strontium distribution in the shell of the aragonite bivalve arctica islandica 1 the behavior of sr in the aragonite shells of the bivalve arctica islandica has been explored to determine its potential for high resolution environmental reconstruction the structural state of sr in the shell was investigated using x ray absorption fine structure xafs and sr ca variations across the prismatic layer in the umbo and outer shell were determined by secondary ionization mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icp ms respectively xafs data suggest that sr randomly substitutes for ca within the shell aragonite sr ca in both the umbo and the outer shell exhibits significant seasonal variation but does not correlate with seawater temperature sr ca varies significantly between parallel transects across the same annual bands sr concentrations are highest in transects along the maximum growth axis of the outer shell but lowest in these transects in the umbo scanning electron microscopy indicates changes in crystal morphology both within and between transects we do not however observe a clear relationship between shell growth rate and sr ca fluctuations in sr ca are most likely to be controlled by a complex interaction of biological and kinetic processes

lithostratigraphy of a cenozoic intra continental basin guadiana basin sw spain by using clay mineral assemblages and geophysical properties in the iberian peninsula alpine tectonics built several cenozoic basins that were mainly filled with continental deposits the guadiana basin is located halfway between two of the most important cenozoic basins of the sw of spain the tajo and the guadalquivir basins in this paper both geophysical and mineralogical studies have been carried out in order to establish the lithostratigraphy of the guadiana basin a combination of electric resistivity properties and variations in clay mineral assemblage content of the basin infill was used to identify several depositional sequences within the cenozoic deposits of the basin three depositional sequences ds1 ds2 and ds3 characterized by differentiated clay content and mineral assemblages were distinguished the lower depositional sequence ds1 consists of reddish siltstones and clays that scarcely crop out in the basin clay content of the 2 m fraction is dominated by illite averaging 60 of the total clay content with kaolinite and a few amount of smectite ds2 deposits lie unconformably over ds1 and the variscan basement and consist of a siliciclastic succession where carbonate units occur at bottom and at the top of the depositional sequence smectite dominates throughout the entire succession except in the basal carbonate unit where up to 70 of palygorskite is found in the younger sequence ds3 kaolinite is the dominant clay mineral electrical resistivity imaging helped in the physical characterization and horizontal and vertical distribution of each unit and provided good insight on the structure of the guadiana basin allowing to infer the basin structure due to high resistivity contrast between the basement and the sedimentary rocks in addition in areas where the lower sedimentary units do not crop out and borehole information is not available the geophysical response of the resistivity units imaged can be used to infer the corresponding depositional sequence the joint interpretation of the clay mineral assemblages and geophysical properties of the sedimentary units showed to be a useful tool to gather a reliable identification of depositional sequences in basins characterized by scarcity of good outcrops lack of borehole information and similarity of sedimentary rocks this is very important to properly correlate the different sedimentary units mapped as well as to infer the basin structure and its evolution through time

high pressure phases in shock induced melt veins of the umbarger l6 chondrite constraints of shock pressure we report a previously undocumented set of high pressure minerals in shock induced melt veins of the umbarger l6 chondrite high pressure minerals were identified with transmission electron microscopy tem using selected area electron diffraction and energy dispersive x ray spectroscopy ringwoodite fa30 akimotoite en11fs89 and augite en42wo33fs25 were found in the silicate matrix of the melt vein representing the crystallization from a silicate melt during the shock pulse ringwoodite fa27 and hollandite structured plagioclase were also found as polycrystalline aggregates in the melt vein representing solid state transformation or melting with subsequent crystallization of entrained host rock fragments in the vein in addition fe2sio4 spinel fa66 fa99 and stishovite crystallized from a feo sio2 rich zone in the melt vein which formed by shock melting of feo sio2 rich material that had been altered and metasomatized before shock based on the pressure stabilities of the high pressure minerals ringwoodite akimotoite and ca clinopyroxene the melt vein crystallized at approximately 18 gpa the fe2sio4 spinel stishovite assemblage in the feo sio2 rich melts is consistent with crystallization of the melt vein matrix at the pressure up to 18 gpa the crystallization pressure of 18 gpa is much lower than the 4590 gpa pressure one would conclude from the s6 shock effects in melt veins stffler et al 1991 and somewhat less than the 25 30 gpa inferred from s5 shock effects schmitt 2000 found in the bulk rock

growth and high resolution paleoenvironmental signals of rhodoliths coralline red algae a new biogenic archive we investigated rhodoliths coralline red algae from a subtropical locality in the gulf of california lithothamnium crassiusculum and a subarctic locality in newfoundland lithothamnium glaciale for their potential as paleoenvironmental archives using microanalytical geochemical techniques to measure variations in 18o mg and ca rhodoliths are potentially well suited as recorders of shallow water paleoenvironmental signals because they 1 have worldwide distribution from the tropics to polar regions 2 are long lived from decades to centuries and 3 display well developed growth bands our results indicate that rhodolith growth bands preserve ultrahigh resolution records of paleoceanographic paleoclimatic change and likely constitute an important new archive for reconstructing the paleoenvironmental history of littoral neritic areas in which these algae are found the 18o content of individually sampled rhodolith growth bands ranges from 2 4 to 4 6 in l crassiusculum and from 3 2 to 0 3 in l glaciale in both cases the range of 18o values suggests a slightly lower amplitude of variation in sea surface temperature than that actually measured in the ocean at the two study sites both l crassiusculum and l glaciale show a negative offset from isotopic equilibrium electron microprobe analysis of magnesium and calcium in growth bands reveals cyclic variations with values ranging between 7 7 18 5 mol mgco3 in l glaciale and 13 2 22 5 mol mgco3 in l crassiusculum in addition electron microprobe element maps highlight individual growth bands provide a powerful approach to study rhodolith formation and indicate that the specimens we analyzed have vertical growth rates of 250 450 m yr

a multiproxy approach to reconstructing sea surface conditions using coral skeleton geochemistry 1 we use elemental ratio mg ca sr ca u ca and ba ca and oxygen isotope data from a porites lutea coral head collected from offshore amedee island new caledonia 22 29 s 166 28 e to assess the degree to which changes in these geochemical variables reflect variations in sea surface conditions we have assessed the robustness of each geochemical proxy by comparing 25 years 1992 1968 of monthly geochemical variations with a local record of sea surface temperature sst and with the appropriate 1 by 1 grid box from a global gridded sst data set we conclude from our comparison that the most consistent proxies of monthly sst variations at this site are 18o r2 0 84 p 0001 and sr ca r2 0 84 p 0001 the fidelity of the coral based sr ca sst proxy was assessed via calibration verification exercises at new caledonia and rarotonga the paleoclimate accuracy of the coral sr ca sst technique is judged to be robust and the precision of the technique is estimated to be 0 3 0 5 2 based on the calibration verification exercise in contrast monthly variations in mg ca and u ca ratios are only moderately correlated with monthly sst variations r2 0 55 p 0001 for mg ca and r2 0 47 p 0001 the strength of the correlation between sst and mg ca and u ca varies as a function of time suggesting that variations in these ratios are not a simple function of sst variations this variability in goodness of fit between u ca sst and mg ca sst may ultimately limit the use of these ratios as coral paleothermometers averaging or stacking individual proxy sst records sr ca mg ca and u ca to generate a composite proxy sst record does not necessarily improve the proxy record if the signal to noise ratio in each proxy is highly variable for example stacking of sr ca mg ca u ca records at new caledonia produces a proxy sst time series that has greater standard error than the individual sr ca sst time series cf ordinary least squares standard error of 1 16 c versus 0 86 c ba ca variations have little correlation with sst sr ca mg ca or u ca variations at new caledonia in conclusion variations in oxygen isotopic composition of seawater calculated by removing the sr ca based temperature component of the 18o signal agree reasonably well with observed variations in sea surface salinity especially at the interannual timescale

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

high resolution sr ca records in sclerosponges calibrated to temperature in situ ratios of strontium to calcium have been analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms in a skeletal section of the sclerosponge ceratoporella nichol soni the growth period representative of 3 yr was stained in the skeleton with a fluorochrome calcein temperatures were record ed at 2 h intervals within the shallow cryptic reef enclosure that the sclerosponge inhabited on the northern coast of jamaica al lowing the formulation of a direct empirical relationship between sr ca and temperature to verify this calibration sr ca ratios of two sclerosponges of the same species from depths of 67 m and 136 m in exuma sound bahamas were analyzed by la icp ms and compared to the temperatures from these depths over a decade prior to collection the result is an independently verified high resolution empirical calibration for the temperature sensitivity of sr ca ratios in the aragonite skeletons of sclerosponges from ja maica and the bahamas the calibration is a first for c nicholsoni and indicates that sclerosponges are more sensitive temperature recorders than zooxanthellate corals it represents an important step in establishing skeletal geochemistry of sclerosponges as a proxy of temperature in the upper 250 m of the ocean

improving sst reconstructions from coral sr ca records multiple corals from tahiti french polynesia we reconstruct sst from coral sr ca ratios measured at three coral cores taken from the lagoon of tahiti french polynesia two coral cores were drilled from the same coral colony one horizontally and one vertically and a third core was drilled vertically from another coral growing at a different site we evaluate several sr ca records as proxies for regional sst variations 1 the three single core records from tahiti 2 an average sr ca record computed from the two cores drilled from the same coral colony 3 an average sr ca record computed from all three tahiti cores and 4 an average sr ca record computed from the three tahiti cores and a fourth core taken from a different island rarotonga on a monthly scale the average sr ca record including the four coral cores from tahiti and rarotonga shows the best correlation with regional sst the variance of the sst reconstruction is very realistic and the residual sst is low this suggests that reconstructing sst from average proxy records gives a better representation of regional sst variations of the three tahiti cores the one that was drilled horizontally shows the best correlation with grid sst on an annual mean scale all three tahiti corals show much larger interannual sst variations than that indicated by grid sst

kaolinitic paleosols in the south west of the iberian peninsula sierra morena region spain paleoenvironmental implications abstract this paper studies the physical and chemical characteristics of eight different soil profiles with paleohorizons rich in kaolinites and developed on different lithologies along the southern border of the hercinian iberian peninsula sierra morena region the paleohorizons of four of these soils are defined by low ph levels desaturation of the exchange complex and proportions of kaolinite of over 75 these characteristics are associated with subtropical pedogenic conditions during the pliocene period a further two soil profiles are contemporary and defined by the following features they occupy depression areas the clay fraction is dominated by kaolinites and smectites the exchange complex is saturated and the ph is above neutral values the last two soil profiles are developed on pliocene continental deposits and have more moderate pedogenic features their kaolinite levels are around 50 and their evolution is associated with shorter periods of exposure to these subtropical alteration conditions

coupled north atlantic slope water forcing on gulf of maine temperatures over the past millennium to investigate ocean variability during the last millennium in the western gulf of maine gom we collected a 142 year old living bivalve arctica islandica l in 2004 and three fossil a islandica shells calibrated 14cams 1030 78 ad 1320 45 ad 1357 40 ad for stable isotope and growth increment analysis a statistically significant relationship exists between modern gom temperature records shell isotope derived 30 m r 0 79 p 0 007 prince 5 50 m r 0 72 p 0 019 boothbay harbor sst r 0 76 p 0 011 and labrador current lc transport data from the eastern newfoundland slope during 1993 2003 in all cases as lc transport increased gom water temperatures decreased the following year decadal trends in the north atlantic oscillation nao and the atlantic multidecadal oscillation amo influence gom water temperatures in the most recent period with water temperatures decreasing during nao and amo negative modes most likely linked to lc transport and gulf stream interaction mean shell derived isotopic changes 18oc during the last 1 000 years were 0 47 and likely reflect a 1 2 c cooling from 1000 ad to present based on these results we suggest that observed cooling in the gom during the last millennium was due to increased transport and or cooling of the lc and decreased gulf stream influence on the gom

petrology and raman spectroscopy of high pressure phases in the gujba cb chondrite and the shock history of the cb parent body abstract high pressure phases majorite possibly majorite pyropess wadsleyite and coesite are present in the matrix and in barred olivine fragments in the gujba cb chondrite grossular pyrope was also observed in some small inclusions the cb chondrites are metal rich meteorites with characteristics that sharply distinguish them from other chondrite groups all of the cb chondrites contain impact melt regions interstitial to their chondrules fragments and metal and a major impact event or events on the cb chondrite parent body is clearly a significant stage in its history we studied three areas interstitial to chondrules and metal in the gujba cba chondrite from raman spectra the barred olivine fragments and matrix in these regions have various combinations of olivine and low ca pyroxene as well as majorite garnet mg4si4o12 a phase that forms by high pressure transformation of low ca pyroxene and wadsleyite a high pressure product of olivine compositions of the majorite suggest both majorite and majorite pyrope solid solution may be present the mineral assemblage of majorite and wadsleyite suggest minimum shock pressures and temperatures of 19 gpa and 2000 c respectively the occurrences of high pressure phases are variable from one area to another on the scale of millimeters or less suggesting heterogeneous distribution of shock and or back transformation to low pressure polymorphs throughout the meteorite the high pressure phases record a high temperature pressure impact event that is superimposed onto and thus postdates formation of the chondrules and other components in the cb chondrites the barred chondrules and metal in the cb chondrites are primary materials formed prior to the impact event either generated in an earlier planetesimal scale impact event or in the nebula

coralline red algae as high resolution climate recorders most high resolution proxy based paleoclimate research has concentrated on tropical oceans while mid and high latitude marine regions have received less attention despite their importance in the global climate system at present sclerochronological analyses of bivalve mollusks supply the bulk of annual to subannual resolution extratropical marine climate data even though interpretation is complicated by a slowdown of growth with increasing shell age hence in order to address the need for additional high resolution proxy climate data from extratropical regions we conducted the first year long in situ field calibration of the coralline red alga clathromorphum compactum in the gulf of maine united states coralline red algae are widely distributed in coastal regions worldwide and individual calcified plants can live continuously for several centuries in temperate and subarctic oceans stable oxygen isotopes extracted at subannual resolution from growth increments of monitored specimens of c compactum relate well to in situ measured sea surface temperatures during the may to december calcification period highlighting the suitability of coralline red algae as an extratropical climate archive furthermore there is a strong correlation between a 30 yr 18 o record of c compactum and an instrumental sea surface temperature record r 0 58 p 0 0008 and a proxy reconstruction derived from the bivalve arctica islandica collected in the central gulf of maine r 0 54 p 0 002

high pressure phases in a shock induced melt vein of the tenham l6 chondrite constraints on shock pressure and duration abstract the microtexture and mineralogy of a 580 m wide melt vein in the tenham l6 chondrite were investigated using field emission scanning electron microscopy and transmission electron microscopy to better understand the shock conditions the melt vein consists of a matrix of silicate plus metal sulfide grains that crystallized from immiscible melts and sub rounded fragments of the host chondrite that have been entrained in the melt and transformed to polycrystalline high pressure silicates the melt vein matrix contains two distinct textures and mineral assemblages corresponding to the vein edge and interior the 30 m wide vein edge consists of vitrified silicate perovskite ringwoodite akimotoite majorite with minor metal sulfide the 520 m wide vein interior consists of majorite magnesiowustite with irregular metal sulfide blebs although these mineral assemblages are distinctly different the pressure stabilities of both assemblages are consistent with crystallization from similar pressure conditions the melt vein edge crystallized at about 23 25 gpa and the vein interior crystallized at about 21 25 gpa this relatively narrow pressure range suggests that the melt vein either crystallized at a constant equilibrium shock pressure of 25 gpa or during a relatively slow pressure release using a finite element heat transfer program to model the thermal history of this melt vein during shock we estimate that the time required to quench this 580 m wide vein was 40 ms because the entire vein contains high pressure minerals that crystallized from the melt the shock pressure duration was at least 40 ms using a synthetic hugoniot for tenham and assuming that the sample experienced a peak shock pressure of 25 gpa near the impact site we estimate that the tenham parent body experienced an impact with collision velocity 2 km s based on a one dimensional planar impact model we estimate that the projectile size was 150 m in thickness

natural occurrence of fe2sio4 spinel in the shocked umbarger l6 chondrite here we report the first natural occurrence of fe 2 sio 4 spinel in a shock induced melt pocket of the umbarger l6 chondrite optical microscopy scanning electron microscopy electron microprobe analysis and analytical transmission electron microscopy were used to examine the sample fe 2 sio 4 spinel was identified by tem using selected area electron diffraction and energy dispersive x ray spectroscopy the symmetry of the diffraction patterns the ratios of d spacings and interplanar angles are consistent with the spinel structure however the cell parameter of fe 2 sio 4 spinel 8 52 a calculated from d spacing data is 3 5 larger than that of synthetic fe 2 sio 4 spinel 8 235 a chemical analyses of the spinel show olivine stoichiometry with fe fe mg ratios ranging from 0 62 to 0 99 fe 2 sio 4 spinel and stishovite occur within feo sio 2 rich zones in the melt pocket surrounded by sio 2 rich glass and fe rich phyllosilicates fe 2 sio 4 spinel plus stishovite also occur with other high pressure minerals in the melt pocket ringwoodite akimotoite augite and hollandite structured plagioclase we infer that the fe 2 sio 4 spinel crystallized from a zone of feo sio 2 rich melt within the shock induced melt pocket two models for feo sio 2 rich melt are discussed it was either a residual melt after crystallization of mgo rich silicates in a chondritic melt pocket or it was produced by shock melting of feo sio 2 rich material

study of weathering processes developed on old piedmont surfaces in western spain new contributions to the interpretation of the rana profiles abstract the hercynian basement of the iberian peninsula was uplifted by the alpine orogeny during the tertiary it gave rise to a set of block mountains and tectonic grabens one of which is the ciudad rodrigo basin it is located in western spain and forms a westward extension of the great tertiary duero basin the sediments filling this graben are of continental origin their ages ranging from palaeogene to quaternary morphologically the southern part of this basin forms a set of piedmont surfaces the rana surfaces appearing above the terrace system of the present rivers this paper examines the weathering processes developed over these old piedmont surfaces using micromorphological xr diffraction scanning electron microscopy sem and microporosity techniques the rana sediments are rich in quartzite pebbles and gravel within a clayey matrix once deposited these materials underwent important in situ weathering processes under somewhat hydromorphic conditions of which hydrolysis ferrolysis and xerolysis were the most important all these processes gave rise to 1 transformation of most of the clasts of shists and slates into a matrix causing the destruction of the original sedimentary structures and a relative concentration of the resistant lithologies quartzites and quartz 2 important changes in the clay fraction leading to a predominance of kaolinite in the upper levels of the profiles 3 release of elements from primary minerals fe being one of the most important and 4 redistribution of matter mainly clay and fe oxyhydroxides within the profiles the coexistence of seasonal periods with pf higher than 4 2 repeated over a long time together with poor internal and external drainage conditions are the cause of the special features displayed by rana deposits

tem study of shock metamorphism in quartz from the sedan nuclear test site abstract nuclear explosions represent a useful simulation of meteorite impacts stresses of tens of gigapascals are produced during detonation and stress pulses can last 0 1 ms or longer which is 3 4 orders of magnitude longer than laboratory experiments samples studied here were taken from the ejecta of the sedan nuclear test site and consist of a coarse grained granodiorite containing quartz plagioclase k feldspar cordierite and hornblende shocked quartz grains were selected optically in thin section and studied by tem tem reveals the presence of planar deformation features pdfs which consist of multiple sets of planar amorphous lamellae with the crystallographic orientations 10 12 10 12 and rarely 10 11 some lamellae exhibit a substructure which consist of amorphous sublamellae organized enechelon no high pressure phases were detected along the transformation lamellae some lamellae show evidence of beginning recrystallization which probably occurred during cooling of the hot ejecta the shock induced defects present at the sedan site are very similar to those seen in laboratory shock recovery experiments and also to those present at meteorite impact craters e g meteor crater or ries crater this suggests that shock induced amorphization in quartz is not strongly dependant on shock pulse duration

natural cati2o4 structured fecr2o4 polymorph in the suizhou meteorite and its significance in mantle mineralogy abstract the first natural occurrence of a high pressure polymorph of chromite has been discovered in the shock metamorphosed suizhou meteorite the composition of this high pressure polymorph is identical to that of the precursor chromite the raman spectrum of this polymorph is distinct from that of chromite synchrotron x ray diffraction analysis revealed that this polymorph has an orthorhombic cati2o4 type structure the cell parameters are a 9 462 6 a b 9 562 9 a c 2 916 1 a v 263 8 4 a3 z 4 space group bbmm and the density 5 63 g cm3 the numbers in parentheses are standard deviations on the last significant digits this polymorph is 11 5 denser than chromite the p t conditions for the phase transformation from chromite to the cati2o4 structured polymorph are estimated at 20 23 gpa and 1800 to 2000 c respectively this dense cati2o4 structured fecr2o4 phase could be a host phase for cr al fe mg and mn and other metallic elements in the deep earth

high pressure minerals in shocked meteorites heavily shocked meteorites contain various types of high pressure polymorphs of major minerals olivine pyroxene feldspar and quartz and accessory minerals chromite and ca phosphate these high pressure minerals are micron to submicron sized and occur within and in the vicinity of shock induced melt veins and melt pockets in chondrites and lunar howardite eucrite diogenite hed and martian meteorites their occurrence suggests two types of formation mechanisms 1 solid state high pressure transformation of the host rock minerals into monomineralic polycrystalline aggregates and 2 crystallization of chondritic or monomineralic melts under high pressure based on experimentally determined phase relations their formation pressures are limited to the pressure range up to 25 gpa textural crystallographic and chemical characteristics of high pressure minerals provide clues about the impact events of meteorite parent bodies including their size and mutual collision velocities and about the mineralogy of deep planetary interiors the aim of this article is to review and summarize the findings on natural high pressure minerals in shocked meteorites that have been reported over the past 50 years

shock induced p t conditions and formation mechanism of akimotoite pyroxene glass assemblages in the grove mountains grv 052082 l6 meteorite akimotoite mg fe sio 3 ilmenite was encountered in shock induced melt veins of grove mountains grv 052082 a highly equilibrated low iron ordinary chondritic meteorite l6 coexistence of ringwoodite majorite and majorite pyrope solid solution indicates the shock pressure at 18 23 gpa and temperature of 2000 2300 c during the natural dynamic event most low ca pyroxene clasts entrained in the melt veins have been partially or entirely transformed into akimotoite pyroxene glass assemblages which contain micrometer sized areas with various brightness in the backscattered electron images different from the chemically homogeneous grains in the host rock fs 20 5 21 3 the transmission electron microscopy study of a focused ion beam fib slice from the heterogeneous areas shows that the assemblages are composed of feo depleted and heterogeneous akimotoite fs 6 19 crystals 100 nm up to 400 nm in size scattered in feo enriched and relatively homogeneous pyroxene glass fs 31 39 all analyses of the akimotoite pyroxene glass assemblages plot on a fractionation line in feo mgo diagram with the host rock pyroxene at the middle between the compositions of feo depleted akimotoite and the feo enriched pyroxene glass these observations are different from previous reports of almost identical compositions of akimotoite bridgmanite mg fe sio 3 perovskite or pyroxene glass to the host rock pyroxene chen et al 2004 ferroir et al 2008 ohtani et al 2004 tomioka and fujino 1997 which is consistent with solid state transformation from pyroxene to akimotoite and preexisting bridgmanite that could be vitrified the observed fractionation trend and the granular shapes of akimotoite suggest crystallization from liquid produced by shock melting of the host rock pyroxene and the pyroxene glass matrix was probably quenched from the residual melt however this interpretation is inconsistent with the static experiments that expect crystallization of majorite mg fe sio 3 garnet instead of akimotoite from pyroxene liquid sawamoto 1987 our discovery raises the issue on formation mechanisms of the high pressure polymorphs of pyroxene and places additional constraints on the post shock high pressure and high temperature conditions of asteroids

majoritic garnet grains within shock induced melt veins in amphibolites from the ries impact crater suggest ultrahigh crystallization pressures between 18 and 9 gpa shock induced melt veins in amphibolites from the nordlinger ries often have chemical compositions that are similar to bulk rock i e basaltic but there are other veins that are confined to chlorite rich cracks that formed before the impact and these are poor in ca and na majoritic garnets within the shock veins show a broad chemical variation between three endmembers 1 text viii text m 2 3 text vi text al 2 text iv text sio 4 3 normal garnet grt 2 text viii text m 2 3 text vi text m 2 text si ti text iv text sio 4 3 majorite maj and 3 text viii text na text m 2 2 text vi text si ti text al text iv text sio 4 3 na majorite50grt50 whereby m2 mg2 fe2 mn2 ca2 in particular we observed a broad variation in vi si ti which ranges from 0 12 to 0 58 cations per formula unit cpfu all these majoritic garnets crystallized during shock pressure release at different ultrahigh pressures those with high vi si ti 0 36 0 58 cpfu formed at high pressures and temperatures from amphibole rich melts while majoritic garnets with lower vi si ti of 0 12 0 27 cpfu formed at lower pressures and temperatures from chlorite rich melts furthermore majoritic garnets with intermediate values of vi si ti 0 24 0 39 crystallized from melts with intermediate contents of ca and na to the best of our knowledge the morb type ca na rich majoritic garnets with maximum contents of 2 99 wt na2o and calculated crystallisation pressures of 16 18 gpa are the most extreme representatives ever found in terrestrial shocked materials at the ries the duration of the initial contact and compression stage at the central location of impact is estimated to only 0 1 s we used a 200 m thick shock induced vein in a moderately shocked amphibolite to model its pressure temperature time p t t path the graphic model manifests a peak temperature of 2600 c for the vein continuum pressure lasting for 0 02 s a quench duration of 0 02 s and a shock pulse of 0 038 s the small difference between the continuum pressure and the pressure of majoritic garnet crystallization underlines the usefulness of applying crystallisation pressures of majoritic garnets from metabasites for calculation of dynamic shock pressures of host rocks majoritic garnets of chlorite provenance however are not suitable for the determination of continuum pressure since they crystallized relatively late during shock release an extraordinary glass and majorite bearing amphibole fragment in a shock vein of one amphibolite documents the whole unloading path

climate records from a bivalved methuselah arctica islandica mollusca iceland we measured annual shell growth rates of a 374 year old radiometrically confirmed bivalve mollusk specimen of arctica islandica linnaeus this bivalve represents the oldest ever reported individual animal in addition we analyzed 1051 individual powder samples from ontogenetic years two to 40 80 of the entire shell height for isotope analyses oxygen and carbon isotopes exhibit clear intra annual cycles the highest measured carbon isotope values on average 2 73x occurred during summer i e during maximum primary productivity the d 18 oaragonite derived temperature time series cover the period of ad 1496 1533 temperatures calculated from oxygen isotopes ranged from 4 5 to 9 3 8c and exhibit a mean value of 6 2 8c the latter coincides well with the 1854 2003 mean value of 6 81 8c for sea surface temperature between february and september growing season of a islandica neither oxygen nor carbon isotopes exhibit age related unidirectional trends however d 13 caragonite and d 18 oaragonite values fluctuated at decadal periods of four six and eight to nine years nao type periods as well as 12 14 years which may represent teleconnections to cycles in the tropical atlantic annual shell growth is positively correlated to intra annual d 18 oaragonite minima i e warm summer temperatures r 2 0 34 and to intra annual d 13 caragonite minima higher food supply r 2 0 42 using a linear multiregression model 65 of the variation in annual shell growth can be explained by summer temperature and food supply the formation of extremely narrow annual increments coincides with major volcanic eruptions e g tambora 1815 a period of extremely variable growth occurred during the culmination of the little ice age in iceland between ca ad 1550 and 1620 shell growth during ad 1765 1780 however was characterized by very little year to year variability probably as the result of extremely mild climate near the end of the little ice age this study demonstrates that shells of a islandica provide

climate proxies from sr ca of coccolith calcite calibrations from continuous culture of emiliania huxleyi abstract continuous culture of the coccolithophorid emiliania huxleyi reveals that coccolith sr ca ratios depend on temperature and growth rate at a constant temperature of 18 c coccolith sr ca ratios increased nearly 15 as growth rate increased from 0 1 to 1 5 divisions per day and calcification rate increased from 1 5 to 50 pg calcite per cell per day when temperature increased from 7 to 26 c sr ca ratios increased by more than 25 i e 1 1 c although the range in growth and calcification rates was the same as for experiments at constant temperature the temperature dependence of sr ca ratios in coccoliths is consistent with that observed in planktonic foraminifera and abiogenic calcites suggesting that it is controlled by thermodynamic processes however the positive correlation of coccolith sr ca with temperature contrasts with field studies in the equatorial pacific where sr ca ratios are highest at the locus of maximum upwelling and productivity despite depressed temperatures this paradox may reflect different calcification rate effects between e huxleyi and the other species dominating assemblages in the equatorial pacific sediments which may be resolved by new techniques for separation of monospecific coccolith samples from sediments models of crystal growth indicate that kinetic effects on sr partitioning in calcite due to surface enrichment could explain the sr ca variations observed in constant temperature experiments but not the larger amplitude calcification rate effects observed in equatorial pacific sediments despite the dual influence of temperature and growth rate on coccolith sr ca coccolith sr ca correlates with b the slope of the dependence of carbon isotope fractionation in biomarkers ep on co2 aq at a range of growth rates and temperatures consequently using coccolith sr ca in combination with alkenone ep may improve paleo co2 determinations

revising the shock classification of meteorites the current shock classification scheme of meteorites assigns shock levels of s1 unshocked to s6 very strongly shocked using shock effects in rock forming minerals such as olivine and plagioclase the s6 stage 55 90 gpa 850 1750 c relies solely on localized effects in or near melt zones the recrystallization of olivine or the presence of mafic high pressure phases such as ringwoodite however high whole rock temperatures and the presence of high pressure phases that are unstable at those temperatures and pressures of zero gpa e g ringwoodite are two criteria that exclude each other each type of high pressure phase provides a minimum shock pressure during elevated pressure conditions to allow the formation of this phase and a maximum temperature of the whole rock after decompression to allow the preservation of this phase rocks classified as s6 are characterized not by the presence but by the absence of those thermally unstable high pressure phases high pressure phases in or attached to shock melt zones form mainly during shock pressure decline this is because shocked rocks 60 gpa experience a shock wave with a broad isobaric pressure plateau only during low velocity 4 5 km s 1 impacts which rarely occur on small planetary bodies e g the moon and asteroids the mineralogy of shock melt zones provides information on the shape and temporal duration of the shock wave but no information on the general maximum shock pressure in the whole rock

transmission electron microscopy of l group chondrites 1 natural shock effects abstract high voltage and analytical transmission electron microscopy are used to characterize fine scale deformational and thermal effects of shock in l group chondrites belonging to shock facies d and e of dodd and jarosewich 1 in facies d olivine showing optical mosaicism has a dislocation substructure exactly like that produced in shock experiments thermal effects become pervasive in olivine of facies e with recovery of dislocation distributions and local recrystallization analogous to that in facies f but less coarse orthopyroxene has behaved more inhomogeneously than in shock experiments no single deformation mechanism being predominant in any specimen twinned clinopyroxene in facies e is attributed to the sequence of inversions ortho proto clino due to heating and rapid cooling in diopside as well as the 100 twinning previously described from less intensely shocked meteorites there is 001 twinning produced by a distinctive mechanism plagioclase is converted to glass maskelynite in lamellae and patches an intimate association of chromite with glass of plagioclase composition is interpreted as a melting phenomenon the characteristic melt pockets of facies d consist of glass with metal and sulphide globules the glass is derived from more than one mineral giving it a mixed silicate composition in facies e crystallization of silicate melts occurred and metal grains crystallized from the same melts volatilization accompanying melting is indicated by vesiculation of melt pockets and thin 1 m veins with high si mg are interpreted as vapour deposition products or melts modified by vapour transport of volatile elements

pressure induced amorphization of albitic plagioclase in an externally heated diamond anvil cell 1 high pressure and high temperature experiments of albitic plagioclase up to 41 gpa and 270 c were carried out using an externally heated diamond anvil cell raman spectroscopy and transmission electron microscopy of the recovered samples revealed that the amorphization of albite was complete at 37 gpa and room temperature the amorphization pressure at 170 c was nearly the same as that at room temperature in contrast the pressure largely decreased to 31 gpa at 270 c in comparison with the amorphization pressure of albite in laboratory shock experiments that in the present static compression experiments is significantly lower 10 gpa even at room temperature this suggests that shorter pressure duration results in a lower degree of amorphization of plagioclase the formation of maskelynite in shocked meteorites does not necessarily require the very high shock pressure 30 90 gpa that was previously estimated on the basis of shock recovery experiments

a shock produced mg fe sio3 glass in the suizhou meteorite ovoid grains consisting of glass of stoichiometric mg fe sio3 composition that is intimately associated with majorite were identified in the shock veins of the suizhou meteorite the glass is surrounded by a thick rim of polycrystalline majorite and is identical in composition to the parental low ca pyroxene and majorite these ovoid grains are surrounded by a fine grained matrix composed of majorite pyrope garnet ringwoodite magnesiowstite metal and troilite this study strongly suggests that some precursor pyroxene grains inside the shock veins were transformed to perovskite within the pyroxene due to a relatively low temperature while at the rim region pyroxene grains transformed to majorite due to a higher temperature after pressure release perovskite vitrified at post shock temperature the existence of vitrified perovskite indicates that the peak pressure in the shock veins exceeds 23 gpa the post shock temperature in the meteorite could have been above 477 c this study indicates that the occurrence of high pressure minerals in the shock veins could not be used as a ubiquitous criterion for evaluating the shock stage of meteorites

coralline algae are global palaeothermometers with bi weekly resolution abstract high resolution palaeoclimate data are required for the holocene to resolve differences recorded by current proxies the pole to pole distribution of rhodoliths coralline algae with their annual and sub annual calcite bands make these attractive candidates for such a role these bands contain climate information in the form of elemental traces in situ temperature ist was recorded at two rhodolith beds for 1 5 years the concentrations of mgco 3 and srco 3 mol deposited in lithothamion glaciale and phymatolithon calcareum over this 18 month period were determined using electron and ion microprobes highly significant linear relationships exist between mg sr and ist as well as sea surface temperature calibration between mg concentration and ist was used to obtain a 2 year temperature profile from a subfossil rhodolith thallus indicating half the seasonal peak to peak temperature amplitude earlier during the holocene than the present day both slow growing species 1 allowed sampling resolutions of 23 year 1 which is equivalent to 1 reading every 2 weeks sub monthly mg and sr records in rhodoliths make them unique globally distributed palaeothermometers which may help refine regional climate histories during the holocene

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

three monthly coral sr ca records from the chagos archipelago covering the period of 1950 1995 a d reproducibility and implications for quantitative reconstructions of sea surface temperature variations in order to assess the fidelity of coral sr ca for quantitative reconstructions of sea surface temperature variations we have generated three monthly sr ca time series from porites corals from the lagoon of peros banhos 71 e 5 s chagos archipelago we find that all three coral sr ca time series are well correlated with instrumental records of sea surface temperature sst and air temperature however the intrinsic variance of the single core sr ca time series differs from core to core limiting their use for quantitative estimates of past temperature variations averaging the single core data improves the correlation with instrumental temperature r 0 7 and allows accurate estimates of interannual temperature variations 0 35 c or better all sr ca time series indicate a shift towards warmer temperatures in the mid 1970s which coincides with the most recent regime shift in the pacific ocean however the magnitude of the warming inferred from coral sr ca differs from core to core and ranges from 0 26 to 0 75 c the composite sr ca record from peros banhos clearly captures the major climatic signals in the indo pacific ocean i e the el nino southern oscillation and the pacific decadal oscillation moreover composite sr ca is highly correlated with tropical mean temperatures r 0 7 suggesting that coral sr ca time series from the tropical indian ocean will contribute to multi proxy reconstructions of tropical mean temperatures

shock experiments with the h6 chondrite kernouve pressure calibration of microscopic shock effects shock recovery experiments were carried out on samples of the h6 chondrite kernouve at shock pressures of 10 15 20 25 30 35 45 and 60 gpa and preheating temperatures of 293 k low temperature experiments and 920 k high temperature experiments using a calculated equation of state of kernouve pressure pulse durations of 0 3 to 1 2 s were estimated the shocked samples were investigated by optical microscopy to calibrate the various shock effects in olivine orthopyroxene oligoclase and troilite the following pressure calibration is proposed for silicates 1 undulatory extinction of olivine gpa 2 weak mosaicism of olivine from 10 15 gpa to 20 25 gpa 3 onset of strong mosaicism of olivine at 20 25 gpa 4 transformation of oligoclase to diaplectic glass completed at 25 30 gpa low temperature experiments and at 20 25 gpa high temperature experiments 5 onset of weak mosaicism in orthopyroxene at 30 35 gpa low temperature experiments and at 25 30 gpa high temperature experiments and 6 recrystallization or melting of olivine starting at 45 60 gpa low temperature experiments and at 35 45 gpa high temperature experiments and completed above 45 60 gpa in the high temperature experiments troilite displays distinct differences between the samples shocked at low and high temperatures in the low temperature experiments the following effects can be observed in troilite 1 undulatory extinction up to 25 gpa 2 twinning up to 45 gpa 3 partial recrystallization from 30 to 60 gpa and 4 complete recrystallization 35 gpa whereas in the high temperature experiments troilite shows 1 complete recrystallization from 10 up to 45 gpa and 2 melting and crystallization above 45 gpa localized shock induced melting is observed in samples shocked to pressures 15 gpa in the high temperature experiments and 30 gpa for the low temperature experiments in the form of feni metal and troilite melt injections and intergrowths and as pockets and veins of whole rock melt obviously the onset and abundance of shock induced localized melting strongly depends on the initial temperature of the sample

minor and trace elements in sclerosponge ceratoporella nicholsoni biogenic aragonite near the inorganic endmember abstract the trace and minor element composition have been investigated in the accretionary skeletons of two specimens of the caribbean sclerosponge species ceratoporella nicholsoni one from tongue of the ocean bahamas toto and the other from pear tree bottom jamaica ptb both sclerosponges were analyzed at high resolution using laser ablation icp ms la icp ms and verified using wet chemical methods icp oes the shallow ptb sclerosponge 25 m was analyzed for a short temperature calibrated record of trace and minor elements while the toto sclerosponge 146 m was analyzed for a century long record from subsurface waters the resulting ba ca mg ca pb ca and u ca ratios were compared with sr ca ratios which have been shown to reliably record seasonal scale temperature change in sclerosponges close to equilibrium precipitation of inorganic aragonite sclerosponge aragonite incorporates minor and trace elements according to general mineralogic constraints with less vital effects than other calcium carbonate secreting organisms this is perhaps most obvious in the behavior of mg ca ratios which show an inverse correlation to temperature unlike any other calcite or aragonite organism despite having mg concentrations 1 mmol mol within published estimates of equilibrium aragonite ratios of mg ca and ba ca show a strong positive correlation despite large differences in ionic radii and u ca values 3 15 mol mol are 2 5 higher in sclerosponge aragonite than in aragonite from corals supporting earlier work ratios of u ca show an insignificant correlation with temperature dependent sr ca ratios r 2 0 05 supporting existing theories that temperature signals recorded by u ca ratios can be convolved with ph co 3 2 and phosphate signals differences between sclerosponge aragonite and other calcium carbonate arising from siliceous spicule contamination are unlikely because of the small mole percent of silicon in the aragonite small differences between the two sclerosponges were noticed in pb ca and sr ca because of the average ages of the sampled material and average temperatures of the ambient environment respectively anomalies between la icp ms and icp oes were noticed in measurements of ba ca and pb ca due to standardization differences for la icp ms ba ca and measurements close to the instrument detection limits of pb icp oes

