climate warming in the latest permian and the permian triassic mass extinction high resolution oxygen isotope records document the timing and magnitude of global warming across the permian triassic p tr boundary oxygen isotope ratios measured on phosphate bound oxygen in conodont apatite from the meishan and shangsi sections south china decrease by 2 in the latest permian translating into low latitude surface water warming of 8 c the oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates suggesting that the addition of isotopically light carbon to the ocean atmosphere system by siberian traps volcanism and related processes resulted in higher greenhouse gas levels and global warming the major temperature rise started immediately before the main extinction phase with maximum and harmful temperatures documented in the latest permian meishan bed 27 the coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems in addition very warm climate conditions in the early triassic may have played a major role in the delayed recovery in the aftermath of the permian triassic crisis

spine growth and seismogenic faulting at mt unzen japan the concluding episode of activity during the recent eruption of mt unzen october 1994 to february 1995 was characterized by incremental spine extrusion accompanied by seismicity analysis of the seismic record reveals the occurrence of two dominant long period event families associated with a repeating nondestructive source mechanism which we attribute to magma failure and fault controlled ascent we obtain constraints on the slip rate and distance of faulting events within these families that analysis is complemented by an experimental thermomechanical investigation of fault friction in mt unzen dacitic dome rock using a rotary shear apparatus at variable slip rates and normal stresses a power density threshold is found at 0 3 mw m 2 above which frictional melt forms and controls the shear resistance to slip inducing a deviation from byerlee s frictional law homogenized experimentally generated pseudotachylytes have a similar final chemistry thickness and crystal content facilitating the construction of a rheological model for particle suspensions this is compared to the viscosity constrained from the experimental data to assess the viscous control on fault dynamics the onset of frictional melt formation during spine growth is constrained to depths below 300 m for an average slip event this combination of experimental data viscosity modeling and seismic analysis offers a new description of material response during conduit plug flow and spine growth showing that volcanic pseudotachylyte may commonly form and modify fault friction during faulting of dome rock this model furthers our understanding of faulting and seismicity during lava dome formation and is applicable to other eruption modes

triggering and runaway processes of catastrophic tsaoling landslide induced by the 1999 taiwan chi chi earthquake as revealed by high velocity friction experiments pliocene sedimentary rocks of about 130 mm3 in volume slid along bedding planes dipping by 14 with an average speed of about 35 m s during the tsaoling landslide we conducted friction experiments to reproduce the initiation processes of this landslide by idealizing landslide movements during the earthquake as accelerating decelerating motion experiments were done on shale from the field at 3 mpa normal stress corresponding to the overburden pressure results indicate that the accelerating decelerating motion causes weakening and strengthening at each oscillation cycle and results in overall slip weakening which can be approximated as an exponential slip weakening behaviors during oscillatory slip are fairly similar to those during sliding at constant slip rates newmark analysis with measured frictional properties reveals that the landslide can be triggered with wet gouge properties but the landslide motion stops with parameters for dry shale gouge delayed initiation of the landslide is consistent with a survivor s witness

trace and rare earth element compositions of silurian conodonts from the vesiku bone bed histological and palaeoenvironmental implications abstract in situ minor trace and rare earth element ree compositions have been measured in conodonts from the lower silurian vesiku bone bed estonia with the aim to visualize and to quantify conodont apatite elemental geochemistry to evaluate compositional differences between conodont histologies and to evaluate the use of conodont chemistry as a palaeobiological or palaeoenvironmental proxy tissue selective analyses of minor trace and rare earth element compositions of albid hyaline and basal tissues demonstrated significant chemical offsets among these histologies the albid tissue had the lowest ree and trace element concentrations suggesting crystallinity determined better resilience to diagenetic alteration as documented in previous studies conversely the basal tissue had highest concentrations of rees and many trace elements except for sr that showed an opposite trend the higher concentrations in albid and hyaline tissues supports the in vivo sr incorporation by conodont crown nonetheless the obtained sn normalized ree patterns were uniform through all the analyzed conodont taxa and different tissues implying common diagenetic history absence of a ce anomaly and defined negative eu anomaly indicate reducing conditions during early burial these results validate current interpretations of the palaeoenvironmental conditions during the deposition of vesiku bone bed and bolsters the use of rees in palaeozoic marine vertebrates as an important palaeoenvironmental proxy

