model for the evolution of the avalonian cadomian belt the inception and termination of the ca 670 550 ma avalonian cadomian orogenic cycle are interpreted in terms of the amalgamation and breakup of a late precambrian supercontinent synorogenic arc related volcano sedimentary and granitoid rocks are attributed to oblique southward directed subduction along the margin of the supercontinent after its amalgamation breakup of the supercontinent and inception of the iapetus cycle led to termination of subduction and its replacement by transform activity the resulting closure of late precambrian arc related basins and the development of early cambrian platform successions with acado baltic fauna accompanied the formation of iapetus but took place on the active margin of a preexisting ocean and do not record the evolution of its rifted european flank

continuing inflation at three sisters volcanic center central oregon cascade range usa from gps leveling and insar observations uplift of a broad area centered 6 km west of the summit of south sister volcano started in september 1997 onset estimated from model discussed in this paper and was continuing when surveyed in august 2006 surface displacements were measured whenever possible since august 1992 with satellite radar interferometry insar annually since august 2001 with gps and leveling surveys and with continuous gps since may 2001 the average maximum displacement rate from insar decreased from 3 5 cm yr during 1998 2001 to 1 4 cm yr during 2004 2006 the other datasets show a similar pattern i e surface uplift and extension rates decreased over time but deformation continued through august 2006 our best fit model to the deformation data is a vertical prolate spheroidal point pressure source located 4 9 5 4 km below the surface the source inflation rate decreased exponentially during 2001 2006 with a 1 e decay time of 5 3 1 1 years the net increase in source volume from september 1997 to august 2006 was 36 5 41 9 x 106 m3 a swarm of 300 small mmax 1 9 earthquakes occurred beneath the deforming area in march 2004 no other unusual seismicity has been noted similar deformation episodes in the past probably would have gone unnoticed if as we suspect most are small intrusions that do not culminate in eruptions

cambro ordovician anatexis and magmatic recycling at the thinned gondwana margin new constraints from the kouřim unit bohemian massif the kou im unit represents one of the largest pre variscan meta igneous complexes in the bohemian massif and a geochronological whole rock geochemical and sr nd isotopic study was conducted to better understand the magmatic evolution of the early paleozoic gondwana margin five orthogneisses yield u pb zircon ages ranging from 492 4 to 484 2 ma two leucogranites give u pb zircon ages of 500 4 and 485 2 ma interpreted to be inherited from their orthogneiss host rock two samples from the metasedimentary host rock are dominated by neoproterozoic cambrian detrital zircons the abundance of zircon inheritance in the orthogneisses and whole rock sr nd isotopic composition imply an origin from relatively mature continental crustal material the subalkaline subaluminous slightly peraluminous and high k calc alkaline arc like geochemical signature of the orthogneisses is interpreted as inherited from the recycled cadomian metasedimentary source and both the magmatic and metasedimentary rocks are correlated with similar occurrences in the adjacent moldanubicum and tepla barrandian unit the late cambrian early ordovician magmatic activity is linked to crustal anatexis which was probably initiated by thermal and gravitational relaxation of the thickened cadomian arc type crust followed by lithospheric thinning assisted by far field forces the extensional event led to the formation of a passive margin associated with the opening of the rheic ocean supplementary material analytical methods petrographic descriptions with photographs of studied samples collections of cl images of representative zircon grains results of la icp ms u pb analyses of zircons and an additional geochemical diagram are available at https doi org 10 6084 m9 figshare c 4649255

multiphase formation of the obři důl polymetallic skarn deposit west sudetes bohemian massif geochemistry and re os dating of sulfide mineralization the ob i d l fe cu as polymetallic sulfide skarn deposit is developed in a metamorphic series in the west sudetes bohemian massif it consists of lenses of marble calc silicate rocks and skarns we studied the gustav orebody which is located few hundred meters away from the contact with a large late orogenic variscan krkonose jizera plutonic complex kjpc emplaced into shallow crust mineralogical and fluid inclusion study evidence indicates that the main sulfide stage dominated by pyrrhotite arsenopyrite and chalcopyrite originated from aqueous hydrothermal fluids with salinity up to 8 wt nacl eq with minimum homogenization temperatures ranging from 324 to 358 c these fluids mainly replaced carbonate rich lithologies carbon oxygen and strontium isotope data in ca rich rocks imply total overprinting by channelized metasomatic fluid flow which is most probably related to the intrusion of the kjpc whereas 34s values of sulfides argue for a magmatic source of sulfur the re os age of arsenopyrite overlaps published age data for the kjpc and suggests synchronous formation of the main sulfide mineralization and pluton emplacement

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

extreme climatic conditions recorded in santa barbara basin laminated sediments the 1835 1840macoma event abstract the santa barbara basin sbb record of laminated sediment well known for its excellent time resolution shows the presence of an unusual once in a millenium event in the period 1835 1840 at a depth of 55 57 cm below the surface of the seafloor this macoma event is the brief flourishing of a macrofaunal community in the deep center of the sbb from which large organisms are normally excluded by the lack of oxygen shells of the pelecypodmacoma leptonoidea dall and associated fossils which congregate in a thin layer dated at 1840 provide evidence for a sudden local extinction of macrobenthos by suffocation various stratigraphic evidence suggests thatm leptonoidea colonized the basin floor for a few years prior to 1840 as a result of temporarily decreased productivity and increased oxygen content in the water spilling over the sill into the basin historical eyewitness reports indicate unusually severe winter storms from southeasterly directions during the 1830s in the sbb we suggest that coastal upwelling was severely reduced during 1835 1839 with the effect of reducing the intensity of the oxygen minimum layer themacoma event apparently is one manifestation of large scale climatic anomalies felt throughout north america and which were possibly linked to the major volcanic eruption of cosiguina nicaragua in 1835

cambrian ordovician depositional sequences in the middle east a perspective from turkey abstract in southern turkey taurus chain or taurides and southeastern turkey border folds of the arabian plate nearly complete cambrian to ordovician successions are preserved four major sedimentary sequences are defined according to the main transgressive events and the subsequent shelf progradations these sequences allow us to link the turkish mostly distal lower palaeozoic detritals to the more proximal arabian formations in spite of contrasting facies the lower palaeozoic development is outlined through four successive steps defined in southern turkey 1 initiation of a cratonic platform regime terreneuvian i e earliest cambrian depositional sequence 1 with fluviatile conglomerates and red bed sediments associated with volcanics 2 development of a stable marine platform late terreneuvian to early ordovician depositional sequences 2 and 3 including widespread but diachronous middle cambrian carbonates and subsequent storm dominated detritals 3 tectonic instability middle ordovician leading to a new palaeogeography on the gondwana platform with the differentiation of a sag basin bedinan qasim depocenter lower part of depositional sequence 4 and 4 glaciation latest ordovician upper part of depositional sequence 4 identified by glaciomarine deposits forming the hirnantian glacial record this thick 2000 m detrital succession records a first order long term subsidence driven cambrian to ordovician transgressive trend and includes second order sequences reflecting interactions between global eustasy and tectonic instability on a larger scale the identification of recurrent sequence stratigraphic features with similar trends in the cambrian ordovician successions on the arabian platform implies that a former location of the taurus domain cannot be situated in the present day eastern mediterranean area but should lie directly north of the arabian platform this location places southern turkey at the junction between the north african segment of the gondwana siliciclastic shelf to the west present day coordinates and the eastern arabian segment in good agreement with mixed faunal signatures from both areas primary control of the tectonostratigraphic development of southern turkey during the lower palaeozoic may be a forced evolution from arc platform to rift drift transitions cordilleran model that has migrated progressively eastwards from the avalonian domain along the northern gondwana margin to the arabian domain throughout the lower palaeozoic

climatically controlled marker layers in santa barbara basin sediments and fine scale core to core correlation varved sediments with annual layering can provide a detailed history of environmental conditions of marginal ocean basins and of lakes to reconstruct this history requires fine scale correlation and correct age assignment in the santa barbara basin a combination of x radiography water content profiles and microfossil stratigraphy yields correlations of the desired resolution x radiography permits identification of individual layers 1 2 mm thick that differ in porosity or pore water content and hence x ray absorption microfossils and sedimentological parameters provide the clues to the presence for el nino years e g in a d 1984 1959 and 1942 varves allowing the tie in to absolute years within this century el nino layers once identified are readily recognized on the radiographs and within the porosity profiles counting of laminae in x radiographs and core to core correlation via water content then allow establishing age scales for other cores a prominent shell layer in the first half of the 19th century is dated at a d 1838 this event macoma i is of supraregional significance

palaeogeographical controls on the cambrian trilobite immigration and evolutionary patterns reported in the western gondwana margin abstract southward drifting of the western gondwanan margin during the cambrian has been demonstrated by means of both palaeomagnetic methods and lithological indicators of climate such as carbonates and evaporites recent improvements in biostratigraphical correlations permit an enhanced understanding of the climatic and palaeobiogeographical constraints that controlled the distribution of cambrian benthic communities palaeogeographical and biogeographical reconstructions based on trilobites are reported in this paper in order to test interaction between migration speciation and extinction rates the variability of the documented biogeographical patterns is directly related to species diversity in which wider distribution coincides with transgressive trends and subsequent connection of neighbouring platforms early cambrian trilobite faunas show a high degree of both substrate control and endemicity although transgressions led to parallel shifts in faunal compositions by contrast mid cambrian trilobite faunas are relatively uniform across western gondwana and latest mid and late cambrian associations document influence of an increased similarity with asian trilobite faunas

