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

the quartz dioritic hospitais intrusion sw iberian massif and its mafic microgranular enclaves evidence for mineral clustering abstract the hospitais pluton is an elliptical body with its long axis oriented wnw ese that belongs to the evora massif iberian variscan belt this intrusion has a quartz dioritic composition with plagioclase quartz amphibole hornblende but locally also cummingtonite and biotite as the main mineral phases mafic microgranular enclaves in the quartz diorite show the same minerals as the host but with a greater abundance of amphibole and lower proportions of felsic minerals especially quartz u pb zircon ages obtained in one sample of the quartz diorite and one sample of a mafic microgranular enclave gave identical ages within error of ca 337 ma geochemical data show that the quartz diorite has a calc alkaline signature with moderate enrichment in lile hfse ratio thn yn 2 71 11 43 and clear negative ti and nb ta anomalies thn nbn 1 33 6 22 the composition of the enclaves shows that they do not represent direct melt compositions instead their geochemical features namely the abundances of fe and mn in variation diagrams and ree patterns in primitive mantle normalized diagrams suggest that they correspond to mineral clustering formed during the previous crystallization stage of quartz dioritic magma overlapping of mineral chemistry and sr nd isotope compositions in the quartz diorite and the enclaves provides further support to that conclusion the values for 87sr 86sr i and endi calculated for 337 ma in the quartz diorite vary from 0 706147 to 0 706491 and from 1 87 to 3 22 respectively this isotope composition may be explained either by differentiation of a mafic magma extracted from a mantle wedge enriched by long lasting subduction processes or by mixing between a mafic magma from a depleted mantle source and a crustal melt in the second case the most likely source for the felsic component should be meta igneous rocks like the lower cambrian alcacovas orthogneisses that outcrop in neighbouring areas

the role of hybridization in the genesis of hercynian granitodis in the gredos massif spain inferences from sr nd isotopes the gredos massif is one the better exposed granitoid complexes of the iberian massif it is composed mainly of peraluminous granitoids with subordinate basic and ultrabasic complexes the massif also contains mega enclaves of migmatites with which the granitoids show transitional contacts two major magmatic associations have been distinguished in this study 1 one comprises the granitoids with microgranular enclaves the enclaves and basic rocks 2 the other is formed by leucogranites intrusive into the former series and free of microgranular enclaves field relationships and microstructures indicate that the rocks of the first series are related by a dominant hybridization process the sr nd isotopic study reveals that this process is complex relating different end members of mantle and crustal affinities and occurred around 295 ma ago late with respect to the main deformation phases of the hercynian orogeny the granitoids with microgranular enclaves gme are part of an overall mixing trend involving palaeozoic mantle derived magma and melts of older crustal material amphibole bearing gme in general contain greater proportions of the mantle derived component than the cordierite bearing gme the actual mixing processes took place on a variety of scales sometimes between melts which were themselves hybrids on a local scale this hybridization process can be modelled by simple binary mixing as documented in the case of a composite dyke the isotopic signatures of the basic rocks are probably to a large degree the result of interaction with crustal melts though additionally the presence of an enriched mantle source cannot be elmininated microgranular enclaves and their immediate hosts have differing initial sr and nd isotopic signatures indicating that isotopic equilibrium was not attained this suggests that the enclaves did not reside in their final granitic melt for long before cooling of the whole system the enclaves are considered to have been derived from basaltic melts which had fractionated and hybridised to varying degrees late stage peraluminous leucogranites have similar initial nd isotopic compositions to the evolved gme a crustal source with a radically different nd isotopic composition or age does not need to be invoked in their petrogenesis

estimates of the amount and rate of sea level change across the rhaetian hettangian and pliensbachian toarcian boundaries latest triassic to early jurassic an attempt is made to determine the amount and rate of sea level change for two major events in the latest triassic to early jurassic both of which are associated with mass extinctions using the best available facies evidence and time scale the amount of marine deepening across the pliensbachian toarcian boundary based on analysis of the excellent yorkshire coast section is likely to have been a few tens of metres at a rate of between 1cm 1 2 ka 1 and 1cm 0 4 ka 1 the change across the rhaetian hettangian triassic jurassic boundary was different in that the sea level rise was immediately preceded by a sea level fall effectively a 9regression transgression9 couplet the earliest jurassic sea level rise is likely to have been much more rapid than that across the pliensbachian toarcian boundary at a rate of at least 1 cm 0 2 ka 1 whereas the speed of pliensbachian toarcian change is consistent with the growth of oceanic ridges the appreciably more rapid triassic jurassic change is suggestive of a different tectonoeustatic mechanism involving stress induced changes in plate density

shrimp u pb zircon geochronology and thermal modeling of multilayer granitoid intrusions implications for the building and thermal evolution of the central system batholith iberian massif spain abstract this work shows the results of a u pb shrimp zircon geochronological study of the central part of the gredos massif spanish central system batholith the studied batholith is composed of several granodiorite and monzogranite tabular bodies around 1 km thick each intruded into partially molten pelitic metasediments granodiorites and monzogranites belonging to three distinct intrusive bodies and samples of anatectic leucogranites have been selected for shrimp u pb zircon geochronology distinct age groups separated by up to 20 ma have been distinguished in each sample important age differences have also been determined among the most representative age groups of the three analyzed granitoid bodies 312 6 2 8 ma for the circo de gredos bt granodiorites floor intrusive layer 306 9 1 5 ma for the barbellido plataforma granitoids top intrusive layer and 303 5 2 8 ma for las pozas crd monzogranites middle intrusive layer these age differences are interpreted in terms of sequential emplacement of the three intrusive bodies contemporary with the late paleozoic d3 deformation phase the anatectic leucogranites are coeval to slightly younger than the adjacent intrusive granodiorites and monzogranites 305 4 1 6 ma for refugio del rey leucogranites and 303 2 ma for migmatitic hornfelses it is suggested that these anatectic magmas were generated in response to the thermal effects of granodiorite intrusions thermal modeling with comsol multiphysics reveals that sequential emplacement was able to keep the thermal conditions of the batholith around the temperature of zircon crystallization in granitic melts around 750 c for several million of years favoring the partial melting of host rocks and the existence of large magma chambers composed of crystal mush prone to be rejuvenated after new intrusions

tracing the cambro ordovician ferrosilicic to calc alkaline magmatic association in iberia by in situ u pb shrimp zircon geochronology gredos massif spanish central system batholith abstract u pb geochronological study of zircons from nodular granites and qtz diorites comprising part of variscan high grade metamorphic complexes in gredos massif spanish central system batholith points out the significant presence of cambro ordovician protoliths among the variscan migmatitic rocks that host the late carboniferous intrusive granitoids indeed the studied zone was affected by two contrasted tectono magmatic episodes carboniferous variscan and cambro ordovician three main characteristics denote a close relation between the cambro ordovician protholiths of the prado de las pozas high grade metamorphic complex strongly reworked during the variscan orogeny and other cambro ordovician igneous domains in the central iberian zone of the iberian massif 1 geochemical features show the ferrosilicic signature of nodular granites they plot very close to the average analysis of the metavolcanic rocks of the ollo de sapo formation iberia qtz diorites present typical calc alkaline signatures and are geochemically similar to intermediate cordilleran granitoids 2 both qtz diorite and nodular granite samples yield a significant population of cambro ordovician ages ranging between 483 and 473 ma and between 487 and 457 ma respectively besides 3 the abundance of zircon inheritance observed on nodular granites matches the significant component of inheritance reported on cambro ordovician metagranites and metavolcanic rocks of central and nw iberia the spatial and temporal coincidence of both peraluminous and intermediate granitoids and specifically in nodular granites and qtz diorite enclaves of the prado de las pozas high grade complex is conducive to a common petrogenetic context for the formation of both magmatic types tectonic and geochemical characteristics describe the activity of a cambro ordovician arc back arc tectonic setting associated with the subduction of the iapetus tornquist ocean and the birth of the rheic ocean the extensional setting is favorable for the generation emplacement and fast rise of subduction related cold diapirs supported by the presence of typical calc alkaline cordilleran granitoids contemporary with ferrosilicic volcanism

eustatic sea level changes interpreted from seismic stratigraphy a critique of the methodology with particular reference to the north sea jurassic record seismic stratigraphic methods for interpreting eustatic sea level change are based on generalized stratigraphic models and chronostratigraphic interpretations that have not been substantiated by publication of the necessary basic supportive data chronostratigraphic correlations of sea level change curves between basins are based partly on circular reasoning onlap and offlap seismic models may not indicate sea level change but flexural subsidence facies shifts or changes in sea level in the opposite direction to that proposed resolution of some of these problems may be achieved by publication of basic data now in confidential industry files the widely acclaimed vail curves should not be used as templates for basin correlation until such data have been provided and such use should be supported by appropriate conventional lithostratigraphic and biostratigraphic documentation from each new basin where such data have been made available as with the north sea jurassic serious questions of interpretation are raised

climatic ups and downs in a disturbed jurassic world the tropical warm and equable climate of the jurassic world is regularly challenged by geoscientists especially since oxygen isotopes 18 o of fossil hardparts have been used to reconstruct the paleotemperature history of seawater by applying the innovative sizer sig nifi cant zero crossings of the derivatives statistical approach to a newly compiled 18 o data base for the jurassic we demonstrate the occurrence of major and multiscale 18 o changes mainly related to climate disturbances for the fi rst time two long term anomalies in 18 o are identifi ed during the toarcian and the late jurassic in conjunction with intensive volcanism in large igneous provinces these results support a strong infl uence of repeated volcanic pulses on the modulation of pco 2 temperatures and polar ice cap volumes over protracted periods at shorter time scales 13 relatively rapid 0 5 1 m y and signifi cant warming and cooling events are identifi ed the causes of which include transient fl uctuations in greenhouse gas con centrations related to still debated mechanisms

