atmospheric vortex streets on a radarsat sar image we analyze the sea surface imprint of two atmospheric vortex streets avs s observed on a radarsat a canadian earth observation satellite synthetic aperture radar sar image of the aleutian islands in the western gulf of alaska acquired on may 5 1999 the radarsat sar instrument is operated in c band with hh polarization these avs s are interpreted as the atmosphere analog of classic von karman vortex streets the sar image along with radiosonde data and surface weather charts reveal that the avs lengths are 196 km and 111 km for avs 1 and avs 2 respectively there are five and two pairs of vortices within each avs the vortex shedding period is estimated to be between 35 and 48 minutes the vortex shedding started approximately 4 6 and 2 6 hours prior to the sar imaging time for avs 1 and avs 2 respectively there are seven and three pairs of vortices within the respective avs s the vortex tangential velocity is estimated to be between 1 7 and 2 3 m s and the energy dissipated during the vortex lifetime is estimated to be between 24 9 and 23 6 j m

analysis and modeling of atmospheric gravity waves observed in radarsat sar images four case studies of radarsat synthetic aperture radar sar observations of atmospheric gravity waves are presented to demonstrate sar s capability to measure associated near surface wind field variations a brief review of the main characteristics and scales of atmospheric gravity waves agws first establishes their importance in atmospheric dynamics the shape and scale of the wave patterns observed in successive sar images are compared with those calculated from agw models there is agreement between the small scale wind variations across wave patterns in sar images and the larger scale wind field that plays a role in the generation of the observed waves

geochemical signatures of the namibian diatom belt perennial upwelling and intermittent anoxia 1 a gravity core from the nambian diatom belt 83 m water depth was analyzed for major al ca fe k mg p si ti and minor elements ag as ba bi cd co cr cu mn mo ni rb re se sr tl u v zn zr as well as c and s the major element geochemistry is dominated by the contribution of biogenic phases opal and minor amounts of carbonate and phosphate whereas terrigenous components of eolian and fluvial origin form only a minor admixture of 15 examination of the fe s c relationship reveals a completion of pyritization close to the sediment seawater interface higher than average shale fe al ratios reflect the presence of highly reactive iron oxides in terrigenous source material from the namibian desert and suggest little loss of fe within the omz the low total fe content likely represents an important factor responsible for sporadic h2s eruptions the upwelling system off namibia may be regarded as an intermediate system combining high productivity typical for upwelling areas with the sporadic presence of h2s in the water column by examining the source sink relationship of individual trace metals two different trends are discernible mo re and u accumulate following seawater availability whereas ag cd cu ni tl and zn require a biological preconcentration step trace metals like as ba cr se and v show an intermediate behavior metal enrichment is favored by high interstitial water sulfide concentrations close to the sediment seawater interface leading to slightly elevated co contents as opposed to extremely low mn al ratios reflecting the overall reducing character of the namibian system maximum contents of cu ni and zn are significantly lower than those reported previously this may in part be related to the absence of fecal material and a stronger dilution by biosiliceous material at this location compared to the seaward flank of the diatom belt

plate tectonic paleoceanographic hypothesis for cretaceous source rocks and cherts of northern south america new paleocontinental reconstructions show a northern migration of the south american plate with respect to the paleoequator from the jurassic to the late cretaceous this movement caused the northern margin of south america to migrate from a position south to a position north of the paleoequator ekman transport generated net surface water movement towards the south during times when northern south america was south of the paleoequator this situation favored downwelling and prevented jurassic and earliest cretaceous marine source rocks from being deposited when northern south america was north of the paleoequator ekman transport forced net water movement to the north favoring upwelling paleoproductivity and the deposition of one of the best marine source rocks known the la luna villeta and equivalents this plate tectonic paleoceanographic hypothesis explains the origin of hydrocarbons in northern south america the stratigraphic record reflects this increase in paleoproductivity through time this can be observed in facies non calcareous shales to calcareous shales to siliceous shales and finally to bedded cherts and in changing planktic communities which were initially dominated by healthy calcareous foraminifer assemblages followed by stressed foraminifer populations and finally by radiolarians total organic carbon and source rock quality were affected by this longmore term increase in paleoproductivity but also and more markedly by a punctuated sequence stratigraphic record dominated by low frequency changes in relative sea level the magnitude of transgressive episodes caused by rise in sea level determined the extent of source rock intervals and indirectly the content of organic carbon less

high resolution geochemical and biotic records of the tethyan bonarelli level oae2 latest cenomanian from the calabianca guidaloca composite section northwestern sicily italy abstract high resolution micropalaeontological and chemostratigraphic records for the upper cenomanian portion of the calabianca guidaloca composite section nw sicily provide new insight into the palaeoclimatic and palaeoceanographic evolution of the tethys ocean the bonarelli level equivalent was identified on the basis of lithology and well constrained by calcareous plankton biostratigraphy and radiolarian assemblages as well as by the 13 c curve showing a marked positive excursion up to 4 7 the bonarelli level equivalent deposition is characterized by highly eutrophic conditions as testified by radiolarian proliferation black shale samples from the calabianca guidaloca composite section contain very high toc up to 26 and moderate to high amounts of caco 3 on average 20 among the planktonic foraminifera hedbergellids and globigerinelloids tolerated the environmental stress induced by the oceanic anoxic event 2 oae2 the occurrence of some benthic foraminifera testifies to dysoxic rather than completely anoxic conditions at the sea floor during the deposition of some portions of the bonarelli level equivalent based on micropalaeontological results and geochemical proxies 13 c d rb ti v ni ba si cr the bonarelli level equivalent is interpreted as a high productivity event driven by increasingly warm and humid climatic conditions promoting an accelerated hydrological cycle we propose that periodically increased riverine influxes triggered by enhanced humidity resulted in a sluggish circulation mode and consequent anoxic euxinic conditions favouring the preservation of organic matter at the sea floor spectral analyses performed on selected geochemical signals reveal within the main high productivity event a strong orbital climatic forcing represented by a long term eccentricity steered humidity cyclicity that amplifies a short term precession controlled productivity fluctuation

thermo mechanical pressurization of experimental faults in cohesive rocks during seismic slip earthquakes occur because fault friction weakens with increasing slip and slip rates since the slipping zones of faults are often fluid saturated thermo mechanical pressurization of pore fluids has been invoked as a mechanism responsible for frictional dynamic weakening but experimental evidence is lacking we performed friction experiments normal stress 25 mpa maximal slip rate 3 ms 1 on cohesive basalt and marble under 1 room humidity and 2 immersed in liquid water drained and undrained conditions in both rock types and independently of the presence of fluids up to 80 of frictional weakening was measured in the first 5 cm of slip modest pressurization related weakening appears only at later stages of slip thermo mechanical pressurization weakening of cohesive rocks can be negligible during earthquakes due to the triggering of more efficient fault lubrication mechanisms flash heating frictional melting etc

tectonic control of guadalupian lopingian cherts in northwestern sichuan basin south china abstact cherts have been considered to be formed mainly through processes involving biosilicification riverine inputs and hydrothermal activities in the permian massive cherts are widely distributed in south china bearing significant implications for the reconstruction of paleogeography and paleoceanography of the eastern paleo tethys ocean the origin of the permian cherts in south china however remains inconclusive due to a lack of systematic petrographic and geochemical study in this article we analyze the petrologic and geochemical characteristics of the cherts collected from five outcrops in the northwestern sichuan basin south china these cherts are found from the upper guadalupian maokou formation ca 268 259 ma and upper lopingian dalong formation ca 254 252 ma field and microscopic observations suggest that cherts from the maokou formation occur mainly in nodular forms and consist of microcrystalline quartz silicified bioclasts and siliceous fossil debris both petrographic observation and geochemical analysis suggest that the maokou cherts are mainly of hydrothermal origin near deep faults in the southwest and of biogenetic origin with less hydrothermal influence in the northeast of the studied area the dalong cherts occur in both nodular and bedded forms with more abundant siliceous fossil debris than the maokou cherts major trace and rare earth element data support that the dalong cherts are influenced by both biosilicification and hydrothermal activities the spatial heterogeneity of the cherts origin in south china is largely controlled by tectonic activities associated with the emeishan large igneous province elip event and the closure of the paleo tethys ocean the troughs formed by the extensional tectonic activity linked to the elip could provide accommodation space and activate deep faults allowing the rise of silicon rich hydrothermal fluids from the deep and nutrient rich water from volcanogenic upwellings subsequent cooling may have facilitated the precipitation of large amounts of silica and the formation of cherts in the study region this work demonstrates that the origin of the guadalupian lopingian cherts in south china is predominantly controlled by tectonic and biological activities which sheds light on the global permian chert event

numerical study on signatures of atmospheric convective cells in radar images of the ocean current and wind variations at the ocean surface can give rise to a modulation of the sea surface roughness and thus become visible in radar images the discrimination between radar signatures of oceanic and atmospheric phenomena can be quite difficult since signatures of different origin can have very similar shapes and magnitudes and are often superimposed upon each other in this work we employ a numerical radar imaging model for an investigation of typical properties of radar signatures of atmospheric convective cells and of theoretical differences between such atmospherically induced radar signatures and those of oceanic phenomena we show that main characteristics of observed multifrequency multipolarization radar signatures of atmospheric convective cells over the gulf stream are reproduced quite well by the proposed model this encourages us to vary wind and radar parameters systematically in order to get a general overview of the dependency of atmospherically induced radar signatures on these parameters finally we compare typical characteristics of radar signatures of atmospheric and oceanic phenomena and we present simulated radar images of a scenario of superimposed atmospheric convective cells and oceanic internal waves we show that the proposed model supports the experimental finding that radar signatures of oceanic phenomena are stronger at horizontal hh than at vertical vv polarization while atmospherically induced radar signatures are better visible at vv polarization

a record of long and short term environmental and climatic change during oae3 la luna formation late cretaceous santonian early campanian venezuela abstract the la luna formation was deposited under anoxic dysoxic conditions in a tropical epicontinental sea on the northwest south america margin sedimentological micropaleontological and geochemical evidence provides insights into factors that influenced the sedimentation and controlled the accumulation of organic rich deposits at decimeter and meter scales during the youngest of the cretaceous oceanic anoxic events oae the la luna formation consists of an alternation of black marlstones interbedded with black limestones and black marly limestones the benthic foraminifera assemblages indicate sedimentation in the upper neritic to upper bathyal environment these rocks contain large amounts of organic matter it is interpreted that a combination of warm global and rainy climate and the presence of bathymetric barriers caused poor circulation and low rates of water column ventilation during a high sea level in the early santonian leading to the preservation of carbon rich deposits in this region during the late santonian a cooling trend in global climate increased wind strength and upwelling this change probably reduced runoff causing a weakening of the pycnocline and destabilized the stratification in the water column providing a progressive increase in oxygen in the water column and on the sea floor and a decrease in total organic carbon preservation in a shallower basin these changes and the establishment of full mid and deep water exchange in response to the deepening and widening of the equatorial atlantic gateway could have been important mechanisms for ending the epeiric sea anoxia changes through time in the vanadium nickel fraction planktonic and benthic foraminifera assemblages productivity proxy elements and lithological characteristics support this model superimposed on the general trend variations in calcium carbonate and total organic carbon percentages at the scale of tens of centimeters reveal high frequency cyclic variations which apparently correspond to the main frequencies of orbital forcing this cyclicity is interpreted as a primary depositional signal and is the result of orbital controlled fluctuations in terrigenous dilution and variations in oxygen concentration at the base of the water column variations in the intensity of upwelling can be observed but they did not control the cyclicity

