shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

87sr 86sr isotope composition of bottled british mineral waters for environmental and forensic purposes mineral waters in britain show a wide range of 87 sr 86 sr isotope compositions ranging between 8 7 sr 86 sr 0 7059 from carboniferous volcanic rock sources in dunbartonshire scotland to 87 sr 86 sr 0 7207 in the dalradian aquifer of aberdeenshire scotland the 87 sr 86 sr composition of the waters shows a general correlation with the aquifer rocks resulting in the waters from older rocks having a more radiogenic signature than those from younger rocks this wide range of values means that the sr isotope composition of mineral water has applications in a number of types of studies in the modern commercial context it provides a way of fingerprinting the various mineral waters and hence provides a method for recognising and reducing fraud from an environmental perspective it provides the first spatial distribution of bio available 87 sr 86 sr in britain that can be used in modern historical and archaeological studies

isorenieratane record in black shales from the paris basin france constraints on recycling of respired co2 as a mechanism for negative carbon isotope shifts during the toarcian oceanic anoxic event the prominent negative stable carbon isotope excursion in both carbonate and organic carbon recorded in organic rich sediments deposited during the toarcian oceanic anoxic event oae has commonly been explained by recycling of 13c depleted co2 the so called kuspert model more recently the massive release of 13c depleted methane or other forms of 13c depleted carbon was also proposed to account for the observed negative 13c excursions in organic carbon of terrigenous as well as of marine origin the occurrence of diagenetic products of the carotenoid isorenieratene isorenieratane and other aryl isoprenoids in toarcian black shales has been regarded as supporting evidence for the kuspert hypothesis as they point to strong stratification of the epicontinental seas a section of a drill core straddling the toarcian of the paris basin cirfontaineen ornois contained intact isorenieratane providing evidence that photosynthetic green sulphur bacteria were present at the time of deposition even prior to the oae however the isorenieratane abundances are very low in the section where the negative 13c excursion in organic carbon and phytane a chemical fossil derived from chlorophyll occurs the abundance of the isorenieratene derivatives increases once the 13c records have shifted to more positive values the 13c of isorenieratane generally circa 13 1 0 5 indicates that the respired co2 contribution at the chemocline was low and is thus not likely to be the main cause of the prominent up to 7 negative 13c shift recorded in toarcian organic carbon records

the toarcian oceanic anoxic event in southwestern gondwana an example from the andean basin northern chile palaeoenvironmental and palaeoclimatic changes during the toarcian oceanic anoxic event t oae are reported from two successions deposited in the andean basin chile based on a high resolution biostratigraphic calcareous nannofossils sedimentological mineralogical and geochemical analysis a large negative carbon isotope excursion was identified in a lower toarcian storm dominated marl limestone alternation underlining the global extent of the carbon cycle perturbation and the occurrence of episodic high energy conditions during the t oae low total organic carbon content and absence of redox sensitive trace element enrichment indicate that the dynamic depositional conditions did not favour the development of oxygen depleted conditions and the preservation of organic matter the decrease in kaolinite reflects a shift to more arid conditions whereas the increase in the chemical index of alteration at the onset of the t oae is probably related to a change in the sediment source less hydrolytic activity probably promoted a decrease in nutrient input in the andean basin mercury anomalies support the link between the onset of the karoo ferrar large igneous province activity the carbon cycle perturbation and the generated environmental change this paper presents one of the most complete t oae studies from the southern hemisphere and reveals that regional conditions strongly modulated the expression of this global event in the andean basin supplementary material the complete dataset the coefficient of correlation r for major and trace elements and the nannofossil assemblages are available at https doi org 10 6084 m9 figshare c 4133687

dynamics of a stepped carbon isotope excursion ultra high resolution study of early toarcian environmental change abstract in the toarcian early jurassic 183 myr ago the ocean atmosphere system was subject to one of the largest perturbations of the carbon cycle in the last 250 myr known as the toarcian oceanic anoxic event t oae this event was accompanied by a 6 negative carbon isotope excursion cie caused by massive injection of isotopically light carbon into the ocean atmosphere system possibly from destabilisation of gas hydrates this study reveals the pacing and sequence of events leading up to the cie and to widespread deposition of organic rich sediments the very high resolution isotopic record from exceptionally well preserved carbonate and organic matter from the paris basin enables recognition of increased co 2 levels 130 kyr in advance of the major negative cie an accelerated increase in the p co 2 is registered 25 kyr before the onset of this negative excursion and was so rapid and so intense that it led to a water column undersaturated with respect to calcium carbonate in the paris basin undersaturation is expressed as a dramatic drop in the accumulation of the biogenic calcite produced by the surface dwelling calcifiers these environmental perturbations representing precursor phases of co 2 injection predate the first step towards relatively light carbon isotopes in carbonate and organic matter and are tentatively attributed to karoo ferrar magmatism this negative shift was registered slightly earlier in terrestrial carbon than marine carbonate subsequent global warming is credited with liberating isotopically light carbon and ultimately fostered anoxia in the paris basin the response of these cumulative inputs of carbon to the earth system isotopic and sedimentological evidence indicates continuously elevated phytoplanktonic productivity throughout the first step of the negative cie suggesting that the biological pump accelerated the drawdown of excess carbon leading to temporary recovery of carbonate sedimentation 45 kyr after the first step of the cie this re establishment of the saturation state of the water column was only fleeting before the later stepwise release of isotopically light carbon

mercury deposition through the permo triassic biotic crisis abstract a 6 7 million year record of marine sedimentation through the permo triassic biotic crisis shows notable shifts in mercury concentrations that varied over an order of magnitude 0 002 to 0 116 g g mercury concentrations correlate strongly with total organic carbon showing both parallel increasing and decreasing trends over geologic time scales results suggest that changes in bioproductivity strongly influence mercury sequestration into marine sediment this may provide insight to potential marine response to modern anthropogenic hg loading and supports models that suggest enhanced bioproductivity that due to recent climate has increased hg sequestration over time

short paper a note on rb sr whole rock ages from cleaved mudrocks in the welsh basin two cleaved epizone grade palaeozoic mudrock suites from snowdonia yield a mean rb sr whole rock age of 409 11 ma this is consistent with resetting of the rb sr whole rock isotope systems of the mudrocks during cleavage development in end silurian early devonian acadian deformation in contrast cleaved palaeozoic anchizone mudrocks from north and central wales give a silurian mean age of 430 9 ma this dates either a pre tectonic isotopic event preserved through acadian anchizone metamorphism or mid silurian deformation and metamorphism at anchizone grade unaffected by the acadian event the precise timing of the main caledonian deformation in wales has never been established firmly powell phillips 1985 suggest that it occurred in north and south wales in latest silurian time whereas ashgill and end llandovery tectonic events were dominant in central wales see also george 1963 however woodcock 1984 1987 and soper et al 1987 have argued in favour of a single tectonic event of early to middle devonian age this chronological study was undertaken to address this controversy the only previous attempt to define precisely the timing of cleavage development in wales was the k ar dating of cleavage parallel chlorite from a volcanic greywacke from north wales fitch et al 1969 when recalculated using modern decay constants these data give an age of 399 10 ma bath 1974 demonstrated the feasibility of obtaining rb sr ages from cleaved mudrocks of the welsh caledonides and this work produced caledonian ages of 409 20ma and 393 22ma from north wales and late

strontium isotopes as indicators of mineral weathering in catchments determination of the 87sr 86sr ratio in rain water stream water soils and rocks in two scottish catchments has provided useful information on mineral weathering over a period of 26 months the 87sr 86sr ratio in rain water had mean values of 0 7095 and 0 7098 n 12 whereas stream water had mean values of 0 7080 n 16 in catchment in devonian andesites with strontium isotope ratios of 0 7117 0 7232 in the rocks and soils and 0 7184 n 16 in catchment of cambrian metamorphic rocks with strontium isotope ratios of 0 7360 0 8218 in the rocks and soils respectively the mineralogy consists predominantly of varying proportions of quartz plagioclase feldspar and k feldspar with some mica and chlorite the fact that the 87sr 86sr ratios in the stream in the andesitic catchment are lower than for the rain water probably indicates preferential weathering of plagioclase feldspar releasing 86sr rather than k feldspar and mica which contain greater amounts of 87sr the 87sr 86sr ratio acts as a tracer for the origin of the solutes in the stream water long term monitoring of the strontium isotope ratio in stream water could be a potential means of detecting relative changes in soil weathering rates due to environmental change

palaeoclimatic interpretation of clay minerals in marine deposits an outlook from the continental origin abstract as distribution of clay minerals in modern oceans seems to be controlled by contemporary climates marine clays in ancient deposits have been widely used to reconstruct palaeoclimates in this review we examine this question mainly from the continental origin of the clay minerals and show the difficulties of retrospective analysis of the influence of climate on common marine deposits we examine successively how soils develop and behave are reworked and palaeoweatherings are preserved focusing the review on kaolinitic soils indicative of tropical wet climates several stages intervene between the time of clay mineral development in soils and their final deposition in the basin 1 the persistence over geological times of huge amounts of kaolinitic palaeoweathering materials in the landscapes may seriously alter the palaeoclimatic signal of kaolinite in the sedimentary record although the kaolinite deposited in recent sediments of the world oceans is consistent with wet climatic zones this is mainly because the major kaolinitic and bauxitic palaeosurfaces coincide with the tropical areas where kaolinite is still developing at present 2 possible development of deep kaolinitic profiles at high latitudes and cold conditions under co 2 enriched palaeoatmospheres or even by unusual acidic weathering linked with dry climates is misleading palaeoenvironments for palaeoclimatic reconstruction 3 erosion and transport processes always cloud the signal to some extent because frequently erosion products from the bedrock and different soil horizons will be mixed and major drainage systems may include soils of different climatic zones 4 the arrival of the soil clay assemblages in the basin inevitably lags against their formation on the continent and may occur several million years after formation of the soils on the continent and climate may have considerably changed at that time it is pointed out that sedimentologists and palaeoclimatologists should consider the complexity of the relations between soil and sedimentary clay minerals soil formation rates are slow and therefore the resolution of the palaeoclimatic record in marine clay may not be closer than 1 or 2 ma at present the palaeoclimatic interpretations of marine clay assemblages are yielding at best nothing more than rather broad palaeoclimatic information this approach cannot achieve the same degree of resolution as other techniques such as isotope or microfossil studies clay mineral assemblages may provide integrated records of overall climatic impacts whereas other techniques are more likely to reveal local or temporary climates

