales of 1 m

the valanginian carbon isotope event a first episode of greenhouse climate conditions during the cretaceous lower cretaceous pelagic carbonates outcropping along the southern alps of northern italy provide a record of tethyan palaeoceanography as well as of low frequency fluctuations in the global carbon cycle the carbonate c isotope stratigraphy established at five selected localities in the southern alps allows an accurate picture to be drawn of the duration and amplitude of the valanginian c isotope event 13c values near 1 25 1 50 determined in berriasian and lower valanginian sediments are replaced by more pdsitive 13c values near 3 in the late valanginian the carbonate c isotope excursion ends in the early hauterivian with values fluctuating between 1 5 and 2 the carbonate c isotope excursion is accompanied by a positive excursion in the total organic carbon c isotope curve the valanginian c isotope excursion identified in tethyan sediments correlates with a c isotope excursion recorded in the western north atlantic in the gulf of mexico and in the central pacific dsdp sites 534 391 535 and 167 by analogy with the aptian stage also marked by a significant positive c isotope excursion the time of positive 13c values is regarded as a time of accelerated carbon cycling coupled with increased burial rates of organic carbon and detrital material in oceanic sediments a warm and humid climate possiblycoupled with a high atmospheric co2 content and a high global sea level may have triggered the acceleration of the global carbon cycling in this case the valanginian c isotope event would reflect a first episode of greenhouse earth conditions during the cretaceous

the upper valanginian early cretaceous positive carbon isotope event recorded in terrestrial plants our understanding of the ancient ocean atmosphere system has focused on oceanic proxies however the study of terrestrial proxies is equally necessary to constrain our understanding of ancient climates and linkages between the terrestrial and oceanic carbon reservoirs we have analyzed carbon isotope ratios from fossil plant material through the valanginian and lower hauterivian from a shallow marine ammonite constrained succession in the crimean peninsula of the southern ukraine in order to determine if the upper valanginian positive carbon isotope excursion is expressed in the atmosphere d 13 cplant values fluctuate around 23x to 22x for the valanginian hauterivian except during the upper valanginian where d 13 cplant values record a positive excursion to 18x based upon ammonite biostratigraphy from crimea and in conjunction with a composite tethyan marine d 13 ccarb curve several conclusions can be drawn 1 the d 13 cplant record indicates that the atmospheric carbon reservoir was affected 2 the defined ammonite correlations between europe and crimea are synchronous and 3 a change in photosynthetic carbon isotope fractionation caused by a decrease in atmospheric pco2 occurred during the upper valanginian positive d 13 c excursion our new data combined with other paleoenvironmental and paleoclimatic information indicate that the upper valanginian was a cool period icehouse and highlights that the cretaceous period was interrupted by periods of cooling and was not an equable climate as previously thought d 2005 elsevier b v all rights reserved

berriasian aptian black shales of the maiolica formation lombardian basin southern alps northern italy local to global events the lower cretaceous maiolica formation represents the classic pelagic succession of the apulian margin of the tethys ocean in the southern alps it consists of white calcilutites with minor marly layers and black shales a multidisciplinary study including lithostratigraphy nannofossil assemblage composition and organic geochemistry was performed on two composite sections in order to characterise the marl shale layers that record production and storage of organic matter om and terrigenous input in the berriasian aptian interval such layers are associated with turbidite deposition and bottom current activity in the late berriasian earliest valanginian late valanginian and early aptian the uppermost hauterivian barremian black shales alternate with pelagic calcilutites forming an interval barren of redeposited layers the quantity of organic carbon increases from the berriasian to the barremian the background composition of the kerogen is continental dominated with varying proportions of marine derived om preservation of om did not necessarily occur under anoxic conditions on the contrary storage of om probably resulted from enhanced terrestrial input of nutrients siliciclastics woody and herbaceous fragments inducing mesotrophic conditions and increased primary productivity higher fertility of surface waters during the late valanginian and early aptian is reflected by distinctive decreases in abundance of oligotrophic nannoconids and increase in abundance of mesotrophic diazomatholithus in the valanginian during the barremian the rhythmic establishment of eutrophic conditions documented by the highest amounts of marine om determined high frequency fluctuations in nannoconid abundance the early aptian nannoconid crisis is interpreted as the result of a major climate change and enhanced primary productivity variations of calcareous nannofloras as well as changes of lithology and om which we describe in the lower cretaceous maiolica formation of the lombardian basin can also be recognised in coeval units from other sites of the apulian side of the tethys similar episodes of siliciclastic and terrestrial om accumulation and major changes in calcareous nannofossils are also recorded in the upper valanginian and lower aptian pelagic sediments of the tethys atlantic and partly pacific oceans such nannofossil variations are coeval with positive excursions of the 13c curve and suggest perturbations of the bio geochemical cycles at a global scale additional minor changes in siliciclastic and terrestrial om accumulation as well as in nannofloras are probably the result of local events strictly related to the physiography and evolution of the tethyan margin

sea level reconstructions from the peri vocontian zone south east france point to valanginian glacio eustasy the valanginian is a period of global environmental change as illustrated by sedimentary palaeontological geochemical and climatic perturbations a production crisis in most of the carbonate platforms suggests important changes in palaeoenvironmental conditions during the same time interval a major positive excursion in 13c the weissert event suggests perturbations of the carbon cycle from the latest early valanginian to the early hauterivian in order to better understand the link between these changes sea level fluctuations have been reconstructed in detail from the middle berriasian to the earliest hauterivian sections from the peri vocontian zone south east france have been investigated because of the good quality of outcrops on the carbonate platforms their margins and in the vocontian basin sections ranging from the most proximal zone swiss jura to the basin were interpreted in terms of sequence stratigraphy and cyclostratigraphy and correlated at high resolutions using the identified small medium and large scale sequences as well as depositional geometries sea level fluctuations were reconstructed two main trends are evidenced during the studied interval i the peak amplitude magnitude of the sea level fluctuations increased gradually from the middle berriasian to the early valanginian and reached a maximum more than 50 m from the middle early valanginian to the valanginian hauterivian boundary and ii sea level variations were quite symmetrical during the late berriasian slightly asymmetrical during the early valanginian and strongly asymmetrical fast sea level rise slow fall from the latest early valanginian to the earliest hauterivian moreover three orders of sea level fluctuations were recognized in the sedimentary rocks of the peri vocontian zone platform basin correlations and cyclostratigraphic interpretations of the basinal sections evidence an astronomical control on the sea level variations mainly by the two eccentricity cycles of 100 and 400 kyr the increase in the amplitude of the sea level fluctuations and their change from symmetrical to asymmetrical can be related to the onset of a major cooling event in the early valanginian fast transgressions followed by slower regressions would correspond to waxing and waning of high latitudinal ice during most of the valanginian especially from the latest early valanginian to the latest late valanginian glacio eustatic sea level fluctuations in tune with the 100 and 400 kyr eccentricity cycles are in agreement with glaciations during the valanginian