deflection of dykes into sills at discontinuities and magma chamber formation abstract many rift zones contain composite volcanoes central volcanoes most of which are supplied with magma from shallow crustal magma chambers volcanotectonic studies of eroded rift zones such as in iceland as well as geophysical studies indicate that many shallow magma chambers evolve from sills here i provide field description of sills and extinct magma chambers in the quaternary and tertiary palaeorift zones of iceland focusing on the felsic pluton of slaufrudalur southeast iceland as a fine example of a magma chamber developed through the injection of sills in this paper i review analyse and develop further two related mechanisms for the deflection of dykes into sills and thus the potential initiation of a magma chamber namely a cook gordon debounding delamination and b stress barriers and propose a third mechanism c favourable material toughness ratios due to elastic mismatch difference in young s moduli or stiffnesses of layers in contact in the cook gordon mechanism a weak contact opens up as a result of dyke induced tensile stress this mechanism is likely to operate primarily at shallow depths as is supported by field observations and numerical models a stress barrier is a layer where the local stress is unfavourable to a particular type of rock fracture here a dyke field observations and numerical models show that on meeting a stress barrier a dyke either changes into a sill or becomes arrested the material toughness mechanism indicates that when the upper layer at a contact has the same or less stiffness than the lower layer hosting the dyke there is little tendency for the dyke to become deflected into the contact however when the upper layer is stiffer such as when a stiff basaltic lava flow is on the top of a soft pyroclastic layer the dyke tends to become deflected into the contact to form a sill field results suggest that all these mechanisms may cause dyke deflection into sills and may operate together particularly where the rock consists of alternating soft and stiff layers since the quaternary lava pile in iceland has many more soft hyaloclastite layers than the tertiary lava pile these mechanisms were probably very efficient in generating sills and by implication shallow magma chambers during the quaternary this may be one reason why in comparison with the tertiary lava pile the quaternary lava pile contains so many sills and extinct plutons and active shallow magma chambers

duration of the early cambrian u pb ages of volcanic ashes from avalon and gondwana volcanic zircons from three ashes give a u pb date of 511 1 ma on trilobite bearing upper lower cambrian upper branchian series strata of southern new brunswick that correlate into the siberian middle botomian toyonian stage interval this very young age on the late but not latest early cambrian of avalon is consistent both with a 519 1 ma age on the older caerfai bay shales of south wales that are tentatively correlated into strata with the oldest avalonian trilobites lower branchian and with a 517 1 5 ma age on the antatlasia gutta pluviae zone trilobites of morocco determination of a 522 2 ma zircon age on the moroccan subtrilobitic lower cambrian lie de vin formation is consistent with an earlier reported 521 7 ma age from the lie de vin but suggests that a 526 4 ma age on australian trilobite bearing lower cambrian rocks may be too old a 33 ma duration of the avalonian early cambrian and an 8 ma length of the avalonian trilobite bearing lower cambrian support proposals that

vestiges of saxothuringian crust in the central sudetes bohemian massif zircon evidence of a recycled subducted slab provenance abstract four detrital zircon concentrates from the metasediments and metavolcanics of the central sudetes bohemian massif have been dated using shrimp ii the wyszki paragneiss yielded precambrian age spectra similar to those characteristic of the cadomian terranes 1 archaean and palaeoproterozoic zircons are scattered between 2830 and 1867 ma and 2 there are abundant neoproterozoic zircons dated at 803 577 ma the estimated maximum sedimentation age for this rock is 566 4 ma the klodzko fortress pyroclastic metarhyodacite gave an igneous emplacement age of 536 2 ma the magmatic precursor to the subvolcanic gniewoszow metarhyolite was dated at 501 3 ma finally the cinawica subvolcanic rhyolite yielded an igneous emplacement age of 338 3 ma and a large population of inherited zircons dated at palaeoproterozoic neoproterozoic cambro ordovician and late devonian early carboniferous the dated samples come from two adjacent suspect terranes the orlica nieznik dome and the klodzko massif in the central sudetes that are characterised by contrasting timing of metamorphism and exhumation despite this difference the results obtained show in conjunction with earlier data a similar provenance of the studied units and their common affinity to the saxo thuringian terrane since the central sudetes are separated from saxo thuringia by a collisional suture the pre variscan rocks must represent the deformed and metamorphosed allochthonous equivalents to saxo thuringian lithologies they were probably subducted together with the saxo thuringian passive margin during a variscan collision and then exhumed within an accretionary wedge in front of brunia east avalonia the central sudetic suspected terranes must have been derived from a dismembered single accretionary complex and were then juxtaposed by strike slip faults

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

sedimentary patterns across the lower middle cambrian transition in the esla nappe cantabrian mountains northern spain in the carbonate platforms of the western gondwana margin the extinction recorded at the lower middle cambrian boundary is accompanied by a profound change in the style of carbonate deposition the lancara formation of the esla nappe cantabrian mountains northern spain contains a distinct sedimentary turnover due to a combination of tectonism eustatic fluctuations and immigration and colonization of new benthic communities such as the youngest archaeocyathan assemblage of the entire iberian peninsula during latest early cambrian times a regressive trend is recorded in the lancara formation this regression was recorded on a peritidal dominant homoclinal ramp that is topped by a tectonically induced discontinuity d1 the latter surface marks the beginning of a last prograding regressive tendency recorded on an intra shelf ramp with ooidal bioclastic shoals protecting archaeocyathan microbial patch reefs the overlying discontinuity d2 corresponds to a major erosive unconformity which coincides with the lower middle cambrian boundary in the cantabrian mountains the subsequent long term earliest middle cambrian rise in relative sea level allowed deposition of low relief bioclastic shoals bearing a diverse and cosmopolitan assemblage of benthic fauna finally the previous evolution is bounded by a third discontinuity d3 which marks the beginning of a rhythmic sedimentation indicative of a major phase of tectonic breakdown and drowning of platforms recognised throughout southwestern europe two associations of calcimicrobes occur in the latest early cambrian regressive trend of the lancara formation i proaulopora and subtiflora are identified in peritidal high energy settings lacking self supported structures whereas ii intergrowths of epiphyton renalcis and girvanella encrusted branching colonies and solitary archaeocyaths in protected back shoal patch reefs the latest early cambrian regression is correlated in southwestern europe in both siliciclastic iberian chains and ossa morena and carbonate dominant platforms cantabrian mountains montagne noire and sardinia its tops are recognised as diachronous unconformities ranging in age from early bilbilian to the bilbilian leonian or lower middle cambrian boundary

location of the rheic suture in the eastern bohemian massif evidence from detrital zircon data introductionthe variscan orogen of europe con tains a collection of terranes that weredispersed along the northern marginof west gondwana in the late neo proterozoic and early palaeozoic e g murphy et al 2002 linnemannet al 2007 nance et al 2008 theseperi gondwanan terranes show anumber of common features as 1 voluminous late neoproterozoic c 640 550 ma arc magmatism 2 extensive volcano sedimentary succes sions of cogenetic arc related basins 3 a widespread cadomian unconfor mity separating deformed precam brian rock units from their earlypalaeozoic cambro ordovician overstep sequence and 4 an overlyingearly middle cambrian shallow marine platform e g murphy andnance 1989 nance et al 1991 2002 the peri gondwanan terranesrepresent dismembered fragments ofthe avalonian cadomian orogenthat was formed in the late neoprote rozoic c 700 540 ma at the north ern edge of gondwana e g nanceet al 2002 linnemann et al 2007 in the early palaeozoic several peri gondwanan terranes were separatedfrom west gondwana e g avalonia while others including the cadomianterranes remained attached togondwana and were accreted intothe appalachian variscan orogenwith the closure of the rheic ocean inthe late palaeozoic e g linnemannet al 2004 nance et al 2008 pres ently the cadomian terranes areincluded within the variscan belt ofeurope as separate blocks that stretchout from the iberian massif to thesaxo thuringian and tepla barran dian zones fig 1 e g linnemannet al 2008 nance et al 2008 the occurrences of neoproterozoicrocks have long been known from thecentral sudetic segment of the easternvariscides fig 2 although their pre cise age and provenance remainedunclear e g aleksandrowski and ma zur 2002 only recently jastrze bskiet al 2010 reported from the orlica s nieznik dome in the central sudetes a metamorphosed volcano sedimen tary succession continuing from thelate neoproterozoic into the early pal aeozoicwithoutacadomianunconfor mity if uninterrupted sedimentationwas actually the case across theneoproterozoic palaeozoic boundary c 542 ma the orlica s nieznik dome would lack a cadomian a nity con sequently the central sudetes wouldrepresent an exotic terrane insertedbetween the cadomian terranesand east avalonia in such a case existing plate tectonic models for theclosure of the rheic ocean wouldrequiresubstantialrevision in this article we present new sen sitive high resolution ion micro probe shrimp u pb data fordetrital zircon grains to constrain theage and provenance of selectedmetasediments from the orlica s nieznik dome fig 2 these geo chronological data in combinationwith eld relations and publishedresults are used to identify the plate tectonic setting s of neoproterozoicto cambro ordovician rock units ofthe orlica s nieznik dome we then compare the new results with theneoproterozoic to early palaeozoicstratigraphy of the saxo thuringianzone to test the cadomian a nity ofthe central sudetes our goal is toconstrain the eastern extent of thecadomian terranes and the location ofthe rheic suture in central europe geological settingthe orlica s nie znik dome fig 2 isdominated by amphibolite grade or thogneiss locally containing lenses of u hp rocks alternating with belts ofstaurolite grade supracrustal rocks don et al 1990 the orthogneiss istraditionally subdivided into two maintextural varieties fig 2 the por phyric augen to banded s nieznik abstract

