the magnetostratigraphy of leg 73 sediments abstract the main objectiveof dsdp leg 73 was to obtain high quality records of major paleooceanographic events in the south atlantic this was achieved by coringsix sites on the african plate the sediments thus recovered span the cenozoic and five of the six sites proved ideally suited for magnetostratigraphic analysis the results presented in this paper and elsewhere in this volume constitute the first opportunity to extend the direct correlation of the magnetostratigraphic and biostratigraphic time scales into the paleogene in deep sea cores the magnetostratigraphic analyses from dsdp leg 73 sediments are presented in this paper the correlation of the magnetostratigraphy to the magnetic polarity time scale provides tight age depth control for the five sites analyzed allowing the accurate calculation of sediment accumulation rates the data presented here represent a remarkable record of the fine scale polarity history of the earth s magnetic field these data place constraints on the interpretation of small scale marine magnetic anomalies which are modelled equally effectively by field intensity fluctuations as polarity reversals at least some of the tiny wiggles correspond to very short polarity units in the magnetostratigraphic record by assuming an axial geocentric dipole the inclination of the time averaged magnetic field recorded in the sediments can be used to calculate the paleolatitude at which the sediments were deposited combining the age and average inclination information available from the magnetostratigraphy we present paleolatitudes versus time for the leg 73 drill sites

metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

saxothuringian zone in germany and poland differences and common features the classical correlation by kossmat 1927 of the saxothuringian belt of germany with the west sudetes of poland is re evaluated with special reference to the crystalline massifs of munchberg and the gory sowie and the surrounding areas important common features are cambro ordovician magmatism and sedimentation silurian to devonian radiolarian cherts in the low grade to unmetamorphosed units early devonian and older pressure dominated metamorphism followed by rapid uplift the incorporation of high pressure and mantle rocks and early carboniferous mass flow deposits with saxothuringian clasts differing features in the west sudetes are tectonic contacts in and around the gory sowie are mostly subvertical and mainly semi brittle in contrast with subhorizontal and ductile contracts in the munchberg the gory sowie has undergone late re equilibration of the earlier tectonic fabrics an ophiolite juxtaposed with the gory sowie crystallized in devonian time and became only statically metamorphosed as opposed to the regionally metamorphosed cambro ordovician mafic rocks of the saxothuringian belt localized depocenters with upper devonian to lower permian elastic rocks relating to north west trending strike slip faults instead of the north east trending cylindroidal foreland basin in the saxothuringian it is possible that the west sudetes originated as an easterly continuation of the saxothuringian belt but then became involved from the late devonian onwards in a strike slip system parallel with the margin of the east european platform

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

the oxidation state of manganese in marine sediments and ferromanganese nodules marine sediments and ferromanganese nodules from the pacific ocean have been analyzed for the omn ratio of solid manganese we tested six chemical methods and concluded that the iodometric and oxalate methods were equivalent and were the best choice in terms of accuracy and precision on natural samples we choose the iodometric method for most of our analyses because the oxalate procedure is a method of differences the ferromanganese nodules that we analyzed were all from manop site h and had mnfe ratios that ranged from 5 6 to 70 these nodules were invariably highly oxidized with omn values ranging from 1 90 to 2 00 our most precise analyses suggest that less than 1 of the total manganese is present as mn ii we also analyzed red clay and hemipelagic sediments from the eastern tropical pacific baja borderland and manop site h and carbonate ooze samples from the equatorial pacific these sediments are also highly oxidized omn 1 90 to 2 00 except when mn ii appears in the interstitial water as dissolved mn ii increases the value of the omn ratio in the solid phase decreases the omn ratio decreases to values as low as 1 40 this decrease appears to be due to a decrease in oxidized manganese by reduction however an increase in reduced manganese in the solid sediments by adsorption or mnco3 formation can not be ruled out in all cases

macrofabric fingerprints of late devonian early carboniferous subduction in the polish variscides the kaczawa complex sudetes we describe a remarkably preserved assemblage of sedimentary and tectonic fabrics in cores from the kaczawa complex sudetes sw poland these fabrics indicate a continuum of process from repeated remobilization of upper devonian lower carboniferous muddy flysch and volcaniclastic sediments as debris flows and olistostromes to fracturing fluid streaming and soft sediment injection triggered by high pore water pressures during the initial stages of tectonic deformation to contractional cleavage formation and local cataclasis while the sediment was still only partially consolidated these structures are similar to those described from odp cores through the toes of active accretionary prisms they indicate active subduction of oceanic crust during the late devonian suggesting that ophiolite obduction and significant overthrusting in the sudetes occurred as an integral part of the variscan orogeny

cadmium diagenesis in laurentian trough sediments the depth distributions of cd mn and fe in pore water and sediment were determined on three replicate box cores collected at a 325 m deep station in the laurentian trough the results reveal a surface layer in which the content of solid phase cd first decreases but then increases sharply with depth in contrast mn decreases regularly over the same depth interval in the oxygenated zone of this layer cd probably associated with organic matter is released to the pore water resulting in concentrations that are more than an order of magnitude higher than in the overlying water column some of the dissolved cd is returned to the water column and some migrates downward and is precipitated at depth this part of the cd cycle is virtually complete within the surface layer the base of which corresponds to the base of the zone of mn enrichment in the subsurface layer solid phase cd and mn show little or no concentration change however dissolved cd which reaches often non detectable concentrations 0 05 nm in this layer increases once again deep within the anaerobic zone and attains concentrations even higher than in the surface layer the presence of dissolved cd complexes revealed by 1 5 to 8 fold increases in electrochemically active cd in pore water following uv treatment as well as inconsistent distributions of dissolved and solid phase cd indicate complexities in diagenesis that merit further investigation

metal diagenesis in a shallow semi enclosed marine system in the aegean sea greece abstract trace metal and organic carbon distributions were examined in core sediments of kalloni bay during september 2000 in order to examine the diagenetic process and its impact on metal mobility solid sediment profiles show significant variations in mn fe and ni concentrations between sampling stations due to geological background variability and diagenetic processes in the sediment for mn solid phase organic carbon profiles reflect episodic input of organic matter from the land the redox status of the sediments can be characterized from sub oxic to anoxic leading to dissolution of mn oxides and enhancement of dissolved mn at the surface sediment layers of the bay dissolved fe maximal concentrations were located at a sediment depth of few centimetres below the mn maximum nickel distribution was mainly influenced by the geological background of a part of the bay s watershed consisting of ultrabasic minerals partition coefficients between solid phase and porewater k d s indicated the increase mobility of mn and to a lesser degree of ni and zn in the upper sediment layers concentrations factors indicated that metals especially mn and zn may flow from porewater to the overlying seawater because of concentration gradients