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

mesozoic resource potential in the southern permian basin area the geological key to exploiting remaining hydrocarbons whilst unlocking geothermal potential it is generally accepted that hydrocarbon exploration in northern europe has reached a mature stage a basin s maturity is defined by the underlying number of new discoveries and the declining production rate of mature fields spe 2015 for geoscientists a mature basin has well defined characteristics in terms of for example reservoir presence or trap formation e g byrne 2012 it is interesting therefore to note how much is still unknown about certain stratigraphic intervals in northern europe the mesozoic overburden of the southern permian basin sensu maystrenko et al 2008 doornenbal stevenson 2010 continues to provide fresh insights into the geological history of an area where as the name suggests historical hydrocarbon exploration has focused on the paleozoic the aim of this special publication is to increase knowledge of the mesozoic overburden as a driver for further hydrocarbon exploration production and the development of new geothermal energy sources the succeeding chapters are introduced by tectonic framework overviews that give a context for the papers that follow the remaining articles are organized in approximate stratigraphic order from old to young and include a variety of examples from semi regional to localized field or sub basin studies an overview of the study area for all the following chapters is given in figure 1 it is recognized that the overprinting mesozoic systems have different naming conventions across the study area e g the central european basin system sensu littke et al 2008 maystrenko et al 2008 here we use the title southern permian basin area to emphasize the resource opportunities associated with a region that has at least in large part been associated with hydrocarbon exploration and very large gas fields in the permian rotliegend for our purposes this includes part of the polish trough the highs surrounding the basin e g the ringkobing fyn high and analogous elements of the danish and norwegian offshore in this introduction an overview of the geological history and resource base of the area is presented as a framework for the chapters that follow a description of further prospective resources is then offered oil and gas plus geothermal potential

the late palaeocene early eocene and toarcian early jurassic carbon isotope excursions a comparison of their time scales associated environmental changes causes and consequences although the earth9s environment is constantly changing there have been a few unusual episodes over the last c 200 ma when change was extreme in terms of its rapidity severity long lasting consequences and unpredictability the geochemical and biotic records for two of these episodes the palaeocene eocene thermal maximum and the toarcian oceanic anoxic event early jurassic possess many significant similarities each event was associated with a major carbon isotope excursion significant levels of biotic extinctions severe global warming an enhanced hydrological cycle and evidence for widespread seawater anoxia both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations based on a detailed comparison the palaeocene eocene thermal maximum may have been an incipient oceanic anoxic event the geochemical and biotic changes during these two events are most readily explained by the abrupt large scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere indicating that ancient events such as these may usefully serve as analogues for present day environmental change

a strontium neodymium and oxygen isotope study of hydrothermal metamorphism and crustal anatexis in the trois seigneurs massif pyrenees france nd sr and o isotope analyses have been made on metamorphic and igneous rocks and minerals from a 310 340 ma hercynian age metamorphic terrane in the pyrenees france lower paleozoic shales and phyllites have 87sr 86sr values of 0 707 0 717 at 310 ma but model values at 310 ma of 0 709 0 736 based on assumed depositional age of 450 ma and an initial 87sr 86sr 0 707 on a regional scale 87sr 86sr was homogenized to about 0 713 to 0 717 in the higher grade pelitic schists during metamorphism much of this 87sr 86sr exchange occurred at very low grades below the biotite isograd but significant changes also accompanied the 18o lowering of the phyllites 13 to 16 during their transformation to andalusite and sillimanite grade schists 18o 11 to 12 all of these effects are attributed to pervasive interactions with hydrothermal fluids wickham and taylor 1985 the data also show that a syn metamorphic plutonic complex dominated by a biotite granite body was derived by mixing of a relatively mafic magmatic end member 87sr 86sr 0 7025 0 7050 and 18o 7 5 to 8 0 with two metasedimentary sources both having 87sr 86sr 0 715 and 18o 10 0 to 12 0 but with one being more homogeneous than the other the more homogeneous component and the mantle derived magmatic end member dominate at low structural levels within the complex the less homogeneous end member that dominates at high levels is clearly derived from the local paleozoic pelitic schists a rb sr age of 330 20 ma was obtained on hornblende from a deep level within the complex which fixes this age for the regional metamorphism as well although a post metamorphic granodiorite magma body at trois seigneurs also displays heterogeneities in 18o and 87sr 86sr and thus does not give a clear cut rb sr isochron the data are consistent with an emplacement age between 260 and 310 ma similar to ages of other late granodiorites in the pyrenees 143nd 144nd is very uniform within the hercynian crust both at trois seigneurs nd 3 to 7 and elsewhere in the pyrenees almost all igneous lithologies have depleted mantle mid proterozoic model ages consistent with efficient recycling of crustal material following original crustal accretion in this area at about 1600 ma or earlier rb sr mineral ages exhibit a complex cooling history reflecting late hercynian and mesozoic thermal events our results show that profound homogenization of the 87sr 86sr and 18o 16o ratios of large volumes of the crust can occur during regional metamorphism and crustal anatexis particularly in regions undergoing extensional tectonics such processes can significantly modify the isotopic compositions of the protoliths of granitic magmas this may explain why many peraluminous hercynian granitoids of western europe have anomalously low 87sr 86sr initial values compared to their probable sedimentary parent rocks

magma mixing in the subvolcanic environment petrology of the gerena interaction zone near seville spain the mechanisms by which felsic and mafic magmas interact and approach a uniform hybrid composition through the processes of mingling and mixing have been studied in a high level subvolcanic setting in the spanish hercynian at gerena near seville the compositions involved are calc alkaline and the situation is one of tonalite quartz diorite synplutonic dykes injected into a granitic magma chamber the resulting hybrids include dykes pillows and globules of tonalite with chilled margins which are variously disrupted and homogenised with the host granite the present investigation is based on field and petrographic observations of hybridization textures the identification of different stages in the crystallisation history of the tonalite through mineral textures and the characterization of mineral compositions at these various stages proportions of the end member magmas involved were obtained by major oxide mixing models and tested satisfactorily with trace elements a mechanistic model is presented to account for these observations which involves the early quenching of the tonalite when it was emplaced into the granite magma chamber after high temperature crystallization had occurred the two magmas attained thermal equilibrium and disruption of the tonalite in the high energy regime of this subvolcanic complex resulted in dispersion of fragments and crystals through the granite giving rise to hybrid granodiorite compositions it is argued that such high energy flow conditions are a necessary requirement for effective hybridization in this environment in contrast to most large scale magma chamber settings where mixing is driven by thermal and buoyancy contrasts

assessing bulk assimilation in cordierite bearing granitoids from the central system batholith spain experimental geochemical and geochronological constraints

a new correlation of triassic jurassic boundary successions in nw europe nevada and peru and the central atlantic magmatic province a time line for the end triassic mass extinction abstract understanding the end triassic mass extinction event 201 36 ma requires a clear insight into the stratigraphy of boundary sections which allows for long distance correlations and correct distinction of the sequence of events however even after the ratification of a global stratotype section and point global correlations of tjb successions are hampered by the fact that many of the traditionally used fossil groups were severely affected by the crisis here a new correlation of key tjb successions in europe u s a and peru based on a combination of biotic palynology and ammonites geochemical 13 c org and radiometric u pb ages constraints is presented this new correlation has an impact on the causality and temporal development during the end triassic event it challenges the hitherto used standard correlation which has formed the basis for a hypothesis that the extinction was caused by more or less instantaneous release of large quantities of light carbon methane to the atmosphere with catastrophic global warming as a consequence the new correlation instead advocates a more prolonged scenario with a series of feedback mechanisms as it indicates that the bulk of the hitherto dated high titanium quartz normalized volcanism of the central atlantic magmatic province camp preceded or was contemporaneous to the onset of the mass extinction in addition the maximum phase of the mass extinction which affected both the terrestrial and marine ecosystems was associated with a major regression and repeated enhanced earthquake activity in europe a subsequent transgression resulted in the formation of hiati or condensed successions in many areas in europe later phases of volcanic activity of the camp producing low titanium quartz normalized and high iron quartz normalized basaltic rocks continued close to the first occurrence of jurassic ammonites and the defined tjb during this time the terrestrial ecosystem had begun to recover but the marine ecosystem remained disturbed

geochronology and geochemistry of the pola de allande granitoids northern spain their bearing on the cadomian avalonian evolution of northwest iberia the pola de allande pre variscan tonalite granodiorite plutons are located in the narcea antiform at the boundary zone between the cantabrian and west asturian leonese zones of the iberian variscan belt these granitoids were intruded into a neoproterozoic siliciclastic sedimentary sequence with subordinate volcanic intercalations and were subsequently overprinted by variscan thrust related shear deformation u pb laser ablation inductively coupled plasma mass spectrometry icp ms dating of zircons from two plutons yielded concordant ages of intrusion of 605 10 and 580 15 ma to the authors knowledge this is the first reported u pb cadomian avalonian age for igneous rocks in this section of the iberian variscan belt these intrusions are coeval with the main episode of dominantly calc alkaline magmatic activity related to cadomian avalonian subduction major and trace element composition of the granitoids is characteristic of i type high k calc alkaline granitoids generated in continental arc se

upper crustal recycling in southern britain evidence from nd and sr isotopes analyses of representative rocks from southern britain are used to examine in detail the evolution of this segment of continental crust the vast majority of late precambrian basement rocks have unradiogenic 87sr 86sr ratios and model tdmnd ages of 1 3 ga although locally the rosslare complex and rushton schists have model tdmnd ages 1 7 ga identifying for the first time an old component in the basement of southern britain following the closure of the iapetus ocean sediments exhibit a progressive increase in model tdmnd ages 1 35 ga in the lower palaeozoic to 1 75 ga in the jurassic this variation demonstrates the southerly transport of detritus tdmnd 2 0 ga from the mixed archaean proterozoic terrains of northern europe and america the granitoids have significantly higher end than those of contemporaneous sediments and thus yield a different nd isotope evolution curve when considered in isolation the majority of rocks analysed have model tdmsr ages in the range 1 2 to 0 46 ga with youngest sediments generally recording the lowest model ages therefore with time the sediments record a striking increase in the ratio of model nd to model sr age the data suggest that the rb sr ratios of the crustal rocks is increased by a factor of approximately 2 every 900 ma implying that on average the british upper crust was reworked by erosion and sedimentation every 600 ma