volcanism co2 and palaeoclimate a late jurassic early cretaceous carbon and oxygen isotope record a composite tethyan late jurassic early cretaceous carbon and oxygen isotope curve is presented c isotope data provide information on the evolution and perturbation of the global carbon cycle o isotope data are used as a palaeotemperature proxy in combination with palaeontological information the resulting trends in climate and in palaeoceanography are compared with biocalcification trends and oceanographic conditions favouring or inhibiting biocalcification positive c isotope anomalies in the valanginian and aptian correlate with episodes of increased volcanic activity regarded as a source of excess atmospheric carbon dioxide a major warming pulse accompanies the aptian but not the valanginian c isotope event the observed change in early aptian temperatures could have triggered the destabilization of sedimentary gas hydrates and the sudden release of methane to the biosphere as recorded as a distinct negative carbon isotope pulse preceding the positive excursion both c isotope anomalies are accompanied by biocalcification crises that may have been triggered by p co 2 induced changes in climate and in surface water chemistry elevated nutrient levels in river influenced coastal waters and in upwelling regions further weakened marine calcification these conditions contrast with normal trophic conditions prevailing in the latest jurassic and favouring biocalcification the c and o isotope curves record a stable mode of carbon cycling and stable temperatures we conclude that biocalcification is mostly triggered and inhibited by co 2 conditions in the atmosphere ocean system

biogeochemical assessment of sources of organic matter and paleoproductivity during the early aptian oceanic anoxic event at shatsky rise odp leg 198 this study investigates organic rich sedimentary sequences deposited during the early aptian oceanic anoxic event oae1a at sites 1207 and 1213 on shatsky rise odp leg 198 in the west central pacific biomarker analyses provide evidence of the algal and bacterial origin of organic matter om in these sediments where the abundance of steroidal components particularly sterenes and sterones suggests that the om includes major contributions from eukaryotic sources in an environment characterized by high phytoplankton productivity the presence of alkenones at site 1213b is diagnostic of om derived from representatives of haptophyte algae among the calcareous nannoplankton and their 13c values average 31 6 are consistent with those expected during elevated pco2 the occurrence and prominence of 2 methylhopanes and 2 methylhopanones indicates significant contributions to the om from cyanobacteria which are also likely contributors of hopanoids based on their 13c compositions these biomarker data suggest that oceanic conditions perhaps nitrate or iron limited were conducive to cyanobacteria production during oae1a which appears to distinguish this event from other cretaceous oae

timing of deposition and deformation of the moodies group barberton greenstone belt south africa very high resolution of archaean surface processes abstract thin and largely discontinuous volcanic tuff beds in the alluvial fluvial and marginal marine siliciclastic strata of the middle archaean moodies group barberton greenstone belt bgb contain rare to abundant zircon dating of magmatic zircon grains from five tuff beds and one cross cutting dike yield ages which span the entire spectrum of bgb history from ca 3550 ma to 3215 ma and show variable degrees of post depositional alteration until ca 2500 ma the youngest pristine zircon grains in all tuff samples analyzed by ca id tims chemical abrasion ion dissolution thermal ion mass spectrometry yield upper intercept and concordia ages between 3227 6 0 3 and 3216 0 3 ma and those grains analyzed by la sf icp ms laser ablation sector field inductively coupled plasma mass spectrometry and shrimp sensitive high resolution ion microprobe yield ages between 3228 9 and 3214 9 ma most of these ages are either identical within error or significantly older than a ca id tims age of 3223 4 0 3 ma obtained from zircon grains of a tuff horizon of the schoongezicht formation at the top of the underlying fig tree group we interpret this age to mark the time of volcanic eruption whereas the significantly older and overlapping ages of the stratigraphically higher moodies tuff zircon grains point either to a high degree of magmatic inheritance and or a detrital contribution from surrounding sedimentary rocks during or after ash tuff deposition the minimum age for deposition of moodies group sediments and deformation is provided by a la icp ms zircon u pb age of 3219 9 ma obtained from an undeformed felsic dike which crosscuts folded moodies strata this age overlaps with a precise ca id tims u pb zircon age of 3216 0 0 3 ma obtained from a tuff horizon of the upper moodies group overall the new age data collectively imply that the up to 3 7 km thick sandstone dominated moodies group was deposited and deformed within

tethyan carbonate carbon isotope stratigraphy across the jurassic cretaceous boundary an indicator of decelerated global carbon cycling the carbon isotope record in four pelagic carbonate sections from the southern alps northern italy across the jurassic cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy the carbon isotope curve from bulk carbonates shows a decrease from kimmeridgian to early tithonian cm24 cm22 values of 13c 2 07 0 14 to late tithonian and berriasian cm18 cm14 values of 13c 1 26 0 16 the change in the carbon isotope record coincides with changes in tethyan calcite and silica accumulation rates with a drop in the calcite compensation depth in the atlantic and tethys oceans and with changes in organic carbon burial along the eurasian margin of the tethys reduced surface water productivity due to diminished transfer rates of biolimiting elements into the atlantic and tethys oceans can explain these observations the decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the tethys and atlantic oceans the proposed changes in tithonian berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles

calcareous nannofossils from late jurassic sediments of the volga basin russian platform evidence for productivity controlled black shale deposition the jurassic cretaceous boundary interval in the northern hemisphere is characterized by the widespread occurrence of black shales about 60 of all petroleum source rocks comprise sediments of late jurassic and early cretaceous age with the origin of such black shales still under discussion in order to better understand the factors that controlled black shale sedimentation 78 samples were analyzed for calcareous nannofossils from two sections gorodische kashpir of the volga basin ne russia calcareous nannofossils are ideal proxies for deciphering nutrient temperature and salinity fluctuations additionally 58 samples from both sections were also analyzed for clay mineralogy 13corg toc and caco3 composition both sections contain calcareous claystones and intercalated organic rich shales overlain by phosphorite beds the presence of the calcareous nannofossil species stephanolithion atmetros throughout both successions allows a biostratigraphic assignment to the s atmetros nannofossil biozone nj 17 which corresponds to the dorsoplanites panderi ammonite biozone of the middle volgian the marlstones of the kashpir section yield a well preserved rich and diverse nannoflora whereas all black shale beds are essentially barren of calcareous nannofossils only the uppermost black shale layers yield an impoverished assemblage of low diversity and abundance geochemical data suggest an early diagenetic nannofossil dissolution in the black shales of the kashpir section this is supported by the occurrence of coccoliths in black shale horizons of the gorodische section the assemblages in both sections are dominated by coccoliths of the watznaueriaceae group watznaueria barnesae watznaueria fossacincta watznaueria britannica watznaueria communis biscutum constans and zeugrhabdotus erectus in kashpir rare specimens of crucibiscutum salebrosum occur in the higher part of the section these taxa indicate boreal affinities b constans and z erectus are considered to be taxa indicative of a higher productive environment while c salebrosum is a cool water species from base to top of the kashpir section consecutive mass occurrences of different taxa groups were observed w barnesae w fossacincta acme w britannica w communis acme z erectus acme b constans acme including sparse occurrences of c salebrosum