recent advances in sar interferometry time series analysis for measuring crustal deformation abstract synthetic aperture radar sar interferometry is a technique that permits remote detection of deformation at the earth s surface and has been used extensively to measure displacements associated with earthquakes volcanic activity and many other crustal deformation phenomena analysis of a time series of sar images extends the area where interferometry can be successfully applied and also allows detection of smaller displacements through the reduction of error sources here we review recent advances in time series sar interferometry methods that further improve accuracy this is particularly important when constraining displacements due to processes with low strain rates such as interseismic deformation we include examples of improved algorithms applied to image deformation associated with the 2010 eruption of eyjafjallajokull volcano in iceland slow slip on the guerrero subduction zone in mexico and tectonic deformation in western anatolia turkey

cambrian ensialic rift related magmatism in the ossa morena zone evora aracena metamorphic belt sw iberian massif sm nd isotopes and shrimp zircon u th pb geochronology abstract the late ediacaran c 560 550 ma serie negra sediments of the evora aracena metamorphic belt ossa morena zone sw iberian massif preserve a record of the erosion of an avalonian cadomian magmatic arc and subsequent related turbiditic sedimentation detrital zircon from the serie negra is characterized by predominantly ediacaran and cryogenian ages with few paleoproterozoic and archean cores and a marked lack of grenvillian ages these features when combined with the metasediments enrichment in lree la yb 14 negative eu anomalies low 147 sm 144 nd values 0 121 and negative e nd 550 5 5 indicate that the protolith serie negra sediments were derived from a continental magmatic arc a period of late cadomian ca 560 540 ma tectonism was followed by an extended episode of widespread bimodal magmatism related to cambrian ca 540 500 ma rifting this tectonic inversion is expressed in the geological record by a regional early cambrian unconformity shrimp zircon u th pb ages from four felsic orthogneisses from the evora massif record cambrian 527 10 ma 522 5 ma 517 6 ma and 505 5 ma crystallization ages for their igneous protoliths this confirms the existence of widespread lower paleozoic igneous activity in the ossa morena zone i a lower cambrian ca 535 515 ma igneous felsic dominated sedimentary complex with calc alkaline signature and associated carbonate and siliciclastic deposition and ii a middle cambrian ordovician ca 515 490 ma igneous bimodal sedimentary complex with calc alkaline and tholeiitic signatures and associated dominant siliciclastic deposition but also carbonate sediments the cambrian felsic magmatism was characterized by negative eu anomalies la lu n 0 8 11 147 sm 144 nd 0 1289 0 1447 and e nd 500 ranging from 1 5 to 0 8 a tendency towards peraluminous compositions suggests late fractionation low degrees of partial melting or the mixing of crustal and mantle derived material in the magma source region some felsic rocks possibly represent the last residual melts of high temperature zircon undersaturated mafic magmas later affected by crustal contamination while others indicate partial melting of crustal metasediments variably contaminated by basaltic liquids the transition from early felsic dominated to later more mafic magmatism suggests the gradual opening of the system to tholeiitic n e morb products th n ta n 147 sm 144 nd 0 1478 0 1797 and e nd 500 values ranging from 6 4 to 7 3 while the n morb amphibolites have 147 sm 144 nd 0 1818 0 1979 and e nd 500 values of 5 8 and 7 0 reaching a maximum of 9 1 in contrast other amphibolites have a negative ta anomaly 1 35 n ta n 147 sm 144 nd values ranging from 0 1639 to 0 1946 and e nd 500 values of 3 5 to 5 2 suggesting derivation by crustal assimilation processes the sub alkaline igneous precursors of the amphibolites were most likely generated in a rift setting by asthenospheric upwelling these results strengthen the proposed geodynamic scenarios for the sw iberian massif by which cadomian accretion gave rise to an ensialic rift that developed into a proto oceanic basin and incipient spreading opening of the rheic ocean a similar transition from a convergent to a divergent plate boundary during the ediacaran to cambrian ordovician has also been reported in other segments of the northern gondwana margin

upper neoproterozoic lower cambrian sedimentary successions in the central iberian zone spain sequence stratigraphy petrology and chemostratigraphy implications for other european zones o3 tio2 zr and nb abundances in shales from all the units strongly suggest a gradual compositional change within this sedimentary succession together with the petrological data the chemical results do not reveal any obvious coeval volcanic contribution to the sediments on the basis of the chemical data a comparison is made with other european zones containing detrital sediments composed of reworked crustal components

from quiescence to unrest 20 years of satellite geodetic measurements at santorini volcano greece periods of unrest at caldera forming volcanic systems characterized by increased rates of seismicity and deformation are well documented some can be linked to eventual eruptive activity while others are followed by a return to quiescence here we use a 20 year record of interferometric synthetic aperture radar insar and gps measurements from santorini volcano to further our understanding of geodetic signals at a caldera forming volcano during the periods of both quiescence and unrest with measurements spanning a phase of quiescence and slow subsidence 1993 2010 followed by a phase of unrest january 2011 to april 2012 with caldera wide inflation and seismicity mean insar velocity maps from 1993 2010 indicate an average subsidence rate of 6 mm yr over the southern half of the intracaldera island nea kameni this subsidence can be accounted for by a combination of thermal contraction of the 1866 1870 lava flows and load induced relaxation of the substrate for the period of unrest we use a joint inversion technique to convert insar measurements from three separate satellite tracks and gps observations from 10 continuous sites into a time series of subsurface volume change the optimal location of the inflating source is consistent with previous studies situated north of nea kameni at a depth of 4 km however the time series reveals two distinct pressure pulses the first pulse corresponds to a volume change v within the shallow magma chamber of 11 56 0 14 106 m3 and the second pulse has a v of 9 73 0 10 106 m3 the relationship between the timing of these pulses and microseismicity observations suggests that these pulses may be driven by two separate batches of magma supplied to a shallow reservoir we find no evidence suggesting a change in source location between the two pulses the decline in the rates of volume change at the end of both pulses and the observed lag of the deformation signal behind cumulative seismicity suggest a viscoelastic response we use a simple model to show that two separate pulses of magma intruding into a shallow magma chamber surrounded by a viscoelastic shell can account for the observed temporal variation in cumulative volume change and seismicity throughout the period of unrest given the similarities between the geodetic signals observed here and at other systems this viscoelastic model has potential use for understanding behavior at other caldera systems

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

the effects of topography on magma chamber deformation models application to mt etna and radar interferometry we have used a three dimensional elastic finite element model to examine the effects of topography on the surface deformation predicted by models of magma chamber deflation we used the topography of mt etna to control the geometry of our model and compared the finite element results to those predicted by an analytical solution for a pressurized sphere in an elastic half space topography has a significant effect on the predicted surface deformation for both displacement profiles and synthetic interferograms not only are the predicted displacement magnitudes significantly different but also the map view patterns of displacement it is possible to match the predicted displacement magnitudes fairly well by adjusting the elevation of a reference surface however the horizontal pattern of deformation is still significantly different thus inversions based on constant elevation reference surfaces may not properly estimate the horizontal position of a magma chamber we have investigated an approach where the elevation of the reference surface varies for each computation point corresponding to topography for vertical displacements and tilts this method provides a good fit to the finite element results and thus may form the basis for an inversion scheme for radial displacements a constant reference elevation provides a better fit to the numerical results

micropaleontologie du proterozoique du massif armoricain france abstract upper proterozoic sediments brioverian of brittany and normandy france contain microfossils of algal affinities 1 1 assemblages of solitary and colonial vegetative cells and possibly sporulating cells which seem strikingly similar to sphaerocongregus variabilis reported from late precambrian sedimentary rocks in north america paleocryptidium described in brittany and reported from proterozoic rocks of bohemia is probably conspecific of sphaerocongregus in brittany and normandy these assemblages are particularly abundant in lower and middle brioverian sedimentary rocks 670 1000 ma 2 2 assemblages of solitary and colonial cells which can be compared with various species of favososphaera reported from the upper proterozoic of europe in brittany these assemblages have only been detected in upper brioverian sandstones and limestones 670 580 ma

early cambrian palaeogeography and the probable iberia siberia connection abstract the end of the proterozoic beginning of the cambrian is marked by some of the most dramatic events in the history of earth the fall of the ediacaran biota followed by the cambrian explosion of skeletonised bilaterians a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from snowball earth to greenhouse conditions all happened within a rather geologically short period of time these events took place against a background of the rearrangement of the prevailing supercontinent some authors view this as a sequence of individual supercontinents such as mesoproterozoic midgardia neoproterozoic rodinia and early cambrian pannotia assembled in the mesoproterozoic this supercontinent appears to have existed through the neoproterozoic into the early cambrian with periodic changes in configuration the final rearrangement took place during the precambrian cambrian transition with the cadomian and related phases of the pan african orogeny the distribution of early cambrian molluscs and other small shelly fossils ssf across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time subsequently rodinia experienced breakup that led to the amalgamation of gondwana separation of laurentia baltica siberia and some small terranes and the emergence of oceanic basins between them spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the vendian early cambrian