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

eustatically controlled sedimentation in the hettangian sinemurian early jurassic of poland and sweden in earliest jurassic times terrigenous continental and marginal marine deposition occurred in a large epeiric basin along the tornquist line in europe detailed sedimentological studies allow recognition of palaeoenvironmental fluctuations in space and time the main earliest jurassic transgressions occurred in the early hettangian early sinemurian mid sinemurian and latest sinemurian and formed bounding discontinuities transgressive surfaces of considerable correlative significance there is a step wise trend of increasing marine extension and influence during the early hettangian early sinemurian mid sinemurian and latest sinemurian earliest pliensbachian transgressions four sequences four transgressive systems tracts three highstand systems tracts and three levels regarded as equivalents of maximum flooding surfaces are distinguished in the case of type 2 sequences when incised valley fill deposits are not developed and regional erosion is less common it may be rather difficult to define the sequence boundaries which are often concealed within the amalgamated fluvial deposits occurring in the neighbouring parts of two adjacent sequences fluvial deltaic sediments terminate the highstand systems tracts and in this setting the transgressive systems tracts start with continental deposits prior to the transgressive surfaces generally an exact correlation can be achieved between the sequence stratigraphy of the northeast and northwest european lower jurassic and the eustatic curve proposed by epr assuming some changes proposed by a hallam the establishment of this correlation hopefully will stimulate future studies of the sequence stratigraphy of poorly dated siliciclastic deposits of marginal basins in this setting even minor changes in sea level may cause major changes in facies development over large areas

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

recycled metaigneous crustal sources for s and i type variscan granitoids from the spanish central system batholith constraints from hf isotope zircon composition abstract the spanish central system scs is one of the largest granite batholiths in the european variscan belt zircons from five granitic intrusions from the eastern scs have been separated and analysed for hf isotopes by laser ablation mc icpms in order to evaluate the nature of granitic magma source two samples are cordierite bearing s type granites the rest are amphibole bearing i type monzogranites hf isotope composition of zircons from these granites defines a narrow range of negative hf values 1 1 to 5 8 typical of crustal protoliths the within sample variation of zircon hf isotope composition is slightly above the analytical uncertainty 1 5 units suggesting the mixing of different magma batches during pluton assembly the s and i type granites display the same range of initial hf values that is in agreement with previous data showing that both scs granite types have similar sr nd o pb isotope signatures these isotopic data suggest that they derived from similar sources while the variation in peraluminosity could be related to different partial melting conditions the presence of a lower ordovician inherited zircon population 478 462 ma at least in i type granites suggests the involvement of cambro ordovician orthogneisses as components in the source of some scs granites inherited zircon population of similar age has also been identified in the scs lower crustal granulites the hf isotope composition of the analysed granite zircons is within that of zircons from the above granulites moreover some evidence of a juvenile input at 560 595 ma is recorded by hf isotope data in zircons from both the scs granites and granulite xenoliths hf isotope signature in conjunction with other chemical isotopic sr nd o pb and geochronological evidences suggests that scs granites were probably derived from metaigneous lower crustal sources the variscan magmatism in central spain is dominantly a crustal reworking event

sequence stratigraphic framework of the lower and middle jurassic in the north german basin epicontinental sequences controlled by boreal cycles in the early jurassic the epicontinental central european basin ceb including the north german basin ngb was covered with a semi enclosed inland sea that was in the late middle jurassic transferred to a continental shelf sea connected with the boreal and the tethyan oceans the pronounced facies architectures of lower to middle jurassic coastal deltaic and basinal deposits challenged many workers to apply sequence stratigraphic methods however resulting regional schemes are in places contradicting which is caused by both common problems with precise dating and processes of regional to local scale obliterating the sea level signal such as tectonically enhanced subsidence enhanced sediment supply thermal doming or salt diapirism this paper proposes a lower to middle jurassic sequence stratigraphic framework of the ngb the application of a multi method approach including intensive macro and micropalaeontological dating as well as mapping of biofacies and lithofacies architecture to an extensive data set of cored and logged wells resulted in a hierarchical framework of 2nd 3rd and 4th order epicontinental sequences this approach enabled the identification and exclusion of areas and locations where subordinated controls such as salt diapirism superimposed the signature of sea level fluctuations within stratal pattern architectures the proposed sequence stratigraphic framework correlates well with the boreal standard but to much lesser extent with the tethyan standard and thus demonstrates the principle control of boreal cycles on epicontinental stratal pattern architectures of the ngb this coincides with more significant faunal exchanges between the boreal and subboreal provinces in particular the opening of a marine strait via the russian platform in the late middle jurassic enabled the immigration of boreal ammonites and ostracods into the ngb and the northern ceb and illustrates the change from a semi enclosed inland sea to a continental shelf sea furthermore the recognition of lower and middle jurassic 4th order sequences supports suggestions of glacio eustatic sea level changes in the jurassic

variscan collisional magmatism and deformation in nw iberia constraints from u pb geochronology of granitoids u pb geochronology of variscan granitoid rocks from the west asturian leonese zone of the nw iberian belt documents the episodic nature of magmatism in this section of the western european variscides each magmatic episode is characterized by granitoids with distinct features and has a duration on the scale of several millions of years the ages of these granitoids place new constraints on the age and duration of magmatic and tectonic events that are consistent with previous structural studies and proposed models for the tectonic evolution and migration of deformation in the nw iberian variscan belt granitoid rocks in this zone belong to two main magmatic episodes syn and post tectonic relative to the variscan orogeny and are broadly representative of the granitoid types found in the nw iberian variscan belt the syntectonic association is formed by i tonalite granodiorite monzogranite intrusions emplaced synchronously with the main phase of crustal deformation d 2 at c 325 ma and ii younger leucogranite intrusions emplaced synchronously with syn convergence extensional structures at c 320 310 ma the post tectonic association is composed of i volumetrically dominant tonalite granodiorite monzogranite intrusions and associated minor mafic intermediate rocks emplaced at c 295 290 ma and ii scarce leucogranite intrusions emplaced at c 290 285 ma

sea level change and facies development across potential triassic jurassic boundary horizons sw britain the late triassic to early jurassic aged succession of sw britain the penarth and lower lias groups comprises mudstone sandstone and limestone strata deposited in a variety of marine to non marine environments faunal and floral characteristics of these successions have led to the proposal that one location in sw england st audrie9s bay should serve as the global stratotype section and point gssp for the base of the hettangian stage and thus for the triassic jurassic tr j boundary the sections of sw britain have also been used previously to infer sea level change history and relate this to potential kill mechanisms associated with the tr j boundary mass extinction chemostratigraphic biofacies and lithofacies data are used here to suggest alternative models of sea level change in relation to possible tr j boundary horizons in the sections of sw britain a sea level lowstand surface of erosion is inferred to occur within the cotham member of the lilstock formation a unit deposited in an environment that was often subaerially exposed in contrast to previous interpretations the top surface of the overlying langport member here inferred to be deposited on a carbonate ramp of depositional or tectonic origin represents a drowning event of at least regional extent all horizons regarded as plausible levels at which to place the tr j boundary based on fossil distributions lie within strata deposited during relative sea level rise however it is doubtful whether the higher horizons proposed to mark the boundary faithfully record times of true biotic change on a global scale and additionally there is no positive evidence that sea level fall had any relation to the genesis of proposed tr j marker horizons it is unlikely that sea level fall played a significant role in the tr j boundary extinctions in either a local or a global context

lead isotopic composition of hercynian granitic k feldspars constrains continental genesis lead isotope compositions have been determined in many k feldspars from granitic rocks emplaced during the variscan hercynian orogeny sensu lato around 300 myr in various parts of europe and the eastern us the ratios show a regular geographical pattern with contours arched around southern france and parallel to the atlantic coast of the us this distribution parallels predriftpalaeogeographical zones during the palaeozoic the lead isotope pattern of variscan granitic rocks is similar to that of some orogenic volcanic suites but is better explained by crustal melting than by an hercynian mantle crust material mixing the continental crust from these areas must be older than 3 000 myr large scale fluid circulation in the crust during orogenic processes apparently explains the observed geographical patterns of lead isotopes

continental crust formation seen through the sr and nd isotope systematics of s type granites in the hercynian belt of western france the isotopic compositions of sr nd and pb in leucogranites which are intercorrelated bernard griffiths et al 1985 1 may be explained by the mixing of ancient basement 1800 ma with juvenile crust late precambrian or early palaeozoic this hypothesis does not involve the existence of mid proterozoic crust as apparently indicated by thetdm model ages of the leucogranites ranging between 1600 and 1100 ma the nd isotopes reveal the crustal reworking while sr isotopes mainly record juvenile crust formation this paradox is explained by the geochemical heterogeneity of the sources involved