phosphogenesis carbon isotope stratigraphy and carbonate platform evolution along the lower cretaceous northern tethyan margin we distinguish three different stages in the evolution of the tithonian late jurassic to aptian early cretaceous northern tethyan carbonate platform 1 carbonate production in the coral oolite mode late tithonian to early valanginian early barremian to early aptian 2 carbonate production in the crinoid bryozoan mode early valanginian haute rivian late aptian and 3 platform retrogradation and destruction condensation and phosphogenesis that is platform drowning early valanginian to early hauterivian middle hauterivian late hauterivian to early barremian early to early late aptian and latest aptian to earliest albian transitions from the coral oolite mode to the crinoid bryozoan mode and consequently to platform drowning may have been driven by increases in nutrient levels on the shelf phases of relative sea level rise in times of carbonate production in the coral oolite mode are named constructive because of the observed platform regeneration following phases of widespread emersion during late sea level highstands in contrast phases of relative sea level rise in times of platform drowning are termed destructive the 13 c stratigraphies obtained from valanginian hauterivian and aptian albian hemipelagic successions beyond the platform correlate well with the early cretaceous pelagic 13 c record positive excursions in the pelagic 13 c record correspond in time to episodes of platform drowning this suggests the existence of a coupling mechanism between changes in the global carbon cycle and platform drowning in our view the early cretaceous crises in carbonate platform growth were the consequence of reinforced greenhouse conditions which may have been triggered by episodes of extensive flood basalt volcanism strong greenhouse conditions may have induced the following chain of feedback mechanisms enabling the biosphere to return to normal conditions climate warming sea level rise accelerated water cycle intensified weathering nutrient mobilization platform destruction increased productivity increased phosphogenesis and carbon burial weakened greenhouse conditions

high resolution solid state sodium 23 aluminum 27 and silicon 29 nuclear magnetic resonance spectroscopic reconnaissance of alkali and plagioclase feldspars

climate and sea level variations along the northwestern tethyan margin during the valanginian c isotope excursion mineralogical evidence from the vocontian basin se france a high resolution mineralogical study bulk rock and clay fraction was carried out upon the hemipelagic strata of the angles section vocontian basin se france in which the valanginian positive c isotope excursion occurs to investigate sea level fluctuations and climate change respectively a detrital index di phyllosilicates and quartz calcite and a weathering index wi kaolinite illite chlorite were established and compared to second order sea level fluctuations in addition the mineralogical data were compared with the high nutrient index hni based on calcareous nannofossil taxa data obtained by duchamp alphonse et al 2007 in order to assess the link between the hydrolysis conditions recorded on the surrounding continents and the trophic conditions inferred for the vocontian basin it appears that the mineralogical distribution along the northwestern tethyan margin is mainly influenced by sea level changes during the early valanginian pertransiens to stephanophorus ammonite zones and by climate variations from the late early valanginian to the base of the hauterivian top of the stephanophorus to the radiatus ammonite zones the sea level fall observed in the pertransiens ammonite zone early valanginian is well expressed by an increase in detrital inputs an increase in the di associated with a more proximal source and a shallower marine environment whereas the sea level rise recorded in the stephanophorus ammonite zone corresponds to a decrease in detrital influx a decrease in the di as the source becomes more distal and the environment deeper interpretation of both di and wi indicates that the positive c isotope excursion top of the stephanophorus to the verrucosum ammonite zones is associated with an increase of detrital inputs under a stable warm and humid climate probably related to greenhouse conditions the strongest hydrolysis conditions being reached at the maximum of the positive c isotope excursion from the verrucosum ammonite zone to the base of the hauterivian radiatus ammonite zone climatic conditions evolved from weak hydrolysis conditions and most likely a cooler climate resulting in a decrease in detrital inputs to a seasonal climate in which more humid seasons alternated with more arid ones the comparison of the wi to the hni shows that the nutrification recorded al the angles section from the top of the stephanophorus to the radiatus ammonite zones including the positive c isotope shift is associated with climatic changes in the source areas at that time increased nutrient inputs were generally triggered by increased weathering processes in the source areas due to acceleration in the hydrological cycle under greenhouse conditions this scenario accords with the widely questioned palaeoenvironmental model proposed by lini et al 1992 and suggests that increasing greenhouse conditions are the main factor that drove the palaeoenvironmental changes observed in the hemipelagic realm of the vocontian basin during the valanginian positive c isotope shift this high resolution mineralogical study highlights short term climatic changes during the valanginian probably associated to rapid changes in the c cycle coeval massive parana etendeka flood basalt eruptions may explain such rapid perturbations c 2011 elsevier b v all rights reserved

mercury anomalies volcanic pulses and drowning episodes along the northern tethyan margin during the latest hauterivian earliest aptian abstract the latest hauterivian earliest aptian time interval includes three episodes of significant environmental change faraoni late early barremian and taxy episodes this time interval appears to partially overlap with large scale volcanic activity related to the tristan da cunha plume along the rio grande rise high arctic large igneous province volcanism and the early phase in the formation of the greater ontong java lip in the pacific the establishment of exact temporal relationships between volcanic activity and environmental change remains however a major challenge due to the scarcity of numerical ages for the early cretaceous we report mercury hg contents in uppermost hauterivian lowermost aptian marl limestone alternations from seven sections along a n s transect in the western tethys the hg contents in marl samples display rather scattered records which are generally well correlated with the total organic carbon toc records in associated limestone beds five distinct spikes in hg concentrations occur in three intervals latest hauterivian early barremian and latest barremian the small amounts of organic matter

from rifting to drifting tectonic evolution of the south alpine upper crust from the triassic to the early cretaceous abstract the tectonic evolution of the south alpine rifted margin is discussed on the base of four palinspastic upper crustal profiles extension related to the movements between adria and europe began in the norian after variscan orogeny late carboniferous to middle permian orogenic collapse and continental scale wrenching from the late triassic to the early liassic stretching was mostly limited to the lombardian basin during this time extension was mainly controlled by four major listric faults symmetrically centred around the late carboniferous early permian collio grabens smaller faults which also started in the norian were progressively de activated during the late triassic after the middle liassic faulting in the lombardian basin gradually ceased and the site of extension shifted westwards i e towards the future site of crustal separation extension was then controlled by a set of west dipping normal faults oceanic crust was formed not later than 157 ma the overall extension along the profile which had a final length of 290 km was 52 km which corresponds to a stretching factor of 1 22 for the whole length of the preserved margin the strain rate is ca 1 10 16 s the sedimentation history suggests that the extension of the south alpine margin was a continuous process from the norian to the middle jurassic the changes in tectonic pattern are related to progressive hardening of the lithospheric segment undergoing slow extension