silica secreting biota and mass extinctions survival patterns and processes abstract high survival and at least regional blooms of siliceous marine groups with coeval retreat of calcareous organisms is known from the frasnian famennian radiolarians silicisponges and end cretaceous diatoms radiolarians mass extinctions a strictly actualistic approach to the palaeoecology of silica secreting biota is of limited significance especially for silica enriched and oligotrophic palaeozoic epeiric seas and in particular during biotic turnovers adaptation among silica secreting marine plankton has led toward more efficient utilization of shrinking dissolved silica resources within surface waters of cenozoic oceans as shown by both radiolarians and diatoms this biosiliceous signal during the major biotic crises is mostly explained by a large scale increase in volcano hydrothermal activity during major plate boundary re arrangements triggering global ecosystem perturbations the cumulative stimulus favoured siliceous versus calcareous biota growth deposition and preservation because of 1 a higher rate of input of silica and other nutrients promoting eutrophication pulses 2 a punctuated or reversed greenhouse climatic effect episodically coupled with 3 vigorous oceanic circulation due to a variety of volcanogenic upwellings and turnovers siliceous communities adapted to more eutrophic conditions have thrived in the stressed niches on the other hand expanding anoxia and nutrification may lead to a stepwise loss of deep water niches and consequent selective decline of more specialized oligotrophic radiolarians and other pelagic biota by contrast siliceous faunas experienced severe non selective losses during the end permian mass extinction recorded as a chert gap thus the greatest environmental disaster of the phanerozoic was driven by a unique set of killing factors extremely effective for radiolarian productivity e g due to the combination of a drastic volcanic winter with expanding superanoxia

searching for the elusive cold type occluded front abstractaccording to the norwegian cyclone model whether a warm type or cold type occluded front forms depends upon which cold air mass is colder the prewarm frontal air mass or the postcold frontal air mass for example a cold type occlusion is said to occur when the occluded front slopes rearward with height because the prewarm frontal air mass is warmer than the postcold frontal air mass this temperature difference and the resulting occluded frontal structure in the norwegian cyclone model is part of what is called the temperature rule paradoxically no clear example of a rearward sloping cold type occluded front has been found in the literature even though the required temperature difference has been documented in several cases this article presents the first documented rearward sloping cold type occluded front this occluded front forms in a cyclone over the north atlantic ocean on 3 5 january 2003 and is documented in model output from the european centre for medium range weather forecasts

rare earth major and trace element composition of monterey and dsdp chert and associated host sediment assessing the influence of chemical fractionation during diagenesis abstract chert and associated host sediments from monterey formation and deep sea drilling project dsdp sequences were analyzed in order to assess chemical behavior during diagenesis of biogenic sediments the primary compositional contrast between chert and host sediment is a greater absolute sio2 concentration in chert often with final sio2 98 wt this contrast in sio2 and si al potentially reflects precursor sediment heterogeneity diagenetic chemical fractionation or both sio2 concentrations and si al ratios in chert are far greater than in modern siliceous oozes however and often exceed values in acid cleaned diatom tests compositional contrasts between chert and host sediment are also orders of magnitude greater than between multiple samples of the host sediment calculations based on the initial composition of adjacent host observed porosity reductions from host to chert and a postulated influx of pure sio2 construct a chert composition which is essentially identical to observed sio2 values in chert thus precursor heterogeneity does not seem to be the dominant factor influencing the current chert composition for the key elements of interest in order to assess the extent of chemical fractionation during diagenesis we approximate the precursor composition by analyzing host sediments adjacent to the chert the sio2 concentration contrast seems caused by biogenic sio2 dissolution and transport from the local adjacent host sediment and subsequent sio2 reprecipitation in the chert along with sio2 other elements are often added with respect to al to monterey and dsdp chert during silicification although absolute concentrations decrease the two monterey quartz chert nodules investigated in contrast to the opal ct and quartz chert lenses formed primarily by extreme removal of carbonate and phosphate thereby increasing relative sio2 concentrations dsdp chert formed by both carbonate phosphate dissolution and sio2 addition from the host manganese is fractionated during chert formation resulting in mno al 2 o 3 ratios that no longer record the depositional signal of the precursor sediment ree data indicate only subtle diagenetic fractionation across the rare earth series ce ce values do not change significantly during diagenesis of either monterey or dsdp chert eu eu decreases slightly during formation of dsdp chert la n yb n is affected only minimally as well during formation of one monterey opal ct chert lens ree al ratios show subtle distribution changes at gd and to a lesser extent near nd and ho ree compositional contrasts between diagenetic states of siliceous sediment and chert are of a vastly smaller scale than has been noted between different depositional environments of marine sediment indicating that the paleoenvironmental ree signature is not obscured by diagenetic overprinting

volcanic edifice weakening via decarbonation a self limiting process 1 the inherent instability of volcanic edifices and their resultant propensity for catastrophic collapse is a constant source of volcanic risk structural instability of volcanic edifices may be amplified by the presence of carbonate rocks in the sub volcanic strata due to the debilitating response of carbonates to thermally induced alteration nonetheless decarbonation reactions the primary weakening mechanism may stall when the system becomes buffered by rising levels of a reaction product carbon dioxide such thermodynamic stalling might be inferred to serve to circumvent the weakness of volcanic structures however the present study shows that even when decarbonation is halted rock physical properties continue to degrade due to thermal microcracking furthermore as a result the pathways for the escape of carbon dioxide are numerous within a volcanic edifice therefore in the case of an edifice with a sub volcanic sedimentary basement the generation of carbon dioxide via decarbonation is unlikely to hinder its impact on instability and thus potentially devastating flank collapse

synthetic aperture radar observation of the sea surface imprints of upstream atmospheric solitons generated by flow impeded by an island 1 two cases of upstream propagation of atmospheric solitons generated by atmospheric flow over topography were identified on two radarsat 1 synthetic aperture radar sar images acquired near st lawrence island in the bering sea on 7 september 1997 and 6 june 2001 respectively in both cases a group of solitons was shown as three dark bright linear features on the sar images the soliton width and peak to peak distance measured from the two sar images are about 3 km and 4 5 km respectively simultaneous radiosonde measurements a surface weather map and operational weather model results confirm that these waves did not propagate on the lee side of the island as is commonly observed with island lee waves but indeed propagated against the flow in the upstream direction in the second case the same group of solitons was also identified as a wave like cloud pattern on a modis image taken about 4 5 hours later in this modis image the soliton train propagated further upstream with the leading crest reaching about 30 km north of the island and the number of crest trough features increased from three to seven in this study we describe the generation and evolution of upstream atmospheric solitons using the force kdv fkdv model with radiosonde and island topography data the numerical solution of the fkdv exhibits a sequence of solitons propagating upstream of the island both temporal and spatial scales of the solitons are in good agreement with that estimated from the successive sar and modis satellite images

geochemical characteristics and depositional environments of cherts and associated rocks in the franciscan and shimanto terranes abstract analyses of 122 jurassic cretaceous rock samples from the franciscan terrane california and 24 cretaceous samples from the shimanto terrane southwest japan show that the cherts and associated rocks accompanied by pillow basalts are enriched in fe and mn which may have been derived from hydrothermal activities the results of the fraction analyses for terrigenous basaltic hydrothermal and biogenic end members in the franciscan rocks show that hydrothermal emanations caused iron and manganese enrichment in the rock samples and played an important role in the formation of siliceous rocks vertical variations of the hydrothermal fraction and tio2 normalized values for hydrothermal elements such as fe mn ni zn y and pb show a possibility that the bedded cherts of the franciscan terrane were deposited in a hydrothermal field on or near some active oceanic ridge for more than 30 ma and were a remnant slice of oceanic crust added to the north american continent on the other hand from the field occurrences and vertical variations of tio2 normalized values of hydrothermal elements the shimanto rocks are inferred to have been deposited in a hemipelagic environment such as marginal and inter arc basins

baroclinic development within zonally varying flows previous idealized modelling studies have shown the importance of across jet barotropic shear to the resulting evolution of cyclones anticyclones surface based fronts and upper level fronts meanwhile many observational studies of cyclones have shown the importance of along jet variations in the horizontal wind speed i e confluence and diffluence this study investigates the importance of these along jet zonal for zonally oriented jets variations in the horizontal wind speed to the resulting structures and evolutions of baroclinic waves using idealized models of growing baroclinic waves an idealized primitive equation channel model is configured with growing baroclinic perturbations embedded within confluent and diffluent background flows when the baroclinic perturbations are placed in background confluence the lower tropospheric frontal structure and evolution initially resemble the shapiro keyser cyclone model with a zonally oriented cyclone strong warm front and bent back warm front later as the baroclinic wave is amplified in the stronger downstream baroclinicity the warm sector of the cyclone narrows becoming more reminiscent of the norwegian cyclone model the upper level frontal structure develops with a southwest northeast orientation and becomes strongest at the base of the trough where geostrophic cold advection is occurring in contrast when the baroclinic perturbations are placed in background diffluence the lower tropospheric frontal structure and evolution resemble the norwegian cyclone model with a meridionally oriented cyclone strong cold front and occluded front the upper level frontal structure is initially oriented northwest southeast on the western side of the trough before becoming zonally oriented weak geostrophic temperature advection occurs along its length these results are compared to those from previous observational and idealized modelling studies copyright 2007 royal meteorological society

geochemical signatures of bedded cherts of the upper la luna formation in tachira state western venezuela assessing material provenance and paleodepositional setting abstract here we undertook an inorganic geochemical study of cenomanian campanian bedded cherts the tachira ftanita member of the la luna formation in the western region of the tachira state venezuela the aim of this study was to determine the paleo oceanographic and paleo environmental conditions that governed the deposition of chert beds and put forward a sedimentation model for the tachira ftanita member in the study area seventy two chert samples were collected and trace rare earth elements la ce pr nd sm eu gd tb dy ho er tm yb lu rb cs th u y co and sc and major trace elements sio2 tio2 al2o3 fe2o3 mgo cao na2o k2o p2o5 mn ba sr cr ni and v were determined by icp ms and icp oes respectively on the basis of the stratigraphic abundance and distribution of relatively immobile elements as well as the distribution of rare earth elements we established that the detrital sediments associated with the sequences studied have matching characteristics with distinct continental materials with an intermediate composition thus pointing to the guayana massif as the main source of sediments in addition we also determined the influence of hydrothermal input on the chemical composition of some cherts from la molina mine on the basis of geochemistry we found a biological influence regarding the uptake of dissolved silica for forming chert beds the application of parameters for relatively immobile elements allowed us to establish a still proximal continental margin hemipelagic for most samples from the zorca river and a continental margin for almost all the cherts from the delicias villa paez section and the remaining samples from la molina mine finally we propose that the rhythmicity that accompanies the sequence of bedded cherts is related to changes in the intensity of upwelling patterns of water and or to variability in the supply of silica dissolved in the tachira sub basin

the late frasnian kellwasser horizons of the harz mountains germany two oxygen deficient periods resulting from different mechanisms in the harz mountains germany three late devonian sections aeketal huhnertal and kellwassertal were analyzed for major and trace element concentration the inorganic geochemical data were used to determine the environmental conditions associated with the deposition of the two late frasnian black kellwasser horizons in a submarine rise environment low ti al and zr al values and slight enrichment in nutrient and organic matter related trace elements e g ba cu and ni suggest that the kellwasser horizons were deposited during two periods of minimum detrital input but relatively elevated primary production enrichments in u v and mo in both black kellwasser horizons and values of redox indices including u th v cr and ni co indicate oxygen restricted conditions prevailed during the late frasnian times under oxygen depleted conditions reductive diagenesis caused precipitation of iron sulphides such as pyrite that are observed with sem however variations in major and trace element concentrations are not similar in the two kellwasser horizons particularly regarding redox markers the lower kellwasser horizon seems to be more o2 depleted than the upper kellwasser horizon in some german sections on the basis of these results we propose that the two kellwasser horizons are not caused by identical conditions the lower kellwasser horizon results from increased primary productivity enhanced by land derived nutrient loading and which triggered the anoxic conditions recorded in drowned platform setting in contrast the upper kellwasser horizon results from the onset of oxygen impoverished bottom water in the deepest part of the ocean due to episodic water stratification during maximum frasnian flooding oxygen depleted water may have impinged shallower environment during the linguiformis transgressive pulse nutrients would have been released from organic matter decay under reducing conditions and brought up to the photic zone during episodic water mixing

atmospheric front over the east china sea studied by multisensor satellite and in situ data 1 a frontal feature visible on a synthetic aperture radar sar image acquired by the radarsat satellite over the east china sea on 19 november 2000 is analyzed in conjunction with data acquired by quikscat topex poseidon tropical rain measurement mission trmm defense meteorological satellite program dmsp and national oceanic and atmospheric administration noaa satellites and with data obtained from ship measurements although this frontal feature is located close to the kuroshio front it is demonstrated that it is not a sea surface manifestation of an oceanic front but rather of an atmospheric front extending over 800 km from an area of the pacific ocean northeast of taiwan to the southern coast of korea it is a cold front moving in the southeast direction with a speed of approximately 45 50 km hour and associated with a 40 km wide rainband trailing the front the radarsat image which has a resolution of 50 m reveals fine scale structures of the atmospheric front in particular small scale convective rain cells embedded in the front conclusion is drawn that accurate interpretation of frontal features in sar images requires use of additional meteorological and remote sensing data and information

provenance and depositional setting of paleozoic chert and argillite sierra nevada california abstract the shoo fly complex the remnants of an early to middle paleozoic subduction system contains the culbertson lake allochthon included in the culbertson lake allochthon are the post cambrian and pre upper devonian quartz hill toms creek and mcmurray lake cherts geochemical data derived from these three units plot on the fe2o3 tio2 versus al2o3 al2o3 fe2o3 and lan cen versus al2o3 al2o3 fe2o3 discrimination diagrams within either the continental margin island arc field or that part of the pelagic field overlapping the continental margin island arc field these relationships a e consistent with the presence of argillaceous turbidites interstratified with radiolarite and suggest a relatively distal continental island arc setting where muddy turbidity currents episodically interrupted pelagic deposition specimens from the quartz hill and toms creek cherts with al2o3 tio2 values 20 make up group i samples whereas specimens with al2o3 tio2 values 10 are classified as group ii samples the al2o3 tio2 ratios of group ii specimens suggest derivation from mafic rock mean th sc and th u values as well as lree enriched patterns are consistent with this interpretation and indicate a source area dominated by alkalic seamount or ocean island material the al2o3 tio2 ratios of group i samples indicate a source area with an average andesitic to rhyodacitic composition chondrite normalized ree distribution patterns as well as mean th sc and th u value support such an interpretation samples from the mcmurray lake chert have al2o3 tio2 values ranging between 19 and 28 and ree patterns characterized by lree enrichment negative eu anomalies and slightly fractionated hree patterns these features along with mean th sc and th u values indicate a source area dominated by old upper continental crust the location of the source area s supplying material to cherts and argillites of the culbertson lake allochthon is unknown however existing tectonic models commonly portray the source of old upper continental crustal material in the shoo fly complex as being located somewhere along the western north american continental margin whereas the source of island arc debris is portrayed as being located in a fringing arc system our data suggest that a relatively high standing seamount or ocean island probably resided on the subducting oceanic plate thus our work supports the idea that al fe ti th sc and the rees in chert and argillite deposited in proximal continental island arc settings can be used to assess the characteristics of sources supplying particulate matter to ancient t ench systems

palaeoceanography of organic rich rocks of the loma chumico formation of costa rica late cretaceous eastern pacific the late cretaceous late cenomanian campanian loma chumico formation consists of laminated to massive bedded siliceous shales cherts ash fall tuffs volcanic glass beds and volcaniclastic sandstones the loma chumico formation is at least 630 m thick core data in the tempisque basin and can be subdivided in the subsurface into organic rich and organic lean total organic carbon 1 facies rock eval total organic carbon toc data show that toc in the organic rich facies averages 15 5 with values as high as 33 inorganic geochemical petrological and sedimentological analyses indicate that all the lithologies of the loma chumico formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc the organic geochemistry and palaeontology of the loma chumico formation help constrain the factors that controlled biological productivity in the region during the late cretaceous biomarkers identified in organic rich facies by gas chromatography mass spectrometry gc ms show a high abundance of total steranes relative to hopanes in the morote 1 core indicating algal dominated organic input the hopane to sterane ratio of the extract from the manzanillo 1 core indicates a relatively high bacterial component to the organic matter upwelling and extrusive volcanism were the most important factors that controlled nutrient supply including silica flux and biological productivity within the loma chumico formation depositional system episodic radiolarian dinoflagellate or diatom blooms instigated by rapid infusions of volcanogenic silica may have resulted in expansion of the oxygen minimum zone omz enhancing the preservation of organic matter productivity appears to have been uniform even during deposition of the organic lean facies the findings of this study suggest that ocean wide anoxia in the eastern pacific was unlikely during the late cretaceous high toc contents of organic rich radiolarites from central caribbean deep sea drilling project dsdp sites may be related to upwelling produced in the eastern pacific by convergence of the easterly trade winds eastern pacific equatorial upwelling zone or may be part of a more complex pacific atlantic ocean interaction the end of deposition of organic rich rocks began near the end of the latest santonian earliest campanian in the central caribbean and costa rica palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the north atlantic south atlantic seaway may explain this observation this may represent the influx of a previously unrecognized source of colder oxygenated intermediate bottom water proto antarctic intermediate water into the late cretaceous central atlantic and eastern pacific oceans

on the remote sensing of oceanic and atmospheric convection in the greenland sea by synthetic aperture radar 1 in this paper we discuss characteristic properties of radar signatures of oceanic and atmospheric convection features in the greenland sea if the water surface is clean no surface films or ice coverage oceanic and atmospheric features can become visible in radar images via a modulation of the surface roughness and their radar signatures can be very similar for an unambiguous interpretation and for the retrieval of quantitative information on current and wind variations from radar imagery with such signatures theoretical models of current and wind phenomena and their radar imaging mechanisms must be utilized we demonstrate this approach with the analysis of some synthetic aperture radar sar images acquired by the satellites ers 2 and radarsat 1 in one case an ers 2 sar image and a radarsat 1 scansar image exhibit pronounced cell like signatures with length scales on the order of 10 20 km and modulation depths of about 5 6 db and 9 10 db respectively simulations with a numerical sar imaging model and various input current and wind fields reveal that the signatures in both images can be explained consistently by wind variations on the order of 2 5 m s but not by surface current variations on realistic orders of magnitude accordingly the observed features must be atmospheric convection cells this is confirmed by visible typical cloud patterns in a noaa avhrr image of the test scenario in another case the presence of an oceanic convective chimney is obvious from in situ data but no signatures of it are visible in an ers 2 sar image we show by numerical simulations with an oceanic convection model and our sar imaging model that this is consistent with theoretical predictions since the current gradients associated with the observed chimney are not sufficiently strong to give rise to significant signatures in an ers 2 sar image under the given conditions further model results indicate that it should be generally difficult to observe oceanic convection features in the greenland sea with ers 2 or radarsat 1 sar since their signatures resulting from pure wave current interaction will be too weak to become visible in the noisy sar images in most cases this situation will improve with the availability of future high resolution sars such as radarsat 2 sar in fine resolution mode 2004 and terrasar x 2005 which will offer significantly reduced speckle noise fluctuations at comparable spatial resolutions and thus a much better visibility of small image intensity variations on spatial scales on the order of a few hundred meters index terms 3314 meteorology and atmospheric dynamics convective processes 4275 oceanography general remote sensing and electromagnetic processes 0689 4279 oceanography general upwelling and convergences 4255 oceanography general numerical modeling

fracture and compaction of andesite in a volcanic edifice the failure mode of lava dilatant or compactant depends on the physical attributes of the lava primarily the porosity and pore size and the conditions under which it deforms the failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit in this contribution we present a systematic experimental study on the failure mode of edifice forming andesitic rocks porosity from 7 to 25 from volcan de colima mexico the experiments show that at shallow depths 1 km while low porosity 10 lava remains dilatant the failure of high porosity lava is compactant and driven by cataclastic pore collapse although inelastic compaction is typically characterised by the absence of strain localisation we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores in terms of volcano stability faulting in the upper edifice could destabilise the volcano leading to an increased risk of flank or large scale dome collapse while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence spreading and destabilisation the failure mode influences the evolution of rock physical properties permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability i e equivalent permeability by about a factor of two and that inelastic compaction to an axial strain of 4 5 reduces sample permeability by an order of magnitude the implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice where rock can fracture but may be impeded deeper in the edifice due to compaction the explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice the mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style effusive versus explosive at stratovolcanoes

coexistence of atmospheric gravity waves and boundary layer rolls observed by sar abstractboth atmospheric gravity waves agw and marine atmospheric boundary layer mabl rolls are simultaneously observed on an environmental satellite envisat advanced synthetic aperture radar asar image acquired along the china coast on 22 may 2005 the synthetic aperture radar sar image covers about 400 km 400 km of a coastal area of the yellow sea the sea surface imprints of agw show the patterns of both a transverse wave along the coastal plain and a diverging wave in the lee of mount laoshan 1133 m peak which indicate that terrain forcing affects the formation of agw the agw have a wavelength of 8 10 km and extend about 100 km offshore model simulation shows that these waves have an amplitude over 3 km finer scale 2 km brushlike roughness features perpendicular to the coast are also observed and they are interpreted as mabl rolls the fft analysis shows that the roll wavelengths vary spatially the two way interactive triply nested grid 9 3 1 km weather research and forecasti

atmospheric circulation upwelling and organic rich rocks in the mesozoic and cenozoic eras abstract by using the basic principles of atmospheric circulation and analogies from present circulation patterns it is possible to construct qualitative atmospheric circulation models on paleogeographic maps the wind patterns predicted by these models then serve as the basis for predicting the locations of ancient upwelling zones atmospheric circulation and upwelling models for seven geologic stages in the mesozoic and cenozoic were constructed and the distribution of the upwelling zones compared with the distribution of organic rich rocks for all time periods together the correlation was statistically significant when the individual time periods were analyzed separately the following pattern emerged significant correspondence between upwelling zones and organic rich rocks in the triassic middle early cretaceous to late cretaceous and middle paleogene to neogene no significant correspondence was found for the intervening times upwelling does not account for all organic rich rocks so called anoxic oceanic events and transgressions play an important role in their deposition it is suggested that upwelling contributes significantly to the pattern of organic rich rock distribution and is important in determining organic facies

origin of chert in lower silurian longmaxi formation implications for tectonic evolution of yangtze block south china abstract upper ordovician katian to lower silurian rhuddanian strata in the middle upper yangtze block south china contain extensive chert beds although the origin of microcrystalline silica in these cherts is largely unknown in this study the mineralogy and structure of chert as well as major trace and rare earth elements are used to determine the origin of microcrystalline silica in 29 chert samples from longmaxi formation rhuddanian in baizitian outcrop west of kangdian uplift ku results show that 21 of the 29 chert samples have a biogenic origin 2 indicate a hydrothermal origin and 6 show a mixed origin cherts from baizitian outcrop are compared to contemporaneous cherts deposited east of ku cherts both east and west of ku are mainly biogenic in origin which is attributed to high productivity in the paleo seaway hydrothermal microcrystalline silica is relatively uncommon in the longmaxi formation across the middle upper yangtze block and only occurs in baizitian outcrop terrigenous influx contributed to chert accumulation both east and west of ku however cherts east of ku received much more clastic material than those in baizitian outcrop a comparison of chert composition and geochemistry to geological reconstructions of the middle upper yangtze block reveal that accumulation of hydrothermal chert is closely linked to tectonic evolution during the early silurian the middle upper yangtze block was in a compressional tectonic regime with limited heat supply and hence low hydrothermal circulation this is manifested in the paucity of hydrothermal microcrystalline silica in cherts east of ku in contrast hydrothermal microcrystalline silica in cherts west of ku is interpreted to have formed in an extensional tectonic regime with sufficient heat supply this research demonstrates that chert source is in part tectonic controlled and chert geochemistry can be used in reconstructing paleoenvironments

atmospheric boundary layer rolls observed by the synthetic aperture radar aboard the ers 1 satellite two synthetic aperture radar sar images acquired by the european remote sensing satellite ers 1 over the jade weser estuary in the german bight of the north sea on january 2 and 20 1992 are analyzed the images show sea surface manifestations of atmospheric boundary layer rolls this is inferred from the orientation of the quasi periodic sea surface patterns which are aligned approximately with the wind direction from the ratio of the wavelength of the patterns to the height of the boundary layer and from the conditions encountered in the atmospheric boundary layer as measured quasi simultaneously by radiosondes the atmospheric boundary layer rolls were generated by a dynamic instability on january 2 and by a thermal instability on january 20 for the first time quantitative estimates of variations of the wind velocity at the sea surface associated with the atmospheric rolls are extracted from a spaceborne radar sar image it is shown that wind velocities derived from sar image intensity variations are in agreement with theoretical estimates

campanian miocene tectonostratigraphy depocenter evolution and basin development of colombia and western venezuela abstract the position of the central axis of deposition over colombian and venezuelan continental crust has varied markedly through time the axis migrated from west to east from late cretaceous to oligocene but at times secondary drainage divides were established by local uplift events in oligocene times with initial inversion of the eastern cordillera the central axis of deposition was divided into two main axes the proto magdalena and the proto orinoco systems the west to east migration of the central axis of deposition had a tectonic origin and it occurred in combination with tectonically driven changes in accommodation space depocenter evolution can be divided as follows 1 the axis of the campanian and early maastrichtian depocenter was located few km east of the present position of the central cordillera of colombia it migrated east with gradual uplift of the central cordillera 2 the central axis of late maastrichtian deposition is positioned approximately over the present day western foothills of the eastern cordillera possibly crosses the eastern cordillera over the santander massif and continues into the maracaibo lake in western venezuela accommodation space decreased from campanian to maastrichtian times in cretaceous tertiary boundary times parts of the eastern margin of the eastern cordillera were uplifted by an initial phase of inversion of deeply rooted jurassic and early cretaceous normal faults 3 in paleocene times the central axis of deposition was located along the spine of the eastern cordillera and extended into the maracaibo basin and accommodation space continued to decrease 4 in latest paleocene times the central axis of deposition shifted to eastern regions of the eastern cordillera and accommodation space decreased 5 the early eocene central axis of deposition was located along the present day eastern foothills of the eastern cordillera accommodation space continued to decrease and the regional middle eocene unconformity began to develop in middle eocene times a regional unconformity developed marking the climax of the pre andean orogeny deposition during these times was dominant in the maracaibo basin area where large amounts of sediment derived from vast exposed areas accumulated 6 the late eocene central axis of deposition was confined to the present position of the llanos foothills late eocene deposition reflects a regional increase in accommodation space in oligocene times the initial uplift of the eastern cordillera divided the main depocenter into two central axes accommodation space diminished in uplifted regions but continued to increase in the depocenters allowing sporadic marine ingressions into the present position of the llanos foothills as uplift of the eastern cordillera continued the eastern depocenter axis proto orinoco migrated east and the western depocenter axis proto magdalena migrated west this process continued through the rest of the cenozoic

an ers 1 synthetic aperture radar image of atmospheric lee waves an ers 1 synthetic aperture radar sar image of the island hopen shows a distinct 7 6 km wavelength wave phenomenon near the island this wave phenomenon is interpreted as the surface imprint on open water of atmospheric lee waves the pattern is visible in the sar image since the lee waves modulate the horizontal wind speed near the ocean surface which in turn modulates the surface roughness and the radar cross section the physical setting for the observation is presented and discussed the lower bound on horizontal wind speed modulation is estimated to range from 3 2 ms 1 for the wind speed minima to 12 2 ms 1 for the wind speed maxima based upon the observed radar cross section modulation and the ers 1 scatterometer wind retrieval model cmod4 the wavelength and wind speed modulation are consistent with linear lee wave model predications the model uses an atmosphere with an exponential profile of the scorer parameter ratio of buoyancy frequency to wind speed to represent a shallow ground based inversion layer observed at bear island and a bell shaped barrier to represent the forcing effects of hopen

regional geologic and tectonic setting of the maracaibo supergiant basin western venezuela this special issue contains eight topical studies on the structure stratigraphy and petroleum system of the maracaibo basin a supergiant basin in western venezuela most of the work reported in this special issue is the product of thesis related research by master s and doctoral level students at the jackson school of geosciences of the university of texas at austin during a collaborative relationship with the venezuelan national oil company petrleos de venezuela s a that was initiated in the late 1980s this introductory article presents a regional overview of the tectonic setting and geology of the maracaibo basin with a cumulative oil production of more than 30 billion bbl since the first production well was drilled in 1914 and estimated ultimate oil reserves of more than 44 billion bbl the maracaibo basin is the most prolific hydrocarbon basin in the western hemisphere unlike the more extensive gulf of mexico giant hydrocarbon provinces the relatively small size 50 000 km2 19 305 mi2 relative simplicity in its structure and stratigraphy and wealth of surface and subsurface data make the maracaibo basin an attractive target for basinwide synthesis the objective of this article is to present a regional compilation of two dimensional 2 d and three dimensional 3 d seismic data wells and outcrop data at a basinwide scale to reveal the basin s 3 d structure and stratigraphy moreover we show regional tectonic reconstructions regional geologic maps and basin subsidence history to better constrain four major tectonic events that affected the basin and that are critical for understanding the timing and distribution of major unconformities and clastic wedges the distribution of the reservoir rocks the reactivation of older fault trends and the timing of maturation for underlying source rocks many of these topics are discussed in greater detail in the other eight articles in this special issue

tectonics basin subsidence mechanisms and paleogeography of the caribbean south american plate boundary zone abstract using a mega regional dataset that includes over 20 000 km of on and offshore 2d seismic lines and 12 wells we illustrate three different stages of fault formation and basin evolution in the caribbean arc south american continent collisional zone transpressional deformation associated with oblique collision of the caribbean arc migrates diachronously over a distance of 1500 km from western venezuela in paleogene time 57 ma to a zone of active deformation in the eastern offshore trinidad area each diachronous stage of pre syn and post collisional basin formation is accompanied by distinct patterns of fault families we use subsidence histories from wells to link patterns of long term basinal subsidence to periods of activity of the fault families stage one of arc continent collision initial collision is characterized by overthrusting of the south and southeastward facing caribbean arc and forearc terranes onto the northward subducting mesozoic passive margin of northern south america northward flexure of the south american craton produces a foreland basin between the thrust front and the downward flexed continental crust that is initially filled by clastic sediments shed both from the colliding arc and cratonic areas to the south as the collision extends eastward towards trinidad this same process continues with progressively younger foreland basins formed to the east on the overthrusting caribbean arc and forearc terranes north south rifting adjacent to the collision zone initiates and is controlled by forward momentum of southward thrusting arc terranes combined with slab pull of the underlying and subducting north dipping south american slab uplift of fold thrust belts arc continent suture induces rerouting of large continental drainages parallel to the collisional zone and to the axis of the foreland basins stage two this late stage of arc continent collision is characterized by termination of deformation in one segment of the fold thrust belt as convergent deformation shifts eastward rebound of the collisional belt is produced as the north dipping subducted oceanic crust breaks off from the passive margin inducing inversion of preexisting normal faults as arc continent convergence reaches a maximum strain partitioning also begins to play an important role as oblique convergence continues accommodating deformation by the formation of parallel strike slip fault zones and backthrusting southward subduction of the caribbean plate beneath the south caribbean deformed belt as subsidence slows in the foreland basins sedimentation transitions from a marine underfilled basin to an overfilled continental basin offshore sedimentation is mostly marine sourced by the collided caribbean terranes localized islands and carbonate deposition stage three this final stage of arc continent collision is characterized by 1 complete slab breakoff of the northward dipping south american slab 2 east west extension of the caribbean arc as it elongates parallel to its strike forming oblique normal faults that produce deep rift and half grabens 3 continued strain partitioning strike slip faulting and folding the subsidence pattern in the caribbean basins is more complex than interpreted before showing a succession of extensional and inversion events the three tectonic stages closely control the structural styles and traps source rock distribution and stratigraphic traps for the abundant hydrocarbon resources of the on and offshore areas of venezuela and trinidad