chemostratigraphy of the jurassic system applications limitations and implications for palaeoceanography current chemostratigraphical studies of the jurassic system primarily involve the use of one sedimentary component marine organic carbon one divalent transition metal substituted in carbonate manganese and two isotopic tracers strontium isotope ratios 87 sr 86 sr and carbon isotope ratios 13 c carb and 13 c org in carbonate and in organic matter other parameters such as mg ca and sr ca ratios in calcite oxygen isotope ratios 18 o in carbonate sulphur isotope ratios 34 s in carbonate hosted sulphate nitrogen isotope ratios 15 n org in organic matter osmium isotope ratios 187 os 188 os in black shales and neodymium isotope ratios 143 nd 144 nd in various mineral phases are also useful but at present give poor resolution because the database is incomplete or compromised by various factors stratigraphical patterns in total organic carbon toc can be of either local or regional significance depending on the lateral extent of the former nutrient rich and productive water mass divalent manganese follows a similar pattern being concentrated most probably as a very early diagenetic phase only in oxygen depleted waters that typically underlie zones of elevated organic productivity shifts in mg ca and sr ca ratios on the time scale of ammonite subzones seem largely to reflect temperature changes strontium isotope ratios from pristine skeletal calcite provide a global signal 13 c values from carbonates with minimal diagenetic overprint potentially do the same although small spatial differences in palaeo water mass composition may have been locally significant oxygen isotope determinations on carbonate rocks and fossils generally yield values that are too scattered to be stratigraphically useful because they reflect palaeotemperature the evaporation precipitation balance in sea water and the impact of any diagenesis involving an aqueous phase nitrogen isotope ratios in organic matter reflect the chemistry of ancient water masses as affected by nitrate utilization and denitrification and the stratigraphical pattern of this parameter is more likely to correlate only on a regional basis neodymium isotope ratios in sea water are also water mass dependent and greatly affected by regional sources and oceanic current systems preliminary data on sulphur isotope ratios in carbonates and osmium isotope ratios in organic rich shales both potentially offering global correlation indicate that these tracers may be valuable although the records at present are not sufficiently well established to allow high resolution regional correlation in all cases biostratigraphically well dated reference sections against which the relevant geochemical data have been calibrated are required in the first instance to date studies on the stratigraphical distribution of organic carbon have been principally carried out in both northern boreal and southern tethyan europe carbon isotope stratigraphy has been undertaken primarily but not exclusively on bulk pelagic sediments from the alpine mediterranean or tethyan domain and strontium isotope stratigraphy has been undertaken largely on calcitic skeletal material belemnites and oysters from northern and southern europe in many sections including those containing ammonites multi parameter chemostratigraphy can give resolution that exceeds that attainable by classic biostratigraphical means strontium isotope ratios in skeletal calcite are a particularly powerful tool for illustrating changes in sedimentary rate and revealing gaps in the stratigraphical record

spatial variation of biologically available strontium isotopes 87sr 86sr in an archipelagic setting a case study from the caribbean this paper presents the results of strontium sr isotope analysis of modern and archaeological animal remains and modern plant samples from the caribbean region the goal is to assess if patterns of human mobility can be determined from the archaeological record in an archipelagic setting the range of variability and spatial distribution of biologically available strontium isotope signatures is reported and data evaluated to determine if sufficient heterogeneity exists to permit the identification of mobility despite the presence of potentially large contributions of marine strontium in island and coastal ecosystems the is landscape is divided into several sub regions based on the age and lithology of underlying geology and the variability of

provenance of the pre devonian sediments of england and wales sm nd isotopic evidence nd values and clast petrography of the longmyndian sediments of shropshire indicate a provenance dominated by juvenile high nd t uriconian volcanic sources but with an increasing detrital contribution from older low nd t metamorphic sources up section by contrast most lower palaeozoic strata of england and wales have low nd t values typical of sediments derived from long established continental crust the sm nd isotopic evidence suggests that avalonia received sediment from an adjacent large continent in the cambrian to lower ordovician and in the silurian ordovician and silurian volcanicity supplied juvenile detritus only during and shortly after active volcanism

paleoceanographic changes of the late pliensbachian early toarcian interval a possible link to the genesis of an oceanic anoxic event abstract secular records of the elemental and isotopic composition of belemnite calcite were studied in pliensbachian and toarcian sections from the yorkshire coast uk and southern germany to investigate oceanographic change during an interval prior to and including the toarcian oceanic anoxic event oae records from southern germany are correlated to the uk stratigraphy using strontium isotope stratigraphy the geochemical trends measured from belemnite calcite are consistent between the two sections and are interpreted in terms of temperature and salinity of the northwest european epi continental sea the data suggest that a dramatic environmental change coincided with the toarcian oae belemnite mg ca sr ca and na ca ratios increase by a factor of between 1 7 and 2 coincident with a 3 negative shift in 18o from the mid tenuicostatum zone until the lower falciferum zone of the uk ammonite biostratigraphy a period of 0 6 0 7 myr taken at face value the mg ca and 18o data argue for an abrupt warming of 6 7 c and substantial freshening during this interval global warming accompanied by an accelerated hydrological cycle and increased runoff is proposed to explain these changes prior to these events data from lower in the yorkshire section suggest a possible cooling accompanied by a shift to more saline waters during the period from the upper pliensbachian margaritatus zone to the toarcian lower tenuicostatum zone this earlier event may also have been important in causing density stratification in the northwest european epi continental sea

the early toarcian oceanic anoxic event in the external subbetic southiberian palaeomargin westernmost tethys geochemistry nannofossils and ichnology abstract the analysis of macroinvertebrates trace fossils calcareous nannofossils and geochemistry from pliensbachian to lower toarcian deposits of the subbetic southern spain allows us to interpret the incidence of the toarcian oceanic anoxic event t oae in the boundary between the tethys and the hispanic corridor trace fossils from the marl limestone rhythmite upper pliensbachian to lower toarcian indicate an oxygenated bottom a dark marly interval occurs above a fossil rich condensed surface with a negative excursion of 18o interpreted as evidence of the early toarcian transgression and a climate warming the carbon cycle perturbation is recorded by decreasing caco3 content and the negative excursion of 13c at the base of the serpentinum zone njt 6 nannofossil zone the barren interval for nektonic and benthic organisms at the beginning of the serpentinum zone confirms the oxygen restricted conditions in the sea floor environmental conditions were unfavourable for the development of calcareous nannoplankton as attested by the drop in absolute abundances the deep photic zone seemed to be particularly hostile to phytoplankton as shown by the decrease in relative abundance of the deep dweller mitrolithus jansae related to shoaling of the oxygen minimum zone in the water column increasing values of redox sensitive elements and total organic carbon as well as the record of pyrite framboids

resolving archaeological populations with sr isotope mixing models strontium isotope analysis of tooth enamel is a useful provenancing technique to investigate the childhood origins and residential mobility of ancient people however where different geographical target regions have similar biosphere 87sr 86sr it is often difficult to resolve the 87sr 86sr ranges of two different groups of people and establish what constitutes the local range at each site here a multi period study is presented from the outer hebrides scotland and an investigation of neolithic and early bronze age populations from the yorkshire wolds ne england the aim is to demonstrate that despite complex human dietary strategies simple mixing systems with only two end members do occur in archaeological human populations in certain geological provinces and despite overlapping 87sr 86sr ranges it is possible to separate two populations based on the structure within the data set

the early toarcian early jurassic and the cenomanian turonian late cretaceous mass extinctions similarities and contrasts abstract the early toarcian eto and cenomanian turonian c t mass extinctions are comparable from a wide range of scales and perspectives from a broad standpoint their similarities include virtually identical extinction intensity at the familial and generic levels widespread basinal facies deposited during sea level highstands an overall greenhouse climate and anoxia as an important causal mechanism the high resolution macroinvertebrate data analyzed here consisting of stratigraphic ranges diversity and abundance point to smaller scale similarities the two events resulted in significant ecological disruption and in both cases the biotic responses were very similar taxa inhabiting the upper water column were unaffected by anoxia and included ammonites and in the eto belemnites in addition epifaunal taxa adapted to low oxygen conditions such as the buchiids posidoniids and inoceramids flourished in the post extinction environment during the survival interval as conditions ameliorated the biota became more diverse and gradually began to resemble pre extinction biotas furthermore the 13c curves predict the end of the survival interval and suggest that the period characterized by carbon isotope excursions represent disrupted environmental conditions this points to the potential application of 13c as a tool for determining the repopulation modes and timing for other mass extinctions

spatial variation of strontium isotopes 87sr 86sr in the maya region a tool for tracking ancient human migration strontium isotope ratios 87sr 86sr in human bones and teeth have become a useful tool to study migration and sedentism of individuals from archaeological contexts here we analyzed 87sr 86sr of water bedrock soils and plants across a broad geographic region to test the potential of this method in the ancient maya area our aims were two fold first to test if the sources of dietary strontium i e plants and water in humans reflect the 87sr 86sr ratio of exposed bedrock and second to determine whether the ranges of 87sr 86sr values were sufficiently distinct among the principal maya geocultural areas to infer past migration we identified five distinct subregions on the basis of geologic maps and evaluated the variability of 87sr 86sr values values given as mean 87sr 86sr 2 standard deviations number of samples 1 northern lowlands 0 70888 0 00066 n 16 2 southern lowlands 0 70770 0 00052 n 86 3 volcanic highlands and pacific coast 0 70415 0 00023 n 34 4 metamorphic province 0 70743 0 00572 n 50 and 5 the maya mountains of belize 0 71327 0 00167 n 3 although the sample size is small and overlap exists in 87sr 86sr values among some subregions most areas can be readily distinguished from one another on the basis of strontium isotopes these subregional 87sr 86sr differences provide archaeologists with a powerful tool to recognize geographic outliers in ancient maya burials and thereby test hypotheses concerning the origin of specific individuals inferred population migration patterns and the possibility of outside cultural influences in the maya region

isotope domain mapping of 87sr 86sr biosphere variation on the isle of skye scotland abstract the potential of 87 sr 86 sr isotope composition for tracking and determining the origin of material whether it is humans animals water or wine can be fully realized only if high quality reference datasets are available against which to compare the unknowns this is currently not the case despite the rapid increase in 87 sr 86 sr based provenance studies of biosphere materials there are no well documented maps available most researchers resort to generating reference maps from a variety of geological datasets plus the analysis of sparse environmental9 samples a major reason for this lack of reference material is the investment needed to undertake systematic sampling and analysis over large areas a further problem is associated with the choice of proxy material as organisms differ in their habitat and exploitation of resources in this paper various approaches to isotope biosphere sampling are considered some of the problems are assessed the precision required for the study of human populations is discussed and a first attempt is made to condense all of the available information into an isotope package9 map the work is based on a study undertaken on the isle of skye in the inner hebrides and reduces the complexity of geological and isotope data into five main 87 sr 86 sr packages package 1 northern area 0 705 0 7092 package 2 ne coast 0 7082 0 7102 package 3 granitic rocks 0 716 0 720 package 4 metamorphic rocks 0 7092 0 7188 package 5 seawater 0 7092 0 005 2 the approach of trying to constrain the isotope composition of certain areas and or lithologies offers the possibility of extrapolating to other similar areas without having to sample at the original density

strontium isotope investigation of ungulate movement patterns on the pleistocene paleo agulhas plain of the greater cape floristic region south africa abstract middle stone age sites located within the greater cape floristic region on the south african southern coast have material culture with early evidence for key modern human behaviors such as projectile weaponry large animal hunting and symbolic behavior in order to interpret how and why these changes evolved it is necessary to understand their ecological context as it has direct relevance to foraging behavior during periods of lowered sea level a largely flat and vast expanse of land existed south of the modern coastline but it is now submerged by higher sea levels this exposed area the paleo agulhas plain likely created an ecological context unlike anything in the region today as evidenced by fossil assemblages dominated by migratory ungulates one hypothesis is that the paleo agulhas plain supported a migration ecosystem of large grazers driven by summer rainfall producing palatable forage during summer in the east and winter rainfall producing palatable forage during winter in the west alternatively ungulates may have been moving from the coastal plain in the south to the interior north of the cape fold mountains as observed for elephants in historic times in this study we assess ungulate movement patterns with inter and intra tooth enamel samples for strontium isotopes in fossil fauna from pinnacle point sites pp13b and pp30 to accomplish our goals we created a bioavailable 87sr 86sr isoscape for the region by collecting plants at 171 sampling sites and developing a geospatial model the strontium isotope results indicate that ungulates spent most of their time on the paleo agulhas plain and avoided dissected plain foothill and mountain habitats located more than about 15 km north of the modern coastline the results clearly exclude a north south coastal interior movement or migration pattern and cannot falsify the east west movements hypothesized in the south coast migration ecosystem hypothesis

secular environmental precursors to early toarcian jurassic extreme climate changes the early toarcian oceanic anoxic event t oae about 183 myr ago was a global event of environmental and carbon cycle perturbations which deeply affected both marine biota and carbonate production nevertheless the long term environmental conditions prevailing prior to the main phase of marine extinction and carbonate production crisis remain poorly understood here we present a similar to 8 myr long record of early pliensbachian middle toarcian environmental changes from the lusitanian basin portugal in order to address the long term paleoclimatic evolution that ultimately led to carbonate production and biotic crises during the t oae paleotemperature estimates derived from the oxygen isotope compositions of well reserved brachiopod shells from two different sections reveal a pronounced similar to 5 degrees c cooling in the late pliensbachian margaritatus spinatum ammonite zones boundary this cooling event is followed by a marked similar to 7 10 degrees c seawater warming in the early toarcian that after a second cooling event in the mid polymorphum zone culminates during the t oae calcium carbonate caco3 contents the amount of nannofossil calcite and the mean size of the major pelagic carbonate producer schizosphaerella all largely covary with paleotemperatures indicating a coupling between climatic conditions and both pelagic and neritic caco3 production furthermore the cooling and warming episodes coincided with major marine regressions and transgressions respectively suggesting that the growth and decay of ice caps may have exerted a strong control on sea level fluctuations throughout the studied time interval this revised chronology of environmental changes shows important similarities with neogene and paleozoic episodes of deglacial black shale formation and thus prompts the reevaluation of ice sheet dynamics as a possible agent of mesozoic events of extinction and organic rich sedimentation c 2010 elsevier b v all rights reserved