isotopic signals from late jurassic early cretaceous volgian valanginian sub arctic belemnites yatria river western siberia this contribution presents the first detailed oxygen and carbon isotope record from the latest jurassic early cretaceous interval of the yatria river subpolar urals siberia isotopic compositions have been determined on well preserved belemnite samples from the genera lagonibelus cylindroteuthis and acroteuthis these new data indicate a shift to lower temperatures from the late volgian into the late valanginian with some warmer phases recognized within the ryazanian and earliest valanginian the lowest temperatures of the late valanginian consistent with subfreezing polar temperatures are coincident with an inferred eustatic sea level fall a late valanginian positive shift in carbon isotopes correlates with the carbon isotope excursion recorded from tethyan successions the most positive carbon isotope values correspond to the most positive oxygen isotope values and hence lowest palaeotemperatures in the absence of widespread valanginian organic rich black shale deposition the carbon isotope excursion may point to increased storage of organic carbon in coastal areas and or enhanced preservation within stratified waters in high latitude basins at these higher latitudes where rates of weathering were presumably much lower because of the prevalent cold climate the isotopic data may point to pulses of productivity being brought about by increased riverine nutrient transfer and also by nutrients being released by the melting of ice the correlation between positive carbon isotopes and cool climates may indicate the effectiveness of these high latitude carbon sinks and their ability to draw down atmospheric co 2 resulting in an inverse greenhouse effect

valanginian to aptian calcareous nannofossil stratigraphy and correlation with the upper m sequence magnetic anomalies abstract calcareous nannofossil stratigraphy has been investigated in lower cretaceous italian sections at gorgo a cerbara presale and frontale all in the umbrian apennines and at cismon southern alps a modified sample preparation technique has allowed a thorough stratigraphic study of the well lithified maiolica limestone and although nannofossil preservation is generally quite poor the major valanginian to aptian marker species can be detected nine nannofossil events can be determined and correlated to magnetic stratigraphies previously established in these sections nannofossil stratigraphy confirms most magnetostratigraphic correlations made between sections and allows a more precise correlation of magnetic chrons m 0 to m 11 with the valanginian hauterivian barremian and aptian stages the results obtained differ considerably from previous timescales nannofossil events recorded in the various sections may be time transgressive by as much as one magnetic chron probably due to differential preservation

nannofossil assemblages fine fraction stable isotopes and the paleoceanography of the valanginian barremian early cretaceous north sea basin calcareous nannofossil assemblages have been investigated in three sections from around the margins of the early cretaceous north sea basin both absolute number of nannofossils per gram and relative percent of the assemblage of different taxa abundance data have been collected absolute abundances up to 10 billion nannofossils per gram are somewhat higher than those reported previously from other stratigraphic intervals stratigraphic correlation of trends in assemblage data in different sections points toward the existence of large uniform water masses stable over long 0 5 to 1 m y time periods these water masses contained a characteristic nannoplankton which appears to have been driven largely by variations in fertility possibly tied to changes in sources of surface waters which in turn may have been controlled by relative sea level fine fraction isotopic data show fluctuations on shorter time periods 0 1 to 0 5 m y we postulate that some of these isotopic fluctuations were controlled by relative changes in sea level which affected the balance of surface waters derived from runoff and those imported from the boreal sea these oceanographic changes appear to have affected nannofossil assemblages only in discrete intervals data are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document p95 001 2 50 payment must accompany order

the palaeoceanographic crisis of the early aptian oae 1a in the vocontian basin se france abstract the vocontian basin se france which presents lower aptian expanded successions characterized by major lithological changes is particularly suitable to determine palaeoenvironmental changes occurring across the oae 1a a multidisciplinary study sedimentology caco3 toc carbon and oxygen stable isotopes micropalaeontology cyclostratigraphy was carried out in the notre dame de rosans section in order to establish a detailed chronological framework of these changes the oae 1a corresponds to carbon isotope segments c3 c6 and it lasted for 1 2 myr a first drop in the carbonate production occurs 500 kyr before the oae 1a upper part of the carbon isotope segment c2 and could result from both onset of urgonian carbonate platform demise and associated reducing export of platform derived sediments into the basin and nannoconid crisis a second drastic drop crash in the carbonate production is recorded within the lower part of the oae 1a latter part of segment c3 to c5 and is explained by a strong dissolution this study then shows that the onset of the major carbonate crisis that occurs before the oae 1a could be due to both rise in sea level and in marine surface water fertility whereas its acme that occurs within the oae 1a could be related to co2 induced ocean acidification black shales of the niveau goguel occur in the upper part of the oae 1a and represent the lower part of segment c6 surface waters primary producers are principally represented by cyanobacteria whereas nannofossil primary productivity is reduced and deep water anoxia prevailed during the deposition of the niveau goguel the last 300 kyr of the oae 1a are characterized by a partial recovery of both nannofossil primary productivity and pelagic carbonate production which sharply increase just after the end of the event this study also shows that organic rich layers associated to the oae 1a are diachronous in the tethyan realm

density measurements on melts at high pressure using the sink float method limitations and possibilities abstract we investigated the use of the sink float method to determine the density of silicate melts with a range of compositions intended to provide a general understanding of density changes as functions of composition and pressure for each composition estimates of both the melting temperature and the melt viscosity which determines the required experimental run time at the pressures of interest are required prior to the density experiments we constrained the melting relationships for two sodium silicate melts and a melt of albite composition and were able to calculate the maximum possible viscosities of the sodium silicate melts the sink float method is limited by the absence of high pressure high temperature density data for minerals that may be used as buoyancy markers in the experiments these data need to be sufficiently precise to justify their use in the determination of melt densities at high pressure at present high quality data are available for only a few minerals such as spinel forsterite quartz and some garnets another limitation is that the markers should not react with the melt reaction between the buoyancy markers melt and capsule material changes the density of both melt and markers errors on the order of 2 on the determined densities may be introduced by the changing density of the mineral markers through reaction with the melt although the sink float method is very elegant it has significant limitations that prohibit the precise determination of the density of an arbitrary silicate melt at high pressure in most cases only loose constraints on the density and compressibility of melts can be obtained as a function of pressure