shrimp u pb zircon geochronology of the strzelin gneiss sw poland evidence for a neoproterozoic thermal event in the fore sudetic block central european variscides zircon ages recorded in gneissic rocks have recently been used as criteria to define and correlate various tectonic units and crustal blocks in the central european variscides a shrimp u pb zircon geochronological study of the strzelin gneiss in the fore sudetic block sw poland indicates the presence of 1 inherited zircon cores of palaeo to mesoproterozoic 206pb 238u ages between ca 2 000 and 1 240 ma and 2 zoned rims of neoproterozoic age with two distinct means of 600 7 and 568 7 ma the proterozoic age range of the cores suggests that different precambrian crustal elements were the source for the protolith of the gneiss a likely scenario is the erosion of various proterozoic granites and gneisses sedimentation after 1 240 ma and partial resistance of the original components to subsequent metamorphic dissolution and or anatectic resorption in neoproterozoic times the zoned zircon rims of both of the younger neoproterozoic ages are indistinguishable in the cathodoluminescence images the data are interpreted in terms of two different thermal events inducing zoned zircon overgrowth at ca 600 and 568 ma in general the new results confirm earlier assumptions of the proterozoic age of the gneiss protoliths and indicate their similarity to orthogneisses in the east sudetes tectonic domain e g the velke vrbno and desna gneisses the neoproterozoic dates are different from the age of 504 3 reported earlier for the go ciecice gneiss from a neighbouring locality in the strzelin massif the new data strongly indicate a moravo silesian bruno vistulian affinity for the strzelin gneiss and support the hypothesis that the strzelin massif lies within the tectonic boundary zone between the west and east sudetes domains which represents the northern continuation of the moldanubian thrust

early diagenesis in sediments from danish coastal waters microbial activity and mn fe s geochemistry abstract depth distributions of bacterial respiration of o2 no3 and so42 were compared with geochemical data for mn fe and s in coastal sediments from water depths between 26 and 520 m as water depth increased the zone of so42 respiration was found deeper in the sediment and was eventually separated from the surface located activity of o2 and no2 respiration at the deepest station additional so42 reduction activity was observed in small detrital aggregates on the sediment surface dissolved mn2 and fe2 appeared between the o2 plus no3 containing surface layer and the h2s plus fes containing sediment below this was a result of mn and fe reductions coupled to either the oxidation of sulfide or the mineralization of organic matter tracer experiments showed that both fes fes2 and s0 were important radiolabelled products of sulfate respiration in this intermediate zone in the same zone the overall degradation of organic matter seemed to be underestimated by the assay of so2 4 respiration and additional mineralization by mn and fe reductions was likely

pore water distributions of dissolved copper and copper complexing ligands in estuarine and coastal marine sediments the distributions and seasonal variability of total dissolved cu tdcu and cu complexing ligands in sediment pore waters have been investigated at two contrasting sites in the chesapeake bay two ligand classes which differ on the basis of the conditional stability constants k9 of their cu complexes were detected at all depths at both sites at the sulfidic muddy mid bay sta m concentrations and values of log k9 ranged from 390 12 500 nm and 7 2 8 9 respectively for the stronger ligand class l1s and 75 6 420 nm and 6 2 7 9 for the weaker ligand class l2s at the bioturbated sandy sta s in the lower bay respective concentrations and values of log k9 ranged from 135 807 nm and 7 6 10 2 for l1s and 40 1 410 nm and 6 6 9 2 for l2s for comparison one pore water profile from a slope station off of the chesapeake bay also showed the presence of two ligand classes with respective concentrations and values of log k9 of 140 270 nm and 8 11 for l1s and 30 180 nm and 7 10 forl2s these ligands are in large excess relative to ambient tdcu concentrations 0 1 24 3 nm thereby maintaining very low inorganic cu concentrations typically 0 1 to 100 pm and a high degree of organic complexation 87 2 99 9 of cu in bay and slope sediment pore waters thus virtually all tdcu fluxing from these sediments is complexed during sediment water exchange a relatively small fraction of the tdcu is exchanged as inorganic species which are widely regarded as the most bioavailable form of cu higher ligand concentra tions at sta m suggest that sulfide or organic ligands containing reduced s contribute to the pool of complexing ligands however the exact nature and sources of the ligands in bay pore waters are not known the progressive increase in conditional stability constants of the cul 2s complexes from the mid bay to the slope sediments may reflect differences in biological or chemical processes at each site as well as differences in the type of cu complexing organic matter total ligand concentrations l1s 1 l2s are 15 to 100 times higher in the upper intervals of the pore waters relative to ligand concentrations in the bottom waters of the chesapeake bay 30 60 nm consistent with previous observations of fluxes of these ligands from the sediments to overlying waters these results suggest that sediments are potentially significant sources of cu complexing ligands to the overlying waters of the chesapeake bay and perhaps other shallow water estuarine and coastal environments copper complexing ligands released from sediment pore waters may play an important role in influencing cu speciation in overlying waters copyright 2000 elsevier science ltd

paleomagnetic record of two successive miocene geomagnetic reversals in western crete abstract two geomagnetic reversals r n followed by n r have been recorded in a sequence of miocene marine clays of tortonian messinian age in western crete greece the time span of each transition is found to be of the order of 5000 10 000 years the transitional vgp paths are largely constrained in longitude either near the site longitude r n or opposite to it n r a normalized magnetization intensity record has also been obtained and its variations during reversals are found to be in excellent agreement with the predictions of hoffman s phenomenological model

trace metals in metalliferous sediments manop site m interfacial pore water profiles we present data showing enrichments of metals mn cu v cr cd and ni and dissolved organic matter dom in surficial pore waters depths 1 cm at a metalliferous sediment site in the pacific we also present a model of metal release during particulate organic carbon poc oxidation and opal dissolution at the sediment seawater interface a comparison of measured interfacial metal concentrations with those predicted from the model suggest that cd ni and cr are released during oxidation of poc at the sediment seawater interface however for v cu and mn additional source s and or processes are required to account for the measured interfacial concentrations for cu recycling via interfacial remineralization and release to bottom waters with subsequent scavenging out of bottom waters by particulates probably provides the major additional source for v we suggest that in addition to some contribution from a benthic flux bottom water scavenging scenario complexation with dom at the interface serves as a trap to accumulate v released from particulates in the zone of oxygen reduction for manganese we suggest that most of the interfacial pore water content is produced from reduction of sedimentary mn iv by reactions with dom at the sediment seawater interface the calculated benthic flux of manganese as a result of this reaction may account for a large fraction of the particulate manganese rain that is apparently not preserved in the sediment at this site

the moldanubian thrust zone a terrane boundary in the central european variscides refined based on lithostratigraphy and u pb zircon geochronology abstract the zircon age populations of metavolcano sedimentary successions in the orlica nieznik dome osd stare m sto belt smb and velke vrbno dome the sudetes poland and czech republic have been used to refine the location of the moldanubian thrust zone mtz which is a boundary between the saxothuringian terrane of gondwana descent and the brunovistulian terrane being a promontory of laurussia in the northern continuation of the mtz a set of multiply activated regional scale thrusts developed and brought into contact rocks of different ages and geological histories metarhyolites in the orlica nieznik dome and the stare m sto belt have similar geochemistry and u pb isotopic zircon records which is taken in favour of their coeval formation and common saxothuringian affinity felsic metavolcanic rocks from the osd and from the thrust bounded upper and lower units of the smb yielded protolith ages of 500 3 ma and 493 4 ma to 498 5 ma respectively which indicates that metavolcano sedimentary successions in the osd and smb were deposited in late cambrian times structurally below these rocks there are the highly sheared brousek quartzites with detrital zircons that yielded a maximum depositional age of 530 ma the mylonitic quartzites accommodate deformation induced by tectonic transport on the east n znerov thrust which is interpreted as the easternmost margin of saxothuringia this fault separates palaeozoic rocks of the saxothuringian terrane from neoproterozoic bimodal volcanogenic succession in the velke vrbno dome of brunovistulia dated at 558 ma the late variscan thermal events in the early carboniferous left imprints in the form of u rich rims around the zircons of the metavolcanic rocks from the stare m sto belt and only a very minor overprint in the zircons from the velke vrbno dome and orlica nieznik dome

