the dead sea transform fault system abstract a new map showing the major features of the dead sea transform fault system based on seismicity satellite imagery geological maps and bathymetric charts is presented special attention is given to the possible northward continuation of the transform system beneath the mediterranean sea near ed damur south of beirut the map shows the dead sea transform system to be a series of offset overlapping left lateral transform faults with a rhombochasm between each pair the system has similarities with the equatorial fracture zones in the atlantic ocean throughout the dead sea transform system is considered in its regional setting i e as extending from the red sea spreading centre in the south to the eurasian collision zone in the north it is suggested that it may intersect the latter somewhere east of cyprus making that area the northernmost termination of the dead sea transform system

inherited smnd isotope components preserved in monazite inclusions within garnets in leucogneiss from east antarctica and implications for closure temperature studies abstract application of the sm nd dating technique using garnet can be hampered by the presence of minor microscopic to submicroscopic ree rich inclusions in particular monazite and to a lesser extent zircon an acid leaching method using a mixture of hno 3 hcl has been used to tackle the monazite contamination problem with this leaching technique we demonstrate that inherited monazite inclusions have been preserved in garnet formed under high grade metamorphic conditions even very low levels of monazite contamination 0 001 wt have a profound effect on the sm nd system in the garnet analysis of a garnet from a leucogneiss dyke in the northern prince charles mountains eastern antarctica reveals that unleached garnet concentrates and the monazite inclusions as represented by the leachates define an apparent isochron of 1150 30 ma mswd 1 88 which represents a mixing age of inclusions preserving their inherited sm nd isotopic systematics in contrast analyses of the leached garnet concentrates yield much younger ages of 630 to 555 ma model calculations show that the presence of as little as 0 01 wt of monazite inclusions would swamp the sm nd isotope signature of the garnet concentrates this very low level of contamination is beyond the reach of physical purification processes and without leaching contamination is inevitable in inclusion bearing garnets such contamination can lead to older apparent ages than those of garnet formation and thus has profound implications for sm nd as well as u pb garnet chronometry

a molecular organic carbon isotope record of miocene climate changes the difference in carbon 13 13c contents of hopane and sterane biomarkers in the monterey formation naples beach california parallels the miocene inorganic record of the change in 18o 18o reflecting the miocene evolution from a well mixed to a highly stratified photic zone upper 100 meters in the pacific steranes 13c 25 4 0 7 per mil versus the pee dee belemnite standard from shallow photic zone organisms do not change isotopically throughout the miocene in contrast sulfur bound c35 hopanes likely derived from bacterial plankton living at the base of the photic zone have systematically decreasing 13c concentrations in middle and late miocene samples 13c 29 5 to 31 5 per mil consistent with the middle miocene formation of a carbon dioxide rich cold water mass at the base of the photic zone

proterozoic blueschist belt in western china best documented precambrian blueschists in the world a coherent blueschist terrane near aksu northwestern china is unconformably overlain by unmetamorphosed sedimentary rocks of sinian age ca 600 800 ma the pre sinian metamorphic rocks termed the aksu group have maintained stratal continuity and were derived from shale sandstone basaltic volcanic rocks and minor pelagic sediments they have undergone multistage deformation and transitional blueschist greenschist facies metamorphism and are represented by strongly foliated chlorite stilpnomelane graphite schist stilpnomelane phengite psammitic schist greenschist blueschist and minor quartzite metachert and metamorphosed ironstone metamorphic minerals present in blueschists include crossitic amphibole epidote chlorite albite quartz and actinolite mineral parageneses and composition of sodic amphibole suggest blueschist facies recrystallization at about 4 to 6 kbar and about 300 400 c post tectonic alkali diabase dikes cut the aksu group the basal conglomerate of the overlying sinian to eocambrian sedimentary succession contains clasts of both the metamorphic and dike rocks clearly demonstrating that conditions required for blueschist facies metamorphism were attained at least 800 m y ago

the oldest uhp eclogites of the world age of uhp metamorphism nature of protoliths and tectonic implications coesite bearing eclogitic rocks from the pan african belt in northern mali were dated by multichronological methods rb sr sm nd and ar ar rb sr and sm nd isotope analyses on whole rock and mineral separates of an omphacite kyanite micaschist and a mafic eclogite yielded concordant ages of about 620 ma this is interpreted as the time of the eclogitisation which represents the oldest ultrahigh pressure uhp metamorphic event so far recorded in the continental crust the nearly identical rb sr and sm nd ages suggest very rapid exhumation as observed in many phanerozoic uhp rocks 40ar 39ar dating of phengites from two uhp micaschists gave much older ages of 1045 and 760 ma phengite from a quartzite collected from the same site yielded a plateau date of 623 3 ma which is in agreement with the rb sr and sm nd dates the two 40ar 39ar ages older than 625 ma testify once more the recurrent problem of excess ar in ultrahigh pressure phengites the occurrence of the mali uhp eclogites indicates that by the late precambrian the earth has cooled enough to sustain the formation and preservation of deeply subducted uhp metamorphic rocks the new ages of ca 620 ma also constrain the amalgamation in nw gondwana to have occurred in the latest proterozoic but not in the middle cambrian this is supported by several recent chronological data for the southern segment of the major suture zone in the dahomeyide orogenic belt

diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

late cenozoic tectonics and volcanism in the northwestern corner of the arabian plate a consequence of the strike slip dead sea fault zone and the lateral escape of anatolia abstract the study area is the northwestern corner of the arabian plate near the triple junction of anatolian arabia and africa late cenozoic tectonics and volcanism have developed essentially east of the dead sea fault zone dsfz the strike slip boundary of the arabian and african plates including vents situated in front of the bitlis collisional belt isotopic and rare elements data indicate deep mantle sources for volcanism our mapping based on radar imagery and digital elevation models suggests that elongate volcanoes volcanic ridges and linear clusters of adjacent volcanic vents are rooted on tension fractures which are a kilometer or several kilometers in length and infers similar development in depth we have also observed non volcanic tension fractures we have been able to map the northern segment of the dsfz as a continuous but broken fault line the ghab pull apart basin connects with appended faults including the choukhour fault that ends northward in a tail crack feature and the aafrine fault that ends in a tail thrust the amik pull apart basin is bounded in the west by a small but distinct scarp shown by radar imagery our image analysis and field data suggest that the left lateral amanos fault has a reverse throw component in consequence the amanos range has to be regarded as an anticline and the karasu valley as a syncline in the southern part of the study area the regional stress field is mainly strike slip with n020 striking tension fractures east of the amanos fault it becomes transpressive with n120 to n140 striking tension fractures in the north near the triple junction albeit compressional faults and belt environment predominate it is influenced by e w lowering horizontal stress component triggered by the lateral escape of anatolia and remains of the strike slip type associated with n020 striking tension fractures more east of the dsfz in front of the bitlis belt isolated volcanoes e g karacadag elongated n160 show in the rigid arabian crust local weak lines that can be influenced at a distance by the lowering horizontal stress component

uncommon steranes in brazilian marginal crude oils dinoflagellate molecular fossils in the sergipe alagoas basin brazil comprehensive two dimensional gas chromatography with time of flight mass spectrometry gc gc tofms was used to identify unusual steranes in branched cyclic hydrocarbon fractions of crude oils from sergipe alagoas basin brazil and infer the geochemical settings of their cretaceous source rocks hopane sterane and sterane ratios and the presence of gammacerane and carotane in the oil samples indicates a saline source rock depositional environment and predominantly marine organic matter om input steroidal hydrocarbons were represented by alkyl steranes and several sterane series including abundant short chain steranes c21 and c22 regular steranes c27 c29 and diasteranes c21 c23 c27 c29 the ring a methyl sterane series contained 3 methyl steranes c22 and c23 c28 c30 abundant 3 methyldiginane c22 and 3 methyldiacholestanes c28 including 4 methyl steranes with abundant c30 4 23 24 trimethylcholestanes in the branched cyclic fraction of these crude oils the c29 sterane isomers 23 24 dimethylcholestane and 24 ethylcholestanes were resolved by gc gc tofms and a c29 dinosterane derivative was identified for the first time in brazilian crude oils the 23 24 dimethyl and 4 23 24 trimethyl steroids can be related to dinoflagellate om and abundant dinosteranes suggests dinoflagellate blooms during source rock deposition in this brazilian marginal basin additionally the detection of c28 c32 3 alkyl cholestanes c29 c33 3 alkyl 24 methylcholestanes and c30 c34 3 alkyl 24 ethylcholestane with ethyl to pentyl groups at c 3 resulted in a complex sterane fingerprint as expected for petroleum generated from source rocks deposited under predominantly marine saline conditions with high microalgal input these biomarker results provide additional insight into the character and geologic processes responsible for the source rocks of crude oils in the brazilian marginal basins this information will be a valuable exploration tool that can be used to constrain the distribution of different oil types in these basins

sulphur and oxygen sequestration of n c37 and n c38 unsaturated ketones in an immature kerogen and the release of their carbon skeletons during early stages of thermal maturation sedimentary rock from the gessoso solfifera formation messinian in the vena del gesso basin northern italy containing immature ro 0 25 s rich organic matter was artificially matured by hydrous pyrolysis at temperatures from 160 to 330 c for 72 h to study the diagenetic fate of n c37 and n c38 di and tri unsaturated methyl and ethyl ketones alkenones biosynthesised by several prymnesiophyte algae during early diagenesis the alkenones are incorporated into the kerogen by both sulphur and oxygen cross linking as indicated by chemical degradation experiments with the kerogen of the unheated sample heating at temperatures between 160 and 260 c which still represents early stages of thermal maturation produces large amounts up to 1 mg g toc of s bound o bound and both s and o bound n c37 and n c38 skeletons saturated n c37 and n c38 methyl ethyl and mid chain ketones c37 and c38 mid chain 2 5 di n alkylthiophenes c37 and c38 1 2 di n alkylbenzenes and c37 and c38 n alkanes with increasing thermal maturation three forms of the n c37 and n c38 skeletons are relatively stable saturated hydrocarbons 1 2 di n alkylbenzenes and saturated ketones whereas the s and o bound skeletons are relatively labile these results suggest that in natural situations saturated ketones with an n c37 and n c38 skeleton can be expected as well as the corresponding hydrocarbons