application of gis techniques to determine areas most suitable for artificial groundwater recharge in a coastal aquifer in southern iran abstract special attention has been paid to artificial groundwater recharge in water resource management in arid and semi arid regions parameters considered in the selection of groundwater artificial recharge locations are diverse and complex in this study factors such as slope infiltration rate depth to groundwater quality of alluvial sediments and land use are considered to determine the areas most suitable for groundwater recharge in a coastal aquifer in the gavbandi drainage basin in the southern part of iran thematic layers for the above parameters were prepared classified weighted and integrated in a gis environment by the means of boolean and fuzzy logic to determine the relationships between geomorphological units and the appropriate sites for groundwater artificial recharge land use and geomorphological maps were developed from satellite images the results of the study indicate that about 12 of the study area is considered as appropriate and 8 moderately appropriate sites for artificial groundwater recharge the relationship between geomorphology and appropriate areas for groundwater recharge indicate that the majority of these areas are located on alluvial fans and pediment units at the reconnaissance stage these geomorphological units can be considered as appropriate sites for artificial recharge in regions with similar characteristics

climate and paleoceanography controlled size variations of calcareous nannofossils during the valanginian weissert event early cretaceous abstract strata of valanginian age early cretaceous 139 8 132 9 ma record a 1 5 positive carbon isotope excursion cie the weissert event it coincides with volcanic activity of the parana etendeka large igneous province unlike the mesozoic oceanic anoxic events oaes no organic rich deposits documenting widespread perturbation of the marine carbon cycle are associated with the weissert event to study the impact of paleoceanographic changes in the valanginian on calcareous nannofossils this study analyzes coccolith size data of three species biscutum constans watznaueria barnesiae zeugrhabdotus erectus from northern germany and the western north atlantic further it presents a new valanginian carbon isotope record of organic material 13corg from northern germany the dataset records the weissert event cie in the late valanginian at both locations biometric analyses reveal size decreases of b constans coccoliths during the weissert event a size reduction of 1 m has been observed for northern germany 37 n and of 0 4 m for the north atlantic 23 n the different magnitudes of size decrease possibly reflect the different paleogeographic positions of the sites and the paleoceanographic response to the late valanginian climate variations proxy data support a link between a humid climate with increased weathering and the observed coccolith size variations this impacted nannoplankton communities either through the availability of light or by eutrophication and possibly nutrient limitation in addition to increased terrigenous input emissions of the parana etendeka volcanism possibly acted fertilizing furthermore widely dispersed volcanic emissions possibly caused increased concentrations of toxic trace metals in the surface ocean which affected marine primary producers

biotic changes linked to a minor anoxic event faraoni level latest hauterivian early cretaceous a conspicuous renewal in the ammonite faunas of the mediterranean tethys occurred in the latest hauterivian this faunal turnover took place following a stepwise pattern the first step occurred at the boundary between the pseudothurmannia ohmi subzone and the pseudothurmannia mortilleti subzone coinciding with the base of the so called faraoni level this is a corgrich interval that has been recognised in several basins of the mediterranean tethys and seems to be the expression of a shortlived oxygen deficient event it correlates with a well documented second order peak transgression the oxygen depletion preferentially affected the deep nektic ammonites which would explain the extinctions within this group around the faraoni level on the contrary an increase in the trophic resources in the photic zone favoured the diversification of epipelagic ammonites concurrently an abrupt change took place at this level in the nannoconid assemblage composition a minor second event located at the base of the pseudothurmannia picteti subzone was marked by the replacement of a few planktic ammonite species by closely related forms and the structure of the ammonite assemblage was not substantially altered the coincidence of this event with a further restructuring of the calcareous nannofossil assemblage suggests that some changes had to occur in the planktic ecosystem during the sea level highstand subsequent to the peak transgression the third and last stage of the renewal process started in the upper part of the p picteti subzone coinciding with a drastic sea level fall it is characterised by the extinction of many of the species that had appeared in the two previous events resulting in an extensive modification of the assemblage structure the regression would probably cause a drop in the primary productivity and consequently an improvement in the oxygenation level of the sea bottom this would explain the extinction of several planktic ammonite species and the appearance of new nektic and nektobenthic lineages d 2005 elsevier b v all rights reserved

integrated stratigraphy of lower cretaceous sediments ryazanian hauterivian from north east greenland abstract the reconstruction of past climates and oceanography requires a solid stratigraphic framework ideally applicable on a global scale the earliest cretaceous however was a time of strong faunal provincialism making supra regional correlation of biostratigraphical zonations difficult the step by step correlations between neighbouring provinces subprovinces that are commonly utilized bear the risk of loosing accuracy in every step here we present 87sr 86sr and stable isotope data 13c 18o from belemnite rostra of the rodryggen section in north east greenland the integrated stratigraphy based on sr isotope ratios ammonite and calcareous nannofossil biostratigraphy offers the opportunity for a direct comparison of the different stratigraphic zonations these are complemented by 13cbel data recording the positive carbon isotope excursion of the valanginian weissert event which is a reliable stratigraphic event the geochemical data furthermore allow a reliable correlation of tethyan and boreal strata the stratigraphic range of the rodryggen section resulting from sr isotope stratigraphy ryazanian barremian is in agreement with the biostratigraphic findings mismatches regarding stage substage boundaries demand a reconsideration of the nannofossil biostratigraphy of the boreal lower cretaceous our findings suggest stratigraphic ranges for two nannofossil index species sollasites arcuatus micrantholithus speetonensis different from published ranges the new observations imply changes in the boreal ryazanian valanginian nannofossil zonation scheme specifically the base of calcareous nannofossil zone bc3 originally defined as uppermost ryazanian is shifted to the lower valanginian based on these new stratigraphic interpretations a decrease in the abundance of nannoconids observed in the rodryggen section can now be identified as the valanginian nannoconid crises this nannoconid decline has been observed in tethyan sections along with the weissert event a positive trend in the 18obel data agrees with a late valanginian cooling that has been postulated based on independent proxies from the boreal realm and the tethys

compression of albite naalsi3o8 the structure and equation of state of low albite naalsi 3 o 8 has been determined using high pressure single crystal x ray diffraction to a maximum pressure of 9 43 gpa low albite remains triclinic in space group c 1 over the entire pressure range and no phase transitions were observed although the evolution of the unit cell parameters and volume exhibit some unusual features at pressures above 4 gpa a third order birch murnaghan equation of state fit to 6 p v data points up to 3 4 gpa has k 0 54 2 7 gpa and k 5 3 6 at higher pressures the volume pressure curve exhibits d 2 v d p 2 p v data set can be approximated with a fourth order birch murnaghan equation of state with k 0 52 3 9 gpa k 0 8 8 6 and k 0 2 8 2 gpa 1 the anisotropy of the compression of albite is typical of that of feldspars with 65 of the volume compression accounted for by the compression of the 100 plane normal this is due to the closing up of the crankshaft chains of tetrahedra that are characteristic of the feldspar structure single crystal x ray intensity data sets collected at 6 4 8 4 and 9 4 gpa also show that the four membered rings of tetrahedra within the structure undergo significant shear at high pressures changes in the rate of shear of the four membered rings with pressure are associated with changes in the variation of the unit cell angles with pressure