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

world energy developments 1981 the papers in this issue review significant petroleum and natural exploration and production activities throughout the world with the exception of the soviet union in addition papers on other energy minerals have been included to prepare these papers well data land status production statistics and geophysical activity information was accumulated from numerous sources such as foreign and domestic scouting services foreign and domestic governmental agencies at all levels industry organizations oil companies individual consultants and local representatives 1 fig 1 tab

isotopic and trace element arguments for the lower crustal origin of hercynian granitoids and pre hercynian orthogneisses massif central france abstract the cadomian hercynian basement of the massif central france contains both pre metamorphic orthogneisses 600 410 ma and post metamorphic undeformed granitoids 360 275 ma major trace element and sr nd isotopic analyses of these intrusions indicate slight differences in source material for orthogneisses and two types of underformed granitoid a granodiorite monzogranites and leucogranites orthogneisses have moderately enriched ree patterns la yb 5 3 13 3 variable hree contents ybn 4 2 25 and strong negative eu anomalies eu eu 0 23 0 36 their tnd values are low 5 8 to 1 7 indicating a strong crustal component in the source but tsr values are also generally low 25 to 100 and overlap the field of age corrected isotopic values for lower crustal granulite xenoliths from the massif central the source of the orthogneisses is therefore considered to be dominated by a lower crustal meta igneous component with additional input from a lower crustal metasedimentary source granodiorites monzogranites tend to show strong lree enrichment la yb 11 26 with small eu anomalies eu eu 0 54 0 75 and ybn values between 6 and 8 5 these granitoids form the least evolved end members of a series trending to highly evolved leucogranites with similar la yb ratios 11 36 but with generally larger eu anomalies eu eu 0 24 0 62 and lower ybn values 3 8 initial isotopic ratios of the leucogranites tnd 7 9 to 4 5 and tsr usually 100 mostly fall within the field of age corrected lower crustal metasedimentary granulite xenoliths from the region and it is proposed that these leucogranites were formed by partial melting of lower crustal metasediments granodiorites and monzogranites have tnd between 6 5 and 3 4 and tsr values

archean protoliths within early proterozoic granulitic crust of the west european hercynian belt possible relics of the west african craton granulites from the bay of biscay area have been studied by using u pb and sm nd methods results on four granulites suggest two major events of crustal growth and high grade metamorphism the first is archean 2 7 ga and the second is early proterozoic 1 9 ga in the hercynian belt the oldest basement remnants known so far are about 2 0 ga and are located in the northern armorican massif the 2 7 ga orthogneiss protolith age from the bay of biscay is the first direct evidence of archean crust involved in the hercynian belt major events at 2 7 1 8 and 0 6 ga in the hercynian belt suggest that european precambrian microplate s were part of the west african craton where the same sequence of events is observed

iberian late variscan granitoids some considerations on crustal sources and the significance of mantle extraction ages a suite of post tectonic granitoids mostly peraluminous broadly i type granodiorites and monzogranites and mafic rocks from nwiberia with crystallization ages between ca 309 and 290 ma has been investigated for sm nd isotopes and inherited zircon content in order to constrain the nature of their source rocks end values at 300 ma vary from 0 2 to 5 9 and tdm values range from 1 01 to 1 58 ga inherited xenocrystic zircons yielded ages ranging from 458 to 676 ma with 90 of data between 490 and 646 ma corresponding to neoproterozoic mostly ediacaran cambrian andordovician ages only three highlydiscordant analyses yielded ages older than 650 ma based on the data reported herein and relevant data fromthe literaturewe contend that post tectonic granitoids of the iberian variscan belt with exception of the scarce anatectic s type granitoids were derived mostly from metaigneous lower crustal sources which in turn were ultimately derived from a subcontinental lithospheric mantle enriched between ca 0 9 and 1 1 ga i type granitoids and mantle derived mafic rocks both underwent varying degrees of contamination by ametasedimentary lower crust depleted in pre 650 ma zircon through previousmelting episodes with a time integrated sm nd evolution different to that of the metaigneous lower crust participation of this metasedimentary crust in the genesis of these granitoids may account for nd isotopic variability and nd model ages well in excess of 1 2 ga

sources of hercynian granitoids from the french massif central inferences from nd isotopes and consequences for crustal evolution the french massif central is characterized by a great abundance and variety of granitoids emplaced during hercynian times 360 280 ma distinct nd i and 87sr86sr i are not associated with particular petrographic types however lower nd i values 8 5 occur among the younger leucogranites from the western part of the massif intermediate nd i 6 correlate with aluminous monzogranites and higher values 6 to 3 with calc alkaline granodiorites in the eastern massif central nd i are homogeneous at the regional scale in the western massif central the leucogranites and the monzogranite granodiorites display different trends of nd i with emplacement ages from these results extreme models involving a depleted mantle or an old archean or early proterozoic source may be ruled out the trend of increasing nd i with decreasing age observed in the monzogranite granodiorite group suggests either an increasing contribution of a mantle component or the progressive melting of more mafic more refractory crustal sources or both the reverse trend displayed by the leucogranites might be explained in terms of the upward migration of partial melting across an isotopically zoned metasedimentary pile the large amount of granites may be the result of favourable processes during the collision tectonics combined with the unusual abundance of fertile materials enriched in water and heat producing elements in the pre carboniferous crust

more than one event in the late triassic mass extinction the recent hypothesis that mass extinctions are discrete phenomena that have occurred with great regularity during the history of life1 2 is testable in several ways two essential elements of the hypothesis are 1 that each extinction event represents a significant departure from normal or background rates of extinction and 2 that such mass extinction events are spaced equally in time the analyses of the cyclicity of mass extinctions so far have concentrated on the past 250 myr with the first event occuring at the permian triassic boundary 245 myr ago1 5 the second event followed 26 33 myr later1 6 in the late triassic here i present a detailed analysis of the fossil record of marine and non marine life during the late triassic which suggests that there were at least two phases of mass extinction during that time separated by 12 17 myr

triassic rifts and facies patterns in western and central europe the triassic evolution of western and central europe was governed by regional crustal extension that induced the subsidence of a complex network of grabens and troughs these formed an integral part of the arctic north atlantic and the tethys central atlantic gulf of mexico rift and rift wrench systems which in the course of the mesozoic and cenozoic developed into major break up axes of pangea

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

the toarcian bajocian deltaic system in the north german basin subsurface mapping of ancient deltas morphology evolution and controls research focussing on the morphology and morphodynamics of modern river deltas has contributed much to the understanding of reservoir geometry and prediction of hydrocarbon splays and deep geothermal aquifers the interplay of allogenic and autogenic controls results in complex histories of modern river deltas comprising subsequent regressive and transgressive stages of delta formation the application to ancient examples is still ambiguous and in particular the detailed morphological description of ancient deltas is often hampered by limited subsurface data this basin scale study employs a data set of 15 cored wells and more than 450 logged wells in combination with lithofacies biofacies and architectural analysis to reconstruct high resolution subsurface facies and sand thickness maps of the toarcian bajocian deltaic system in the north german basin the results of this study show the evolution from smaller elongate river dominated delta types in the lower and upper toarcian 15 000 to 20 000 km and a larger lobate river dominated delta in the upper aalenian 40 000 km to a cuspate mixed river dominated and wave modified delta in the upper bajocian 25 000 km the river dominated parts are composed of subsequently formed of distributary deltaic channel belts and associated sheetsands of the delta plain and distributary mouth bar complexes with bar finger sand architectures of the delta front increasing marine processes in the bajocian resulted in modification of delta complexes forming a shoreface setting with foreshoals arc like chains of ooid bearing barrier shoals and back barrier lagoons the complex history of the toarcian bajocian deltaic system was mainly controlled by allogenic sea level fluctuations that triggered the delta progradation and subordinately by allogenic basin reorganisation autogenic process change of channel avulsion led to locally reduced sediment flux and culminated in lobe abandonment and transgressive shorelines differential compaction of underlying deltaic deposits result in strong differences in accommodation space and contributed to much to large scale delta shifts 300 km this article is protected by copyright all rights reserved

