fertilizing potential of volcanic ash in ocean surface water the fertilization potential of newly erupted and well preserved ash from the 2000 hekla eruption in iceland was measured for the first time by flow through experiments as previously shown 1 the north atlantic ocean including the subarctic seas surrounding iceland is the largest net sink of the world s oceans for atmospheric co 2 owing to biological drawdown during summer 2 almost complete consumption of phosphate in chlorophyll rich areas of the north atlantic ocean might limit primary production and 3 in the southern pacific ocean and parts of the equatorial pacific ocean iron might limit primary production we found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate 1 7 mmol g 21 h 21 iron 37 0 mmol g 21 h 21 silica 49 5 mmol g 21 h 21 and manganese 1 7 mmol g 21 h 21 dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water macronutrients and bioactive trace metals are released fast enough to become available to support primary production

late ordovician mass extinction in the selwyn basin northwestern canada geochemical sedimentological and paleontological evidence we present a detailed study of the trace element and stable isotope geochemistry sedimentology and fossil distributions in two avalanche lake av4b av1 ordovician silurian boundary sections in the selwyn basin trilobites and conodonts indicate a profound extinction at the end of the ordovician which is constrained stratigraphically within a 3 in magnitude is recorded in the extinction interval iridium abundances 0 051 ppb in the extinction interval are low and fail to provide evidence for an impact the highest ir abundance is found to be associated with reduced sedimentation in a condensed horizon cerium anomalies indicate a s

controls on trace metal authigenic enrichment in reducing sediments insights from modern oxygen deficient settings any effort to reconstruct earth history using variations in authigenic enrichments of redox sensitive and biogeochemically important trace metals must rest on a fundamental understanding of their modern oceanic and sedimentary geochemistry further unravelling the multiple controls on sedimentary enrichments requires a multi element approach of the range of metals studied most is known about the behavior of fe mn and mo in this study we compare the authigenic enrichment patterns of these elements with a group whose behavior is not as well defined cd cu zn and ni in three oxygen poor settings the black sea the cariaco basin venezuela and the peru margin these three settings span a range of biogeochemical environments allowing us to isolate the different controls on sedimentary enrichment our approach relying on the covariation of elemental enrichment factors ef defined for element x as efx x al sample x al lithogenic has previously been applied to mo and u to elucidate paleoenvironmental information on for example benthic redox conditions the particulate shuttle and the evolution of water mass chemistry we find two key controls on trace metal enrichment first the concentration of an element in the lithogenic background sediment used in calculating efx controls the magnitude of potential enrichment maximum enrichment factors of 376 and 800 are calculated for mo 1 ppm in detrital sediments and cd 0 3 ppm respectively compared to values not greater than 17 in any setting for the other five metals 45 ppm to 4 5 wt in detrital sediments second there is a relationship between the aqueous concentration of the element in overlying seawater and its degree of enrichment in the sediment we further identify four important processes for delivery of trace metals to the sediment these are 1 cellular uptake especially important for zn and cd 2 interaction co precipitation with sulfide mo cu and cd 3 passive scavenging via the traditional particulate shuttle mo ni and cu and 4 an association with the benthic fe redox shuttle mn ni finally we summarize the oceanic mass balance of cd and mo and place the first constraints on the contribution of reducing sediments to the oceanic mass balance of cu zn and ni we show that reducing sediments are the ultimate repository for up to half the total output flux of these elements from the oceanic dissolved pool

possible deep fault slip preceding the 2004 parkfield earthquake inferred from detailed observations of tectonic tremor 1 earthquake predictability depends in part on the degree to which sudden slip is preceded by slow aseismic slip recently observations of deep tremor have enabled inferences of deep slow slip even when detection by other means is not possible but these data are limited to certain areas and mostly the last decade the region near parkfield california provides a unique convergence of several years of high quality tremor data bracketing a moderate earthquake the 2004 magnitude 6 0 event here i present detailed observations of tectonic tremor from mid 2001 through 2008 that indicate deep fault slip both before and after the parkfield earthquake that cannot be detected with surface geodetic instruments while there is no obvious short term precursor i find unidirectional tremor migration accompanied by elevated tremor rates in the 3 months prior to the earthquake which suggests accelerated creep on the fault 16 km beneath the eventual earthquake hypocenter

