planktonic foraminiferal mg ca as a proxy for past oceanic temperatures a methodological overview and data compilation for the last glacial maximum as part of the multi proxy approach for the reconstruction of the glacial ocean margo incentive published and unpublished temperature reconstructions for the last glacial maximum lgm based on planktonic foraminiferal mg ca ratios have been synthesised and made available in an online database development and applications of mg ca thermometry are described in order to illustrate the current state of the method various attempts to calibrate foraminiferal mg ca ratios with temperature including culture trap and core top approaches have given very consistent results although differences in methodological techniques can produce offsets between laboratories which need to be assessed and accounted for where possible dissolution of foraminiferal calcite at the sea floor generally causes a lowering of mg ca ratios this effect requires further study in order to account and potentially correct for it if dissolution has occurred mg ca thermometry has advantages over other paleotemperature proxies including its use to investigate changes in the oxygen isotopic composition of seawater and the ability to reconstruct changes in the thermal structure of the water column by use of multiple species from different depth and or seasonal habitats presently available data are somewhat limited to low latitudes where they give fairly consistent values for the temperature difference between late holocene and the lgm 2 3 5 c data from higher latitudes are more sparse and suggest there may be complicating factors when comparing between multi proxy reconstructions

an effect of dissolved nutrient concentrations on alkenone based temperature estimates the ratio of 37 carbon diunsaturated to diunsaturated and triunsaturated alkenones uk 37 produced by some haptophytes is widely used as a proxy for past sea surface temperatures however our isothermal culturing experiments with emiliania huxleyi clone ccmp372 show uk 37 values to also vary with nutrient availability and cell division rate these results provide a reasonable explanation for large isothermal variation in uk 37 values of single coccolithophorid strains grown in culture they also suggest that alkenone based estimates of past sea surface temperatures may have been influenced by dissolved nutrient concentrations as well as by temperature

tectonic denudation of the shuswap metamorphic terrane of southeastern british columbia large scale over thrusting and regional extension are both known to have been operative within the shuswap metamorphic terrane of the southern omineca belt the monashee core complex of the northern shuswap terrane is interpreted to be a crustal scale duplex that was developed during late mesozoic shortening and thickening of the crust uplift of the monashee complex caused by basement duplexing is estimated to have been in excess of 25 km late cretaceous overthrusting of high grade metamorphic and related plutonic rocks during later stages of uplift and basement duplexing led to weakening of the crust and to gravitationally driven extension of a regional crustal welt shuswap culmination denudation and spreading of this uplifted metamorphic terrane are attributed to displacements across listric normal shear zones and faults localized along the outward dipping flanks of the shuswap culmination total extension across the shuswap culmination at the northern end of the monashee complex is estimated to be no greater than 30 this model of denudation and gravity induced spreading is extrapolated southward into the valhalla and okanagan regions where extension may be far more significant

facies classification and patterns of lacustrine carbonate deposition of the barra velha formation santos basin brazilian pre salt abstract the lacustrine carbonate rocks of the giant pre salt oil fields in the santos and campos basins differ in a number of important aspects from classic lake deposits prior work has described distinctive and unusual features of deposition early diagenesis and reservoir quality with in these rocks that defy classification using established schemes in addition to their unusual textures debate continues as to how to interpret the vertical stacking pattern of facies a new facies classification scheme is proposed based on the relative abundance of three end member components mud micrite and clay minerals calcite spherulites and fascicular calcite shrubs although focused on the main textural and mineralogical features of the rocks as seen today the proposed scheme takes into account the relative contribution of depositional and early diagenetic components sediment mineralogy and the degree of dissolution application of this scheme offers insight into depositional conditions whilst also linking to reservoir quality basic elementary cycles can be defined using this classification in combination with the variation in the abundance of detrital grains and the chemical composition three possible models are suggested to interpret the origin of the basic cycle within the barra velha formation in the context of variation in climate lake level and water chemistry integration of data from different sources including petrographic core description and chemical data for the basic cycle offers improved process based understanding of metre scale facies patterns and provides a foundation for understanding larger scale vertical variations within and between unconformity bound sequences

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

basalt magmatism along the passive continental margin of se brazil campos basin the se brazil passive continental margin is characterized by tholeiitic magmatism that is particularly widespread in the marginal campos basin facing the inland flood basalts of the adjacent parana basin campos magmatism is represented by early cretaceous ec 134 122 ma flood basalts and minor upper cretaceous early tertiary basalt flows and intrusives which were emplaced in a basin with attenuated crustal thickness 20 km petrography mineral chemistry wholerock geochemistry and sr nd isotope composition emphasize that the ec campos basalts have suffered extensive seawater interaction which caused enrichment in mgo feo total k2o rb and ba and depletion in sio2 and cao while zr nb y and ree remained virtually constant in samples with loss on ignition values less than 4 wt in general campos basalts have bulkrock chemistry similar to those of the inland parana tholeiites 140 130 ma with relatively low concentrations of incompatible elements and tio2 16 morb mid ocean ridge basalt mantle in simple binary mixing models on the whole the early cretaceous campos basalts appear as an easterly younger extension of the northern parana volcanism and probably erupted during early stages of the major riftingprocesses which caused continental thinning it is notable that in the campos marginal basin both the basalt magmatism contemporaneous with the continental break up as well as that which occurred after the s america africa separation appears substantially related to subcontinental lithosphere and a dupal like oib ocean island basalt e g tristan da cunha source components

geometric test for late cretaceous paleogene intracontinental transform faulting in the canadian cordillera the tintina trench northern rocky mountain trench tt nrmt fault zone and the fraser river straight creek fr sc fault zone are separate en echelon concentric small circle fault segments of a composite intracontinental transform fault zone more than 2500 km long that cuts diagonally across the canadian cordillera from the outboard part of a tectonic collage of accreted foreign terranes in the south into the north american preaccretionary continental margin in the north most of the 450 km of right hand slip on the tt nrmt fault zone was transformed southward during the late cretaceous and paleocene into oblique convergence in the southern canadian rockies the remainder probably comprising less than 100 km was transformed southwestward during early and middle eocene time via a zone of distributed shear and east west crustal stretching into right hand slip on the en echelon fr sc fault zone these interpretations based on regional systematic mapping of geologic structures are in conflict with interpretations of paleomagnetic measurements that call for more than 1000 km of post mid cretaceous right hand displacement along the general locus of the tt nrmt fault zone involving foreign terranes and the parts of north america to which they had been accreted this paradox must be resolved

deep seismic reflectors in the campos basin offshore brazil summary some deep crustal features underlying the campos basin are best recognized in a few reflection seismic sections that have been reprocessed recently to 10 s two way traveltime a prominent climbing to the basin reflector is interpreted as the moho and a relatively steep fracture zone is probably the first example so far of an extensional fault crossing the whole crust and offsetting the moho further constraints on the deep structure of the basin are provided by estimating the thinning of the crust from shallow seismic data and gravity modelling and by cross plotting backstripped subsidence curves against curves predicted by the lithospheric stretching model

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

thermotectonic history of the maastrichtian reservoir in campos basin abstract the present study of the carapebus formation on well samples refines our understanding of the thermotectonic history of the maastrichtian oil reservoir in campos basin our investigations are based on the thermal analysis of 55 cuttings samples of which 45 have also been analyzed with apatite fission track aft dating in addition to eleven cores analyzed for vitrinite reflectance vr and spore color the apatites are partially annealed and the aft central ages does not provide precise information on exhumation and thermotectonic events that occurred in the source terrain whereas the youngest aft ages provide a minimum age of 45 9 5 5 ma due to significant track annealing in the rocks the vr 0 37 0 48 ro spore color and thermal alteration index tai data correspond to the immature zone of hydrocarbons the thermal history integrated with seismic profiles demonstrate that two phases of heating happened to reservoir separated by a cooling event 65 37 ma the first heating phase started after deposition of the carapebus formation until 65 ma and the second during late eocene and reflect the subsidence at the basin the cooling event shows a strong correlation with subaerial unconformity related in the basin and an important thermal uplift coeval with the last volcanic pulses of the trindade mantle plume in the basin during the uplift phase the generation of hydrocarbon in reservoir was ceased and no more generation occurred until the recent