impact of dia and catagenesis on sulphur and oxygen sequestration of biomarkers as revealed by artificial maturation of an immature sedimentary rock hydrous pyrolysis of an immature ro 0 25 sulphur rich marl from the gessoso solfifera formation messinian in the vena del gesso basin was carried out at 160 c t 330 c for 72 h to study the effect of progressive diagenesis and early catagenesis on the abundance and distribution of sulphur containing and sulphur and oxygen linked carbon skeletons in low molecular weight and high molecular weight fractions e g kerogen to this end compounds in the saturated hydrocarbon fraction monoaromatic hydrocarbon fraction polyaromatic hydrocarbon fraction alkylsulphide fraction and ketone fraction were quantified as well as compounds released after desulphurisation of the polar fraction and hilialh4 treatment of the desulphurised polar fraction sulphur bound phytane and 20r 5 14 17 h and 20r 5 14 17 h c27 c29 steranes in the polar fraction become less abundant with increasing maturation temperature whereas the amount of their corresponding hydrocarbons increases in the saturated hydrocarbon fraction carbon skeletons that are bound in the kerogen by multiple bonds e g c38n alkane and isorenieratane are first released into the polar fraction and then as free hydrocarbons these changes occur at relatively low levels of thermal maturity ro 0 6 as evidenced by the immature values of biomarker maturity parameters such as the c35 hopane ratio and the 22s 22s 22r 17 21 h c35 hopane ratio sulphur and oxygen bound moieties present in the polar fraction are not stable with increasing thermal maturation however alkylthiophenes ketones 1 2 di n alkylbenzenes and free n alkanes seem to be stable thermal degradation products of these sulphur and oxygen bound moieties thus apart from free n alkanes which are abundantly present in more mature sedimentary rocks and crude oils alkylthiophenes 1 2 di n alkylbenzenes and ketones can also be expected to occur the positions of the thiophene moiety and the carbonyl group coincide with the original positions of the functional groups of their precursors thus important information about palaeobiochemicals is retained throughout the sequestration degradation process

pan african granulite formation in the kabye massif of northern togo west africa pb pb zircon ages metamorphic zircons from seven granulite facies orthogneisses of tonalitic composition enderbites collected from four different nappes of the kabye massif in the dahomeyide belt of northern togo were dated by the pb pb evaporation method they yielded consistent neoproterozoic ages with a mean of 612 5 0 8 ma interpreted to reflect the peak of regional granulite facies metamorphism following pan african continental collision between the west african and benin nigerian plates these results support previous ages obtained by various chronometers on high grade rocks from the same suture zone and from surrounding units in togo benin and ghana they are also similar to zircon ages from granulites in the mozambique belt of souteastern africa these pan african metamorphic ages reflect continental amalgamation resulting in the formation of the gondwana supercontinent towards the end of the neoproterozoic

methane derived carbonate conduits from the late aptian of salinac marne bleues vocontian basin france petrology and biosignatures abstract peculiar carbonate bodies occur in distinct marl layers of the marnes bleues formation aptian albian vocontian basin southern france the carbonate conduits exhibit pipe or sausage like forms and a central channel their sizes range between 30 and 60 cm in length and 5 10 cm in diameter the conduit carbonates consist of automicrite authigenically formed within the sediment millimeter sized aggregates of framboidal pyrite are abundant within the conduit automicrites probably representing former colonies of sulfate reducing bacteria the central channel reflects former pathways of reduced fluids in the carbonate conduit ni enrichments at the margins of the central cavity are may be due to the activity of methane related metabolism as ni is an important bio element for respective microbes light stable carbon isotope ratios of the conduit automicrites 25 86 to 23 10 vpdb point to carbonate precipitation linked to anaerobic oxidation of methane aom while less depleted stable carbon isotope ratios of microspar in marginal zones of the central opening 8 96 vpdb are in line with microbial sulfate reduction a methane related origin of the conduit carbonates is confirmed by the presence of authigenic lipid biomarkers tentatively sourced by archaea most of which are characterized by strong 13 c depletions 13 c values down to 104 the presence of organically bound sulfur is well in line with microbial sulfate reduction isorenieratane potentially point to the presence of brown pigmented green sulfur bacteria the methane was probably sourced by older oae black shales which are known to contain isotopically 13 c heavy biomarkers of archaea as reported elsewhere

talc magnesite and ti clinohumite bearing ultrahigh pressure meta mafic and ultramafic complex in the dabie mountains china

a high resolution historical record of holocene anoxygenic primary production in the black sea i reconstruct the historical record of anoxygenic primary production in the black sea over the last 8200 years by an analysis of chlorobium carotenoids in sediments anoxygenic photosynthesis in the black sea occurs only when hydrogen sulfide containing deep water penetrates the euphotic zone the data show that the black sea has experienced large fluctuations in the extent of anoxygenic primary production and therefore the depth of the h2s chemocline throughout much of the holocene changes in the depth of the h2s chemocline also shift the dominant phytoplankton populations in the water column to noncarbonate bearing species and result in the formation of intense dark bands in sediments

3 d modeling of geologic maps from surface data recent discoveries in earth sciences are mostly related to technologies allowing graphical representations of volumes we present a way to produce mathematically and geometrically correct three dimensional 3 d geologic maps consisting of the volume and shape of all geologic features of a given area the method is innovative in that it only uses surface information based on the combination of a standard geologic map a satellite image and a digital elevation model it is based on a modeling algorithm that only uses surfaces calculated from scattered data points and that intersects them following a series of geologically sound rules the major advantage of using such technology is that it provides the user with a way to quantify geology to illustrate how a 3 d geologic map can be computed we explain the steps taken to build a dummy model with simple faulting and depositional sequencing the case study chosen to illustrate the method is the beirut watershed lebanon an area with relatively simple geology the 3 d visualization and cross sections help in the understanding of the geometrical relationship between the different geologic features allowing a reexamination of the tectonic history of the area during the late mesozoic

latitudinal change of normal paraffin composition in the northwest pacific sediments abstract we analyzed normal saturated paraffins n paraffins in 70 surface sediments in the northwest pacific to examine the spatial distribution of organic materials all sediments show bimodal n paraffin abundance patterns against carbon number with maxima at c 16 and c 31 indicating that n paraffins in marine sediments are a mixture of long chain n paraffins from land based higher plant waxes and short ones from marine organisms we observed in this study a significant change of carbon preference index cpi from 2 5 in low latitudes to 4 5 in mid high latitudes around 19 25 n the following influences are discussed as the cause of cpi offset between low and mid high latitudes 1 meteorological conditions 2 n paraffin composition of higher land plants 3 contribution of petroleum components and 4 mixing ratio of higher land plants and marine organisms however none of them can be the possible cause of the cpi offset because n paraffin content and composition vary significantly according to the species of a bacterium difference of the species of bacterial communities between low and mid high latitudes may be a possible reason for the cpi offset found in sediment from the northwest pacific

ar ar geochronology of ultrahigh pressure metamorphism in central china the dabie shan of china contain the largest areal exposure of ultrahigh pressure regional metamorphic rock known on earth the thermal history of these unusual rocks is central to understanding the tectonic processes responsible for their creation preservation and exhumation published ages of ultrahigh pressure metamorphism and subsequent cooling range from archean to jurassic by analyzing 21 dabie hornblende phengite and biotite samples by the 40ar 39ar method we find that 1 cooling from peak metamorphic temperatures to 300 c occurred between about 206 and 178 ma 2 widespread cretaceous ages reflect reheating by a postultrahigh pressure magmatic extensional episode 3 40ar 39ar and k ar ages older than 230 ma and perhaps 210 ma are geologically meaningless due to the incorporation of excess 40ar and 4 dabie ultrahigh pressure metamorphic rocks are temporally related to blueschist facies rocks farther west in the suture zone

nd and sr systematics in an eclogite xenolith from tanzania evidence for frozen mineral equilibria in the continental lithosphere combined isotopic nd sr and petrographic analyses are reported for an eclogitic xenolith from the vissury mine tanzania an exceedingly large difference in measured nd values in garnet and clinopyroxene 200 units suggest a major mineral equilibration at 1 75 0 014 ga nd isotopic heterogeneities are demonstrated in different generations of garnet and zonation in sr and nd isotope compositions is present within the clinopyroxene the variation in measured nd isotope compositions in different generations of garnet corresponds to 16 units exsolution of garnet from clinopyroxene occurred in an essentially closed system with respect to sr and nd petrographically different generations of garnet are present one garnet with rutile inclusions as well as the rims of clinopyroxene are clearly off the isochron features like this can originate either if a system is not closed e g affected by a migrating fluid or if a remanent isotopic heterogeneity survived the homogenisation at 1 75 ga the subsolidus partitioning of sm and nd between garnet and clinopyroxene results in higher fractionation of the smnd ratio in garnet than in the liquid crystal partitioning since the closure temperature for the sm nd exchange between garnet and clinopyroxene may be around 850 c in a dry system many of the lithospheric ultramafic rocks may exhibit frozen mineral equilibria the isotopic data suggest that this eclogite was emplaced at 1 75 ga into the lithosphere mantle at temperatures of about 1040 c and then cooled as a closed system at a rate of 6 50 c my down to 840 c where all the exchange reactions were efficiently frozen in at 1 75 ga ago the coincidence of the emplacement of granites 1 7 1 8 ga into the central part of the tanzanian craton with the age of the eclogite suggests that lower crustal melting was triggered by a thermal event in the upper lithosphere

eclogitized gabbros from the eastern grenville province textures metamorphic context and implications undeformed lenses of olivine orthopyroxene gabbro belonging to the 1429 ma shabogamo intrusive suite parautochthonous belt of the eastern grenville province host the first occurrence of eclogite mineral assemblages reported from the grenville province these rocks preserve igneous textures overprinted by eclogite mineralogy and by textures related to subsequent unloading high pressure signatures include omphacite pseudomorphs after augite plagioclase replacement by garnet kyanite corundum and orthopyroxene omphacite garnet coronas between olivine and plagioclase transformations related to decompression include replacement of garnet kyanite corundum by spinel plagioclase growth of plagioclase collars between clinopyroxene and garnet and de jadeitization of omphacite clinopyroxenes with numerous plagioclase inclusions and garnets surrounded by clinopyroxene plagioclase symplectites in granoblastic mafic rocks from the same area are also evidence of decompression from high pressures these