magnetostratigraphy of the jurassic cretaceous boundary in the maiolica limestone umbria italy the magnetic stratigraphy of a 110 m section of the early cretaceous maiolica pelagic limestone in the bosso valley umbria italy shows clearly defined magnetozones that are correlated with the geomagnetic polarity record derived from the m sequence marine magnetic anomalies m19 to m14 and possibly m13 using an established paleontological zonation of this section based on calpionellids the position of the jurassic cretaceous boundary is located close to the base of the negative magnetozone corresponding to anomaly m17

copper and manganese in hemipelagic sediments at 21 n east pacific rise diagenetic contrasts abstract relatively rapidly accumulating 7 cm kyr and organic rich 1 5 corg epr sediments near 21 n are characterized by pronounced nitrate reduction in the upper decimetre and by an enrichment of mn and increased fe al ratio in surficial sediments joint consideration of solid phase and pore water data indicates that the distributions of both mn and fe in the sediments are in disequilibrium with their respective pore water profiles precipitation of upward diffusing mn and fe is occurring at present below the enriched horizons producing perched enrichments indicative of non steady state diagenesis consideration of a high resolution 14c age vs depth curve and a decrease toward the interface from 1 51 to 1 37 wt over the top 7 cm of the corg profile suggests that the diagenetic disequilibrium evident for mn and fe may be due to a geologically recent decrease in productivity such a decrease would be manifest in the sediments by a downwardly migrating oxidation front which would progressively erode the mn and fe pore water profiles producing the existing decoupled surface enrichments in contrast to mn the distribution of cu has apparently not been perturbed by non steady state phenomena a first order decrease with depth of the dissolved copper concentration is accompanied by a first order increase in solid phase cu application of a diffusion reaction model to these data predicts a sedimentation rate of 8 cm kyr 1 which agrees well with the 14c determined rate of 7 3 cm kyr 1 implying that the pore water and solid phase distributions are in diagenetic equilibrium available evidence suggests that the major host for non detrital cu in hemipelagic sediments is authigenic nontronite because this phase appears to form slowly there may be a kinetic constraint on the amount of copper which can be incorporated authigenically in rapidly accumulating hemipelagic deposits support for this hypothesis is given by the observed inverse proportionality between the sedimentation rate and the concentration of non detrital cu in surface sediments from at least seven widespread locations in the eastern pacific it is suggested that the variation observed in the salt and caco3 free cu concentration in hemipelagic sediments is a consequence largely of the residence time of sediments at the surface where high dissolved cu concentrations prevail

u pb ages from sw poland evidence for a caledonian suture zone between baltica and gondwana faunal and palaeomagnetic evidence suggests the existence of a c 3000 km wide tornquist sea between gondwana and baltica in early ordovician times which narrowed to 50 2 ma an unmetamorphosed ophiolite gives a 420 20 2 ma age whilst in two other terranes amphibolite facies island arc lavas have fossiliferous lower ludlow 424 415 ma sequences all are unconformably overlain by unmetamorphosed upper devonian conglomerates a sinistral transpressive regime is observed in regionally extensive mylonite zones titanite and zircon ages 338 2 3 and 339 4 ma record variscan magmatism the data suggest considerable narrowing of the tornquist sea during the ordovician continuing ocean floor and island arc activity in the silurian and final sinistral transpressive closure by the mid devonian

trace metal remobilization in the interstitial waters of red clay and hemipelagic marine sediments interstitial water samples from the guatemala basin and the coast of baja california have been analyzed for manganese iron copper nickel and nitrate the data provide a systematic look at changes in trace metal diagenesis proceeding from red clay to highly reducing nearshore sediments in red clay sediments the nitrate concentrations suggest that only aerobic respiration is occurring manganese and iron are below detection nickel concentrations remain the same as in bottom seawater but copper shows a pronounced maximum just at the sediment water interface proceeding to hemipelagic sediments denitrification becomes increasingly important and manganese and iron remobilization occur in the sediments the linear manganese and nitrate profiles suggest regions of production or consumption separated by zones of diffusion this differs from the conventional picture of a continuous series of reactions within the sediments manganese reduction always occurs before iron reduction the pore water nickel correlates well with manganese in these sediments suggesting that nickel is associated with mno2 in the solid phase the pore water flux ratio of manganese and nickel agrees well with the ratio in solid phase authigenic oxides copper still displays a core top concentration maximum as well as a second maximum associated with the remobilized manganese the calculated ratio of the cu c flux ratios support the argument for copper remobilization during organic carbon oxidation comparison of the upward and downward diffusive fluxes with the rate of copper buried by sedimentation shows that at least half of the copper buried must be of diagenetic origin and less than 25 of the copper reaching the sediments is buried

the late neoproterozoic magmatism in the ediacaran series of the eastern pyrenees new ages and isotope geochemistry geochronological u pb la icp ms geochemical and isotopic data from metavolcanic felsic rocks of the canigo and cap de creus massifs in the eastern pyrenees provide evidence of an ediacaran magmatic event lasting 30 ma in ne iberia these data also constrain the age of the late neoproterozoic succession in the cap de creus massif where depositional ages range from 577 to 558 ma and in the canigo massif where the data 575 568 ma represent minimum ages the geochemistry of the felsic rocks indicates that they were formed in a back arc environment and they record a fragment of a long lived subduction related magmatic arc 620 520 ma in the active northern gondwana margin the homogeneity shown by all these crustal fragments along this margin suggests that the individualization of the pyrenean basement from the iberian massif started later probably during its transition from an active to a passive margin in cambro ordovician times

a structural model for the western central sudetes a deformed stack of variscan thrust sheets a model based on new structural and geochemical data is presented it unifies the structural history of the izera rudawy janowickie and kaczawa complexes with the fore sudetic block despite their current separation by the intra sudetic and marginal sudetic faults above the granitoid izera kowary and w droze gneisses at the base of the structural sequence the ductile kowary shear zone marks the basal decollement of the wierzawa thrust sheet comprising often highly strained metasediments associated with enriched tholeiitic and alkaline metabasites above it the ductile kaczorow shear zone corresponding to the main mylonitic zone within the leszczyniec shear zone in the rudawy janowickie complex marks the base of the dobromierz thrust sheet characterized by voluminous morb like meta tholeiites and minor metasediments in the higher parts of the rudawy janowickie and kaczawa complexes and the pyszczynska hill area of the fore sudetic block in the east the sleza ophiolite and the gory sowie block override the entire nappe stack kinematic fabrics in the major and related shear zones indicate d 1 compressional transport towards the northwest followed by minor d 2 extensional movements the thrust stack was deformed during d 3 by southwest verging folds was subsequently intruded by post orogenic granites and later disrupted by the intra sudetic marginal sudetic and associated faults

long lasting cadomian magmatic activity along an active northern gondwana margin u pb zircon and sr nd isotopic evidence from the brunovistulian domain eastern bohemian massif manuscript published version available in international journal of earth sciences 2016 doi 10 1007 s00531 016 1416 y