scavenged excess aluminum and its relationship to bulk titanium in biogenic sediment from the central equatorial pacific ocean we present results from chemical analyses of al and ti in surface sediment sampled along two cross equator latitudinal transects at 135w and 140w in the central equatorial pacific ocean although traditionally both al and ti are considered to reside exclusively within terrigenous phases in marine sediment these sediments present extremely high al ti ratios that are several times that of average shale and other potential crustal sources a sharp maximum in al ti is observed slightly south of the equator where sedimentary bulk accumulation rate bar is also highest reflecting elevated productivity in the overlying water caused by surface water divergence bulk al ti decreases sharply away 2 latitude to near crustal values at 4 north and south the latitudinal profiles of al ti are entirely unrelated to the concentration of the biogenic components as well as to the absolute accumulation of al and ti these results indicate the presence of a significant scavenged component of al sourced directly from seawater during particle settling the data from the two transects analytically and oceanographically confirms our earlier work that was based on the single 135w transect calculations of alexcess indicate that the highest al ti ratios correspond to 50 of the total al being unsupported by the small amount of terrigenous phases present these results are consistent with previous and ongoing studies of biogenic sediment suspended particulate matter and sediment trap material quantitative use of al as an index of terrigenous material may therefore lead to an overestimation by a factor of two of the true terrigenous load in marine sediment sedimentary rock and settling particles because bulk al ti appears to respond to sedimentary bar which in biogenic regimes is linked to surface water productivity downcore records of al ti in biogenic sediment may track productivity changes through time such al ti proxy records may be applicable in sediment of all ages unlike radionuclide tracers which are limited by radioactive decay to use over the past hundreds of kyr

geochemistry of late permian to early triassic pelagic cherts from southwest japan implications for an oceanic redox change major trace and rare earth element abundances were determined for the southwestern japanese pelagic chert sequence from the early late permian to early early triassic to investigate a redox change in deep sea pelagic environments before and at the permo triassic boundary ptb 251 ma the sequence was primarily deposited in the deep sea of the superocean panthalassa and then was accreted to japan in the middle jurassic a remarkable lithostratigraphic change from red chert to siliceous carbonaceous claystone through gray chert is observed in this sequence constituent elements for these sedimentary rocks are essentially derived from two sources 1 an ancient seawater via biogenic mainly radiolarian hydrothermal and authigenic materials and 2 an average shale like terrigenous material the present measurement demonstrates significant stratigraphic changes of the ce cenon ter value estimated ce anomaly value of non terrigenous component recalculated by subtraction of terrigenous rees from bulk rees and the mn te sample mn te paas value excess mn component other than terrigenous one te terrigenous elements including ti al nb hf th paas post archean average australian shale in the permian chert the ce cenon ter values increase from 0 2 to 1 and the mn te sample mn te paas values decrease up section suggesting that the redox condition of deep sea open ocean changed from oxic to suboxic in an interval of approximately 10 myr the fe te sample fe te paas and mn te sample mn te paas values of carbonaceous claystone near or at the ptb are less than unity suggesting that reductive dissolution of iron and manganese occurred under an anoxic condition this supports the idea of the ptb oceanic anoxia in the superocean panthalassa the present data suggest that the anoxic condition prevailed in the deep sea pelagic regions for an extremely long period much more than 10 myr from the middle late permian to early early triassic this long term development of widespread oceanic anoxia may have been linked to the greatest mass extinction of the phanerozoic

hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication od ocean ridge activity adachi m yamamoto k and sugisaki r 1986 hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication of ocean ridge activity sediment geol 47 i25 148 analyses of 42 cretaceous rock samples from deep sea drilling project dsdp leg 32 in tile northern pacific show that chert and porcellanite are enriched in fe mn p cu ba mo ni and pb relative to both triassic biogenic cherts of central japan and cretaceous dsdp cherts of leg 62 the iron enrichment up to 6 68ve fe20 as total iron is most prominent in chert immediately overlying basal basah which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions chemical features characterized by a low ratio for a1 ai fe mn and ai z tio 2 and a high ratio for total fe2oj tio 2 mno tio 2 and mo tio 2 as well as petrological evidence indicatc that the cherts formed in an intense submarine hydrothermal environment on or near the cretaceous japanese spreading center which separated the kula plate from the pacific plate the spreading rate of the cretaceous japanese spreading center estimated from the chemical composition of the cherts was about 3 7 cm r i the rate is comparable to that inferred from the geomagnetic data

geochemistry of sandstones from the upper miocene kudankulam formation southern india implications for provenance weathering and tectonic setting abstract petrographic major trace and rare earth element compositions of sandstones from the upper miocene kudankulam formation southern india have been investigated to determine their provenance tectonic setting and weathering conditions all sandstone samples are highly enriched in quartz q but poor in feldspar f and lithic fragments l the major element concentrations of these sandstones reveal the relative homogeneity of their source geochemically the kudankulam sandstones are classified as arkose subarkose litharenite and sublitharenite the cia values chemical index of alteration mean value 44 5 for these sandstones and the a cn k diagram suggest their low weathering nature similarly their fe2o3 mgo mean 2 7 al2o3 sio2 0 09 k2o na2o 2 2 ratios and tio2 contents 0 3 are consistent with a passive margin setting the eu eu 0 5 la lu cn 21 la sc 5 9 th sc 1 9 la co 5 7 th co 1 8 and cr th 5 3 ratios support a felsic source for these sandstones chondrite normalized ree patterns with lree enrichment flat hree and negative eu anomaly also are attributed to felsic source rock characteristics for kudankulam sandstones total ree concentrations of these sandstones reflect the variations in their grain size fractions the source rocks are probably identified to be proterozoic gneisses charnockites and granites of the kerala khondalite belt which must have been exposed at least since the late miocene finally the unusual ni enrichment in the kudankulam sandstones unaccompanied by a similar enrichment in cr co and v may be related to either the presence of pyrite in the sandstones or more likely the fractionation of garnet from the source rocks during transportation

hydrothermal venting and basin evolution devonian south china constraints from rare earth element geochemistry of chert this paper presents rare earth element ree geochemistry of siliceous deposits from which hydrothermal activity and basin evolution are elucidated in the late devonian in the yangshuo basin south china where siliceous deposits widely occurred as nodular chert in the deep water limestones and bedded chert interbeded with tuffaceous chert in the early late devonian both nodular and bedded cherts are characterized by very low la abundances avg 2 07 and 2 49 ppm respectively intermediate negative ce anomalies ce ce avg 0 69 and 0 61 slight to intermediate positive eu anomalies eu eu avg 1 33 and 1 57 and low to intermediate shale normalized lan ybn values avg 0 86 and 0 52 and intermediate lan cen values avg 1 61 and 1 72 these suggest both nodular and bedded cherts formed in the open marine basin of south china rather than in the intracontinental rift basin as previously assumed with involvement both with seawaters as indicated by intermediate negative ce anomalies and generally lree depleted patterns and hydrothermal vent fluids as indicated by convex less lree depleted patterns with apparent positive eu anomalies in comparison with nodular and bedded chert the tuffaceous chert has the highest la abundances avg 17 11 ppm similar ranges of ce anomalies avg 0 63 and lan cen values avg 1 77 but lower lan ybn values avg 0 48 and no apparent positive eu anomalies avg 0 97 this suggests that the tuffaceous fallouts were also significantly modified by the hydrothermal fluid and seawater rapid spatial variations of eu eu values and degree of lree depletions in the studied basin are recognized characterizing a spatially differential hydothermal activity that is not well discriminated by major element features such a difference in hydrothermal activity is interpreted as having been related to the intensity and depth of syndepositional tectonic activity reconciling the structural pattern unraveled by stratigraphic packages d 2005 elsevier b v all rights reserved

basin development and tectonic history of the llanos basin eastern cordillera and middle magdalena valley colombia the middle magdalena valley eastern cordillera and llanos basin constituted a major regional sedimentary basin from the triassic to the middle miocene basin development began during the triassic to the earliest cretaceous with a synrift megasequence related to the separation of north and south america in the proto caribbean the synrift megasequence began with deposition in a continental environment that became paralic and shallow marine in the early cretaceous basin development continued into the cretaceous in a back arc setting east of the andean subduction zone the back arc megasequence was dominated by shallow marine sedimentation and produced an excellent regional source rock during the turonian coniacian marine deposition was abruptly terminated during the ear y maastrichtian due to the final accretion of the western cordillera accretion of the western cordillera created the early pre andean foreland basin megasequence of late maastrichtian to early eocene age this depositional episode consists of coal rich alluvial plain coastal plain and estuarine deposits throughout the middle magdalena valley eastern cordillera and eastern llanos basin the megasequence was terminated by middle eocene deformation in the magdalena valley which ended sediment deposition throughout colombia loading effects of this deformation reestablished the basin in which the late pre andean foreland basin megasequence was deposited until the early miocene this megasequence also consists of alluvial plain coastal plain and estuarine deposits including the primary reservoir in the llanos foothills the upper eocene mirador fo mation the megasequence also includes a series of four major grossly coarsening upward cycles in the llanos basin these cycles correspond to changes in sea level sediment supply and foreland basin loading the mudstone in the lowermost of these cycles is the regional seal in the llanos basin and foothills the middle miocene onset of andean deformation in the eastern cordillera isolated the middle magdalena valley from the llanos basin the deformation was dominated by inversion of the basin controlling faults the resultant loading of the lithosphere created the accommodation space for the andean foreland basin megasequence a major transgression into the llanos basin coeval with this deformation caused deposition of marine mudstones in the lower part of the megasequence however the majority of the andean foreland basin megasequence consists of the guayabo formation a classic molasse sequence deposited in a high energy coarse grained bed load dominated fluvial system that was supplied by the developing mountains of the eastern cordillera

some examples of detection of oceanic mesoscale eddies by the seasat synthetic aperture radar this note presents images of three dynamically different regions in the ocean to demonstrate the variety of mesoscale variabilities detected by the seasat synthetic aperture radar sar south of the grand banks of newfoundland a cold eddy is observed to form as the result of the southward intrusion of labrador sea water perhaps having led to the birth of a gulf stream extension ring off the northern coast of california features resulting from the offshore intrusions of cold upwelling water are observed two topographically generated eddies are detected near misteriosa bank on the cayman ridge in the northwestern caribbean comparisons are made with concurrent noaa 5 infrared images whenever the eddies have thermal signatures

interoceanic variation in the rare earth major and trace element depositional chemistry of chert perspectives gained from the dsdp and odp record rare earth element ree major and trace element abundances and relative fractionations in forty nodular cherts sampled by the deep sea drilling project dsdp and ocean drilling program odp indicate that the ree composition of chert records the interplay between terrigenous sources and scavenging from the local seawater major and non ree trace element ratios indicate that the aluminosilicate fraction within the chert is similar to nasc north american shale composite with average pacific chert including 7 nasc like particles indian chert 11 nasc atlantic chert 17 nasc and southern high latitude shl chert 53 nasc using la as a proxy for ree approximations of laex the amount of la in excess of that supplied by the detrital aluminosilicate fraction indicate that pacific chert contains the greatest laex 85 of latotal and shl chert the least 38 of latotal as shown by interelement associations this laex is most likely an adsorbed component onto aluminosilicate and phosphatic phases accordingly chert from the large pacific ocean where deposition occurs relatively removed from significant terrigenous input records a depositional ree signal dominated by adsorption of dissolved rees from seawater pacific chert cece 1 and lanybn 0 8 1 resulting from adsorption of local ce depleted seawater and preferential adsorption of lrees from seawater e g lanybn 0 4 which increases the lanybn ratio recorded in chert chert from the atlantic basin a moderately sized ocean basin lined by passive margins and with more terrigenous input than the pacific records a mix of adsorptive and terrigenous ree signals with moderately negative ce anomalies and lanybn ratios intermediate to those of the pacific and those of terrigenous input chert from the shl region is dominated by the large terrigenous input on the antarctic passive margin with inherited cece 1 and inherited lanybn values of 1 2 1 4 cece does not vary with age either throughout the entire data base or within a particular basin overall cece does not correlate with p2o5 concentrations even though phosphatic phases may be an important ree carrier this and previous studies of the large scale controlling parameters of sedimentary rees across ocean basins collectively indicate that ree indices of depositional regime e g cece lanybn laex are reproducible in a variety of sediment and rock lithologies ages and ocean basins and present a coherent tool for paleoceanographic and tectonic basin reconstructions