erratum to the posidonia shale lower toarcian of sw germany an oxygen depleted ecosystem controlled by sea level and palaeoclimate palaeogeogr palaeoclimatol palaeocol 165 2001 27 52 abstract the lower toarcian posidonia shale is famous for its excellently preserved fossils and its high amount of organic matter up to 16 both quality of preservation and accumulation of organic matter have been explained by permanent anoxic bottom water conditions high resolution geochemical sedimentological and palaeoecological investigations of various sections of the posidonia shale in sw germany however indicate that oxygen availability was variable and ranged from short oxygenated periods to longer term anoxia the benthic macrofauna consists of nine fossil communities and was used in combination with geochemical data to reconstruct a time averaged oxygen curve anoxic conditions prevailed during the deposition of the toarcian black shales they were however punctuated by various short periods weeks to years with oxygenated bottom water conditions sedimentological e g distinctiveness of microlamination siliciclastic content and geochemical parameters e g organic matter content isotopic signatures 18 o and 13 c molecular redox parameters pristane phytane ratio arylisoprenoids exhibit a remarkable covariation and seem to be controlled by sea level fluctuation maximum oxygen depletion and an extreme negative shift of 13 c org values 34 occurred during the early falciferum zone this is explained by the recycling of 12 c enriched carbon derived from remineralization of organic matter on and within the substrate during low sea level stand and a highly elevated redox boundary including photic zone anoxia the subsequent transgression permitted enhanced water exchange with the tethyan ocean and caused improvement of living conditions at the end of the falciferum zone other important factors controlling the depositional environment are the overall palaeogeographic situation and climate the early jurassic is the latest period before break up of pangaea and probably was ruled by a strong meridional atmospheric circulation system with pronounced seasonal changes of prevailing trade and monsoon wind systems an estuarine circulation with a positive water balance and surface water with slightly reduced salinity in the summer alternated with an anti estuarine circulation and a negative water balance in the winter during the summer months a stratified water column with anoxic conditions below the halocline developed 18 o data indicate low salinity in the surface water during the monsoon influenced summer high productivity was then located in the photic zone and the corresponding isotopically light 18 o signal was fixed in the calcareous nannoplankton during the winter months a saline circulation system brought oxygen to the benthic environment favouring temporary benthic colonization especially during times of relative sea level high stand

marine and terrestrial sedimentation across the t j transition in the north german basin abstract the global mesozoic sea level rise contributed to the stepwise flooding of the central european basin ceb across the t j transition and transformed the ceb from a late triassic inland playa to an early jurassic semi enclosed inland sea the calibration of sections from north germany and thuringia using high resolution palynomorph and ammonite biostratigraphy contributes to the improved temporal and spatial resolution of this decisive period the herein proposed deltoidospora concavisporites dc zone placed between the rhaetian ricciisporites polypodiisporites rp zone and the hettangian pinuspollenites trachysporites zone marks the transitional zone of overlapping rhaetian and hettangian palynomorphs in brackish marine brackish and terrestrial environments of the north german basin ngb thus the dc zone enables the identification of the t j transition in the ngb following a short term ingression in the late norian corollina porcellispora subzone the first rhaetian transgression contributed to substantial marine terrestrial facies shifts the diachronous transgressive onlap of brackish marine strata culminated in a first rhaetian maximum flooding in the upper corollina enzonalasporites zone to lower rhaetipollis limbosporites rl zone after a regressive maximum in the middle rl zone the next transgression culminated in a second rhaetian maximum flooding in the upper rl zone following the end triassic regression herein assigned to the upper rp zone the diachronous transgressive onlap of marine shales marks the change to marine jurassic environments the herein proposed deltoidospora concavisporites dc zone placed between the rhaetian ricciisporites polypodiisporites rp zone and the hettangian pinuspollenites trachysporites zone marks the transitional zone of overlapping rhaetian and hettangian palynomorphs in brackish marine brackish and terrestrial environments of the north german basin ngb thus the dc zone enables the identification of the t j transition in the ngb at the western gate of the ceb the onset of marine hettangian strata with ammonites dated as the p erugatum biohorizon at st audrie s bay postdates the base hettangian gssp by 250 kyr from there to thuringia the diachronous onlap of marine hettangian strata with ammonites herein dated as the p plicatulum biohorizon took place over 100 kyr the first jurassic maximum flooding is dated as the interval of the p psilonotum to p plicatulum biohorizons lower planorbis zone rhaetian hettangian 3rd order sequences of the ceb correlate with contemporaneous sequences described from tethyan and peri tethyan basins pointing to circum tethyan eustatic cycles the 4th order sequences are evident in the rhaetian hettangian but only a set of rhaetian 4th order sequences can be correlated in the ngb so far

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

fabric evidence for granodiorite emplacement with extensional shear zones in the variscan gredos massif spanish central system abstract three granitoid bodies in the central part of the gredos massif spanish central system batholith are tabular around 1 km in thickness and intruded into a migmatitic middle crust during the d3 deformation phase of the variscan orogeny petrologically they are composed of bt granodiorite and crd monzogranite and they show varying abundance of large cm scale feldspar megacrysts a detailed study of the shape preferred orientation spo magmatic fabric defined by these megacrysts together with a kinematic analysis of the structures due to interactions between them and the measurement of quartz c axis fabrics in migmatites and granitoids suggests that granitic magma and country rocks were mechanically coupled during deformation the emplacement took place along large scale extensional shear zones active during the first stages of the d3 phase the shape of the spo ellipsoids varies from constrictional at the centre of the granitic bodies to flattening or even oblate at their external contacts with the migmatitic host rocks the favoured interpretation of this spatial fabric variation is the overprinting of the emplacement fabrics by a constrictional tectonic regime associated with the growth of tabular magma chambers along extensional detachments followed by shear zone development commonly at the top of the granitic bodies the entire structure was later folded during the last stages of the d3 phase

recycling processes in granite granodiorite complex genesis the querigut case studied by ndsr isotope systematics abstract using the isotopic rb sr and sm nd petrogenetic tracers we have studied the calc alkaline plutonic complex of querigut pyrenees france which is famous for its acid to mafic rock association and is a typical post tectonic hercynian granitoid its age of 280 m y is already known 2 23 24 and our purpose is to examine the relationship between its different petrographic units and the problem of their source composition the sm nd isotopic results rule out any genetic process involving a unique homogeneous source and imply the presence of old recycled continental materials in contrast the rb sr isotope system seems to have been homogenized by hot fluids maybe post magmatic this is also true for pb isotopes as shown previously by michard vitrac et al 18 on the basis of the isotopic results and the major element data a model of combined fractional crystallization assimilation of country rocks is proposed for the basic part of the complex in contrast acid parts are mainly the result of the continental anatexis this study also constrains the basement s age 1200 1900 m y of the area and suggests a scheme for the gological history of the eastern pyrenees

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

lake mire deposition earthquakes and wildfires along a basin margin fault ronne graben middle jurassic denmark abstract regional uplift of structural highs took place in the greater north sea region in early middle jurassic times resulting in a change from marine shelf deposition in the early jurassic to widespread emergence erosion and localized deposition in grabens the middle jurassic baga formation exposed on the island of bornholm in the baltic sea was deposited in the ronne graben which forms a dog leg pull apart basin linking the northern and southern branches of the tornquist zone the studied succession is situated on the hanging wall immediately adjacent to the main eastern graben margin fault and the footwall consists of deeply weathered granite it is the only locality along the northern branch of the tornquist zone where active tectonic influence on middle jurassic deposition can be demonstrated in outcrop small alluvial fans composed of poorly sorted washout sands and muddy debris flows with weathered granite boulders fringed the footwall scarp syn depositional soft sediment deformation and chaotic bedding structures interpreted as seismites caused by earthquake shocks are characteristic at several levels on the hanging wall further away from the active fault the depositional environment was dominated by shallow freshwater lakes with deposition of clay lake deposition outpaced subsidence and open oxygen deficient freshwater mires were formed during periods of no or only incremental fault movement the mires were only occasionally isolated from clastic input due to doming and dense vegetation resulting in accumulation of pure peat beds the content of spores and pollen shows that the mires were covered by a vegetation of arborescent and herbaceous filicopsida ferns lycopsida club mosses cycadales bennettitales ginkgoales caytoniales taxodiaceae or cupressaceae and araucariaceae wildfires were common in the mires and also on the footwall probably followed by episodes of increased run off and erosion of the upland the presence of common washout sands debrites seismites and abundant lacustrine flooding surfaces indicating sudden drowning of the mires was caused by abrupt movements on the fault with associated earthquakes the succession thus provides an example of temporal changes in deposition in response to changes in tectonic conditions the study illustrates how regional uplift of structural highs caused a restriction of deposition to narrow grabens like the ronne graben facies patterns changed dramatically from laterally extensive uniform packages controlled by sea level changes in the early jurassic to strongly localized deposition with marked facies changes controlled by faulting and earthquakes in the middle jurassic the succession thus serves as an excellent example of tectonically controlled deposition under humid conditions in a continental graben

the nd and sr isotopic composition of i type microgranitoid enclaves and their host rocks from the swifts creek pluton southeast australia abstract initial nd and sr isotopic compositions have been determined for microgranitoid enclaves and their host rocks from the siluro devonian swifts creek pluton within the lachlan fold belt of southeastern australia enclaves are of quartz dioritic to tonalitic composition and their textures support an igneous origin host rocks range from tonalite to granite the isotopic data form an array in nd 87 sr 86 sr space with enclaves systematically displaced towards higher nd and lower 87 sr 86 sr values enclaves range in nd t 405 ma from 7 3 to 3 1 with a narrow range in 87 sr 86 sr from 0 70613 to 0 70718 whereas host rocks range from 9 0 to 6 4 and 0 70761 to 0 70946 in nd and 87 sr 86 sr respectively the isotopic relations rule out simple crystal liquid fractionation or restite unmixing alone as the major genetic link between enclaves and host rocks the data are also incompatible with an origin of the enclaves by crystal accumulation or liquid immiscibility instead mixing between a mafic mantle derived and a crustal derived end member to generate the host rock enclave spectrum is compatible with the data because the initial isotopic ratios of enclaves and host rocks are well within the range of crustal rocks we favour the alternative view that both enclave and host rock magmas are of crustal origin consequently we avoid extrapolations to hypothetical end members we suggest that the enclaves from the swifts creek pluton are derived by partial melting of a mafic lower crust and mixed at or near the site of magma generation with a chemically less primitive and isotopically more evolved component to generate the enclave and host rock spectrum the isotopic heterogeneities within the enclave and host rocks survived the superimposed effects of crystal liquid fractionation model ages tdm for enclaves and host rocks are almost identical averaging 1 7 and 1 6 ga respectively these model ages indicate that both the enclave and host rock protoliths were derived from a mantle reservoir during the proterozoic