magnetotactic bacteria at the geomagnetic equator magnetotactic bacteria are present in fresh water and marine sediments of fortaleza brazil situated close to the geomagnetic equator both south seeking and north seeking bacteria are present in roughly equal numbers in the same samples this observation is consistent with the hypothesis that the vertical component of the geomagnetic field selects the predominant polarity type among magnetotactic bacteria in natural environments

a model for a continental accretionary wedge developed by oblique collision the ne bohemian massif structural and metamorphic investigations of the northeastern margin of the bohemian massif indicate three main sequential devonian carboniferous tectonic events 1 devonian rifting 2 early carboniferous oblique underthrusting and formation of a continental accretionary wedge 3 eduction of the wedge and late carboniferous transpression devonian rifting of the brunia microcontinent resulted in the formation of two crustal scale boudins associated with the development of two syn rift devonian basins this extensional template strongly influenced the nature of the ensuing variscan contractional deformation early carboniferous 350 330 ma progressive highly oblique underthrusting of the two crustal boudins beneath the lugian terrane to the west generated syn deformational barrovian metamorphism and the formation of a continental accretionary wedge the wedge was further compressed by continued underthrusting of brunia which resulted in the successive vertical extrusion eduction of an upper and lower allochthon derived from the more deeply underthrust crustal boudin the eduction was terminated by a late carboniferous 330 310 ma transpressional event resulting from continued plate convergence release of mantle derived magma during late stage eduction thermally softened the transpressional zones in the more external parts of the wedge the resultant differential displacements gave rise to extensional unroofing of the internal part of the wedge

deducing the ancestry of terranes shrimp evidence for south america derived gondwana fragments in central europe we present here an example of how the sensitive high resolution ion microprobe shrimp zircon dating method can provide a terrane specific geochronological fingerprint for a rock and thus help to reveal major tectonic boundaries within orogens this method applied to inherited zircons in a ca 580 ma metagranitoid rock from the eastern bohemian massif has provided for the first time in the central european variscan basement unequivocal evidence for mesoproterozoic and late paleoproterozoic geologic events ca 1 2 ga 1 5 ga and 1 65 1 8 ga the recognition of such zircon ages has important consequences because it implies that parts of the precambrian section of variscan central europe were originally derived from a grenvillian cratonic province as opposed to the common assumption of an african connection a comparison with previously published shrimp data suggests however that these mesoproterozoic and late paleoproterozoic zircon ages may be restricted to the moravo silesian unit in the eastern variscides whereas the saxothuringian and moldanubian zones appear to contain a typical north african i e neoproterozoic plus eburnian inherited zircon age spectrum this finding supports new tectonic concepts according to which variscan europe is composed of a number of completely unrelated terranes with extremely different paleogeographic origins the moravo silesian unit can be best interpreted as a peri gondwana terrane which was situated in the realm of the amazonian cratonic province by the late precambrian comparable to the avalonian terranes of north america and the united kingdom

processes and sources during late variscan dioritic tonalitic magmatism insights from plagioclase chemistry gesiniec intrusion ne bohemian massif poland the ge siniec intrusion strzelin massif east sudetes 307 290 ma is composed predominantly of dioritic to tonalitic rocks with sr sr ratios ranging from 0 7069 to 0 7080 and end1 4 3 1 to 4 2 emplaced as post collisional magmas following thevariscan orogeny in situ sr isotope and trace element analyses of plagioclase were carried out on five diorite tonalite samples with variable whole rock sr sr compositions to constrain magma sources and elucidate magma chamber processes plagioclase is characterized by complex zoning patterns such as patchy zoning asymmetrical zoning and strong resorption between an rich cores and more albitic rims the range of sr isotopic compositions recorded in plagioclase is 0 7069 0 7091 greater than that of the whole rocks no change in isotopic composition is observed across resorbed core rim boundaries as would be expected if the resorption was caused by magma mixing two samples are close to sr isotopic equilibrium between plagioclase and the whole rock three samples are isotopically heterogeneous and exhibit the largest variations in sr isotope ratios within high an plagioclase cores associated with only slight resorption and almost no change in an content consequently we interpret the core resorption to be due to decompression during emplacement of phenocryst bearing magmas in the upper crust rather than to magma mixing whereas we interpret the isotopic heterogeneity in the high an plagioclase cores to be due to open system processes in the lower crust the trace element and sr isotopic compositions of the high an plagioclase cores provide an insight into the lower crustal processes that took place prior to decompression we show that different diorite tonalite types cannot be related to each other by assimilation fractional crystallization processes and consequently they probably evolved as separate magma batches processes recorded in plagioclase core compositions include contamination by high sr sr crustal material and interaction with water rich magma the studied samples represent magmas that probably formed either by continuous differentiation and crustal contamination of originally more mafic magmas or by remelting of 1 3 2 1 ga basaltic materials in the lower crust this study emphasizes the importance of integrating textural and in situ data to elucidate the processes that contribute to the formation of texturally and compositionally complex plagioclase crystals in plutonic rocks

interactions between dioritic and granodioritic magmas in mingling zones plagioclase record of mixing mingling and subsolidus interactions in the gesiniec intrusion ne bohemian massif sw poland dioritic and granodioritic rocks coexist in the gesiniec intrusion in sw poland showing typical relationships in many mafic felsic mingling zones worldwide such as dioritic syn putonic dykes and microgranular enclaves within granodioritic host plagioclase zonation from granodioritic rocks suggests late stage mixing probably with dioritic magma whereas no magma mixing is recorded in plagioclase from dioritic rocks the diorites seem to show effects of interaction with evolved leucocratic melts derived from granodiorite not with the granodioritic melt itself we conclude that the diorites compositions were modified after their emplacement within the granodioritic host when the diorites were essentially solidified and injection of evolved melt from granodiorite did not involve marked modification of plagioclase composition compositional zoning patterns of plagioclase in diorites can be modeled by closed system fractional crystallization interrupted by resorption induced probably by decompression granodioritic plagioclase seems to be affected by the same resorption event plagioclase that crystallized in dioritic magma before the resorption does not record interaction between dioritic and granodioritic magmas suggesting that both magmas evolved separately

paleomagnetic evidence for fossil biogenic magnetite in western crete abstract previous paleomagnetic research has shown that the concentration of fine grained magnetite preserved in miocene marine clays of western crete drops during two successive geomagnetic transitions although the mechanism responsible for this effect was not known magnetite precipitation by magnetotactic bacteria offers a straightforward explanation for this decrease reduced field strengths during a reversal will strain the competitive advantage of having intracellular magnetite and will force bacteria to precipitate correspondingly more magnetite if they are to maintain the same alignment in the geomagnetic field their ability to do this is limited by several magnetophysical constraints which should act to reduce the numbers of magnetite precipitating cells particularly in fields of less than about 12 of the present level this would lead to a decrease in the supply of bacterial magnitude to the sediments recovery of intact magnetotactic bacterial fossils may lead to a new method for estimating paleointensities from sedimentary rocks

new u pb monazite and zircon data from the sudetes mountains in sw poland evidence for a single cycle variscan orogeny new u pb monazite and zircon data combined with a study of their internal morphologies significantly clarifies the controversy surrounding the palaeozoic geodynamic evolution of the sudetes mountains in the northeastern bohemian massif variably thin rims of secondary magmatic overgrowth on zircons from an anatectic granite in the gory sowie block are dated by a u pb zircon lower intercept age of 353 61 ma by magmatic monazite growth at 378 2 ma and by xenotime crystallization at 383 370 ma in a late syntectonic pegmatite reflecting the anatectic event associated with a single cycle variscan orogeny in this area