decoupling of the carbon cycle during ocean anoxic event 2 the cenomanian to turonian boundary transition ca 95 93 ma represents one of the most profound global perturbations in the carbon cycle of the past 140 m y this interval is characterized by widespread deposition of organic rich fine grained sediment marked by a globally recognized positive carbon isotope excursion cie reflecting the widespread removal of 12 c enriched organic matter in marine sediments under global anoxic greenhouse conditions however the exact timing and trigger of this inferred global phenomenon termed oceanic anoxic event 2 oae 2 is still debated with recent studies showing diachroneity between the deposition of the organic rich sediment and the cie and conflicting interpretations on detailed redox analyses in several of these inferred anoxic settings here we present the first evidence for widespread and persistent oxygenation during oae 2 based primarily on the distribution of redox sensitive trace metals and biota preserved in sedimentary rocks from the western interior seaway of north america our data indicate anoxic euxinic conditions in the mid to late cenomanian but improved bottom water oxygenation prior to and during the cie trace metal enrichments support large volumes of mafic volcanism possibly from the high arctic large igneous province halip which occur within the middle of the cie indicating that the emplacement of lips was not the primary trigger of the cenomanian turonian cie the apparent paradox of an oxygenated phase within oae 2 suggests a much more complex carbon cycle during these global perturbations than previously thought these findings have important implications for greenhouse carbon cycle changes over time scales of 0 1 10 m y

periodic chaotic and doubled earthquake recurrence intervals on the deep san andreas fault earthquake recurrence histories may provide clues to the timing of future events but long intervals between large events obscure full recurrence variability in contrast small earthquakes occur frequently and recurrence intervals are quantifiable on a much shorter time scale in this work i examine an 8 5 year sequence of more than 900 recurring low frequency earthquake bursts composing tremor beneath the san andreas fault near parkfield california these events exhibit tightly clustered recurrence intervals that at times oscillate between 3 and 6 days but the patterns sometimes change abruptly although the environments of large and low frequency earthquakes are different these observations suggest that similar complexity might underlie sequences of large earthquakes

subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth evidence from biogeochemical experiments and satellite data volcanoes confront earth scientists with new fundamental questions can airborne volcanic ash release nutrients on contact with seawater thereby excite the marine primary productivity mpp and most notably can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood here we present results from biogeochemical experiments showing that 1 volcanic ash from subduction zone volcanoes rapidly release an array of nutrients co limiting algal growth in vast oceanic areas 2 at a speed much faster minute scale than hitherto known and that marine phytoplankton from low iron oceanic areas can swiftly within days utilize iron from volcanic sources we further present satellite data possibly indicating an increase of the mpp due to the seaward deposition of volcanic particulate matter our study supports the hypothesis that oceanic iron fertilization with volcanic ash may play a vital role for the development of the global climate

the cenomanian turonian eagle ford group of south texas insights on timing and paleoceanographic conditions from geochemistry and micropaleontologic analyses abstract the interbedded organic rich marls and limestones of the eagle ford group of south texas were deposited on the shelf of the central texas platform during the upper cenomanian through the turonian micropaleontological analyses of thin sections and residue samples from subsurface cores taken in atascosa and karnes counties yielded 13 biostratigraphic datums which were integrated with calcareous nannofossil datums stable carbon isotopic and bulk inorganic geochemical analysis to gain an understanding of the paleoceanographic conditions of the study area and their relationship to regional and global events the paired thin section residue sampling was necessitated by poor recovery of planktonic foraminifera in washed samples which were however abundant in most thin sections lower eagle ford marls were deposited under euxinic conditions produced by a stratified water column periodic enhanced water column mixing increased oxygen levels and surface water primary productivity which promoted calcite diagenesis and generation of limestones containing calcispheres and radiolaria an oxygenated bottom water mass entered the basin in the uppermost cenomanian prior to the onset of oceanic anoxic event oae 2 causing a spike in benthic foraminiferal diversity and decreasing preservation of organic matter although the lower portion of the upper eagle ford is age equivalent to oae2 as indicated by positive shift in 13corg it contains less organic matter and evidence of more oxygen than the lower eagle ford so deposition of the eagle ford black shales is not contemporaneous to oae2