molecular indicators for palaeoenvironmental change in a messinian evaporitic sequence vena del gesso italy i variations in extractable organic matter of ten cyclically deposited marl beds abstract a screening by direct desulphurization of extracts was employed for 21 immature organic sulphur rich marl samples from 10 of the 14 evaporite cycles in an italian messinian evaporitic basin vena del gesso gessoso solfifera fm the combined information retrieved from free and sulphur bound carbon skeletons enabled a detailed palaeoenvironmental reconstruction the biomarker compositions of the marls point to large variations in the composition of species in the water column e g dinoflagellates diatoms and other algae cyanobacteria methanogens green sulphur bacteria and bacterivorous ciliates and in contributions from the continent i e land plants within each marl bed and between marl beds the marl beds were deposited within a stratified lagoon where anoxic conditions extended into the photic zone for much of the time

transcurrent fault activity on the dead sea transform in lebanon and its implications for plate tectonics and seismic hazard fault activity within the lebanese transpression zone one of the classic examples of restraining bend development on a continental transform is here investigated using dated geomorphological features the northern part of the yammouneh fault commonly considered to be the principal active strand on this part of the dead sea transform has been inactive for the past 5 ma field observations show that basalts dated as late pliocene hi age apparently offset by the yammouneh fault unconformably overlie it the active transcurrent structure is principally perhaps exclusively the roum fault the lebanese transpressive zone has evolved through tune with migration of fault activity these results confirm the overlapping transform hypothesis for the dead sea system require the active triple junction between the transform and the tethyan collision belt to lie offshore se cyprus and have profound implications for assessing seismic hazard hi the levant

geochemical study of macromolecular organic matter from sulfur rich sediments of evaporitic origin messinian of sicily by chemical degradations abstract selective chemical degradations have been performed on sulfur rich macromolecular organic matter from sediments of the messinian of sicily upper miocene italy the biomarkers released upon different desulfurization experiments are much more abundant than the free lipids and display completely different distributions which reflect the selective trapping of poly functionalized molecules by inorganic sulfur species at an early stage of diagenesis the bound biomarker distributions reveal a dominant phytoplanktonic input originating from an upper oxic water layer and a moderate bacterial reworking of the organic matter a contribution from cyanobacteria to the organic matter cannot be excluded the presence of carotenoids typical from photosynthetic sulfur bacteria attests to a stratified water body where an anoxic photic zone occurred lialh4 hydrogenolysis of sulfur rich macromolecules revealed that polysulfide bridges contribute to a large extent in the cross linking the results of deuterium labelling experiments are discussed in terms of sulfur incorporation on functionalized lipids

detecting major terrain parameters relating to mass movements occurrence using gis remote sensing and statistical correlations case study lebanon abstract among the various natural hazards mass movements mm are probably the most damaging to the natural and human environment in mediterranean countries including lebanon which represents a good case study this research deals with how to use geographic information systems gis for establishing the relationships between mm occurrence and different factor terrain parameters over a representative region of lebanon parameters expressed by 1 ancillary data like lithology proximity to fault zone soil type land cover use distance to drainage line and rainfall quantity and 2 derived data like slope gradient and slope aspect were correlated with mm using gis approaches the mm were first detected through visual interpretation of two stereo pairs of spot 4 images anaglyph at 10 m resolution this study indicates depending on bivariate remote sensing and gis statistical correlations kendall tau b correlation that the lithology is the most influencing factor on mm occurrence it also shows that statistical correlations to mass movements exist best between factors at the following decreasing order of importance lithology proximity to fault line lithology soil type and lithology distance to drainage line at 1 level of significance and soil land cover use slope aspect land cover use and soil slope gradient at 5 level of significance these correlations were verified and checked through field observations and explained using univariate statistical correlations therefore they could be extrapolated to other mediterranean countries having similar geoenvironmental conditions

the neoproterozoic brasiliano orogeny in northeast brazil 40ar39ar and petrostructural data from ceara abstract the borborema province in ne brazil comprises paleoproterozoic basement and its proterozoic cover that experienced a complex tectonometamorphic history during the brasiliano pan african orogeny in ceara four major domains separated by continental scale steeply dipping dextral shear zones have been identified 40 ar 39 ar step heating of mineral separates and laser probe fusion of single grains have been used in conjunction with petro structural observations to delineate the cooling tectonic history of these domains to the north of the senador pompeu shear zone spsz amphibole and biotite pairs from low pressure granulite belts exposed along the granja shear zone and spsz record plateau ages in the range 575 560 ma corresponding to cooling rates close to 20 c m y 40 ar 39 ar laser probe muscovite dates from the chaval augen gneiss point to a similar age for shearing responsible for the exhumation and fast cooling of the granulite belts a muscovite biotite pair from the central ceara high pressure nappes lying between the shear zones documents a lower cooling rate in the interval 534 525 ma related to the decompression and uplift of previously deelly buried rocks to the south of the spsz only moderate crustal thickening occurred within the various schist belts a distinct cooling pattern is indicated for these belts and the western patos shear zone attesting to a different crustal development 40 ar 39 ar dates of amphibole phlogopite muscovite and biotite range from 550 to 522 ma recording a postmetamorphic cooling rate of 6 9 c m y slower cooling rates of 3 4 c m y between amphibole and biotite closure ages in the range 540 500 ma are reported for the eastern part of the palos shear zone system the diachronous cooling recorded along this shear zone is interpreted to reflect the variations in thickness of the high temperature mylonitic belts earlier more rapid cooling occurred where the belts are narrow in the west late slower cooling occurred in wider zones to the east these thermochronological data reveal an age and cooling rate distribution at the scale of the borborema province that provides new constraints on the development of the brasiliano orogeny between 580 and 500 ma

present day kinematics of the middle east and eastern mediterranean the middle east and eastern mediterranean regions contain three major strike slip fault zones the dead sea fault zone dsfz and the north and east anatolian fault zones nafz and eafz these accommodate northward motion of the african and arabian plates relative to eurasia and westward motion of the small turkish plate this study deduces an internally consistent solution for the present day kinematics of these plates which is accurate to better than 20 and applicable throughout time since 5 ma by constraining the slip senses and rates on these strike slip fault zones the 7 0 5 mm yr 1 left lateral slip rate on the dsfz is associated with counterclockwise rotation of arabia relative to africa at 0 33 m y 1 around an eulcr pole near 33 n 23 e the nafz takes up counterclockwise rotation of the turkish plate relative to eurasia at 0 83 m y 1 13 around a pole at 31 n 35 5 e with right lateral slip rate 15 mm yr 1 the resulting prediction for the eafz involves 14 mm yr 1 left lateral motion and 2 mm yr 1 of shortening between arabia and turkey the triple junction of africa arabia and turkey is near the city of kahramanmaras this locality contains a narrow promontory bounded by ssw trending left lateral faults at the edges of the arabian and turkish plates which is loosely attached to the african plate moving westward relative to its interior at 4 mm yr 1

the deep water counterpart of the messinian lower evaporites in the apennine foredeep the fanantello section northern apennines italy abstract a possible deep water non evaporitic unit equivalent of the messinian lower evaporites has been recognised in the northern apennine foredeep this unit whose existence is implicitly admitted in the two step model of the mediterranean messinian salinity crisis is documented here for the first time it occurs throughout the apennine foredeep basin below a thick horizon of resedimented gypsum deposits usually ascribed to the lower evaporites actually the lower evaporites of the apennine foredeep basin include both shallow water in situ precipitated facies and deep water resedimented facies deposited in distinct depocenters the usually envisaged coeval nature of the two deposits has been recently challenged in several works based on a physical stratigraphic considerations about the downbasin correlation of the messinian erosional surface cutting on top the in situ evaporites with the sharp base of the resedimented evaporites unit and b the common occurrence of a barren unit below the resedimented evaporites which has no obvious equivalents in pre evaporitic successions underlying the in situ precipitated evaporites in this work a multidisciplinary study has been carried out on a 140 m thick composite section fanantello section to definitely assess the age and palaeoenvironmental characteristics of the unit underlying the resedimented gypsum deposits the topmost part of the section comprises a 60 m thick succession of barren euxinic shales falling entirely within a reversed polarity chron and characterised by a the complete disappearance of foraminifera b the occurrence of high salinity tolerant thecosomatous pteropods creseis sp c the abundance peaks of the calcareous nannofossil sphenolithus abies interpreted as related to highly stressed likely hyperhaline conditions d the appearance of hyperhaline and or stratified water molecular indicators gammacerane based on a multidisciplinary integrated stratigraphic approach this barren interval is here proposed to be a deeper water time equivalent of the in situ primary lower evaporites thus allowing to assess the events connected to the onset and the first phase of the messinian salinity crisis from a basinal perspective these data lend support to the hypothesis that the resedimented evaporite deposits of the apennine foredeep basin postdate the in situ evaporites thus implying that the term lower evaporites actually comprises rock bodies with different origins and separated in time and space by the messinian erosional surface and its correlative conformity this could be true also for other mediterranean basins where the stratigraphy of deep water successions should be carefully re examined

tectonics of the pliocene homs basalts syria and implications for the dead sea fault zone activity timing of activity along the yammuneh segment lebanon syria of the dead sea fault zone and its northward continuation is still a subject of controversy our field structural analysis and observations on radar landsat and digital elevation model imagery of the homs region syria are of concern for plio quaternary tectonics of the whole northern part of the dead sea fault zone we show in this paper that the northern dead sea fault zone has remained active since the onset of the homs basalts at c 6 ma continuing movement in recent times is indicated by the occurrence of quaternary pull apart structures and offset of active ravines along the fault the homs basalts are related to the distinct oval shaped shin volcanic edifice of which the long axis trends nw the volcano was fed through nw striking tension fractures which now form dykes and volcanic ridges these patterns are consistent with a ne sw extension that occurred c 6 ma ago the northwestern end of the shin volcano is left laterally displaced c 20 km yielding a c 3 3 mm a 1 mean rate of relative movement between the arabian and african plates in the northern part of the dead sea fault zone the overall trace of the main active dead sea fault zone is not a single transform but forms an irregular plate boundary composed of transform fault and collision belt segments fine grained mylonite developed in the fault corridor may have favoured aseismic deformation in the shin volcano area