sequential granite emplacement a structural study of the late variscan strzelin intrusion sw poland the strzelin massif in sw poland central european variscides records a protracted igneous evolution with three main magmatic stages 1 tonalitic i 2 granodioritic and 3 tonalitic ii granitic in the northern part of this massif the strzelin intrusion proper comprises three successively emplaced rock types a medium grained biotite granite 303 2 ma a fine grained biotite granite 283 8 ma and a fine grained biotite muscovite granite based on field evidence the third variety postdates both types of the biotite granites the structural data from the three granites including their parallel approximately e w striking and steeply dipping lithological contacts and ene wsw trending subhorizontal magmatic lineations suggest that the emplacement of all three successive granite varieties was controlled by an active long lived strike slip fault striking ese wnw with a dextral sense of movement after the emplacement of the youngest biotite muscovite granite the intrusion underwent brittle extension which produced q joints striking nnw sse to n s and dipping at 55 70 wsw to w and showing evidence of broadly n s directed sinistral displacements the structural observations supported by new geochronological data indicate that the internal structure of the composite granitoid intrusion including the faint magmatic foliation and lineation formed in a long lived strike slip setting different from the subsequent post emplacement extensional tectonics that controlled the development of brittle structures

electron optical characterization of bacterial magnetite abstract magnetic grains isolated from magnetococcoid bacterial cells were studied by means of transmission electron microscopy electron diffraction and electron microprobe analysis observed in situ the magnetic grains are each surrounded by an organic membrane and are usually found in a random array although chains are also seen electron diffraction confirms the magnetite mineralogy and provides additional evidence in favor of vacancies in the structure electron microprobe analysis shows the magnetite to be slightly titaniferous electron microscopy indicates that the grains rather than being flake shaped are parallelepiped crystals with a mean length of 99 3 8 7nm a mean width of 62 3 6 1nm yielding a width to length ratio of 0 63 these data support the contention that the magnetic bacterial grains are single domain crystals capable of producing a natural remanent magnetization in sediments

terranes and terrane boundaries in the sudetes northeast bohemian massif in the sudetes seven distinct lithostratigraphic terranes exhibit a symmetric distribution a central region of basinal oceanic and ophiolitic rocks the central sudetic terrane is bordered respectively to the northwest and southeast by the sialic saxothuringian and moldanubian terranes these exhibit contrasting metasedimentary metavolcanic successions and tectonic metamorphic sequences but both are characterized by palaeozoic plutonism these are in turn bordered again respectively to the northwest and southeast by the lusatian and moravian terranes which are also sialic but contain cadomian granitoids and represent rifted and now widely separated fragments of gondwana along the southwestern flank of the sudetes the barrandian terrane largely covered by younger sediments extends to the southwestern margin of the bohemian massif the sowie gory terrane forms a klippe of high grade gneisses tectonically emplaced on top of low grade sheared ophiolites of the central sudetic terrane the sowie gory terrane exhibits a history of three distinct probably multi orogenic regional metamorphic events an early high pressure granulite eclogite metamorphism followed by medium to low pressure granulite and in turn by amphibolite facies metamorphism all the terrane boundaries are complex zones of ductile to brittle shearing modified by later brittle movements some such as the leszczyniec shear zone mark lines of old pre variscan rift and suture zones reactivated and overprinted during a series of variscan ductile to brittle events of extensional shearing with related metamorphism and plutonism

factors controlling the mineralogy and geochemistry of the recent surface sediments of the kalloni gulf lesvos island greece detailed chemical and mineralogical data are presented for 37 samples of surface sediments collected from the kalloni gulf eastern half lesvos island northern greece the sediments are largely carbonate rich muds though near the eastern and northern coast of the gulf higher proportions of biogenic and lithogenic sands and gravels occur the main minerals are quartz feldspar andesine clay minerals montmorillonite illite kaolinite and the carbonate minerals calcite mg calcite aragonite the mathematical method of factor analysis was applied in order to explain the mineralogical and geochemical variations these variations can be interpreted in terms of variations in provenance and depositional environment six factors were produced accounting for 83 6 of the total data variance a a si al na k ti rb ba y zr factor controlled by clays and detrital minerals such as feldspars and zircon opposed by a caco2 cu sc sr la association carbonate minerals b an organic carbon factor c fe ce zn rb ni y nb c a fe mg cr ni factor representing control by peridotite d a ce nd fe ni zn la factor controlled by silicate minerals e a al fe ti p v factor controlled by chlorite amphiboles or pyroxenes of volcanic or basaltic intrusions f a mn fe zn factor controlled by iron manganese oxides similarities in trace element composition among kalloni gulf bottom sediments and source lithologies indicate that the trace elements are derived from the adjacent landmasses the ai ti ratio of the sediments is consistent with the terrigenous nature of sendimentation in the kalloni gulf

composition and behaviour of trace metals in post oxic sediments of the gulf of papua papua new guinea trace metal composition and behaviour were examined in post oxic muds of the gulf of papua in january 1993 porewater profiles and flux measurements indicate significant fe and mn reduction in these coastal muds vertical profiles rates of sediment water exchange and correlation analyses imply that these silt dominated muds mobilize al and are a sink for mo undetectable or very low porewater concentrations and flux rates of other metals ni cu cr co pb cd indicate immobilization into solid phase minerals solid phase metal concentrations are consistent with those in average shale suggesting pristine conditions in the gulf low 1 2 m free sulphides low clay content and bioturbation are partly responsible for trace metal composition and concentrations but several lines of evidence imply non steady state diagenesis in these muds 1 the lack of a clear zonational sequence of solutes with sediment depth 2 lack of agreement between vertical profiles of dissolved and solid phases of most metals 3 significant but weak correlations between dissolved metals and dissolved organic carbon and between solid phase metals and total organic carbon and 4 lack of correlation between conservative elements e g dissolved mo and cl dissolved al and sioh intense massive physical reworking is cited as the major factor fostering apparent non steady state behaviour of trace metals in the surface muds of the gulf of papua this scenario is very similar to that occurring on the amazon shelf and may be typical of other wet tropical regions with high energy coastlines receiving large amounts of highly weathered river borne material

variscan granitoids related to shear zones and faults examples from the central sudetes bohemian massif and the middle odra fault zone the granitoid intrusions of the central sudetes cs and of the middle odra fault zone mofz ne part of the bohemian massif are both spatially and temporally related to large scale shear zones and faults including possible terrane boundaries that provided effective channels for melt migration summarizing common features of the cs and mofz granitoids we have delineated a set of characteristics of the fault related and shear zone related granitoids 1 they are mainly generated by partial melting of crustal sources with variable contribution or no contribution of mantle materials 2 the sheet like steeply inclined narrow and rather small granitoid intrusions are emplaced within shear zones at mid crustal level c 20 km depth whereas the larger flat lying plutons intrude into the upper crust outside or above these shear zones 3 the magmatic foliation and lineation in granitoids of the deeper sheet like intrusions are concordant with those in the surrounding metamorphic rocks suggesting that the solidification of granitoids was coeval with the deformation in the shear zones instead the magmatic foliation in the shallower and larger dome like plutons reflects magma flow 4 ductile transcurrent movements along the shear zones postdate medium pressure regional metamorphism and are accompanied by an increase in the local thermal gradient as documented by the crystallization of cordierite andalusite and sillimanite 5 the increase in the thermal gradient precedes the emplacement of granitoids and their concomitant thermal influence on the country rocks the granitoids related to the final stages of tectonothermal activity of the shear zones are good time markers of their evolutionary path