early cretaceous polarity chrons cm0 to cm11 recorded in northern italian land sections near brescia abstract three lower cretaceous pelagic limestone sections located in the lombardian prealps northwest of brescia record polarity chrons cm0 to cm11 the polarity chrons are correlated to nannofossil and foraminiferal events the polaveno section records polarity chrons cm3 to cm11 with excellent fit to the larson and hilde 1 polarity model derived from hawaiian oceanic magnetic anomalies this is the first complete magnetostratigraphic record in this interval and indicates that this part of the hawaiian polarity model represents an approximately constant spreading rate record the pie del dosso section records cm0 and cm1 with correlations to the biostratigraphic record the san giovanni section records part of the cm3 to cm9 interval with the cm6 to cm8 interval cut out by faulting the correlations of polarity chrons to nannofossil datum planes are generally consistent with previously published correlations based on data from the southern alps and central italy umbria we present new biostratigraphic data from a previously studied section capriolo southern alps which result in revised identification of cm0 and cm1 at this locality

steryl ethers in a valanginian claystone molecular evidence for cooler waters in the central pacific during the early cretaceous abstract coring on shatsky rise by ocean drilling project leg 198 recovered sediments rich in organic matter 2 0 corg from three time intervals the early aptian corresponding to oceanic anoxic event oae 1a the valanginian and the berriasian episodes of enhanced sequestration of organic matter during the valanginian are well documented in the tethyan realm notably those associated with a positive 13c isotopic excursion and with changes in plankton assemblages including a demise in nannoconids the 13c excursion has been previously reported in the pacific but the occurrence of valanginian sediments rich in organic matter 1 corg is unprecedented a distinctive feature of the biomarker composition of these valanginian sediments at shatsky rise is the presence of a suite of steryl ethers which extends the temporal record of these compounds from the neogene to the early cretaceous the biological source of steryl ethers remains enigmatic although the sedimentary occurrences of these compounds in quaternary and neogene environments characterized by cool water high seasonal productivity and or nutrient enrichment by upwelling in combination with their liquid crystal properties raise the possibility that they may represent storage lipids akin to wax esters and triacylglycerols prior occurrences of steryl ethers suggest that their presence in the valanginian may reflect an oceanic environment characterized by upwelling consistent with the likely position of shatsky rise within the equatorial divergence zone of the pacific during the early cretaceous alternatively or in addition the appearance of these compounds may represent a biological response to cooler temperatures and thereby augment evidence for global cooling during the early valanginian consistent with independent paleontological evidence for contemporaneous upwelling induced increases in productivity in the western atlantic

the mid valanginian weissert event as recorded by calcareous nannoplankton in the vocontian basin the mid valanginian weissert event represents one of the most significant paleoceanographic events of the early cretaceous and is characterized by a major perturbation of the carbon cycle testified by a positive carbon isotope shift a crisis of both neritic and pelagic carbonate producers and climatic fluctuations here we propose a paleoreconstruction of paleoenvironmental changes that occurred in the reference vergol and la charce sections vocontian basin se france during the weissert event based on the analysis of calcareous nannofossil absolute abundance and assemblages these latter are compared to newly acquired and already published sedimentological and organic geochemical analyses our approach is novel for the time interval considered indeed principal component analysis was applied for the first time to the entire nannofossil assemblage to reconstruct environmental conditions instead of using paleoecological preferences of single species the comparison of calcareous nannofossils and biomarker analyses indicates that a phase of severe sea water stratification occurred prior to the carbon positive excursion of the weissert event in the vocontian basin this was followed by a raise in fertility of surface waters as attested by increased nannofossil abundances in particular of meso eutrophic taxa and biomarkers likely produced by dinoflagellates this increase in fertility was likely triggered by a humid climate and enhanced continental input of clays and nutrients to surface oceanic waters calcareous nannofossils also proved to react to sea level changes that occurred in the valanginian as inferred by previous works species likely inhabiting proximal areas were recorded in higher proportions during a major sea level drop in the peregrinus ammonite zone late valanginian the results of this study also permit to revise previously proposed paleoecological affinities of some nannofossil species we suggest that watznaueria barnesiae one of the most widely used species in the literature should be used cautiously because of its high plasticity with respect to environmental conditions also nannoconids that are usually regrouped in papers with paleoceanographic purposes should be analyzed separately because they show distinct species specific ecological preferences

experimental determination of the effect of dissolved co2 on the dissolution kinetics of mg and ca silicates at 25 c dissolution rates of diopside forsterite fo100 and fo92 wollastonite and hornblende were measured at 25 c in nacl solutions as a function of ph 1 ph 12 pco2 0 and 1 atm and activity of hco3 and co32 10 5 co2 0 1 m dissolution rates of diopside forsterite and horneblende are not affected within the experimental uncertainty by 1 atm pco2 at ph 4 and by the presence of bicarbonate up to 0 1 m and carbonate up to 0 01 m ions at ph of 8 and 11 12 respectively although wollastonite dissolution rates are unaffected by pco2 at ph 4 its rates are increased by the presence of hco3 at 0 01 hco3 0 1 m and ph 7 8 and decreased slightly by co32 at co32 0 0001 m and ph 12 these results should be useful for modeling the effect of silicate rock weathering on the global biogeochemical cycle of carbon for the first time we were able to distinguish the net effect of pco2 versus that of ph it is observed in general accord with previous results that the direct effect of co2 on basic silicates dissolution rates is very weak as a result the major parameter governing basic silicates dissolution is ph of soil solutions in contact with minerals