response of the cr isotope proxy to cretaceous ocean anoxic event 2 in a pelagic carbonate succession from the western interior seaway abstract chromium offers a redox sensitive isotopic proxy with potential for tracing past oxygen levels in the oceans we explore this potential in a pelagic succession of marine carbonate sediment deposited during cretaceous ocean anoxic event 2 oae 2 in the western interior seaway colorado wis using the usgs portland 1 core reduction of cr vi causes light isotopes of cr to preferentially partition into cr iii because cr vi is the thermodynamically favoured species in oxygenated seawater and cr iii is relatively insoluble under the same conditions increased removal of cr iii into anoxic marine sediment during ocean anoxic events should cause positive shifts in seawater 53cr values this assumes that isotopic fractionation associated with all cr removal fluxes from the oceans was constant during oae 2 and that there was no change in cr input fluxes to the oceans here we report findings that counter this prediction namely evidence for a negative shift in seawater 53cr during oae 2 of 1 1 in the wis the magnitude of the excursion depends on the speciation of cr removed in this setting over the duration of oae 2 as well as the fractionation factor accompanying the removal flux of chromate into carbonate sediment both of which are uncertain the 53cr excursion reaches values as low 0 09 during oae 2 which is indistinguishable from the high temperature igneous rock baseline value of 0 124 0 101 2 moreover the minima in the 53cr profile coincides with a peak in cr concentrations in the study core as well as anomalous enrichments of other trace metals of basaltic affinity building on previous studies linking oae 2 to a massive episode of submarine volcanic activity we attribute the decrease in carbonate 53cr values during oae 2 to the expansion of a hydrothermal superplume created during eruptions of the caribbean large igneous province lip this metal laden plume enriched in cr iii and probably anoxic moved from deep waters of the eruption site in the eastern pacific into deep waters of the proto north atlantic through an oceanic gateway in the central americas once inside anoxic metal rich waters upwelled against the surrounding continental margins where isotopically unfractionated cr iii whose solubility was improved by organic complexation and or oxidation to cr vi mixed with the isotopically heavy pool of oceanic chromate in surface waters above the redoxcline application of a simple mixing equation shows that hydrothermal cr contributed 90 of the authigenic cr in the trace metal enriched interval of the study core the increased flux of hydrothermal cr was large enough to mask the expected isotopic response of the ocean cr cycle to increasing anoxia we consider this interpretation to be robust in that it is not substantially affected by uncertainty in the speciation of hydrothermal cr nor uncertainty in the fractionation factor sw caco 3 associated with chromate removal into marine carbonate sediment which we measured in the modern caribbean sea to be 0 46 0 14 2

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

remote triggering of tremor along the san andreas fault in central california received 30 august 2008 accepted 16 april 2009 published 18 july 2009 1 we perform a systematic survey of triggered tremor along the san andreas fault in central california for the 31 teleseismic earthquakes with mw 7 5 since 2001 we identify 10 teleseismic events associated with clear triggered tremor about 52 of the tremor is concentrated south of parkfield near cholame where ambient tremor has been identified previously and the rest is widely distributed in the creeping section of the san andreas fault north of parkfield tremor is generally initiated and is in phase with the love wave particle velocity however the pattern becomes complicated with the arrival of the rayleigh waves and sometimes tremor continues after the passage of the surface waves we identify two cases in which tremor is triggered during the teleseismic pkp phase these results suggest that while shear stress from the passage of the love waves plays the most important role in triggering tremor in central california other factors such as dilatational stresses from the rayleigh and p waves also contribute we also examine the ambient tremor occurrence rate before and after the teleseismic events and find a transient increase of stacked tremor rate during the passage of the teleseismic surface waves this observation implies that the occurrence time of tremor is temporally advanced by the dynamic stresses of the teleseismic waves the amplitude of the teleseismic waves correlates with the occurrence of triggered tremor and the inferred tremor triggering threshold is 2 3 kpa the relatively low triggering threshold indicates that the effective stress at the tremor source region is very low most likely due to near lithostatic fluid pressure