diagenetic magnetite carries ancient yet secondary remanence in some paleozoic sedimentary carbonates many sedimentary carbonate rocks carry stable magnetizations that can be shown to reside in magnetite when such magnetizations are observed it is often argued or demonstrated that the magnetite was incorporated into the sediment during deposition however paleomagnetic and rock magnetic studies in conjunction with analyses of magnetic extracts from the helderberg and bonneterre carbonates united states indicate that the magnetite present in these rocks is most likely of diagenetic i e postdepositional origin

crystallization and resorption in plutonic plagioclase implications on the evolution of granodiorite magma gesiniec granodiorite strzelin crystalline massif sw poland abstract granodiorite from the gesiniec intrusion strzelin crystalline massif sw poland contains complexly zoned plagioclases five chemically and structurally distinct zones can be correlated among crystals cores 25 35 an inner mantles 40 45 an outer mantles 40 25 an resorption zones 35 50 an and rims 35 30 an good structural and chemical major and trace elements correlation of zones between crystals indicates that zonation was produced by changes in conditions of crystallization on a magma chamber scale plagioclase being the liquidus phase records a time span from the beginning of crystallization to emplacement and rapid cooling of granodiorite as thin dykes crystallization began with the formation of inner mantles the paucity and different sizes of inner mantles suggests slow crystallization in high temperature magma normally zoned inner mantles were formed under increasing undercooling compositional trends in mantles suggest closed system crystallization the major resorption zones were caused by injection of less evolved magma as indicated by the strontium increase in plagioclase the injection triggered a rapid rise of magma and plagioclase crystals facilitating mixing but also inducing fast kinetically controlled growth of complex multiple oscillatory zonation within resorption zones the ascent of magma caused decompression melting of plagioclase and produced melt inclusions within inner mantles the cores the decompression range is estimated at a minimum of 2 kbar emplacement of granodiorite as thin dykes allow rapid cooling and preservation of magmatic zonation in plagioclases melt inclusions crystallized completely during post magmatic cooling the zonation styles of plutonic plagioclase differ markedly from volcanic ones suggesting different magma evolution zones in plutonic plagioclase are well correlated indicating crystallization in quiescent magma where crystals accumulation and compositional magma stratification may occur crystals probably did not travel between different regimes resorption occurred but as single albeit complex episodes good correlation of zones in plutonic plagioclases allows a distinction between the main processes controlling zonation and superimposed kinetic effects

protolith age and provenance of metasedimentary rocks in variscan allochthon units u pb shrimp zircon data from the orlica śnieznik dome west sudetes new u pb sensitive high mass resolution ion microprobe shrimp data from detrital zircons within the orlica nieznik dome provide new insights into the stratigraphic and palaeogeographic position of assumed relict precambrian basement preserved in the variscan collisional orogen of the west sudetes sw poland hitherto the mlynowiec formation and the stronie formation within the orlica nieznik dome were assumed to represent two metavolcano sedimentary successions of proterozoic and early palaeozoic age respectively however when previous u pb data and mapping data from the orlica nieznik dome are combined with the new detrital zircon isotopic ages both from paragneisses within the mlynowiec formation and from light coloured quartzites and mica schists within the stronie formation the result strongly suggests that the protoliths of these two formations actually form a continuous succession this continuous succession is herein designated the mlynowiec stronie group the rocks of this group were deposited during middle cambrian early ordovician times c 520 470 ma presumably at the northern edge of west gondwana after the 10 20 ma period of tectonic quiescence that followed the terminal stage of the cadomian collisions monotonous mlynowiec metagreywackes form the lower part of the succession and the lithologically diverse schistose stronie formation forms its upper part the change from greywacke mlynowiec to volcano sedimentary stronie facies coincided with the onset of rather short lived volcanic activity which climaxed around 505 495 ma and which supplied the volcanogenic components to the stronie formation no cadomian unconformity has been observed in the region xenocrystic zircons from the mlynowiec stronie group retain records of archaean 3 0 2 3 ga palaeoproterozoic 2 1 1 8 ga and neoproterozoic to early cambrian 660 530 ma zircon forming events these zircon ages together with the lack of 1 7 1 2 ga zircon ages suggest that the source areas for the metasedimentary rocks may have been the west africa craton which therefore differs from the amazonian affinity of the adjacent brunovistulia terrane nevertheless two zircons c 1 0 and 1 1 ga old respectively indicate that the mlynowiec stronie group sedimentary basin must have still been within the delivery reach of detritus ultimately derived from the grenvillian age belt s the detrital components of the supracrustal formations of the orlica nieznik dome were mainly derived from neoproterozoic zircon bearing crystalline rocks that were accreted to and included in the cadomian basement in several intrusive pulses that culminated at 660 640 ma 620 ma and 570 530 ma

copper lead and zinc trapping in mediterranean deep sea sediments probable coprecipitation with mn and fe abstract in the deepest area of the western mediterranean sea between sardinia and minorca sediments are relatively rich in zn and fe on the periphery of this area the sediments are rather rich in cu pb and mn and to a lesser extent in zn in this last case the vertical profile of mn in the sediment suggests that the mn enrichment in the top level with an mn concentration of 1500 g g 1 is due to an ascending mn flux from deeper levels reducing for mn oxyhydroxides to the surficial 0 4 cm thick oxidizing sediment the concentrations of cu pb and zn dissolved in the surficial sediment pore waters are too low to allow direct precipitation of mere oxides or hydroxides of these metals but enrichment in the mn rich deep sea zone can be explained by a coprecipitation process during the precipitation of mn oxides or hydroxides since mn dissolved in surficial sediment pore water is present in an apparent slight oversaturation with respect to the solubility product in the deepest areas where zn seems to precipitate with fe hydroxides the surficial sediments appear to be too reducing to allow mn oxides to precipitate cu and pb are trapped not so well there calculations of chemical equilibria of the species concerned are consistent with these considerations since mn seems to be released from sediments in the deepest zone with total mn concentrations g g 1 it can be assumed that there the surficial sediments correspond nearly to a reducing medium for the mn oxides therefore the bottom seawaters of these deepest area of the western mediterranean sea seem to have rather low o 2 concentrations and to be only rarely renewed