quantifying the effect of diagenetic recrystallization on the mg isotopic composition of marine carbonates abstract the mg and sr isotopic compositions 26mg and 87sr 86sr of pore fluids and bulk carbonates from ocean drilling project site 1171 south tasman rise 2148 2 m water depth are reported in order to evaluate the potential of diagenesis to alter carbonate based geochemical proxies in an open marine system given the trace amounts of mg in marine carbonates relative to coexisting pore fluids diagenesis can alter carbonate 26mg a promising proxy for seawater 26mg that may help elucidate long term changes in the global mg cycle constraints on the effect of diagenetic recrystallization on carbonate 26mg are therefore critical for accurate proxy interpretations this study provides context for assessing the fidelity of geochemical proxy reconstructions using the primary components i e foraminiferal tests and nannofossils of bulk carbonate sediments we find that pore fluid 26mg values on the dsm3 scale at site 1171 increase systematically with depth from 0 72 to 0 39 in the upper 260 m while the 26mg of bulk carbonates decrease systematically with depth from 2 23 to 5 00 in the upper 260 m this variability is ascribed primarily to carbonate recrystallization with a small proportion of the variability due to down hole changes in nannofossil and foraminiferal species composition the inferred effect of diagenesis on bulk carbonate 26mg correlates with down core changes in mg ca sr ca na ca and 87sr 86sr a depositional reactive transport model is employed to validate the hypothesis that calcite recrystallization in this system can generate sizeable shifts in carbonate 26mg model fits to the data suggest a fractionation factor and a partition coefficient that are consistent with previous work assuming calcite recrystallization rates of 7 ma constrained by sr geochemistry in addition either partial dissolution or a distinctly different previous diagenetic regime must be invoked in order to explain aspects of the elemental chemistry and 87sr 86sr of relatively deep sediments from holes a and c this study indicates that the dynamics of a given sedimentary system can significantly alter bulk carbonate geochemistry and presents a framework for considering the potential impact of such alteration on picked archives such as foraminiferal tests and nannofossils ultimately this study contributes to the development of 26mg as a proxy for seawater 26mg by quantifying the susceptibility of carbonate 26mg to diagenetic alteration particularly in sediments in open marine systems this study suggests that because of the sensitivity of carbonate 26mg to diagenetic recrystallization it can in certain systems be used to quantify the impact of diagenesis on carbonate based geochemical proxies

late cretaceous truncation of the western idaho shear zone in the central north american cordillera the mesozoic boundary separating accreted oceanic rocks and continental north america in west central idaho forms a prominent right angle bend the origin and kinematic significance of which have had a great influence on models for the evolution of the north american cordilleran orogen based on structural and geochronologic relations we conclude that the bend in the steep crustal boundary is formed by the intersection of two shear zones with different ages structural fabrics of the north striking western idaho shear zone are overprinted by penetrative structures of the west northwest striking orofino shear zone u pb sensitive high resolution ion microprobe ages on metaplutonic rocks and late synkinematic leucocratic dikes constrain the age of deformation in the orofino shear zone to ca 90 70 ma distinctly younger than ca 120 90 ma magmatism and deformation within the western idaho shear zone the orofino shear zone is interpreted as a southwest vergent contractional relay structure that linked basement cored foreland thrusts of the middle and southern rocky mountains with the deep crustal duplex of the shuswap complex in the canadian rockies truncation ca 90 ma terminated late cretaceous margin parallel translation of terranes along the western idaho shear zone and required displacement to step outboard to poorly understood structures to the west

strontium and oxygen isotopic variations in mesozoic and tertiary plutons of central idaho regional variations in initial 87sr 86sr ratios r i of mesozoic plutons in central idaho locate the edge of precambrian continental crust at the boundary between the late paleozoic mesozoic accreted terranes and precambrian sialic crust in western idaho the r i values increase abruptly but continuously from less than 0 704 in the accreted terranes to greater than 0 708 across a narrow 5 to 15 km zone characterized by elongate lens shaped highly deformed plutons and schistose metasedimentary and metavolcanic units the chemical and petrologic character of the plutons changes concomitantly from ocean arc type diorite tonalite trondhjemite units to a weakly peraluminous calcic to calcalkalic tonalite granodiorite granite suite the idaho batholith plutons in both suites yield late cretaceous ages but permian through early cretaceous bodies are confined to the accreted terranes and early tertiary intrusions are restricted to areas underlain by precambrian crust the two major terranes were juxtaposed between 75 and 130 m y ago probably between 80 and 95 m y oxygen and strontium isotopic ratios and rb and sr concentrations of the plutonic rocks document a significant upper crustal contribution to the magmas that intrude precambrian crust magmas intruding the arc terranes were derived from the upper mantle subducted oceanic lithosphere and may have been modified by anatexis of earlier island arc volcanic and sedimentary units plutons near the edge of precambrian sialic crust represent simple mixtures of the precambrian wall rocks with melts derived from the upper mantle or subducted oceanic lithosphere with r i of 0 7035 rb sr varies linearly with r i producing pseudoisochrons with apparent ages close to the age of the wall rocks measured 18o values of the wall rocks are less than those required for the assimilated end member by sr o covariation in the plutons however indicating that wall rock 18o was reduced significantly by exchange with circulating fluids metasedimentary rocks of the belt supergroup are similarly affected near the batholith documenting a systematic depletion in 18o as much as 50 km from the margin of the batholith plutons of the bitterroot lobe of the idaho batholith are remote from the accreted terranes and represent mixtures of precambrian wall rocks with melts dominated by continental lower crust r i 0 708 rather than mantle pseudoisochrons resulting from these data are actually mixing lines that yield apparent ages less than the true age of the wall rocks and meaningless ri assimilation fractional crystallization models permit only insignificant amounts of crystal fractionation during anatexis and mixing for the majority of plutons of the region

tectonic significance of the florianopolis dyke swarm parana etendeka magmatic province a reappraisal based on precise u pb dating abstract the first precise id tims u pb baddeleyite zircon dating of dykes representative of the main activity in the florianopolis dyke swarm parana etendeka magmatic province south brazil reveals a restricted age range 134 7 0 3 to 133 9 0 7 ma this is at least 5 ma older than indicated by previous 40 ar 39 ar stepwise heating dating and precludes a direct relationship with syn rifting magmatism connected with opening the south atlantic ocean instead as indicated by their age and geochemical signature these dykes are feeders to the nearby urubici lavas and coeval khumib lavas in etendeka these new geochronological results also cast doubt on a large 10 ma time span for the emplacement of the florianopolis dyke swarm implied by 40 ar 39 ar dates but the determination of its upper age limit still requires accurate dating of younger low volume fine grained dykes with distinct low ti chemistry crystals suitable to u pb dating were not obtained thus far from these dykes

a first look at paleotemperature prospects from mg in coccolith carbonate cleaning techniques and culture measurements 1 although coccolith calcite is abundant in carbonate sediments it has not been previously utilized for mg ca paleothermometry cleaning experiments with synthetic composite samples reagent caco3 powder and organic matter from noncalcifying marine algae chlorella are used to evaluate which traditional and or novel cleaning methods permit us to recover the known carbonate mg ca ratio the most effective cleaning treatment causing the least effect on carbonate chemistry and most complete and rapid oxidation of algal organic matter was oxidation in an equal volume mixture of sodium hypochlorite 2 8 and hydrogen peroxide 30 however in some organic rich samples this method may not remove sufficient noncarbonate mg to permit precise determination of carbonate mg ca mg ca ratios in small culture samples may be determined precisely relative standard deviation of 0 65 using sector field inductively coupled plasma mass spectrometry measurements of mg ca in coccoliths from several species suggest that temperature may be an important control over mg partitioning in coccolith calcite although cleaning issues are likely to be an important limitation on paleoceanographic application

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

effect of preservation state of planktonic foraminifera tests on the decrease in mg ca due to reductive cleaning and on sample loss during cleaning four species of planktic foraminifera from core tops spanning a depth transect on the ontong java plateau were prepared for mg ca analysis both with cd cleaning and without mg cleaning a reductive cleaning step reductive cleaning caused etching of foraminiferal calcite focused on mg rich inner calcite even on tests which had already been partially dissolved at the seafloor despite corrosion there was no difference in mg ca of pulleniatina obliquiloculata between cleaning methods reductive cleaning decreased mg ca by an average all depths of 4 for globigerinoides ruber white and 10 for neogloboquadrina dutertrei mg ca of globigerinoides sacculifer above the calcite saturation horizon only was 5 lower after reductive cleaning the decrease in mg ca due to reductive cleaning appeared insensitive to preservation state for g ruber n dutertrei and p obliquiloculata mg ca of cd cleaned g sacculifer appeared less sensitive to dissolution than that of mg cleaned mg cleaning is adequate but sem and contaminants al ca fe ca and mn ca show that cd cleaning is more effective for porous species a second aspect of the study addressed sample loss during cleaning lower yield after cd cleaning for g ruber g sacculifer and n dutertrei confirmed this to be the more aggressive method strongest correlations between yield and co32 in core top samples were for cd cleaned g ruber r 0 88 p 0 020 and cd cleaned p obliquiloculata r 0 68 p 0 030 in a down core record wind28k correlation r between yield values 30 and dissolution index xdx was 0 61 p 0 002 where cleaning yield 30 most mg cleaned mg ca values were biased by dissolution

inside story an x ray computed tomography method for assessing dissolution in the tests of planktonic foraminifera x ray computed tomography ct provides an insight into the progression of dissolution in the tests of planktonic foraminifera four species of foraminifera g ruber white g sacculifer n dutertrei and p obliquiloculata from pacific atlantic and indian ocean core top samples were examined by ct and sem inner chamber walls began to dissolve at co32 values of 12 14 mol kg close to the calcite saturation horizon dissolution and precipitation of calcite may occur simultaneously inner calcite of g sacculifer n dutertrei and p obliquiloculata from such sites appeared altered or replaced whereas outer crust calcite was dense with no pores unlike the other species there was no distinction between inner and outer calcite in ct scans of g ruber empty calcite crusts of n dutertrei and p obliquiloculata were most resistant to dissolution and were present in samples where co32 20 mol kg five stages of preservation were identified in ct scans and an empirical dissolution index xdx was established xdx appears to be insensitive to initial test mass mass loss in response to dissolution was similar between species and sites at 0 4 g mol kg we provide calibrations to estimate co32 and initial test mass from xdx