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

continental weathering and redox conditions during the early toarcian oceanic anoxic event in the northwestern tethys insight from the posidonia shale section in the swiss jura mountains abstract the geochemistry and mineralogy of organic rich sediments of the rietheim succession in northern switzerland were studied to evaluate the main impacts of the early toarcian oceanic anoxic event t oae 183 ma ago on the depositional environment in the nw tethys ocean the geochemical data obtained notably 13corg 13ccaco3 rock eval pyrolysis toccff support the hypothesis that the negative c isotope excursion at the onset of the t oae mainly reflects a major perturbation in the global carbon cycle rather than local environmental changes e g basinal restriction productivity rock eval pyrolysis and 13corg 15ntotal crossplots indicate that the organic matter was primarily of marine origin during the t oae and deposited in an epicontinental sea setting detrital proxies notably detritus index siliciclastic balance and ln al2o3 na2o suggest that the elevated pco2 levels and greenhouse climate prevailing during the t oae induced significant acceleration of the hydrologic cycle and an increase in continental chemical weathering rates redox sensitive proxies relative pyrite contents organic and sulfide balances v v ni ratios trace elements enrichment factors trace element toc co variation patterns and toc ptotal molar ratios indicate that the rietheim posidonia shale sediments accumulated under oxic to dysoxic bottom water conditions with more reducing conditions during the t oae anoxic and possibly euxinic these changes in redox conditions were probably induced by substantial thermohaline stratification driven by enhanced freshwater input and the recurrent influx of brackish arctic seawater into the nw tethys through the viking corridor in agreement with previous sedimentological and geochemical evidences from the nw tethys ocean in the studied succession such conditions were perhaps also responsible for sequestration of most of the regenerated p in the deeper water column by adsorption and or co precipitation into authigenic phases overall the major palaeoenvironmental changes documented in this study provide a robust example of earth s possible responses to the rapid onset of extreme greenhouse conditions

tracking multiple sr sources through variations in 87sr 86sr ratios of surface waters from the aljustrel massive sulphide mining area geological versus anthropogenic inputs abstract this study presents major and trace element data and 87sr 86sr ratios for surface waters from a small watershed draining the aljustrel sulphide mining area south portugal the watershed is located in a geologically complex area comprising two main compartments the northern compartment is dominated by cenozoic formations and does not bear any mining activity whilst the southern compartment is underlain by rocks from both the cenozoic sedimentary cover and the mineralized sequences of the variscan paleozoic basement of the south portuguese zone based on the available geochemical and isotopic data the analysed water samples can be roughly divided into five main groups a group 1 corresponds to amd contaminated water drainages from the southern part of the catchment showing ph 8 marked depletions in so4 and heavy metals and displaying sr isotopic compositions similar to rainwater 87sr 86sr 0 7097 0 7098 c group 3 includes mixed type stream waters with ph and elemental isotopic signatures intermediate between those of groups 1 and 2 d group 4 comprises the samples collected at two lime treated water dams from the mining area that are clearly distinguished from the impacted waters of group 1 by their elevated ca mg and sr concentrations and low 87sr 86sr ratios 87sr 86sr 0 7085 0 7091 e group 5 includes clean waters from two dams located upstream of the ore processing site which are dominantly supplied by direct precipitation and surface runoff and have ph 6 very low so4 and metal concentrations and 87sr 86sr ratios varying between 0 7094 and 0 7108 variations in the 87sr 86sr ratios and sr concentrations of the analysed waters are attributed to mixing of two main end members atmospheric meteoric waters local rainfall runoff with low sr contents and 87sr 86sr ratios 0 7095 and more radiogenic waters derived from the aljustrel mining area the highly radiogenic signatures of the southern tributaries appear to have been controlled by weathering of plagioclase from the acid volcanic rocks of the paleozoic basement enhanced by mining activities pyrite oxidation although released strontium from gangue carbonates could have locally contributed to the fluctuations of sr contents and 87sr 86sr ratios observed in some of these water samples by contrast the low 87sr 86sr ratios and relatively high sr cl and na concentrations shown by the surface waters draining the northern compartment suggest that these tributaries correspond to meteoric waters that have gained cl na and sr through wash out of cenozoic deposits containing finely disseminated halite layers finally the decrease in the 87sr 86sr ratios and elevation of sr contents observed in the samples from the lime treated water dams support the involvement of an anthropogenic source of sr with 87sr 86sr ratios lower than that of rainfall

mercury as a proxy for volcanic activity during extreme environmental turnover the cretaceous paleogene transition abstract the usually low geological background concentrations of hg makes this trace element suitable for identifying accumulation pulses in sediments that can be tentatively related to weathering processes and thus to climatic changes intense volcanism has witnessed the cretaceous paleogene transition ktb and was perhaps responsible for dramatic climatic changes and decrease in biodiversity and mass extinction we have used hg concentrations as a proxy for volcanic activity and atmospheric hg and co2 buildup across the ktb at three localities in the salta basin argentina hg contents display several spikes across the ktb with a maximum value of 250 ng g 1 in three drill cores across the ktb in the paraiba basin northeastern brazil hg contents increase from the late maastrichtian to early danian and hg spikes predate the ktb perhaps as a record of volcanic activity before but very close to this transition at stevns klint denmark hg contents reached almost 250 ng g 1 within a 5 cm thick clay layer the fiskeler member fish clay that comprises the ktb some co variation between hg and al2o3 contents has been observed in all of the studied sections across the ktb suggesting that hg is probably adsorbed onto clays thermo desorption experiments in selected samples from the yacoraite formation showed hg 2 as the major species present which is in agreement with a volcanic origin combined hg and c isotope chemostratigraphy may become a powerful tool for the eventual assessment of the role of volcanic activity during extreme climatic and biotic events such as those during the ktb

pliensbachian toarcian ostracod biogeography in nw europe evidence for water mass structure evolution abstract this paper examines the role played by palaeoceanographic and climatic conditions on the palaeobiogeography of the pliensbachian toarcian ostracods early jurassic in the european epicontinental sea ees the influence of the palaeogeography ocean currents and sea level temperature and salinity variations on ostracod abundance diversity and migration patterns is reconstructed ostracod migration follows an anticlockwise circulation in the eastern side of the ees with a leading northeast southwest movement and the frequent arrival of tethyan faunas into the central and western parts of the ees during the pliensbachian a three fold classification of water masses based on salinity temperature lithological and fossil data is proposed the repeated inflow of tethyan ostracods into the ees ended by the earliest toarcian this ostracod event is related to the opening of the hispanic corridor and to the reorganization of the surface and deep circulations that may have generated a cold episode at the beginning of the toarcian

phosphogenesis and organic carbon preservation in the miocene monterey formation at naples beach california the monterey hypothesis revisited the middle part of the miocene monterey formation at naples beach west of santa barbara california is predominantly composed of organic rich mudstone interstratified with phosphatic laminae minor lithologies include volcanic ash dolomite porcelanite and chert and condensed phosphatic beds sediments dated as 14 3 13 5 ma have average total organic carbon toc values around 8 5 wt and organic carbon oc accumulation rates are around 565 mg cm2 k y sediments dated as 13 5 13 ma are characterized by average toc values of 12 6 wt and oc accumulation rates of around 1130 mg cm2 k y the interval between 13 and 10 6 ma is marked by condensation average toc values are around 8 6 wt and oc accumulation rates diminished to around 55 mg cm2 k y the last interval studied is dated as 10 6 9 4 ma and average toc values are around 6 wt whereas oc accumulation rates rose again to 320 mg cm2 k y the presence of erosional surfaces angular unconformities and reworked clasts and nodules suggests that bottom current activity and gravity flow deposition have been instrumental in sediment accumulation the phosphatic laminae were precipitated at a very early stage of diagenesis during periods of nonsedimentation they formed less permeable sedimentary lids and may as such have contributed to enhanced oc preservation between 13 and 10 6 ma the thus formed phosphatic laminae were frequently subjected to subsequent sediment winnowing and reworking resulting in the formation of condensed phosphatic beds calculated p c molar ratios suggest that 1 the measured section is highly enriched in phosphorus p relative to oc 2 regeneration of organic p from organic matter decomposition was negligible and 3 the source of p was external likely upwelled bottom water rich in inorganic p in spite of good preservation conditions and correspondingly high toc contents the overall oc accumulation rates are moderate in comparison to those of actual high productivity areas which is mainly due to the episodic character of depositional processes and the intervening long periods of nondeposition and sediment reworking they preclude this section and by extrapolation the monterey formation in general from being an important oc sink during the middle miocene alternatively large oc sinks were probably created on the continent lignite deposits and in sedimentary depocenters which received increasing amounts of detrital sediments due to a combination of climate change spreading of grasslands and the increasing importance of mountain chains such as the himalaya the associated high nutrient fluxes may have been involved in the backstepping and drowning of carbonate platforms and in the generation of widespread phosphat rich deposits during the late early and early middle miocene

the paleoclimatic interpretation of clay minerals in sediments a review abstract the application of paleoclimatic interpretation to clay minerals from continental and marine sediments is reviewed and the advantages of this method are indicated levels relatively rich in chlorite illite palygorskite and quartz are interpreted as corresponding to relatively dry periods while more humid periods lead to more intensive weathering and consequently to the dominance of clay minerals more advanced in the relative stability scale such as kaolinite smectite is taken to indicate a climate with contrasting seasons and a pronounced dry season using this and similar schemes the paleoclimates of areas adjoining the mediterranean basin north sea north atlantic southern arctic equatorial and north west pacific and north phillipine sea are reconstructed clay minerals in sediments particularly marine sediments can be useful indicators of paleoclimatic conditions while they do not produce direct indications of climatic parameters they provide integrated records of overall climatic impact occasionally they may be superior to the more conventional paleoclimatic methods such as pollen or oxygen isotope analysis the limitations imposed on the paleoclimatic interpretation of clay minerals in sediments are discussed on the basis of examples the distinction between authigenic and detrital clay minerals is shown to be problematic particularly with regard to smectite the relationship between climatic parameters and clay mineral formation is complicated by the intervention of extra climatic factors such as topography geomorphology lithology and time post depositional diagenetic changes may not be recognized differentiation during transport due to size sorting or differential flocculation may overlap climate induced differentiation the association of clay mineral assemblages with specific source areas presents difficulties due to dispersal pathways that are affected by type of transport agency i e water ice or wind transport agencies are not constant with time by an interdisciplinary approach with the paleoclimatic information derived from clay minerals being correlated with that obtained from the analysis of microfossils and oxygen isotope data many of these limitations can be overcome