frictional sliding of dolomite a variation in constitutive behavior fault slip occurs via earthquakes or stable creep depending on the manner in which frictional resistance varies with sliding velocity and displacement if the form of this dependence is a function of rock type observed spatial variations in slip behavior along faults could be explained by lithologic variation we have used a rotary shear apparatus to investigate the frictional response of dolomite marble to changes in sliding velocity we have modeled the results using a state variable constitutive law for rock friction and a numerical method to solve for the interaction between the friction law and the compliance of our machine dolomite marble displays steady state velocity strengthening as contrasted with granite and quartzite which show velocity weakening at the same conditions to model the dolomite results it is necessary to use two state variables and surprisingly the parameters specifying the decay magnitudes associated with these state variables differ in sign from each other the magnitude of the parameter associated with the longer decay is negative leading to a downward decay of frictional strength associated with a decrease in velocity if the shorter decay is of sufficient magnitude as we observe at low velocity it is possible for the machine rock system to exhibit instability and oscillatory behavior even though the steady state response is velocity strengthening another way in which dolomite contrasts with granite and quartzite is that the friction parameters vary strongly with velocity a transition from unstable to stable sliding with increasing velocity has been observed previously and our observed variation of the constitutive parameters with velocity can explain this behavior there is some indication that the evolution of the state variables for dolomite occurs as a function of time rather than displacement in contrast with granite and quartzite the frictional behavior of dolomite shows that the constitutive laws that have been developed based on results from granite and quartzite are inadequate to describe all rock types and that more general laws are required

assessing the fidelity of marine vertebrate microfossil δ18o signatures and their potential for palaeo ecological and climatic reconstructions abstract conodont biogenic apatite has become a preferred analytical target for oxygen isotope studies investigating ocean temperature and palaeoclimate changes in the palaeozoic despite the growing application in geochemically based palaeoenvironmental reconstructions the paucity or absence of conodont fossils in certain facies necessitates greater flexibility in selection of robust oxygen bearing compounds for analysis vertebrate microfossils teeth dermal denticles spines offer a potential substitute for conodonts from the middle palaeozoic vertebrate bioapatite is particularly advantageous given a fossil record extending to the present with representatives across freshwater to fully marine environments thus widening the scope of oxygen isotope studies on bioapatite however significant tissue heterogeneity within vertebrates and differential susceptibility of these tissues to diagenetic alteration have been raised as potential problems affecting the reliability of the oxygen isotope ratios as palaeoclimatic proxies well preserved vertebrate microfossils and co occurring conodont fossils from the upper devonian and lower carboniferous of the lennard shelf canning basin western australia were analysed using bulk gas isotope ratio mass spectrometry girms and in situ secondary ion mass spectrometry sims methodologies with the latter technique allowing investigation of specific tissues within vertebrate elements the 18oconodont results may be interpreted in terms of palaeolatitudinally and environmentally sensible palaeo salinity and temperature and provide a baseline standard for comparison against vertebrate microfossil 18o values despite an absence of obvious diagenetic modification girms of vertebrate denticles yielded 18o values depleted in 18o by 2 4 relative to co occurring conodonts sims analysis of dentine tissues exhibited significant heterogeneity while hypermineralised tissues in both scales and teeth produced 18o values comparable with those of associated conodonts the susceptibility of permeable phosphatic fossil tissues to microbial activity fluid interaction and introduction of mineral precipitates post formation is demonstrated in the dentine of vertebrate microfossils which showed significant heterogeneity and consistent depletion in 18o relative to conodonts the hypermineralised tissues present in both teeth and scales appear resistant to many diagenetic processes and indicate potential for palaeoclimatic reconstructions and palaeoecological investigations

thermal maturity of carbonaceous material in conodonts and the color alteration index independently identifying maximum temperature with raman spectroscopy abstract the color alteration index cai of conodont specimens is commonly used for identifying the maximum temperature to which units of sedimentary rock particularly carbonates have been heated observable color variations in these fossils are thought to be a result of the thermally induced structural evolution of organic carbonaceous matter cm such temperature history information is extremely valuable for applications in hydrocarbon exploration as well as for constraining other temperature related geological processes in sedimentary systems however the identification of cai depends on the qualitative visual assessment of color which along with a host of other potential complications may yield inaccurate determinations of maximum temperature raman spectroscopy allows thermally induced structural changes in cm to be quantified and it has been used to estimate the thermal maturity in metasedimentary rocks for almost two decades here we use raman spectroscopy of carbonaceous material rscm in conodont specimens and their mississippian to upper triassic host rocks from british columbia canada to estimate maximum temperatures based on the transformation structural reorganization of disordered carbon to graphite this study demonstrates that the maximum temperatures experienced by conodont specimens as calculated from rscm using the iterative fitting of raman spectra ifors technique correlate well with cai but lie outside the suggested ranges in some instances this may be due to complex thermal histories of these conodont specimens or the influence of diagenetic alteration not thermal histories on conodont color we recommend the application of raman spectroscopic analyses of cm in conodonts and their host rocks to obtain more confident accurate and precise estimations of maximum temperature that are independent of cai

diagenetic alteration of the structure and δ18o signature of palaeozoic fish and conodont apatite potential use for corrected isotope signatures in palaeoenvironmental interpretation abstract the oxygen isotopic compositions of carboniferous conodonts and fish microfossils ichthyoliths from identical samples were analysed in tandem in order to test whether these phosphatic media can be reliably used for palaeoclimatic reconstruction the structure of conodonts and of most ichthyoliths analysed are somewhat analogous to the enamel and dentine bone tissue respectively of modern mammals therefore the diagenetic susceptibilities of the taxa analysed may provide important clues to other palaeoclimatic studies utilising a variety of biogenic apatite thermal maturation indices and scanning electron microscopy were used to characterise the preservation of biogenic apatite despite a high conodont colour alteration index cai of 5 5 conodont elements appear to have been only mildly affected by diagenetic alteration in contrast ichthyoliths were commonly recrystallised and exhibited diagenetic apatitic overgrowths containing amorphous pyrolytic carbon interpreted as indicating that at least some overgrowth material derived from the original biogenic apatite diagenetic alteration has resulted in ichthyolith 18 o values being systematically lower by on average 2 9 1 0 3 relative to conodont apatite conodont samples yielded regionally correlatable isotope values which can be interpreted in terms of more palaeoenvironmentally sensible palaeotemperatures relative to ichthyolith values densely crystalline enamel like conodont elements are interpreted as the more robust phosphatic medium to preserve original isotopic compositions the strong correlation r 0 8 of the 18 o values of the more structurally pristine conodont and commonly recrystallised ichthyolith apatite indicates that i despite diagenetic lowering of absolute isotope values original palaeoenvironmental records may be preserved and ii diagenetic overprinting may result in a stable offset and therefore be correctable locally

nd isotope composition of conodonts an accurate proxy of sea level fluctuations abstract analyses of the nd isotope composition of conodonts from the anti atlas morocco the montagne noire france and the rhenohercynian domain germany provide insight into the temporal and lateral variations in seawater geochemistry in the western part of the variscan sea during the late devonian most of the isotopic excursions accurately record changes in sea level the end values decreased during regression phases when erosion accelerated supply of unradiogenic nd from old continental sources a rise in sea level generated a positive shift in end values due to input of more radiogenic oceanic water into the seawater reservoir of the shelf areas the method has great potential for sea level research paleoceanography and correlation because sea level changes can be precisely recognized even in successions with uniform monotonous lithologies however it has a significant limitation being valid only in epeiric seas and shelf areas we have used the nd isotope record to reconstruct the eustatic sea level changes in late frasnian early famennian time the onset of the organic rich kellwasser units coincides with negative trends in end values this accords with oxygen deficiency at the sea bottom being initiated by short term regressive events which in turn would be consistent with cooling periods of glacial origin as previous authors have suggested

fault roughness at seismogenic depths from lidar and photogrammetric analysis fault surface roughness is a principal factor influencing earthquake mechanics and particularly rupture initiation propagation and arrest however little data currently exist on fault surfaces at seismogenic depths here we investigate the roughness of slip surfaces from the seismogenic strike slip gole larghe fault zone exhumed from ca 10 km depth the fault zone exploited pre existing joints and is hosted in granitoid rocks of the adamello batholith italian alps individual seismogenic slip surfaces generally show a first phase of cataclasite production and a second phase with beautifully preserved pseudotachylytes of variable thickness we determined the geometry of fault traces over almost five orders of magnitude using terrestrial laser scanning lidar ca 500 to 1 10 m is not anisotropic and less evolved than at smaller scales these observations are consistent with an evolution of roughness due to fault surface processes that takes place only at scales smaller or comparable to the observed net slip differences in roughness evolution between shallow and deeper faults the latter showing evidences of seismic activity are interpreted as the result of different weakening versus induration processes which also result in localization versus delocalization of deformation in the fault zone from a methodological point of view the technique used here is advantageous over direct measurements of exposed fault surfaces in that it preserves in cross section all of the structures which contribute to fault roughness and removes any subjectivity introduced by the need to distinguish roughness of original slip surfaces from roughness induced by secondary weathering processes moreover offsets can be measured by means of suitable markers and fault rocks are preserved hence their thickness composition and structural features can be characterised providing an integrated dataset which sheds new light on mechanisms of roughness evolution with slip and concomitant fault rock production