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

shifts in the source of the parana basalts through time magmatism occurred intermittently in the parana region of south america between 240 50 ma with the peak of magmatic activity between 138 126 ma comprising the parana continental flood basalts cfb detailed chemical subdivision of the parana basalts into six units allowed stratigraphic correlations to be made implying a northward migration of magmatism following the rifting of the south atlantic however 40ar 39ar ages do not uphold the chronostratigraphic nature of such magmatic units instead they indicate a southeastwards migration major elements extrapolated to 8 wt mgo are used to investigate changes in magma type with time and are interpreted in terms of parameters such as pressure depth of melting and the nature of the source region fertile refractory and water content the oldest parana unit originated by melting at the greatest depths 90 120 km shifting to shallow levels 30 60 km for the younger units accompanying this decrease in pressure the source material undergoing partial melting became progressively more refractory in major elements and also more hydrous this hydrous metasomatism occurred after major element depletion of the lithosphere at shallow levels the data is consistent with conductive heating of a stratified source region inferred to lie within the lithospheric mantle which is relatively fertile but anhydrous at depth and also appears to be younger in age than the relatively major element refractory hydrous lithosphere at shallower depths thus the interaction of asthenosphere and lithosphere can be determined within an integrated age tectonic and thermal framework

coccolith sr ca as a new indicator of coccolithophorid calcification and growth rate 1 polyspecific coccolith separates from core top sediments in the eastern equatorial pacific show variations of 15 in sr ca ratios across the equatorial upwelling zone with sr ca highest at the equator and decreasing off axis these variations cannot be due to changes in the sr ca of seawater which varies by less than 2 in the surface ocean variations in sr ca of coccolith sediments are similar to variations in primary productivity and alkenone estimated coccolithophorid growth rates in overlying surface waters and to caco3 rain rates measured in sediment traps because of these relationships and because calcification rate exerts a strong control on sr ca in abiogenic calcites we suggest that the observed sr ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates although temperature may also influence coccolith sr ca to a lesser degree changes in dissolution intensity and coccolith assemblages appear to exert a minor influence if any on coccolith sr ca in these sediment core tops if further work confirms relationships between coccolith sr ca and coccolithophorid productivity sr ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon an important control on deep ocean ph and partitioning of co2 between the atmosphere and ocean in addition coccolith sr ca might provide an independent record of past changes in coccolithophorid growth rates which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved co2 in the surface ocean

role of subaerial volcanic rocks and mantle plumes in creation of south atlantic margins implications for salt tectonics and source rocks abstract seaward dipping reflectors sdrs represent flood basalts rapidly extruded during either rifting or initially subaerial sea floor spreading evaporites can form on this basaltic proto oceanic crust as in the afar triangle today evidence for sdrs in south atlantic deep water regions comes from proximity to the uniquely large parana etendeka volcanic province onshore the tristan and gough hot spots drilled volcanic rocks and seismic profiles showing sdr provinces more than 100 km wide as much as 7 km thick and thousands of kilometers long sdrs are clearest adjoining the aptian salt basins however we speculate that sdrs are also present but seismically obscured below the salt basins we argue that the conjugate aptian salt basins are post breakup not pre breakup they were separated from the start by a mid oceanic ridge distal salt accumulated on proto oceanic crust not rift basins this hypothesis is supported by seismic stratigraphy and structure magnetic anomalies plate reconstructions and hydrothermal potash evaporites an important implication for exploration is that thick basalts rather than rift age source rocks may underlie distal parts of the salt basins

seasonal and interannual variation in santa barbara basin water temperatures observed in sediment trap foraminiferal mg ca 1 we have generated a santa barbara basin sediment trap mg ca record to evaluate culture based calibration equations for the temperate subpolar planktonic foraminiferal species globigerina bulloides and neogloboquadrina pachyderma dextral g bulloides and n pachyderma mg ca are significantly correlated with seasonal variations in temperature of the near surface and subthermocline depths respectively the average deviation between mg based and 18o based temperature estimates is 0 6 c for g bulloides and 0 8 c for n pachyderma differences between mg derived temperatures and instrumental temperatures may be due to cleaning methods environmental factors such as seasonal variations in foraminiferal depth habitats or possible secondary effects on mg ca core top mg ca of both g bulloides and n pachyderma is in excellent agreement with average values from the sediment trap lending strong support for the interpretation of downcore mg ca from these species as annual average near surface and thermoclinal temperatures

an experimental investigation of high temperature interactions between seawater and rhyolite andesite basalt and peridotite natural seawater was allowed to react with rhyolite andesite basalt and peridotite at 200 500 c and 1 000 bars at water rock mass ratios of 5 and 50 in order to investigate the effects of rock type water rock ratio and temperature on solution chemistry and alteration mineralogy the results indicate that interactions of seawater with various igneous rocks are similar in the production of a hydrous mg silicate and anhydrite as major alteration products fluids involved in the interactions lose mg to alteration phases while leaching fe mn and si from the rocks the ph of the solutions is primarily controlled by mg oh silicate formation and therefore varies with mg and si concentration of the system other reactions which involve mg such as mg ca exchange or which produce free h cause major differences in fluid chemistry between different seawater rock systems high water rock ratio systems 50 1 are generally more acidic and more efficient in leaching than low ratio systems 5 1 due to relatively more seawater mg available for mgsilicate production the experiments show that large scale seawater rock interaction could exert considerable control on the chemistry of seawater as well as producing large bodies of altered rock with associated ore deposits

geochemistry and petrology of the jequie granulitic complex brazil an archean basement complex the jequie granulitic complex is part of the extensive high grade metamorphic terrain located within the sao francisco craton of northeastern brazil some jequie rocks appear to have been formed in the middle archean 3 1 ga from preexisting sialic crust the dominant mineral composition of these rocks is quartz microcline plagioclase hyperstene and occurs over an extensive area 2 000 km2

a method for precise analysis of trace element calcium ratios in carbonate samples using quadrupole inductively coupled plasma mass spectrometry an improved method has been developed using a quadrupole inductively coupled plasma mass spectrometer q icp ms to analyze carbonate samples for multiple trace element to calcium ratios problems alleviating shorter term drift have been overcome by manipulating the instrument to bracket each trace metal measurement with a calcium measurement while longer term drift is corrected by bracketing each sample analysis with external matrix matched standards of typical foram composition our method is optimized for measuring the ratios sr ca mg ca zn ca cd ca ba ca mn ca and u ca from a single carbonate sample but could be adapted to include a range of alternative ratios evaluation has shown the method to be extremely precise at less than 1 rsd 1 for 3 trace metal to calcium ratios we have achieved comparable precision to a sector field icp ms instrument and an advance over previous methods using the q icp ms instrument precision rsd for each ratio based on 96 sample analyses in 5 batches made over a period of 9 months using a 100 mg l ca standard is 2 2 for u ca 1 7 for cd ca 1 9 for zn ca 1 1 for ba ca 0 7 for mn ca and 0 7 and 0 6 for sr ca and mg ca respectively accuracy of the method is confirmed by comparing standard ratios with those obtained from an icp aes instrument and by comparing sample analyses of neap4b material from the north atlantic with data measured using thermal ionization mass spectrometry tims and flame atomic absorption spectroscopy faas

relationship between coccolith sr ca ratios and coccolithophore production and export in the arabian sea and sargasso sea coccolithophore caco3 production can account for 20 80 of biogenic carbonate exported from the photic zone and coccoliths are a dominant biogenic carbonate in many deep sea sediments a new method for picking individual coccoliths from sediment traps and sediments for analysis using secondary ion mass spectrometry ion probe allows us to make precise sr ca and mg ca determinations on coccoliths from single species even in samples where material is limited there are large biological effects in sr ca partitioning in coccoliths that have been related to variations in coccolithophore productivity in sediment traps from the sargasso sea at bermuda and arabian sea in the somali basin we can identify sr ca variations in several species that are consistent with inferred seasonal variations in coccolithophore productivity in surface waters in the arabian sea coccolith sr ca ratios in calcidiscus leptoporus and helicosphaera carteri are lowest during the nonproductive intermonsoon they are highest during the upwelling of southwest monsoon and during the nutrient entrainment from strong winds of the northeast monsoon these sr ca variations match seasonal trends in coccolith export flux furthermore sr ca variations in c leptoporus are larger and this species also has the greater variation in export flux between southwest monsoon and intermonsoon seasons at bermuda a 1996 fall bloom driven by passage of a warm mode water eddy induced a large increase in sr ca of c leptoporus coincident with an increase of c leptoporus export over an annual series for 2004 highest sr ca ratios of c leptoporus in the summer months match the typical summer peak in surface standing stock of this species and the stimulation of its productivity by mesoscale cyclonic eddies and eddy eddy interactions high sr ca did not coincide with the highest export of c leptoporus coccoliths likely because cyclonic eddies unlike mode water eddies are dominated by small phytoplankton with low export efficiency these data confirm a relationship between coccolith sr ca ratios and productivity sr ca ratios of the smaller and more slowly sinking emiliania huxleyi at bermuda show very small o4 seasonal sr ca variations in contrast nutrientlimited culture experiments for this species reveal significant 435 increases in sr ca with nitrate stimulated growth

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

petrogenesis of coexisting sio2 undersaturated to sio2 oversaturated felsic igneous rocks the alkaline complex of itatiaia southeastern brazil abstract the itatiaia alkaline complex is a late cretaceous intrusion 72 myr made up of felsic differentiates with syenitic rocks dominant throughout and with presence of both nepheline and quartz rich varieties dykes with phonolitic or trachytic composition cross cut the coarse grained facies the rocks are arranged concentrically with the core of the complex being formed by sio 2 oversaturated syenites with a small outcrop of granites and are radially displaced by faults related to regional tectonic lineaments the minerals show gradual but significant changes in composition salitic and augitic to aegirine rich pyroxenes hastingsite and actinolite to richterite and arfvedsonite amphiboles sodic plagioclase to orthoclase feldspars and so on and the whole rock trends are broadly consistent with fractional crystallization processes dominated by alkali feldspar removal sr isotopic data indicate more radiogenic ratios for the sio 2 oversaturated rocks 0 7062 0 7067 against 0 7048 0 7054 for the sio 2 undersaturated syenites consistent with small amounts of crustal input the favored hypothesis for the petrogenesis of the different syenitic groups is the prolonged differentiation starting from differently sio 2 undersaturated mafic parental magmas potassic alkali basalts to ankaratrites present in the late cretaceous dyke swarms of the area accompanied by variable crustal contamination prior to the final emplacement the lack of carbonatite as a significant lithotype the potassic affinity of the itatiaia complex and the relatively high sr isotopic ratios match the characteristics of the other complexes of the rio de janeiro sa o paulo states coastline and confirm the ultimate derivation of these differentiated rocks from an enriched lithospheric mantle source

palaeohydrology of the lower cretaceous pre salt lacustrine system from rift to post rift phase santos basin brazil abstract large oil accumulation discoveries in the last decade in the pre salt rock succession off the brazilian coast aroused renewed interest in carbonate reservoirs prompting several studies aiming at unravelling the conditions of formation of these rocks despite that there are still many gaps in the knowledge concerning environmental conditions of the deposition of the pre salt carbonates of santos basin located at the southeastern brazilian margin in this study we present and discuss a new suite of geochemical and biostratigraphic data of the lacustrine rift to post rift succession broadly correlated with itapema and barra velha formations of the santos basin whose deposition occurred in the aptian the integration of the petrographic biostratigraphic and geochemical data serves the ultimate purpose of the study which is to apply the new radiogenic strontium data as a proxy for the reconstruction of the evolution of the lake hydrology associated with the deposition of the carbonates of the itapema and barra velha formations these data are integrated into numerical models whose results bring new ideas on the general hydrologic conditions of the lake system and on its evolution through time the mass balance calculations indicate that two end members alone can account as potential sources of sr to the palaeolake a mafic and a felsic component respectively the latter likely contributed with significantly higher fluxes roughly one to two and up to four orders of magnitude higher than the former end member for most of the depositional history in order to generate the 87sr 86sr trends observed in the carbonate rocks finally the results obtained from the integration of the observations with the numerical models point to decreasing fluxes of water with time as contributed from both sources suggesting that the formation of the deposits became very likely constrained to progressively more evaporitic and alkaline lake waters these results also open up a new window into the environmental conditions of the interior gondwana continent immediately prior to the definitive opening of the south atlantic ocean

the helmut geophysical anomaly a regional left lateral transtensional shear zone system connecting santos and campos basins southeastern brazil abstract in the ultradeep water of santos and campos basins eastwards from the area of present day pre salt exploration in southeastern brazil there is a nearly 1000 km long curved magnetic anomaly here named helmut on a magnetic map the anomaly orientation switches from ne sw in santos basin to nearly n s in campos mimicking the curved neoproterozoic shear zone pattern of the basement exposed onshore from the comparison between the position of such anomaly and gravity derived modeling and residual maps it is suggested that the magnetic anomaly also corresponds to a major gravimetric boundary separating different crustal domains this boundary is slightly oblique to the rift related normal fault trend in santos basin based on interpreted 3d seismic data the nne trending normal faults are dragged to the ne direction close to the magnetic anomaly in southern santos basin where an en echelon array of oblique magnetic anomalies occurs which resulted mainly from the left lateral component of an overall transtensional displacement field in regional 2d deep reflection seismic profiles the helmut anomaly is correlated to major eastward dipping down to the basin stepped faults sometimes arranged in a fan like fashion in santos basin and as a landward dipping normal fault zone in campos basin north of the e w araruama transfer zone in some areas the fault zone displaces the base salt reflector and cross cuts the entire stretched continental crust the analysis of potential field and seismic data suggests that the helmut anomaly may be interpreted as a crustal scale shear zone system active after salt deposition during the late aptian regionally the helmut anomaly connects two approximately n s trending branches of the south atlantic rift system the northern branch that runs from espirito santo basin northwards up to the camamu south of the reconcavo tucano jatoba aborted trough and the southern branch running southwards from santos basin through pelotas basin in brazil as far as the basins offshore uruguay and argentina basins southwards extensional faulting of the salt reflector along early nne rift related normal faults and dextral transtension on the nw trending fault zones are all consistent with a sinistral transtensive motion on the ne trending helmut anomaly during the late aptian

the mg isotopic composition of cenozoic seawater evidence for a link between mg clays seawater mg ca and climate abstract cooling of earth s climate over the cenozoic has been accompanied by large changes in the magnesium and calcium content of seawater whose origins remain enigmatic the processes that control these changes affect the magnesium isotopic composition of seawater rendering it a useful tool for elucidating the processes that control seawater chemistry on geologic timescales here we present a cenozoic magnesium isotope record of carbonate sediments and use a numerical model of seawater chemistry and the carbon cycle to test hypotheses for the covariation between cenozoic seawater chemistry and climate records are consistent with a 2 3 increase in seawater mg ca and little change in the mg isotopic composition of seawater these observations are best explained by a change in the cycling of mg silicates we propose that mg ca changes were caused by a reduction in removal of mg from seawater in low temperature marine clays though an increase in the weathering of mg silicates cannot be excluded we attribute the reduction in the mg sink in marine clays to changes in ocean temperature directly linking the major element chemistry of seawater to global climate and providing a novel explanation for the covariation of seawater mg ca and climate over the cenozoic

paleomagnetism and dating of the early cretaceous florianopolis dike swarm santa catarina island southern brazil abstract the florianopolis fl basaltic dikes are well exposed on santa catarina island close to the present southeastern border of the parana magmatic province in southern brazil and their intrusion was related to the tectonic and magmatic evolution of rifting in the southern atlantic the dikes are vertical or subvertical and cut the crystalline basement rocks mainly late proterozoic granites most of the dikes exhibit ne trends corresponding to structural trends of the crystalline basement a few nw trending dikes can also be observed occasionally crosscutting the ne dikes samples from 73 dikes were collected for paleomagnetic work and subjected to both alternating field and thermal demagnetization characteristic magnetizations of normal and reversed polarities interpreted as original thermoremanences are carried by ti poor magnetites showing remanent coercive forces in the range 18 45 mt the corresponding paleomagnetic pole fl pole is located at 3 3 e 89 1 s n 65 95 2 6 k 47 samples for 40 ar 39 ar dating were collected at the same paleomagnetic sites plagioclase samples from nine dikes were analyzed by stepwise heating the apparent age spectra are strongly discordant due to excess 40 ar contamination but five samples yielded plateau ages ranging from 119 0 0 9 ma to 128 3 0 5 ma one additional sample yielded an isochron age of 121 5 0 5 ma the inferred ages apparently define two modes at 119 122 ma and 126 128 ma although the data set is probably insufficient to determine whether dike intrusion was continuous or episodic the ages of 128 119 ma are coeval with the final stages of the rifting at this latitude suggesting that the emplacement of the fl dikes is related to extension of the continental crust just prior to the formation of oceanic crust by comparing the fl pole with the existing paleomagnetic poles for the nw ponta grossa dike swarm mainly 130 5 ma to the north the parana volcanics mainly 133 132 ma and the central alkaline province 127 130 ma on the western side of the parana province it is concluded that the differences in pole positions reflect plate displacements and therefore the fl pole is probably dominated by the dikes with ages younger than 127 ma

