diagenesis and geochemistry of porites corals from papua new guinea implications for paleoclimate reconstruction coral proxy records of sea surface temperature sst and hydrological balance have become important tools in the field of tropical paleoclimatology however coral aragonite is subject to post depositional diagenetic alteration in both the marine and vadose environments to understand the impact of diagenesis on coral climate proxies two mid holocene porites corals from raised reefs on muschu island papua new guinea were analysed for sr ca 18 o and 13 c along transects from 100 aragonite to 100 calcite thin section analysis showed a characteristic vadose zone diagenetic sequence beginning with leaching of primary aragonite and fine calcite overgrowths transitional to calcite void filling and neomorphic fabric selective replacement of the coral skeleton average calcite sr ca and 18 o values were lower than those for coral aragonite decreasing from 0 0088 to 0 0021 and 5 2 to 8 1 respectively the relatively low sr ca of the secondary calcite reflects the sr ca of dissolving phases and the large difference between aragonite and calcite sr ca partition coefficients the decrease in 18 o of calcite relative to coral aragonite is a function of the 18 o of precipitation carbon isotope ratios in secondary calcite are variable though generally lower relative to aragonite ranging from 2 5 to 10 4 the variability of 13 c in secondary calcite reflects the amount of soil co 2 contributing 13 c depleted carbon to the precipitating fluids diagenesis has a greater impact on sr ca than on 18 o the calcite compositions reported here convert to sst anomalies of 115 c and 14 c respectively based on calcite sr ca compositions in this study and in the literature the sensitivity of coral sr ca sst to vadose zone calcite diagenesis is 1 1 to 1 5 c per percent calcite in contrast the rate of change in coral 18 o sst is relatively small 0 2 to 0 2 c per percent calcite we show that large shifts in 18 o reported for mid holocene and last interglacial corals with warmer than present sr ca ssts cannot be caused by calcite diagenesis low level calcite diagenesis can be detected through x ray diffraction techniques thin section analysis and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions copyright 2003 elsevier science ltd

is quartz cathodoluminescence color a reliable provenance tool a quantitative examination abstract we examined cathodoluminescence cl colors of quartz by using red 590 780 nm green 515 590 nm and blue 380 515 nm optical filters interfaced with a cathodoluminescence cl detector attached to a scanning electron microscope sem sem cl images taken through these filters were captured digitally and transferred to a computer luminescence intensities luminosities of the images were measured by using available commercial software measured luminosities of these cl images are directly related to relative intensities of red green and blue cl emissions luminosity data were then used to construct plots that display relative luminosities of the cl images acquired through the red green and blue filters an unfiltered cl image of each quartz grain generated by photons with wavelengths ranging from 200 700 nm was also acquired by subtracting the numerical luminosity values of the images acquired through the red green and blue filters from the luminosity value of the unfiltered image the contribution to total luminosity provided by cl emission in the near ultraviolet uv was calculated the cl colors of quartz from a variety of volcanic plutonic and metamorphic rocks and hydrothermal deposits were examined volcanic quartz phenocrysts have the most restricted cl color range with strongest emission intensity in the blue wavelength band cl colors of plutonic quartz overlap those of volcanic phenocrysts but extend over a broader range to include quartz that displays higher intensity of red emission cl emission in hydrothermal vein quartz is similar to that in plutonic quartz although some hydrothermal quartz exhibits stronger green cl emission than does plutonic quartz the cl colors of metamorphic quartz exhibit the widest variation overlapping the color fields of both volcanic and plutonic quartz and extending further into the red cl emission in the near uv makes a significant contribution 5 85 percent to the total luminosity of sem cl images particularly images of plutonic quartz because of overlap in the cl color ranges of volcanic plutonic metamorphic and hydrothermal quartz unambiguous identification of quartz provenance on the basis of cl color alone is problematic it is difficult to distinguish between volcanic and some plutonic quartz and between some plutonic and hydrothermal quartz or to distinguish magmatic quartz from metamorphic quartz that exhibits blue cl color only metamorphic quartz that exhibits moderately strong red emission appears distinguishable on the basis of color from quartz of other origins our work thus suggests that cl color is not a reliable indicator of quartz provenance

two dimensional x ray diffraction as a tool for the rapid nondestructive detection of low calcite quantities in aragonitic corals paleoclimate reconstructions based on reef corals require precise detection of diagenetic alteration secondary calcite can significantly affect paleotemperature reconstructions at very low amounts of 1 x ray powder diffraction is routinely used to detect diagenetic calcite in aragonitic corals this procedure has its limitations as single powder samples might not represent the entire coral heterogeneity a conventional and a 2 d x ray diffractometer were calibrated with gravimetric powder standards of high and low magnesium calcite 0 3 to 25 calcite calcite contents 1 can be recognized with both diffractometer setups based on the peak area of the calcite 104 reflection an advantage of 2 d xrd over convenient 1 d xrd methods is the nondestructive and rapid detection of calcite with relatively high spatial resolution directly on coral slabs the calcite detection performance of the 2 d xrd setup was tested on thin sections from fossil porites sp samples that based on powder xrd measurements showed 1 calcite quantification of calcite contents for these thin sections based on 2 d xrd and digital image analysis showed very similar results this enables spot measurements with diameters of 4 mm as well as systematic line scans along potential tracks previous to geochemical proxy sampling in this way areas affected by diagenetic calcite can be avoided and alternative sampling tracks can be defined alternatively individual sampling positions that show dubious proxy results can later be checked for the presence of calcite the presented calibration and quantification method can be transferred to any 2 d x ray diffractometer