geochemical and isotopic disequilibrium in crustal melting an insight from the anatectic granitoids from toledo spain in the hercynian anatectic complex of toledo act the anatectic granitoids include leucogranitic leucosomes leucogranitic massifs and restite rich granites they show a broad range of initial sr and nd isotope ratios from 0 711 to 0 720 and 0 51164 to 0 51203 respectively which clearly indicate the absence of isotopic homogenization in the melts broadly the ranges reflect the isotopic variation of the metapelitic protoliths if crustal melting occurs under water undersaturated conditions as is the case of the act the generated melts do not isotopically and chemically equilibrate with the granulitic residuum the preservation of heterogeneities could arise through a number of processes 1 duration of the process in which the presence of melts with disequilibrium features and the high solid content of several of the granites in the act point to a very short lived magmatic system 2 limited diffusion in which poorly segregated and volatile undersaturated granitoids have a very restricted opportunity for isotopic and chemical homogenization and 3 magma dynamics in which the low melting rates the high restite and low water contents and the silica rich composition of these granites together with the small volume and high viscosity values of the melts seriously restrict the physical processes leading to homogenization

granite emplacement in orogenic compressional conditions the la alberca bejar granitic area spanish central system variscan iberian belt abstract the la alberca bejar granitic area comprises a set of intrusions of upper carboniferous to lower permian age located in the hinterland of the variscan belt of western spain gravity data anisotropy of magnetic susceptibility and microstructural studies carried out in the granitoid and its country rocks indicate that the granitoids of this region have tabular and inverted drop shapes and show sub horizontal magmatic fabrics and sw ne lineations the granitoid bodies were intruded episodically with single intrusive pulses recorded by deformation in the country rocks all intrusive events took place during d 3 compressive stage in the core of large d 1 anticlines and are not related to structures in the country rock a syn orogenic emplacement model for granite intrusion in such conditions is proposed the proposed model implies the activity of coeval emplacement mechanisms and room generation

origin of peraluminous granites and granodiorites iberian massif spain an experimental test of granite petrogenesis the discrimination between potential source materials involved in the genesis of iberian granites and granodiorites as well as the role of mantle crust inter actions are examined using constraints imposed by melting experiments melting assimilation experiments and sr nd isotope systematics the sr nd isotope re lationships indicate the existence of diaerent genetic trends in which juvenile mantle materials are involved by diaerent mechanisms 1 a source trend traced by a particular evolution of the pre hercynian basement and indicating mantle participation at the time of sedimen tation 2 a set of magmatic trends traced by gabbro tonalite enclave granodiorite associations implying the incorporation of new mantle material at the time of granite generation these relationships strongly support a pure crustal origin for the peraluminous leucogranites derived from partial melting of crustal protoliths and a hybrid origin for the peraluminous granodiorites these granodiorites are the most abundant granitic rocks of the central iberian zone ciz of the iberian massif implying that processes of hybridisation by assimilation and or magma mixing played an important role in granitoid production during the hercynian orogeny these hypotheses have been tested by means of melting and assimilation experiments melting experiments in the range 800 900 c and at pressures of 3 6 10 and 15 kbar indicate that 1 several potential source materials such as bt ms gneisses and metagreywackes are suitable for the production of peraluminous leucogranite melts 2 the melt compositions are always leucogranitic re gardless of pressure 3 pressure exerts a strong influ ence on the fertility of the source experiments at 3 kbar produce more than 20 vol of melt compared with less than 5 vol of melt produced at 10 and 15 kbar and at the same temperature the melting assimilation experi ments carried out at 1000 c and 4 7 and 10 kbar and using a proportion of 50 gabbro and 50 gneiss give high melt proportions more than 50 vol and noritic residues these melts have the composition of le ucogranodiorites and overlap with part of the compo sitional range of peraluminous granodiorites of the iberian massif the generation of more mafic granodiorites may be explained by the incorporation of some residual orthopyroxene to the granodiorite mag mas the low solubility of fe mg prevents the gen eration of granodiorite melts with more than 3 wt of mgo feo at all crustal pressures the large volumes of peraluminous hybrid granodiorites produced by assimilation of crustal rocks by mantle magmas imply that an important episode of crustal growth took place during the late palaeozoic hercynian orogeny in the iberian massif

tectonic evolution of the mid polish trough modelling implications and significance for central european geology abstract the polish basin forms the easternmost part of the permian mesozoic northwest european basin the depocentral axis of the polish basin the mid polish trough mpt is superimposed on the boundary between the west european phanerozoic and east european proterozoic crustal domains within the trans european suture zone the presence of this fundamental crustal boundary may be paramount in structurally controlling the position of the mpt concentrating stresses during post variscan wrench and extensional tectonics in central europe tectonic subsidence analysis of the preserved and reconstructed stratigraphic record of the polish basin indicates the occurrence of an initial late permian early triassic 255 241 ma rifting phase that was followed by subsequent episodes of increased tectonic subsidence during the oxfordian kimmeridgian 157 152 ma and beginning in the cenomanian 97 ma the oxfordian kimmeridgian episode is interpreted as corresponding to a second extensional event which correlated with intersified rifting and wrench activity within the arctic north atlantic rift system and along the northern tethyan margin while the cenomanian may be considered a precursor of compressional deformations in the basin which culminated in basin inversion in the latest cretaceous and paleocene forward modelling results in view of existing geophysical interpretations which show the presence of a deep moho and a very velocity lower crustal layer beneath thempt suggest that permo mesozoic basic development may be related at least in part to the intrusion of mantle material into and densification of the lower crust rather than exclusively to crustal extension and thinning

mantle and crustal sources in the genesis of late hercynian granitoids nw portugal geochemical and sr nd isotopic constraints abstract large volumes of granitoids were emplaced in the hercynian central iberian zone during the last ductile deformation phase d3 300 320 ma the biotite rich granitoids are the most abundant 1 syn d3 granodiorites monzogranites 313 319 ma with calc alkaline and aluminopotassic affinities 2 late d3 granodiorites monzogranites 306 311 ma related to subalkaline and aluminopotassic series these granitoids are associated with coeval gabbro norite to granodiorite bodies and or mafic microgranular enclaves both granitoids and basic intermediate rocks show petrological geochemical and isotopic evidence of interaction between felsic and mafic magmas the mantle derived melts represented by shoshonitic gabbro norites were probably derived from an enriched and isotopically homogeneous source sr i 0 7049 to 0 7053 e nd 2 1 to 2 5 in some syn and late d3 plutons there are evidences of essentially crustal granites represented by moderately peraluminous monzogranites of aluminopotassic affinity they have similar nd model ages 1 4 ga but different isotopic compositions sr i 0 7089 to 0 7106 e nd 5 6 to 6 8 revealing a heterogeneous crust potential protoliths are metasedimentary immature sediments and or felsic meta igneous lower crust materials large amounts of hybrid magmas were generated by the interaction of these coeval mantle and crust derived liquids giving rise to slightly peraluminous monzogranites granodiorites of calc alkaline and subalkaline affinities which display more depleted isotopic compositions than the crustal end members sr i 0 7064 to 0 7085 e nd 4 4 to 6 2 petrogenetic processes involving mingling and or mixing and fractional crystallization at variable degrees in multiple reservoirs are suggested a major crustal growth event occurred in late hercynian times 305 320 ma related to the input of juvenile mantle magmas and leading to the genesis of composite calc alkaline and subalkaline plutons largely represented in the central iberian zone

crustal origin of hercynian peraluminous granitic batholiths of central spain petrological geochemical and isotopic sr nd constraints abstract in central spain it is possible to distinguish two main types of peraluminous late hercynian granites the pi types and the ps types the distinction between both types is made on the basis of differences in peraluminosity ps types are more peraluminous than pi types and also on the appearance of some characteristic mafic minerals ps types have biotite cordierite and monazite as the most typical accessory phase whereas pi types have biotite amphibole in the less evolved facies and allanite as the accessory mineral both granite types have similar trace element ratios and initial sr nd and pb isotopic signatures initial 87sr 86sr ratios of both types exhibit a large range from 0 7073 to 0 7193 whereas initial end varies in a restricted range from 5 4 to 6 6 the scarce associated basic rocks do not play a significant role in the chemical variability of these peraluminous granites which follow low pressure crystal fractionation trends from granodiorite monzogranite parental magmas mixing and afc modelling of sr and nd isotopic data reveal an unrealistically high mantle contribution based on major and trace element and isotopic data an orthogneissic protolith for both granitic series is proposed nevertheless none of the metamorphic country rocks of central spain has the appropriate sr isotopic composition to satisfy the origin of these granitic rocks and so it is argued that progressive isotopic re equilibration of crustal material during the granulization of the lower hercynian crust together with the possibility of isotopic disequilibrium during melting as has been demonstrated in migmatitic terranes in nearby areas may explain the isotopic differences between the granites and the high level metamorphic country rocks