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

an experimental approach to the sequence of the stability of rock forming minerals towards chemical weathering abstract the dissolution rates of milligrams per square metre per day for some main rock forming minerals were measured in experiments over prolonged periods of time rectangularly cut pieces of single crystals or monomineralic polycrystalline specimens were used the experimental set up provided for the rapid removal of all dissolved cations from the solution in order to maintain conditions far from chemical equilibrium experiments were performed at ph 5 5 and 4 0 at 20 c the stability towards chemical weathering decreases in the order muscovite alkali feldspar biotite amphibole pyroxene plagioclase nepheline olivine calcite a decrease of the ph from 5 5 to 4 0 accelerates the weathering process considerably

groundwater resources protection and aquifer recovery in china the groundwater resources in china and especially the northern part represent a vital water resource both the shallow and deep aquifers are highly overexploited in a large area of north china the heavy overexploitation of groundwater resources is causing major environmental damage to protect groundwater resources several technical feasibility studies were performed artificial recharge using floodwater and wastewater was tried surface spreading systems are applicable in many areas of the yellow river basin and hai river basin deep aquifer injections were undertaken in the urban area a far better strategy is to reduce the extraction of groundwater especially to stop or slow down land subsidence and seawater intrusion to address the problem of falling groundwater levels and aquifer recovery there is a need reduce groundwater extraction and artificial recharge

the valanginian isotope event a complex suite of palaeoenvironmental perturbations abstract the valanginian records a severe crisis of carbonate systems both on platforms and in the pelagic realm this crisis is roughly concomitant with the weissert event characterized by a positive 13c excursion of about 2 in marine carbonates however it is unclear if the response of these two carbonate systems to the global perturbations is contemporaneous or if they react differently for this purpose accumulation rates of pelagic carbonates produced by nannofossils and of platform derived carbonates have been quantified in a hemipelagic environment the vocontian basin se france that has the potential to record the reaction of both shallow water and pelagic carbonate production to a major perturbation of the carbon cycle testified by the isotope excursion also changes through time of clay input have been measured in order to evaluate variations in continental weathering rates and thus in continent derived nutrient input and climatic conditions in terms of humidity aridity accumulation rates of pelagic carbonates of platform derived carbonates and of clays were calculated on the basis of nannofossil absolute abundance and species specific masses of weight percent carbonate content of rocks and a high resolution timescale given by cyclostratigraphy the onset of the positive 13c excursion and the demise of the platforms testify for a synchronous but inverse response of the shallow water and pelagic carbonate systems to an increase in nutrient influx to marine waters as carbonate production by nannofossils decreased during the late valanginian in time of still low platform production the low temperature of marine waters coeval to a still high nutrient input recorded in the latest late valanginian possibly could explain that both platform and pelagic carbonate production contemporaneously decreased

multistratigraphic records of the lower cretaceous valanginian cenomanian puez key area in n italy abstract we present a stratigraphic investigation of a hauterivian to cenomanian hemipelagic succession from col puez in the dolomites southern alps northern italy a composite section of seven segments was studied with bio magneto and chemostratigraphy which enabled detailed and robust age calibration of the puez succession it also revealed the paleoceanographic history and helped identify the important global climatic events of that period the age of the lower cretaceous puez formation in the dolomites is refined as late hauterivian to early cenomanian ammonoids provide a detailed biostratigraphic subdivision that forms the basis for analyses of the faunal distribution and the paleoenvironmental evolution of basins and plateaus across the tethys the succession consists of facies similar to those of coeval units in the tethys apart from the late barremian to late aptian interval which is marked by a major hiatus followed by a few meters thick redbed of late aptian age the lower cretaceous was characterized by a weak 1 positive 13c trend punctuated by a positive shift in the late hauterivian corresponding to the faraoni level oxygen isotope values show a decreasing trend from the hauterivian to the albian cenomanian which mirrors a long term increasing trend in paleotemperatures from 15 18 c to 25 30 c this is in agreement with global paleotemperature reconstructions for this period representing the onset of mid cretaceous super greenhouse conditions nonetheless no black shale occurs at the intervals equivalent to aptian albian oceanic anoxic events oae suggesting unique paleoceanographic conditions enhanced current activity on a submarine height on the trento plateau area during the mid cretaceous

the durability of rocks developing a test of rock resistance to chemical weathering dissolution rates of 39 rock forming minerals were determined at 20 c and 100 c and different ph values using experimental set ups which achieve near zero cation concentrations weathering rates in nature for rock above surface were estimated from data in this study and data in the literature extraction in a soxhlet extractor with boiling 2 5 m acetic acid causes an acceleration of such estimated natural weathering rates by a factor of 0 25 103 to 7 104 for nearly all important rock forming minerals including the carbonates the applicability of such a comparative test for rock resistance to chemical weathering was corroborated by testing 32 different rocks and building stones run times of only one to four days were needed for a reliable result

organic facies as a tool for recording eustatic variations in marine fine grained carbonates example of the berriasian stratotype at berrias ardeche se france abstract sediments of the berriasian stratotype in southeastern france consist of marine fine grained carbonates deposited on an outer shelf at the western edge of the vocontian trough the limestones are monotonous but display some erosional surfaces and a condensed interval they are well dated by ammonites and calpionellids except at the base of the section where the boundary with the tithonian is not clearly established despite their very high carbonate content the limestones yielded enough organic residue to allow a study of palynofacies variations in time organic content consists of two fractions one is made of terrestrial components represented essentially by humic fragments of the inertinite and vitrinite maceral groups and accessorily by pollen and spores the other comprises marine components essentially dinocysts and accessorily foraminiferal linings absence of amorphous organic matter and the oxidized nature of dinocysts observable in uv light indicate that aerobic conditions prevailed throughout the berriasian probably associated with a low sedimentation rate the following qualitative and quantitative criteria indicating distal proximal trends were used to convert palynofacies observations into a tentative palaeoenvironmental curve ratio of continental to marine organic constituents diversity of dinocysts degree of biodegradation affecting humic fragments proportion of blade shaped inertinite and finally size sorting and rounding of equidimensional inertinite particles the palaeoenvironmental curve derived from organic matter shows oscillations between more proximal i e shallower water and more distal i e deeper water conditions these variations combined with biostratigraphic information and the few significant sedimentological data can be interpreted in terms of sequence stratigraphy and compared with the global sea level curve published earlier the fairly good correlation between this global curve and that established from palynofacies demonstrates the influence of relative sea level on the organic facies of the berriasian carbonates and the contribution of palynofacies studies to sequence stratigraphy

the late hauterivian faraoni oceanic anoxic event at rio argos southern spain an assessment on the level of oxygen depletion abstract an integrated study of multiple geochemical proxies toc 13ccarb trace metallic elements iron speciation on the late hauterivian faraoni oceanic anoxic event has been performed along the hemi pelagic section of rio argos south eastern spain in order to better constrain the environmental perturbations linked to this event in the subbetic domain in the studied section the toc is relatively low for the inorganic signal the trace metallic elements show contrasted record during the late hauterivian while detrital proxies th ti zr record rather constant signal the productivity cu ni p and redox u v mn fe proxies show noticeable variations the organic rich interval at the base of the faraoni horizon records higher values of cu ni and p as well as of u and v linked to bottom water oxygen depletion and enhanced primary productivity the rest of the faraoni horizon records punctual peaks of productivity and redox proxies but rather constant toc concentration as for organic and isotopic signals parts of inorganic signal linked to organic matter as those of productivity proxies have been probably reworked and partly influenced by carbonates however inorganic geochemical proxies are consistent suggesting rather oxygenated water masses associated with moderate productivity during the late hauterivian based on redox ratios u th vs v v ni fehr fet fepy fehr oxygen concentrations were determined and it clearly appears that only the organic rich interval at the base of the faraoni horizon might record ferruginous anoxic conditions compared to other hemi pelagic mediterranean regions the ultrahelvetic basin from switzerland and the vocontian trough from france the rio argos section shows good similarities concerning toc and 13ccarb signals suggesting moderate organic matter burial during the faraoni event in proximal environments the main difference concerns the redox variations contrary to italy and france sections where anoxic bottom water conditions persist up to the end of the faraoni event the rio argos section shows no truly anoxia onset except at the base of the faraoni horizon which we rather interpret as local intra basinal chemical variations