spatial variations in biosphere 87sr 86sr in britain abstract strontium isotopes are a powerful tool for investigating the geographical origins of people and animals but assignment of provenance requires reference maps and databases this paper presents a map of strontium isotope variations across britain for use in archaeological and other studies and is produced by direct measurement of strontium isotope compositions of biosphere components predominantly plants the map characterizes the biosphere signature of specific lithologies a technique that is applicable worldwide marine derived strontium from both rainwater and coastal sea splash and spray is an important contribution to the british biosphere particularly on the western seaboard which is subject to high rainfall and prevailing westerly winds supplementary material methods full data table and full size version of figure 1b are available at http www geolsoc org uk sup18388

water rock tailings interactions and sources of sulfur and metals in the subtropical mining region of taxco guerrero southern mexico a multi isotopic approach abstract multi isotope h o s sr pb systems coupled with conventional major and trace element hydrogeochemical analysis were applied to determine the origin of water to model water rock tailings interactions and for source apportionment of sulfur and associated toxic metals in the mining region of taxco guerrero in southern mexico oxygen and h isotopes indicate that meteoric water in the zone is rainwater undergoing varying degrees of isotopic fractionation by atmospheric evaporation whereas sr isotopes trace the interaction of pristine water from volcanics of the regional recharge zone and subsequently flowing through sandstone and shale to spring points leachates form from two distinctive sources spring water and surface water having differential interactions with bedrocks prior to entering the tailings compared to pristine water leachates are enriched in sulfate metals e g fe mn pb and zn and metalloids e g as the sulfur isotopic composition of ore sulfides leachates secondary precipitates regional surface water and hypogenic sulfates is described in terms of a two component mixing model with shale of mexcala and limestone of morelos formations representing the light and heavy end members respectively whereas sr isotopic composition is bracketed combining three lithogenic mexcala morelos tilzapotla and taxco schist sources finally leachates have a mixture of lead from ore sulfides and taxco schist formation family i or from ore sulfides alone family ii the application of multiple environmental isotopic techniques is an outstanding tool for elucidating complex interactions of water with bedrocks and tailings and for determining the source of sulfur and toxic metal from mining and other metal polluted environments

faunal replacement in the early jurassic of northern chile implications for the evolution in mesozoic benthic shelf ecosystems abstract long term within habitat species replacement is either evolutionary or ecological in nature ecological replacement of dominant species by unrelated species which share essentially the same niche requirements is a very characteristic feature of early jurassic benthic shelf faunas from northern chile more than that an examination of the relevant literature reveals that the process was significant in mesozoic benthic shelf ecosystems on the whole it occurred among all important guilds and in a broad range of environmental subdivisions salinity controlled environments coarse grained and fine grained shallow shelf mid to outer shelf and oxygen controlled environments in contrast evolutionary replacement of dominant faunal elements appears to have been limited to restricted basins faunal replacement was the underlying process of several distinctive patterns in the temporal distribution of mesozoic benthic shelf faunas that is the evolutionary stability of dominant morphoptypes the widespread occurrence of parallel associations and the persistence of guild assemblages through time fluctuations of relative sea level are regarded as a substantial controlling factor of within habitat species replacement

ostracode mg ca paleothermometry in the north atlantic and arctic oceans evaluation of a carbonate ion effect 1 the reconstruction of deep sea bottom water temperature bwt is important to assess the ocean s response to and role in orbital and millennial scale climate change deep sea paleothermometry employs magnesium to calcium mg ca ratios in calcitic benthic microfaunas foraminifera ostracodes as a primary proxy method mg ca paleothermometry may however be complicated by bottom water carbonate ion chemistry which might affect mg ca ratios in shells to address temperature and carbonate ion influence on mg ca ratios we studied mg ca ratios in the benthic ostracode genus krithe in the north atlantic and arctic oceans using a 686 specimen core top collection including 412 previously unpublished analyses mg ca ratios are positively correlated to temperature in multiple species from the north atlantic bwt 0 885 mg ca 5 69 r2 0 73 and for k glacialis in the arctic ocean and nordic seas bwt 0 439 mg ca 5 14 r2 0 50 consistent with previously published calibrations we found no evidence for a relationship between krithe mg ca and carbonate ion saturation in the north atlantic ocean nordic seas and arctic ocean supporting the use of krithe mg ca for reconstructing past bwt

dating the transition of smectite to illite in palaeozoic mudrocks using the rb sr whole rock technique the interpretation of mudrock rb sr whole rock regression ages using stratigraphically well constrained samples from the ordovician and silurian of central wales is re examined two new rb sr whole rock regressions are presented along with k ar and rb sr data from the

multiproxy geochemical analysis of a panthalassic margin record of the early toarcian oceanic anoxic event toyora area japan abstract the early toarcian oceanic anoxic event oae was a significant palaeoenvironmental perturbation that led to marked changes in ocean chemistry and climate and which also had a long lasting impact on marine ecosystems the global significance of the event has been recognised from the widespread occurrence of a 3 7 negative excursion in the carbon isotope 13 c composition of marine organic and inorganic matter and terrestrial plant material this feature of the event is indicative of a pronounced perturbation to the global carbon cycle an inference further supported by widespread evidence for seawater deoxygenation and elevated rates of organic carbon burial nevertheless the precise palaeoenvironmental impacts of this event from sections outside of the boreal and tethyan realms are uncertain here we present the results of a multiproxy geochemical study of an expanded record of the early toarcian event from the northwest panthalassa ocean margin exposed in southwest japan toyora area yamaguchi prefecture our results indicate that in the studied succession organic matter enrichment persisted through the early toarcian event but elemental redox proxies do not support persistent seawater anoxia analyses of terrigenously derived major and trace element abundances coupled with sedimentological observations reveal an increase in coarse grained sediment close to the onset of a 4 excursion in 13 c org and coincident with an inferred increase in terrestrial organic matter flux these observations are consistent with previously published evidence for a marked strengthening of hydrological cycling and increased runoff that occurred contemporaneously with abrupt warming at the onset of the carbon isotope event

update of the carbon and oxygen isotopic records of the early late pliensbachian early jurassic 187ma insights from the organic rich hemipelagic series of the lusitanian basin portugal abstract a high resolution carbon and oxygen isotopic bulk carbonate record from organic rich hemipelagic series of early late pliensbachian age 187 ma is presented for the lusitanian basin portugal and compared to the record of other sedimentary basins this dataset provides an excellent basis for discussing newly raised questions concerning the hypothesis of major carbon cycle perturbations prior to the toarcian oceanic anoxic event in addition to the recognition in the studied series of two positive carbon isotope excursions previously defined elsewhere corresponding to the ibex and margaritatus uppermost stokesi gibbosus subzones zones a third positive excursion is identified here for the first time at the davoei zone in the lusitanian basin these excursions are associated with organic rich facies intervals the younger excursion may be related to worldwide enhanced preservation of organic matter in the margaritatus zone we suggest that until these organic rich facies are well age constrained at a wider scale and high resolution carbon data are provided from other locations and that worldwide anoxia is proven this interval should be referred to as an organic matter preservation interval late pliensbachian ompi this period is probably linked with the complex chain of events that eventually led to the toarcian oceanic anoxic event

distribution of strontium isotopes in river waters across the tarim basin a map for migration studies as the junction of the silk roads the tarim basin played a critical role in human migration and cultural interaction between the east and the west recently population migration patterns have been increasingly reconstructed from strontium isotope ratios 87 sr 86 sr in archaeological human skeletons and further constraints on their provenance require a bioavailable 87 sr 86 sr map across the basin based on measurement data from 44 river samples in this study and 29 samples from published data we generate the first map of bioavailable 87 sr 86 sr values across the tarim basin and the neighbouring area from the baseline map three geologically distinct regions can be identified 1 the yili block tian shan orogenic belt and northern tarim block with lower ratios 0 7105 0 0007 1 n 25 2 the southern tarim block with higher ratios 0 7118 0 0008 n 29 and 3 the eastern pamir block with diverse values 0 7110 0 0009 n 19 this map is a promising tool for recognizing the origins of immigrants in the tarim basin and may aid understanding of the migration patterns and cultural communication along the silk roads

late cretaceous to early paleocene climate and sea level fluctuations the tunisian record abstract climate and sea level fluctuations across the cretaceous tertiary k t transition in tunisia were examined based on bulk rock and clay mineralogies biostratigraphy and lithology in five sections el melah el kef elles ain settara and seldja spanning from open marine to shallow inner neritic environments late campanian to early danian trends examined at el kef and elles indicate an increasingly more humid climate associated with sea level fluctuations and increased detrital influx that culminates at the k t transition this long term trend in increasing humidity and runoff in the tethys region is associated with middle and high latitude cooling results of short term changes across the k t transition indicate a sea level lowstand in the latest maastrichtian about 25 100 ka below the k t boundary with the regression marked by increased detrital influx at el kef and elles and a short hiatus at ain settara a rising sea level at the end of the maastrichtian is expressed at elles and el kef by deposition of a foraminiferal packstone a flooding surface and condensed sedimentation mark the k t boundary clay which is rich in terrestrial organic matter the p0 p1a transition is marked by a sea level lowstand corresponding to a short hiatus at ain settara where most of p0 is missing and a period of non deposition and erosion in the lower part of p1a 64 95 ma at seldja p0 and possibly the topmost part of cf1 are missing these sea level fluctuations are associated with maximum humidity these data suggest that in tunisia long term environmental stresses during the last 500 ka before the k t boundary and continuing into the early danian are primarily related to climate and sea level fluctuations within this long term climatic trend the pronounced warm and humid event within the latest maastrichtian zone cf1 may be linked to greenhouse conditions induced by deccan volcanism the absence of any significant clay mineral variations at or near the k t boundary and ir anomaly suggests that the bolide impact had a relatively incidental short term effect on climate in the tethys region

carbon isotope record of the early jurassic toarcian oceanic anoxic event from fossil wood and marine carbonate lusitanian basin portugal thetoarcianoceanicanoxicevent oae intheearlyjurassic 183maago wascharacterizedbywidespreadnear synchronous deposition of organic rich shales in marine settings as well as perturbations to several isotopic systems characteristically two positive carbon isotope excursions in a range of materials are separated by an abrupt negative shift carbon isotope profiles from toarcian fossil wood collected in england and denmark have previously been shown to exhibit this large drop 7 i n 13 c values interpreted as due to an injection of isotopically light co2 into the ocean atmosphere system however the global nature of this excursion has been challengedonthebasisofcarbon isotopedatafromnektonicmarinemolluscs belemnites whichexhibitheavierthanexpectedcarbonisotope values here we present new data principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at peniche coastal portugal this section is low in organic carbon average toc 0 5 and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin the carbon isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion which parallels exactly the profile based on bulk carbonate samples from the same section albeit with approximately twice the amplitude 8 in wood versus 3 5 in carbonate these data indicate thatthe negative carbon isotope excursion affected the atmosphereand by implication the global ocean as well the difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion for which there is independent evidence from marine osmiumisotope records and plausibly changes in atmospheric co2 content for which independent evidence is also available the peniche succession is also notable for the occurrence of re deposited sediments their lowest occurrence coincides with the base of the negative excursionandtheirhighestoccurrencecoincideswithitstop thus slopeinstabilityandsedimentsupplycouldhavebeenstronglylinked to the global environmental perturbation an association that may misleadingly simulate the effects of sea level fall