astronomical calibration of the toarcian stage implications for sequence stratigraphy and duration of the early toarcian oae the toarcian oceanic anoxic event t oae of the early jurassic period involves one of the largest perturbations of the carbon cycle in the past 250 ma recorded by a pronounced negative carbon isotope excursion cie numerous studies have focused on potential causes of the t oae and cie but are hampered by an uncertain timescale here we present high resolution 2 kyr magnetic susceptibility ms measurements from the marine marls of the sancerre couy drill core southern paris basin spanning the entire toarcian stage the ms variations document a rich series of sub milankovitch to milankovitch frequencies precession obliquity and eccentricity with the periodic g2 g5 405 kyr and quasi periodic g g 2 4 myr cenozoic mean periodicity eccentricity terms being the most prominent the ms related g g variation reflects third order eustatic sequences and constrains the sequence stratigraphic framework of the toarcian stage in addition ms variations reveal a modulation of g g by g g eccentricity related cycles suggesting that sea level change was the main control on the deposition of the toarcian sancerre marls in tune with the astro climatic frequencies the stable 405 kyr cyclicity constrains a minimum duration of the toarcian stage to 8 3 myr and the well documented cie associated with the t oae to 300 to 500 kyr the 405 kyr ms timescale calibrates the periodicity of the prominent high frequency c cycles that occur in the decreasing part of the cie to 30 to 34 kyr consistent with the toarcian obliquity period predicted for an earth experiencing sustained tidal dissipation

h type hybrid granitoids a proposed revision of the granite type classification and nomenclature abstract recent studies on calc alkaline plutonic rocks reveal field and petrographic relationships with strong implications for the processes involved in their genesis the presence of magmatic inclusions and magma mingling zones in these rocks supports an origin by magma mixing compositional variations and isotopic anomalies are a good test for such petrogenetic models most of these calc alkaline plutonic rocks which characterize both collision related and active plate margin environments have been classically identified as i igneous type granitoids following chappell and white s 1974 classification and then interpreted as derived from partial melting of older igneous rocks restite model if the magma mixing origin of a type of granitoids can be demonstrated from field and petrographic evidence and supported by chemical and isotopic variations the nomenclature must be changed in this sense the new category of h hybrid type is tentatively introduced it includes most of the so called i type granitoids and some of the s type as deduced from field relationships of magma mingling zones a mixing model is suggested that can operate on a large scale to explain the petrogenesis of the hercynian calc alkaline granodiorites of iberia finally a modified classification of common plutonic rocks in orogenic environments is proposed

late pliensbachian early toarcian palaeoenvironmental dynamics and the pliensbachian toarcian event in the middle atlas basin morocco abstract geochemical and palynofacies analysis of 38 samples from the middle atlas basin ait moussa and issouka sections morocco allowed to investigate sea level changes climate and tectonics and impact on depositional environments in the westernmost tethyan gondwana margin during the late pliensbachian early toarcian and the pliensbachian toarcian event pl toa event the studied sections from the middle atlas basin have low total organic carbon contents overall kerogen assemblages are dominated by the phytoclast group thus showing a strong terrestrial affinity and some degree of proximity to the source deposition occurred dominantly in oxic and proximal environments upper pliensbachian kerogen assemblages from ait moussa are dominated by terrestrial particles and agree with the overall regressive character of the sedimentary succession uppermost pliensbachian lowermost toarcian kerogen assemblages from ait moussa show an increase in marine particles considering the overall sedimentological context of the middle atlas basin these kerogen assemblages are interpreted to reflect local variation in accommodation space driven by different sedimentation rates or tectonic compartmentalization or ecological conditions such as nutrient availability temperature turbidity etc in the early toarcian above a major regional discontinuity and at the beginning of the pl toa event increases in botryococcus sp aom and terrestrial palynomorphs suggest episodes of coastal erosion associated with transgression likely driven by a combination of eustatic tectonic changes and warmer and more humid climates leading to an increase in continental weathering and fluvial runoff on the other hand increases in sporomorphs and pollen grains occurring in tetrads and agglomerates indicate regressive episodes associated with increased sedimentation rates driven by enhanced continental weathering and fluvial runoff this study shows the strong relationship between sea level and the combined response of litho hydro and biosphere during the early toarcian with implications to understand organic productivity and organic matter accumulation and preservation in the tethys ocean during the pl toa event

high resolution sequence stratigraphy of a hettangian sinemurian paralic succession bornholm denmark sequence stratigraphic interpretation of paralic successions is complicated by the complex interfingering of marine and continental strata the successions may also include terrestrial extensions of marine parasequences and completely independent lacustrine parasequence analogues failure in recognizing the possible interbeddding of these two independent parasequence types may lead to construction of sequence stratigraphic schemes based on incompatible data sets we have studied a lower jurassic paralic section from the baltic island of bornholm situated in the tornquist zone which demarcates the transition from the stable precambrian baltic shield to the subsiding danish basin and danish polish trough the hettangian sinemurian sose bugt member ronne formation of bornholm includes lacustrine fluvial and restricted marine estuarine deposits reflecting the basin margin position biostatigraphic resolution is poor and a sequence stratigraphic interpretation of the paralic succession is far from straightforward a multidisciplinary approach including facies analysis recognition and lateral trading of key surfaces palynostratigraphy palynofacies coal petrography palaeopedology clay mineralogy and source rock geochemistry is applied in order to obtain a high degree of precision in the interpretation of the paralic facies in this way four sequences are recognized in the overall backstepping lacustrine to estuarine succession marine and marginal marine parasequences are distinguished from their purely lacustrine analogues and an internally consistent sequence stratigraphic scheme is proposed this is compared and tentatively correlated with fossiliferous marine sediments in the danish basin and with published eustatic cycle charts

neodymium and strontium isotope content of microdiorite enclaves points to mantle input to granitoid production microdiorite enclaves are arguably the most poorly understood of the more prominent features of granitoids surprisingly they have been invoked as support for completely different models for the origin of chemical zonation in granitoids depending on whether they are interpreted as restites syn plutonic blobs of magma remobilized cumulate or basified country rock xenoliths here we present the first detailed neodymium and strontium isotope study of suites of such enclaves from two plutons in both cases we find relatively high nd values most readily explained if enclaves represent syn plutonic injections of mafic magma into the host granitoid magma as such they are the tangible remains of a very important process of mantle derived heat and mass transfer operating in the generation of granitic magmas

sedimentological palynological and geochemical studies of the terrestrial triassic jurassic boundary in northwestern poland the kamien pomorski ig 1 borehole pomerania nw poland yields a profile through the triassic jurassic t j transition in continental deposits an integrated study of the sedimentology sequence stratigraphy palynology biostratigraphy and geochemistry of these deposits has been carried out on the boundary interval which represents a time of major environmental change two lithological units within the transitional section are distinguished the lower middle rhaetian wielichowo beds of alluvial plain facies which shows evidence of a semi arid climate and the upper rhaetian to lower hettangian zagaje formation lying above a marked erosional sequence boundary composed of mudstone claystone and sandstone deposited in a fluvial lacustrine environment carbon isotope values obtained from palynomaceral separates and thus reflecting isotopic changes in atmospheric co 2 show significant fluctuations through the rhaetian the most conspicuous negative 13 c org excursion is correlated with the rhaetian initial excursion and shows two sub peaks pointing to short term carbon cycle disturbances of lesser magnitude above the initial negative excursion there is a positive excursion followed again by more negative values representing subordinate fluctuation within a positive excursion and is correlated with the t j boundary seventy two miospore taxa have been determined from the studied t j transitional section two major palynological assemblages have been distinguished the lower one typically rhaetian named the cingulizonates rhaeticus limbosporites lundblandii association which corresponds to the rhaetipollis ricciisporites rhaetipollis limbosporites zone and the upper one typically hettangian named the conbaculatisporites mesozoicus dictyophyllidites mortoni cerebropollenites thiergartii association with the age diagnostic pollen c thiergartii which corresponds to the pinuspollenites trachysporites trachysporites heliosporites zone the t j palynofloral turnover occurred in a humid period and is more conspicuous then palynofloral changes observed in greenland the tethyan domain or other parts of ne europe the osmium isotope system is studied herein for the first time from t j continental deposits and shows marked disturbances similar to those measured in marine deposits and attributed to volcanic fallout carbon and osmium isotope correlation and coeval increase in polycyclic aromatic hydrocarbon pah content and darkening of miospores confirm that eruptions of the central atlantic magmatic province camp contributed to the perturbances in climate and crisis in the terrestrial biosphere a series of periodical atmospheric loading by co 2 ch 4 or alternatively by so 2 sulphate aerosols and toxic compounds is inferred to have caused a series of rapid climatic reversals directly influencing the ecosystem and causing the triassic floral crisis a floral turnover period commenced at the initial 13 c excursion with the onset of camp volcanism obtained values of initial 187 os 186 os between 2 905 and 4 873 and very low iridium content about 5 ppt lend no support to a role for an extraterrestrial impact at the t j boundary event the position of the initial negative carbon isotope excursion about 12 m below the t j boundary position of sequence boundaries emergence surfaces and other isotope excursions allow reliable correlation with marine profiles including st audrie9s bay uk csovar hungary and the gssp profile at kuhjoch austria