precise tremor source locations and amplitude variations along the lower crustal central san andreas fault 1 we precisely locate 88 tremor families along the central san andreas fault using a 3d velocity model and numerous p and s wave arrival times estimated from seismogram stacks of up to 400 events per tremor family maximum tremor amplitudes vary along the fault by at least a factor of 7 with by far the strongest sources along a 25 km section of the fault southeast of parkfield we also identify many weaker tremor families which have largely escaped prior detection together these sources extend 150 km along the fault beneath creeping transitional and locked sections of the upper crustal fault depths are mostly between 18 and 28 km in the lower crust epicenters are concentrated within 3 km of the surface trace implying a nearly vertical fault a prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6 0 parkfield earthquake

natural iron fertilization by the eyjafjallajokull volcanic eruption aerosol deposition from the 2010 eruption of the icelandic volcano eyjafjallajokull resulted in significant dissolved iron dfe inputs to the iceland basin of the north atlantic unique ship board measurements indicated strongly enhanced dfe concentrations up to 10 nm immediately under the ash plume bioassay experiments performed with ash collected at sea under the plume also demonstrated the potential for associated fe release to stimulate phytoplankton growth and nutrient drawdown combining fe dissolution measurements with modeled ash deposition suggested that the eruption had the potential to increase dfe by 0 2 nm over an area of up to 570 000 km2 although satellite ocean color data only indicated minor increases in phytoplankton abundance over a relatively constrained area comparison of in situ nitrate concentrations with historical records suggested that ash deposition may have resulted in enhanced major nutrient drawdown our observations thus suggest that the 2010 eyjafjallajokull eruption resulted in a significant perturbation to the biogeochemistry of the iceland basin

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

scaling relationship between the duration and the amplitude of non volcanic deep low frequency tremors 1 we investigate a duration amplitude relation of non volcanic deep low frequency dlf tremors in the tokai region southwest japan to constrain the source process of the tremors we apply two models to the distribution one is an exponential model as a scale bound distribution and the other a power law model as a scale invariant distribution the exponential model shows a better fit to the duration amplitude distribution of the tremors than a power law model implying that the dlf tremors are caused by a scale bound source process the source process of the dlf tremors therefore differs from those for earthquakes we suggest that the non volcanic dlf tremor is possibly caused by a fixed source dimension with variable excess pressure of fluid or variable stress drop

low frequency tremors intraslab and interplate earthquakes in southwest japan from a viewpoint of slab dehydration 1 low frequency tremors lft recently found in the southwest japan fore arc likely occur due to hydro fracturing from fluids leaving the dehydrating philippine sea slab however there are some places without such lft they are n izu kanto e shikoku and s kyushu these are the places where island arc type crust is subducting we propose that dehydration of the subducted crust does not occur beneath these regions because it is composed mainly of tonalite lacking the quantity of hydrous minerals seen in normal subducting oceanic crust we show that almost no earthquake occurs within the subducted crust in such regions consistent with dehydration embrittlement hypothesis for intraslab seismicity the lack of dehydration from the crust would also affect the mode of occurrence of interplate earthquakes because pore fluid pressure is more difficult to rise at the thrust zone this might be reflected in the irregular occurrence of great earthquakes in these regions