the strontium magnesium and sodium composition of recent scleractinian coral skeletons as standards for palaeoenvironmental analysis to establish standards for the palaeoenvironmental interpretation of scleractinian coral bearing strata the geochemistry of the three major trace element constituents of living scleractinian coral skeletons is discussed in relation to possible controls on their concentrations experiments were conducted in which the sr ca and mg ca ratios of the seawater were altered and the resultant change in skeletal composition monitored the partition coefficient of strontium ksr was shown to be linear ranging from approximately half to over ten times the normal seawater sr ca ratio increases in the magnesium concentration of seawater decreased ksr growth rates were increased through the addition of calcium and strontium but decreased by magnesium the sodium and magnesium contents of the skeleton were unaffected by their seawater concentrations relative to calcium or strontium magnesium however was affected by growth while sodium by salinity

evaluation of the effect of diagenetic cements on element ca ratios in aragonitic early miocene 16ma caribbean corals implications for deep time palaeo environmental reconstructions abstract early miocene corals siderastrea conferta and montastraea limbata from the paraguana peninsula venezuela and a modern coral s radians from bermuda were examined in order to quantitatively assess the effect of skeletal preservation on element ca proxies used for palaeo environmental reconstructions the biostratigraphic age burdigalian of the corals was confirmed via sr isotope stratigraphy to 16 5 0 4 ma light and scanning electron microscopy revealed the presence of aragonite and calcite cements in both fossil and modern corals but brucite cements were found only in the modern coral cement distribution is very heterogeneous resulting in zones of excellent preservation juxtaposed with less well preserved regions in both modern and fossil coral oil filled pore spaces were noted in the fossil specimens targeted la icpms depth profile analyses showed significant differences in sr ca mg ca b ca ba ca and u ca in aragonite and calcite cements compared to primary skeletal aragonite increased sr ca and decreased mg ca ratios were found in aragonite cements compared to skeletal aragonite whereas in calcite cements these trends were reversed b ca ratios were lower in both aragonite and calcite cements compared to primary aragonite estimates of the effect of 1 contamination by aragonite cements on coral sr ca mg ca b ca and u ca palaeo sea surface temperature reconstructions for the fossil corals produced anomalies of 1 2 c 0 2 c 0 3 c and 0 1 c respectively similar percentage calcite cement contamination produced temperature anomalies of 1 7 c 2 7 c 0 3 c and 0 1 c because of both highly elevated and depleted ba ca signatures in aragonite and calcite cements respectively care has to be exercised when reconstructing past flood or upwelling events from fossil corals when using targeted spatially resolved analysis well preserved early miocene corals may overall yield reliable deep time palaeo proxy information in much the same way as commonly utilised holo pleistocene corals

extending the radiocarbon calibration beyond 26 000 years before present using fossil corals fossil coral is an excellent archive to extend the radiocarbon 14c calibration beyond tree ring records however published coral data older than 26 000 years before present are too disparate for practical calibration we propose an explanation for these discrepancies trace amounts of secondary calcite and organic matter in fossil corals shift the 14c ages toward younger ages in a series of acid leaching experiments to simulate the standard cleaning procedure prior to 14c analysis we measure up to a 300 enrichment of diagenetic calcite in corals due to the solubility differences between calcite and aragonite in model calculations we show the 14c age offsets produced by acid leaching could be hundreds to thousands of years when typical amounts of calcite are present in samples we demonstrate the necessity and our ability to detect 0 2 calcite in aragonite by x ray diffraction and apply 0 2 calcite as our a priori criterion for our coral samples the estimated age offsets of samples with 0 2 calcite fall within the reported analytical uncertainty of 14c dating in addition we present 14c results from an extended hydrogen peroxide h2o2 pretreatment for coral samples to remove organic matter our data show that treated samples yield consistent or older 14c dates compared to non treated samples these rigorous but necessary screening and cleaning techniques provide precise reproducible and accurate radiocarbon calibration data

geochemical mineralogical and sedimentological studies on the taklimakan desert sands major element composition mineral composition and grain size distribution have been studied for quaternary aeolian sediments from the taklimakan desert north western china together with the variation of chemical and mineralogical compositions of different grain size fractions aeolian sediments from the taklimakan desert have higher ratios of feldspar quartz and calcite quartz finer grain size poorer roundness of quartz and feldspar grains and lower abundances of frosted quartz than found in aeolian sediments from other deserts such as the saudi arabian desert in spite of these immature mineralogical and sedimentological features the aeolian sediments from the taklimakan desert show low regional variations in major element and mineral compositions and are homogenized these observations confirm that two processes glacial activity within surrounding mountains and aeolian activity at the tarim basin are important in the homogenization of the taklimakan desert sands taklimakan desert sediments are constantly and effectively supplied from basement rocks in the surrounding mountains by glacial erosion the supplied sediments are further homogenized by aeolian activity in the desert and are partly blown away serving as the source of chinese aeolian loess compositional differences are observed between loess mainly 10 40 m particles and the 45 m fraction of the taklimakan desert sediments as well as between loess and whole rock of the taklimakan desert sediments these observations provide constraints for precise modelling of loess formation and for assessment of the chemical composition of the upper continental crust based on the chemical composition of aeolian loess