carboniferous permian magmatism and mo cu w mineralization in the contact zone between the malopolska and upper silesia blocks south poland an echo of the baltica gondwana collision the krakow lubliniec tectonic zone klfz in southern poland which divides the malopolska block mb from the upper silesia block usb is a portion of the sw margin of the trans european suture zone zircon u pb dating of a variety of igneous rocks granodiorites dacites lamprophyre and diabase from the subsurface krakow lubliniec igneous belt along the klfz shows that magmatism spanned within a narrow time period ca 10 ma between 303 8 2 2 and 292 7 4 9 ma the earlier magmatism 303 8 2 2 294 7 2 3 ma was felsic calc alkaline and the contemporaneous or and slightly later alkaline volcanism 294 4 4 9 292 7 4 9 ma was of mafic intermediate composition the felsic rocks granitoids and dacitoids are weakly peraluminous medium to high k moderate mg 0 39 0 46 weakly evolved and i type rocks due to the intensive development of hydrothermal alteration these rocks are commonly strongly altered and locally mineralized by porphyry and other types of mo cu w ores that are closely related to the felsic magmatism in space and time the zircon u pb dating yielded ages which are similar to the previously measured re os ages of molybdenites from the klfz felsic magmatism at the myszkow mo cu w deposit yielded ages in the range 301 0 2 1 295 9 2 9 ma the youngest rocks dated are from the myslow area in the usb volcanic alkaline rocks lamprophyre and diabase of shoshonitic character with low mg 0 49 and 0 69 respectively and ni contents 62 ppm indicative of a relatively juvenile magma composition inherited zircon cores remnant detrital zircon from a sediment component in the source rocks were dated to be ranging from ca 2775 to 575 ma inheritance of ca 600 ma cadomian basement and ca 1 40 ga mesoproterozoic is common in the rocks from both blocks but those from the mb contain additional inheritance with dates of 2 78 2 67 and 2 05 1 92 ga both ages characteristic of zircon from the svecofennian of northern europe baltica the inherited zircon from the youngest alkaline rocks provided evidence for mesoproterozoic ca 1 55 1 44 and 1 09 ga and palaeoproterozoic 1 96 ga thermal events in the usb and its possible affinity to avalonian cratonic crust as a source for its igneous protolith u pb isotopic studies of zircons from kl igneous belt indicate its inherited signatures from the crustal sources and magma emplacements during the klfz wrenching which allowed channels and room for magma emplacement along the mb and usb in upper carboniferous lower permian on sw margin of the east european craton mo cu w ore mineralization associated with the 300 ma felsic magmatism represents rather the product of decompression melting induced in the areas of decreased pressure undergone in the regional wrench fault zones than the classic mo cu porphyry style mineralization

diagenesis of magnetic minerals in recent haemipelagic sediments rapidly deposited sediments from marine and lake environments are being used increasingly to study decadal to millennial fluctuations in the earth s magnetic field the objectives are to gain more fundamental understanding of the geodynamo and to establish a new dating technique for sediments while lacustrine sections are generally restricted to temperate latitude glacial lakes 20 000 yr old rapidly deposited marine sediments along continental margins potentially offer continuous high resolution yet long term records of geomagnetic secular variation however to interpret the sedimentary magnetic record accurately geochemical processes that affect the reliability of the magnetic signal must be understood we now report downcore magnetic profiles from undisturbed kasten cores taken in rapidly deposited laminated sediments from the gulf of california and in bioturbated haemipelagic muds on the oregon continental slope which give apparently reliable directions but show dramatic decreases in the intensities of natural nrm and artificial arm irm remanences with depth downcore porewater and solid sulphur analyses show concave down decreases in porewater sulphate and systematic increases in pyrite and metastable monosulphides the maximum curvature of the sulphide profile occurs directly below the high magnetization zone combined with other compositional and mineralogical analyses these data suggest that due to oxidative decomposition of organic matter magnetites and other iron oxides become progressively reduced and subsequently sulphidized and pyritized with depth iron reduction seems to occur before sulphide formation changes in magnetic stability parameters are consistent with selective dissolution of the finer sized grains causing downcore coarsening of the magnetic fraction

episodic and long lasting paleozoic felsic magmatism in the pre alpine basement of the suretta nappe eastern swiss alps the suretta nappe of eastern switzerland contains a series of meta igneous rocks with the rofna porphyry complex rpc being the most prominent member we present la icp ms u pb zircon data from 12 samples representing a broad spectrum of meta igneous rocks within the suretta nappe in order to unravel the pre alpine magmatic history of this basement unit fine grained porphyries and coarse grained augengneisses from the rpc give crystallization ages between 284 and 271 ma which either represent distinct magma pulses or long lasting magmatic activity in a complex magma chamber there is also evidence for an earlier variscan magmatic event at 320 310 ma mylonites at the base of the suretta nappe are probably derived from either the rpc augengneisses or another unknown carboniferous permian magmatic protolith with a crystallization age between 320 and 290 ma two polymetamorphic orthogneisses from the southern suretta nappe yield crystallization ages of 490 ma inherited zircon cores are mainly of late neoproterozoic age with minor neo to paleoproterozoic sources we interpret the suretta nappe as mainly representing a gondwana derived crustal unit which was subsequently intruded by minor cambrian ordovician and major carboniferous permian magmatic rocks finally the suretta nappe was thrust into its present position during the alpine orogeny which hardly affected the u pb system in zircon

ultrafine grained magnetite in deep sea sediments possible bacterial magnetofossils a new extraction technique now permits ultrafine magnetite crystals to be separated from a variety of deep sea sediments morphologic characterization of these particles with transmission electron microscopy reveals the presence of several distinct crystal types some of which closely resemble those formed by the magnetotactic bacteria the apparently biogenic magnetite particles are of single domain size and dominate the population in calcareous deep sea sediments bacterially precipitated magnetite may therefore be a major source of the stable magnetic remanence in some marine sediments these objects possibly constitute the smallest mineral fossils yet recovered from the sedimentary record

particulate manganese and iron in recent sediments of the gulf of lions continental margin north western mediterranean sea deposition and diagenetic process abstract this study aims at apprehending the major forcing factors which govern the spatial and vertical mn and fe distributions in ten cores from the gulf of lions speciation by chemical leaching experiments helps understanding their chemical behaviour during the early diagenetic processes in a marine environment under strong continental influence the distribution and chemical behaviour of mn and fe differ drastically the strong dependence of mn distribution on chemical conditions is expressed by a marked solid phase mn enrichment in the oxic layers of sediment deposits this enrichment increases with decreasing sedimentation rate increasing water depth it is illustrated by an enhanced portion of total mn in the reducible phase and the precipitation of todorokite on calcareous supports in the upper part of the deepest cores as a result 65 of the margin total particulate mn is thought to be stored in slope deposits in a relatively strongly held association conversely the low chemical mobility of iron in the sedimentary column is indicated by uniform depth profiles and an exclusive location in the residual chemical phase in all the studied sites the fe distribution is largely controlled by the dispersion of particulate material on the margin from the rhone river main source a budget of mn and fe accumulation based on the average amount of total mn and fe content of sediments deposited during the last 100 yr has been made taking into account diagenetic readjustments the total mn and fe amount stored on the margin during the last century is estimated to be 1 5 106 and 54 106 t respectively these values are seven times higher than the total secular external inputs calculated on the basis of present day riverine and atmospheric fluxes this large discrepancy is mainly explained by the sharp decrease of the rhone river discharge after dam buildings between 1950 and 1958 a residual discrepancy dating before 1950 is likely to be due to seafloor erosion and gravity induced mechanisms