the importance of along margin terrane transport in northern gondwana insights from detrital zircon parentage in neoproterozoic rocks from iberia and brittany abstract detrital zircons from late neoproterozoic rocks of the peri gondwanan cadomian belt of sw iberia and north armorican domain of brittany record neoproterozoic ca 860 550 ma palaeoproterozoic ca 2300 1800 and archaean ca 3300 2600 ma u pb ages the absence of mesoproterozoic zircons suggests that these terranes evolved in a peri w african realm this is in contrast to other western european terranes that preserve mesoproterozoic zircons and are likely to have evolved in a peri amazonian realm such a contrast in detrital zircon populations coupled with the presence of mesoproterozoic zircons in the ordovician armorican quartzite deposited in a peri african platform is interpreted to record along margin terrane transport the change in provenance suggests that subduction was replaced by transform faults that juxtaposed amazonia derived terranes against w africa derived terranes to form the avalonia and armorica microcontinents subsequent extension along the margin resulted in the birth of the rheic ocean and the outboard drift of avalonia

community benthic paleoecology from high resolution climate records mollusca and foraminifera in post glacial environments of the california margin abstract paleoecological reconstructions of past climate are often based on a single taxonomic group with a consistent presence less is known about the relationship between multi taxon community wide change and climate variability here we reconstruct paleoecological change in a late quaternary 16 1 3 4 ka sediment core from the california margin 418 m below sea level of santa barbara basin sbb usa using mollusca animalia and foraminifera rhizaria microfossils building upon previous investigations we use multivariate ordination and cluster analyses to interpret community scale changes in these distinctly different taxonomic groups across discrete climate episodes the strongest differences between seafloor biological communities occurred between glacial prior to termination ia 14 7 ka and interglacial climate episodes holocene communities were well partitioned indicating that sub millennial oceanographic variability was recorded by these microfossils we document strong evidence of chemosynthetic trophic webs and sulfidic environments from gastropod alia permodesta and bivalve lucinoma aequizonata which characterized restricted intervals previously interpreted as well oxygenated such as the pre bolling warming mollusc records indicate first order trophic energetic shifts between detrital and chemosynthetically fixed carbon molluscs associated with widely different physiological preferences occur here within single decadal intervals of sediment and as such mollusc assemblages may reflect significant inter decadal oceanographic variability foraminifera assemblages provide exceptional records of the sequential chronological progression of the deglacial climatic and oceanographic events whereas mollusc assemblages reflect non chronological similarities in reoccurring communities foraminifera taxa that drive community similarity here are also independently recognized as marker species for seafloor hypoxia regimes which provides support for the idea that oxygenation change is a principal driver of seafloor environmental variability

deep intrusions lateral magma transport and related uplift at ocean island volcanoes abstract oceanic intraplate volcanoes grow by accumulation of erupted material as well as by coeval or discrete magmatic intrusions dykes and other intrusive bodies within volcanic edifices are comparatively well studied but intrusive processes deep beneath the volcanoes remain elusive although there is geological evidence for deep magmatic intrusions contributing to volcano growth through uplift this has rarely been demonstrated by real time monitoring here we use geophysical and petrological data from el hierro canary islands to show that intrusions from the mantle and subhorizontal transport of magma within the oceanic crust result in rapid endogenous island growth seismicity and ground deformation associated with a submarine eruption in 2011 2012 reveal deep subhorizontal intrusive sheets sills which have caused island scale uplift of tens of centimetres the pre eruptive intrusions migrated 15 20 km laterally within the lower oceanic crust opening pathways that were subsequently used by the erupted magmas to ascend from the mantle to the surface during six post eruptive episodes between 2012 and 2014 further sill intrusions into the lower crust and upper mantle have caused magma to migrate up to 20 km laterally resulting in magma accumulation exceeding that of the pre eruptive phase a comparison of geobarometric data for the 2011 2012 el hierro eruption with data for other atlantic intraplate volcanoes shows similar bimodal pressure distributions suggesting that eruptive phases are commonly accompanied by deep intrusions of sills and lateral magma transport these processes add significant material to the oceanic crust cause uplift and are thus fundamentally important for the growth and evolution of volcanic islands we suggest that the development of such a magma accumulation zone in the lower oceanic crust begins early during volcano evolution and is a consequence of increasing size and complexity of the mantle reservoir system and potentially the lithospheric stresses imposed by increasing edifice load

deep magma storage at hekla volcano iceland revealed by insar time series analysis 1 hekla volcano is one of the most active volcanoes in iceland the most recent eruption occurred from 26 february to 8 march 2000 when about 0 19 km3 of magma was erupted we present deformation data from multitemporal analyses of synthetic aperture radar sar images acquired between 1993 and 2008 focusing on pixels with low phase variance using persistent scatterer and small baseline approaches prior to and after the 2000 eruption we find a broad area of inflation around the volcano radius about 20 km with satellite line of sight los shortening of up to 5 mm yr we interpret this signal as the result of pressure increase in a deep seated magma chamber which we model as a spherical source at 14 20 km depth increasing in volume by 0 003 0 02 km3 yr within a 6 km radius of the summit of the volcano a los lengthening is superimposed on the broad inflation signal which correlates partly with recent lava flows we interpret this signal as the result of thermally contracting lava flows combined with viscoelastic yielding due to the load of the volcano and its lavas coeruptive deflation during the 2000 eruption was similar to the cumulative inflation from 1993 to 2000 and is consistent with a spherical magma chamber at 14 18 km depth that decreases in volume by 0 04 0 08 km3 interferograms spanning the 2000 eruption show a local coeruptive deformation signal near the eruptive fissure this is consistent with a dike opening from the surface to depths up to 5 8 km with a volume of 0 005 0 006 km3

the cadomian orogeny in saxo thuringia germany geochemical and nd sr pb isotopic characterization of marginal basins with constraints to geotectonic setting and provenance abstract the cadomian basement and the cambro ordovician overstep sequence in saxo thuringia is characterized by clastic sedimentation from the late neoproterozoic to the ordovician magmatism in the avalonian cadomian arc preserved in saxo thuringia occurred between ca 570 and 540 ma peri gondwanan basin remnants with cadomian to early palaeozoic rocks are exposed as very low grade metamorphosed rocks in six areas schwarzburg anticline berga anticline doberlug syncline north saxon anticline lausitz anticline and elbe zone a hiatus in sedimentation between 540 and 530 ma cadomian unconformity is related to the cadomian orogeny a second gap in sedimentation occurred during the upper cambrian 500 to 490 ma and is documented by a disconformity between lower to middle cambrian rocks and overlying tremadocian sediments major and trace element signatures of the cadomian sediments reflect an active margin continental arc those of the ordovician sediments a passive margin the cambrian sediments have inherited the arc signature through the input of relatively unaltered cadomian detritus initial nd and pb isotope data from the six saxo thuringian areas demonstrate that there is no change in source area with time for each location but that there are minor contrasts among the locations 1 cadomian sediments from the lausitz anticline the doberlug syncline and the elbe zone have lower 207pb 204pb than all other areas 2 the core of the schwarzburg anticline which is overprinted by greenschist facies conditions and detached is isotopically heterogeneous one part of its metasedimentary units has less radiogenic nd than sediments from other low grade units of similar age in the same area 3 cadomian sediments from the schwarzburg anticline show an input of younger felsic crust 4 the rothstein group shows distinct input of young volcanic material also 5 cadomian sediments from the lausitz anticline the elbe zone and parts of the north saxon anticline are characterized by input from an old mafic crust nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1 5 1 9 ga which suggests derivation from an old craton as found for other parts of the iberian armorican terrane collage similarly the pb isotope data of all areas indicate sediment provenance from an old craton the rapid change of lithologies from greywacke to quartzite from the late neoproterozoic cadomian basement to the ordovician does not reflect changes in sediment provenance but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation this change in sediment maturity takes its chemical expression in lower overall trace element contents in the quartzite dilution effect by quartz and relative enrichment of some trace elements zr mree hree due to detrital zircon and garnet the rb sr systematics of the quartzites and one ordovician tuffite was disturbed most likely during the variscan orogeny which suggests a lithology controlled mobility of alkali and calc alkali elements by comparison with available data it seems unlikely that only nd tdm model ages are useful to distinguish between west african and amazonian provenance nd tdm model ages of 1 5 to 1 9 ga in combination with paleobiogeographic aspects age data from detrital zircon and palaeogeographic constraints especially through tillites of the saharan glaciation in the hirnantian strongly indicate a provenance of saxo thuringia from the west african craton

superposed hercynian and cadomian orogenic cycles in the ossa morena zone and related areas of the iberian massif polyphase ductile deformation and metamorphism in the ossa morena zone of the iberian massif are related to a complex evolution including two major tectonothermal episodes of cadomian late proterozoic to early cambrian and hercynian age middle to late paleozoic petrological structural and geochronological data attest to a number of tectonic episodes in the 620 480 ma interval the model presented for this orogeny comprises stages of volcanic arc generation backarc extension tectonic inversion crustal thickening and cratonization in an andean type continental margin the hercynian cycle began in the early paleozoic with episodes of continental rifting orogenic events occurred in the 390 300 ma interval and affected both the cadomian basement which was heterogeneously reworked and overprinted and the paleozoic cover hercynian regional metamorphism was generally of low grade high pressure assemblages and thermal domes developed locally and were related to subduction and late extensional events the geodynamic model proposed for the cadomian and hercynian orogenies and the correlation with comparable areas from pre mesozoic massifs elsewhere in western europe account for the geodynamic scenarios that drove the fate of cadomian terranes

precursory inflation of shallow magma reservoirs at west sunda volcanoes detected by insar 1 we use 2006 2009 alos interferometric synthetic aperture radar data over the entire west sunda arc indonesia home of 13 of the world s active volcanoes to derive arc wide time dependent ground deformation data we present unambiguous evidence of inflation at six volcanoes three of which erupted after the observation period we show that these volcanoes have shallow magma reservoirs at 1 3 km depth below the average regional elevation a global comparison of reservoir depths at arc volcanoes suggests that volcanoes in extensional and strike slip settings west sunda can develop shallow reservoirs whereas volcanoes in compressional settings may lack them thus magma ascend through the upper crust could be influenced by intra arc tectonic settings

foraminiferal proxy response to ocean temperature variability and acidification over the last 150 years in the santa barbara basin california abstract the last 150 years on the california margin have been marked by high variability in precipitation temperature sea surface temperature and ocean chemistry in response to both natural and anthropogenic changes deciphering climate history from ocean sediments is dependent on our understanding of the various influences on marine proxies sediment from santa barbara basin sbb california box core spr0901 10bc provides an opportunity to compare multiple marine proxies with instrumental records of climate of the past 150 years and extend them beyond the historical record here we use three planktonic foraminiferal proxies 18ocalcite mg ca and size normalized shell weight to reconstruct the surface temperature and 18owater in sbb california at near annual resolution from ad 1850 2000 results indicate that globigerina bulloides mg ca reflects the instrumental temperature trends over the last 150 years with average mg ca temperatures approximately 2 c lower than instrumental values due to the slightly deeper habitat preference of g bulloides similarly temperature is the dominant control on g bulloides 18ocalcite and both mg ca and 18ocalcite reflect variability consistent with changes in the intensification of enso over the past 150 years shell weights of the planktic foraminifer g bulloides are inversely correlated with historical sea surface temperatures over the last 150 years in sbb sediments greater shell weight associated with cooler surface ocean temperatures does not support the anticipated relationship between coastal upwelling of cool low ph water and shell thinning due to co 3 2 undersaturation however in contrast to the previous 130 years g bulloides shells deposited on the sea floor since the late 1970s exhibit a distinctive smooth shell structure indicative of partial dissolution we hypothesize that a mid 1970s shift in intermediate water flow from predominantly equatorward to anomalously poleward led to the influx of relatively corrosive bottom water into sbb with subsequent carbonate dissolution at the sediment water interface

neoproterozoic cambrian synsedimentary magmatism in the central iberian zone spain geology petrology and geodynamic significance petrographic geochemical and field studies in low grade metamorphic areas ciudad rodrigo hurdes sierra de gata domain crhsg central western spain show that neoproterozoic lowermost cambrian series in the central iberian zone ciz record two kinds of provenance sources including 1 detrital material derived from recycled orogens and 2 a cadomian coeval juvenile contribution that governs their isotopic signature evidence of magmatism contemporaneous with neoproterozoic cambrian sedimentation is provided by the presence of coherent massive volcanic rocks metabasalts metaandesites and metarhyolites volcaniclastic shales sandstones conglomerates and breccias the appearance of volcanogenic lithic fragments and crystals mixed in different proportions with siliciclastic constituents and also present within calcareous components in the sedimentary succession reinforces this evidence although most of the selected volcanic and volcaniclastic samples appear to show tholeiitic affinity some of them display calc alkaline affinity different trace element ratios such as sm nd nb yb and ta yb suggest a magmatic evolution in the same tectonic setting the geochemical results reported here support the existence of an active geodynamic setting as a direct contributor to the synsedimentary and magmatic content of the neoproterozoic lowermost cambrian successions in the ciz in particular the relatively high end t values and the high range of f sm nd ratios are consistent with an active margin during the neoproterozoic early cambrian the existence of tectonic activity is also confirmed by the presence of synsedimentary deformation and volcanic rocks all of these traits favour a geodynamic model in which the iberian cadomian segment represented in the ciz would have been part of an active northern margin of gondwana with an associated magmatic arc and related basins during neoproterozoic lower cambrian times a proposed link between the ossa morena and the central iberian zones might account for late cadomian pull apart basins developed on both sides of the magmatic arc sharing the same scenario and involving similar magmatic activity during the neoproterozoic cambrian transition

the cadomian unconformity in the saxo thuringian zone germany palaeogeographic affinities of ediacaran terminal neoproterozoic and cambrian strata abstract the most complete ediacaran terminal neoproterozoic to early cambrian record in the saxo thuringian zone is provided by the cadomian deformed ediacaran rothstein formation and the unconformably overlying early cambrian zwethau formation in the torgau doberlug syncline tds conglomerates and greywackes of the marine rothstein formation are of continental magmatic arc provenance and record detrital zircon shrimp ages that indicate a late cryogenian to early ediacaran 700 580 ma age for the arc source and its emplacement into palaeoproterozoic 2000 ma crust tuffaceous intercalations record extrabasinal eruptions of evolved calc alkaline lavas that point to ongoing cadomian continental arc magmatism shrimp zircon ages from a tuffaceous layer date this volcanic activity and the formation s deposition as late ediacaran 566 10 ma close correlation in provenance and age to other ediacaran units of the saxo thuringian zone points to a common palaeogeographic setting in the avalonian cadomian belt detrital and inherited zircon ages and nd isotopic ratios from these ediacaran siliciclastic rocks suggest a position on the active margin of gondwana near the west african craton the early cambrian zwethau formation records the erosion of the underlying ediacaran rocks followed by the successive evolution of i a carbonate dominated subtidal ramp with calcimicrobial archaeocyathan buildups ii a shallow subtidal to intertidal mixed ramp with peritidal sediments and oolite shoal complexes and iii a more siliciclastic depositional environment calcimicrobial archaeocyathan buildups oolite shoals and sulfate nodules in intertidal sediments indicate warm arid to semi arid climatic conditions and a palaeogeographic setting in equatorial to sub equatorial latitudes archaeocyaths the trilobite taxon dolerolichia and the sedimentary facies assemblages compare closely to those of the mediterranean early cambrian constraining the palaeogeographic setting to the european sub equatorial western gondwana shelf realm archaeocyaths record a mid early cambrian middle issendalenian ovetian age making these the oldest cambrian sediments in both the saxo thuringian zone and the bohemian massif the middle cambrian lithological and palaeontological records of the tds closely resemble those of the frankenwald area of the saxo thuringian zone as well as those of other fragments of the western gondwana shelf in spain morocco and bohemia archaeocyaths early cambrian trilobites and correlations with morocco suggest cambrian deposition commenced at ca 520 ma such that the cadomian unconformity represents a time gap of about 35 55 ma latest ediacaran to early lower cambrian this gap which is related to the cadomian orogeny and so common to all areas of the cadomian belt obscures some of palaeobiological palaeogeographic and climatic change that marks the precambrian cambrian transition

bromine counts from xrf scanning as an estimate of the marine organic carbon content of sediment cores 1 xrf sediment core scanning technology is increasingly used to quantify sediment composition the overall good correlation between biophilic halogen bromine br and sedimentary total organic carbon toc potentially allows the fast estimation of down core toc profiles by xrf scanning in order to test this approach we present data from the arabian sea and a mediterranean brine basin comparing xrf core scanning br data with discrete sample toc analyses overall br counts and toc show a clear correlation except when stable carbon isotope and c n data indicate intervals characterized by enhanced input of terrestrial organic matter hence solid phase br is exclusively associated with marine organic matter moc and can be used as a direct estimate of this parameter after a calibration is established high pore water br in the brine core steepens the br toc correlation but after salt correction shows a nearly identical gradient to that of the arabian sea core

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

diagenesis and iron paleo redox proxies new perspectives from magnetic and iron speciation analyses in the santa barbara basin abstract sedimentary redox proxies are usually employed to reconstruct the paleo redox conditions of bottom water environments assuming that porewater and bottom water dissolved oxygen concentrations are similar using a combination of geochemical and magnetic techniques we investigate the relationship between iron speciation and mineralogy in recent 1760 2009 ce sediments retrieved from the santa barbara basin sbb a modern silled basin with low oxygen dissolved o2

calcareous phytoplankton response to the half century of interannual climatic variability in santa barbara basin california 1 a high resolution study of calcareous phytoplankton in a box core from the santa barbara basin sbb reveals floral assemblage fluctuations which can be related to climatic and paleoceanographic changes during the last half century 1940 1996 in particular gephyrocapsa oceanica production increased during el nino periods in response to high temperatures silica depletion and increased iron availability conversely helicosphaera carteri flux increases in conjunction with lower surface temperatures associated with la nina episodes increasing abundances of florisphaera profunda and umbilicosphaera sibogae after 1970 reflect a warming trend and increased stratification within the basin associated with the warm phase of the pacific decadal oscillation pdo conversely increased abundances of coccolithus pelagicus and calcidiscus leptoporus before 1970 mark the cold phase of pdo these coccolithophore production rate data are consistent with instrumental records of surface and thermocline temperatures monitored since 1950 this is the first study to document the response of calcareous phytoplankton to surface water warming occurring in sbb since 1970