shale microfacies eagle ford group cenomanian turonian north central texas outcrops and subsurface equivalents abstract the eagle ford group is a mixed siliciclastic carbonate unit that records a late cretaceous cenomanian to turonian transgression a major condensed interval cycle 2 5 of the uza 2 supercycle occurs within the eagle ford shale eagle ford strata are overlain disconformably by the austin chalk the austin eagle ford contact represents the turonian coniacian boundary 89 ma the cenomanian turonian 92 ma boundary occurs within the eagle ford group regionally eagle ford strata consist of two major depositional units a lower transgressive unit dominated by dark well laminated shales exhibiting only minor evidence of bioturbation and an upper regressive unit consisting of thinly interstratified high frequency cycles shales limestones and carbonaceous quartzose siltstones petrographic characterization of shales from eagle ford outcrops near austin waco and dallas texas and subsurface equivalents in a core getty 1 j t wilson from lasalle county texas reveals six microfacies 1 pyritic shales 2 phosphatic shales 3 bentonitic shales 4 fossiliferous shales 5 silty quartzose shales and 6 bituminous claystone and shales transgressive eagle ford shales consist mainly of microfacies 1 4 and 6 the eagle ford condensed interval consists of microfacies 1 2 and 3 and highstand eagle ford shales are comprised of microfacies 4 and 5 eagle ford microfacies exhibit distinctive sedimentological aspects and have source rock characteristics that vary systematically within a sequence stratigraphic framework transgressive eagle ford shales occurring below the condensed interval have optimum oil prone source potential whereas overlying regressive shales are gas prone transgressive and condensed eagle ford strata represent poorly oxygenated low energy below storm wave base marine paleoenvironments of deposition in contrast overlying regressive eagle ford lithofacies accumulated in higher energy above storm wave base well oxygenated shallow marine paleoenvironments

organic matter accumulation of the wufeng longmaxi shales in southern sichuan basin evidence and insight from volcanism abstract the wufeng longmaxi formations wf lm fms in the sichuan basin are sets of graptolite bearing shale strata containing high frequency bentonite layers in order to investigate the influence of volcanism on the organic matter om accumulation in shales detailed observations of several typical profiles and wells were performed also analyses including total organic carbon toc contents and mineral compositions were conducted on 126 shale and 5 bentonite core samples major and trace element analyses were conducted on the selected 25 shale and 5 bentonite samples in the wf lm fms of well lu a results show that wf and lm1 4 members are the bentonites concentrated sections while lm5 6 are the bentonites relatively concentrated sections and no bentonite is found in lm7 9 members the high potassium k content of bentonites have the typical characteristics of intermediate acid calcium alkaline volcanic rocks such as andesite and dacite which probably originated from intraplate collision or volcanic arc structural backgrounds related to the collision belt of the cathaysia block to the yangtze block productivity indicators p content excess si p al cu al and ni al in the wf and lm1 3 members are all significantly higher than those in the lingxiang lx and lm4 5 members the higher biological productivity during the ordovician silurian o s transition was attributed to the massive and intensive volcanism the fertilization by volcanic ash brought abundant biologically relevant nutrient elements n p si fe and al into the ocean thus triggering the phytoplankton bloom and enhancing primary biological productivity all the redox condition indexes moef uef nief vef mo toc corg p and u th positively correlate with toc content during the o s transition the intensive and massive volcanic eruptions triggered global cooling sea level changes late ordovician mass extinction and primary productivity increases thus promoting anoxic and possibly intermittently euxinic bottom conditions in addition the deposited bentonite layers had a strong capacity for oxygen isolation volcanism should be considered when modeling the om accumulation of the wf lm shales