coralline algal growth increment widths archive north atlantic climate variability over the past decade coralline algae have increasingly been used as archives of paleoclimate information encrusting coralline algae which deposit annual growth increments in a high mg calcite skeleton are amongst the longest lived shallow marine organisms in fact a live collected plant has recently been shown to have lived for at least 850 years based on radiometric dating while a number of investigations have successfully used geochemical information of coralline algal skeletons to reconstruct sea surface temperatures less attention has been paid to employ growth increment widths as a temperature proxy here we explore the relationship between growth and environmental parameters in clathromorphum compactum collected in the subarctic northwestern atlantic results indicate that growth increment widths of individual plants are poorly correlated with instrumental sea surface temperatures sst however an averaged record of multiple growth increment width time series from a regional network of c compactum specimens up to 800 km apart reveals strong correlations with annual instrumental sst since 1950 hence similar to methods applied in dendrochronology averaging of multiple sclerochronological records of coralline algae provides accurate climate information a 115 year growth increment width master chronology created from modern collected and museum specimens is highly correlated to multidecadal variability seen in north atlantic sea surface temperatures positive changes in algal growth anomalies record the well documented regime shift and warming in the northwestern atlantic during the 1990s large positive changes in algal growth anomalies were also present in the 1920s and 1930s indicating that the impact of a concurrent large scale regime shift throughout the north atlantic was more strongly felt in the subarctic northwestern atlantic than previously thought and may have even exceeded the 1990s event with respect to the magnitude of the warming

planar deformation features in shocked quartz a transmission electron microscopy investigation abstract we present a detailed investigation by transmission electron microscopy tem of the fine structure of planar deformation features pdf in quartz grains within which shock metamorphism has been detected optically and which originate from various sites slate islands la malbaie and manicouagan lake canada ries crater germany the toba caldera sumatra the vredefort complex in south africa and the k t boundary at raton basin colorado pdfs appear on tem micrographs as straight and very narrow tem reveals many more pdfs than are optically detected probably because only concentrations of such defects in narrow areas can induce an optically detectable contrast caution should therefore be exercised when applying criteria based on the optical observation of single or multiple sets of pdfs pdfs in samples from slate islands and raton basin exhibit a peculiar morphology a high density of very tiny bubbles precipitated on the dislocation lines comparison with the behavior of wet quartz strongly suggests that these materials experienced lengthy annealing at moderate pressure and temperature

annual cycles of u ca in coral skeletons and u ca thermometry abstract we have discovered annual variations in the 238 u 40 ca ratio of porites coral skeletons measurements were made using thermal ionization mass spectrometric techniques yielding precisions of 2 2 for 238 u 40 ca and l 2 for 88 sr 40 ca coralline aragonite subsamples weighed 2 mg enabling submillimeter sampling resolution corresponding to monthly temporal resolution the annual nature of the cycles was confirmed by comparison with annual banding observable in x radiographs for two modern and one fossil sample the amplitude of the u ca variation ranges from 6 to 23 well outside of analytical error as annual u ca cycles appear to be a general feature of primary coralline aragonite the preservation of such features will be important in identifying unaltered coral for u series dating studies u ca variations mimic and are in phase with annual variations in 88 sr 40 ca for a given fractional shift in sr ca the fractional shift in u ca is about 6 times larger for the two modern corals 238 u 40 ca is strongly anticorrelated with measured temperature suggesting that 238 u 40 ca has potential as a paleothermometer if temperature is the only significant control on coralline 238 u 40 ca we reach the following conclusions from analyses of fossil samples a vanuatu sample which grew halfway through the last deglaciation gives u ca temperatures 4 to 5 c below modern values u ca thermometry applied to published data for barbados corals indicates that 1 temperature generally correlates with sea level 2 glacial temperatures stages 2 and 4 were 4 to 6 c lower than interglacial temperatures stages 7a 5e and 1 and 3 temperatures rose from glacial to interglacial values early in the last deglaciation thermometry applied to papua new guinea corals indicates that 1 temperatures were 5 to 6 c lower than interglacial temperatures from 13 to 10 ky bp then rose to present values 9 ky bp 2 the temperature depression between 13 and 10 ky bp is consistent with low temperatures observed in vanuatu during the same time interval and 3 the papua new guinea deglacial temperature history differs from that of barbados the results generally support estimates of tropical temperatures obtained from sr ca thermometry and snow line elevation data but disagree with those based on foram transfer functions a thermodynamic model suggests that coralline 238 u 40 ca may also be sensitive to marine carbonate ion concentration raising the possibility that some of the observed glacial interglacial 238 u 40 ca variation may result from glacial interglacial carbonate ion changes however the key experiments that might establish a coralline 238 u 40 ca carbonate ion relationship have yet to be performed

the soils and ages of the rana surfaces related to the villuercas and altamira mountain ranges western spain summary the soils of rana surfaces related to the sierra de las villuercas and the sierra de altamira western spain were studied with reference to vegetation cover and geomorphic position these soils were highly weathered with kaolinite dominant in the clay fraction and almost no weatherable minerals in the sand fraction iron oxides were segregated in some of the horizons giving a formation of pseudoplinthite this high degree of weathering and the patina of their quartzite stones are comparable to those of soils developed on the oldest ran a surfaces studied in central spain the soils classified as palehumults and palexerults are given tentatively a middle upper pliocene age

estimating shock pressures based on high pressure minerals in shock induced melt veins of l chondrites here we report the transmission electron microscopy tem observations of the mineral assemblages and textures in shock induced melt veins from seven l chondrites of shock stages ranging from s3 to s6 the mineral assemblages combined with phase equilibrium data are used to constrain the crystallization pressures which can be used to constrain shock pressure in some cases thick melt veins in the tenhaml6 chondrite contain majorite and magnesiowstite in the center and ringwoodite akimotoite vitrified silicate perovskite and majorite in the edge of the vein indicating crystallization pressure of 25 gpa however very thin melt veins 5 30 m wide in tenham contain glass olivine clinopyroxene and ringwoodite suggesting crystallization during transient low pressure excursions as the shock pressure equilibrated to a continuum level melt veins of umbarger include ringwoodite akimotoite and clinopyroxene in the vein matrix and fe2sio4 spinel and stishovite in sio2 feo rich melt indicating a crystallization pressure of 18 gpa the silicate melt veins in roy contain majorite plus ringwoodite indicating pressure of 20 gpa melt veins of ramsdorf and nakhon pathon contain olivine and clinoenstatite indicating pressure of less than 15 gpa melt veins of kunashak and la lande include albite and olivine indicating crystallization at less than 2 5 gpa based upon the assemblages observed crystallization of shock veins can occur before during or after pressure release when the assemblage consists of high pressure minerals and that assemblage is constant across a larger melt vein or pocket the crystallization pressure represents the equilibrium shock pressure

anatomy of black veins in zagami clues to the formation of high pressure phases abstract black melt veins in the martian basaltic meteorite zagami were investigated using analytical transmission electron microscopy with the goal to constrain the mechanisms and ptt conditions that result in the formation of high pressure phases therein our study reveals the existence of a number of high pressure minerals stishovite k and na ca rich hollandites akimotoite silicate ilmenite as well as amorphous grains of silicate perovskite composition crystals of a ferro magnesian silicate titanite with a low ca content have been identified for the first time the veins formed by rapid shear melting and solidified in extremely short times as a consequence the vein melt could not homogeneously mix and it partially preserves the chemical heterogeneity of precursor minerals accounting for the large diversity of high pressure minerals most of the tiny phases directly crystallized from the melt under high pressure at very high temperatures silicate perovskite probably amorphized upon decompression and evolved at its grain boundaries by solid state diffusion toward the lower pressure assemblage wustite stishovite not only do these observations help to understand the formation of high pressure phases in shock events but they also provide clues to the mineralogical complexity that can be expected in planetary mantles

shocked chromites in fossil l chondrites a raman spectroscopy and transmission electron microscopy study chromites from middle ordovician fossil l chondrites and from matrix and shock melt veins in catherwood tenham and coorara l chondrites were studied using raman spectroscopy and tem raman spectra of chromites from fossil l chondrites showed similarities with chromites from matrix and shock melt veins in the studied l chondrite falls and finds chromites from shock melt veins of l chondrites show polycrystallinity while the chromite grains in fossil l chondrites are single crystals in addition chromites from shock melt veins in the studied l chondrites have high densities of planar fractures within the subgrains and many subgrains show intergrowths of chromite and xieite matrix chromite of tenham has similar dislocation densities and planar fractures as a chromite from the fossil meteorite golvsten 001 and higher dislocation densities than in chromite from the fossil meteorite sextummen 003 using this observation and knowing that the matrix of tenham experienced 20 22 gpa and 1000 c an upper limit for the p t conditions of chromite from golvsten 001 and sextummen 003 can be estimated to be 20 22 gpa and 1000 c shock stage s3 s6 and 20 gpa and 1000 c s3 s5 respectively and we conclude that the studied fossil meteorite chromites are from matrix