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

fracture surface energy of the punchbowl fault san andreas system the energetics of earthquake rupture slip weakening and rupture surface formation are poorly understood by measuring the energy associated with fracture damage along the punchbowl fault in the devil s punchbowl los angeles county park part of the san andreas system chester et al show that the fracture surface energy for rupture along a mature fault of this type accounts for only a small fraction of the energy released during large earthquakes as determined by seismologists this suggests that mechanisms such as melt lubrication and thermal pressurization are responsible for slip weakening fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening1 2 3 fracture energy has been estimated from seismological and experimental rock deformation data4 5 6 7 8 yet its magnitude mechanisms of rupture surface formation and processes leading to slip weakening are not well defined8 9 10 here we quantify structural observations of the punchbowl fault a large displacement exhumed fault11 12 in the san andreas fault system and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake if fracture energy is attributed entirely to the production of fracture surfaces then all of the fracture surface area in the punchbowl fault could have been produced by earthquake displacements totalling 1 km but this would only account for a small fraction of the total energy budget and therefore additional processes probably contributed to slip weakening during earthquake rupture

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

low frictional strength of quartz rocks at subseismic slip rates 1 laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0 6 0 85 here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of room dry quartz rocks at rates faster than in most laboratory experiments but slower than seismic slip rates in some cases the friction coefficient decreases from low speed values by more than a factor of 3 this extraordinary weakening likely results from the formation of finely comminuted amorphous wet material on the sliding surface

flow in natural shear zones the consequences of spinning flow regimes abstract the ancient flow regime in natural shear zones is often considered to have followed a deformation path comparable to that in theoretical shear zones i e progressive simple shear between rigid wall rocks with a persistent flow plane orientation parallel to the edges of the zone this is often based on the presence of monoclinic fabric elements in the zones which indicate a dominantly non coaxial flow regime though not necessarily persistent simple shear the deformation fabric of a shear zone from the pyrenees illustrates that even at a kinematic vorticity number of w 1 simple shear along the entire deformation path obliqueness of the flow planes with the edges of the zone is possible for some time if incremental stretching axes were rotating with respect to zone edges this implies that ductile deformation must have taken place in the wall rock of the zone such a flow regime may be difficult to recognize with the fabric criteria used at present but leads to an unusual kinematic significance of the shear zone involved in extreme cases the zone may have acted as a passive marker in a ductilely deforming medium it also means that not only w must be known to reconstruct the ancient flow regime in natural shear zones but at least also the time dependence of the orientation of the incremental stretching axes

frictional strength and wear rate of carbonate faults during high velocity steady state sliding article history we ran an extensive series of shear experiments to test the effect of shear velocity and normal stress on wear rate and frictional strength the experiments were conducted on three types of carbonate samples with a rotary shear apparatus on solid ring shaped rock samples that slipped for displacements up to tens of meters at slip velocity of v 0 002 0 96 m s and normal stress n 0 25 6 9m pa the analysis reveals that during steady state stage the values of wear rate and frictional strength depend on both slip velocity and normal stress the wear rates at low slip velocity show linear relations to the normal stress archard s model however at high velocity v 0 5m s the wear rates are independent of the normal stress and may vanish at the highest velocity and normal stress of the present experiments the steady state friction coefficient correlates best with the experimental power density shear stress slip velocity we recognized three friction regimes high 0 8a t low power density low 0 3 at high power density and a transition regime of fast drop of friction coefficient as the power density increases from 0 03 to 0 3 mw m 2 runs of low power density high friction displayed fault surfaces covered with fine grained gouge whereas runs of high power density low friction displayed shiny smooth fault surfaces we interpret the observed intensity variations of wear rate and frictional strength as indicating a brittle to ductile transition associated with frictional heating

experimental rock on rock frictional wear application to subglacial abrasion 1 rock on rock wear under known normal loads was measured experimentally using 62 mm diameter rotating discs machined from a range of silicic rock types one granite two metamorphic rocks and three sandstones of porosities varying between 7 and 28 wear debris was removed continuously from the contacting surfaces by water we obtained a wear law of the form dt dx a n m where is contact normal stress mpa dt dx is a dimensionless wear rate meter wear t per meter shear displacement x is porosity and a n and m are empirical constants 10 8 11 8 33 and 4 50 respectively low porosity rocks displayed surface polishing and abraded particle size was substantially smaller than the starting grain size whole grains were plucked from high porosity rocks without any surface polishing so that the wear product particle size remained the same as that of the starting material the empirical wear law describes abrasion beneath a hard bedded temperate glacier provided we can estimate both the in situ normal stress between entrained clasts and the bed and the horizontal velocity of the clasts in the flowing ice normal stress concentration is expected to develop at clast bed contacts from drag against ice flowing toward the bed where pressure melting occurs these experimental data are consistent with wear rates inferred from silt outflow in subglacial streams provided a tenfold stress concentration can occur relative to the ice overburden pressure the rate of production of fine grained wear products under subglacial conditions is substantially less than by tectonic faulting