maskelynite formation via solid state transformation evidence of infrared and x ray anisotropy we present the results of a combined study of shocked labradorite from the lonar crater india using optical microscopy micro raman spectroscopy nuclear magnetic resonance nmr spectroscopy high energy x ray total scattering experiments and micro fourier transform infrared micro ftir spectroscopy we show that maskelynite of shock class 2 is structurally more similar to fused glass than to crystalline plagioclase however there are slight but significant differences preservation of original preimpact igneous zoning anisotropy at infrared wavelengths x ray anisotropy and preservation of some intermediate range order which are all consistent with a solid state transformation from plagioclase to maskelynite

onset of the mid cretaceous greenhouse in the barremian aptian igneous events and the biological sedimentary and geochemical responses basalts and biostratigraphy dated at 125 120 ma from the ontong java and manihiki plateaus in the western pacific evidence the largest volcanic event in earth history in at least the past 160 m y the intervening nova canton trough rifted at about 121 118 ma and a number of guyots and seamounts formed concurrently or slightly later geological events that probably were responses to these volcanic tectonic events occurred in the following chronostratigraphic order biotic fluctuations began at about 122 5 ma at about 122 0 ma 87sr 86sr began to decline slowly metal concentrations of co mn pb yb and cu in sediments peaked at about 121 5 121 2 ma changes in planktonic communities and sedimentation culminated in a nannoconid crisis just prior to 120 5 ma and in the selli black shale oae la at about 120 5 119 5 ma a sharp drop in 13c occurred at the beginning of the selli event and rebounded into a longer positive excursion that reached a peak after the selli event at about 119 5 118 5 ma at 120 5 ma 87sr 86sr declined rapidly and reached a minimum at about 116 113 ma we speculate that the intensity of these latter responses suggests a corresponding peak in volcanic tectonic activity at about 121 119 ma

the valanginian δ13c excursion may not be an expression of a global oceanic anoxic event abstract marine and terrestrial sediments of the valanginian age display a distinct positive 13 c excursion which has recently been interpreted as the expression of an oceanic anoxic episode oae of global importance here we evaluate the extent of anaerobic conditions in marine bottom waters and explore the mechanisms involved in changing carbon storage on a global scale during this time interval we asses redox sensitive trace element distributions rste uranium vanadium cobalt arsenic and molybdenum and the quality and quantity of preserved organic matter om in representative sections along a shelf basin transect in the western tethys in the polish basin and on shatsky rise om rich layers corresponding in time to the 13 c shift are generally rare in the tethyan sections and if present the layers are not thicker than several centimetres and total organic carbon toc contents do not surpass 1 68 wt palynological observations and geochemical properties of the preserved om suggest a mixed marine and terrestrial origin and deposition in an oxic environment in the polish basin om rich layers show evidence for an important continental component rste exhibit no major enrichments during the 13 c excursion in all studied tethyan sections rste enrichments are however observed in the pre 13 c excursion om rich barrande levels of the vocontian trough in addition all tethyan sections record higher mn contents during the 13 c shift indicating rather well oxygenated bottom waters in the western tethys and the presence of anoxic basins elsewhere such as the restricted basins of the north atlantic and weddell sea we propose that the valanginian 13 c shift is the consequence of a combination of increased om storage in marginal seas and on continents as a sink of 12 c enriched organic carbon coupled with the demise of shallow water carbonate platforms diminishing the storage capacity of 13 c enriched carbonate carbon as such the valanginian provides a more faithful natural analogue to present day environmental change than most other mesozoic oaes which are characterized by the development of ocean wide dysaerobic to anaerobic conditions

fertilization of the northwestern tethys vocontian basin se france during the valanginian carbon isotope perturbation evidence from calcareous nannofossils and trace element data a high resolution calcareous nannofossil study associated with a geochemical analysis major trace elements and carbon and oxygen isotope stratigraphies was carried out in the angles section hemipelagic setting of the vocontian basin se france during the valanginian positive carbon isotope excursion the behaviour of calcareous nannofossil taxa in relation to fertility conditions was studied to elaborate new nutrient indices in this environment a high nutrient index based on biscutum spp discorhabdus rotatorius zeugrhabdotus fissus high fertility indicators and watznaueria barnesae low fertility indicator and a medium nutrient index based on lithraphidites carniolensis medium fertility indicator and w barnesae low fertility indicator these two indices show a major fertilization from the stephanophorus ammonite zone to the trinodosum ammonite zone with a maximum during the positive carbon isotope excursion since high values of the nutrient indices are in phase with high values of chemical elements related to terrigenous material and low values of the coccolith total abundance it is proposed that pulses of detrital inputs into the basin triggered the nutrification which in turn caused a biocalcification crisis of the calcareous nannofossils nutrification is also responsible for the reef demise in the surrounded platforms as indicated by the increased sr ca seawater ratio at that time the intensification of the parana etendeka volcanic activity triggering co2 excess in the atmosphere is probably responsible for an acceleration of the hydrological cycle the increased weathering and the subsequent higher terrigenous and nutrient transfer from continents to the vocontian basin in such a scenario nutrification is a dominant factor controlling neritic and hemipelagic biocalcification however one cannot exclude that the global increase of atmospheric co2 could generate chemical changes of the sea surface waters acting with the nutrification to modify the biocalcification of the carbonate producers

recognition of alkenones in a lower aptian porcellanite from the west central pacific odp leg 198 drilling on shatsky rise recovered a lower aptian porcellanite 120 5 ma deposited during oceanic anoxic event oae 1a that contains c36 c39 alkadienones c37 2 and c39 2 alkadien 2 ones and c36 2 and c38 2 alkadien 3 ones this alkenone distribution differs from that typical of contemporary sediments and haptophyte algae but resembles that of cretaceous sediments from the blake bahama basin the discovery of alkenones in the early aptian extends their sedimentary record by 15 m y to 120 5 m y and demonstrates the potential for long term survival of these diagnostic functional lipids under favorable depositional conditions and subsequent shallow burial it also contributes to the understanding and reconstruction of evolutionary developments in alkenone distributions and biosynthesis over geologic time 2003 elsevier ltd all rights reserved

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton