conodont color and textural alteration an index to regional metamorphism contact metamorphism and hydrothermal alteration experimental and field data are used to extend the utility of conodonts as semi quantitative thermal indices into the regimes of regional and contact metamorphism as well as hydrothermal alteration an arrhenius plot of data from induced conodont color alteration by pyrolysis in air at 1 atm was used to generate the geologic temperatures for conodont color alteration indices cai above 300 c that is for cai values of 5 through 8 such cai values occur in very low to medium grade regionally metamorphosed contact metamorphosed and hydrothermally altered rocks the uniformity or variability of cai values within a sample together with conodont texture can help to distinguish grades and environments of metamorphism particularly in metacarbonate sequences induced cai by pyrolysis in a water methane mixture at kbar results in retardation of cai and in a disparate mixture of both low and high cai values within each experimental sample in this system color alteration processes above a cai of 2 to 3 seem to change from predominantly carbonization to predominantly loss of organic matter presumably by oxidation and volatilization of oxides these experiments approximate the type of cai mixture characteristically found in conodonts recovered from hydrothermally altered rocks these data indicate that cai values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization

management of ambiguities in magnetostratigraphic correlation abstract magnetostratigraphy is a powerful tool to provide absolute dating of sediments enabling robust and detailed chronostratigraphic correlations it is based on the correlation of a magnetic polarity column observed and measured in a given sediment section to a magnetic polarity reference scale where polarity changes are well dated via other independent methods however magnetostratigraphic correlations are loose as they are only constrained by binary magnetic chrons i e normal or reversal and their thickness which are both defined from depth variations of the magnetic remanent directions the thickness of a given magnetic polarity zone is a function of time and sediment accumulation rate which may not be stationary leading to ambiguities when performing the correlations to address these ambiguities a numerical method based on the dynamic time warping algorithm is proposed magnetostratigraphic correlations are computed in order to minimise the local variation of the accumulation rate the main advantage of the proposed method is to automatically provide a set of reasonably likely correlations this set can then be scrutinised for further analysis and interpretation however the likelihood of a correlation should be handled carefully as it depends on the information content of the magnetostratigraphic section itself and remain ultimately valid by ancillary constraint nevertheless the method gives consistent results on difficult synthetic cases that simulate abrupt variations of the sedimentation rate insights on true sections debated by previous authors are also given

the neogene xiyu formation a diachronous prograding gravel wedge at front of the tianshan climatic and tectonic implications the tarim and junggar basins in central asia are capped by a thick pile of conglomerates called the xiyu formation that are commonly linked to a change in climate and or accelerated uplift near the plio pleistocene boundary in order to better understand their origin and significance we carried out a combined structural and magnetostratigraphic study in the quilitage syncline southern tianshan where the base of the xiyu conglomerates is observed at both sides of the syncline a balanced cross section shows that even at a local scale the base of the xiyu conglomerates cannot be regarded as a single continuous stratigraphic layer on the southern flank of the quilitage syncline we collected 172 samples collected for magnetostratigraphic dating identify 17 polarity chrons that date the new section from 5 2 to 1 7 ma and constrain the base of the xiyu conglomerate here at 1 7 ma this is 4 2 ma younger than the age of the xiyu previously found on the northern limb of the same syncline together with other magnetostratigraphic studies carried out around the tianshan our study unambiguously demonstrates that the onset of deposition of the xiyu conglomerates is diachronous and that the conglomerates are systematically younger toward the basin consequently the xiyu formation should not be considered as a chronostratigraphic marker related to any particular tectonic or climatic event but is instead a prograding gravel wedge that has prograded over the underthrusting forelands a synthesis of chronologic and structural results yields progradation rates over the last 10 ma on the order of 2 0 mm yr and 3 9 mm yr south and north of the tianshan mountains respectively these rates are comparable to the shortening rate across the tianshan range suggesting that underthrusting is the main factor governing the progradation rate of the xiyu formation

intratest oxygen isotope variability in the planktonic foraminifer n pachyderma real vs apparent vital effects by ion microprobe abstract intratest oxygen isotope variations in the planktonic foraminifer neogloboquadrina pachyderma sinistral left coiling from north atlantic core top and multi net samples were assessed by ion microprobe analysis from 2 to 6 m spots with precision and accuracy better than 0 7 in 18 o 2 sd within a single foraminiferal test from a core top sample comprising both ontogenetic calcite and outer crust 18 o values vary from 0 5 to 3 7 pdb exceeding the range of equilibrium 18 o in the specimens habitat by a factor of three the isotopic difference between the ontogenetic calcite and the crust averages 1 8 neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater the ontogenetic calcite exhibits a negative vital effect 18 o m e 18 o measured 18 o equilibrium ranging from 0 5 to 1 the largest negative fractionation is associated to the inner walls of juvenile chambers in contrast a positive vital effect of about 0 8 was observed in the crust with respect to the highest equilibrium 18 o values at water depths below 200 m hence two vital effects that are opposite in sign are effective within a single foraminiferal test indicating that whole test values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals the negative vital effect of the ontogenetic calcite was verified by ion microprobe analysis of four nonencrusted net sampled specimens reflecting three different depth intervals intra ontogenetic oxygen isotope ratios in these juvenile tests range from 0 6 to 3 0 and exhibit a negative vital effect even larger than that observed in core top samples based on these data the large range of apparent vital effects reported for this foraminiferal species can be assessed by a mass balance calculation assuming that the degree of encrustation is variable

comparing oxygen isotope records of silurian calcite and phosphate δ18o compositions of brachiopods and conodonts oxygen isotope compositions of silurian calcitic brachiopod shells from gotland are compared with those of phosphatic inarticulate brachiopod shells and conodonts from identical stratigraphic horizons the 18ophosphate values of inarticulate brachiopod shells vary widely 13 0 to 17 5 v smow and are significantly lower than those of coeval conodont samples 17 5 to 19 5 v smow conodont samples from individual beds have homogenous 18ophosphate values with variations close to the analytical precision 0 2 together with a significant correlation of conodont 18ophosphate and articulate brachiopod shell 18ocarbonate values r 0 85 this observation suggests that primary marine oxygen isotope compositions are better preserved in conodont apatite than in inarticulate brachiopod shell apatite however with decreasing 18ocarbonate values the 18ophosphate values of conodonts are higher than expected for theoretical isotopic equilibrium with brachiopod calcite different habitats of conodonts and brachiopods cannot account for the observed offset in 18o because both organisms were thriving on a broad shallow marine carbonate platform whereas 18ophosphate values of silurian conodonts are close to 18ophosphate values of modern and mesozoic tropical biogenic apatites most silurian calcitic brachiopod shells from gotland are depleted in 18o when compared to modern or mesozoic brachiopods we therefore suggest that silurian conodonts from gotland record paleotemperature and 18o of silurian sea water more faithfully than coeval calcitic brachiopod shells

oxygen isotope variations in phosphate of biogenic apatites ii phosphorite rocks abstract phosphorites from sedimentary sequences ranging in age from archaean to recent were analysed for 18 o in both the po 4 18 o p and co 3 18 o c in the apatite lattice the oxygen isotope record is considerably better preserved in phosphates than in either carbonates or cherts the use of the longinelli and nuti 8 temperature equation yields temperatures for recent phosphorites that are in good agreement with those measured in the field the 18 o p values of ancient phosphorites decrease with increasing age these changes with time are not likely to be due to post depositional exchange changes in 18 o values of seawater and variations of temperature with time can account for the 18 o p time trend but the latter explanation is preferred in ancient phosphorites 18 o c in structurally bound carbonate in apatite is not a reliable geochemical indicator

comment on magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china baochun huang john d a piper shoutao peng tao liu zhong li qingchen wang rixiang zhu earth planet sci lett 2006 doi 10 1016 j epsl 2006 09 020 abstract the recent publication of magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china by b c huang j d a piper s t peng t liu z li q c wang r x zhu earth planet sci lett 2006 doi 10 1016 j epsl 2006 09 020 discusses the cenozoic uplift history of the tianshan mountains by studying the magnetostratigraphy of paleogene to neogene continental sediments from two sections located in the kuche basin at the northern edge of the tarim basin to support their conclusion they reinterpreted a magnetostratigraphic study of the yaha section which lies 10 km south of their sections we previously published j charreau s gilder y chen s dominguez j p avouac s sen m jolivet y li and w wang magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tianshan mountains geology 34 3 2006 181 184 here 1 we argue that the interpretations of the sedimentation rate changes they proposed for the kuche sections are partially invalid 2 we disagree with their reinterpretation of the age of the yaha section and 3 we think that the way they interpret their ams data is incorrect

δ18o composition of conodont apatite indicates climatic cooling during the middle pridoli phosphatic microfossils such as conodonts and fish microremains dermal scales from the upper silurian pridoli of lithuania have been studied for their oxygen isotope composition the conodont c

reply to the comment by j charreau et al on magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china earth planet sci lett 2008 doi 10 1016 j epsl 2008 01 025

thermal maturation of the lower palaeozoic strata of northern greenland from conodont colour alteration index cai data implications for burial history and hydrocarbon exploration conodont colour alteration data for the lower palaeozoic strata of the north greenland carbonate platform indicate a pattern of increased thermal maturity northwards within the franklinian basin there is little variation in values through the canadian llandovery lower ordovician lower silurian interval at any given locality a simplified thermal model for the platform suggests that the predominant control of conodont colour alteration and thermal maturation was maximum depth of burial which occurred during the mid to late silurian a preliminary integrated scheme for conodont and organic thermal maturity indicators can be compiled from the data now available from north greenland

ordovician low to intermediate mg calcite marine cements from sweden marine alteration and implications for oxygen isotopes in ordovician seawater petrography demonstrates the presence of three types of fibrous calcite cement in buildup deposits of the kullsberg limestone middle caradoc central sweden translucent fibrous calcite has intrinsic blue luminescence cl indicative of pure calcite this cement has 2 5 mol mgco3 low mn and fe 100 p p m and is considered to be slightly altered to unaltered primary low to intermediate mg calcite grey turbid fibrous calcite has variable but generally low mgco3 content most analyses 2 mol and variable cl response with mn and fe concentrations up to 1200 and 500 p p m respectively the heterogeneous characteristics of this variety of fibrous calcite are caused by diagenetic alteration of a translucent fibrous calcite precursor light brown turbid fibrous calcite has low mgco3 near 1 mol and variable mn up to 800 p p m and fe up to 500 p p m concentrations with an abundance of bright luminescent patches which formed during alteration caused by reducing diagenetic fluids the 13c and 18o values of all fibrous calcite form a tight field 13c 1 7 to 3 1 pdb 18o 2 6 to 4 1 pdb compared with fibrous calcite isotope values from other units fibrous calcite 18o values are larger than adjacent meteoric or burial cements which have 18o 8 pdb consequently most diagenetic alteration of kullsberg fibrous calcite is interpreted to have occurred in the marine diagenetic realm first generation equant and bladed calcite cements which pre date fibrous calcite are interpreted as unaltered low mg calcite marine cements based on 13c and 18o data 13c 2 3 to 2 7 pdb 18o 2 8 to 3 5 pdb unlike fibrous cement which reflects global sea water chemistry first generation equant and bladed calcite are indicators of localized modification of seawater chemistry in restricted settings kullsberg abiotic marine cements have larger 18o values than most caradoc marine precipitates from equatorial laurentia positive kullsberg 18o values are attributed to lower seawater temperatures and or slightly elevated salinity on the baltic platform relative to seawater from which other marine precipitates formed

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

constraints on pennsylvanian glacioeustatic sea level changes using oxygen isotopes of conodont apatite conodonts from u s midcontinent cyclothems were studied for oxygen isotopes in order to constrain pennsylvanian glacioeustatic sea level fluctuations pennsylvanian deposits of the midcontinent united states are composed of cyclic alternations of thin transgressive limestones offshore gray to black phosphatic shales and thick regressive limestones a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds glacioeustatic sea level fluctuations are considered the primary cause for the formation of these cyclothems oxygen isotope analyses of conodont apatite from the black 20 1 0 5 vienna standard mean ocean water vsmow and gray shale units 20 5 0 5 vsmow show lowest average 18 o values whereas conodont elements from the regressive 21 0 0 3 vsmow and transgressive limestone units 21 1 0 6 vsmow are enriched in 18 o the maximum change in 18 o of conodonts from the black shale and carbonate units from individual cyclothems is 1 7 the 1 7 c difference in 18 o compares relatively well to pleistocene interglacial glacial changes in 18 o of equatorial surface dwelling foraminifers and suggests that pennsylvanian glacioeustatic sea level changes may have been of comparable amplitude however since the pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record pennsylvanian glacioeustatic sea level changes were probably larger than the 120 m fluctuations recorded for the pleistocene glaciations

stratigraphic and oxygen isotope evidence for my scale glaciation driving eustasy in the early middle devonian greenhouse world article i nfo million year scale 3rd order depositional sequences few 10s to 100 m thick are common in the devonian marine record and are correlated between sedimentary basins and across widely separated continents implying a eustatic origin tectonically driven changes in mid ocean ridge spreading rates lengths are too slow to account for the calculated 3rd order rise fall rates and typical orbital frequencies 20 400 ky are too fast we analyzed oxygen isotopes from conodont apatite to evaluate if early middle devonian 3rd order sea level changes were controlled by paleoclimatically driven ice volume glacio eustasy and seawater temperature change thermo eustasy two successive depositional sequences in the western u s nevada and czech republic prague basin were sampled the 18 o values range from 17 8

conodont u th he thermochronology initial results potential and problems abstract we performed he diffusion experiments and u th he age determinations on conodonts from a variety of locations to explore the potential of conodont u th he thermochronology to constrain thermal and exhumation histories of some sedimentary rock dominated terrains based on two diffusion experiments and age results from some specimens he diffusion in conodont elements appears to be similar to that in durango apatite fragments of similar size and closure temperatures are approximately 60 70 c for cooling rates of 10 c m y u th he ages of conodonts from some locations yield reproducible ages consistent with regional thermal history constraints and in at least two cases require a closure temperature lower than 80 c other samples however yield irreproducible ages and in one case yield ages much younger than expected based on regional geologic considerations these irreproducible samples show inverse correlations between parent nuclides and age consistent with late stage open system u th behavior

oxygen isotope analyses of co existing carbonate and phosphate in biogenic apatite a way to monitor diagenetic alteration of bone phosphate abstract the oxygen isotopic composition of phosphate 18 op and structural carbonate 18 oc of hydroxylapatite was determined in 31 bone and tooth samples of modern mammals from different countries these two variables are highly correlate r 2 0 98 and the calculated best fit of linear regression is very similar to the equation calculated from the phosphate and carbonate palaeotemperature equations 1 2 according to previous measurements 3 6 on fossils of different ages from different areas it seems quite improbable to find isotopically altered skeletal remains showing a good correlation between 18 op and 18 oc as is the case with modern samples it therefore seems possible at least in some cases to use these measurements for monitoring fossil bone and tooth diagenetic alteration when a set of points lie on the equilibrium line or close to it the 18 o values could be considered close to the original values in contrast when the points lie to the left or to the right of this line this probably means that the values are diagenetically modified due to interaction with meteoric water or 18 o enriched water respectively

reply to the comment by q q qiao et al on cenozoic tectonic deformation and uplift of the south tian shan implications from magnetostratigraphy and balanced cross section restoration of the kuqa depression by tao zhang xiaomin fang chunhui song erwin appel and yadong wang tectonophysics 2014 doi 10 1016 j tecto 2014 04 044 qiao et al 2016 commented on our work zhang et al 2014 and rejected our reinterpretation of the magnetostratigraphic results of huang et al 2006 and li et al 2006 with the results gained using the dynamic time warping algorithm technique dtwat as their main basis however qiao et al 2016 did not provide details of their modeling inputs and in particular the parameters they chose for their calculations where such parameters can have a serious impact upon any results we therefore performed calculations using the same software i e qupydon as qiao et al 2016 using reliable parameter settings the results showed that the interesting correlation of a 6000 minimum cost output completely correlate with the magnetostratigraphic chrons c18r to c3an 1n similar to 40 6 ma which is consistent with our reinterpreted magnetostratigraphic results furthermore we summarized previous biostratigraphic studies of nearby areas the data resulting from this process also supported our reinterpreted magnetostratigraphic correlation we were therefore able to confirm the revised magnetostratigraphic correlation of zhang et al 2014 c 2017 elsevier b v all rights reserved

provenance of microcrystalline carbonate cement in limestone marl alternations lma aragonite mud or molluscs aragonite derived from marine molluscs is evaluated as the source for microcrystalline carbonate cements of limestone marl alternations lma calculations demonstrate that extremely low levels of mollusc derived aragonite well below the production rates of molluscs in modern marine settings could have provided sufficient carbonate to cement examples of ordovician silurian and jurassic lma in non tropical or tropical settings it is likely that even in the palaeozoic molluscs provided sufficient carbonate entirely to source microcrystalline cements of lma autochthonous molluscan aragonite is the only viable aragonite precursor for lma microcrystalline cements of cool water settings where temperatures precluded calcified algae and abiotic carbonate precipitation in calcite seas where mg ca ratios inhibited both abiogenic aragonite precipitation and aragonite generation by calcified algae molluscan aragonite was again the most likely main contributor in some epeiric seas where brackish wedges switched off the shallow water carbonate mud factories molluscan aragonite is the parsimonious source of carbonate for lma microcrystalline cements

oxygen isotope variations in phosphate of biogenic apatites i fish bone apatite rechecking the rules of the game abstract the major advantage of the oxygen in phosphate isotope paleothermometry is that it is a system which records temperatures with great sensitivity while bone and teeth building organisms are alive and the record is nearly perfectly preserved after death fish from seven water bodies of different temperatures 3 23 c and different 18 o values 16 to 3 of the water were analysed the 18 o values of the analysed po 4 vary from 6 to 25 the system passed the following tests a the temperatures deduced from isotopic analyses of the sequence of fish from lake baikal are in good agreement with the temperatures measured in the thermally stratified lake b the isotopic composition of fish bone phosphate is not influenced by the isotopic composition of the phosphate which is fed to the fish but only by temperature and water composition isotopic analysis of fossil fish in combination with analysis of mammal bones should be a useful tool in deciphering continental paleoclimates

scales of thelodont and shark like fishes from the ordovician of colorado the phylogeny of primitive vertebrates has been investigated over the past fifteen years1 3 and there has been a notable increase in the amount of data by which such phylogenies can be tested4 7 stratigraphic data should provide constraints to such analyses and we record here descriptions of putative shark and thelodont scales from the harding sandstone caradoc late ordovician of colorado the fossil record of sharks is extended back from the llandovery lower silurian by some 25 million years and that of thelodonts by 10 million years from the ashgill late ordovician the new data indicate that a major radiation of lower vertebrates took place during the ordovician

magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china abstract magnetostratigraphic and rock magnetic results from 1006 horizons in paleogene and neogene sediments between the upper kumugeliemu formation and the base of the kuche formation within the kuche depression of the tarim basin nw china are used to evaluate postcollisional uplift and deformation in the tian shan range characteristic remanences with both normal and reversed polarity were isolated by thermal demagnetization generally between 300 and 690 c and a composite magnetostratigraphy is constructed from data at 969 accepted levels correlating with polarity chrons c12n to c3r dated between 31 0 and 5 5 ma on the ck95 geomagnetic polarity time scale observed height dependent changes of rock magnetic parameters km and ams ellipsoid parameters indicate that these sediments were influenced by weak deformation with the succession accumulated before 15 ma recording the effects of compressive deformation this finding together with two substantial increases in accumulation rate at 16 17 and 7 ma define a framework for cenozoic uplift and deformation of the tian shan range we argue that thrusting in the south of the range was probably initiated at 20 ma and followed by rapid uplift at 16 17 ma on the assumption that sediment accumulation in western china was still predominately tectonically controlled at 7 ma another later pulse of rapid uplift with a much larger regional influence is also recognized in the tian shan the kuche depression was subjected to two postcollisional phases of rotational deformation with clockwise rotation prior to 12 ma 1 36 ma succeeded by counterclockwise rotation at 1 64 ma after 12 ma and possibly continuing to the present day this rotational deformation is not temporally related to the history of basin formation resolved from the magnetostratigraphy and may be linked to block interactions with adjoining terranes

magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tian shan mountains we report a magnetostratigraphic and rock magnetic study of the yaha section located on the southern flank of the central tian shan mountains asia our results show a two fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca 11 ma after 11 ma sedimentation rate remained remarkably constant until at least 5 2 ma these findings are consistent with sedimentary records from other sections surrounding the tian shan we conclude that uplift and erosion of the tian shan accelerated ca 11 ma long after the onset of the collision between india and asia and that the range rapidly evolved toward a steady state geometry via a balance between tectonic and erosion processes

cenozoic tectonic deformation and uplift of the south tian shan implications from magnetostratigraphy and balanced cross section restoration of the kuqa depression abstract the collision of india with eurasia has caused rejuvenated deformation and uplift of the remote tian shan intracontinental orogenic range and has led to deposition of thick cenozoic sediments in its flank depressions however our knowledge when and how the range was deformed and uplifted is still limited we carried out detailed tectonic investigations seismostratigraphic analysis and paleomagnetic dating of the thrust fold belt in the kuqa depression at the southern tian shan flank combined with re interpretation of other magnetostratigraphic results in the depression we determined ages of major stratigraphic boundaries and constructed and restored the balanced cross section across the depression the results show that the total cenozoic shortening along the cross section in the depression is 13 95 km significant shortening began at 36 ma accelerated since 13 ma and further increased two to three fold since 6 5 ma especially since 2 6 ma this shortening process caused the development of the kuqa thrust fold system associated with the variation of the sedimentation rate upward coarsening of sediments and a progressive development of growth strata we therefore argue that significant deformation and uplift of the south tian shan began at 36 ma becoming more evident since 13 ma and culminating since 6 5 ma reaching its peak after 2 6 ma

sr c and o isotope geochemistry of ordovician brachiopods a major isotopic event around the middle late ordovician transition here we present sr c and o isotope curves for ordovician marine calcite based on analyses of 206 calcitic brachiopods from 10 localities worldwide these are the first ordovician wide isotope curves that can be placed within the newly emerging global biostratigraphic framework a total of 182 brachiopods were selected for c and o isotope analysis and 122 were selected for sr isotope analysis seawater 87sr 86sr decreased from 0 7090 to 0 7078 during the ordovician with a major quite rapid fall around the middle late ordovician transition most probably caused by a combination of low continental erosion rates and increased submarine hydrothermal exchange rates mean 18o values increase from 10 to 3 through the ordovician with an additional short lived increase of 2 to 3 during the latest ordovician due to glaciation although diagenetic alteration may have lowered 18o in some samples particularly those from the lower ordovician maximum 18o values which are less likely to be altered increase by more than 3 through the ordovician in both our data and literature data we consider that this long term rise in calcite 18o records the effect of decreasing tropical seawater temperatures across the middle late ordovician transition superimposed on seawater 18o that was steadily increasing from 3 standard mean ocean water smow by contrast 13c variation seems to have been relatively modest during most of the ordovician with the exception of the globally documented but short lived latest ordovician 13c excursion up to 7 nevertheless an underlying trend in mean 13c can be discerned changing from moderately negative values in the early ordovician to moderately positive values by the latest ordovician these new isotopic data confirm a major reorganization of ocean chemistry and the surface environment around 465 to 455 ma the juxtaposition of the greatest recorded swings in phanerozoic seawater 87sr 86sr and 18o at the same time as one of the largest marine transgressions in phanerozoic earth history suggests a causal link between tectonic and climatic change and emphasizes an endogenic control on the o isotope budget during the early paleozoic better isotopic and biostratigraphic constraints are still required if we are to understand the true significance of these changes we recommend that future work on ordovician isotope stratigraphy focus on this outstanding middle late ordovician event

oxygen isotope variations in phosphate of biogenic apatites iii conodonts abstract the method for measurement of the isotopic composition of oxygen in phosphates has been improved and adapted for analysis of small quantities of apatite down to 10 mg this extension enables one to analyze hand picked conodont samples with an analytical reproducibility better than 0 5 1 46 samples of conodonts ranging from the ordovician to the pennsylvanian of north america were analysed some insoluble phosphatic residues ichthyoliths and inarticulate brachiopods of the same time range were also measured the range of the 18o values of the analysed conodonts is between 15 and 19 it shows a general trend of decreasing d18o with increasing age from an average value of about 19 in the pennsylvanian to 17 in the ordovician this trend parallels that previously detected in marine phosphorites for the time range between the devonian and pennsylvanian our data are in agreement with independent paleoclimatic information specifically we detect maximum18o enrichment at the end of the pennsylvanian and minimum enrichment at the end of the devonian the difference between these two extremes is equivalent to about 10 c from about 40 to 30 c assuming constant isotopic composition of ocean water the success of oxygen isotopic analysis of conodonts raises the possibility of their use in paleozoic paleo oceanography in a similar way to foraminifera in the mesozoic cenozoic

substratum transverse faults in kuqa foreland basin northwest china and their significance in petroleum geology abstract the importance of transverse faults in basin evolution and petroleum geology has been often emphasized however the transverse faults in the kuqa foreland basin the most important gas producing area in china have rarely been studied interpreted seismic sections and earthquake focal mechanism solutions as well as other geological and geophysical data allow us to identify a few widely spaced approximately ns trending transverse strike slip faults separating major structural units and to clarify the geometry and kinematics of these transverse faults hidden below thrust faults in the kuqa foreland basin two major structural domains can be distinguished transverse faults in the northern kuqa foreland basin are mainly nne trending sinistral indicating clockwise rotation of fault bounded blocks in contrast the predominant nw trending dextral faults in the southern kuqa foreland basin imply counterclockwise rotation of fault bounded blocks we propose a tectonic model in which crustal blocks are bounded by strike slip faults in a zone of simple shear rotation about vertical axis the strike slip faulting and thrust faulting in the kuqa foreland basin suggest that some of the convergence between south tianshan and tarim blocks may have been accommodated not only by obvious crustal shortening and thickening along thrust faults but also by rotation and possible lateral movement of the crust along transverse faults controlled by the remote collision of indian block with eurasian block since the miocene these reactivated substratum faults which may inherit from paleozoic deformation control various elements relevant to gas accumulation in the kuqa foreland basin which should expect to be paid more attention in the future these elements include maturity of tertiary and jurassic source rocks a difference in the regional cap of kumugelimu salt beds from east to west reservoir bed properties gas migration channels and traps formation in addition the strike slip faulting of the transverse faults may affect deformation of the sedimentary cover including making the western qiulitag structural belt to form an arcuated structure curved to the ssw

assessment of cover collapse sinkholes in sw sardinia italy the sw part of sardinia has been afflicted in recent years by several cover collapse sinkholes mostly occurring in low density population areas the study area that lies in the iglesiente sulcis region is characterized by the cropping out of the palaeozoic basement related to the south european hercynian chain covered with tertiary quaternary sediments the main rock types that crop out are palaeozoic metasandstones metadolostones metalimestones shales and metaconglomerates and tertiary quaternary fluvial lacustrine continental sediments the combined application of several geophysical techniques integrated with boreholes and geotechnical as well as hydrogeological measurements proved to be very useful and promising in defining in detail the geological context in which each sinkhole has formed moreover the gravity method even when used alone proved to be very effective in detecting the regional geological structures to which sinkholes are related eventually the historical analysis of phenomena the geological knowledge of the iglesiente sulcis area and the results of properly designed geophysical surveys allows the most probable areas for cover collapse sinkholes to occur in the future to be determined in fact this research pointed out that the depth of the sediment covered palaeozoic bedrock is one of the major constraints in delimiting hazardous areas leading to the construction of a preliminary hazard map this map shows a belt of high risk and also suggests the areas in which further geophysical and geotechnical investigations should be carried out to estimate the depth of the bedrock cover collapse sinkholes forming on karst terrains covered with more or less loose sediments have been described from many areas of the world beck 1986 newton 1987 twidale 1987 soriano simon 1995 kaufmann quinif 1999 salvati sasowsky 2002 waltham et al 2005 these phenomena are often triggered by human intervention especially by water extraction and modifications in surface drainage patterns and are further enhanced by the increasing occurrence of extreme meteorological events similar hazards have been occurring in several areas of sw sardinia italy since the early 1990s with increasing frequency balia et al 2001 de waele muntoni 2001 one of the most interesting and impressive sinkholes formed in october 1998 in the cixerri valley at guardia su merti only 50 m away from the main railway that connects cagliari to iglesias balia et al 2001 other major sinkholes occurred 1 year later some kilometres south in an area named planu francau close to the main road from villamassargia to carbonia fadda fais 2002 de waele et al 2003 the increase in the formation of these sinkholes has led local and regional stakeholders and decision makers to consider studying these phenomena that could seriously endanger local infrastructures and human lives in the near future geological setting cover collapse sinkholes have been reported from several covered karst areas in sw sardinia near the villages of carbonia iglesias narcao sant anna arresi and villamassargia balia et al 2001 de waele muntoni 2001 fadda fais 2002 de waele et al 2003 the study area fig 1 is characterized by the outcrops of palaeozoic metasediments ranging in age from early cambrian to upper carboniferous covered with tertiary quaternary sediments and volcanic rocks from bottom to top the palaeozoic sequence is composed of metasandstones shales oolithic limestones calcareous sandstones dolostones intensely karstified limestones and shales pillola 1989 bechstadt boni 1996 carmignani et al 2001 postpalaeozoic sedimentation starts only during the lower tertiary with marly limestones marls and mudstones with coal seams of eocene age murru matteucci 2002 sedimentation continues with alluvial and lacustrine deposits composed of conglomerates and sandstones of the cixerri formation of middle eocene upper oligocene age carmignani et al 2004 immediately south of villamassargia these sediments are overlain with andesites and basaltic andesites of oligocene lower miocene age beccaluva et al 1985 from parise m gunn j eds natural and anthropogenic hazards in karst areas recognition analysis and mitigation geological society london special publications 279 47 57 doi 10 1144 sp279 5 0305 8719 07 15 00 the geological society of london 2007 fig 1 geological map of the study area and surrounding region f ardau et al 48

oxygen isotope variability in conodonts implications for reconstructing palaeozoic palaeoclimates and palaeoceanography conodonts have the potential to elucidate the intricacies of palaeozoic climates especially if 18 o values of single apatitic tooth like elements can be used to map evolving sea surface temperatures and differentiate oceanic water masses their ecological distribution as pelagic and nektobenthic organisms high resolution biostratigraphy and abundance in cambrian triassic rocks qualifies them as potentially robust climate archives previous ion microprobe conodont 18 o studies have proceeded directly to palaeotemperature interpretation without appreciation of inter and intra element variability or post mortem artefacts here ion microprobe analyses of ordovician and silurian conodonts establishes that intra element crown tissue 18 o typically varies by 1 53 of conodonts analysed is normally 2 92 of analyses and rarely varies by 2 4 18 o can vary across elements suggesting a microstructural and or diagenetic control 18 o can vary between species representatives by c 3 18 o of pelagic and nektobenthic taxa can be offset by 2 3 elements processed with formic acid have highly variable 18 o and thermal alteration does affect 18 o conodont ion microprobe 18 o values are comparable with those of bulk methods but utilization of material with no consideration of geological context or processing history may introduce significant artefacts a protocol for future conodont oxygen isotope ion microprobe studies is proposed supplementary material full results of oxygen isotope analyses reported in this paper are available at www geolsoc org uk sup18516

conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides kronprins christian land lies at the northernmost limit of the east greenland caledonides and may be divided into four main tracts foreland parautochthon thin skinned thrust sheets containing neoproterozoic sediments and thick skinned thrust sheets of crystalline basement the eastern part of the foreland and the parautochthon are composed of ordovician silurian shelf carbonates overlain by llandovery lower wenlock turbidites deposited at the southern margin of the franklinian basin deformation of the parautochthon occurred beneath a major detachment the vandredalen thrust with neoproterozoic sediments of the rivieradal group lying in the hanging wall the rivieradal group was deposited in an e facing half graben and was displaced westwards across its rift shoulders during caledonian thrusting extensive sampling for conodonts has been carried out within the lower palaeozoic rocks of the foreland and parautochthon in order to increase the precision of structural interpretations and to provide data on maximum burial temperature and in turn the thickness of overburden in contrast to earlier studies conodont colour alteration indices cai show a gradual and continuous increase from cai 3 in the eastern part of the foreland to cai 5 in the easternmost parts of the parautochthon the isopleths are not disrupted or truncated by thrusting as previously suspected indicating that the heating is not attributable to pre thrusting stratigraphic overburden furthermore considerations of the regional geology indicate that there was no significant accumulation of sedimentary overburden in post caledonian time the predominant component is thus considered to be loading by thrust sheets modelling of the overburden thickness suggests that prior to erosion it increased from 3 9 km cai 3 in the easternmost foreland to a maximum of 12 5 km beneath the vandredalen thrust sheet in the easternmost part of the area providing constraints for restoring cross sections across the orogen

oxygen isotope evolution of biogenic calcite and apatite during the middle and late devonian oxygen isotope ratios of well preserved brachiopod calcite and conodont apatite were used to reconstruct the palaeotemperature history of the middle and late devonian by assuming an oxygen isotopic composition of 1 v smow for devonian seawater the oxygen isotope values of eifelian and early givetian brachiopods and conodonts give average palaeotemperatures ranging from 22 to 25 c late givetian and frasnian palaeotemperatures calculated from 18o values of conodont apatite are close to 25 c in the early frasnian and increase to 32 c in the latest frasnian and early famennian oxygen isotope ratios of late givetian and frasnian brachiopods are significantly lower than equilibrium values calculated from conodont apatite 18o values and give unrealistically warm temperatures ranging from 30 to 40 c diagenetic recrystallization of shell calcite different habitats of conodonts and brachiopods as well as non equilibrium fractionation processes during the precipitation of brachiopod calcite cannot explain the 18o depletion of brachiopod calcite moreover the 18o depletion of brachiopod calcite with respect to equilibrium 18o values calculated from conodont apatite is too large to be explained by a change in seawater ph that might have influenced the oxygen isotopic composition of brachiopod calcite the realistic palaeotemperatures derived from 18o apatite may suggest that biogenic apatite records the oxygen isotopic composition and palaeotemperature of palaeozoic oceans more faithfully than brachiopod calcite and do not support the hypothesis that the 18o 16o ratio of devonian seawater was significantly different from that of the modern ocean

comment on cenozoic tectonic deformation and uplift of the south tian shan implications from magnetostratigraphy and balanced cross section restoration of the kuqa depression by tao zhang xiaomin fang chunhui song erwin appel and yadong wang tectonophysics 2014 doi 10 1016 j tecto 2014 04 044 abstract the recent paper entitled cenozoic tectonic deformation and uplift of the south tian shan implications from magnetostratigraphy and balanced cross section restoration of the kuqa depression by zhang et al tectonophysics 2014 doi 10 1016 j tecto 2014 04 044 discusses the cenozoic tectonic deformation and uplift of the south tianshan mountains by integrating tectonic investigations seismostratigraphic analysis and paleomagnetic dating of the thrust fold belt in the kuqa depression at the southern border of the tianshan to support their conclusions the authors have reinterpreted a high resolution magnetostratigraphic study of the kezilenuer section in a paper entitled magnetostratigraphic study of the kuche depression tarim basin and cenozoic uplift of the tian shan range western china by huang et al earth and planetary science letters volume 251 pages 346 364 2006 we note here i that apparent conflicts in definition of the xiyu formation in the kuche depression as proposed by zhang et al 2014 require amplification and ii argue that their age assignment for the kezilenuer section is incorrect and yields an anomalously low sedimentation rate for the infilling of this foreland basin

magnetostratigraphic data on neogene growth folding in the foreland basin of the southern tianshan mountains the tianshan range is one of the longest and highest mountain belts in central asia stretching east west for 2500 km uplift of this late paleozoic orogenic belt resulted from intracontinental deformation caused by the collision of the indian and eurasian plates during the cenozoic era to constrain the timing of cenozoic tectonic deformation of the tianshan range we analyzed the magnetostratigraphy of 3780 m thick neogene deposits from the kuqa foreland basin of southern tianshan the geometry measurements and magnetic fabric data show that syntectonic growth strata began to accumulate at 6 5 ma ago indicating that crustal shortening initiated in the latest miocene the increase in sedimentation rate and an abrupt change of the magnetic fabric parameters also occurred at 6 5 ma accompanied by onset of syntectonic growth strata the latest miocene crustal shortening is a signifi cant tectonic event in the foreland basin of the southern tianshan range in response to the india eurasia collision