pb sr nd isotopic behavior of deeply subducted crustal rocks from the dora maira massif western alps italy abstract pb nd and sr isotope data are reported on mineral separates and whole rock samples of mg rich metapelites and associated rocks that have been subducted to depths of ca 100 km in the mantle within the last 100 ma and returned to the surface and for which metamorphic conditions were estimated to be 700 800 c at 28 kilobars pressure three rock types fine and coarse grained pyrope quartzites and nafe rich jadeite kyanite quartz layers were collected from a single outcrop in the coesite bearing portion of the dora maira massif samples analyzed include pyrope pseudomorphs after pyrope phengite zircon the new mineral ellenbergerite and whole rocks isotope data from all three decay systems indicate minimal if any isotopic exchange with mantle rocks isotope ratios from minerals with low parent daughter ratios cluster around 143 nd 144 nd 0 51225 nd 7 6 87 sr 87 sr 0 7 15 75 15 80 with 206 pb 204 pb 19 4 20 7 these compare closely with ratios from precambrian granitic rocks or their derived sediments from the pb isotope data and the sm nd whole rock model ages we estimate a mean age of 2000 500 ma for the sediment protoliths pyrope mineral separates record approximate ages for alpine metamorphism of 34 38 ma by the sm nd method the u pb method applied to zircon and ellenbergerite yields possible additional metamorphic ages of 50 55 ma these data illustrate a possible mechanism for creating isotopically enriched mantle had these rocks yielded their isotopes to the mantle enriched mantle could have resulted the magnitude of the enrichment depending upon the total volume attained by the mixing process similarly the metasediments could also provide the high potassium abundances and appropriate pb sr and nd isotope ratios that are postulated to accompany mantle metasomatic processes

late proterozoic thrust tectonics high pressure metamorphism and uranium mineralization in the domes area lufilian arc northwestern zambia abstract the following main lithostratigraphic units have been distinguished in the domes area the kibaran basement complex composed of gneisses migmatites with amphibolite bands and metagranites is exposed in dome structures metamorphic features of kibaran age have been almost completely obliterated by extensive lufilian reactivation the post kibaran cover sequence is subdivided into the lower roan group consisting of well preserved quartzites with high mg content talc bearing extremely foliated schists intercalated with pseudo conglomerates of tectonic origin and the upper roan group including dolomitic marbles with rare stromatolites metapelites and a sequence of detrital metasediments with local volcano sedimentary components and interlayered banded ironstones the sediments of the lower roan group are interpreted as continental to lagoonal evaporitic deposits partly converted into the talc kyanite garnet assemblage characteristic of white schists the dolomites and metapelites of the upper roan group are attributed to a carbonate platform sequence progressively subsiding under terrigenous deposits whilst the detrital metasediments and bif may be interpreted as a basinal sequence probably deposited on oceanic crust grading laterally into marbles metagabbros and metabasalts are considered as remnants of an ocean floor type crustal unit probably related to small basins alkaline stocks of silurian age intruded the post kibaran cover significant ancestral tectonic discontinuities promoted the development of a nappe pile that underwent high pressure metamorphism during the lufilian orogeny and all lithostratigraphic units rb sr and k ar and u pb data indicate an age of 700 ma for the highest grade metamorphism and 500 ma for blocking of the k ar and rb sr system in micas corresponding to the time when the temperature dropped below 350 400 c and to an age of about 400 ma for the emplacement of hypabyssal syenitic bodies a first phase of crustal shortening by decoupling of basement and cover slices along shallow shear zones has been recognized fluid rich tectonic slabs of cover sediments were thus able to transport fluids into the anhydrous metamorphic basement or mafic units during the subsequent metamorphic re equilibration stage of high pressure pre existing thrusts horizons were converted into recrystallized mylonites due to uplift rocks were re equilibrated into assemblages compatible with lower pressures and slightly lower temperatures this stage occurs under a decompressional nearly adiabatic regime with pfluid plithostatic it is accompanied by metasomatic development of minerals activated by injection of hot fluids new or reactivated shear zones and mylonitic belts were the preferred conduits of fluids the most evident regional scale effect of these processes is the intense metasomatic scapolitization of formerly plagioclase rich lithologies uraninite mineralization can probably be assigned to the beginning of the decompressional stage a third regional deformation phase characterized by open folds and local foliation is not accompanied by significant growth of new minerals however pitchblende mineralization can be ascribed to this phase as late stage short range remobilization of previously existing deposits finally shallow alkaline massifs were emplaced when the level of the domes area now exposed was already subjected to exchange with meteoric circuits activated by residual geothermal gradients generally related to intrusions or rifting most of the superficial u showings with u oxidation products were probably generated during this relatively recent phase

an approach using sar ers images to relate extension fractures to volcanic vents examples from iceland and madagascar abstract a new approach to the study of geometric relationships between tectonic structures and volcanic vents is presented it is based on the mapping of tectonic and volcanic features using high resolution imagery including synthetic aperture radar sar images of the european remote sensing satellite number one ers 1 we have evidenced new faults 1 n striking normal faults in the husavik fault zone of the north atlantic ridge and 2 nw striking faults belonging to the husavik transform fault zone associated to drag folds which testify to a dextral strike slip movement component we show that most of the volcanic edifices are located on extension fractures responsible for fissure eruptions volcanic linear clusters and elongated volcanoes this relationship is studied first in iceland where the geodynamics is well known using sar ers 1 imagery applied to the montagne d ambre in northern madagascar using aerial photographs this approach makes it possible to identify faults and the regional plio quaternary direction of extension i e n65 e to n85 e volcanoes forming linear clusters together with elongated volcanoes are interpreted to be located on extension fractures s or z shape of the linear clusters allowed us to determine the tips of extension fractures and consequently the orientation of the regional tension alignments of extension fractures depending on their s or z shape permitted us to infer conjugated faults

product distributions from chemical degradation of kerogens from a marl from a miocene evaporitic sequence vena del gesso n italy abstract lithium in ethylamine li etnh 2 treatment has been carried out on sulphur rich kerogens from 10 sub samples of the cycle iv marl from the vena del gesso evaporitic sediments upper miocene italy the treatment releases after chromatography of the resulting solvent extracts up to 30 of the kerogen total organic carbon the biomarkers released are dominated by components of algal origin the concentrations of the aliphatic hydrocarbons obtained are of the same order of magnitude as the bound alkanes released upon desulphurization of polar fractions from organic extracts and show similar distributions the presence of diaromatic isoprenoids derived from chlorobiaceae indicates that photic zone anoxia occurred during the deposition of the cycle iv marl such conditions being more prevalent at the middle of the section polar material makes up by far most of the organic material released and contains in particular alcohols and amides which may result from the cleavage of ester bonds present in these immature kerogens the amides being secondary products formed by reaction with the etnh2 in the case of the alcohols however these components could also arise from cleavage of sulphide bound moieties

sm nd and rb sr isotopic chronology and cooling history of ultrahigh pressure metamorphic rocks and their country rocks at shuanghe in the dabie mountains central china abstract ultrahigh pressure metamorphic uhpm rocks at shuanghe area in the dabie mountains occur as a uhpm block within the regional granitic gneiss a sm nd isochron defined by garnet omphacite rutile from coesite bearing eclogite yield an age of 226 3 3 2 ma another sm nd isochron defined by garnet two phengites form uhp gneiss yield a similar age of 226 5 2 3 ma the two consistent sm nd ages defined by three uhpm minerals suggest that nd isotopic equilibrium between uhpm minerals in these rocks during uhp metamorphism has been achieved this may correspond to the age of peak metamorphism with an average metamorphic temperature of 800 c it is demonstrated that the retrograde metamorphism of uhpm rocks occurred in an open chemical system whereas the nd and sr isotopic systematics of uhpm minerals may have remained closed nd and sr isotopic disequilibrium between uhpm minerals and retrograde metamorphic minerals has been observed therefore the tie line of garnet or phengite and whole rock containing retrograde metamorphic minerals gives an old sm nd age and a young rb sr age respectively with no geologic significance however a rb sr ages of 219 0 6 6 ma defined by phengite garnet from a uhpm gneiss indicates that the uhpm rocks at shuanghe cooled down to 500 c at that time it suggests that the uhpm rocks at shuanghe experienced the first rapid cooling during 226 219 ma on the other hand the rb sr ages of 174 7 8 to 169 2 3 3 ma defined by retrograde minerals amphibole or biotite with closure temperature ranging from 450 to 300 c and intensely retrograded metamorphic rocks reflect a second rapid cooling during this time interval this is consistent with the rapid cooling time of 190 170 ma of the orthogneiss in the dabie su lu uhpm belt obtained by ar ar dating method in contrast to uhpm rocks the nd isotopic composition of the garnet in granitic gneiss has been reset during retrograde metamorphism and is in equilibrium with those of retrograde epidote and biotite which yields a sm nd isochron age of 213 5 ma indicating the retrometamorphic time corresponding to amphibolite facies in addition the biotites from the granitic gneiss yield rb sr ages of 171 173 ma similar to those of the uhpm rocks these data suggest that the country rocks granitic gneiss may have a similar cooling history to the uhpm rocks at shuanghe two stages of rapid cooling of uhpm rocks at shuanghe may correspond two stages of fast uplift the initial rapid uplifting and cooling of uhpm rocks during 226 219 ma may be caused by compression tectonics during subducting time of the continental crust whereas the later rapid cooling may reflect the exhumation of the entire subducted continental crust by extension during the early middle jurassic

high pressure granulite facies metamorphism in the pan african dahomeyide orogen west africa high pressure hp granulite facies rocks are associated with eclogites in the pan african dahomeyide orogen west africa the hp granulite and eclogite facies mineral assemblages occur in mafic gneisses within the suture zone exposed in southeastern ghana and the adjoining part of togo thermobarometric calculations and phase equilibria considerations indicate that the hp metamorphic rocks preserve a record of i prograde garnet crystallization during eclogite facies metamorphism as temperature increased to a maximum of 600 c and pressure reached 18 kbar followed by ii hp granulite facies metamorphism when temperatures reached 800 900 c at p 14 kbar resulting in partial melting to produce leucocratic veins decompression along a retrograde path is inferred from granulites that yield temperatures down to 700 c at 10 kbar the inferred p t path of the metamorphic record defines a clockwise loop in the kyanite stability field compatible with orogeny involving subduction during the pan african as

novel functionalised chlorins in sediments of the messinian vena del gesso evaporitic sequence evidence for a facile route to reduction for biomarkers fossil pigment distributions from sediments of the messinian vena del gesso italy include two novel sedimentary chlorins as revealed by high performance liquid chromatography and liquid chromatography multistage mass spectrometry the two novel chlorin components are meso derivatives of chlorophyllone a and represent early stage diagenetic intermediates in the formation of bicycloalkano chlorin and porphyrin structures that occur in these and other carbonaceous sediments their presence indicates the operation of a facile route to reduction during early diagenesis