a review of modern coral δ18o and δ14c proxy records abstract this paper is a review of published modern coral 18 o and 14 c isotopic records that are at least 30 and 20 years long respectively the data are presented to show basin scale trends in both of these proxy records on decadal to centennial timescales the goal was to qualitatively integrate the general inter annual to centennial timescale variability revealed in these data as well as the statistical and modeling output results that have been produced using these coral records while many review papers typically include a representative subset of the data available this review aims to include as much of the available data as possible in general coral 18 o records show a long term warming and or freshening throughout the tropical oceans and agree with the noaa extended reconstruction sea surface temperature 2 ersst on decadal timescales in the western pacific it is most likely a freshening of the seawater 18 o that dominates the signal el nino southern oscillation enso variability dominates most 18 o records either by varying local seawater temperature or salinity depending on the regional oceanography climatology outside of the pacific enso affects seawater temperature and salinity via atmospheric or oceanic teleconnections post bomb coral 14 c records collectively show that the uptake of 14 c has been greatest in gyre water fed sites followed in descending order by western boundary current areas equatorial upwelling regions and eastern tropical pacific upwelling sites these surface water 14 c values indicate the proportion of surface water and or the residence time of water at the surface at a given location and can be used to model water mass mixing rates such models have only begun to be run and show that the amount of eastern pacific water entering the central south pacific increases during el ninos and that the indonesian throughflow is supplied year round by the north pacific comparing ocean circulation models with coral 14 c modelled circulation enables researchers to explore the mechanisms that drive seawater 14 c variability and fine tune their models in addition our comparison between the rate of coral 14 c increase between 1960 and 1970 and total anthropogenic co 2 uptake rates show general agreement demonstrating the value of coral records in understanding past carbon fluxes overall coral 18 o and 14 c proxy records represent natural archives of seawater conditions and are critical for studying the natural variability in local and regional patterns within and teleconnection patterns between the tropics extra tropics temperate and polar regions on intra annual to centennial timescales

images of diagenetic textures in porites corals from papua new guinea and indonesia diagenesis is now recognized as a potentially major source of error in paleoclimatic reconstructions from fossil and modern coral geochemical records key to avoiding spurious results caused by diagenesis is thorough screening of coral material prior to geochemical analysis in this data brief we present color images from thin sections of fossil and modern porites corals and demonstrate the effectiveness of thin sections in detecting low levels of diagenesis the images presented here cover a range of coral preservation levels from pristine aragonite to 100 calcite we particularly focus on samples containing around 1 diagenetic material a level known to create artifacts in key climate parameters such as sea surface temperature and close to the detection limits of other screening methods such as x ray diffraction xrd a qualitative scheme is also presented to rate the degree of diagenesis in a coral where xrd results are not available or where secondary aragonite is present overall this collection of images is designed as a starting point in combination with other techniques to assist in identifying and screening corals for diagenesis

provenance of loess material and formation of loess deposits on the chinese loess plateau abstract results of a multiple isotopic chemical and mineralogical analysis of loess from the three northwestern inland basins the junggar basin the tarim basin and the qaidam basin and the loess plateau region of china are summarized they suggest a qualification of the conventional views that the three northwestern basins were the important source areas of the loess plateau and that the sand deserts were the primary single source of the chinese loess it is argued that the gobi stony desert in southern mongolia and the adjoining gobi and sand deserts the badain jaran desert tengger desert ulan buh desert hobq desert and mu us desert in china rather than the three inland basins are the dominant source areas of the loess plateau however although these gobi and sand deserts are regarded as the main source regions they serve as dust and silt holding areas rather than dominant producers the mountain processes including glacial grinding frost weathering salt weathering tectonic processes and some fluvial comminution in the gobi altay mts hangayn mts and the qilian mts have played an important role in producing the vast amounts of loess sized material for forming the loess plateau

sst artifacts in coral proxy records produced by early marine diagenesis in a modern coral from rabaul papua new guinea 1 we investigated the effects of early marine diagenesis on the skeletal geochemistry of a porites coral collected live offshore of rabaul papua new guinea the lowermost 14 cm of the 1 9 m coral core contains physical evidence of alteration which is clearly visible in x radiograph sem and petrography images abrupt and significant increases in coral 18o and sr ca and decreases in coral mg ca occur at the transition from unaltered to altered skeleton all of which imply significant sst cooling if the altered nature of the coral skeleton went unrecognized screening for the effects of early marine diagenesis should become a standard procedure in coral climate studies

impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in porites corals restricted zones of recent dissolution and secondary aragonite infilling were identified in a coral core collected in 1986 from a living massive porites colony from the central great barrier reef australia secondary aragonite needles 20 m long cover skeletal surfaces deposited from 1972 to late 1974 and increase bulk density by 10 dissolution is observed above this zone whereas older skeleton is pristine we investigate the impact of both types of early marine diagenesis on skeletal geochemistry and coral paleoclimate reconstructions by comparison with similar records from eight contemporary porites colonies collected at nearby reefs secondary aragonite overgrowth causes anomalies in skeletal density mg ca sr ca u ca o and c the secondary aragonite is consistently associated with a cool temperature anomaly for each of the sea surface temperature sst proxies o sst 1 6 c sr ca sst 1 7 c mg ca sst 1 9 c u ca sst 2 8 c dissolution through incongruent leaching also causes cool sst artifacts but only for trace element ratios mg ca sst 1 2 c sr ca sst 1 2 c u ca sst 2 1 c the sequence of preference with respect to dissolution of coral skeleton in seawater is mg ca sr u rigorous screening of coral material for paleoclimate reconstructions is therefore necessary to detect both dissolution and the presence of secondary minerals the excellent agreement between apparent sst anomalies generated by different modes of diagenesis means that replication of tracers within a single coral cannot be used to validate climate proxy interpretations poor replication of records between different coral colonies however provides a strong indication of nonclimatic artifacts such as dissolution and secondary aragonite copyright 2007 by the american geophysical union

calcite filled borings in the most recently deposited skeleton in live collected porites scleractinia implications for trace element archives abstract skeletons of the scleractinian coral porites are widely utilized as archives of geochemical proxies for among other things sea surface temperature in paleoclimate studies here we document live collected porites lobata specimens wherein as much as 60 of the most recently deposited skeletal aragonite i e the part of the skeleton that projects into the layer of living polyps and thus is still in direct contact with living coral tissue has been bored and replaced by calcite cement calcite and aragonite were identified in situ using raman microspectroscopy the boring filling calcite cement has significantly different trace element ratios sr ca mmol mol 6 3 1 4 mg ca mmol mol 12 0 5 1 than the host coral skeletal aragonite sr ca mmol mol 9 9 1 3 mg ca mmol mol 4 5 2 3 the borings appear to have been excavated by a coccoid cyanobacterium that dissolved aragonite at one end and induced calcite precipitation at the other end as it migrated through the coral skeleton boring activity and cement precipitation occurred concomitantly with coral skeleton growth thus replacing skeletal aragonite that was only days to weeks old in some cases although the cement filled borings were observed in only 20 of sampled corals their occurrence in some of the most recently produced coral skeleton suggests that any corallum could contain such cements irrespective of the coral s subsequent diagenetic history in other words pristine skeletal aragonite was not preserved in parts of some corals for even a few weeks although not well documented in coral skeletons microbes that concomitantly excavate carbonate while inducing cement precipitation in their borings may be common in the ubiquitous communities that carry out micritization of carbonate grains in shallow carbonate settings thus such phenomena may be widespread and failure to recognize even very small quantities of early cement filled borings in corals used for paleoclimate studies could compromise high resolution paleotemperature reconstructions the inability to predict the occurrence of cement filled borings in coralla combined with the difficulty in recognizing them on polished blocks highlights the great care that must be taken in vetting samples both for bulk and microanalysis of geochemistry

seychelles coral record of changes in sea surface temperature bimodality in the western indian ocean from the mid holocene to the present we report fossil coral records from the seychelles comprising individual time slices of 14 20 sclerochronological years between 2 and 6 2 kyr bp to reconstruct changes in the seasonal cycle of western indian ocean sea surface temperature sst compared to the present 1990 2003 these reconstructions allowed us to link changes in the sst bimodality to orbital changes which were causing a reorganization of the seasonal insolation pattern our results reveal the lowest seasonal sst range in the mid holocene 6 2 5 2 kyr bp and around 2 kyr bp while the highest range is observed around 4 6 kyr bp and between 1990 and 2003 the season of maximum temperature shifts from austral spring september to november to austral autumn march to may following changes in seasonal insolation over the past 6 kyr however the changes in sst bimodality do not linearly follow the insolation seasonality for example the 5 2 and 6 2 kyr bp corals show only subtle sst differences in austral spring and autumn we use paleoclimate simulations of a fully coupled atmosphere ocean general circulation model to compare with proxy data for the mid holocene around 6 kyr bp the model results show that in the mid holocene the austral winter and spring seasons in the western indian ocean were warmer while austral summer was cooler this is qualitatively consistent with the coral data from 6 2 to 5 2 kyr bp which shows a similar reduction in the seasonal amplitude compared to the present day however the pattern of the seasonal sst cycle in the model appears to follow the changes in insolation more directly than indicated by the corals our results highlight the importance of ocean atmosphere interactions for indian ocean sst seasonality throughout the holocene in order to understand holocene climate variability in the countries surrounding the indian ocean we need a much more comprehensive analysis of seasonally resolved archives from the tropical indian ocean insolation data alone only provides an incomplete picture

aragonite cycles diagenesis caught in the act organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession a record from the early pliocene of the maldives ocean drilling program odp leg 115 is presented containing precession and eccentricity cycles expressed as variable aragonite content additional sub milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval comparison with palaeo productivity indicators nannofossils chlorin total organic carbon suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity the coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment the observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on milankovitch and sub milankovitch scales diagenetically stable proxies for palaeo productivity such as nannofossil assemblage data were used to distinguish between palaeoclimate and diagenetic influences

cathodoluminescence characterization of quartz particles in mature arenites a combination of cathodoluminescence cl microscopy with digital image analysis and spectroscopic analysis allows the detailed investigation of the commonly occurring colour shift from initial to final cl colours in detrital quartz with increasing irradiation a method for the quantification of the colour shift is presented and applied to different quartz sands unlithified sands of the lower cretaceous kuhfeld formation from ottenstein w germany and holocene sands from the barrier island of wangerooge n germany the colour shift depends on the defect structure of the quartz grains the defect structure is determined by the physico chemical conditions during crystallization and therefore can help trace the source of quartz grains a total of 25 different types of quartz grains in the ottenstein sands indicates a highly variable southern provenance many of the grains have recycled quartz cement overgrowths indicating an at least second cycle origin in contrast only 16 different quartz types have been observed in the wangerooge sands reflecting a less varied plutonic to metamorphic scandinavian provenance the study demonstrates the potential of quantified cl initial colour and colour shift in assessing the provenance of quartz rich sands and sandstones

displacement and deformation associated with a lateral thrust termination southern golden gate range southern nevada u s a abstract the golden gate thrust offers an excellent opportunity to study displacement and deformation at a lateral thrust tip slip across this e vergent thrust is uniformly about 2 4 km for the southern 2 km of exposed strike length and dies out to zero in the northern 5 km constant displacement and uniform hangingwall structure along the southern one third of exposed strike length suggest that along strike displacement variation and consequent deformation are localized near the lateral tip structures located at and north of the lateral tip are consistent with transpression and later uplift as slip accumulated on the thrust fold and fault orientations and calcite twinning strain record possible transpression north of the lateral tip e w striking normal faults at the thrust tip record extension that is interpreted to be the result of the uplift and translation of a structurally continuous rigid block located north of the normal faults this block is connected to and was uplifted with the crest of the hangingwall anticline and was separated by the normal faults from thrust related folding to the south the main hangingwall structure is an anticline that in southern exposures trends n s parallel to the thrust but bends westward and opens into a box fold to the north the hangingwall anticline superficially resembles a classic fault propagation fold formed by a migrating ductile bead however we are forced to reject the ductile bead hypothesis for the fold because 1 the geometry of the hangingwall anticline far from the thrust tip cannot have evolved from the geometry at the thrust tip and 2 twinned calcite strain data from along the thrust suggest that strain was homogeneous and coaxial rather than inhomogeneous and progressively non coaxial as predicted for a migrating ductile bead the three dimensional structural and kinematic relations at the lateral tip of the golden gate thrust appear to be the result of deformation around a pinned tip although the reason that the tip was pinned at its present location is unclear we interpret the thrust to have propagated relatively quickly to its ultimate extent with little initial displacement indicating that it was easier to fault the rocks than to fold them

fault propagation ductile strain and displacement distance relationships abstract displacement distance analysis of fault related fold structures can reveal important information about the distribution of fault displacement and in some cases the history of fault propagation this method is commonly used to 1 determine the ratio of displacement rate to propagation rate s p ratio 2 predict the location of unconstrained fault tips 3 determine the location of fault nucleation points and 4 evaluate structural interpretations although the displacement distance approach represents a potentially useful method for gaining information about displacement parallel fault propagation histories of natural fault related fold structures the theoretical relationship between s p and relative stretch er that forms the basis of this method remains essentially untested because displacement rates and propagation rates are generally unknown for natural structures these relationships can only be objectively tested by analysing model structures with known geometries strain distributions and fault propagation histories displacement distance analysis of different fault related fold models reveals that 1 displacement distance relationships are highly dependent on the nature of the hanging wall strain 2 relative stretch is not related to s p in any general way 3 fault tip locations cannot always be predicted by linear extrapolation of displacement distance trajectories 4 displacement maxima are not necessarily indicative of fault nucleation points in all cases and 5 although calculation of s p ratios from observed relative stretch magnitudes may not be appropriate the use of displacement distance relationships can nonetheless be useful in comparing structures and improving structural interpretations

asian dustfall in the st elias mountains yukon canada in april 2001 a major atmospheric dustfall event occurred in the st elias mountains yukon territory canada field samples were collected and analyzed for particle size mineralogy chemical composition and sr nd and pb isotopes dusts found above 3000 m had their source in the gobi desert region of northern china and inner mongolia and were transported to the yukon following a series of major dust storms that took place in early april dusts found below 3000 m had local yukon or mixed source s the asian dusts had a modal volume diameter of 4 m typical of far traveled mineral aerosols however larger 10 m particles were also found at 5000 m suggesting a very rapid trans pacific transport in the mid troposphere we estimate that the april 2001 event deposited from 5500 to 6335 tons of dust over an area of 21 000 km2 in the southwestern yukon most of which probably fell within a week our findings are consistent with instrumental observations and model simulations of the april 2001 event while the dust cloud was reportedly mixed with volatile pollutants from asia we found no evidence of metal pollution associated with the dustfall in the yukon our findings contribute to clarify the dynamics and the geochemical impact of asian dust long range transport events and to better estimate eolian fluxes of dustborne elements e g fe to the ocean associated with such events they may also assist in identifying past asian dust events in ice cores drilled from the st elias mountains icefields to develop a long term record of their frequency magnitude and source s

palaeoenvironmental records from fossil corals the effects of submarine diagenesis on temperature and climate estimates the geochemistry of coral skeletons may reflect seawater conditions at the time of deposition and the analysis of fossil skeletons offers a method to reconstruct past climate however the precipitation of cements in the primary coral skeleton during diagenesis may significantly affect bulk skeletal geochemistry we used secondary ion mass spectrometry sims to measure sr mg b u and ba concentrations in primary coral aragonite and aragonite and calcite cements in fossil porites corals from submerged reefs around the hawaiian islands cement and primary coral geochemistry were significantly different in all corals we estimate the effects of cement inclusion on climate estimates from drilled coral samples which combine cements and primary coral aragonite secondary 1 calcite or not vert similar2 aragonite cement contamination significantly affects sr ca sst estimates by 1 c and 0 4 to 0 9 c respectively cement inclusion also significantly affects mg ca b ca and u ca sst estimates in some corals x ray diffraction xrd will not detect secondary aragonite cements and significant calcite contamination may be below the limit of detection not vert similar1 of the technique thorough petrographic examination of fossils is therefore essential to confirm that they are pristine before bulk drilled samples are analysed to confirm that the geochemistry of the original coral structures is not affected by the precipitation of cements in adjacent pore spaces we analysed the primary coral aragonite in cemented and uncemented areas of the skeleton sr ca b ca and u ca of primary coral aragonite is not affected by the presence of cements in adjacent interskeletal pore spaces i e the coral structures maintain their original composition and selective sims analysis of these structures offers a route to the reconstruction of accurate ssts from altered coral skeletons however mg ca and ba ca of primary coral aragonite are significantly higher in parts of skeletons infilled with high mg calcite cement we hypothesise this reflects cement infilling of intraskeletal pore spaces in the primary coral structure

fault displacement distance relationships as indicators of contractional fault related folding style we present a method of using fault displacement distance profiles to distinguish fault bend shear fault bend and fault propagation folds and use these insights to guide balanced and retrodeformable interpretations of these structures we first describe the displacement profiles associated with different end member fault related folding models then provide examples of structures that are consistent with these model based predictions natural examples are imaged in high resolution two and three dimensional seismic reflection data sets from the niger delta sichuan basin sierras pampeanas and cascadia to record variations in displacement with distance updip along faults termed displacement distance profiles fault bend folds exhibit constant displacement along fault segments and changes in displacement associated with bends in faults shear fault bend folds demonstrate an increase in displacement through the shearing interval and fault propagation folds exhibit decreasing displacement toward the fault tip more complex structures are then investigated using this method demonstrating that displacement distance profiles can be used to provide insight into structures that involve multiple fault related folding processes or have changed kinematic behavior over time these interpretations are supported by comparison with the kinematics inferred from the geometry of growth strata overlying these structures collectively these analyses illustrate that the displacement distance approach can provide valuable insights into the styles of fault related folding

the puzzling presence of calcite in skeletons of modern solitary corals from the mediterranean sea the skeleton of scleractinian corals is commonly believed to be composed entirely of aragonite due to the current mg ca molar ratio of seawater which thermodynamically favours the deposition of this polymorph of calcium carbonate caco3 however some studies have shown that other forms of caco3 such as calcite can be present in significant amount 1 20 inside tropical coral skeletons significantly impacting paleo reconstructions of sst or other environmental parameters based on geochemical proxies this study aims at investigating for the first time 1 the skeletal composition of two mediterranean solitary corals the azooxanthellate leptopsammia pruvoti and the zooxanthellate balanophyllia europaea across their life cycle 2 the distribution of the different caco3 forms inside skeletons and 3 their implications in paleoclimatology the origin of the different forms of caco3 observed inside studied coral skeletons and their relationships with the species habitat and ecological strategies are also discussed caco3 composition of l pruvoti and b europaea was investigated at six sites located along the italian coasts skeleton composition was studied by means of x ray powder diffraction and fourier transform infrared spectroscopy a significant amount of calcite 1 23 was found in more than 90 of the studied coral skeletons in addition to aragonite this calcite was preferentially located in the basal and intermediate areas than at the oral pole of coral skeletons calcite was also mainly located in the epitheca that covered the exposed parts of the coral in its aboral region interestingly in b europaea the calcite content was negatively correlated with skeleton size age the presence of calcite in scleractinian corals may result from different mechanisms 1 corals may biologically precipitate calcite crystals at their early stages in order to insure their settlement on the substrate of fixation especially in surgy environments 2 calcite presence may result from skeletons of other calcifying organisms such as crustose coralline algae and or 3 calcite may result from the infilling of galleries of boring microorganisms which are known to colonize coral skeletons we suggest that more than one of the above mentioned processes are involved