calcium magnesium and strontium cycling in stratified hardwater lakes lake kinneret sea of galilee israel abstract in stratified hardwater lakes calcite crystallization in the epilimnion and partial dissolution in the hypolimnion play important roles in the cycling of ca2 in the water column mg2 and sr2 coprecipitate with this mineral to be released together with ca2 upon its dissolution here we focus on lake kinneret sea of galilee israel a stratified warm hardwater lake searching for an interpretable high resolution picture of the processes that drive ca2 mg2 and sr2 cycling in this and similar lakes elsewhere in total 1428 water samples were collected from the lake and another 81 samples were collected from the jordan river and two small streams discharging into it covering a full monomictic cycle from december 2001 through march 2003 particulate material was retrieved from sediment traps in the hypolimnion the water samples were analyzed for na k mg2 ca2 sr2 cl so42 hco3 and br and the trapped particulates were examined under sem and analyzed for their ca mg and sr content individual calcite crystals within the particulate material underwent la icp ms analysis for ca mg and sr downward transport of ca2 involves crystallization of calcite in the epilimnion followed by its settling through the water column followed by its partial dissolution in the hypolimnion magnesium and sr2 follow ca2 by coprecipitation in calcite and are released upon its dissolution in the hypolimnion upward cycling of the three solutes occurs through an admixture of the hypolimnetic water into the epilimnion during thermocline deepening terminated by overturn of the lake removal rates of mg2 and sr2 from the lake relative to that of ca2 and the water calcite distribution coefficients dmg and dsr were calculated from the analyses using 1 epilimnion water and bulk particulates 2 epilimnion water only and 3 epilimnion water and calcite crystals in the particulates the dsr values obtained were internally consistent 0 194 5 9 0 22 0 28 and 0 204 0 232 respectively however the dmg value for the bulk particulates 0 0477 was 6 times higher than that corresponding to calcite crystals included therein 0 00841 this difference is attributed to phytoplankton debris in the bulk particulates and should be of concern to geochemists using mg ca ratios in limestone to reconstruct ancient aquatic environments the cycling of ca2 mg2 and sr2 in the stratified lake is monitored by mg ca vs sr ca regression diagrams where each line represents the water column composition on a specific date the distance of the data points from the initial mixed lake coordinates reflects the fractionation of ca2 mg2 and sr2 after the onset of stratification the regression lines rotate in an orderly anticlockwise direction in response to the high calcite flux from the epilimnion in spring and the higher rate of mg2 replenishment than that of sr2 compensating for their loss in calcite the release of mg2 and sr2 from dissolving calcite in the hypolimnion at an mg sr ratio 7 5 eq eq much lower than that in the surrounding water 160 eq eq lends additional support to the anticlockwise rotation reversal of rotation occurs in summer when calcite crystallization and the freshwater supply slow down and brackish and saline water sources take control over the mg sr ratio in the lake subsequent turnover and mixing of the lake in winter reset the mg ca and sr ca ratios to their original values before the next stratification

deep burial hydrothermal alteration of the pre salt carbonate reservoirs from northern campos basin offshore brazil evidence from petrography fluid inclusions sr c and o isotopes abstract petrographic mineralogical elemental isotopic and fluid inclusion analyses were integrated to unravel the diagenetic evolution of brazilian pre salt lacustrine carbonate reservoirs of northern campos basin southeast brazilian margin detailed thin section and cathodoluminescence petrography scanning electron microscopy and electron microprobe analyses established a paragenetic evolution of diagenetic processes and products comprising extensive dolomitization silicification and dissolution a paragenesis including saddle dolomite macrocrystalline calcite mega quartz sr barite celestine fluorite dickite sphalerite galena and other metallic sulfides filling fractures and dissolution porosity and aqueous fluid inclusions with homogenization temperatures of 92 152 c and salinities between 13 and 26 wt eq nacl characterized a hydrothermal system with some analogy to carbonate hosted pb zn mississippi valley mvt and irish type deposits petroleum inclusions and solid bitumen testify atypical oil generation and migration associated with the hydrothermal flow the host pre salt spherulitic and fascicular carbonates present highly radiogenic 87sr 86sr ratios indicating strong interaction with continental crust materials hydrothermal phases show 18o values more negative than syngenetic and diagenetic carbonates the 13c values are interpreted as result of interaction between the hydrothermal fluids and the host rocks the combined data set provides clear evidence of intense hydrothermal alteration of northern campos basin pre salt reservoirs at deep burial conditions 2 km possibly related to late cretaceous or more probably paleogene magmatic activity mixed sourced fluids bearing a basinal signature fed the hydrothermal system and promoted dissolution of the host rocks the hydrothermal alterations had strong impact on the porosity permeability and heterogeneity contributing together with the associated fracturing to the excellent production performance of the pre salt reservoirs

re sedimented deposits in the rift section of the campos basin abstract an integrated petrologic sedimentologic stratigraphic seismic study of the lagoa feia group rift section of the campos basin has shown that rift sedimentation was dominantly intrabasinal carbonate and stevensitic deposits with siliciclastic deposits restricted to the proximity of graben border faults the bivalve bioclastic rudstones coquinas that constitute the rift reservoirs show commonly limited abrasion of the bioclasts and were deposited both on basement highs and lows throughout the rift section although in situ deposits of stevensite ooids and peloids occur dominantly at the base of the succession these particles are ubiquitous to the entire rift section mixed in variable proportion with siliciclastic and carbonate sediments the environmental conditions required for the formation of stevensite and the growth of bivalves are mutually exclusive as stevensite forms only at ph greater than 10 while bivalves cannot tolerate ph greater than 9 the common mixture of well rounded basaltic rock fragments with angular granitic gneissic rock fragments and feldspars in the sandstones and conglomerates indicates recycling of epiclastic deposits from the early rift section combined with first cycle contribution from the plutonic basement the studied cores show no evidence of subaerial exposure and there is a lack of bioturbation suggesting harsh environmental conditions the rift deposits are dominantly massive or faintly laminated with diffuse facies boundaries structures indicative of unidirectional or oscillatory flow are subordinate integration of seismic sedimentologic and petrographic evidence indicates that the campos basin rift section is formed mostly by re sedimented gravitational deposits the onset of the rift sedimentation occurred in synformal depressions where bivalve banks or stevensite ooids were formed in shallow lacustrine environments under variable alkalinity conditions with the development of half grabens and concentration of the tectonic activity along the border faults recurrent tectonic events promoted the mixing and gravitational re deposition of stevensitic clastic and bioclastic sediments in deeper fault bounded troughs large scale units hundreds of meters thick were generated by major tectonic events whereas compositional variations in the scale of meters were possibly a product of lake level climatic fluctuations thus due to syn rift and mainly to post rift erosion the neo aptian unconformity the preserved rift section of the lagoa feia group comprises mostly sediments deposited in the central troughs of the half graben structures marginal sediments were extensively eroded and re sedimented as gravity driven mixed deposits this new model constructed form the integration of seismic stratigraphic sedimentologic and petrologic data diverges substantially from the presently accepted model for the sedimentation of the rift section opening new possibilities for the exploration of campos basin as well as of similar settings as in the adjacent santos basin

strontium oxygen and hydrogen isotope geochemistry of hydrothermally altered and weathered rocks in dsdp hole 504b costa rica rift dsdp hole 504b was drilled into 6 ma crust about 200 km south of the costa rica rift galapagos spreading center penetrating 1 35 km into a section that can be divided into four zones zone i oxic submarine weathering zone ii anoxic alteration zones iii and iv hydrothermal alteration to greenschist facies in zone iii there is intense veining of pillow basalts zone iv consists of altered sheeted dikes isotopic geochemical signatures in relation to the alteration zones are recorded in hole 504b as follows zone depth m average87sr 86sr average 18o o average d o i 275 550 0 7032 7 3 63 ii 550 890 0 7029 6 5 45 iii 890 1050 0 7035 5 6 31 iv 1050 1350 0 7032 5 5 36 full size table table options view in workspace download as csv alteration temperatures are as low as 10 c in zones i and ii based on oxygen isotope fractionation strontium isotopic data indicate that a circulation of seawater is much more restricted in zone ii than in zone i fluid inclusion measurements of vein quartz indicate the alteration temperature was mainly 300 20 c in zones iii and iv which is consistent with secondary mineral assemblages the strontium oxygen and hydrogen isotopic compositions of hydrothermal fluids which were responsible for the greenschist facies alteration in zones iii and iv are estimated to be 0 7037 2 and 3 respectively strontium and oxygen isotope data indicate that completely altered portions of greenstones and vein minerals were in equilibrium with modified seawater under low water rock ratios in weight of about 1 6 this value is close to that of the end member hydrothermal fluids issuing at 21 n epr basement rocks are not completely hydrothermally altered about 32 of the greenstones in zones iii and iv have escaped alteration thus 1 g of fresh basalt including the 32 unaltered portion are required in order to make 1 g of end member solution from fresh seawater in water rock reactions

the role of basement tectonic reactivation on the structural evolution of campos basin offshore brazil evidence from 3d seismic analysis and section restoration abstract the structural analysis of regional 3d seismic data shows evidence of long term tectonic inheritance in campos basin offshore brazil main lower cretaceous rift structures controlled themselves by strike slip deformation belts related to proterozoic orogenic events have been episodically reactivated during the divergent margin phase of campos basin from the albian to the miocene balanced cross sections of major salt structures indicate that such tectonic reactivations have been controlling thin skinned salt tectonics triggering pulses of gravitational gliding above the aptian salt detachment additionally major basin features like the neogene progradation front and the salt tectonic domains are constrained by the main proterozoic orogenic trends of the ribeira belt ne sw and the vitoria colatina belt nnw sse as the basement involved structures observed in campos basin can be attributed to general geodynamic processes it is suggested that basement tectonic reactivation can be as relevant as isostatic adjustment and detached thin skinned tectonics on the structural evolution of divergent margin settings