magnetic properties of marine limestones numerous paleomagnetic investigations have been carried out on limestones but their rock magnetic properties have often been neglected in this review geological and rock magnetic factors which determine whether marine limestones are suitable for paleomagnetic study are summarized and laboratory techniques for the identification of the magnetic mineralogy are evaluated the conditions under which pelagic limestones form are especially favorable for the acquisition of a stable primary natural remanence nrm probably by a postdepositional alignment process the effectiveness and timing of acquisition of this remanence are influenced by the thoroughness of bioturbation other remanence components can be acquired during diagenesis in the soft sediment right after deposition or much later even in the indurated limestone the magnetic mineralogy of a limestone is difficult to describe optically because of the small grain size and low concentration magnetic techniques are more convenient direct analysis of extracted magnetic minerals is handicapped by the difficulty of obtaining a representative extract a particularly useful technique involves combined observations of isothermal remanent magnetization irm acquisition in strong fields up to at least 4 t and the subsequent destruction of this irm during stepwise or continuous thermal demagnetization the magnetic minerals most commonly identified by these techniques are magnetite goethite hematite and maghemite these magnetic minerals occur in different combinations in the marine limestones of central europe and the mediterranean realm pyrite is common in certain limestones where it can be the precursor of an unwelcome late goethite pyrrhotite may be responsible for unstable magnetization in the swiss helvetic limestones but otherwise is rare thermal demagnetization of some limestones causes changes of susceptibility and coercivity at quite low temperatures 300 400 c due to the breakdown of a metastable mineral such as maghemite goethite or pyrrhotite at high temperatures above 500 c pronounced changes of magnetic mineralogy occur in all limestones because of the growth of new magnetite this necessitates great care in interpretation of thermal demagnetization of high blocking temperature components and often results in observational difficulties due to viscous remanent vrm behavior of the newly formed magnetite vrm is a widespread component of nrm in many limestones but it can usually be removed effectively by standard magnetic cleaning techniques the susceptibility serves as a simple control of mineralogical change during heating and can serve as an indicator of lithologic variation of magnetic mineral concentration and type in magnetostratigraphic profiles the susceptibility is anisotropic and shows a classical depositional pattern of the distribution of principal axes however the probable postdepositional mechanism of nrm acquisition especially in bioturbated sediments implies that the anisotropy pattern results from postdepositional compaction of the sediment

metal and organic carbon distribution in water column of a shallow enclosed bay at the aegean sea archipelago kalloni bay island of lesvos greece metals and organic carbon concentrations in dissolved and particulate phases were determined seasonally wet and dry periods in four different sites of the semi enclosed shallow marine system of kalloni bay in the island of lesvos greece the bay is a typical system of many mediterranean islands which combine intermittent stream discharges lengthy dry periods and relatively light anthropogenic activities on the coastal zone and the study aimed at the investigation of heavy metal partitioning mechanisms under such conditions seasonal and spatial variations in metal concentrations showed that fluvial transport is the major pathway for cu fe ni and particulate al and li to the bay wet deposition during winter probably determines the distributions of pb and zn manganese distribution appears to be regulated by diagenetic processes in the sediment leading to mn release in the overlying water column lithium is transported in the very fine fraction of suspended particulate matter spm and is uniformly distributed in the area dissolved phase is the major metal carrier for cd cu ni pb and organic carbon while fe and mn are mainly transported in the particulate phase important spatial variations in metal partitioning were observed only for ni because of the presence of nickeliferous ultrabasic minerals at the northeastern part of the bay the concentrations of the human related metals cd cu and zn were low indicating very small anthropogenic influence in the area the concentrations of organic carbon in dissolved doc and particulate poc phases were regulated by primary production as well as fluvial transport and were similar to enclosed eutrophic systems or estuaries

anthropogenic and lithogenic sources of lead in lower silesia southwest poland an isotope study of soils basement rocks and anthropogenic materials to discriminate possible anthropogenic and lithogenic sources of pb in lower silesia sw poland the pb isotope composition was investigated in a spectrum of rocks and anthropogenic materials as well as within 10 soil profiles silicate rocks in lower silesia have 206 pb 207 pb ratios that vary from 1 17 for serpentinites to 1 38 for gneisses and this variability is reflected in the isotope composition of the mineral soil horizons the pb isotope composition of coals ores and anthropogenic materials slags and fly ashes is rather uniform with 206 pb 207 pb ratios ranging from 1 17 to 1 18 similar ratios were observed in ore and coal samples from upper silesia the o soil horizons also have uniform 206 pb 207 pb ratios of 1 17 1 18 and the heterogeneity of the 206 pb 207 pb ratios increases with depth in the soil profiles five soils with varying pb concentrations analysed far from contamination centres show consistent approximately 2 fold enrichment in pb concentration from the c to a horizons which is consistent with natural re distribution of pb within the profiles the increase in the pb concentration is accompanied by a decrease in 206 pb 207

early diagenesis of trace metals used as an indicator of past productivity changes in coastal sediments in sediments of kiel bight which differ significantly in their redox states and the rates of corg degradation depth profiles of both dissolved and solid phase fe mn cd cu ni and co were measured porewater fluxes of cd cu and ni were significantly higher at shallower more oxic stations as compared to highly reducing deeper subthermocline sediments while mn fluxes behaved the opposite way when normalized to fe for grain size correction the measured solid phase metal contents revealed that the high porewater flux has led to a near surface depletion of mn from more anoxic sediments and to a reduced rate of accumulation of anthropogenic cd in more oxic sediments this difference in early diagenetic behaviour suggests the use of these metals as a proxy for the redox state and the intensity of carbon recycling contrary to the recent sediment layers the normalized metal contents of preindustrially deposited sediment layers were similar for both metals at all stations thus at stations having highly anoxic sediments today the preindustrial benthic flux must have been lower for mn and higher for cd reflecting a shift from more oxic to more reducing conditions in subthermocline sediments during the last 100 years this change of the redox state in subthermocline sediments reflects an increase of primary production and of subsequent corg input to the sediment due to eutrophication which accompanied industrialization

single zircon u pb ages and geochemistry of granitoid gneisses from sw poland evidence for an avalonian affinity of the brunian microcontinent seven granitoid gneisses from the contact zone between the eastern margin of the variscan belt and the brunian microcontinent in sw poland have been dated by ion microprobe and 207 pb 206 pb single zircon evaporation methods the zircons define two age groups for the gneiss protoliths 1 late neoproterozoic c 576 560 ma and 2 early palaeozoic c 488 503 ma granites the granitoid gneisses belonging to the basement of the brunian microcontinent contain abundant mesoproterozoic to latest palaeoproterozoic inherited material in the range of 1200 1750 ma the gneisses of the variscan crustal domain lack mesoproterozoic inherited zircon cores trace element geochemistry of proterozoic gneisses reveals features resembling either volcanic arc or post collisional granites the studied rocks are geochemically similar to other proterozoic orthogneisses derived from the basement of the brunian microcontinent gneisses with early palaeozoic protolith ages are geochemically comparable to granitoid gneisses widespread in the adjacent sudetic part of the bohemian massif and are considered characteristic of peri gondwanan crust our data prove the dissimilarity between the brunia plate and the westerly terranes of the variscan belt the occurrence of granitic gneisses with late neoproterozoic protolith ages and widespread mesoproterozoic inheritance in our dated samples support an east avalonian affinity for the brunian microcontinent in contrast the abundance of gneisses derived from an early palaeozoic granitic protolith and devoid of mesoproterozoic zircon cores supports the armorican affinity of the variscan domain bordering on the brunia plate from the west structural evidence shows that the eastern segment of the variscan belt is juxtaposed against the brunian microcontinent along a n s trending tectonic contact possibly equivalent to the rheic suture