oxygen isotope signatures of quartz from major asian dust sources implications for changes in the provenance of chinese loess abstract we present a systematic investigation of the oxygen isotopic composition of quartz in both fine and coarse fractions 18 o values of both the fine and coarse fractions from the various sources are overlapped to varying degrees thus making it difficult to differentiate them nevertheless the quartz 18 o values of both fractions exhibit an increasing trend from the mongolian gobi to the northern chinese deserts and then to the taklimakan desert this implies that the geological settings of the source areas are different which in turn results in differing contributions of high temperature igneous rocks the combination of quartz 18 o results with other quartz based provenance tracers can clearly differentiate the three major source areas i e the taklimakan desert the mongolian gobi and the northern chinese deserts in addition comparison of our results with previous 18 o measurements of fine grained quartz from the luochuan loess sequence suggests the likely glacial interglacial fluctuations in dust provenance finally we suggest that the combination of quartz 18 o signatures and other dust provenance tracers can potentially improve the recognition of long term fluctuations in the provenance of chinese loess red clay deposits

tracking the extent of the south pacific convergence zone since the early 1600s 1 the south pacific convergence zone spcz is the largest and most persistent spur of the intertropical convergence zone at the southeastern edge of the spcz near 170 w and 15 20 s a surface ocean salinity frontal zone exists that separates fresher western pacific warm pool water from saltier and cooler waters in the east this salinity front is known to shift east and west with the phase of the el nino southern oscillation we have generated subannually resolved and replicated coral oxygen isotopic time series from fiji 17 s 179 e and rarotonga 21 5 s 160 w that have recorded interannual displacements of the salinity front over the last 380 years and also indicate that at lower frequencies the decadal mean position of the salinity front and eastern extent of the spcz has shifted east west through 10 to 20 of longitude three times during this interval the most recent and largest shift began in the mid 1800s as the salinity front progressively moved eastward and salinity decreased at both sites our results suggest that sea surface salinity at these sites is now at the lowest levels recorded and is evidence for an unprecedented expansion of the spcz since the mid 1800s the expansion of the spcz implies a gradual change in the south pacific to more la nina like long term mean conditions this observation is consistent with the ocean thermostat mechanism for the pacific coupled ocean atmosphere system whereby exogenous heating of the atmosphere would result in greater warming in the western pacific and a greater east west surface temperature gradient components 8034 words 7 figures 2 tables

exhumation history of the west kunlun mountains northwestern tibet evidence for a long lived rejuvenated orogen abstract how and when the northwestern tibetan plateau originated and developed upon pre existing crustal and topographic features is not well understood to address this question we present an integrated analysis of detrital zircon u pb and fission track double dating of cenozoic synorogenic sediments from the kekeya and sanju sections in the southwestern tarim basin these data help establishing a new chronostratigraphic framework for the sanju section and confirm a recent revision of the chronostratigraphy at kekeya detrital zircon fission track ages present prominent triassic early jurassic 250 170 ma and early cretaceous 130 100 ma static age peaks and paleocene early miocene 60 21 ma to eocene late miocene 39 7 ma moving age peaks representing source exhumation triassic early jurassic static peak ages document unroofing of the kunlun terrane probably related to the subduction of paleotethys oceanic lithosphere in combination with the occurrence of synorogenic sediments on both flanks of the kunlun terrane these data suggest that an ancient west kunlun range had emerged above sea level by triassic early jurassic times early cretaceous fission track peak ages are interpreted to document exhumation related to thrusting along the tam karaul fault kinematically correlated to the main pamir thrust further west widespread middle late mesozoic crustal shortening and thickening likely enhanced the early mesozoic topography paleocene early eocene fission track peak ages are presumably partially reset limited regional exhumation indicates that the early cenozoic topographic and crustal pattern of the west kunlun may be largely preserved from the middle late mesozoic the main pamir tam karaul thrust belt could be a first order tectonic feature bounding the northwestern margin of the middle late mesozoic to early cenozoic tibetan plateau toward the tarim basin late oligocene early miocene steady exhumation at a rate of 0 9 km myr is likely related to initial thrusting of the tiklik fault and reactivation of the tam karaul thrust thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the west kunlun orogen at this time this episode of exhumation and uplift associated with magmatism across western tibet is compatible with a double sided lithospheric wedge model primarily driven by breakoff of the indian crustal slab accelerated exhumation of the mountain front at a rate of 1 1 km myr since 15 ma supports active compressional deformation at the margins of the northwestern tibetan plateau we thus propose that the west kunlun mountains are a long lived topographic unit dating back to triassic early jurassic times and have experienced middle late mesozoic to early cenozoic rejuvenation and late oligocene miocene expansion