helium loss from martian meteorites mainly induced by shock metamorphism evidence from new data and a literature compilation noble gas data from martian meteorites have provided key constraints about their origin and evolution and their parent body these meteorites have witnessed varying shock metamorphic overprinting at least 5 to 14 gpa for the nakhlites and up to 45 55 gpa e g the lherzolitic shergottite allan hills alh a77005 solar heating cosmic ray exposure and weathering both on mars and earth influences on the helium budgets of martian meteorites were evaluated by using a new data set and literature data concentrations of 3he 4he u and th are measured and shock pressures for same sample aliquots of 13 martian meteorites were determined to asses a possible relationship between shock pressure and helium concentration partitioning of 4he into cosmogenic and radiogenic components was performed using the lowest 4he 3he ratio we measured on mineral separates 4he 3he 4 1 pyroxene of alha77005 our study revealed significant losses of radiogenic 4he systematics of cosmogenic 3he and neon led to the conclusion that solar radiation heating during transfer from mars to earth and terrestrial weathering can be ruled out as major causes of the observed losses of radiogenic helium in bulk meteorites for bulk rock we observed a correlation of shock pressure and radiogenic 4he loss ranging between 20 for chassigny and other moderately shocked martian meteorites up to total loss for meteorites shocked above 40 gpa a steep increase of loss occurs around 30 gpa the pressure at which plagioclase transforms to maskelynite this correlation suggests significant 4he loss induced by shock metamorphism noble gas loss in rocks is seen as diffusion due to 1 the temperature increase during shock loading shock temperature and 2 the remaining waste heat after adiabatic unloading post shock temperature modeling of 4he diffusion in the main u th carrier phase apatite showed that post shock temperatures of 300 c are necessary to explain observed losses this temperature corresponds to the post shock temperature calculated for bulk rocks shocked at about 40 gpa from our investigation data survey and modeling we conclude that the shock event during launch of the meteorites is the principal cause for 4he loss

importance of porosity and transfer of matter in the rock weathering processes two examples in central spain some physical properties bulk and free porosity pore size distribution and the chemical composition and mass balance of two deeply weathered profiles one developed on hercynian granodiorite and the other on pre cambrian slates were studied hydric and mercury porosimetry nitrogen adsorption techniques chemical analyses and xrd techniques were used on granodiorite weathering has created increased porosity with a pore diameter 5 m whereas on slates the weathering has produced of ca 1 m in diameter these pore sizes have played an important role in the weathering processes assuming that weathering preserves volumes except in the uppermost part of the profiles it brought about a loss of matter of more than 12 300 kg m3 on granodiorite and ca 30 800 kg m3 on slates these changes are related to shifts in the mineralogical evolution with the appearance of new 2 1 and 1 1 phyllosilicates and fe oxy hydroxides as the main authigenic minerals the release of matter at least since the upper neogene until the present has led to the lowering of relief in a more or less homogeneous way giving rise to gentle hillsides and flat surfaces below which the current river networks are incised porosity studies have the potential to explain several specific landforms as well as affecting landscape development in general

sea surface temperature and salinity reconstruction from coral geochemical tracers massive scleractinian corals secrete an aragonitic skeleton which incorporates a large array of chemical tracers corals present several advantages for palaeoclimate research they grow continuously and can live up to 1000 years they are easy to date and they can be sampled at high resolution weekly to monthly resolution both live and fossil corals can be collected in the field in the past two decades significant efforts have been made to identify robust tracers of sea surface temperature sst and salinity sss in corals to date sr ca and 18o are considered to be the most reliable sst tracers although changes in seawater 18o can significantly alter sst reconstructed from coralline 18o because these variations in seawater 18o can be linked to sss changes this initial problem can in fact be turned into an advantage and provide us with an sss tracer the sst component in the coral 18o signal can either be evaluated through sr ca measurements or in some case simply filtered out however there is still much uncertainty concerning the exact mode of incorporation of trace elements and stable isotopes into the coral skeleton the effects of growth rate light intensity feeding habits ph and water chemistry are still poorly documented a review of the strength and weaknesses of sr ca and 18o is presented together with some examples of sst and sss reconstructions other potential sst tracers are also reviewed it is expected that the ability to grow corals in aquarium under controlled conditions and that the development of sophisticated analytical techniques at the micrometric level should help us understand better the robustness of each tracers and the factors controlling their incorporation in coral aragonite

high pressure and high temperature phase relations in diopside camgsi2o6 abstract phase transformations in diopside ca 0 92 mg 1 08 si 2 o 6 were studied by quench experiments at pressures of 18 24 gpa and temperatures of 1000 2400 k using an ma8 type multi anvil apparatus at moderate temperatures diopside decomposed into the assemblage of two components one with mgsio 3 stoichiometry and the other with casio 3 stoichiometry the mgsio 3 component crystallized into mg 2 sio 4 stishovite then transformed into mg 2 sio 4 stishovite mgsio 3 ilmenite and mgsio 3 perovskite with increasing pressure the casio 3 component was observed always as a glass in the recovered samples it is likely that casio 3 formed the cubic perovskite type structure under pressure at higher temperature diopside transformed into mg ca sio 3 garnet and casio 3 perovskite and then to mgsio 3 and casio 3 perovskites the solubility of ca into mg ca sio 3 garnet decreases with increasing pressure the stability field of ca bearing garnet is expanded to lower temperature range compared to that of pure mgsio 3 garnet the present results clarify the phase relations of diopside to the uppermost part of the lower mantle

east african soil erosion recorded in a 300 year old coral colony from kenya 1 soil erosion is a key socio economic and environmental problem in kenya which has been poorly documented due to the lack of long continuous records here we present ba ca records from porites corals from the malindi coral reef documenting the flux of suspended sediment from the sabaki river with a sub weekly resolution for the last 300 years while sediment flux from the sabaki river is almost constant between 1700 and 1900 a continuous rise in sediment flux is observed since 1900 first due to british settlements and afterwards due to steadily increasing demographic pressure on land use the peak in suspended sediment load and hence soil erosion occurred between 1974 and 1980 when there is a five to tenfold increase relative to natural levels this is attributed to the combined effects of dramatically increasing population unregulated land use deforestation and severe droughts in the early 1970 s we conclude that despite laudable attempts to instigate soil conservation measures it is unlikely that there will be a sustainable reduction in soil erosion without a significant improvement in socio economic conditions

an assessment of the sr ca ratio in shallow water hermatypic corals as a proxy for sea surface temperature the high precision measurement of the sr ca ratio in corals has the potential for measuring past sea surface temperatures at very high accuracy however the veracity of the technique has been questioned on the basis that there is both a spatial and temporal variation in the sr ca ratio of seawater and that kinetic effects such as the calcification rate can affect the sr ca ratio of corals and produce inaccuracies of the order of 2 4 c in the present study a number of cores of the massive hermatypic scleractinian coral porites from the central great barrier reef have been analyzed for sr ca at weekly to monthly resolution results from a 24 year record from myrmidon reef show an overall variation from 22 7 c to 30 4 c the record shows a warming cooling trend with maximum warming centred on the 1986 1987 summer while some bleaching was reported to have occurred at myrmidon reef in 1982 the sr ca record indicates that subsequent summer temperatures were much higher the 4 5 year record from stanley reef shows a maximum sst of 30 c during the 1997 1998 el nino event the calibrations from myrmidon and stanley reefs are in excellent agreement with previously published calibrations from nearby reefs while corals do not calcify in equilibrium with seawater due to physiological control on the uptake of sr and ca into the lattice of coralline aragonite it can be argued that provided only a single genus such as porites sp is used and that the coral is sampled along a major vertical growth axis then the sr ca ratio should vary uniformly with temperature similarly objections based on the spatial and temporal variability of the sr ca activity ratio of seawater can be countered on the basis that in most areas where coral reefs grow there is a uniformity in the sr ca activity ratio and there does not appear to be a change in this ratio over the growth period of the coral evidence from several corals in this study suggest that stress can be a major cause of the breakdown in the sr ca sst relationship thermal stress resulting from either extremely warm or cool temperatures can produce anomalously low sr ca derived ssts as a result of the breakdown of the biological control on sr ca fractionation it is considered that other stresses such as increased nutrients and changes in light intensity can also lead to a breakdown in the sr ca sst relationship two of the main issues affecting the reliability of the sr ca method are the calibration of the sr ca ratio with measured sst and the estimation of tropical last glacial maximum lgm palaeotemperatures instead of producing a constant calibration just about every one published so far is different from the others what is obvious is that for most calibrations while the slope of the calibration equation is similar the intercepts are not while the cause for this variation is still unknown it would appear that corals from different localities around the world are responding to their own particular environment or that certain types of environments exert a control on the corals physiology sr ca derived sst estimates for the lgm and deglaciation of 5 c 6 c cooler than present are at odds with estimates of 2 c 3 c cooling by other climate proxies the apparent lack of reef growth during the lgm suggests that ssts were too cold in many parts of the tropics for reefs to develop this would lend support to the idea that tropical ssts were much cooler than what the climap data suggests

high pressure phases in shock induced melt of the unique highly shocked ll6 chondrite northwest africa 757 northwest africa 757 is unique in the ll chondrite group because of its abundant shock induced melt and high pressure minerals olivine fragments entrained in the melt transform partially and completely into ringwoodite plagioclase and ca phosphate transform to maskelynite lingunite and tuite two distinct shock melt crystallization assemblages were studied by fib tem analysis the first melt assemblage which includes majoritic garnet ringwoodite plus magnetite magnesiowustite crystallized at pressures of 20 25 gpa the other melt assemblage which consists of clinopyroxene and wadsleyite solidified at 15 gpa suggesting a second veining event under lower pressure conditions these shock features are similar to those in s6 l chondrites and indicate that nwa 757 experienced an intense impact event comparable to the impact event that disrupted the l chondrite parent body at 470 ma