global and local controls influencing the deposition of the la luna formation cenomanian campanian western venezuela bulk and molecular geochemical micropalaeontological and carbon isotopic data are used to address the different local and global factors influencing the environment of sedimentation of the la luna formation cenomanian campanian approximate palaeolatitude 15 n in a single section in western venezuela based on the constructed chronostratigraphic framework oxygen depleted bottom water conditions and black shale deposition started in western venezuela well before the widespread occurrence of organic rich sediments in higher palaeolatitude regions such as the tethys and the north atlantic near or at the cenomanian turonian boundary in the la luna formation palaeoenvironmental conditions that allowed the preservation of organic matter mainly of marine origin prevailed until santonian times in a distal platform facies with very low siliciclastic input changes in lithology appear to reflect the local response to eustatic sea level variations and the presence of a migrating upwelling belt affecting the bioproductivity of silica and carbonate a marked 13corg isotopic excursion is recognised in the middle part of the section and is apparently unrelated to local palaeoenvironmental changes in bioproductivity and oxygen depletion biological marker data show no variations in association with the isotopic excursion being mainly controlled by local fluctuations in organic matter input and preservation

the archean proterozoic transition evidence from the geochemistry of metasedimentary rocks of guyana and montana abstract chemical and isotopic compositions of ancient sedimentary rocks have in some cases provided evidence of first order changes yin the composition and extent of continental crust from the archean to the proterozoic we reversed the typical sampling pattern comparing metapelites and carbonates from proterozoic greenstone belts with those from an archean continental margin sequence and found the reverse of the typical age composition relations metapelites and volcaniclastic metagreywackes from the early proterozoic greenstone belts of northern guyana resemble those of many archean greenstone belts in ree trace and major element compositions mean ratios la sm 5 0 la th 5 1 eu eu 0 80 th u 3 4 median k 2 o na 2 o 0 8 schists from an archean continental marginal sequence in montana have compositions like many post archean metapelites derived from continental sources mean ratios la sm 6 8 la th 2 7 eu eu 0 67 th u 5 2 median k 2 o na 2 o 1 7 other archean continental basin sediments also resemble their post archean counterparts implying that upper continental crusts of these eras may not have differed significantly in these respects however temporal change may have occurred in upper crustal contents of ni and cr many archean clastic metasedimentary rocks of both continental and greenstone belt provenance have contents of these compatible elements higher than in their post archean equivalents dolomitic limestone from a greenstone belt of northern guyana has a very low 87 sr 86 sr ratio of 0 7007 such low values may reflect the local influence of mantle derived volcanic rocks during carbonate deposition diagenesis or metamorphism and they may not be reliable indicators of the evolution of sr in seawater archean dolomitic marbles from the continental marginal sequence of montana have 87 sr 86 sr ratios of 0 7065 and higher significantly more radiogenic than many accepted values for carbonates of archean greenstone belts

origin of rhythmical bedding in middle miocene siliceous rocks of the onnagawa formation northern japan abstract centimeter to decimeter scale rhythmical alternation of dark and light layers is common in siliceous rocks of the middle miocene onnagawa formation of northern japan the siliceous rocks may also show micrometer scale laminae considered to be varves dark layer frequency shows meter scale cyclic variation with dominant spectral peaks of approximately 10 5 4 3 4 2 3 and 1 6 m for these a varve tuned average sedimentation rate of 139 m yr yields periods of 72 39 24 17 and 12 kyr respectively a sedimentation rate of 100 m yr which is within the range of biostratigraphically calculated rates yields 100 54 34 23 and 16 kyr respectively considering the uncertainty in the estimation of the average sedimentation rate these values are in relatively good agre ment with orbital eccentricity obliquity and precessional cycles respectively bottom water oxygenation levels deduced from the lamina preservation index are in phase with the frequency variation of dark layers suggesting that it is also controlled by orbital cycles mineral and chemical analyses suggest that the siliceous rocks are mainly composed of biogenic diagenetic silica terrigenous detritus dolomite and organic matter with minor amounts of carbonate fluorapatite the dark colors are due to detritus and organic matter thus alternation of dark and light layers and variation in the frequency of dark layers reflect compositional variation mass accumulation rates mars of biogenic silica and terrigenous detritus are calculated from the average thickness of a lamina couplet dry bulk density and chemical composition of individual samples at the level of centimeter to decimeter layers mar of detritus is nearly constant whereas mar of biogenic silica varies by a factor of 2 on the other hand mar of detritus shows meter scale variation with amplitudes as high as a factor of 10 which is in phase with frequency cycles of dark layers whereas mar of biogenic silica does not show significant meter scale variation compositional variation represented by dark and light alternation and frequency cycles of the dark layers are a result of the interplay of centimeter to decimeter scale 102 3 years variation in mar of biogenic silica and meter scale 104 years variation in mar of detritus the latter could be related to global sea level oscillation caused by orbital cycles

coastal katabatic winds imaged by sar 1 sea surface imprints of coastal katabatic winds are observed on a radarsat 1 synthetic aperture radar sar standard mode image off the u s west coast taken on january 21 2003 the katabatic wind pattern is shown in the sar image as a striking finger like bright dark region that mirrors the coastal mountain topography we simulate the low level atmospheric circulation using the numerical weather model mm5 with a triply nested grid technique the model simulation reproduces the finger like katabatic wind pattern at the sar imaging time katabatic wind is strongest in the morning when the surface temperature gradient between ocean and land reaches a maximum the sea surface wind simulated by the mm5 model and that derived from the calibrated sar normalized radar cross section are in good agreement the katabatic wind variation along the coastline is between 5 8 ms 1 and the longest wind finger stretches over 20 km offshore

palaeoecology palaeogeography and depositional environments of upper cretaceous rocks of western venezuela abstract the end of the early cretaceous in northern south america was marked by regional palaeoceanographic change in western venezuela this change was highlighted near the end of the albian by drowning of the maraca formation shallow water carbonate platform regional marine transgression continued during the cenomanian and turonian in western venezuela with drowning of the more southerly guayacan member capacho and escandalosa formations carbonate platform deposition of organic carbon rich intervals of the la luna and navay formations occurred unconformably on maraca formation and guayacan member shallow water carbonates and continued through the early santonian during this interval the maracaibo and barinas apure basins were characterized by low oxygen or anoxic bottom water conditions away from the basin margins deposition of organic carbon lean upper la luna and navay formation strata show that bottom water oxygen content increased from the late santonian through the end of the cretaceous the siliceous and phosphatic late santonian to early maastrichtian tres esquinas member and the glauconitic late campanian to early maastrichtian socuy member both of the la luna formation represent the final phase of la luna deposition in the maracaibo basin tectonic uplift in eastern colombia during the campanian and maastrichtian caused progradation of the colon mito juan and burguita formation deltas and eventual infilling of the maracaibo and barinas apure basins

origin of silica paleoenvironment and organic matter enrichment in the lower paleozoic niutitang and longmaxi formations of the northwestern upper yangtze plate significance for hydrocarbon exploration abstract lower paleozoic shale is an important source rock and reservoir for gas in the northwestern upper yangtze plate the paleoenvironment and its impact on organic matter enrichment of the shale plays a vital role in the exploration and development of the resource based on the analysis of the results of total organic carbon toc maceral examination bitumen reflectance rb major elements trace elements rare earth elements rees and x ray diffraction xrd of shale samples from the niutitang and longmaxi formations the origin of silica the paleoenvironment and the mode of organic matter enrichment of the shale were examined the shales of the niutitang and longmaxi formations have high toc abundance with type i organic matter and high maturity quartz and clay minerals dominate the mineral constituents leading to characterization as siliceous shale the average sio2 content of the shale in the niutitang and longmaxi formations is above 70 wt al2o3 and tfe2o3 total iron are the next most abundant major elements with average values of 12 80 wt and 1 95 wt in the niutitang formation and average values of 11 44 wt and 4 09 wt in the longmaxi formation compared with the upper continental crust ucc v mo and u are the most enriched elements the average lree hree of the shale samples is very low and the chondrite normalized ree distribution pattern shows sloping lree trends and flat hree trends towards the right the total rare earth elements of the shale vary within the range of 147 85 219 60 ppm and 159 90 222 02 ppm in both the niutitang and longmaxi formations suggesting that the shale has not been subject to obvious hydrothermal fluid activities the correlation diagrams of sio2 al2o3 sio2 toc and siexcess toc the diagrams of hydrothermal origins and the elemental parameters indicate that the silica of the shales from the niutitang and longmaxi formations are mainly of biogenic origins with a lesser contribution from terrigenous detrital sources the ratios of mno2 tio2 and al2o3 al2o3 tfe2o3 of the shale samples all show limited variability illustrating that the shales are mainly deposited on the continental margin the average chemical alteration index cia values of the niutitang and longmaxi formations are 71 25 and 72 77 with little variation and the average sr cu ratios are 4 38 and 2 22 reflecting a warm and humid paleoclimate for both formations the average ni co th u and u readings of the shale samples of the formations are 10 91 0 97 and 1 51 and 12 69 0 43 and 1 75 indicating that the redox conditions during the sedimentation of the formations were anoxic the positive correlations between toc and paleoenvironmental proxies reveal a warm and humid climate and that anoxia had a positive effect on organic matter enrichment these conditions have laid a geological foundation for the enrichment of shale gas and that the upper yangtze plate is favorable for future shale gas exploration

footprints of storms on the sea a view from spaceborne synthetic aperture radar synthetic aperture radar sar on board seasat observed images of stormlike echoes on the sea in 1978 the core of these images is usually an echo free hole which is attributed to the damping of the short 30 cm radar detectable gravity waves by the intense rain in the storm core although the beating down of waves by rain is consistent with observations by seafarers and with the first scientific explanation of the phenomenon by reynolds 1875 neither theory nor experiment has provided definitive support one experiment appears to provide the key it shows that the kinetic energy of the rain produces sufficient turbulence in a thin fresh water layer to damp 30 cm waves in 10 20 s thus producing the echo free hole a sequence of positive feedbacks then serves to damp the longer waves the angular dependence of the sea surface echo cross sections seen by seasat sar outside the echo free hole indicates winds diverging from the downdraft induced by the intense rain core the wind generated waves and associated echoes extend out to a sharply defined gust front the sea surface footprint thus mimics the features of a storm microburst the variations in surface radar cross section due to a combination of rain and wind effects impacts spaceborne measurements of surface winds by scatterometry and rainfall measurements by radar portions of this synthesis remain speculative but serve as hypotheses for further research