chronology of nappe assembly in the pan african dahomeyide orogen west africa evidence from 40ar39ar mineral ages abstract the pan african dahomeyide orogen represents the southwestern segments of the eastern tectonic zone along which the west african craton was incorporated into gondwana orogenic contraction produced nappe complexes comprised of passive margin sediments and accreted exotic magmatic rocks in ghana and togo external nappes include the atacora composed of lower amphibolite facies quartzite and mica schist which were structurally imbricated with mylonitic gneiss derived from c 2 0 ga foreland basement the suture zone is represented by high pressure granulite facies garnet homblende gneiss we have analyzed muscovite and homblende concentrates from external and suture zone nappes in incremental heating 40 ar 39 ar experiments muscovites which define the penetrative foliation in the atacora nappes and a shear foliation in the basement parautochthon record 40 ar 39 ar plateau ages of 579 4 0 8 ma and 578 1 0 5 ma respectively in contrast c 600 km to the north muscovite in quartz schist near the base of the atacora nappes displays a spectrum which gives a minimum age of 608 1 1 2 ma whereas muscovite in the overthrust kara nappes yields a plateau age of 633 8 0 5 ma the c 30 m y difference between the atacora nappes in the northern dahomeyides and the younger dates of the southern external nappes indicate out of sequence thrust imbrication however forward imbricating thrusting is also suggested by the older age of kara nappes relative to atacora nappes in the northern segment the youngest ages are inferred to date orogen parallel nappe transport at c 575 ma hornblende from the structurally lower sections of the suture zone nappes record a 36 ar 40 ar versus 39 ar 40 ar isotope correlation age of 587 4 3 ma hornblende from a tonalitic vein in the host garnet mafic gneiss yields an isotope correlation age of 581 9 2 4 ma these ages are interpreted to date the exhumation of the suture zone nappes and thus provide a minimum age of crustal thickening in the dahomeyide orogen the age data are consistent with coeval forward and hindward propagating thrusting and nappe imbrication and constrain the amalgamation in northwest gondwana to have occurred in the latest proterozoic rather than cambrian

strain accommodation at the lateral margin of an active transpressive zone geological and seismological evidence from the lebanese restraining bend geological geomorphological and seismological data are used to postulate the existence of a lateral domain bounding fault the roum fault zone in sw lebanon the fault zone accommodates transpression at the margins of the lebanese restraining bend abruptly dividing the transpressional mount lebanon jebel barouk uplift from the extension of the tyre nabatiye plateau transpressional deformation at the sw margin of the restraining bend is mainly seen through large scale folding trending parallel to the restraining bend such folding is thought to be accommodated laterally along a 100 km length of fault zone in sw lebanon the roum fault zone mapped lineaments and topographic expression show the fault zone to die out to the south of beirut offsets of incised river valleys decrease northwards from 7 2 km to 0 2 km along the length of the fault zone over a distance of 80 km also inferring a postulated fault tip to the south of beirut strain gradients along both sides of the fault zone wall rocks shows several deformation mechanisms to be involved pressure solution folding distributed shear and normal faulting the postulated fault tip coincides with the extent of transpression of the mount lebanon block a new seismicity catalogue 2100 bc ad 1995 32 35 n 34 37 e 1725 events all magnitudes converted to isn reported m l was compiled from published sources seismicity is apparently sparse around the northern yammouneh fault but concentrates in sw lebanon especially in a diffuse 50 100 km wide zone around the southern roum fault zone epicentral uncertainties are typically 10 25 km for modern reporting although depths are poorly known the seismic b value is 0 75 0 07 for the beirut area compared to 0 88 0 09 for the dead sea transform to the south mapping of b values for the sw lebanon area suggests a gradual reduction northward along the roum fault zone these observations are interpreted as the signature of a fault zone whose tip lies to the south of beirut the transition from transpression to extended crust at the western edge of the lebanese restraining bend is accommodated along a 100 km length of fault zone decreasing seismic activity over the time of the catalogue and seismic b values imply a differing style or mechanism of faulting in the short term along the roum fault zone toward beirut

reconstructing the palaeoecosystem and palaeodepositional environment within the upper devonian lower mississippian bakken formation a biomarker approach abstract biomarkers have been used extensively to correlate oil families oil source rock relationships and source inputs and to help identify the palaeodepositional environment for a given geological sedimentary unit despite their application in characterising the bakken formation shales a number of biomarkers still appear unable to provide us a consistent understanding regarding heterogeneity in source organic matter and palaeoenvironment here we infer the palaeodepositional environment within the bakken formation shales using a biomarker suite and biomarker depth profiles we also use the occurrence and abundance of biomarkers to define organic facies and to make inferences regarding biotic interactions drawn from modern analogues the variations and co occurrence of biomarkers is explained by the existence of a proposed complex algal bacterium bacteriovore palaeoecosystem this approach not only helps explain the depth variation in occurrence and concentration of biomarkers and the molecular composition of associated organic matter but also advances the use of biomarker analysis and biomarker associations to determine a complex environment sensitive palaeoecosystem

identification of carotenals in sediments abstract high performance liquid chromatography with photodiode array uv vis detection and atmospheric pressure chemical ionization mass spectrometry was used to analyze sediment samples from the meromictic ace lake antarctica as well as a pliocene sapropel from the mediterranean sea and a miocene marl from the vena del gesso formation italy the ace lake samples contained intact chlorobactene isorenieratene and carotene and two series of carotenoid breakdown products the first and more abundant series was identified as aryl carotenals of increasing chain length c13 c15 c18 c20 c22 c25 c27 c30 and c32 on the basis of their uv vis and mass spectra they appear to be formed from chlorobactene through oxidative cleavage of the double bonds of the polyene chain the minor series carotenals was also identified and may be formed from carotene in a similar manner intact isorenieratene and the carotenal series were also found in the mediterranean sea sapropel only a trace of the c32 carotenal could be detected suggesting isorenieratene as the predominant source of these carotenals additionally intact carotene and c13 c30 carotenals were found in the sapropel the absence of the c32 carotenal strongly suggests these breakdown products are derived from carotene the vena del gesso marl contained both intact isorenieratene and the c13 c25 carotenals the absence of the longer chain length carotenals from this sample may indicate more advanced oxidation of isorenieratene the carotenals are likely formed during storage of samples and or extracts under non ideal conditions i e not frozen and exposed to oxygen although they may also be formed by diagenetic processes they can be relatively abundant and sometimes be an order of magnitude higher in concentration than the parent carotenoid hence not including the carotenals could lead to an underestimation of the persistence of photic zone euxinia

evidence for excess argon during high pressure metamorphism in the dora maira massif western alps italy using an ultra violet laser ablation microprobe 40 ar 39 ar technique ultra high pressure eclogite amphibolite grade metamorphism of the dora maira massif in the western alps is a well established and intensively studied event however the age of peak metamorphism and early cooling remains controversial the 40ar 39 ar step heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 ma which have been interpreted as the time of early cooling after the high pressure event recent u pb and sm nd results challenge this assertion indicating a much younger age for the event around 45 ma and hence a radically different timing for the tectonic evolution of the western alps in a new approach to the problem samples from the undeformed hercynian metagranite brossasco were studied using an ultra violet laser ablation microprobe technique for 40ar 39 ar dating the new technique allowed selective in situ analysis at a spatial resolution of 50 urn of quartz phengite biotite and k feldspar the results demonstrate the frequent occurrence of excess argon with high 40ar 39 ar ratios 1000 10000 and a strong relationship between apparent ages and metamorphic textures the highest excess argon ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases the best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high pressure event then mixed with an atmospheric component during rapid cooling and retrogression producing a wide range of argon concentrations and 40ar 36ar ratios step heating analysis of minerals with this mixture would produce linear arrays on a40ar 36ar versus 40ar 36 ar correlation diagram leading to geologically meaningless plateau ages older than the true closure age in the present case some ages in the range 60 110 ma could be explained by the presence of excess argon incorporated around 40 50 ma ago similar results found in other high pressure terrains in the alps may reconcile the argon geochronometer with other systems such as rb sr u pb or sm nd this study therefore calls for an increasing use of high resolution in situ sampling techniques to clarify the meaning of 40ar 36 ar ages in many high pressure terrains

isotopic dating in metamorphic belts isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions of these temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed the central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated in order to illustrate the factors which control closure temperatures and limit their application in practice the possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined taking examples involving k ar rb sr sm nd and u pb analyses the indirect dating of metamorphism via structurally dated plutons is briefly considered and the problems of interpreting both discordant u pb zircon ages and rb sr whole rock isochrons in metamorphosed granites are discussed the value of near concordant zircon ages is emphasized the extent of isotopic equilibration during metamorphism specifically of sr isotopes in metasediments is shown not to be a simple function of metamorphic grade the flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently the concluding discussion briefly examines existing data for the dalradian and indicates the potential for further progress using both well established and novel approaches

excess argon in phengite from eclogite evidence from dating of eclogite minerals by smnd rbsr and 40ar39ar methods the existence of excess ar in phengites from coesite bearing ultrahigh pressure eclogites of the dabie mountains and su lu terrain china has been confirmed by dating of minerals using sm nd rb sr and 40ar39ar methods 40ar39ar ages of phengites for two samples studied are much older than the sm nd and rb sr mineral isochron ages sample ql 1 has rb sr age of 219 5 0 5 ma sm nd age of 226 3 4 5 ma and phengite 40ar39ar age of 877 5 15 9 ma the corresponding ages for sample zb 4 are 223 9 0 9 ma rb sr 228 4 6 0 ma sm nd and 943 3 12 4 ma 40ar39ar phengite an age of 225 ma based on the sm nd and rb sr mineral isochron ages is consistent with the time inferred from paleomagnetic and geological data for collision of the north china and yangtse blocks and formation of these eclogites we call for greater caution in 40ar39ar dating of phengites from other occurrences of ultrahigh pressure environments