a novel application of wet oxidation to retrieve carbonates from large organic rich samples for ocean climate research 1 for ocean climate research carbonates are extracted from large organic rich bulk sediments for specific geochemical analyses this is conventionally achieved by time consuming dry oxidation or nonoxidative preprocessing to significantly shorten sample preparation time we designed and evaluated a rapid technique that uses sequential wet oxidization of bulk samples in a hot alkaline 18 h2o2 solution we successfully tested this wet oxidation technique on multiple bulk aliquots from two sediment trap samples and a core top sediment that were also processed by dry oxidation and without oxidation from all aliquots four calcitic foraminifera species and an aragonitic juvenile bivalve from the 250 315 m fraction were analyzed for size normalized weight snw 18o 13c mg ca and sr ca in addition these proxies were determined on powdered bulk aliquots from the 150 250 m fraction processed by wet oxidation dry oxidation and without oxidation at an initial ph of 8 and temperature of 70 c the alkaline h2o2 solution appeared to be most stable and reactive carbonate dissolution did not occur as no reduction was observed in snw of the four foraminifera species g ruber g trilobus n dutertrei g bulloides and the aragonitic bivalve shells for sediment traps the 18o and 13c between the three cleaning methods only deviated between 0 05 and 0 3 compared to 0 1 and 0 6 in sediments with equally small variation in mg ca and sr ca ratios 0 1 0 4 mmol mol lowest ba ca ratios show that wet oxidation successfully removed organic matter along with residual salts no significant systematic differences between samples or methods were found but a residual scatter remained particularly in the nonoxidized sediment because of intraspecies and intrashell inhomogeneity given proper preprocessing all three techniques performed well with the proposed wet oxidation method emerging as a fast technique for extracting carbonate shells from wet gram sized bulk samples within 3 h wet oxidation produced clean dry residues of unaltered calcareous shells from batches of four wet bulk samples without time consuming intermediate steps for mg ca thermometry on time series sediment trap samples wet oxidation results approached those obtained using the barker et al 2003 protocol with improved sample recovery consequently the proposed wet oxidation offers a rapid alternative to conventional extraction techniques for carbonate geochemistry

87 sr 86 sr and 18 o 16 o isotopic systematics and geochemistry of granitoid plutons across a steeply dipping boundary between contrasting lithospheric blocks in western idaho a spatially abrupt geochemical boundary is preserved within four plutonic complexes along the western margin of the cretaceous idaho batholith near mccall idaho these intrusives ranging in composition from tonalite to granite were emplaced across a regional boundary between accreted oceanic arc terranes and the continental margin and their isotopic major element and trace element geochemistry provide detailed information about this change in crustal characteristics at depth indicating that the boundary is nearly vertical and extends deep into the lithosphere the hazard creek complex emplaced west of the transition in wall rock lithology has initial 87sr 86sr ri less than 0 7045 and 18o greater than 7 5 indicating little or no continental crust in its source region however elevated 18o requires some incorporation of rocks formed or altered at the earth s surface a large shift in ri and 18o is observed across the 5 8 km wide little goose creek complex which was emplaced across the wall rock boundary this is interpreted as mixing between 1 a basaltic or andesitic magma with low k2o and high na2o al2o3 and sr similar to that forming the hazard creek complex and 2 materials similar to precambrian sedimentary sedimentary rocks with low sr high 18o 15 and high ri 0 83 at 100 ma the payette river complex emplaced east of the wall rock boundary exhibits at least one additional component with low 18o 6 moderate ri 0 708 and mafic composition this component is inferred to be old basaltic material in the lower crust or upper mantle similar to that inferred to be a minor part of the peninsular ranges batholith in se california silver et al 1979 hill et al 1986 the easternmost complex in the idaho transect is made up of granites that may contain a component of granitic cratonal basement the entire west to east geochemical transition from oceanic arc magmas to cratonal magmas takes place over a lateral distance of less than 20 km although the zone of transitional protolith dominated by metasedimentary rocks is unusually narrow and may have been in part tectonically removed the striking geochemical similarities between this traverse and several other transects across much broader areas of nevada and california suggest that the craton itself was not rifted apart but that juxtaposition of the accreted oceanic arc terranes occurred along the preexisting craton margin the data confirm that the isotopic geochemistry of granitoid plutons can be used as a probe of deep lithospheric character and that major lateral variations in the lithosphere on the order of one to two kilometers in width can be recognized in favorable circumstances

assessment of the precision of smart phones and tablets for measurement of planar orientations a case study abstract although paper and pencil approaches to geological mapping continue digital mapping tools are being increasing implemented in field geology of particular note is the use of an electronic compass inclinometer built into tablets and smartphones for obtaining orientation data where an important question is the reliability of these digital devices relative to conventional analogue compass inclinometers this paper deals with this question through detailed tests of two android devices an honor 3c smartphone and a lenovo b8080 f tablet in order to evaluate potential electronic noise effects the devices were tested in two modes standard and airplane over 14 000 readings from the sensors were collected to evaluate the stability of the sensor s readings and showed that the magnetic sensor in the tablet was unacceptably unstable seven geological compass applications were installed on the honor 3c smartphone and tested against the analogue freiberg geological compass in a field experiment during the experiment 25 fractures varying in azimuth and dip were measured using both devices a high level of disagreement was observed with discrepancies as high as 80 with azimuthal errors dominant analysis of the time series in the data suggest the source of the problem was instability in the magnetic sensor for the smartphone despite the fact the device passed the initial stability test although only two devices were studied these data indicate care must be taken to evaluate compass accuracy on these devices

rift zone magmatism petrology of basaltic rocks transitional from cfb to morb southeastern brazil margin compositions of basaltic samples from the southeastern brazil passive margin 18 24 s depict the change from continental to oceanic lithosphere during the opening of the south atlantic ocean samples studied range from 138 to 105 m y old and are from 12 petrobras drill cores recovered from the coastline to about 150 km offshore in the espirito santo campos and santos basins compositions vary ranging for example from 49 54 wt sio2 0 5 3 0 wt tio2 0 6 5 0 feo mgo and 1 6 la yb n but can be grouped i basalts enriched in incompatible elements such as k some k2o 2 0 wt rb 18 ppm zr 120 ppm and lree some feo 16 wt most with sio2 51 54 wt and resembling serra geral continental flood basalts sg cfb of southern brazil ii basalts less enriched or transitional in incompatible elements having k2o 30

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

provenance of deep water reservoir sandstones from the jubarte oil field campos basin eastern brazilian margin the provenance of the maastrichtian deep water reservoir sandstones from the jubarte oil field campos basin eastern brazil was studied using an integrated approach that included quantitative petrography conventional heavy mineral analysis garnet mineral chemistry and zircon geochronology the reservoirs are predominantly coarse poorly sorted sandstones with feldspathic composition derived from uplifted basement terrains the fourth and fifth order depositional sequences analyzed show no major variations in composition or in provenance through time however variations in apatite tourmaline presents potential to be used as a parameter for sandstone correlation within the field the composition of heavy minerals indicates derivation from high temperature and low to medium pressure aluminous metapelitic rocks from granites and subordinate mafic rocks derived from the cabo frio tectonic domain and the oriental terrain of ribeira orogen characterizing a supply route from sw to ne the low ztr index as well as the absence of low grade stable heavy minerals and of metasedimentary rock fragments suggest that by the end of cretaceous all supracrustal low grade terrains had already been totally eroded and that plutonic infracrustal rocks were exposed similarly to the present situation the integration of the compositional and textural aspects suggests a tectonically active source area located relatively close to the basin the active tectonic uplift of the basement terrains provided a large volume of coarse poorly sorted sediments carried directly from mountain streams and alluvial fans to deep water the high frequency shifts in apatite tourmaline values support a direct derivation of the deep water sandstones from adjacent alluvial systems with short but differential exposure to weathering the voluminous deposition of such coarse grained and immature turbidites under the general transgressive conditions of the maastrichtian indicates a tectonic rather than eustatic control on their deposition with important implications for the exploration of similar reservoirs in campos basin and in similar basins of eastern brazilian margin

density and p wave velocity structure beneath the parana magmatic province refertilization of an ancient lithospheric mantle we estimate density and p wave velocity perturbations in the mantle beneath the southeastern south america plate from geoid anomalies and p wave traveltime residuals to constrain the structure of the lithosphere underneath the parana magmatic province pmp and conterminous geological provinces our analysis shows a consistent correlation between density and velocity anomalies the p wave speed and density are 1 and 15 kg m3 lower respectively in the upper mantle under the late cretaceous to cenozoic alkaline provinces except beneath the goias alkaline province gap where density 20 kg m3 and velocity 0 5 are relatively high underneath the pmp the density is higher by about 50 kg m3 in the north and 25 kg m3 in the south to a depth of 250 300 km these values correlate with high velocity perturbations of 0 5 and 0 3 respectively profiles of density perturbation versus depth in the upper mantle are different for the pmp and the adjacent archean sao francisco sfc and amazonian ac cratons the paleoproterozoic pmp basement has a high density root the density is relatively low in the sfc and ac lithospheres a reduction of density is a typical characteristic of chemically depleted archean cratons a more fertile proterozoic and phanerozoic subcontinental lithospheric mantle has a higher density as deduced from density estimates of mantle xenoliths of different ages and composition in conjunction with re os isotopic studies of the pmp basalts chemical and isotopic analyses of peridodite xenoliths from the gap in the northern pmp and electromagnetic induction experiments of the pmp lithosphere our density and p wave speed models suggest that the densification of the pmp lithosphere and flood basalt generation are related to mantle refertilization metasomatic refertilization resulted from the introduction of asthenospheric components from the mantle wedge above proterozoic subduction zones which surrounded the parana lithosphere the high density pmp lithosphere is presently gravitationally unstable and prone to delamination

distributed deformation in an oceanic transform system applying statistical tools to structural and paleomagnetic data near the husavik flatey fault northern iceland