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

modeling evidences for global warming arctic seawater freshening and sluggish oceanic circulation during the early toarcian anoxic event 1 the paleoecological disturbances recorded during the early toarcian warming event 183 myr ago including marine anoxia sea level rise seawater acidification carbonate production crisis and species extinctions are often regarded as past examples of earth s possible responses to the rapid emergence of super greenhouse conditions however physical mechanisms explaining both the global and local expressions of paleoenvironmental events are still highly debated here we analyze the paleoclimatic and paleoceanographic consequences of increases in atmospheric pco2 levels at a multiscale resolution using a fully coupled ocean atmosphere model foam we show that in association with stronger high latitude precipitation rates and enhanced continental runoff the demise of polar sea ice due to the global warming event involved a regional freshening of arctic surface seawaters these disturbances lead to progressive slowdowns of the global oceanic circulation accountable for widespread ocean stratification and bottom anoxia processes in deep oceanic settings and epicontinental basins in agreement with very negative oxygen isotope values measured on fossil shells from the nw tethys our simulations also show that recurrent discharges of brackish and nutrient rich arctic surface waters through the viking corridor could have led to both vertical and geographical gradients in salinity and seawater 18o in the nw tethyan seas locally contrasted conditions in water mass density and rises in productivity rates due to strong nutrient supplies could partly explain the regional severity of the anoxic event in the restricted euro boreal domains as it has been previously suggested and modeled regionally

migration and viking dublin paleomobility and paleodiet through isotopic analyses abstract during the early medieval period in ireland dublin was established as the largest viking settlement on the island in the ninth century ad a previous biodistance study has suggested that the population of the town consisted of a polyethnic amalgam of immigrant and indigenous in this study we use biogeochemistry to investigate paleomobility and paleodiet in archeological human remains from the ninth to eleventh century levels at the sites at fishamble street ii national museum of ireland excavation number e172 fishamble street iii e190 and john s lane e173 as well as twelfth century remains from wood quay e132 through radiogenic strontium isotope stable oxygen carbon and nitrogen isotope and elemental concentration analyses we investigate the origins of the individuals who lived and died in early and late viking dublin mean archaeological human enamel and bone isotope values from dublin are 87 sr 86 sr 0 70975 0 00139 2 n 22 13 c carbonate v pdb 14 8 0 8 1 n 12 and 18 o carbonate v pdb 7 2 1 0 1 n 12 archaeological human bone samples exhibit mean 13 c collagen v pdb 20 8 0 5 1 n 12 and mean 15 n collagen air 10 0 1 7 1 n 12 comparing these data with archaeological faunal data from dublin and published data from northern europe we argue that there are no clear immigrants from other parts of the north atlantic although there is one clear outlier in both origins and diet overall the relative homogeneity in both paleomobility and paleodiet may support models of acculturation in viking dublin rather than a high number of first generation immigrants or continued migration from scandinavia

rare earth elements neodymium and strontium isotopic systematics in mineral waters evidence from the massif central france abstract rare earth elements rees and sr and nd isotope distributions have been studied in mineralized waters from the massif central france the co 2 rich springs are characterized by a neutral ph 6 7 associated with total dissolved solids tds from 1 to 7 g l 1 the waters result from the mixing of very mineralized water pools thought to have equilibrated at a temperature of around 200 c with superficial waters these two mineral water pools evidenced by sr isotopes and dissolved rees could reflect 2 different stages of water rock interaction and an equilibrium with different mineral assemblages the concentrations of individual dissolved rees and total dissolved rees ree in the mineral waters examined vary over several orders of magnitude but are not dependent on the main parameters of the waters tds t c ph total organic c the dissolved ree concentrations presented as upper continental crust normalized patterns show hree enrichment in most of the samples the time evolution of ree patterns does not show significant fluctuations except in 1 borehole located in the limagne d allier area which was sampled on 16 occasions over an 18 month period ten samples are hree enriched whereas 6 samples show flat patterns the aqueous speciation of rees shows that co 2 3 complexes dominate 80 over the free metal f so 2 4 and hco 3 complexes the detailed speciation demonstrates that the fractionation of rees i e the hree enrichment in co 2 rich and ph neutral fluids is due essentially to the predominance of the co 2 3 complexes the sr isotopic composition of the mineral waters in the massif central shows different mixing processes in the cezallier area at least 3 end member water types exist the most dilute end member is likely to originate as poorly mineralized waters with minimal groundwater circulation two other mineralized end members are identified although the link between the geographical location of spring outflow and the mixing proportion between the 2 end members is not systematic the range in nd 0 for mineralized waters in the massif central correlates well with that of the known parent rocks except for 4 springs one way to explain the nd 0 in these instances is a contribution from drainage of volcanic rocks the isotopic systematics help to constrain the hydrogeological models for this area

the first large scale bioavailable sr isotope map of china and its implication for provenance studies abstract strontium isotope ratio 87sr 86sr has been widely used to trace human migrations across geologically distinct landscapes in archaeological and forensic sciences 87sr 86sr based provenance studies require a detailed strontium reference map to make valid interpretations of mobility patterns for a given region in this study we first review the previous development for 87sr 86sr isoscapes relevant to research on migration and then present the first map of bioavailable 87sr 86sr ratios for china based on 1935 measurements on biosphere samples collated from published research and supplemented by our targeted collection strategy the results show that 87sr 86sr ratios in china span a large range and exhibit regional patterns largely dependent on the divergent geological conditions of each of china s tectonic blocks we further combine river water 87sr 86sr ratios with lithology integrated elemental data and chemical weathering rates to determine which dominant weathering patterns e g silicate carbonate or evaporite have the most significant influence on 87sr 86sr ratios the low ranges of 87sr 86sr ratios 0 7125 appear in the cathaysia block as well as some orogenic belts and the southeastern margin of the tibetan plateau likely due to the influence of the metamorphic rocks and granitoid sources additionally topography differential weathering among lithologies and eolian deposits e g loess are also significant factors that influence 87sr 86sr ratios in china our study reveals that the large variation of 87sr 86sr ratios across china is predominately driven by geological conditions revealing that future sr isotope provenance studies can shed on ancient and historical migrations in china

high resolution sea surface reconstructions off cape hatteras over the last 10 ka 1 this study presents high resolution foraminiferal based sea surface temperature sea surface salinity and upper water column stratification reconstructions off cape hatteras a region sensitive to atmospheric and thermohaline circulation changes associated with the gulf stream we focus on the last 10 000 years 10 ka to study the surface hydrology changes under our current climate conditions and discuss the centennial to millennial time scale variability we observed opposite evolutions between the conditions off cape hatteras and those south of iceland known today for the north atlantic oscillation pattern we interpret the temperature and salinity changes in both regions as co variation of activities of the subtropical and subpolar gyres around 8 3 ka and 5 2 3 5 ka positive salinity anomalies are reconstructed off cape hatteras we demonstrate for the 5 2 3 5 ka period that the salinity increase was caused by the cessation of the low salinity surface flow coming from the north a northward displacement of the gulf stream blocking the southbound low salinity flow concomitant to a reduced meridional overturning circulation is the most likely scenario finally wavelet transform analysis revealed a 1000 year period pacing the 18o signal over the early holocene this 1000 year frequency band is significantly coherent with the 1000 year frequency band of total solar irradiance tsi between 9 5 ka and 7 ka and both signals are in phase over the rest of the studied period

the toarcian oceanic anoxic event in the ionian zone greece abstract the early jurassic was characterized by a global disturbance of the carbon cycle known as the toarcian oceanic anoxic event t oae this event is recorded worldwide by a negative excursion in marine and terrestrial carbon isotope ratios typically interrupting an overarching positive trend attributed to large scale burial of marine organic matter under oxygen depleted conditions the negative excursion is attributed to introduction of isotopically light carbon into the ocean atmosphere system three sections from the ionian zone in greece have been analysed in terms of biostratigraphy total organic carbon toc caco 3 13 c carb 18 o carb and 13 c org on the basis of bio and chemostratigraphy the age of pliensbachian toarcian formations from the ionian zone in greece has been refined and the geochemical signature of the t oae recognized all sections illustrate the characteristic negative excursion in carbon isotopes from both carbonates and organic matter and in only one locality a positive excursion has also been recorded the recognition of the t oae in this part of the tethyan continental margin offers additional information on the global impact and amplitude of this important jurassic palaeoceanographic event

synchrony between early jurassic extinction oceanic anoxic event and the karoo ferrar flood basalt volcanism a well known second order mass extinction took place during the pliensbachian and toarcian stages of the early jurassic first recognized as a minor pliensbachian peak in the global extinction rate it has alternatively been interpreted as a regional response to the early toarcian oceanic anoxic event detailed studies established it as a global long term event spanning five successive ammonoid zones here we present a revised time scale based on highprecision u pb ages resolved to the zone level which suggests that elevated extinction rates were sustained for about 4 m y and peak extinction occurred at 183 ma recent isotopic dating of flood basalts from the southern gondwanan karoo and ferrar provinces documents a culmination in volcanic activity ca 183 ma the onset of volcanism is recorded as an inflection and start of a rapid rise of the seawater 87 sr 86 sr curve the synchrony of voluminous flood basalt eruptions and biotic crises as already noted for three of the major mass extinctions permits a causal relationship which in this case may be mediated by widespread oceanic anoxia

osmium isotope evidence for the regulation of atmospheric co2 by continental weathering the long term stability of earth9s climate throughout the phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years reflecting the high efficiency of longer term climate regulation through negative feedbacks a fundamental mechanism is thought to involve control of co 2 in the ocean atmosphere system through continental weathering although unambiguous high resolution data supporting this hypothesis have hitherto not been available organic rich mud rocks from yorkshire england which were deposited during the toarcian oceanic anoxic event ca 181 ma early jurassic contain evidence of an exceptionally large excursion in the 187 os 188 os ratio of contemporaneous seawater from 0 4 to 1 0 the most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of 400 800 the os isotope excursion coincided with a well documented global 13 c excursion of 6 that affected all the major biospheric reservoirs of the time higher mean global temperatures caused global chemical weathering rates to increase substantially while in turn chemical weathering was very effective in reducing the elevated levels of atmospheric co 2 and the high temperatures to preexcursion levels

the geographic distribution of sr isotopes from surface waters and soil extracts over the island of bornholm denmark a base for provenance studies in archaeology and agriculture abstract in this paper we report the sr isotope signatures and sr al and na concentrations of 30 surface waters lakes ponds and rivers creeks and 19 soil sample extracts from the island of bornholm denmark and present a categorized 87 sr 86 sr value distribution map that may serve as a base for provenance studies including archaeological migration and authenticity proof for particular food products the sr isotopic compositions of surface waters range from 87 sr 86 sr 0 7097 0 7281 average 0 7175 0 0049 1 whereas 0 1 m hno 3 0 05 m hno 3 and 0 01 m cacl 2 soil extracts range from 87 sr 86 sr 0 7095 0 7197 and define somewhat lower but statistically indistinguishable averages of 0 7125 0 003 1s these compositions are lower than the values expected from the precambrian granitoid basement 87 sr 86 sr 0 758 0 944 and from the overlying mainly clastic paleozoic sediments combined sr isotope composition vs sr na and al concentration relationships of soil extracts imply that lowering of the isotopic composition of leachable sr on bornholm results as a consequence of significant admixture to this fraction of sr deposited as marine salts aerosols and that rainwater only has a minor influence on the sr budget of the surface waters positively correlated al na and 1 sr vs 87 sr 86 sr relationships in soil extracts and surface waters indicate that the surface run off on bornholm is characterized by two predominant sources namely marine aerosols sea salts with high sr and low 87 sr 86 sr values and a source with lower sr delivering radiogenic sr to the surface waters which we equate with sr leached from the products of mineral weathering soils a feasibility study for using sr isotopic compositions of surface waters and soil extracts as a proxy for bioavailable sr signatures was performed with a few samples collected in the vicinity of the eleventh century ad ndr grodbygard cemetery site in sw bornholm from where sr isotope compositions of modern fauna samples and tooth enamel of humans buried in the cemetery have been reported waters and soil extracts studied herein from around this site range from 87 sr 86 sr 0 7104 0 7166 and correspond to sr compositions extracted from snail shells in this area which span a range of 87 sr 86 sr 0 7095 0 7160 some human tooth enamel is characterized by more radiogenic values 87 sr 86 sr up to 0 718 which points to a possible provenance of these humans from the granite gneiss terrain in the north of the island and or to immigration of these humans in their childhood from other places for example from mainland sweden to bornholm if the total compositional range of 87 sr 86 sr 0 709 0 718 n 44 recorded in human enamel from the ndr grodbygard site is considered representative for the variation of bioavailable sr on bornholm then our soil leachate and surface water data entirely covers this range we therefore propose that the combination of sr isotope analyses of surface waters and soil leachates are an easy fast and relatively cost efficient way to characterize a local bioavailable 87 sr 86 sr signature and consequently propose that the overall average of 87 sr 86 sr 0 7153 0 0048 1 n 50 can be taken as a band for bioavailable sr fractions suitable to discriminate between local and non local signatures in provenance studies in the field of archaeology and for food and plant authenticity control in agricultural applications