seismic geomorphology and growth architecture of a miocene barrier reef browse basin nw australia abstract the cenozoic succession of browse basin is characterized by a carbonate system that developed from a non tropical ramp in eocene lower miocene times to a tropical rimmed platform in the middle miocene the evolution of the platform was unraveled through the interpretation of the seismic geomorphology and borehole data of the middle miocene tropical reef system the first reef structures developed during the early middle miocene as narrow linear reef belts with an oblique orientation with respect to shelf strike direction subsequently they prograded toward the platform margin to form a barrier reef with a minimum length of 40 km the barrier reef itself comprises three distinct ridges separated by progradational steps the second and third step are separated by a karstified horizon which is interpreted to represent the global sea level fall shortly before the serravallian tortonian boundary the following third ridge formed in a slightly downstepped position during the sea level lowstand and initial transgressive phase further sea level rise during the early tortonian first drowned the barrier reef system and subsequently also the patch reefs and relic atolls that had established in a backstepped position in the platform interior the similar evolution of the browse basin reef system and other contemporaneous carbonate systems indicates a strong impact of eustatic sea level changes relatively large subsidence rates in the study area possibly augmented the eustatic sea level rise in the tortonian and hence contributed to the drowning of the reef system however the initiation and final demise of the reef system was also governed by global and regional climate variations the first seismically defined reefs developed simultaneous to a maximum in the transport capacity of the indonesian throughflow which brings warm low salinity waters to the north west shelf reef drowning followed the restriction of this seaway close to the middle to early miocene boundary this near closure of the indonesian seaway possibly led to a regional amplification of the global middle to late miocene cooling trend and hampered the potential of the reef system to keep up with the rising sea level

nd and sr isotopic characteristics of chinese deserts implications for the provenances of asian dust silicate nd sr isotopes of the fine grained fractions of the 10 major deserts and sandy lands in north china and the loess in chinese loess plateau were systematically investigated wide ranges in nd sr isotopic compositions have been observed the results of the 7 0 b the deserts on the northern margin of tibetan plateau with end 0 ranging from 11 9 to 7 4 and c the deserts on the ordos plateau with the lowest end 0 11 5 the distribution of the threes isotopic regions is controlled by the tectonic setting in north china which implies that the materials of the deserts are derived from the locally eroded rocks from the surrounding mountains and the nd sr isotopic signatures of these deserts could be quit stable over the past million years on the sub tectonic time scales if there is any desert at those times the nd sr isotopic compositions of the loess are mostly close to those of the deserts in isotopic region b suggesting that the main source regions of the last glacial loess in the chinese loess plateau are badain jaran desert tengger desert and qaidam desert also the comparison between the nd sr isotopes of the 5 lm silicate fractions of the deserts and the ancient dust falls in the north pacific and greenland show that the asian end members of these dust falls are derived most from the deserts in the isotopic region b and less from those in the isotopic region c

bulk and single particle mineralogy of asian dust and a comparison with its source soils 1 the mineralogical properties of asian dust have been examined in detail and the results have been compared with the chinese source soils using high resolution scanning electron microscopy transmission electron microscopy x ray diffraction and chemical analysis mineralogical classification of asian dust particles showed that the most common single particles were clay aggregates 48 that were often mixed with nanosized calcite followed by particles of quartz 22 plagioclase 11 coarse calcite 6 k feldspar 5 muscovite chlorite kaolinite amphibole gypsum fe and ti oxides which were either partly or entirely attached with clay size mineral grains the clay minerals in asian dust were mostly illite and interstratified illite smectite the average mineral composition of the bulk dust samples by x ray diffraction was quartz 28 plagioclase 11 k feldspar 8 calcite 8 illite 19 interstratified illite smectite 22 chlorite 2 smectite 1 and kaolinite 1 in the silty soils from the source regions the clay minerals and nanosized pedogenic calcite aggregated and covered silt size minerals while the sands were mostly composed of quartz and feldspars and were lined with clay minerals the mineralogy of asian dust was similar to that of the silty soil from the loess plateau but the total phyllosilicate content increased from desert sands 7 silty soil 23 to asian dust 45 fining eastward the optical properties of asian dust and its interaction with atmospheric gases and cloud are probably affected by the clay rich mineral composition the aggregation and attachment of the clay minerals on the coarser minerals and the nanosized calcite

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

balancing cross sections with kinematic constraints the dolomites northern italy balancing of structural cross sections is often hindered by a limited database or tectonic complications in such cases kinematic constraints may help to better constrain the construction of a cross section and its extrapolation to depth the kinematic implications of a known structure generally at the surface have to be considered for the unknown structure and for the internal consistency of a cross section a key point is the quantification of shortening of the known structure the extrapolation of this parameter allows balancing in an approximate way emphasizing major structures while minor structures are either neglected or treated in a simplified way with this approach a quick overview can be achieved on how much leeway for interpretation exists critical points for testing various working hypotheses become more evident and the trial and error effort during the construction of a balanced section is considerably shortened still the implications the observed structures have on the deeper crustal levels can be assessed this concept is applied to a section across the italian dolomites a brittle fold and thrust belt lacking reflection seismic data so far and thus with a poorly known deep structure still active south vergent alpine thrusting is oriented approximately perpendicular to previous dinaric thrusting the ramp flat style is dominant due to rheological constrasts within the stratigraphic sequence thanks to kinematic balancing based on surface data three alpine thrust systems could be identified each defining a thrust sheet with its particular basement unit and its sedimentary part superposition of the two more external basement units led to the presently observed high elevation of the triassic sequence in the dolomites shortening since late miocene times amounts to more than 50 km retrodeformation of alpine thrusting is a key for better understanding the previous dinaric structures and kinematics