slip on the san andreas fault at parkfield california over two earthquake cycles and the implications for seismic hazard parkfield california which experienced m 6 0 earthquakes in 1934 1966 and 2004 is one of the few locales for which geodetic observations span multiple earthquake cycles we undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of geodetic data collected prior to the 1966 event through joint inversion of the variety of parkfield geodetic measurements trilateration two color laser and global positioning system including previously unpublished two color data we estimate the spatial distribution of slip and slip rate along the san andreas using a fault geometry based on precisely relocated seismicity although the three most recent parkfield earthquakes appear complementary in their along strike distributions of slip they do not produce uniform strain release along strike over multiple seismic cycles since the 1934 earthquake more than 1 m of slip deficit has accumulated on portions of the fault that slipped in the 1966 and 2004 earthquakes and an average of 2 m of slip deficit exists on the 33 km of the fault southeast of gold hill to be released in a future perhaps larger earthquake it appears that the fault is capable of partially releasing stored strain in moderate earthquakes maintaining a disequilibrium through multiple earthquake cycles this complicates the application of simple earthquake recurrence models that assume only the strain accumulated since the most recent event is relevant to the size or timing of an upcoming earthquake our findings further emphasize that accumulated slip deficit is not sufficient for earthquake nucleation online material model fault geometry fit to the data for the inversions and model resolution

tracing paleoredox conditions across the devonian carboniferous boundary event a case study from carbonate dominated settings of belgium the czech republic and northern france the devonian carboniferous boundary was coeval with the hangenberg crisis which is regarded as a first order mass extinction event related with large sea level changes and widespread anoxia this study aims to trace the geochemical paleoproductivity and paleoredox proxies across the devonian carboniferous carbonate dominated successions of the namur dinant basin belgium northern france and the moravo silesian basin czech republic located in the variscan rhenohercynian zone the research was focused on the distribution of oxides sio2 al2o3 fe2o3 cao na2o k2o tio2 mno and trace elements th u v zr mo zn pb ni cu measured by icp oes and icp ms respectively the enrichment factors of mo and u and their ratios were used as the main paleoredox proxies whereas the enrichment factors of zn cu pb and ni were employed to trace the paleoproductivity changes high values of zr al2o3 0 001 tio2 al2o3 0 06 and fe ti 20 and low values of al al fe mn 035 coinciding with an increase of paleoredox proxies suggest a possible volcanic and hydrothermal source of nutrients related to late devonian and early carboniferous extensional magmatism in the rhenohercynian domain although a relationship between higher paleoproductivity and enhanced continental runoff of volcanic material cannot be excluded the studied devonian carboniferous boundary sections from the namur dinant basin gendron celles ardennes quarry reveal three levels with similar vectors of mo and u enrichments the pre crisis famennian pattern is typical for weakly restricted basins with fe mn redox cycling accompanying vertical fluctuations of the oxic anoxic chemocline close to the sediment water interface with the influence of particulate shuttle the mo ef and u ef patterns corresponding to the unrestricted or weakly restricted basin with alternating suboxic to anoxic conditions are considered to represent the transgressive hangenberg black shale event the lower tournaisian mo ef and u ef patterns fall along a vector in the direction of the strongly restricted marine conditions with prevailing suboxic conditions in the moravo silesian basin lesni lom section the pre crisis famennian mo ef and u ef vector indicates an unrestricted marine trend which converges with that of restricted systems redox conditions range from suboxic to euxinic in the tournaisian mo ef and u ef oscillate between oxic and anoxic conditions and fall along a vector of strongly restricted marine conditions increased isolation of both studied basins in the early tournaisian is regarded as a reflection of a significant eustatic fall during the hangenberg crisis linked to a severe episode of the gondwana glaciation these paleohydrographic patterns have correlative potential that should be considered for a revised devonian carboniferous boundary definition

widespread triggering of nonvolcanic tremor in california we identified seven locations on or near the transform plate boundary in california where nonvolcanic tremor was triggered by the 2002 denali earthquake this result implies that the conditions essential for nonvolcanic tremor exist in a range of tectonic environments models explaining tremor typically require conditions endemic to subduction zones that is high temperatures and fluid pressures because previously tremor was nearly exclusively documented in subduction zones the absence of tremor in geothermal areas is inconsistent with such models additionally we found no correlation between creeping or locked faults and tremor contrary to predictions of frictional models of tremor