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

volcano deformation and eruption forecasting recent advances in global positioning system gps tilt and interferometric synthetic aperture radar insar have greatly increased the availability of volcano deformation data these measurements combined with appropriate source models can be used to estimate magma chamber depth and to provide information on chamber shape and volume change however kinematic models cannot constrain magma chamber volume and provide no predictive

climate and anthropogenic controls of coastal deoxygenation on interannual to centennial timescales understanding dissolved oxygen variability in the ocean is limited by the short duration of direct measurements however sedimentary oxidation reduction reactions can provide context for modern observations here we use bulk sediment redox sensitive metal enrichment factors moef reef and uef and scanning x ray fluorescence xrf records to examine annual scale sedimentary oxygen concentrations in the santa barbara basin from the industrial revolution ad 1850 to present enrichments are linked to measured bottom water oxygen concentrations after 1986 we reveal gradual intensification of the coastal oxygen minimum zone omz on the southern california margin coinciding the 20th century anthropogenic warming trend that leads to reduced oxygen solubility and greater stratification high frequency interannual oscillations become more prominent over the last three decades these are attributed to local flushing events triggered by the transition from el nino to la nina conditions which further amplify changes in the extratropical southern californian omz

a multiscale approach to estimating topographically correlated propagation delays in radar interferograms when targeting small amplitude surface deformation using repeat orbit interferometric synthetic aperture radar insar observations can be plagued by propagation delays some of which correlate with topographic variations these topographically correlated delays result from temporal variations in vertical stratification of the troposphere an approximate model assuming a linear relationship between topography and interferometric phase has been used to correct observations with success in a few studies here we present a robust approach to estimating the transfer function k between topography and phase that is relatively insensitive to confounding processes earthquake deformation phase ramps from orbital errors tidal loading etc our approach takes advantage of a multiscale perspective by using a band pass decomposition of both topography and observed phase this decomposition into several spatial scales allows us to determine the bands wherein correlation between topography and phase is significant and stable when possible our approach also takes advantage of any inherent redundancy provided by multiple interferograms constructed with common scenes we define a unique set of component time intervals for a given suite of interferometric pairs we estimate an internally consistent transfer function for each component time interval which can then be recombined to correct any arbitrary interferometric pair we demonstrate our approach on a synthetic example and on data from two locations long valley caldera california which experienced prolonged periods of surface deformation from pressurization of a deep magma chamber and one coseismic interferogram from the 2007 mw 7 8 tocapilla earthquake in northern chile in both examples the corrected interferograms show improvements in regions of high relief independent of whether or not we pre correct the data for a source model we believe that most of the remaining signals are predominately due to heterogeneous water vapor distribution that requires more sophisticated correction methods than those described here

new data on the neoproterozoic cambrian geotectonic setting of the tepla barrandian volcano sedimentary successions geochemistry u pb zircon ages and provenance bohemian massif czech republic the tepla barrandian unit tbu of the bohemian massif was a part of the avalonian cadomian belt at the northern margin of gondwana during neoproterozoic and early cambrian times new detrital zircon ages and geochemical compositions of late neoproterozoic siliciclastic sediments confirm a deposition of the volcano sedimentary successions of the tbu in a back arc basin a change in the geotectonic regime from convergence to transtension was completed by the time of the precambrian cambrian boundary the accumulation of around 2 500 m lower cambrian continental siliciclastics in a basin and range type setting was accompanied by magmatism which shows within plate features in a few cases but is predominantly derived from anatectic melts displaying the inherited island arc signature of their cadomian source rocks the geochemistry of clastic sediments suggests a deposition in a rift or strike slip related basin respectively a marine transgression during middle cambrian times indicates markedly thinned crust after the cadomian orogeny upper cambrian magmatism is represented by 1 500 m of subaerial andesites and rhyolites demonstrating several geochemical characteristics of an intra plate setting zircons from a rhyolite give a u pb shrimp age of 499 4 ma the cambrian sedimentary and magmatic succession of the tbu records the beginning of an important rifting event at the northern margin of gondwana

expansion of the southern california oxygen minimum zone during the early to mid holocene due to reduced ventilation of the northeast pacific abstract oceanic deoxygenation observed since the 1950s has drawn increasing concern as dissolved oxygen do regulates marine biodiversity and biogeochemical cycles yet the do time series from direct instrumental measurements is insufficiently long several decades to constrain the centennial to millennial variability here we present redox sensitive metal re u and mo records from santa barbara basin sbb california to reconstruct subsurface do through the holocene significantly higher authigenic metal fluxes and coherent benthic foraminifera faunal responses along a published depth transect reveal vertical expansion and intensification of the southern california oxygen minimum zone omz prior to 6 ka comparison with post industrial trace metal records suggests low oxygen conditions were more extreme during early to mid holocene mh highlighting the magnitude of omz variability in the absence of anthropogenic influences inconsistencies between authigenic metal fluxes and local oxygen control indicate a remote weakening of the north pacific intermediate water npiw formation prior to the mh reduced ventilation of the mid depth north pacific is supported by state of the art earth system model simulations with realistic mh 6 ka forcing highlighting the importance of brine rejection during sea ice formation in changing the buoyancy of npiw and its basin wide influences on north pacific omz evidence from holocene marine lake records and model simulations further suggests a southward intertropical convergence zone itcz migration and a consequent deepening of the aleutian low al towards late holocene which favors more sea ice brine rejection thus mid depth ventilation in the north pacific was closely associated with atmospheric circulation during the holocene

early paleozoic rifting and bimodal volcanism in the ossa morena zone of south west spain lower paleozoic volcanic members have been investigated by geological petrographical and geochemical means in a traverse across the ossa morena zone omz in south west spain

changes in sediment redox conditions following the bp dwh blowout event abstract following the blowout of the macondo well a pulse in sedimentation resulted in changes in sedimentary redox conditions this is demonstrated by downcore and temporal changes in the concentration of redox sensitive metals mn re and cd sediment cores collected in the ne gulf of mexico gom reveal increased sedimentation after the deepwater horizon dwh blowout the formation of mucous rich marine snow in surface waters and subsequent rapid deposition to underlying sediments is the likely cause respiration of this material resulted in decreased pore water oxygen concentration and a shoaled redoxcline resulting in two distinct mn peaks in sediments following the event one typically in the top 10 mm with the other at 20 30 mm most cores near the wellhead reveal this non steady state behavior for up to two years after the event associated with the mn minimum between the two mn peaks a modest 15 30 enrichment of re consistent with reducing sediments typically exists a three year time series of three stations following the event reveal that sediment re increased 3 4 times compared to the pre impact baseline value for two years indicating sediments are increasingly more reducing for two years in the third year re concentration decreased suggesting a return towards pre impact conditions in select sites where the density of benthic foraminifera was determined an assemblage wide decrease occurred coincident with reducing conditions as determined by redox sensitive metals demonstrating the important consequences of changing redox conditions on benthic ecosystems determination of redox sensitive metals will continue to constrain the temporal evolution of reducing conditions which will serve to document the long term effects of the spill and the possible return to pre event conditions

some late precambrian microfossils from the bohemian massif and their correlation abstract a brief account is given of the main biostratigraphical conclusions resulting from the micropalaeontological study of the bohemian upper proterozoic the relatively rich microfossil material presently known from the barrandian area enables comparison to be made both with middle and upper brioverian microfossils of the west european brioverian complex and also with those from the upper riphean and vendian platform sediments a correlation between the relatively close geographical areas of bohemia lusatia and saxony on the basis of microorganisms is evident biocommunities from siliceous rocks display algal mat assemblages their features are very similar to those of biogenic rocks reported from other regions especially australia and north america in the moldanubian supergroup the cesk krumlov formation in which graphitized phytoclasts with anatomical structures of primitive land plants have recently been found was examined the question of the age of this formation remains open and its study is still in progress the correlation of the sedimentary complex of the east sudeten the presumably proterozoic zab eh formation with the palaeozoic assemblage is possible due to the finds of chitinozoa remains of megascopic algae were recently found in this assemblage along with chilinozoan chambers this association is highly specialized and comprises new taxa of higher thallophytes

from extreme rainfall to drought 250 years of annually resolved sediment deposition in santa barbara basin california abstract the mediterranean climate of southern california is marked by droughts and extreme precipitation events here we use elemental variations generated by scanning x ray fluorescence xrf to identify droughts and floods in recently deposited 1755 2008 sediments of santa barbara basin sbb from box core spr0901 04bc the first principal component pc1 of the scanning xrf elements has high loadings for elements associated with the lithogenic component of sbb laminae couplets while the second pc2 is associated with biogenic components we interpret pc1 as a proxy for river runoff and pc2 as a proxy for marine productivity high values of pc1 are associated with el nino events and positive warm phases of the pacific decadal oscillation pdo while low values of pc2 are associated with el nino events and negative cool phases of the pdo droughts such as the 1934 40 1949 56 and 1989 91 events coincide with low pc1 values in addition to distinguishing interannual and decadal variability in the elemental composition of sbb sediments several historic floods can be recognized including a gray flood layer associated with the 1861 62 flood and a peak in pc1 associated with the flood following the st francis dam disaster in 1928

from cadomian subduction to early palaeozoic rifting the evolution of saxo thuringia at the margin of gondwana in the light of single zircon geochronology and basin development central european variscides germany