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

massive dissociation of gas hydrate during a jurassic oceanic anoxic event in the jurassic period the early toarcian oceanic anoxic event about 183 million years ago is associated with exceptionally high rates of organic carbon burial high palaeotemperatures and significant mass extinction heavy carbon isotope compositions in rocks and fossils of this age have been linked to the global burial of organic carbon which is isotopically light in contrast examples of light carbon isotope values from marine organic matter of early toarcian age have been explained principally in terms of localized upwelling of bottom water enriched in 12c versus 13c refs 1 2 5 6 here however we report carbon isotope analyses of fossil wood which demonstrate that isotopically light carbon dominated all the upper oceanic biospheric and atmospheric carbon reservoirs and that this occurred despite the enhanced burial of organic carbon we propose that as has been suggested for the late palaeocene thermal maximum some 55 million years ago the observed patterns were produced by voluminous and extremely rapid release of methane from gas hydrate contained in marine continental margin sediments

pitfalls of normalization of marine geochemical data using a common divisor abstract normalization of trace element contents of sediment through division by the content of an immobile element usually aluminum is common practice in marine geochemical studies this might appear to be a simple way of correcting for dilution by sedimentary phases barren of a particular trace element for instance carbonates or silica and for comparison with its content in a standard clay or shale the purpose of this paper is to revive the awareness of the pitfalls of this practice by giving numerical examples of the often unexpected results of normalization taking a statistical perspective it is first shown that uncorrelated variables acquire spurious correlations when normalized but normalization can also increase decrease change sign of or even blur the correlations between unmodified variables next a number of realistic scenarios are worked out to show that the correlations between normalized element contents still suffer from the closure effect only in a few simple cases it is possible to extract from the normalized data realistic estimates of trace element contents in distinct sedimentary phases such as organic matter this is ascertained from data on copper contents in sediment from the black sea and arabian sea when the coefficient of variation i e standard deviation divided by the mean of the aluminum data is relatively low and much lower than for the original values of the trace elements comparisons of correlations can equally well or even better be made on the basis of the unmodified values then the comparison of trace element data with their values for standard shales is discussed the inherent problem is that the composition of the commonly used standard shale and consequently the reference values of normalized elements are not necessarily representative of the local or regional sediments in the study area also this method falls short of identifying the processes responsible for enrichment or diminution in trace element contents finally consideration is given to some aspects of a proper use of al normalization

first record of the early toarcian oceanic anoxic event from the southern hemisphere neuquen basin argentina abstract the first record of the early toarcian oceanic anoxic event c 183 ma from the southern hemisphere is described from the neuquen basin argentina identified chemostratigraphically on the basis of a relative increase in marine organic carbon and a characteristic negative carbon isotope excursion 13 c org in bulk rock and fossil wood the negative excursion of 6 in bulk organic carbon falling to 31 3 crosses the boundary of the tenuicostatum hoelderi andean ammonite zones equivalent to the tenuicostatum falciferum serpentinum zones of europe these data indicate that the early toarcian oceanic anoxic event was a global phenomenon supplementary material a detailed stratigraphic log chemostratigraphic data and nannofossil data are available at http www geolsoc org uk sup18411

dynamics of north atlantic deep water masses during the holocene high resolution flow speed reconstructions of two core sites located on gardar drift in the northeast atlantic basin and orphan knoll in the northwest atlantic basin reveal a long term decrease in flow speed of northeast atlantic deep water neadw after 6 500 years benthic foraminiferal oxygen isotopes of sites currently bathed in neadw show a 0 2 depletion after 6 500 years shortly after the start of the development of a carbon isotope gradient between neadw and norwegian sea deep water we consider these changes in near bottom flow vigor and benthic foraminiferal isotope records to mark a significant reorganization of the holocene deep ocean circulation and attribute the changes to a weakening of neadw flow during the mid to late holocene that allowed the shoaling of lower deep water and deeper eastward advection of labrador sea water into the northeast atlantic basin

the timing of paleoenvironmental change and cause and effect relationships during the early jurassic mass extinction in europe the early jurassic marine mass extinction is one of several crises thought to coincide with anoxia transgression and warming caused by catastrophic release of gas hydrates however high resolution study of expanded sections in yorkshire england reveal that only the first of these factors is truly coincidental with extinction the well known transgression and large negative carbon isotope perturbation attributed to massive release of methane from gas hydrates occur after these events the anoxic event is developed diachronously in the european area with anoxia developing and fading away earlier in the mediterranean region compared with the nw european record however for a brief interval in the mid semicelatum subzone anoxia was simultaneously developed throughout the european region and it is this time that is marked by extinction of both benthic and pelagic marine fossils the sea level curve is also more complex than hitherto assumed with a minor regression occurring late in the semicelatum subzone shortly after the extinction the toarcian crisis occurred during a phase of global warming but the postulated release of methane from gas hydrates is too late to be implicated in the extinction mechanism as indeed is a recently reported cooling event from within the warming trend

analysis of marine environmental conditions based onmolybdenum uranium covariation applications to mesozoic paleoceanography article i nfo article history accepted 13 september 2011 available online 17 september 2011 patterns of uranium molybdenum covariation in marine sediments have the potential to provide insights re garding depositional conditions and processes in paleoceanographic systems specifically such patterns can be used to assess bottom water redox conditions the operation of metal oxyhydroxide particulate shuttles in the water column and the degree of water mass restriction the utility of this paleoenvironmental proxy is due to the differential geochemical behavior of u and mo 1 uptake of authigenic u by marine sediments begins at the fe ii fe iii redox boundary i e suboxic conditions whereas authigenic mo enrichment re quires the presence of h2s i e euxinic conditions and 2 transfer of aqueous mo to the sediment may be enhanced through particulate shuttles whereas aqueous u is unaffected by this process in the present study we examine u mo covariation in organic rich sediments deposited mostly in the western tethyan region during oceanic anoxic events oaes of early jurassic to late cretaceous age our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regard ing water mass restriction and the operation of particulate shuttles in depositional systems these insights will help to address contentious issues pertaining to the character and origin of mesozoic oaes such as the degree to which regional paleoceanographic factors controlled the development of the oaes

calcium isotope evidence for dramatic increase of continental weathering during the toarcian oceanic anoxic event early jurassic abstract the early toarcian was punctuated by pulses of massive carbon injection that are thought to have triggered through increased greenhouse conditions elevated continental discharge and nutrient input marine anoxia seawater acidification and species extinctions nevertheless the mode and tempo of changes in continental weathering across this interval remains highly debated leading to considerable uncertainty about the main causes of these perturbations in this study we present calcium isotope measurements 44 40ca of well preserved brachiopods and bulk rock samples from the hemipelagic strata of pliensbachian toarcian age of peniche in portugal in order to constrain changes in the calcium cycle and hence changes in continental weathering during the early toarcian the data reveal a similar trend as carbon isotope data from the same section and show negative excursions of about 0 5 at the pliensbachian toarcian transition pl to and at the base of the toarcian oceanic anoxic event t oae interval the comparison of 44 40ca ratios recorded in brachiopods and bulk rock corrected for variable dolomite contribution indicates that these excursions reflect changes in the global isotopic composition of seawater rather than changes in the dominant mineralogy of calcifying organisms or in hydrological budget of the considered basin box modeling results suggest that the pl to and t oae 44 40ca excursions can be explained by a transient 90 decrease of carbonate accumulation due to seawater acidification followed by a 500 increase in continental weathering rates the sharp increases in continental weathering inferred from the 44 40ca ratios seem overall consistent with lower toarcian sedimentological and biotic records that document rapid crises in carbonate production followed by episodes of increased calcium carbonate burial nevertheless the maximum of carbonate burial recorded by most nw european basinal successions occurs several hundreds of kyrs after that predicted by box modeling results this mismatch either implies that the european records of carbonate accumulation do not reflect global trends or that the fundamental processes related to the removal of excess alkalinity caused by increased continental weathering are more complex than previously appreciated based on the amount of ca input simulated by box modeling the injection of tens of thousands of gigatons of carbon with an isotopic composition 13c comprised between 6 and 14 appears as the most likely causes of the 13c excursions characterizing these two events these results indicate that environmental and biotic changes of the pl to and t oae were mainly caused a cascade of environmental changes triggered by the massive carbon emissions from the karoo ferrar volcanism

toarcian extreme warmth led to tropical cyclone intensification abstract models predict that tropical cyclone intensity should increase on a warming planet observing this relationship remains however a difficult task since no clear trend is yet emerging from the anthropogenic record the geological past offers the opportunity to study this relationship by looking at episodes of extreme warmth such as the toarcian oceanic anoxic event t oae early jurassic ca 181 ma in this study we document an increase in the occurrence of storm related deposits during the onset of the t oae in the tide dominated high atlas basin of morocco associated with a drastic deepening of the mean storm weather wave base the palaeolatitude of the high atlas basin 18 north during the early jurassic rules out winter storms as the driving mechanism behind the formation of these deposits and points to a dramatic intensification of tropical cyclone intensity during the t oae global warming these new results combined with the previously reported ubiquitous appearance of storm deposits during the t oae in tropical seas of the western tethyan area support the concept that the globally averaged intensity of tropical cyclones will increase in the coming century due to the anthropogenic climate change