the primary lower gypsum in the mediterranean a new facies interpretation for the first stage of the messinian salinity crisis abstract the detailed facies and physical stratigraphic analysis of the primary lower gypsum in the mediterranean indicates a surprising bed by bed correlation at basin scale spain italy hellenic arc and cyprus arc that is tuned to the orbital calibration for the first stage of the messinian salinity crisis from 5 96 to 5 61 ma ago a total of 16 precessionally controlled gypsum cycles were deposited rapidly in less than 350 ka forming sequences up to 300 m thick the lack of subaerial exposure features and the common facies associations and stacking pattern for sections located thousands of kilometers apart in different geological settings indicates a modest depositional depth not extremely shallow selenite deposition occurred only at the bottom of restricted marginal basins less than 200 m deep while no gypsum could precipitate in the deeper euxinic mediterranean portions where only thin and barren shale dolostone couplets formed the lowermost selenite beds pass laterally to dolomite rich limestones interbedded with barren euxinic shales in poorly oxygenated settings indicating that the gypsum sedimentation was diachronous and did not necessarily mark the onset on the messinian salinity crisis evaporite facies sequences ef1 to 8 within individual gypsum beds show small scale subaqueous sedimentary cycles that mimic regressive transgressive cycles a initial evaporite precipitation at relatively low supersaturation produced the massive selenite facies ef3 in a relatively deep setting b continuous evaporation and drawdown by oscillating brine level formed the banded selenite ef4 at the aridity acme of the precessionally controlled cycle c general progressive brine level rise with strong brine flow led to the formation of large selenite supercones branching laterally supercones in spain and branching selenite ef5 in the rest of the mediterranean and d flooding by undersaturated continental water terminated gypsum precipitation with the deposition of argillaceous sediments ef1 northern apennines and or limestone ef2 sicily and spain during the humid phase in the precession climate cycle the stacking pattern and selenite facies associations suggest an overall shallowing upward trend with a basin wide hydrologic change starting from the 6th cycle 5 84 ma which is marked by the appearance of the branching selenite facies supercones in spain and indicates that the brines became current dominated the sr isotope stratigraphy suggests that in the northern apennines the brines were strongly modified by continental waters 87 sr 86 sr 0 708893 to 0 708998 and received direct pulses of atlantic seawater 87 sr 86 sr 0 70900 to 0 709024 only in the upper part of the section in areas away from the mainland such as sicily the continental input was by far less important

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

kinematics and geochronology of the proterozoic dongxiang shexian ductile shear zone with hp metamorphism and ophiolitic melange jiangnan region south china abstract a kinematic and geochronological analysis of the 10 20 km wide northeast trending dongxiang shexian ductile shear zone that trends along a length of 250 km in the eastern part of the jiangnan belt indicates a sinistral strike slip ductile shear that was formed during the neo proterozoic the zone experienced polyphase deformation related to tectonic collision between the huaiyu and the jiuling terranes geochronological data and kinematic analysis of macroscopic structures microscopic shear indicators and quartz c axes fabrics shows that a ductile southeastward thrusting occurred at about 950 900 ma followed by a sinistral strike slip shearing along a northeast trend at about 770 ma coarse clastic sedimentary rocks of sinian age were deposited unconformably on the entire jiangnan belt including the huaiyu and the jiuling terranes this paper emphasizes that the jiangnan belt in the se margin of yangzi plate is a neo proterozoic orogenic belt with hp metamorphism and ophiolitic melange not a late paleozoic mesozoic collisional orogen

field occurrences and petrology of eclogites from the dabie mountains anhui central china four distinct types of eclogites are recognized according to their field occurrences and mineral parageneses in a gneiss terrane of the dabie mountains a collision zone between the sino korean and yangtze cratons in central china some eclogites contain coesite and its quartz pseudomorphs enclosed in garnet and omphacite type i eclogites occur as layers in serpentinites and contain garnet clinopyroxene orthopyroxene phengite rutile and coesite pseudomorph type ii eclogites occur as lenticular bodies inside serpentinites and contain garnet clinopyroxene quartz rutile and edenitic hornblende type iii eclogites occur as blocks of 2 cm to 20 m in size in a matrix of hornblende gneiss and biotite gneiss and type iv eclogites occur as thin layers interbedded with amphibolites p t estimates for these different eclogites indicate that they were formed under different physical conditions all the eclogites were affected by later regional metamorphism for which the p t conditions are estimated this paper provides an introduction to the abundant eclogites from central china which have not been reported previously in western literature specifically the mode of field occurrence petrography mineral chemistry and formation conditions of the four types of eclogites are described the paper is thus designed to establish a petrological framework for future detailed studies of the eclogites and their country rocks in an ancient zone of collision

variations in origin and composition of kerogen constituents as revealed by analytical pyrolysis of immature kerogens before and after desulphurization abstract kerogens isolated from nine samples from a single marl bed of the gessoso solfifera formation in the vena del gesso basin upper miocene italy were treated with crcl 2 and li etnh 2 to remove inorganic and organic sulphur respectively the untreated and desulphurized crcl 2 and li etnh 2 kerogens were qualitatively and quantitatively analyzed by flash pyrolysis gas chromatography mass spectrometry typically significant variations in the relative contributions and abundances of n alk 1 enes n alkanes alkylated pyrroles thiophenes and supposedly s bound moieties released as phytenes and sterenes were observed the first series of products n hydrocarbons contributed relatively more to the pyrolyzates of the desulphurized kerogens suggesting an enrichment of microalgal derived aliphatic macromolecules these marine micro organisms are thought to belong in part to the class of eustigmatophyceae alkylated pyrroles were barely detectable in the untreated kerogen pyrolyzates whereas they contributed significantly to those from the treated kerogens similar treatment of a porphyrin octaethylporphyrin revealed that alkyl porphyrins are thermally too stable to be cleaved upon pyrolysis however li etnh 2 treatment reduced the porphyrin standard such that it could generate mainly monopyrroles upon pyrolysis it is concluded that li etnh 2 treatment reduced tetrapyrrole moieties bound to the desulphurized kerogen network

thermal stability of thiophene biomarkers as studied by hydrous pyrolysis abstract an immature r o 0 25 sulphur rich calcareous shale from the gessoso solfifera formation messinian in the vena del gesso basin northern italy was artificially matured by hydrous pyrolysis at constant temperatures ranging from 160 to 330 c for 72 h to study the applicability of alkylthiophenes as molecular indicators during progressive diagenesis and early catagenesis artificial maturation at temperatures up to 330 c generated large amounts of alkylthiophenes from the thermal degradation of kerogen the importance of the kerogen in the production of alkylthiophenes is supported by the observation that the isomer distributions of alkylthiophenes at high temperatures coincide with the isomer distributions of alkylthiophenes in the curie point pyrolysate of the isolated kerogen of the original sample the generation profiles of the thiophenes with a phytane carbon skeleton and the 3 4 di n alkylthiophenes suggest that continuous degradation of alkylthiophenes is also taking place so that the overall effect is alkylthiophene concentrations with intermediate values the structural isomer distribution of linear alkylthiophenes does not change significantly when these compounds are generated at different temperatures this implies that important information regarding the original positions of functionalities in the precursor molecules is retained and thus that alkylthiophenes are useful biomarkers at relatively high levels of thermal maturity up to r o 0 95 1 1

how dry was the mediterranean during the messinian salinity crisis the messinian salinity crisis msc 5 97 5 33 ma is an enigmatic episode of paleoceanographic change when kilometers thick evaporite units were deposited in the mediterranean basin it is generally accepted that during the msc interval there was a dry climate in the mediterranean region it is difficult to assess how dry the climate was during the msc because a modern analogue in size and duration is absent here we reconstruct hydrological changes in the mediterranean basin during the three main msc stages using excellently preserved biomarkers we used the hydrogen isotopic composition of the long chain n alkanes dn alkanes to reconstruct the hydrological changes on the land adjacent to the mediterranean sea additionally the d of long chain alkenones dalkenones is used to observe changes in the mediterranean sea water source the dn alkanes recorded during the deposition of primary lower gypsum stage 1 in monte tondo indicate a d of the precipitation comparable to the present day mediterranean implying a similar hydrologic regime indicated by experiments modelling the miocene pliocene transition elevated dalkenones values from halite unit stage 2 of the realmonte mine are associated with kainite and giant polygons consistent with presumably high evaporative conditions during halite deposition the dn alkanes recorded during the deposition of upper gypsum stage 3 in eraclea minoa indicate a dprecipitation typical for much drier settings similar to the red sea region the relative contribution of the different alkenones from eraclea minoa is similar to the one observed in present day marine settings suggesting that during stage 3 connections to the open ocean were likely maintained however the dalkenones records during deposition of the evaporites in eraclea minoa are similar to those synchronously registered in the black sea implying that a similar hydrologic regime characterized by extended drought covered large areas of southeastern europe based on the dalkenones similarity and the paratethys type of lago mare fauna in the mediterranean we speculate that the surface water during stage 3 was at times derived from the black sea

some outstanding issues in the geology of lebanon and their importance in the tectonic evolution of the levantine region abstract the concept of pervasive and disruptive late neogene quaternary strike slip tectonics in lebanon has made establishing a satisfactory pre neogene palaeogeographic and palaeotectonic history for the area difficult research has allowed clarification of three fundamental issues that permit the setting of lebanon against its adjacent regions to be more firmly assigned the first issue is the identification of the significance of the 100 km long nne ssw trending monocline of the western lebanon flexure this feature is interpreted as a modified and rejuvenated early mesozoic hinge line that is presumed to be the northern continuation of the carmel sinai hinge line to the south the second issue is the correlation of the mount lebanon bekaa and anti lebanon complex with the adjacent intracontinental palmyride fold belt of syria through recognition in each of common divisions in structural style between a higher northern zone dominated by broadly spaced box folds and a lower southern zone with more numerous closely spaced and more internally complex folds the third issue involves the identification of major two stage late cretaceous to palaeogene syrian arc tectonism within lebanon resolution of these issues suggests a tectonic model for the region whereby the levantine region formed in two main phases the first of these was the multiphase late palaeozoic early mesozoic rifting of the area which imposed a fundamental extensional fabric over much of the region the second tectonic phase was the subsequent inversion of these extensional structures in the two stage syrian arc deformation of senonian and late palaeogene age which gave rise to the main lebanon structures it is this syrian arc tectonism rather than the late cenozoic strike slip that was probably the main structuring agent which affected the lebanon area the transpression from the braided dead sea fault motion although locally complex is an essentially neotectonic overprint on an already existing fabric offset of syrian arc structures in lebanon suggests that the total sinistral motion of the yammouneh fault segment of the dead sea fault is around 47 km