rare earth geochemistry of arenig cherts from the ballantrae ophiolite and leadhills imbricate zone southern scotland implications for origin and significance to the caledonian orogeny rare earth element ree data from low to mid arenig cherts are used to test competing models for the early ordovician evolution of the laurentian margin in the northern british isles cherts from the ballantrae ophiolite complex have chondrite normalized ree patterns typical of continental margin settings with lree enrichment a slight negative eu anom and shale and chondrite normalized la yb values of 0 97 1 41 and 7 78 11 4 respectively this pattern together with a large positive chondrite normalized ce anom 1 44 1 70 is virtually identical to that found in radiolarian chert of the gascoyne abyssal plain in the timor sea cherts from the raven gill formation within the leadhills imbricate zone northern belt southern uplands have typical continental margin ree patterns chondrite normalized ce anom 0 9 1 21 and eu anom 0 61 0 79 values indicating that they formed closer to the continental margin than those from ballantrae shale and chondrite normalized and la yb values of 0 95 1 27 and 4 92 13 88 respectively confirm this interpretation it is concluded that the ballantrae ophiolite formed in a rifted arc basin above a northwards dipping intra oceanic subduction zone the modest depth of burial of the raven gill formation precludes it being part of a marginal basin which was subsequently trapped as the ballantrae ophiolite was obducted in the late arenig the arenig rocks of the leadhills imbricate zone represent an allochthonous terrane accreted to the western extension of the midland valley in ireland in pre caradoc times here it formed the basement to the southern uplands basin palaeontological evidence places this basin adjacent to pomeroy co tyrone in the early caradoc sinistral strike slip faulting from the late ashgill transported the southern uplands terrane to its present location a distance of less than 250 km

chert in the pacific biogenic silica and hydrothermal circulation abstract data on sections drilled by dsdp and odp in the pacific have been compiled for 187 sites 105 of which contain chert the spatial pattern of siliceous deposits in the pacific generally follows the pattern of biologic productivity there is some evidence that enhanced vertical diffusivity in the ocean during the eocene warm climate gave rise to siliceous deposits on and near bathymetric highs and basin margins the most common occurrence of chert is in eocene and older sections however cherts do occur in sections as young as 7 ma in the sites investigated over half of the youngest chert occurrences in sedimentary sections are within 150 m of basement nearly all the chert occurrences on crust younger than 60 ma are within 150 m of basement the deficit in heat flow over ocean crust younger than 60 ma is explained as the result of heat advection by hydrothermal waters circulating in the upper part of the ocean crust these waters appear to dissolve biogenic silica and deposit it as chert in the lower parts of sedimentary sections diffusion of these waters into the lower sediment section is enhanced by small scale faulting this faulting may be associated with intra plate stresses that develop during ridge jumps and reorientations of plate motion the relatively warm bottom waters of the early cenozoic may have also enhanced the dissolution of biogenic silica during hydrothermal circulation in the upper oceanic crust and basal sediment section

katabatic wind fields in coastal areas studied by ers 1 synthetic aperture radar imagery and numerical modeling synthetic aperture radar sar images acquired over mediterranean coastal waters from the first european remote sensing satellite ers 1 showing sea surface manifestations of katabatic wind fields are presented in particular sea surface roughness patterns generated by katabatic winds blowing from 1800 in high mountains through a broad valley at the western coast of calabria southern italy into the gulf of gioia is investigated the ers 1 sar images show that their areal extent and shape vary strongly depending on the meteorological conditions the roughness pattern sometimes has the form of a mushroom an elongated tongue a broad blob or a narrow truncated band for one event september 8 1992 we have simulated the wind field at the sea surface by using a nonhydrostatic mesoscale atmospheric model and then compared it with the wind field derived from the ers 1 sar image by using the c band wind scatterometer model cmod4 the comparison shows that the atmospheric model reproduces quite well the mushroom like form of the wind field pattern while the wind speed is obtained somewhat lower than the one inferred from the sar image this study demonstrates that sar images acquired over coastal waters are well suited to study local wind fields in coastal areas and to test numerical models that describe local wind fields which extend from the coast onto the sea

geochemistry of chert rocks from the sikhote alin taukha terrane russia far east significance for determination of their depositional environment the first geochemical data of the benevka section chert rocks belonging to the taukha terrane of the sikhote alin late jurassic early cretaceous accretionary prism russia far east are discussed in this work in particular the geochemical data obtained show that the content of ce increases progressively from the low horizons of stratigraphic succession represented by bedded cherts to the upper horizons composed of clayey cherts which gradually pass to siliceous mudstones at the uppermost part correspondingly the value of the negative ce anomaly ce ce decreases progressively up the benevka section the ce anomaly value of bedded cherts ranges 0 34 0 69 well developed negative ce anomalies whereas those of upper horizons of bedded cherts and lower horizons of clayey cherts vary from 0 75 to 0 87 slightly less but also well developed negative ce anomalies slight negative ce anomalies 0 91 0 94 were revealed in the upper horizons of clayey cherts and in siliceous mudstones in addition the nasc normalized la ce ratio i e lan cen has been calculated the value of which also decreases progressively upward of the measured stratigraphic section from 2 87 to 1 02 the totality of all geochemical data indicates that the benevka section chert rocks were formed in an oceanic depositional environment but in different paleo ocean locations the lowermost horizons of bedded cherts were deposited to near spreading ridge proximal depositional environment the open ocean and transition zone between open ocean and near continental margin depositional environments are reconstructed for the upper horizons of bedded cherts and low horizons of clayey cherts the upper horizons of clayey cherts and siliceous mudstones were accumulated at near continental margin depositional environment

rare earth elements as indicators of hydrothermal processes within the east scotia subduction zone system the east scotia subduction zone located in the atlantic sector of the southern ocean hosts a number of hydrothermal sites in both back arc and island arc settings high temperature 348 c black smoker vents have been sampled at three locations along segments e2 and e9 of the east scotia back arc spreading ridge as well as white smoker 212 c and diffuse 28 c hydrothermal fluids from within the caldera of the kemp submarine volcano the composition of the endmember fluids mg 0 mmol kg is markedly different with ph ranging from 1 to 3 4 cl from 90 to 536 mm h2s from 6 7 to 200 mm and f from 35 to 1000 m all of the vent sites are basalt to basaltic andesite hosted providing an ideal opportunity for investigating the geochemical controls on rare earth element ree behaviour endmember hydrothermal fluids from e2 and e9 have total ree concentrations ranging from 7 3 to 123 nmol kg and chondrite normalised distribution patterns are either light ree enriched lacn ybcn 12 8 30 0 with a positive europium anomaly eucn eu cn 3 45 59 5 or mid ree enriched lacn ndcn 0 61 with a negative eu anomaly eucn eu cn 0 59 by contrast fluids from the kemp caldera have almost flat ree patterns lacn ybcn 2 1 2 2 eucn eu cn 1 2 2 2 we demonstrate that the ree geochemistry of fluids from the east scotia back arc spreading ridge is variably influenced by ion exchange with host minerals phase separation competitive complexation with ligands and anhydrite deposition whereas fluids from the kemp submarine volcano are also affected by the injection of magmatic volatiles which enhances the solubility of all the rees we also show that the ree patterns of anhydrite deposits from kemp differ from those of the present day fluids potentially providing critical information about the nature of hydrothermal activity in the past where access to hydrothermal fluids is precluded

geochemical discrimination of clastic sedimentary rock sources abstract factors controlling the geochemistry of a clastic sedimentary rock can include 1 composition of source terrain 2 chemical weathering 3 hydraulic sorting 4 diagenesis 5 metamorphism and 6 hydrothermal alteration a linear solution inferring source terrain composition from geochemistry of the sediment is impossible in this multivariate system as several unknowns will commonly be present the use of graphical analysis of element pairs circumvents the problem chemically immobile elements will maintain invariant ratios during rock mass change caused by either addition or depletion of mobile elements this results in chemically immobile element scattergrams exhibiting linear trends along radians extending from the origin if the major mineral phases of the immobile elements have behaved in a hydrodynamically similar manner as chemically mobile element plots will produce a scatter of points this relationship can be used to test chemical immobility and similarity in hydrodynamic sorting history the constraint on analysis is that the source area must be compositionally uniform or the sediment well mixed prior to delivery to the basin a second technique using sio2 plots has also been developed to investigate element mobility and hydrodynamic behaviour of the mineral phases containing the elements sio2 immobile element plots result in a linear arrangement of points extending towards either 0 or 100 sio2 the 0 intercept position occurs for elements with major mineral phases concentrated in sand the 100 intercept for those concentrated in clays plotting chemically mobile elements produces different patterns and this can be used to gain information on alteration and sorting history elemental ratios for chemically immobile elements with similar hydrodynamic behaviour will be the same as those for the weighted average composition of the source material this provides a powerful tool for deducing source terrain from sediment geochemistry techniques outlined above were tested on archaean metasandstones from superior province canada immobile element ratio diagrams for nb al ti and zr al ti indicate that a calc alkaline extrusive intrusive suite lying to the north of the study area was the source and not five other volcanic suites in the region this conclusion agrees with previous clast lithology studies and accentuates the applicability of the geochemical techniques

boundary layer roll statistics from sar the atmospheric boundary layer abl mean flow frequently consists of an organized secondary circulation in the form of counter rotating rolls embedded in it theory predicts this is the case for a range of thermodynamic conditions although generally associated with the formation of cloud streets numerical and theoretical studies suggest that rolls should be present whenever there is sufficient shear to organize the convection including cloud free conditions through their association with clouds and their modification of the mean low level flow abl rolls alter air sea interaction processes surface energy fluxes and the earth radiational balance despite their potential importance to climate there exist no prior studies that can establish the extent and statistical frequency of roll occurrence synthetic aperture radar sar can detect abl roll signature on the ocean surface a first regional climate scale attempt to construct abl roll frequency statistics from the radarsat sar observations is described

late cretaceous upwelling and anoxic sedimentation in northwestern south america abstract black shales and bituminous limestones were widely deposited in northwestern south america during the maximum transgression of late cretaceous seas these cenomanian to santonian campanian anoxic sediments are distributed in two main subprovinces thick chert and phosphorite accumulated in the trough subprovince landward of a possibly partially emergent cordillera central colombia only minor intercalations of chert were deposited in the platform subprovince lying northward in the maracaibo basin northwestern venezuela faunal evidence depauperate benthic fauna planktic foraminiferal assemblages high dominance clupeoid fish assemblages and sedimentological evidence suggest anoxic condition prevailed throughout the region probably the result of dynamic upwelling in the trough subprovince but the reflection of a global anoxic event within the platform subprovince