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

high precision geochronology links the ferrar large igneous province with early jurassic ocean anoxia and biotic crisis abstract apparent synchrony between eruption emplacement of large igneous province lip magmas and mass extinction has led to the implication of magmatism as a primary trigger of global scale environmental change evaluating the efficacy of magmatism as a driver of global change depends on the relative timing of magmatism and environmental change and the magma effusion intrusion rate both of which can be constrained by high precision geochronology early jurassic pliensbachian toarcian global ocean anoxia and acidification carbon isotope perturbations and biotic crisis have been linked to synchronous eruption and emplacement of the karoo and ferrar lips to better constrain the timing and duration of ferrar magmatism we apply the single crystal chemical abrasion u pb id tims method to zircon crystals isolated from twenty ferrar lip sills and lavas and the dufek intrusion dates suggest that both intrusive and extrusive ferrar magmatism occurred over an interval of 349 49 kyr beginning with intrusive magmatism as early as 182 779 0 033 ma lava eruption was synchronous with and in some cases postdates intrusion when coupled with existing geochronology on the karoo province our dates confirm broad synchrony between karoo and ferrar magmatism though karoo magmatism began demonstrably prior to ferrar magmatism starting as early as 183 246 0 045 ma the short lived magmatic history of the ferrar lip makes it a plausible trigger for early jurassic environmental change

the geographic distribution of strontium isotopes in danish surface waters a base for provenance studies in archaeology hydrology and agriculture abstract in this paper sr isotope signatures are reported for 192 surface water lakes ponds and rivers creeks samples from within denmark and an isotope distribution map is presented that may serve as a base for provenance applications including archaeological migration studies ground water surface water seawater interaction contamination monitoring and potentially for agricultural applications including cases of authenticity proof for particular food products the sr isotopic compositions of surface waters range from 87sr 86sr 0 7078 to 0 7125 average 0 7096 0 0016 2 this average value lies above the range of 87sr 86sr values between 0 7078 and 0 7082 expected from late cretaceous to early tertiary oligocene limestones which form the dominant bedrock type in a nw se trending belt in denmark the elevated 87sr 86sr signatures 0 7095 are explained by additions to the surface waters of radiogenic sr predominantly derived from the near surface weathering and wash out of quarternary glaciogenic tills and soils deposited and formed during and after the last two ice age stages saale and weichsel the sr isotopic compositions and concentrations of the surface waters can therefore best be modeled by a two component mixing involving carbonaceous bedrock and glaciogenic cover sediments as the two predominant sr sources a feasibility study for using sr isotopic compositions of surface waters as a proxy for bio available sr signatures was conducted in a representative test area on zealand land of legends lejre where there is no use and application of commercial fertilizers it is demonstrated that the sr isotopic signatures of lake waters from within this area are slightly higher but statistically still indistinguishable from the average value defined by snail shells and soil leachates considered to characterize the true bio available sr in combination with results from other studies this is interpreted to reflect the wash out of sr with a higher 87sr 86sr signature released by weathering in the topsoils into the saturated water tables a component which is consequently not readily transferred into the shallow rooting plants and into small herbivores feeding on them since drinking water is a likely important source of sr uptake of humans and larger animals the contention is that a surface water isotopic composition can potentially characterize the bio available component relevant for human and carnivorous large animals spline functions and ordinary linear kriging were used for modeling the geographic distribution of bio available sr isotopes over territorial denmark as expected based on the two source mixing scenario the water 87sr 86sr ratio contour maps with some notable exceptions neither mirror the pre quarternary bedrock geology nor a pleistocene soil type distribution map of denmark as a conservative suggestion the use of the average 87sr 86sr ratio of 0 7096 0 0015 2 is recommended as an average for bio available sr from within denmark bornholm excluded for human and larger animals and as a confidence band for distinguishing local from non local signatures in archaeological provenance studies the study also reveals that the average 87sr 86sr ratio of 0 7088 defined from soil extracts and small herbivores lies approximately 0 15 lower than that defined by the surface waters the authors recommend using this lower value as a local non local discriminator for food and plant authenticity control in agricultural applications

the importance of silicate weathering of a sedimentary aquifer in arid central australia indicated by very high 87sr 86sr ratios with the exception of brine systems and crystalline rock aquifers groundwater 87sr 86sr ratios rarely differ by more than 0 01 from the phanerozoic seawater value of 0 70923 groundwater 87sr 86sr ratios from central australia 0 72562 0 76248 are the highest ever recorded for a low salinity sedimentary aquifer we propose a model for the evolution of these 87sr 86sr ratios and demonstrate how the lowest 87sr 86sr ratios reflect water rock interactions with predominantly carbonate minerals while the highest 87sr 86sr ratios are ultimately controlled by weathering of old primary silicate minerals detailed analysis of aquifer core material identified albite and microcline as the most prevalent primary silicates and where these minerals were abundant relatively high rb concentrations were measured high rb combined with long time scales since deposition has produced very high 87sr 86sr ratios in the rocks and subsequently the groundwater therefore strontium isotopes can provide further constraints for chemical models of arid zone groundwater systems particularly when silicate hydrolysis is believed to significantly contribute to dissolved solute compositions

polar record of early jurassic massive carbon injection abstract the toarcian oceanic anoxic event t oae ca 182 myr early jurassic represents one of the best recognized examples of greenhouse warming decreased seawater oxygenation and mass extinction the leading hypothesis to explain these changes is the massive injection of thermogenic or gas hydrate derived 13 c depleted carbon into the atmosphere resulting in a 3 per mil negative carbon isotope excursion cie accelerated nutrient input and dissolved oxygen consumption in the oceans nevertheless the lack of a precisely dated record of the t oae outside low latitudes has led to considerable debate about both its temporal and spatial extent and hence concerning its underlying causes here we present new isotopic and lithological data from three precisely dated n siberian sections which demonstrate that mass extinction and onset of strong oxygen deficiency occurred near synchronously in polar and most tropical sites and were intimately linked to the onset of a marked 6 negative cie recorded by bulk organic carbon rock eval pyrolysis data from siberia and comparisons with low latitudes show that the cie cannot be explained by the extent of stratification of the studied basins or changes in organic matter sourcing and suggest that the negative cie reflects rapid 13 c depleted carbon injection to all exchangeable reservoirs sedimentological and palynological indicators show that the injection coincided with a change from cold abundant glendonites and exotic boulder sized clasts to exceptionally warm conditions dominance of the thermophyllic pollen genus classopollis in the arctic which likely triggered a rapid possibly partly glacioeustatic sea level rise comparisons with low latitude records reveal that warm climate conditions and poor marine oxygenation persisted in continental margins at least 600 kyr after the cie features that can be attributed to protracted and massive volcanic carbon dioxide degassing our data reveal that the t oae profoundly affected arctic climate and oceanography and suggest that the cie was a consequence of global and massive 13 c depleted carbon injection

reconstructing past sea surface temperatures correcting for diagenesis of bulk marine carbonate abstract a numerical model which describes oxygen isotope exchange during burial and recrystallization of deep sea carbonate is used to obtain information on how sea surface temperatures have varied in the past by correcting measured 18o values of bulk carbonate for diagenetic overprinting comparison of bulk carbonate and planktonic foraminiferal 18o records from odp site 677a indicates that the oxygen isotopic composition of bulk carbonate does reflect changes in sea surface temperature and 18o at odp site 690 we calculate that diagenetic effects are small and that both bulk carbonate and planktonic foraminiferal 18o records accurately reflect paleogene warming of high latitude surface oceans biased from diagenesis by no more than 1 c the same is likely to be true for other high latitude sites where sedimentation rates are low at dsdp sites 516 and 525 the effects of diagenesis are more significant measured 18o values of eocene bulk carbonates are more than 2 lower at deeply buried site 516 than at site 525 consistent with the model prediction that the effects of diagenesis should be proportional to sedimentation rate model corrections reconcile the differences in the data between the two sites the resulting paleotemperature reconstruction indicates a 4 c cooling of mid latitude surface oceans since the eocene at low latitudes the contrast in temperature between the ocean surface and bottom makes the carbonate 180 values particularly sensitive to diagenetic effects most of the observed variations in measured 18o values are accounted for by diagenetic effects rather than by sea surface temperature variations we show that the data are consistent with constant equatorial sea surface temperatures through most of the cenozoic with the possible exception of the early eocene when slightly higher temperatures are indicated we suggest that the lower equatorial sea surface temperatures for the eocene and oligocene reported in other oxygen isotope studies are artifacts of diagenetic recrystallization and that it is impossible to reconstruct accurately equatorial sea surface temperatures without explicitly accounting for diagenetic overprinting

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

ca sr and sr isotope systematics of a himalayan glacial chronosequence carbonate versus silicate weathering rates as a function of landscape surface age we explored changes in the relative importance of carbonate vs silicate weathering as a function of landscape surface age by examining the ca sr and sr isotope systematics of a glacial soil chronosequence located in the raikhot watershed within the himalaya of northern pakistan bedrock in the raikhot watershed primarily consists of silicate rock ca sr 0 20 mol nmol 87 sr 86 sr 0 77 to 1 2 with minor amounts of disseminated calcite ca sr 0 98 to 5 3 mol nmol 87 sr 86 sr 0 79 to 0 93 and metasedimentary carbonate ca sr 1 0 to 2 8 mol nmol 87 sr 86 sr 0 72 to 0 82 analysis of the exchangeable carbonate and silicate fractions of seven soil profiles ranging in age from 0 5 to 55 kyr revealed that carbonate dissolution provides more than 90 of the weathering derived ca and sr for at least 55 kyr after the exposure of rock surfaces even though carbonate represents only 1 0 wt of fresh glacial till the accumulation of carbonate bearing dust deposited on the surfaces of older landforms partly sustains the longevity of the carbonate weathering flux as the average landscape surface age in the raikhot watershed increases the ca sr and 87 sr 86 sr ratios released by carbonate weathering decrease from 3 6 to 0 20 mol nmol and 0 84 to 0 72 respectively the transition from high to low ca sr ratios during weathering appears to reflect the greater solubility of high ca sr ratio carbonate relative to low ca sr ratio carbonate these findings suggest that carbonate weathering controls the dissolved flux of sr emanating from stable himalayan landforms comprising mixed silicate and carbonate rock for tens of thousands of years after the mechanical exposure of rock surfaces to the weathering environment copyright 2002 elsevier science ltd

cosmopolitan catterick isotopic evidence for population mobility on rome s northern frontier in order to investigate how the population diversity at major romano british urban centres compared to small towns and military outposts we conducted multi isotope carbon nitrogen oxygen and strontium analyses of bones 42 individuals and teeth 26 individuals of human skeletons from cataractonium roman catterick in north yorkshire u k the results suggest a markedly less diverse population at catterick than at the larger towns significant differences are observed between burials from the town and fort area and the suburb of bainesse to the south and it is suggested that these reflect a shift to more localised recruitment for the roman army in the late roman period isotope data for the bainesse eunuch an unusual 4th century burial that has been interpreted as the remains of a transvestite priest of cybele are not ultimately conclusive but consistent with origins in southern britain or areas with a similar climate abroad this paper also presents strontium isotope data for modern vegetation samples from 17 sites in the catterick northern vale of york area which contribute to a continuing effort to map the biosphere 87sr 86sr variation in britain

mineral dissolution in the cape cod aquifer massachusetts usa i reaction stoichiometry and impact of accessory feldspar and glauconite on strontium isotopes solute concentrations and rey distribution abstract to compare relative reaction rates of mineral dissolution in a mineralogically simple groundwater aquifer we studied the controls on solute concentrations sr isotopes and rare earth element and yttrium rey systematics in the cape cod aquifer this aquifer comprises mostly carbonate free pleistocene sediments that are about 90 quartz with minor k feldspar plagioclase glauconite and fe oxides silica concentrations and ph in the groundwater increase systematically with increasing depth while sr isotopic ratios decrease no clear relationship between 87sr 86sr and sr concentration is observed at all depths the 87sr 86sr ratio of the groundwater is considerably lower than the sr isotopic ratio of the bulk sediment or its k feldspar component but similar to that of a plagioclase rich accessory separate obtained from the sediment the si 87sr 86sr depth relationships are consistent with dissolution of accessory plagioclase in addition solutes such as sr ca and particularly k show concentration spikes superimposed on their respective general trends the k sr 87sr 86sr systematics suggests that accessory glauconite is another major solute source to cape cod groundwater although the authigenic glauconite in the cape cod sediment is rich in rb it is low in in grown radiogenic 87sr because of its young pleistocene age the low 87sr 86sr ratios are consistent with equilibration of glauconite with seawater the impact of glauconite is inferred to vary due to its variable abundance in the sediments in the cape cod groundwater the variation of rey concentrations with sampling depth resembles that of k and rb but differs from that of ca and sr shale normalized rey patterns are light rey depleted show negative ce anomalies and super chondritic y ho ratios but no eu anomalies rey input from feldspar therefore is insignificant compared to input from a k rb bearing phase inferred to be glauconite these results emphasize that interpretation of groundwater chemistry even in relatively simple aquifers may be complicated by solute contributions from exotic accessory minerals such as glauconite to detect such peculiarities groundwater studies should combine the study of elemental concentration and isotopic composition of several solutes that show different geochemical behavior