recognition of paleobiochemicals by a combined molecular sulfur and isotope geochemical approach study of organic matter in immature sediments from a messinian evaporitic basin shows that consideration of structures modes of occurrence and carbon isotopic compositions of free and sulfur bound carbon skeletons allow identification of biochemical precursors detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way moreover unprecedented biochemicals were recognized these extend the horizon of biomarker geochemistry

origin of eclogites from the austroalpine otztal basement tirol austria geochemistry and smnd vs rbsr isotope systematics geochemical and combined sm nd vs rb sr isotope data from the otztal metabasite suite point to production of gabbros and basalts in an extensional regime in late cambrian times the source of these magmas and cumulates had a chemical and isotopic composition similar to morb the time of intrusion is constrained by sm nd mineral isochrons clinopyroxeneplagioclase of relictic gabbro occurrences within the eclogite amphibolite series in the time span between 530 and 521 ma subsequently the basic eclogite precursors suffered three metamorphic stages the imprint of the caledonian event is unclear during the hercynian cycle the basic magmatic rocks were transformed into eclogites at surprisingly high p t conditions of 27 kbar 730 c the time of this subduction event is given by mineral isochrons garnet clinopyroxene zoisite whole rock as 370 340 ma with a most probable time span for the pressure peak between 360 and 350 ma during subsequent exhumation and pressure release the eclogites were partly transformed into amphibolites alpine overprint during a greenschist facies grade metamorphism caused further and partly intense retrograde alterations in the metabasic suite

distributions of pigments in the organic matter of marls from the vena del gesso evaporitic sequence abstract the porphyrins and carotenoids of marl horizons within the messinian evaporitic cycles of the vena del gesso basin show variations in abundance and composition throughout a sequence of ten cycles significant variations are also apparent within individual marl horizons the differences in pigment distribution reflect significant changes in the environmental conditions during sediment deposition the presence of significant amounts of isorenieratene and co occurrence of an alkyl porphyrin with a c 34 skeleton provide evidence for anoxic conditions extending into the photic zone of the palaeo water column variations in the free pigment contents of the marls reflect a regressive trend both during deposition of an individual marl and over the entire sequence

stepwise chemical degradation of immature s rich kerogens from vena del gesso italy stepwise chemical degradation involving cleavage of ester bonds koh meoh sulfide and remaining ester bonds li etnh2 ether bonds hi lialh4 and sub units linked to aromatic moieties ruo4 has been carried out on the kerogens of two immature sulfur rich marls iv 1 4 and 1 8 toc ca 1 5 from evaporitic cycle iv of the gesosso solfifera formation messinian vena del gesso italy up to 80 of the organic matter was converted to solvent soluble material with the greatest proportion released by li etnh2 the majority by far of the extracts comprises polar macromolecular material which is thought to correspond to high molecular weight sub units of the kerogen quantification of the small amounts 1 of the released gc amenable components indicates that diagenetic sulfurization was more important in the case of kerogen iv 1 4 but that the extent of oxygen sequestration was similar in both cases the distributions of biomarkers released by ether cleavage of the desulfurized residue and polar fraction showed differences which reveal heterogeneity in the building blocks making up different macromolecular fractions

excess 40ar transport scale and mechanism in high pressure phengites a case study from an eclogitized metabasite of the dora maira nappe western alps application of the bulk separate furnace heating laser step heating and in situ laser agemapping 40ar 39ar techniques reveals that high pressure phengites from an alpine eclogite of the dora maira basement nappe western alps were pervasively contaminated with excess 40ar to yield ages 130 ma spot fusion dating of individual grains with the 40ar 39ar laserprobe reveals concentric radial patterns with core ages as high as 320 ma showing that this excess component was trapped at an early stage and subsequently remobilized by volume diffusion during a late greenschist thermal pulse the single grains and population from this hand sample retain major differences in apparent ages indicating that the extent of the excess 40ar contamination varies from grain to grain attempt to model these differences in terms of grain size dependent fractional loss falls short and demonstrates that strong cm scale argon isotopic gradients locally prevailed during syn kinematic high pressure metamorphism on petrostructural grounds a model of internal isotopic buffering is outlined whereby the excess 40ar is argued to have been internally derived from within the eclogite protolith itself low intergranular ar diffusion rates due to reduced water activity buffered below unity by the phengite assemblage resulted in the local segregation and partitioning of the excess 40ar along grain boundaries during ongoing ductile deformation supporting evidence for this model comes from the recent literature on fluid and stable isotope behaviour in alpine eclogites and very high pressure metasediments which shows that volatile recycling during high pressure metamorphism may occur on a very limited scale

thermobarometry of phengite bearing eclogites in the dabie mountains of central china pressure temperature conditions for formation of the peak metamorphic mineral assemblages in phengite bearing eclogites from dabieshan have been assessed through a consideration of fe2 mg2 partitioning between garnet omphacite and garnet phengite pairs and of the reaction equilibrium celadonite pyrope grossular muscovite diopside which incorporates an evaluation of the extent of the strongly pressure dependent inverse tschermak s molecule substitution in the phengites for the latter equilibrium the calibration and recommended activity composition models indicated by waters martin 1993 have been employed and importantly yield results consistent with petrographic evidence for the stability at peak conditions of coesite in certain samples and quartz in others confirmation that in some phengite eclogite samples peak silicate mineral assemblages have equilibrated at confining pressures sufficient for the stability of coesite and in some cases even diamond rather negates previous suggestions that coesite may have been stabilized in only very localized possibly just intracrystalline domains inherent difficulties in the evaluation of peak metamorphic temperatures from fe2 mg2 partitioning between mineral phases due to uncertainties over fe3 fe2 ratios in the minerals especially omphacites and to re equilibration during extensive retrograde overprinting in some samples are also assessed and discussed our results indicate the existence in south central dabieshan of phengite eclogites with markedly different equilibration conditions within two structurally distinct tectonometamorphic terranes thus our data do not support earlier contentions that south central dabieshan comprises a structurally coherent continental crust terrane with a regional p t gradient signalling previous deepest level subduction in the north instead we recognize the central dabie ultra high pressure coesite eclogite bearing terrane to be structurally overlain by a southern dabie high pressure quartz eclogite bearing terrane at a major southerly dipping shear zone along which late orogenic extensional collapse appears to have eliminated at least 20 km of crustal section

geochemical characterization of malm zeta laminated carbonates from the franconian alb sw germany ii abstract during jurassic times especially within the malm stage local depressions formed on the eastern bavarian carbonate platform that were surrounded by wall reefs this created a unique depositional environment where in an open marine setting stagnant and anoxic bottom waters developed in an intra reef depression anoxic conditions were stabilized below wave base by enhanced salinity in the bottom waters and establishment of a density stratification biomarker analysis was applied to characterize palaeosalinity and redox conditions utilizing organic sulfur compound methylated chroman hopanoid and saturated isoprenoid distributions prevention of terrigenous influx by protecting reef walls lead to iron deficiency in intra reefal sediments causing early diagenetic sulfurization of functionalized lipids absence of clay mineral catalysts and early sulfurization favored an unusual steroid distribution lacking rearranged analogues but providing coexistence of saturated steranes with and configuration 13 17 spirosterenes unknown sterenes and steradienes as well as mono di and triaromatic steroids desulfurization of the polar fraction was carried out for two samples to verify that palaeoenvironment reconstruction based on free hydrocarbon and heterocompound distribution was not invalidated by sulfur quenching of selected compounds gammacerane was found to be the only component to occur exclusively in the sulfur bound fraction only minor amounts of hydrocarbons were released upon desulfurization implying that free bitumen analysis was applicable for organofacies characterization organic petrological investigation of organic mats revealed the presence of two different types of such structures comparison of organoclast fluorescence spectra with those of extracted porphyrin fractions indicate an origin of porphyrins exclusively from cyanobacterial mats whereas algal dominated mats yield no porphyrins this aims towards a better localization of specific biomarker origin in geological samples

molecular isotopic evidence of environmental and ecological changes across the cenomanian turonian boundary in the levant platform of central jordan abstract we evaluated the structure of planktonic communities and paleoenvironmental conditions throughout the cenomanian turonian oceanic anoxic event oae2 by studying bulk geochemical properties and the molecular isotopic composition of source specific hydrocarbons from organic rich sediments deposited in an intrashelf basin at the levant platform central jordan high concentrations of desmethyl and 4 methylsteranes as well as dinosteranes indicate that marine algae including dinoflagellates were the main primary producing organisms the presence of 2 methylhopanes and 13 c enriched hopanes in addition to isotopically enriched aryl isoprenoids evidenced the contribution of cyanobacteria and green sulfur bacteria respectively additionally variable but fairly low 15 n values during oae2 suggest the occurrence of diazotrophy as a likely important process fueling primary production during oae2 in this stratified anoxic continental platform variations in the relative contribution of biomarkers revealed changes in planktonic communities associated with sea level change and water column stratification oae2 was characterized by strong stratification anoxic bottom waters and a deep chemocline as evidenced by high gammacerane and homohopane indices and the absence of photic zone euxinia pze markers respectively however the presence of isorenieratane and its derivatives in post oae black shales points to a shoaling of the chemocline and to pze this interval was also characterized by an exceptionally high abundance of chlorophyll derived pristane and phytane up to 2 mg g 1 toc likely as a result of highly enhanced primary production and organic matter preservation remarkably this high productivity event co occurs with an exceptionally high abundance of calcispheres reported elsewhere to be part of a global bio event

the eclogites of the lato hills south togo west africa relics from the early tectonometamorphic evolution of the pan african orogeny abstract the eclogites of the lato hills outcrop within the pan african orogenic belt of south togoland dahomeyides are located within the western border of the benin plain structural unit ex dahomeyen they are closely associated with epi to mesozonal metasediments which are similar to the pan african cover formations of the atacora unit two groups of eclogites have been distinguished according to field relations and to the nature of the country rocks but they display a similar metamorphic history the mineralogical and textural transformations of eclogites indicate 1 a progressive increase of the p t regime 2 a mylonitization event close to the culmination of eclogitic metamorphism and 3 a retrograde evolution towards amphibolite facies conditions likewise quartzites closely associated with eclogites exhibit high p parageneses compatible with that of the eclogite formation these observations allow us to consider the eclogitisation processes as a crustal transformation of mafic igneous rocks and to assign a pan african age to these recrystallizations therefore the mount lato eclogites represent rare witnesses from the early tectonometamorphic evolution of the dahomeyides range