the flow of the undercurrent over the continental borderland off southern california 1 iniroduction 2 background the bottom topography off southern california has been the cc a slow had equatornard flow is the eastern limb of termed a continental borderland to distinguish it from the ordinary the large scale anticyclonic gyre of the temperate north pacific shelf slope morphology found along most continental margins ocean the cc carries relatively cool low salinity waters of shepard and emuy 19411 islands shallow banks basins and subarctic origin to lower latitudes on average the core of the cc troughs form a complex bathymetric region extending from the has velocities of 0 10 to 0 15 m s and traces a path roughly coast to 200 lon offshore the southern california coastline has a parallel to the california baja california coastline localized concave curvature between the headland at point conception to measurements of flow can exceed 0 5 m s davis 19851 an the u s mexican border as a whole this region is referred to as instantaneous realization of the cc includes a tangle of meanders the california bight the geographic bathymetric dguration eddies and narrow jetlike flows and counterllows the cc lies at of the bight exm a pronounced influence upon the local circula varying distances off the coast and at the latitude of the tion patterns and heme upon the distributions of physical e u s mexican border there is a strong shoreward component to sverdrup and fleming 19411 and biological quantities e g the flow in most seasons especially summa the flow splits one allen 1945 owen 19801 during 1985 we conducted an oceano branch turns and flows northward into the california bight graphic survey off southern california the sampling grid was becoming the eastern limb of a cyclonic eddy centered about the designed to reveal the mumce of the geographic bathymetric offshore banks seasonally fall and winter a weak inshore features upon the circulation of the california current system countercurrent ic develops at the surface along various portion6 ccs especially the flow of the california undercurrent cu of the coastline reid et d 19581 at depth the cu cdes the survey grid also includes station lines mss the core of the waters of subtropical origin poleward along the continental slope california current cc and transects an offshore dipole eddy these waters are relatively warm and saline and have low mm simpson and lym this issue the station grid of this study trations of dissolved oxygen the cu also demonstrates a welldiffers considerably from that used by the california cooperative defined seasonality and at times opposes the overlying dace oceanic fisheries investigations calcofi surveys in both its flow maps and sections of the long term seasonal means of relaspatial resolution and depth of sampling the objectives of thic tive geostrophic velocity and distributions of ocean characteristics report are 1 to examine the spatial continuity of the cu through for the ccs are available in calcofi atlas 30 lym et d 19821 the complex bathymeny of the bight 2 to trace the poleward for a comprehensive review of the long term seasonal large scale paths and offshore spread of waters of southern origin transported description of the ccs the readex is referred to recent papas by by the cu 3 to contrast this subsurface flow with the surface hickey 1979 chelton 19841 and lynn andslnpsm 19871 and flow and 4 to compare these results with the long term calcofi to important references of pioneering work given therein mean conditions

the impact of ocean deoxygenation on iron release from continental margin sediments in the oceans high nitrate low chlorophyll regions such as the peru humboldt current system and the adjacent eastern equatorial pacific1 primary productivity is limited by the micronutrient iron within the peruvian upwelling area bioavailable iron is released from the reducing continental margin sediments2 the magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones3 4 here we show that measurements of molybdenum uranium and iron concentrations can be used as a proxy for sedimentary iron release and use this proxy to assess iron release from the sea floor beneath the peru upwelling system during the past 140 000 years we observe a coupling between levels of denitrification as indicated by nitrogen isotopes trace metal proxies for oxygenation and sedimentary iron concentrations specifically periods with poor upper ocean oxygenation are characterized by more efficient iron retention in the sediment and a diminished iron supply to the water column we attribute efficient iron retention under more reducing conditions to widespread sulphidic conditions in the surface sediment and concomitant precipitation of iron sulphides we argue that iron release from continental margin sediments is most effective in a narrow redox window where neither oxygen nor sulphide is present we therefore suggest that future deoxygenation in the peru upwelling area would be unlikely to result in increased iron availability whereas in weaker oxygen minimum zones partial deoxygenation may enhance the iron supply

temporal development of the 1999 intrusive episode in the eyjafjallajokull volcano iceland derived from insar images eyjafjallajokull volcano located in southern iceland is characterized by its quiet nature only about a handful of earthquakes associated with the volcanic system had been detected prior to the 1990s earthquake swarms did however occur in 1994 and 1999 here we investigate the spatio temporal evolution of a magmatic intrusion associated with the 1999 earthquake swarm via analysis of produced surface deformation a series of interferometric synthetic aperture radar insar images spanning various periods of the intrusion show that in 1999 surface deformation occurred mainly on the southern flanks of the volcano the deformation amounts to more than 20 cm of range change inverse modeling resolves the deformation source to be a sill intrusion at 6 3 km depth sill opening was up to 1 m and the total intruded volume amounts to 0 03 km3 the insar data display a migration of the center of deformation through time enabling us to create time dependant sill opening models furthermore we investigate the spatio temporal distribution of earthquakes and find that the distribution supports the insar derived model and additionally provides indications for a possible site of a feeder channel magmatic flow rate estimates indicate an initial intrusion rate of 4 6 m3 s declining over a few weeks

an insar based survey of volcanic deformation in the central andes we extend an earlier interferometric synthetic aperture radar insar survey covering about 900 remote volcanos of the central andes 14 27 s between the years 1992 and 2002 our survey reveals broad 10s of km roughly axisymmetric deformation at 4 volcanic centers two stratovolcanoes are inflating uturuncu bolivia and hualca hualca peru another source of inflation on the border between chile and argentina is not obviously associated with a volcanic edifice here called lazufre and a caldera cerro blanco also called robledo in northwest argentina is subsiding we explore the range of source depths and volumes allowed by our observations using spherical ellipsoidal and crack like source geometries we further examine the effects of local topography upon the deformation field and invert for a spherical point source in both elastic half space and layered space crustal models we use a global search algorithm with gradient search methods used to further constrain best fitting models inferred source depths are model dependent with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure source depths relative to sea level are 8 18 km at hualca hualca 12 25 km for uturuncu 5 13 km for lazufre and 5 10 km at cerro blanco deformation at all four volcanoes seems to be time dependent and only uturuncu and cerro blanco were deforming during the entire time period of observation inflation at hualca hualca stopped in 1997 perhaps related to a large eruption of nearby sabancaya volcano in may 1997 although there is no obvious relation between the rate of deformation and the eruptions of sabancaya we do not observe any deformation associated with eruptions of lascar chile at 16 other volcanoes that had recent small eruptions or fumarolic activity or associated with a short lived thermal anomaly at chiliques volcano we posit a hydrothermal system at cerro blanco to explain the rate of subsidence there for the last decade we calculate the ratio of the volume of magma intruded to extruded is between 1 10 and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

vertical oxygen minimum zone oscillations since 20 ka in santa barbara basin a benthic foraminiferal community perspective 1 here we present a history of deoxygenation of upper intermediate waters during the last deglaciation from santa barbara basin sbb based on quantitative analyses of benthic foraminiferal assemblages from a new shallow piston core above basin sill depth mv0811 15jc 418m and previously described sequences in the deeper basin md02 2504 481m and md02 2503 570m we document a 152m depth transect of benthic foraminiferal assemblages to extract changing community structure density diversity and evenness and improve paleoenvironmental interpretation of late quaternary vertical oscillations in the upper boundary of the oxygen minimum zone omz close interaction between changes in open margin omz and that of the restricted sbb is documented using these quantitative techniques mv0811 15jc while being unlaminated contains strongly hypoxic foraminiferal assemblages including species bolivina tumida and nonionella stella coeval with preserved sediment laminations in the deeper cores last glacial maximum lgm assemblages across this transect contained oxic fauna and high diversity at 14 7ka glacial termination ia hypoxic benthic fauna appeared across the transect recording hypoxic waters 0 5mll 1 300m from the ocean surface bolling allerod b a assemblages uniquely stand out in the record exhibited by low density diversity and evenness and taxonomic composition reflecting extreme and stressful hypoxia and methane rich environments younger dryas assemblages were diverse and composed of oxic fauna similar to lgm assemblages termination ib initiated another deoxygenation shift followed by omz associated faunal and density patterns this analysis strengthens the quantitative assessment of oxygen concentrations involved in deglacial omz change and reveals the unexpected remarkable shallowness of omz influence during the b a

nitrogen isotope and productivity variations along the northeast pacific margin over the last 120 kyr surface and subsurface paleoceanography 1 glacial interglacial changes in sedimentary 15n over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical north pacific etnp where subsurface denitrification is active to the oregon margin where no denitrification occurs today low 15n values 4 6 generally characterize glacial stages 2 and 4 and higher 15n values 7 10 are representative of the holocene millennial scale periods within stage 3 and stage 5 the inferred synchroneity of 15n variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen poor subsurface waters in the etnp is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone similar to 15n primary production indicators percent corg ba al and percent opal show glacial interglacial as well as millennial scale variations along the ne pacific margin with higher primary production during warm periods however the relative phasing between 15n and paleoproduction tracers within individual records changes latitudinally whereas 15n and primary production vary approximately synchronously in the midlatitudes production lags 15n in the etnp by several kiloyears this lag calls for a new understanding of the processes driving denitrification in the etnp we suggest that oxygen input by the equatorial undercurrent as well as local organic matter flux controls denitrification rates in the etnp moreover the differences in relative timing point to a time transgressive development of upwelling favorable winds along the ne pacific margin after the last glaciation with those in the north developing several kiloyears earlier