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

synergistic use of satellite observations and numerical weather model to study atmospheric occluded fronts synthetic aperture radar sar images reveal the surface imprints of atmospheric occluded fronts an occluded front is characterized as a low wind zone located between and within two zones of higher winds blowing in the opposite directions on the left and right sides of the occluded front a group of four sar images reveal that the width of an individual occluded frontal zone and the wind magnitudes outside fronts vary greatly from case to case in this paper we performed a case study to analyze an occluded front observed by an environmental satellite envisat advanced sar and ascat scatterometer along the west coast of canada on november 24 2011 the two way interactive triply nested grid 9 3 1 km weather research and forecasting wrf model was utilized to simulate the evolution of the occluded front the occluded front moved toward the east during a 24 h model simulation and the movement between 18 00 and 21 00 utc matched the occluded front positions derived from the concurrently collected surface weather maps from the national oceanic and atmospheric national weather service archives the wrf simulated low wind zone associated with the occluded front and ocean surface wind speed match well with the sar and scatterometer wind retrievals high wind outside the front zone became weaker during the front evolution whereas the width of the occluded frontal zone was contracted laterally analysis of the wrf model derived potential temperature field suggests that the occlusion process occurred below the 800 mb level the structure of the occluded front studied here not only follows the conventional conceptual model and also supports the findings of a novel wrap up conceptual model for an atmospheric frontal occlusion process

rare earth major and trace elements in chert from the franciscan complex and monterey group california assessing ree sources to fine grained marine sediments abstract rare earth element ree major and trace element analyses of 77 samples from the mesozoic franciscan complex and miocene monterey group of california usa indicate that magnitudes of the ce anomaly ce ce and total ree abundances sree in these rocks are controlled dominantly by a the amount of included metalliferous material b the amount of direct terrigenous input and c the overall burial rate the relative importance of these individual processes varies across an ocean basin in such a way that ree relative fractionations and sree correspond with its depositional environment our conclusions are supported by an extensive review of published ree data from various river coastal open ocean and ridge influenced waters as well as terrigenous pelagic and metalliferous sediment the chert sequences record deposition in spreading ridge open ocean basin and continental margin environments the relative importance of metalliferous and terrigenous influences and the role of scavenging from seawater may be estimated from a sample s inferred depositional distance km from the spreading ridge the major element chemistry and the stratigraphie context the ce ce values are low 0 29 in the vicinity of spreading ridges and trend to successively higher 1 values with decreasing metalliferous and increasing terrigenous influences other ree indicators ree lu n la n eu eu also respond to metalliferous and terrigenous influences near the spreading ridge chert ree appears determined by burial rate while shale ree responds to metalliferous abundance in open ocean and continental margin environments ree is controlled by sediment exposure time and therefore is related inversely to burial rate ree data are consistent with the major elements fe2o3 mno and al2o3 in reflecting the respective metalliferous and terrigenous sources p2o5 and cao do not vary with ce ce in any environment but cao shows a weak negative correlation with ree trace element trends e g v cr cu ge si rb sr y th u in general can similarly be accounted for in the context of depositional position relative to metalliferous and terrigenous inputs rees in chert appear less affected by post depositional processes than either major or trace elements indicating that rees are better tools for paleoceanographic or tectonic reconstructions that are based on chert chemistry this work complements recent efforts to elucidate the factors determining large scale ree distributions in marine sediments and has direct bearing on previous attempts to use the ce anomaly in older rocks and sediments as a recorder of secular variations and anoxic events in the overlying water column

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

sea surface imprints of coastal mountain lee waves imaged by synthetic aperture radar 1 a group of mountain lee waves is observed on an envisat advanced synthetic aperture radar sar image on the lee side of mountain laoshan 1133 m along the yellow sea coast of china the lee waves are shown as alternating bright and dark patterns on the sar image indicating the ocean surface wind oscillation associated with the atmospheric wavefield the horizontal wind variation between wave crest and trough is from 7 to 17 m s a moderate resolution imaging spectroradiometer image acquired about 8 5 h prior to the sar pass also showed the same group of standing lee waves the cloud pattern matches the high wind pattern in the sar derived wind image the mesoscale weather research and forecasting wrf model is used to simulate the lee wave phenomenon we run the triply nested grid model with the highest horizontal resolution of 1 km the wrf model successfully captures the characteristics of the lee wave the waves are generated by the terrain forcing and the wave induced perturbation propagates very strongly upward to the 500 hpa level the event lasts about 24 h based on the wrf model wind results we run a radar imaging model to simulate the sar observation the normalized radar cross section nrcs variations induced by the lee wave are compared between the radar simulation and the actual sar observation reasonable agreement is reached

geochemistry of the sedimentary rocks from the nanxiong basin south china and implications for provenance paleoenvironment and paleoclimate at the k t boundary cretaceous and tertiary clastic sedimentary rocks from the nanxiong basin south china have been analyzed to constrain their provenance depositional climate and environment evidence from discrimination diagrams for sedimentary provenance and tectonic setting show that the nanxiong basin sediments were derived from typical continental sources geochemical signatures e g eu eu th ti la ti ta ti y b ti and y ti ratios of the claystone are nearly constant suggesting the provenance of the nanxiong basin remained similar throughout the late cretaceous to early paleocene 83 56 ma in contrast rb ti cs ti ratios and toc and caco3 concentrations require an obvious change in climate across the late cretaceous and early paleocene boundary singularly higher caco3 contents and lower toc values and rb ti cs ti ratios in the late cretaceous indicate that a long period extreme dry climate occurred at that time in south china rb ti cs ti ratios and toc values escalated and caco3 contents decreased in the early paleocene suggesting that the climate became relatively wet which resulted in greater vegetation cover the lasting extreme dry climate in the late cretaceous may provide a clue to the extinction of the dinosaurs in the nanxiong basin c 2006 elsevier b v all rights reserved

the occlusion process in a midlatitude cyclone over land abstract a historical review highlights the lack of consensus regarding the structure and evolution of occluded fronts and cyclones in order to better understand the occlusion process this paper and its companion examine a model simulation of the 14 16 december 1987 cyclone over the eastern united states the structure of an occluded front was observed at low levels as the cold front caught up with the warm front while aloft an upperlevel frontal zone appeared to play a role in the occlusion process although the thermal structure of this storm suggested that a cold type occlusion should have formed the model simulation produced a warm type occlusion structure an extensive review of the literature on occluded fronts suggested that cold type occlusions are rare if they exist at al1 finally the occluded front simulated in this case is compared critically to the norwegian t bone and other conceptual models of cyclone evolution

widespread formation of cherts during the early eocene climate optimum radiolarian cherts in the tethyan realm of jurassic age were recently interpreted as resulting from high biosiliceous productivity along upwelling zones in subequatorial paleolatitudes the locations of which were confirmed by revised paleomagnetic estimates however the widespread occurrence of cherts in the eocene suggests that cherts may not always be reliable proxies of latitude and upwelling zones in a new survey of the global spatio temporal distribution of cenozoic cherts in deep sea drilling project dsdp and ocean drilling program odp sediment cores we found that cherts occur most frequently in the paleocene and early eocene with a peak in occurrences at 50 ma that is coincident with the time of highest bottom water temperatures of the early eocene climatic optimum eeco when the global ocean was presumably characterized by reduced upwelling efficiency and biosiliceous productivity cherts occur less commonly during the subsequent eocene global cooling trend primary paleoclimatic factors rather than secondary diagenetic processes seem therefore to control chert formation this timing of peak eocene chert occurrence which is supported by detailed stratigraphic correlations contradicts currently accepted models that involve an initial loading of large amounts of dissolved silica from enhanced weathering and or volcanism in a supposedly sluggish ocean of the eeco followed during the subsequent middle eocene global cooling by more vigorous oceanic circulation and consequent upwelling that made this silica reservoir available for enhanced biosilicification with the formation of chert as a result of biosilica transformation during diagenesis instead we suggest that basin basin fractionation by deep sea circulation could have raised the concentration of eeco dissolved silica especially in the north atlantic where an alternative mode of silica burial involving widespread direct precipitation and or absorption of silica by clay minerals could have been operative in order to maintain balance between silica input and output during the upwelling deficient conditions of the eeco cherts may therefore not always be proxies of biosiliceous productivity associated with latitudinally focused upwelling zones 2007 elsevier b v all rights reserved

genesis of the tuokesai zn pb deposit in the sayram massif xinjiang nw china constraints from geology jasperite geochemistry and si s pb isotopes abstract the zn pb potential of the sayram massif has drawn significant attention since the discovery of the large tekeli sedex zn pb deposit which is located 15 km from the kazakhstan and chinese border in xinjiang the tuokesai zn pb deposit was discovered in 2009 in the northern margin of the sayram massif a major precambrian terrane of the kazakhstan yili block the geological characteristics of the ore bearing strata at tuokesai are similar to those of the nearby large tekeli sedex mineral system tuokesai s lens shaped zn pb orebodies are stratiform and conformable with marble of the neoproterozoic wenquan group the ore bearing marbles are commonly interbedded with jasperite that is mainly composed of fine microcrystalline quartz the ore minerals include sphalerite galena and pyrite with minor pyrrhotite and they are mainly fine grained with a laminate texture the gangue minerals are mainly calcite and quartz both the jasperite s relatively high 30siv nbs 28 values 1 3 2 2 and it s ree patterns show a seawater signature whereas both its y ho ratios concentrated at 30 48 48 57 and its weakly positive eu anomalies imply a minor hydrothermal influx the jasperite s fe al ti compositions and la ce ratios combined with the lithology of the host wenquan group suggest that the ore bearing strata were formed in a passive margin basin the s isotopic compositions of tuokesai s zn pb ores 8 1 20 4 suggest that the sulfur was derived from contemporaneous seawater sulfate the pb isotopic compositions of the metallic ore minerals 206pb 204pb 17 227 17 549 207pb 204pb 15 447 15 547 208pb 204pb 36 912 37 097 indicate that they came from a mixed crustal mantle source in summary tuokesai is a sedex type zn pb deposit that was formed in a passive margin basin during neoproterozoic the tuokesai deposit s discovery suggests that the sayram massif may represent the eastern extension of the tekeli metallogenic belt and has a high potential for successful zn pb prospecting

rare earth elements in chert clasts as provenance indicators in the ordovician and silurian of the southern uplands of scotland abstract rare earth element ree patterns in chert clasts provide both an indication of the environment of deposition of the source succession and a means of recognising their provenance the ree compositions of chert clasts in three ordovician and silurian conglomerates in the southern uplands of scotland are compared to the ree fingerprints of their possible sources the ree patterns of the clasts show that they were derived from successions deposited close to a continental margin the absence of clasts with large positive cerium anomalies suggests that the ballantrae complex was not exposed and supplying material to the basin from at least the mid caradoc onwards although a single chert clast from the lower llandovery conglomerate on pinstane hill has an almost identical ree pattern to a black chert from the ballantrae complex a chert clast from a monomict chert conglomerate in the mid caradoc kirkcolm formation has an ree signature identical to that of bedded cherts in that formation indicating an intrabasinal provenance the ree patterns of a chert clast from the caradoc blackcraig formation and of some of the clasts from the pinstane conglomerate lie at the extreme end of those of the bedded arenig and caradoc cherts in the southern uplands but the ree patterns of other clasts from pinstane and one from caradoc ashgill shinnel formation lie beyond this suggesting an extrabasinal source