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

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany ii lead isotope evolution of the european hercynides

stepwise atmospheric carbon isotope excursion during the toarcian oceanic anoxic event early jurassic polish basin abstract during the mesozoic 250 64 ma intervals of about 0 5 myr were subject to severe environmental changes including high sea surface temperature and very low oxygen content of marine water these oceanic anoxic events or oaes occurred simultaneously with profound disturbance to the carbon cycle the carbon isotope anomaly in the early jurassic that marks the toarcian oceanic anoxic event t oae at 182 ma is characterized in marine sections by a series of dramatic steps towards lighter values herein we present new carbon isotope data from terrestrial organic matter phytoclast separates collected through a late pliensbachian middle toarcian coastal and marginal marine succession in the polish basin a setting where hinterland climate and sea level change are well recorded the results show that the shift to light carbon isotope values in the woody organic matter and therefore also in atmospheric carbon dioxide similarly occurred in major steps the steps are here correlated with those identified from marine organic matter where they have previously been attributed to 100 kyr eccentricity forcing of climate the results provide strong support for orbitally and climatically controlled release of isotopically light carbon from gas hydrates into the ocean atmosphere system in a series of rapid bursts additionally a link between the carbon isotope steps and shoreline movements can be demonstrated individual peaks of the negative excursion are mostly associated with facies indicative of sea level rise flooding surfaces however at the same time inferred higher atmospheric carbon dioxide content may be expected to have resulted in increased rainfall and temperature leading to accelerated weathering and erosion and consequently increased sediment supply progradation and regression causing some mismatches between isotope shifts and inferred sea level changes enhanced abundance of megaspores derived from hydrophilic plant groups and marked increase in kaolinite are coincident with the overall development of the negative isotope excursion the combined data suggest that each 100 kyr cycle in carbon isotope values was characterized by increasingly severe palaeoclimatic change culminating in extremely hot and humid conditions co incident with the peak of the final most negative carbon isotope excursion the chemostratigraphic correlation allows very precise dating of the late pliensbachian middle toarcian coastal and marginal marine sedimentary succession in the polish basin

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

two phased collapse of the shallow water carbonate factory during the late pliensbachian toarcian driven by changing climate and enhanced continental weathering in the northwestern gondwana margin abstract the end pliensbachian toarcian is characterized by several carbon cycle perturbations and faunal turnovers e g ammonites and foraminifera which are most likely triggered by pulses of the karoo ferrar chon aike large igneous province the majority of information about these events is based on detailed studies of sites deposited in deep water settings which leaves vast uncertainties about the expression of and response to these events in shallow marine ecosystems here we present a comprehensive assessment of paleoclimatic impacts on neritic depositional environments from the latest pliensbachian through the middle toarcian in the central high atlas basin morocco and compare those with changes observed in coeval neritic environments within the western tethyan realm a total of four new stratigraphic sections were investigated in the southern part of central high atlas basin and these new sections are synthesized with six previously published sections distributed over eight localities correlations between sections are based on biostratigraphy chemostratigraphy and lithostratigraphy in morocco two episodes of carbonate factory shutdown are observed spanning the pliensbachian toarcian boundary and the polymorphum levisoni transition each carbonate factory collapse correlates to well documented environmental disturbances during the latest pliensbachian middle toarcian interval including the toarcian oceanic anoxic event t oae moreover each episode of carbonate factory shutdown coincides with an interval characterized by a significant increase of coarse siliciclastic input in the basin further demonstrating the link between global warming increased continental weathering and ecosystem turnovers furthermore these two episodes of carbonate factory shutdown are each followed by episodes of renewed carbonate production showing the resilience of the neritic carbonate factory in this region the first recovery interval occurring during the late polymorphum zone is associated with a mixed siliciclastic carbonate system the second episode of carbonate recovery quickly follows the shutdown associated with the onset of the t oae it is associated with an abiotic dominated carbonate production mode resulting in an elevated ooid production a full recovery of biotic carbonate production only occurs in the late stage of the t oae although biotic turnover occurs at both events from a shallow marine perspective the major biotic and abiotic crisis occurred at the pliensbachian toarcian boundary and not during the t oae this is in contrast to the deep marine record where the t oae is often inferred to be the most significant event an enhanced hydrological cycle and the subsequent increase of continental nutrient shedding might have triggered the most severe changes of the carbonate productivity at the pliensbachian toarcian transition whereas ocean acidification and increased storm activity likely played a significant role at the onset of the t oae

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany lead isotopes of k feldspars from five granites of the se schwarzwald and from metamorphites are positively correlated in 207 204 as well as 208 204 vs 206 204 diagrams

origin of microgranular enclaves in granitoids equivocal sr nd evidence from hercynian rocks in the massif central france we examined the rb sr and sm nd systematics of three different high level to subvolcanic granitoid plutons and their microgranular enclaves the host granitoids are adamellites and grano diorites while the enclaves are mostly microtonalites with igneous textures the enclaves are rounded in shape and vary from 1 m across contacts with the enclosing granitoids are sharp and mostly nonlobate the microtonalitic enclaves are similar in mineralogy to their hosts initial 87sr 86sr are all 0 7070 and initial end is 3 0 to 6 6 for both the enclaves and their hosts this precludes a major input of an unmodified mantle derived component at the time of magma genesis nd isotopic contrasts between enclaves and hosts are 1 e nd unit at most these data indicate broadly cogenetic origins for enclave host systems though some enclaves have slightly less crustal signatures than the enclosing granitoids there are several possible interpretations 1 there may have been nearly complete isotopic homogenization between enclaves and host magmas derived from different starting parents 2 the enclaves and granitoids could all have purely crustal origins enclaves might represent magmas derived from slightly less evolved protoliths or parental magma or they could be concentrations of early formed crystals with interstitial melt 3 basaltic magma from the depleted mantle could have thoroughly mixed with a large volume of crustal melt in the lower crust 4 there could have been a significant input of melt derived from an enriched mantle source several of these mechanisms may have played roles in the genesis of the granitoids and their enclaves nd isotopes do not always allow unequivocal recognition of mantle components in granitoid magmatism we argue that enclaves of this type are probably not products of major mixing processes relevant to granitoid protoliths and large scale crustal evolution they commonly result from second order mingling of broadly cogenetic magma fractions that may have a variety of different origins

meta igneous origin of hercynian peraluminous granites in n w french massif central implications for crustal history reconstructions seventy samples of hercynian peraluminous granites gueret millevaches and saint sylvestre massifs and metamorphic units of the limousin area were analysed for rb sr and sm nd the source rocks of the peraluminous granites can be found in the metamorphic rocks of limousin among them meta igneous rocks were largely predominent over meta sedimentary rocks in the source of the three granites millevaches and gueret granites were generated by the partial melting of rocks comprising meta volcanics and meta sediments whereas the saint sylvestre granite was produced exclusively by the melting of late precambrian granites this leads to confusing t dm nd values the confusion being amplified by the segregation of monazite during the petrogenetic evolution of the peraluminous granites which leads to dramatic fractionation in sm nd ratios the data of the present study tend to demonstrate that peraluminous granites do not give a good representation of isotopic mean crustal estimates late precambrian time seems however to have been a period of extensive crustal generation in western europe

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

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

nature and composition of the lower continental crust in central spain and the granulite granite linkage inferences from granulitic xenoliths xenolith bearing alkaline ultrabasic dykes were intruded into the of the hercynian basement of the spanish central system in early mesozoic times the suite of lower crustal xenoliths in the dykes divided into three groups felsic peraluminous granulites metapelitic granulites and charnockitic granulites the felsic granulites form 95 of the total volume of the xenoliths whereas the charnockitic and metapelitic granulites are much less abundant 0 01 5 respectively thermobarometric calculations based on mineral paragenesis indicate equilibration conditions around 850 950 c 7 11 kbar thus the xenoliths represent lower continental crustal material superimposed on this high t high p assemblage is a high t low p paragenesis represented mainly by kelyphitic coronas reflecting re equilibration during transport in the clearly restitic mineral assemblages with up to 50 garnet and 37 sillimanite major and trace element modelling supports the idea that the late hercynian peraluminous granites of central spain represent liquids in equilibrium with restitic material of similar composition to the studied lower crustal xenoliths 87sr 86sr and end of the felsic xenoliths calculated at an average hercynian age of 300 ma are in the range 0 706 0 712 and 1 4 to 8 2 respectively these values match the isotopic composition of the outcropping late hercynian granites the sr isotopic composition of the xenoliths is lower than that of the outcropping mid crustal lithologies orthogneisses pelites a major contribution from the lower crust to the source of hercynian granites greatly reduces the necessity of invoking a large mantle contribution in models of granite petrogenesis the felsic nature of the lower continental crust in central spain contrasts with the more mafic lower crustal composition estimated in other european hercynian areas suggesting a non underplated crust in this region of the hercynian orogenic belt

glendonites from an early jurassic methane seep climate or methane indicators abstract an early jurassic late pliensbachian section margaritatus to spinatum ammonite zone northeast of cremlingen germany revealed three horizons with abundant glendonites calcite pseudomorphs after ikaite caco3 6h2o as well as authigenic carbonates these pseudomorphs have previously been used as indicators for organic and phosphate rich paleoenvironments with near freezing bottom water temperatures stable isotope measurements clearly show that the ikaite glendonite was precipitated at a methane seep location with methanotrophic sulfate reduction as the triggering geochemical process for ikaite formation at the sulfate methane interface the termination of methane seepage probably led to the disintegration of the primary mineral ikaite and successive pseudomorph formation reconstructed paleo bottom water temperatures ca 10 c from belemnites and ostracods indicate temperatures well above the previously observed range of ikaite stability near freezing raising the question if methane seeps are distinct geochemical sites promoting ikaite formation at higher temperatures