architecture and tectono magmatic evolution of the campos rifted margin control of oct structure by basement inheritance abstract the formation of rifted margins involves the deformation of pre existing lithosphere whose rheological and mechanical behavior during extension is complex since it is the product of numerous earlier tectonic events in this work we investigate the campos rifted margin crm architecture with the aim of exploring the role of basement inheritance and early magmatism on margin evolution we present a new compilation of high resolution aeromagnetic data integrated with seismic interpretation and crustal thickness from 3d gravity inversion to resolve margin architecture ocean continent transition oct structure and the oceanward extent of continental basement we examine the lateral variation of crustal rheology necking geometry and rift segmentation revealing striking spatial heterogeneities that separate three distinct sectors along the campos margin the basement of the campos rifted margin consists of precambrian eo paleozoic ribeira belt rb and the easternmost cabo frio tectonic domain cftd whose neoproterozoic cambrian nappes and thrusts are well preserved offshore and give a rheologically layered crust this pre rift basement configuration along with the mesozoic magmatism has resulted in different crustal responses to extension which vary from north to south it influenced the temporal and spatial distribution of deformation and as a consequence the necking geometry subsidence and sedimentary evolution of the margin we show that the campos basin evolution was controlled by crustal inheritance corresponding to that observed in onshore basement terranes the more massive basement of the northern campos basin can be correlated with the post collisional cambro ordovician magmatic province of the aracuai belt that partially obliterated the earlier orogenic structures the lack of a structured crust localized the strain generating the observed narrow necking zone in addition its more mafic composition resulted in a competent crust which also influenced the rifting processes in contrast the basement of the central and southern campos margin represented by the cabo frio tectonic domain is structurally and petrologically distinct from the aracuai belt and has layered orogenic crust which responded differently to rifting stresses forming the observed wide necking zone we propose that the campos rifted margin evolved from a pre rift complex inherited rheology which dominated the first stages of rifting however once the crust was highly extended the deformation was nearly synchronous regionally leading to giant salt basin formation and breakup

hydrothermal alteration of basalt by seawater under seawater dominated conditions fresh mid ocean ridge basalt glass and diabase have been reacted with seawater at 150 300 c 500 bar and water rock mass ratios of 50 62 and 125 using experimental apparatus which allowed on line sampling of solution to monitor reaction progress these experiments characterize reaction under what we have called seawater dominated conditions of hydrothermal alteration in an experiment at 300 c basalt glass undergoing alteration removed nearly all mg2 from an amount of seawater 50 times its own mass in the process the glass was converted entirely to mixed layer smectite chlorite anhydrite and minor hematite removal of mg from seawater occurred as a mg oh 2 component incorporated into the secondary clay this produced a precipitous drop in solution ph early in the experiment accompanied by a dramatic increase in the concentrations of fe mn and zn in solution as mg removal neared completion and the glass was hydrolyzed ph rose again and heavy metal concentrations dropped at water rock ratios of 62 and 125 and 150 300 c the mineral assemblage produced was similar to that at a water rock ratio of 50 solution chemistry however contrasted with the earlier experiment in that mg concentrations in solution were greater and ph lower this caused significant leaching of heavy metals at 300 c nearly all of the na ca cu zn and co2 and most of the k ba sr and mn were leached from the silicates h2s al si and possibly co were also significantly mobilized whereas v cr and ni were not little or no seawater sulfate was reduced although submarine hot spring solutions sampled to date along mid ocean ridges clearly come from rock dominated hydrothermal systems evidence from ocean floor metabasalts and from heat flow studies indicates that seawater dominated conditions of alteration prevail at least locally both in axial hightemperature systems and in ridge flank systems at lower temperatures

late triassic back arc spreading and initial opening of the neo tethyan ocean in the northern margin of gondwana evidences from late triassic babb type basalts in the tethyan himalaya southern tibet abstract the tectonic evolution of the neo tethyan oceanic plate between the indian plate and the lhasa terrane is a key issue for the evolution of gondwana and formation of the tibetan plateau in this paper we report on the geochemistry sr nd isotope compositions and zircon u pb dating of late triassic basalts from the nieru formation t3n in the kampa region southern tibet the basalts have relatively low contents of mgo tio2 and total alkalis k2o na2o and they have affinities to tholeiitic basalt they exhibit weakly fractionated rare earth element ree patterns with slight depletions in lrees and slightly negative eu anomalies on a chondrite normalized diagram on a primitive mantle normalized spider diagram they are characterized by slight enrichments in large ion lithophile elements liles and relatively flat patterns of high field strength elements hfses except for depletions in ba nb ta and ti their initial 87sr 86sr ratios vary from 0 718133 to 0 738977 and end t values are relatively depleted 4 09 5 22 similar to mid ocean ridge basalts in the yarlung zangbo ophiolite we propose the t3n basalts were derived from a shallow and depleted mantle source by relatively high degree partial melting in the spinel stability field they underwent slight crustal contamination as well as the fractional crystallization of clinopyroxene the t3n basalts are similar to typical back arc basin basalts babb such as the okinawa babb this indicates an extensional back arc basin setting along the northern margin of gondwana during the late triassic the initial opening of the neo tethyan ocean was related to the southwards subduction of the paleo tethyan oceanic plate and back arc basin spreading during the late triassic magmatic activity along the passive continental margin records key information on continental break up and incipient ocean development

disintegration of aggregates and coccospheres in sediment trap samples abstract a method for non destructive disaggregation of coccoliths contained in fecal pellets marine snow and on coccospheres is described it consists of repeated chemical oxidation of organic material with naclo and h2o2 combined with brief periods of ultrasonification

strong kinetic effects on sr ca ratios in the calcitic bivalve pecten maximus although sr ca ratios in abiogenic calcite are strongly controlled by precipitation rates such a kinetic effect has never been demonstrated in calcitic bivalve shells therefore we report sr ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve pecten maximus age class i ratios of sr ca were found to be variable among individuals that grew at the same location illustrating that vital effects dominate over environmental controls although daily growth rate was correlated with shell sr ca ratios it explained only half of the sr ca variations however daily shell surface area increment an estimation of the total quantity of carbonate precipitated for a given time explained 74 of the sr ca variability in the shells of p maximus this proves for the first time in a calcitic bivalve that shell sr ca partitioning is mainly controlled by kinetic effects the sr ca ratio should therefore be tested as a potential proxy of calcification rate in modern or fossil calcitic biocarbonates

geological geochemical and isotope diversity of 134 ma dykes from the florianopolis dyke swarm parana magmatic province geodynamic controls on petrogenesis abstract the florianopolis dyke swarm fds one of the major dyke swarms belonging to the early cretaceous 135 131 ma parana magmatic province is largely dominated by high sr ti p basalts that are confirmed here as feeders of the unique urubici khumib lavas of the parana and edendeka lava piles on the basis of their age and geochemistry our study integrates field petrographic whole rock geochemistry and sr nd pb isotope geochemistry of representative samples from three main areas of exposition santa catarina island garopaba and pinheira beaches thus encompassing the whole extension of the fds compared to the urubici lavas the dykes have usually higher contents of lile and lree more radiogenic sr and pb and more unradiogenic nd features attributed to a more pronounced interaction with melts derived from the country rocks registered in the basic magmas that remained in the conduits some of these dykes show strongly interactive contacts that must be part of a wider zone of crustal melting probably more developed at greater depths small volumes of intermediate to acidic rocks form the cores of some composite dykes and correspond to products of fractional crystallization from urubici basalts contaminated with high rb sr and u th crustal melts probably derived from neoproterozoic granites as indicated by geochemical and sr nd pb isotope data the chemical and isotope signatures of the less contaminated fds basalts and related urubici lavas do not show clear evidence of inputs from primitive mantle and seem heavily influenced by enriched mantle this suggests that the mantle wedge that was affected by subduction during the neoproterozoic may have been frozen and coupled to the base of the lithospheric plate where the early cretaceous magmatism occurred a control of previous tectonic limits on the sources of the urubici basalts seems evident since they seem to be related to the younger lithosphere from the south domain related to the florianopolis batholith and no influence from the older cratonic lithosphere of the central domain can be identified in their feeders

the first 150 million years history of calcareous nannoplankton biosphere geosphere interactions abstract the mesozoic evolution of calcareous nannoplankton is here compared to global changes in the earth system to derive possible causal links between biosphere geosphere interactions the late triassic appearance of nannofossils represents an innovation that affected the marine carbonate system the global carbon cycle and the ocean atmosphere co2 nannofossil biodiversity generally increases through the jurassic and cretaceous with development of approximately 30 coccolith nannolith families speciations mass extinctions diversifications and turnovers correlate with global changes in the geosphere hydrosphere and atmosphere suggesting that the evolutionary patterns are intimately linked to environmental modifications coccolithophore biocalcification involves conversion of ca2 and co32 ions into caco3 when high fluxes of ca2 and inorganic c from the external environment into the cell are maintained seawater co2 availability and nutrient type and abundance are also important for the functioning of photosynthesis and calcification the role of coccolith secretion with respect to photosynthesis remains uncertain current dating of events suggests that pco2 and chemistry of the oceans ca2 mg ca ratio are instrumental in coccolith and particularly nannolith appearance and development whereas climate and sea level apparently play a secondary role availability of nutrients and biolimiting metals certainly influence nannoplankton evolution it is suggested here that there is a causal link between levels of co2 and calcite secretion by nannoplankton namely when pco2 in the ocean atmosphere system is minimum production of heavily calcified coccoliths nannoliths might provide sufficient co2 inside the cell to sustain photosynthesis on the contrary excess carbon dioxide makes calcification less indispensable or even inhibits calcite production smaller and less calcified coccoliths become dominant natural variations in atmospheric co2 are essentially triggered by igneous activity that also controls the ocean chemistry and nutrient cycling in particular the seawater mg ca ratio is related to seafloor spreading and hydrothermal processes high production of ocean crust results in high ca2 concentrations low mg2 concentrations and low mg ca ratio and vice versa accordingly the phanerozoic is subdivided into intervals of calcite and aragonite seas the appearance of calcareous nannoplankton and its maximum diversification indeed correlate with the shift from the paleozoic triassic aragonite sea to the jurassic paleogene calcite sea and the core of the latter respectively although there is a logical connection between pco2 and ca2 concentration and nannofossil diversity species richness alone cannot measure the productivity production of coccolithophores through time absolute abundances are necessary to interpret and model the distribution of calcareous nannofossils relative to the environment and quantify positive and negative feedbacks of coccolithophore biocalcification improved chronology of paleobiological and geological events will be crucial for the understanding of evolutionary processes