the significance of an early jurassic toarcian carbon isotope excursion in haida gwaii queen charlotte islands british columbia canada abstract during the early toarcian there was a significant disruption in the short term active carbon reservoir as revealed by carbon isotope records which show a broad positive shift that is interrupted by a large 5 7 negative excursion 13 c org carbon isotope excursion co occurs with the deposition of organic rich shales in many areas this perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia the two leading hypotheses as to the cause of this event invoke either global or regional controls here we present carbon isotope data from haida gwaii british columbia canada showing a significant perturbation within a temporally constrained early toarcian succession that was deposited in the northeastern paleo pacific ocean these data reinforce the concept that the short term active carbon reservoir was affected globally and assist with the correlation of ammonite zonal schemes between western north america and europe the 13 c org data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7 8 5 in 13 c wood in the early toarcian kanense zone this negative excursion also coincides with increasing total organic carbon toc from 0 4 to 1 2 these data suggest that the early toarcian carbon isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle deep marine shallow marine atmospheric

astronomical forcing and chronology of the early toarcian early jurassic oceanic anoxic event in yorkshire uk 1 during the early toarcian 183 ma ago a high rate of organic carbon burial globally over a brief interval of time has led to the recognition of a major oceanic anoxic event oae a pronounced negative excursion in the carbon isotope composition of marine organic matter marine carbonate and terrestrial plant material is a key feature of this event but the precise timescale and cause s of this isotopic anomaly are debated associated with the negative carbon isotope excursion is evidence for a coeval rise in seawater palaeotemperature an increase in continental weathering rates and the mass extinction of marine invertebrate species the early toarcian oae provides evidence for the earth s response during rapid climate change and critical to our understanding of the event is a high resolution timescale that allows us to quantify the rates duration and lead lag times of environmental processes in this study we present 2743 new high resolution organic carbon sulphur and carbonate concentration data from samples of well preserved organic rich mudrocks spanning the early toarcian oae in yorkshire uk we have used these data to document the geochemical changes and significantly extend and refine the astronomical timescale across this event our detailed analysis of the relationship between astronomical forcing and carbon isotope changes in both yorkshire and a section from peniche portugal indicates that astronomical forcing paced the timing of major shifts in 13c and hence climate in both sections our analyses also demonstrate that there was a marked increase in the relative strength of astronomical forcing recorded at the onset of the oae and that the recorded nature of astronomical forcing changed during the event both the yorkshire and peniche cyclostratigraphies suggest that one astronomical forcing parameter paced environmental change through the 13c event and that this parameter was obliquity or precession

calibrating the magnitude of the toarcian carbon cycle perturbation sedimentary rocks recording the toarcian oceanic anoxic event t oae are marked by a negative carbon isotope excursion cie reaching up to 7 and ranking among the largest known in the phanerozoic these records suggest a dramatic perturbation of the carbon cycle that has been linked to the transfer of juvenile carbon from the endogenic to the exogenic reservoirs nevertheless the magnitude of the toarcian cie varies significantly from one substrate to another hence complicating mass balance evaluation of the potential driving mechanisms here we show using high resolution paired records of 13ctotal organic carbon toc and hydrogen index from the denkingen core and dotternhausen quarry germany that the amplitude of the negative cie in marine organic matter is considerably exaggerated by changes in organic matter sourcing our corrected 3 4 cie implies a constant carbon isotope fractionation between organic and carbonate carbon across the t oae and may point to a prominent role of cyanobacteria as organic matter producers during the early jurassic these results also suggest that the difference between inorganic and organic carbon isotope values in marine strata constitutes a poor proxy of pco2 levels across the t oae moreover this corrected 3 4 cie together with evidence for 5 c seawater warming across the t oae point to the input of 25 000 gt c with much more 13c enriched signature than previously modeled our results thus allow reconciling inorganic and organic 13c records of the t oae and have important implications for the evaluation of their causal mechanisms

pliensbachian early jurassic calcareous nannofossils from the peniche section lusitanian basin portugal a clue for palaeoenvironmental reconstructions abstract quantitative analysis of early jurassic calcareous nannofossil assemblages from the peniche section in portugal have been performed in order to interpret palaeoenvironmental changes occurring in the lusitanian basin during the late pliensbachian davoei margaritatus and spinatum ammonite zones nannofossil data are compared to already published carbon and oxygen stable isotope data organic matter content wt total organic carbon toc and biomarker analysis a significant change in calcareous nannofossil assemblages and species diversity at the transition between the margaritatus and spinatum ammonite zones matches with the pattern shown by geochemical data this suggests that a profound change in environmental conditions occurred at that time in the davoei and margaritatus ammonite zones in a context of general sea level rise the lusitanian basin was characterized by water column stratification that favoured the sedimentation and preservation of organic matter biomarkers and oxygen isotope trends suggest that stratification of water masses occurred because of low salinity in surface waters the shallowest part of the water column characterized by oligotrophic conditions was inhabited by the probable calcareous dinocyst schizosphaerella spp while the deep dweller crepidolithus crassus flourished in the lower photic zone layers in the spinatum ammonite zone a regressive trend occurred and a salinity increase is inferred on the basis of oxygen isotope values water masses were probably less stratified at that time the upper photic zone nannofossil assemblages were still dominated by schizosphaerella spp whilst in the deep photic zone mitrolithus jansae a mediterranean taxon replaced c crassus a taxon with nw european affinity this pattern may indicate a change in palaeoceanographic conditions related to surface current circulation the sea level fall occurring during the spinatum ammonite zone may have resulted in the partial isolation of the lusitanian basin from the nw europe basins because of the creation of a threshold alternatively tectonic drowning of north african carbonate platforms in the late pliensbachian may have promoted better exchanges of nannoplankton between the lusitanian basin and the mediterranean tethys via the creation of new seaway connections

environmental versus biological controls on mg ca variability in globigerinoides ruber white from core top and plankton tow samples in the southwest pacific ocean 1 laser ablation inductively coupled plasma mass spectrometry was used to analyze the individual chambers from tests of foraminiferal fossil and plankton tow globigerinoides ruber from the southwest pacific ocean from latitudes 3 s to 42 s the variability of mg ca between chambers of an individual intraindividual and individuals of the same population interindividual is such that when converted to temperature the extent of intra individual and interindividual variability appears to exceed that attributable to either calcification or seasonal temperature variability the pooled mean chamber mg ca from each core top and plankton tow site demonstrates a significant p 0 05 positive correlation with temperature we derive chamber specific calibrations where mg cach f 2 0 798 exp0 070 t mg cach f 1 0 891 exp0 067 t and mg cach f 0 590 exp0 072 t we do not observe any bias between the two morphotypes gs ruber ruber and gs ruber pyramidalis the chamber specific calibrations potentially offset mg ca based temperature reconstructions if used on bulk whole test mg ca or applied to misidentified chambers nevertheless these calibrations can be used to reliably estimate sea surface temperature although there is a general overriding temperature control on mg ca we show that removal of the effect of temperature at each site reveals a lognormal mg ca distribution this suggests that mg ca variability at each site is also affected by biological mechanism s that may control the distribution of interindividual mg ca in addition other te ca data al ca and mn ca from laser ablation trace element depth profiles can be used to identify detrital or diagenetic phases that may bias the trace element ca signal

evaluating the temporal link between the karoo lip and climatic biologic events of the toarcian stage with high precision u pb geochronology the karoo large igneous province k lip is considered to have substantially influenced global warming marine anoxia and concomitant marine extinction in the toarcian lower jurassic the sequence and duration of these events has been uncertain thus precluding direct comparison between sedimentary successions and the k lip two relatively narrow time intervals of the early toarcian one approximately within the lower portion of the h falciferum ammonite zone and the other near the pliensbachian toarcian boundary pl to b have received much attention because they are associated with carbon isotope excursions cies and marine extinctions potential causal mechanisms have been proposed such as the release of massive amounts of carbon to the atmosphere via a catastrophic magmatic intrusive episode related to the k lip here we test the timing with four new high precision ca id tims u pb zircon ages from the toarcian stage collected from tephra interstratified with ammonite bearing carbonates in southernmost peru we also present new u pb zircon and baddeleyite data from three sills and one rhyolite of the k lip in south africa our new data permit a substantial reinterpretation of the toarcian timescale the pliensbachian toarcian boundary pl to b a prominent global extinction level must be older than 183 5 ma on the basis of our oldest tephra the h falciferum cie equivalent to the so called toarcian oceanic anoxic event is bracketed by two ash fall bed dates between 183 22 0 26183 22 0 26 and 181 99 0 13 ma181 99 0 13 ma all 2 analytical and tracer errors the cie duration is estimated at approximately 300 ka on the basis of minimum error interpolation of ammonite zone boundaries the base of the h falciferum cie appears to correlate in time with the onset k lip sill emplacement dated by the oldest sill at 183 014 0 072 ma183 014 0 072 ma however sill emplacement appears to have lasted for a minimum of 2 million years at least until 181 31 0 19 ma181 31 0 19 ma which is in disagreement with a short duration of the h falciferum negative cie furthermore our data suggest that the timing of the main volume of the k lip may have been approximately 4 5 ma this prolonged and possibly pulsed magmatic activity of the k lip may be correlated with extinction pulses and climate changes in the middle and late toarcian stage each event occurring within a unique set of global environmental conditions

distribution of clay minerals in early jurassic peritethyan seas palaeoclimatic significance inferred from multiproxy comparisons article i nfo a set of published unpublished and new clay mineral data from 60 european and mediterranean localities allows us to test the reliability of clay minerals as palaeoclimatic proxies for the pliensbachian toarcian period early jurassic by reconstructing spatial and temporal variations of detrital fluxes at the ammonite biochronozone resolution in order to discuss their palaeoclimatic meaning a compilation of low latitude belemnite 18 o 13 c mg ca and 87 sr 86 sr values is presented for the first time for the whole pliensbachian toarcian period once diagenetic and authigenic biases have been identified and ruled out kaolinite content variation is considered as a reliable palaeoclimatic proxy for the early jurassic major kaolinite enrichments occur during times of low 18 o high mg ca and increasing 87 sr 86 sr implying warm climates and efficient runoffs during the davoei falciferum and bifrons zones conversely cooler and drier times such as the late pliensbachian or the late toarcian are characterized by low hydrolysis of landmasses and correspond to kaolinite depleted intervals secondary factors as modifications of sources or hydrothermalism may sporadically disturb the palaeoclimatic signal e g in the bakony area during the late pliensbachian in addition a spatial comparison of clay assemblages displays significant kaolinite enrichments towards northern parts of the peritethyan realm probably related to the latitudinal zonation of hydrolyzing conditions this implies enhanced runoffs on northern continental landmasses that reworked kaolinite rich