deep sea coral geochemistry implication for the vital effect abstract deep sea corals hold a great potential as a key to important aspects of paleoceanography for at least two reasons 1 they offer temporal high resolution records of deep sea environment because they have growth banding structures 2 and they are well suited for studying vital effects because the deep sea environment does not change over short time scales however the relationship between the chemical composition of deep sea coral skeletons and environmental factors is not well understood in this study the chemical composition of deep sea corals was measured in bulk individuals and along skeletal micro structures among the bulk individuals 18 o value and sr ca ratio show a negative but weak correlation with ambient temperature on the other hand the mg ca ratio has a positive weak correlation with the temperature large variations were found among samples collected from similar temperature the variation is up to 3 8 for 18 o 0 9 mmol mol for sr ca ratios and 0 78 mmol mol for mg ca ratios among samples with ambient average temperature within 1 c this variation may be due to a large vital effect the centers of calcification cocs which were formed at high calcification rate have lower sr ca u ca and higher mg ca ratios than surrounding fasciculi this chemical distribution supports the model that elemental incorporation depends on calcification rate this suggests that calcification rate is a very important factor for the chemical composition in deep sea corals and is one of the most significant mechanisms of the vital effect because of this large vital effect further investigations are essential to use the deep sea coral as a temperature proxy

the ages and soils of two levels of rana surfaces in central spain abstract the geomorphology of two ranas and a specimen soil profile on each have been studied in the province of guadalajara central spain the ranas were first delineated on an aerial photograph then examined in the field for further identification and for the preparation of topographic profiles two soil profiles were described and sampled by horizons analyses were made of the samples for particle size distribution ph cation exchange relations and organic matter plus some observations on mineralogy of clay and fine sand fractions results of the study support earlier suggestions that the younger ran asurface s 1 is of donau age middle villafranchian but indicate that the second s 2 should be assigned to the middle upper pliocene lower villafranchian the soil profiles were found to be an alfisol on the younger and an ultisol on the older rana which is consistent with a greater age for the latter

a new mineral with an olivine structure and pyroxene composition in the shock induced melt veins of tenham l6 chondrite we report a new mineral that occurs in shock induced melt veins of the tenham l6 chondrite the new mineral identified by transmission electron microscopy tem occurs as acicular nanocrystals in a glassy matrix at the edge of shock induced melt veins that crystallized during rapid quench at high pressure the elongate crystals have aspect ratios up to 25 widths range from 5 to 40 nm and lengths are up to 500 nm energy dispersive x ray spectroscopy eds analyses provide the relative cation abundances that are consistent with a pyroxene like stoichiometry na 0 06 ca 0 02 mg 0 71 fe 0 20 al 0 11 si 0 94 o 3 selected area electron diffraction saed patterns from single crystal and polycrystalline aggregates indicate an olivine structure with refined cell parameters a 4 78 b 10 11 and c 5 94 a and a calculated density of 3 32 g cm 3 synchrotron x ray microdiffraction data are consistent with an olivine structure and provide similar cell parameters a 4 778 b 10 267 c 5 937 a the pyroxene composition represents a large deviation from olivine stoichiometry na 0 08 ca 0 03 mg 0 95 fe 0 26 al 0 15 si 0 25 0 28 2 si 1 o 4 with 0 28 formula units of vacancies 0 11 of na plus ca 2 and 0 25 of si 4 in octahedral sites our observations indicate that a metastable and nonstoichiometric olivine structure can crystallize from a silicate melt during rapid quench trace amounts of such defects may be present in stable olivines in the deep upper mantle

high resolution analysis of trace elements in crustose coralline algae from the north atlantic and north pacific by laser ablation icp ms we have investigated the trace elemental composition in the skeleta of two specimens of attached living coralline algae of the species clathromorphum compactum from the north atlantic newfoundland and clathromorphum nereostratum from the north pacific bering sea region amchitka island aleutians samples were analyzed using laser ablation inductively coupled plasma mass spectrometry la icp ms yielding for the first time continuous individual trace elemental records of up to 69 years in length the resulting algal mg ca sr ca u ca and ba ca ratios are reproducible within individual sample specimens algal mg ca ratios were additionally validated by electron microprobe analyses amchitka sample algal sr ca u ca and ba ca ratios were compared to algal mg ca ratios which previously have been shown to reliably record sea surface temperature sst ratios of sr ca from both clathromorphum species show a strong positive correlation to temperature dependent mg ca ratios implying that seawater temperature plays an important role in the incorporation of sr into algal calcite linear sr ca sst regressions have provided positive but weaker relationships as compared to mg ca sst relationships both algal mg ca and sr ca display clear seasonal cycles inverse correlations were found between algal mg ca and u ca ba ca and correlations to sst are weaker than between mg ca sr ca and sst this suggests that the incorporation of u and ba is influenced by other factors aside from temperature

two distinct assemblages of high pressure liquidus phases in shock veins of the sixiangkou meteorite shock produced complex veins including earlier and later veins are identified in the sixiangkou l6 chondrite the early vein is intersected by the late vein and consists of coarse grained aggregates of ringwoodite majorite and lingunite and fragments of olivine pyroxene plagioclase metal and troilite as well as a fine grained matrix of garnet ringwoodite metal and troilite the late vein mainly consists of a fine grained matrix of garnet magnesiowustite metal and troilite as well as a small amount of coarse grained aggregates the amount of fine grained matrix suggests that the late vein was nearly completely melted whereas the early vein underwent partial melting both fine grained assemblages of garnet plus ringwoodite in the early vein and garnet plus magnesiowustite in the late vein are liquidus phases crystallized from shock induced melt based on our understanding of the liquidus assemblages the late vein experienced a higher pressure and temperature than the early vein

experimental generation of shock induced pseudotachylites along lithological interfaces to understand the mechanism of formation of shock induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation shock recovery experiments were carried out on samples consisting of two distinct lithologies dunite and quartzite it was possible to generate melt veins of 1 6 m width along lithological interfaces at moderate shock pressures 6 to 34 gpa the magnitudes of displacement along the interface strain rate and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins the experimentally produced veins resemble natural s type pseudotachylites the geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness formation of melt pockets and injection veins sudden changes in vein orientation and sharp vein margins two types of melt were observed vesicle free and vesicular melts dense vesicle free melt rock is likely to represent high pressure melts vesicular melts were also generated during shock compression but they remained in a molten state during pressure release and continued shearing intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine the composition of the frictional melts ranges from olivine normative to enstatite normative and is thus largely determined by olivine melting the validity of the sequence of friction melting susceptibilities of rock forming minerals inferred from tectonically produced pseudotachylites is confirmed and can now be applied to ultra high strain rates during shock compression

a high resolution sr ca and δ18o coral record from the great barrier reef australia and the 1982 1983 el nino abstract a high resolution near weekly sr ca and oxygen isotopic record is presented for a coral from the pandora reef in the great barrier reef gbr of australia during the period 1978 to 1984 the records are well correlated except for periods of high rainfall when river runoff has significantly modified the 18o value of seawater using the sr ca temperature calibration of de villiers et al 1994 the sr ca records exhibit seasonally controlled cyclical sst sea surface temperature variations of from 21 to 28 c during the very strong el nino of 1982 1983 the sr ca systematics indicate a sharp drop in the winter sst to 18 5 c this represents a temperature anomaly of 3 c which is approximately twice that given by the 18o variations suggesting an 2 amplification of the anomaly by the sr ca system possibly due to the increasing dominance of inorganically controlled aragoniteseawater fractionation the oxygen isotopic systematics show the combined effects of both temperature and changing seawater 18o values the latter reflecting the influx of 18o depleted runoff during periods of high rainfall due to the extremely low 10 3 sr and ca contents of river run off relative to seawater it is possible to use the sr ca thermometer to calculate temperatures independent of major floods and hence deconvolve the combined effects in the oxygen isotopic record of variable temperature and the 18o value of seawater using this approach it is possible to quantitatively reproduce the volume of runoff from the burdekin river during the periods of major flooding that occurred in early 1979 and 1981 the results of this study demonstrate that the combined use of high resolution sr ca and 18o systematics in scleractinian corals is a powerful tool for providing quantitative constraints on past climate

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

experimental shock metamorphism of the murchison cm carbonaceous chondrite abstract a series of shock recovery experiments were carried out on the murchison cm carbonaceous chondrite by using a single stage propellant gun the murchison samples were shocked in nine experiments at peak pressures from 4 to 49 gpa the recovered samples were studied in detail by using an optical microscope a scanning electron microscope and an electron probe microanalyzer chondrules are flattened in the plane of the shock front at 4 to 30 gpa the mean aspect ratio of chondrules increases from 1 17 to 1 57 roughly in proportion to the intensity of shock pressure up to 25 gpa at 25 to 30 gpa the mean aspect ratio does not increase further and chondrules show increasingly more random orientations and degrade their preferred orientations and at 35 gpa they are extensively disrupted most coarse grains of olivine and pyroxene are irregularly fractured fracture density increases with increasing shock pressure and at 30 gpa almost all are thoroughly fractured with subgrains of local shock melting occurs as melt veins and pockets at 20 to 30 gpa fracture filling veins of fine grains of matrix are also produced at 25 to 30 gpa the melts and the fine grains seem to result mainly from frictional heating due to displacement along fractures at 35 gpa melting occurs pervasively throughout the matrix the melts are mainly produced from the matrix however they are consistently more enriched in fe s and ca which indicates that these elements are selectively incorporated into the melts the melts contain tiny spherules of fe ni metal fe sulfide and numerous vesicles at 49 gpa the matrix is totally melted and coarse grains of olivine are partially melted the melts contain much larger vesicles 50 300 m in diameter than those in the samples shocked at lower pressures which indicates that much more intense devolatilization and gas expansion took place for the purpose of comparing shock thermal effects between the experimentally shocked samples and naturally shocked targets surface materials in the murchison parent body we calculated internal energy increase for compression by multiple shock wave reflections experimental case and for compression by a single shock wave natural case the results suggest that postshock thermal effects observed at each experiment may be attained by impact on the natural targets at a considerably lower shock pressure than the peak shock pressure from the results of our experiments and calculations we conclude that if the murchison parent body were shocked on the surface at pressures higher than 25 gpa shocked material would probably undergo drastic increase in the degree of comminution and simultaneous generation of strong expansive forces on pressure release thus the results support the hypothesis of scott et al 1992 that volatile rich carbonaceous chondrites shocked above 20 to 30 gpa escaped from the parent body and formed particles that are too small to survive as meteorites