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

molecular fossils and other organic markers as palaeoenvironmental indicators of the messinian calcare di base formation normal versus stressed marine deposition rossano basin northern calabria italy a multidisciplinary study has been carried out on the late miocene messinian calcare di base formation in northern calabria italy with the aim of understanding the depositional conditions of these enigmatic carbonate sediments that have been interpreted as evaporitic or diagenetic limestone the research has been developed through sedimentological microfacies organic petrography and geochemical analyses palynofacies rock eval pyrolysis and gas chromatography mass spectrometry the carbonates studied preserve their original mineralogy aragonite and microstructure the prevailing microfacies consists of clotted peloidal micrite with antigravitative fabric larger and darker cylindrical subcylindrical micritic grains attributable to faecal pellets are more or less randomly dispersed in the peloidal micrite the faecal pellets have been ascribed to copepods because zooclasts of these arthropods were observed in the palynofacies bright epifluorescence characterizes the faecal pellets and peloidal micrite indicating their high content of organic matter detrital and stromatolitic microfacies occur rarely around a few percent the detrital microfacies is characterized by silt sized grains organized in thin sometimes bioturbated graded laminae the stromatolitic microfacies shows planar to gently curved wrinkled laminae organized in dark and light couplets the associated sedimentary organic matter shows low maturity and preserves the original signatures of the source organisms rock eval pyrolysis revealed a transitional composition between type ii and type iii kerogen suggesting a mixture of marine and terrigenous organic matter input the molecular biogeochemical data indicate three main biological signatures algae bacteria and higher plants organic markers together with sedimentary evidence indicate a marine depositional scenario influenced by freshwater input rather than evaporitic concentration we conclude that the most probable bacterial process involved in carbonate precipitation of the calcare di base considering the freshwater input and consequent probable enrichment in organic matter and ca2 ions is ammonification of amino acids in aerobic conditions

flocculent layers and bacterial mats in the mudstone interbeds of the primary lower gypsum unit tertiary piedmont basin nw italy archives of palaeoenvironmental changes during the messinian salinity crisis abstract the recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the messinian late miocene primary lower gypsum unit 5 97 5 60 ma of the piedmont basin nw italy provides information on the palaeoenvironmental evolution at precessional insolation maxima these cyclic layers consist of irregular alternation of cm thick grey terrigenous laminae and whitish composite packets the latter is in turn composed of sub mm thick wrinkled dolomite rich laminae that alternate with terrigenous ones two types of layers can be distinguished i peloidal layers composed of faecal pellets and irregular diatom rich aggregates interpreted as marine snow floccules and ii filament bearing layers composed of interwoven filaments up to 150 m across corresponding to remains of beggiatoa like giant sulphide oxidising bacteria by comparison with present day settings the peloidal layers are interpreted as flocculent layers deposited on anoxic sea bottoms following episodes of phytoplankton bloom in the upper water column the filament bearing layers are considered as chemotrophic microbial mats growing on dysaerobic sea bottoms the uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface induced by bacterial sulphate reduction the laminated layers are the first reported example of a high frequency climate driven cyclicity in the non evaporitic portion of the primary lower gypsum unit their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle culminating with gypsum deposition at the onset of the arid phase

pb sr nd isotopic behavior of deeply subducted crustal rocks from the dora maira massif western alps italy ii what is the age of the ultrahigh pressure metamorphism pb nd and sr isotope data are reported from two localities on mineral separates from mg rich metapelites and associated rocks that have been subducted to depths of at least 100 km for which metamorphic conditions are estimated at 28 33 kilobars pressure and 700 800 c and then returned to the surface initial isotope ratio data from the granitoid country rock are similar to those found in the metapelites the initial ratios indicate predominantly recycled aged granitic crustal materials for the sources of all of the samples five zircon samples 4 from pyrope megacrysts and 1 from fine grained pyrope quartzite lenses in the metapelites accurately define a chord yielding intercept ages of 304 10 and 38 0 1 4 ma in a concordia diagram zircon from the country rock also plots along the chord the zircon data together with initial nd and sr data indicate that the sedimentary sources of the rocks were derived mainly or entirely from sialic hercynian rocks ellenbergerite from pyrope megacrysts and monazite from the fine grained ground mass yield slightly younger ages of 30 34 ma apparently reflecting lower blocking temperatures than that of zircon sm nd data from a pyrope megacryst give an errorchron corresponding to an age of 38 ma in agreement with the zircon date a major question concerns the timing of the ultrahigh pressure metamorphism experimental data suggest that pyrope and quartz coesite as well as ellenbergerite formed by various metamorphic reactions if as generally assumed the ultrahigh pressure metamorphism occurred ca 100 ma ago our data require that the zircon did not experience measurable lead loss at that time but lost major amounts of lead 38 ma ago during late alpine metamorphism estimates of diffusion rates for nd in pyrope further suggest that the apparent sm nd age of 38 ma for the megacryst is not consistent with that model those problems are resolved if the ultrahigh pressure metamorphism occurred 38 40 ma ago but problems remain from ar ar dates of 100 ma on phengite an inferred 120 ma age for zircon lead loss from another study and possibly by the very rapid uplift required if the metamorphism is that young

staircase 40 ar39ar spectra of fine grained white mica timing and duration of deformation and empirical constraints on argon diffusion staircase 40 ar 39 ar spectra of 2 to 6 m white micas in ductile carbonate mylonites morcles doldenhorn nappe switzerland record ages between 32 and 13 ma these ages are within independent geochronologic and biostratigraphic time limits for the beginning and ending of deformation of this fold thrust nappe we interpret these data to record protracted white mica neocrystallization and growth during low temperature ductile deformation such that the differences between the maximum and minimum ages in the 40 ar 39 ar spectra record the time span over which mica formed and grew we have modeled the argon concentrations in these micas taking into account the thermal history of the nappe mica growth and diffusional loss of argon our results indicate that available experimental data underestimate the activation energy for argon diffusion in muscovite and that the retentivity of argon in white mica is greater than generally thought

molecular indicators for palaeoenvironmental change in a messinian evaporitic sequence vena del gesso italy iii stratigraphic changes in the molecular structure of kerogen in a single marl bed as revealed by flash pyrolysis abstract kerogens of nine samples from a single marl bed of the gessoso solfifera formation in the vena del gesso basin messinian italy were qualitatively and quantitatively studied by analytical pyrolysis relationships between the nature of the pyrolysis products and the source organisms were determined the high abundance of i algal derived components n alkanes and n alk 1 enes and ii sulphur containing and sulphur bound products signifying a high degree of early diagenetic sulphurization were observed presence of photic zone anoxia during the deposition of these sediments was discussed via the presence of 1 2 3 4 tetramethylbenzene in the pyrolysates unusual distributions were found for three series of pyrolysis products i e c13 and c14n alkylated thiophenes and thiolanes and c12 and c13n 1 3 alkadienes were by far the major products of these series in the pyrolysates of two samples corresponding to the middle of the cycle samples 3 and 5 which also have the highest 13ctoc values and the highest pyrolysis yields therefore the contribution of organisms biosynthesizing resistant algal biopolymer was considered as much more important during the deposition of the sediments associated with samples 3 and 5 we finally proposed partial structural elements from which the specific low molecular weight compounds of samples 3 and 5 can be derived upon pyrolysis

identification of a sulfide derivative with a bicyclic hydrocarbon skeleton related to squalene part ii synthesis of a s spiro like dithiolane triterpenoid abstract a sulfide with a bicyclic squalene hydrocarbon skeleton present in sediments from various depositional settings and of different geological age has been identified by synthesis of a reference compound in contrast to previous expectations cf schouten s sinninghe damste j s de leeuw j w 1995 a novel triterpenoid carbon skeleton in immature sulphur rich sediments geochimica et cosmochimica acta 59 953 958 gug s schaeffer p adam p klein s motsch e albrecht p 2009 identification of a sulfide derivative with a bicyclic hydrocarbon skeleton related to squalene part i synthesis of a dithiane triterpenoid organic geochemistry 40 876 884 this sulfide bears two s spiro type thiolane moities but not the two thiochromane moieties originally envisaged the synthesis resulted in the formation of a complex isomeric mixture of compounds all co eluting in gas chromatography gc in the form of one broad peak as is the case with the geochemical compound the spiro type sulfide was formed by intramolecular sulfurization of a polyunsaturated bicyclic squalene derivative of unknown biological origin the presence of this sulfide in a number of triassic to miocene marine sediments from various and contrasting depositional settings upwelling environments shallow continental platforms lagoonal sub basins hypersaline environments all characterized by strongly anoxic conditions but with or without photic zone anoxia indicates that the microorganisms biosynthesizing the precursor bicyclic squalene occupy diverse ecological niches

the response of water column and sedimentary environments to the advent of the messinian salinity crisis insights from an onshore deep water section govone nw italy

ultrahigh ϵnd eclogites from an ultrahigh pressure metamorphic terrane of china the su lu ultrahigh pressure uhp metamorphic terrane is part of the qinling dabie suture zone formed by the collision between the sino korean and yangtze cratonic blocks geochemical and isotopic investigation of the uhp metamorphic rocks has revealed a spectacular history for some eclogitic rocks retrograded coesite bearing eclogites from the weihai area in the eastern end of the su lu terrane have recorded an extraordinary nd isotopic growth with a world record high nd value of 264 range 170 to 264 such isotopic characteristics are consistent with the observed extreme lree fractionation and very high sm nd ratios the sm nd isotopic data allow us to calculate the minimum age of protolith formation at 1 7 ga assuming their evolution from a depleted or a chondritic mantle geochemical data indicate that the eclogite protoliths were of basaltic compositions originally but underwent metasomatism water rock interaction at high pressures and temperatures leading to the present apparent andesitic composition and extreme lree depletion this process took place in the proterozoic 1 7 ga and was not related to the mesozoic continental collision and ultrahigh pressure metamorphism at 210 220 ma ago because of a protracted retrograde metamorphism garnet sm nd systems were not closed until 160 ma ago 50 ma after the peak eclogite metamorphism this implies that the exhumation history is significantly different in different parts of the dabie and su lu uhp metamorphic terranes from geochemical analyses and isotopic age determinations we argue that at least two ancient tectonic events in the middle and late proterozoic can be identified prior to the last mesozoic continental collision and accompanying uhp metamorphism in the su lu and dabie terrane