submillimeter life positions of bacteria protists and metazoans in laminated sediments of the santa barbara basin to provide insights into the biogeochemistry of environments where steep chemical gradients place anaerobes microaerophiles and aerobes in close proximity it might be necessary to survey biotic distributions on scales that are not possible using conventional ecological approaches to overcome such limitations we adapted sedimentological and cell biological methods to examine the life positions of microbes within sediments this fluorescently labeled embedded core flec technique was used to survey the submillimeter distributions of eukaryotic nanobiota and meiofauna plus co occurring prokaryotes inhabiting laminated sediments of the bathyal santa barbara basin sbb 34 13 n 120 02 w although sbb sediments were vertically structured on the scale of millimeters i e as laminae and microelectrode profiles suggested vertically distinct oxygenated and anoxic sulfidic layers the distributions of aerobes microaerophiles and sulfide tolerant anaerobes were not concomitantly structured unprecedented associations were observed among microorganisms for example relatively deep in the sediments where high sulfide concentrations were expected flagellates were intimately associated with beggiatoa ciliates were typically solitary whereas flagellates were often aggregated in nearly monomorphotypic swarms of 3 104 mm 3 such aggregations could significantly affect geochemical pore water processes at scales 1 l our observations indicate that a mosaic of chemically heterogeneous microhabitats exist in both vertical and horizontal dimensions suggesting that biogeochemical processes in the sbb are more complex than predictions based on standard biotic assessments and microelectrode profiling

increased capture of magma in the crust promoted by ice cap retreat in iceland retreating ice caps overlying volcanoes are thought to relieve surface pressure causing enhanced magma generation and volcanic activity analysis of crustal stress during a dyke intrusion event associated with retreat of iceland s largest ice cap indicates that ice retreat could instead promote storage of magma in the crust rather than eruption at the surface

first u pb geochronology on detrital zircons from early middle cambrian strata of the torgau doberlug syncline eastern germany and palaeogeographic implications la icp ms u pb data from detrital zircons of the ediacaran to cambrian siliciclastic sequence of the torgau doberlug syncline tds saxo thuringia germany are reported for the first time the majority of 203 analysed zircon grains is proterozoic with minor amount of archean and palaeozoic grains the u pb ages fall into three groups 2 8 2 4 ga 3 neoarchean to earliest palaeoproterozoic 2 3 1 6 ga 46 early to late palaeoproterozoic 1 0 0 5 ga 47 neoproterozoic to cambrian this age distribution is typical for the west african craton as the source area and for cadomian orogenic events in northwestern gondwana the samples show an age gap between 1 6 and 1 0 ga which is characteristic for west african provenance and diagnostic in distinguishing this unit from east avalonia and baltica the dataset shows clusters of palaeoproterozoic ages at 2 2 1 7 ga that is typical for western gondwana which was affected by abundant magmatic intrusions ca 2 2 1 8 ga during the eburnean orogeny west african craton neoarchean zircon ages 3 point to recycling of magmatic rocks formed during the liberian and leonian orogenies ediacaran to earliest cambrian rocks of the tds originated in an active margin regime of the gondwanan shelf the following early palaeozoic overstep sequence was deposited within rift settings that reflects instability of the west gondwanan shelf and the separation of terranes from ordovician onward the results of this study demonstrate distinct northwestern african provenance of the cambrian siliciclastics of the tds due to th u ratios from concordant zircon analysis igneous origin from felsic melts is concluded as the source of these grains

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

cambroclaves from the cambrian of sardinia italy and germany constraints for the architecture of western gondwana and the palaeogeographical and palaeoecological potential of cambroclaves cambroclaves represent a group of problematic microfossils previously known from strata close to the early middle cambrian boundary of only a few palaeogeographic regions kazakhstan china australia because of their frequent occurrence as disarticulated remains they have hitherto been assumed to be provincially restricted microfossils of unclear palaeobiological affinity discoveries of cambroclaves from the early to early middle cambrian of southern sardinia and central germany europe point to a much wider distribution during their short stratigraphic range and imply closer palaeogeographic relations between the european shelf of western gondwana and the areas from which cambroclaves were previously known these relations are also supported by the common occurrence of other small shelly fossils these facts support the existence of a widespread uniform facies belt shelf around parts of gondwana during the early middle cambrian time interval and contradict the interpretation of the european depositional areas as isolated basins or as distinctly separate cambrian terranes the western gondwana cambroclaves occur in carbonate successions indicative of special palaeoecological conditions the specimens are limited to distinct layers formed during transgressive phases that opened inner and partly restricted platform areas to open marine and more distal deeper subtidal environments possibly accompanied by a transition from a rather arid to more humid climatic conditions because of the short stratigraphic window of occurrence and of distinctive facies characteristics cambroclaves are palaeoecologically and palaeobiogeographically useful and consequently contribute important evidence for both the reconstruction of the perigondwana realm and the relations to other palaeocontinents in the cambrian 7 2003 elsevier science b v all rights reserved

subduction driven shortening and differential exhumation in a cadomian accretionary wedge the tepla barrandian unit bohemian massif abstract the tepla barrandian unit tbu of central europe s bohemian massif exposes perhaps the best preserved fragment of an accretionary wedge in the avalonian cadomian belt which developed along the northern active margin of gondwana during late neoproterozoic in the central tbu three ne sw trending lithotectonic units domains 1 3 separated by antithetic brittle faults differ in lithology style and intensity of deformation magnetic fabric ams and degree of cadomian regional metamorphism the flysch like domain 1 to the nw is the most outboard trenchward unit which has never been significantly buried and experienced only weak deformation and folding the central melange like domain 2 is characterized by heterogenous intense deformation developed under lower greenschist facies conditions and was thrust nw over domain 1 along a se dipping fault to the se the most inboard arcward domain 3 is lithologically monotonous dominated by graywackes and slates was buried to depths corresponding up to the lower greenschist facies conditions where it was overprinted by a pervasive se dipping cleavage and then was exhumed along a major nw dipping normal fault we interpret these domains to represent allochtonous tectonic slices that were differentially buried and then exhumed from various depths within the accretionary wedge during cadomian subduction the nw directed thrusting of domain 2 over domain 1 may have been caused by accretion at the wedge front whereas the se dipping cleavage and se side up exhumation of domain 3 may record inclined pervasive shortening during tectonic underplating and subsequent horizontal extension of the rear of the wedge the boundary faults were later reactivated during cambro ordovician extension and variscan compression compared to related terranes of the cadomian belt the tbu lacks exposed continental basement evidence for regional strike slip shearing and extensive backarc magmatism and lp ht metamorphism which could be interpreted to reflect flat slab cadomian subduction this in turn suggests that cadomian accretionary wedges developed in a manner identical to those of modern settings elevating the tbu to a key position for understanding the style kinematics and timing of accretionary processes along the avalonian cadomian belt

persistently declining oxygen levels in the interior waters of the eastern subarctic pacific abstract fifty years of measurements at ocean station papa osp 50 n 145 w show trends in the interior waters of the subarctic pacific that are both impacted by short term few years to bi decadal atmospheric or ocean circulation oscillations and by persistent climate trends between 1956 and 2006 waters below the ocean mixed layer to a depth of at least 1000 m have been warming and losing oxygen on density surfaces found in the depth range 100 400 m 26 3 27 0 the ocean is warming at 0 005 0 012 c y 1 whereas oxygen is declining at 0 39 0 70 mol kg 1 y 1 or at an integrated rate of 123 mmol m 2 y 1 decrease of 22 over 50 years during this time the hypoxic boundary defined as 60 mol o 2 kg 1 has shoaled from 400 to 300 m in the alaska gyre the 26 2 isopycnal occasionally ventilates whereas at osp 26 0 has not been seen at the ocean surface since 1971 as the upper ocean continues to stratify to interpret the 50 year record at osp the isopycnal transport of oxygenated waters within the interior of the subarctic pacific is assessed by using a slightly modified no parameter broecker w 1974 no a conservative water mass tracer earth and planetary science letters 23 100 107 the highest nitrate oxygen signature in interior waters of the north pacific is found in the bering sea gyre western subarctic gyre and east kamchatka current region as a consequence of winter mixing to the 26 6 isopycnal by mixing with low no waters found in the subtropics and okhotsk sea this signature is diluted as waters flow eastward across the pacific evidence of low no waters flowing north from california is seen along the coasts of british columbia and se alaska oxygen in the subsurface waters of the alaskan gyre was supplied 60 by subarctic and 40 by subtropical waters during woce surveys whereas such estimates are shown to periodically vary by 20 at osp other features discernable in the osp data include periods of increased ventilation of deeper isopycnals on an 18 year cycle and strong short term few month variability caused by passing mesoscale eddies the potential impacts of declining oxygen on coastal ecosystems are discussed

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

tsunamis within the eastern santa barbara channel several locally generated tsunamis have been reported in southern california during the past 200 years yet the hazard from locally generated tsunamis has received considerably little attention we consider here tsunamis generated by coseismic displacements on the channel islands thrust cit system as well as waves generated by slope failures along the walls of the santa barbara channel we find that purely tectonic sources could generate regional tsunamis with 2m runup whereas combinations of tectonic sources and submarine mass movements could generate local runup as large as 15m