subtropical coral reveals abrupt early twentieth century freshening in the western north pacific ocean instrumental climate observations provide robust records of global land and ocean temperatures during the twentieth century unlike for temperature continuous salinity observations in the surface ocean are scarce prior to 1970 and the magnitude of salinity changes during the twentieth century is largely unknown surface ocean salinity is a major component in climate dynamics as it influences ocean circulation and water mass formation here we present an annually resolved reconstruction of salinity variations in the surface waters of the western subtropical north pacific ocean since 1873 based on bimonthly records of 18o sr ca and u ca in a coral from the ogasawara islands the reconstruction indicates that an abrupt regime shift toward fresher surface ocean conditions occurred between 1905 and 1910 observational atmospheric data suggest that the abrupt freshening was associated with a weakening of the winds that drive the kuroshio current system and the associated subtropical gyre circulation we note that the abrupt early twentieth century freshening in the western subtropical north pacific precedes abrupt climate change in the northern north atlantic by a few years the potential for abrupt regime shifts in surface ocean salinity should be considered in climate predictions for the coming decades

study of paleoweathering on the spanish hercynian basement montes de toledo central spain summary the hercynian basement of the iberian peninsula consists of a series of late hercynian blocks that were unleveled by the alpine orogeny the montes de toledo range is found in one of the elevated blocks of the central zone and shows ancient alterations affecting different rocks which are fossilized by sediments of different ages two of these weathering profiles under the plio pleistocene sediments of rana formations are studied one is developed on granodiorite with some intercalated metamorphic rocks and the other on a slaty series in both profiles smectite is formed in a first weathering process a second weathering process yielding kaolinite and affecting rana sediments is superimposed on older one both processes seem to be widely spread in the western part of the iberian peninsula

formation mechanisms of planar deformation features in naturally shocked quartz abstract shock waves induce peculiar defects in quartz shock mosaics high pressure polymorphs coesite and stishovite diaplectic glass and planar deformation features pdfs together these features are the indices of shock metamorphism pdfs appear under the optical microscope as straight and narrow defects parallel to the 10 1n rhombohedral planes with n 3 and 2 as most frequent values although n 1 4 and i e basal plane are also found we report in the first part of this paper a detailed investigation by transmission electron microscopy of the fine structure of pdfs in shocked quartz grains from a variety of sites slate islands la malbaie and manson in north america the vredefort complex in south africa the ries crater in germany and the cretaceous tertiary boundary layer at raton basin colorado we distinguish four pdf fine structures 1 bands of dislocations 2 lamellae of mixtures in various proportions of amorphous silica and small crystallites 3 thin brazil twin lamellae 4 short parallel lamellae forming serrated ladder structures the possible formation mechanisms of these pdfs are discussed in the second part of the paper it is suggested that the dislocation bands are probably not original pdf structures but stem from a later recrystallization stage the brazil twins have been produced by relatively large deviatoric stresses which accompanied the shock wave the other pdf structures which consist of partial amorphization in the 10 1 n planes must result from elastic instabilities of the shear modulus of the quartz structure at high pressure in these planes theoretical estimates of the elastic stiffness coefficients indicate that amorphization should start at approximately 10 gpa the growth of the straight and narrow amorphous lamellae would be driven by the front of the shock wave

corals at their latitudinal limits laser ablation trace element systematics in porites from shirigai bay japan the rapid analytical technique of laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure the trace elements b mg sr ba and u in a high latitude coral colony porites lobata taken from shirigai bay japan 32 n a wide range of sea surface temperatures ssts 14 5 28 c and upwelling events influenced this coral cold winter ssts caused a decrease and or cessation of skeletal extension measurements of u ca and sr ca indicate an approximately linear response to ssts above 18 c and a non linear response below 18 c mg ca and b ca measurements both showed annual cycles broadly consistent with sst variations but also exhibited intra annual fluctuations not associated with temperature suggesting that the incorporation of mg and b into the coral skeleton was not simply regulated by temperature it is shown that ba ca ratios provide a proxy for wind induced seasonal upwelling this is inferred from the strong correlations between the strength of zonal winds 1 month prior to the sst minimum and the ba ca maximum secondary upwelling events occurred during the summers of 1982 1987 1991 and 1992 these summers were cooler than average and were associated with el nino southern oscillation events

origin of the eclogitic clasts with graphite bearing and graphite free lithologies in the northwest africa 801 cr2 chondrite possible origin from a moon sized planetary body inferred from chemistry oxygen isotopes and ree abundances abstract in order to clarify the origin of the eclogitic clasts found in the nwa801 cr2 chondrite kimura et al 2013 especially that of the high pressure and temperature p t condition 3 gpa and 1000 c we conducted ion microprobe analyses of oxygen isotopes and rare earth element ree abundances in the clasts oxygen isotopic compositions of the graphite bearing lithology gbl and graphite free lithology gfl show a slope 0 6 correlation slightly below the cr ch cb chondrites field in the o three isotope diagram with a large variation for the former and almost homogeneous composition for the latter the average ree abundances of the two lithologies show almost unfractionated patterns based on these newly obtained data as well as mineralogical observations bulk chemistry and considerations about diffusion timescales for various elements we discuss in detail the formation history of the clasts consistency of the geothermobarometers used by kimura et al 2013 suggesting equilibration of various elements among different mineral pairs provides a strong constraint for the duration of the high p t condition we suggest that the high p t condition lasted 102 103 years this clearly precludes a shock high pressure hp model and hence strongly supports a static hp model a static hp model requires a moon sized planetary body of 1500 km in radius furthermore it implies two successive violent collisions first at the formation of the large planetary body when the clasts were placed its deep interior and second at the disruption of the large planetary body when the clasts were expelled out of the parent body and later on transported to the accretion region of the cr chondrites we also discuss possible origin of o isotopic variations in gbl and presence absence of graphite in gbl gfl respectively in relation to smelting possibly occurred during the igneous process es which formed the two lithologies finally we present a possible formation scenario of the eclogitic clasts

melting experiments on the enstatite pyrope join at 80 152 kbar melting temperatures of the assemblage pyroxene garnet on the enstatite pyrope join were experimentally determined at 11 different pressures between 80 and 152 kbar with a split sphere anvil apparatus ussa 2000 the compositions of pyroxene garnet and melt coexisting along the solidus were also determined comparison with previous data at lower temperatures revealed a large temperature dependence of the compositions of garnet coexisting with pyroxene it is proposed that the observed variation in the garnet composition is caused by disorder in garnet the obtained alumina contents of orthopyroxene coexisting with garnet on the solidus at 80 110 kbar contributed to an improvement of the garnet peridotite thermobarometry an internally consistent set of thermodynamic parameters was derived which allows calculation of the temperature pressure phase diagram for the enstatite pyrope join at 20 260 kbar

a large shock vein in l chondrite roosevelt county 106 evidence for a long duration shock pulse on the l chondrite parent body a large shock induced melt vein in l6 ordinary chondrite roosevelt county 106 contains abundant high pressure minerals including olivine enstatite and plagioclase fragments that have been transformed to polycrystalline ringwoodite majorite lingunite and jadeite the host chondrite at the melt vein margins contains olivines that are partially transformed to ringwoodite the quenched silicate melt in the shock veins consists of majoritic garnets up to 25 m in size magnetite maghemite and phyllosilicates the magnetite maghemite and phyllosilicates are the terrestrial alteration products of magnesiowustite and quenched glass this assemblage indicates crystallization of the silicate melt at approximately 20 25 gpa and 2000 c coarse majorite garnets in the centers of shock veins grade into increasingly finer grained dendritic garnets toward the vein margins indicating increasing quench rates toward the margins as a result of thermal conduction to the surrounding chondrite host nanocrystalline boundary zones that contain wadsleyite ringwoodite majorite and magnesiowustite occur along shock vein margins these zones represent rapid quench of a boundary melt that contains less metal sulfide than the bulk shock vein one dimensional finite element heat flow calculations were performed to estimate a quench time of 750 1900 ms for a 1 6 mm thick shock vein because the vein crystallized as a single high pressure assemblage the shock pulse duration was at least as long as the quench time and therefore the sample remained at 20 25 gpa for at least 750 ms this relatively long shock pulse combined with a modest shock pressure implies that this sample came from deep in the l chondrite parent body during a collision with a large impacting body such as the impact event that disrupted the l chondrite parent body 470 myr ago

high pressure polymorphs of magnesian orthopyroxene from a shock vein in the yamato 000047 lherzolitic shergottite abstract we found a simple thin shock vein less than or equal to about 60 m in width and 1 8 mm in length in the poikilitic area in the yamato y 000047 lherzolitic shergottite the shock vein occurs only in magnesian ca poor clinopyroxene which may have transformed from orthopyroxene during the pressure increase at the shock event the shock vein consists of mg0 8 fe0 2 sio3 pyroxene polymorphs such as columnar akimotoite two kinds of pyroxene glasses dendritic akimotoite and framboidal pyroxene glass in the order from the periphery to the center the compositions and textures suggest that columnar akimotoite in the periphery of the shock vein crystallized from solid state phase transition of clinopyoroxene during the cooling of the vein and the remains in the shock vein solidified from shock produced melt the glass includes two kinds of massive glass in the vein and framboidal glass in the vein center the framboidal glass is the most magnesian and may have been vitrified from perovskite crystallized from high pressure melt produced at high temperature 3000 c and high pressure 23 40 gpa dendritic akimotoites in the vein center metastably crystallized from residual shock melt the formation sequences of the constituent phases in the shock vein happen in the following order columnar akimotoites rim glass center glass framboidal glass and dendritic akimotoites the increase of the raman intensity of 660 670 cm 1 in the order of rim glass center glass and framboidal glass suggests that the formation of the pyroxene chain proceeds faster in the vein center than in the vein rim due to its slower cooling the finding of the shock vein consisting merely of high pressure polymorphs of pyroxene akimotoite and framboidal glass vitrified perovskite is the first reported among all martian meteorites