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

the utility of statistical analysis in structural geology abstract recent advances in statistical methods for structural geology make it possible to treat nearly all types of structural geology field data these methods provide a way to objectively test hypotheses and to quantify uncertainty and their adoption into standard practice is important for future quantitative analysis in structural geology we outline an approach for structural geologists seeking to incorporate statistics into their workflow using examples of statistical analyses from two locations within the western idaho shear zone in the west mountain location we test the published interpretation that there is a bend in the shear zone at the kilometer scale directional statistics on foliations corroborate this interpretation while orientation statistics on foliation lineation pairs do not this discrepancy leads us to reconsider an assumption made in the earlier work in the orofino location we present results from a full statistical analysis of foliation lineation pairs including data visualization regressions and inference these results agree with thermochronological evidence that suggests that the orofino area comprises two distinct subparallel shear zones the r programming language scripts that were used for both statistical analyses can be downloaded to reproduce the statistical analyses of this paper

palaeomagnetism of the mesozoic serra geral formation southern brazil abstract palaeomagnetic results from 20 volcanic sequences and 11 intrusive bodies sills and dykes of the serra geral formation parana basin are reported in this paper the sequences are widespread all over the basin while sills and dykes ponta grossa arch come from the northeastern portion three mean palaeomagnetic poles were computed for the serra geral formation which account for a time interval of 15 ma pole sg1 is located at 85 s 108 e 95 1 1 n 18 and represents the main phase of the magmatic activity in the basin with a mean age of 135 ma pole sg2 is located at 82 s 38 e 95 7 8 n 2 and represents a younger magmatic phase with an associated age of 130 ma pole sg3 72 s 37 e 95 6 8 n 10 is the youngest pole it is computed from the intrusive rocks and its age is assumed to be not younger than 118 ma the lower limit of the cretaceous normal magnetic interval these three poles describe a shifting path which suggest that the south american platform moved 5 southwards and rotated 10 clockwise during the lower cretaceous preceding the south atlantic opening

k ar ages and the opening of the south atlantic ocean basaltic rock from the brazilian margin abstract new k ar ages for 13 samples of basalt gabbro wehrlite and trachyandesite drilled from the brazilian continental shelf and coastline yield information about the timing of the opening of the south atlantic and the nature of the crust seaward from the brazil margin the oldest basalt is 138 1 3 5 m y old and from offshore at 24 5 s it represents serra geral flood basalt on attenuated crust in the santos basin basalts from the coastline at 19 5 s are mixed with terrigenous graben sediments and their ages confirm that rifting was underway before 130 m y offshore sites in the campos basin 22 23 s 41 w have basalt ranging from 124 to 112 m y in age and mostly continental flood basalt in composition one 112 m y basalt however is morb like and could therefore represent oceanic lithosphere mixed with continental crust about 50 km from the shoreline at 22 5 s other samples reveal compositionally varied intraplate passive margin magmatism occurring 75 43 m y ago they correlate with profuse contemporary alkalic magmatism on the southeastern brazil coast and probably represent reactivation of zones of weakness i e fracture zone lineaments

selkirk fan structure southeastern canadian cordillera tectonic wedging against an inherited basement ramp a revised cross section through the selkirk fan structure provides the basis for a new model for the middle jurassic tectonic evolution of the southern omineca belt canadian cordillera palinspastic restoration of this cross section shows that the southwest verging structures along the west flank of the selkirk fan structure formed as a result of tectonic wedging of distal north american strata clachnacudainn complex beneath more proximal north american strata and that the selkirk fan structure developed outboard from a crustal ramp dogtooth high inherited from late proterozoic early paleozoic rifting along the western margin of north america the first episode of mesozoic deformation in southeastern british columbia occurred between 187 and 173 ma and involved the northeastward juxtaposition of the intermontane superterrane over the outer part of the north american continental terrace wedge it resulted in deep burial 20 25 km of the outer margin of north america a crustal ramp localized along the western edge of the late proterozoic early paleozoic dogtooth high impeded the northeastward propagation of the orogenic wedge comprising the intermontane superterrane and the imbricate underlying northeast verging thrust sheets of north american supracrustal rocks tectonic wedging involving southwest verging deformation occurred within the orogenic wedge and the resulting crustal thickening established sufficient topography and gravitational potential to drive the propagation of the deformation eastward into the dogtooth range and the rocky mountains the southwest verging structures along the west flank of the selkirk fan developed between approximately 173 and 168 ma concurrent with synorogenic extension and 10 km of exhumation the initial subsidence of the foreland basin during kimmeridgian time ca 154 ma provides the first indication of tectonic loading and lithospheric flexure of the north american plate it is interpreted to mark the time at which the orogenic wedge overrode the crustal ramp of the dogtooth high and advanced onto relatively thick and rigid continental lithosphere the tectonic model proposed for the selkirk fan structure illustrates how the configuration of the rifted margin influenced the style of crustal thickening during subsequent compressional deformation

regional variations within the parana flood basalts southern brazil evidence for subcontinental mantle heterogeneity and crustal contamination abstract continental flood volcanism of the parana basin lower cretaceous is represented by two pyroxene tholeiitic basalts 90 vol the northern parana province npp is dominated by basalts high in tio2 and incompatible elements htib while the southern parana province spp is dominated by basalts low in tio2 and incompatible elements ltib npp basalts show relatively small variations of initial 120 ma 87 sr 86 sr r0 and 143 nd 144 nd nd ratios r0 0 7051 0 7062 and nd 0 5124 0 5125 respectively relative to those occurring in spp r0 0 7046 0 7120 and nd 0 5122 0 5128 respectively the latter basalts show significant positive correlations between r0 vs sio2 k2o rb and ba and negative correlations between r0 vs cr ni and mg value believed to be due to crustal granitic contamination in general the effects of contamination are pronounced in spp and tend to vanish towards npp 18o values range from 6 5 to 10 0 in the basalts from npp and spp and essentially reflect water magma interactions uncontaminated ltib and htib basalts from npp are isotopically distinct from the uncontaminated analogues from spp ltib r0 0 7055 vs 0 7046 nd 0 5124 vs 0 5128 respectively all chemical data consistently indicate distinct sources and a large scale mantle heterogeneity the npp mantle source is expected to have relatively high content of enriched components possibly related to small volume melts and metasomatic fluids tentatively the last stabilization age of the parana mantle heterogeneity is 0 5 1 0 ga old the existence of high and low tio2 basalt suites in both parana and karoo provinces in brazil and southern africa respectively indicates a large scale heterogeneity in the subcontinental mantle and suggests that basalt generation occurred in the lithospheric mantle

trace metal mg ca and sr ca analyses of single coccoliths by secondary ion mass spectrometry here we present the first multi species comparison of modern and fossil coccolith trace metal data obtained from single liths we present both trace metal analyses sr ca mg and al and distribution maps of individual paleogene fossil coccoliths obtained by secondary ion mass spectrometry sims we use this data to determine the effects of variable coccolith preservation and diagenetic calcite overgrowths on the recorded concentrations of strontium and magnesium in coccolith calcite the analysis of coccoliths from deep ocean sediments spanning the eocene oligocene transition demonstrates that primary coccolith calcite is resistant to the neomorphism that is common in planktonic foraminifera from similar depositional environments instead where present diagenetic calcite forms distinct overgrowths over primary coccolith calcite rather than replacing this calcite diagenetic overgrowths on coccoliths are easily distinguished in sims analyses on the basis of relatively higher mg and lower sr concentrations than co occurring primary coccolith calcite this interpretation is confirmed by the comparable sims analyses of modern cultured coccoliths of coccolithus braarudii further with diagenetic calcite overgrowth being the principle source of bias in coccolith based geochemical records we infer that lithologies with lower carbonate content deposited below the palaeo lysocline are more likely to produce geochemical records dominated by primary coccolith calcite than carbonate rich sediments where overgrowth is ubiquitous the preservation of primary coccolith carbonate in low carbonate lithologies thus provides a reliable geochemical archive where planktonic foraminifera are absent or have undergone neomorphism