the effect of diagenesis on oxygen isotope ratios of biogenic phosphates the effect of diagenesis on the oxygen isotope composition of ancient biogenic phosphates was evaluated by measuring different types of material from middle triassic localities in the southern alps dentin bone and tooth enamel of different taxa hosted by different rock types and metamorphosed to differing degrees were analyzed for their 18 o and 13 c values using a new microanalytical gc irmms technique the 18 o values of the majority of bone and bulk tooth samples were 18 to 19 permil smow with three samples below this range and one close to 20 permil in contrast samples of tooth enamel were 19 4 to 20 7 permil significantly higher than bone and bulk tooth without the enamel data the 18 to 19 permil data could be misinterpreted as primary only when the higher 18 o values of the enamel are considered is it apparent that the bulk data have undergone diagenesis and temperature estimates are 5 c lower than would otherwise be calculated alteration of bulk tooth is also seen in a miocene shark tooth where 18 o values of enamel are 3 permil higher than those of bulk tooth although enamel is routinely analyzed for paleoclimate work of herbivorous mammals bulk bone teeth or shells are almost exclusively used for older marine samples the results of the present study indicate that bulk data should be treated with caution

δ18o values of mudrocks more evidence for an 18o buffered ocean abstract the whole rock 18 o of mudrocks as well as the 18 o of the clay sized silicate fraction does not change in any systematic manner over paleozoic and late proterozoic time therefore the 18 o of the ocean has not changed except a per mil or so as the result of glaciation deglaciation over the last billion years of earth history

organic maturation levels thermal history and hydrocarbon source rock potential of the namurian rocks of the clare basin ireland abstract vitrinite reflectance data from two inland cored boreholes confirm high maturation levels throughout the onshore part of the irish clare basin and suggest erosion of 2 to 4 km of late carboniferous cover and elevated palaeogeothermal gradients in the carboniferous section the observed maturation gradients are fully consistent with the published hypothesis of a late carboniferous permian superplume beneath pangaea but local vertical reversals in gradients also suggest a complex thermal regime probably involving advective heating the uppermost visean lower namurian clare shale is laterally extensive and up to 300 m thick although this unit is post mature toc values of up to 15 suggest that it could have considerable hydrocarbon source rock potential in any less mature offshore parts of the basin

the eigenvalues of steady flow in mohr space abstract the eigenvalues of the velocity gradients tensor and of the position gradients tensor describing instantaneous flow or incremental deformations are easily determined in mohr space as the points of intersection between a mohr circle and the horizontal mohr axis intersections occur only if the tensor has real eigenvalues eigenvectors associated with the eigenvalues are directions of no rotation a line of material particles under an eigenvector does not rotate during steady flow although the line is instantaneously stretching at a rate equal to its corresponding eigenvalue for non spinning steady sub simple shearing there will always be two eigenvectors the angle between the eigenvectors is dependent on the ratio of pure to simple shearing rates this angle decreases as the pure shearing component decreases relative to the simple shearing component superimposed increments of pure shear and simple shear produce an equivalent set of non rotated material lines but the deformation histories of these lines are rotational the influence of eigendirections on geological structures is constrained by the rheology of a rock during deformation in homogenous steady flow no influence may be obvious spatially periodic material softening along eigenvectors during bulk hardening may result in a complex fabric of intersecting shear zones the geometry of the fabric elements provides important information on the bulk deformation of the rock particularly on the bulk shear sense

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

determination of position gradient tensor from strain measurements and its implications for the displacement across a shear zone abstract a method is proposed for determination of the position gradient tensor from conventional strain measurements the position gradient tensor can be multiplicatively decomposed into two components left stretch and rotation tensors the former is readily supplied by field strain data whereas the latter is generally unknown in nature in order to determine the position gradient tensor using strain data it is assumed that structures within a shear zone are symmetric about the plane common to the transport direction and the pole to the shear zone or alternatively that the shear strain in the direction parallel to the pole to the shear zone on the plane normal to the transport direction in a parallel sided shear zone is negligible with these assumptions the position gradient tensor is fully determined from the attitude and principal ratios of the strain ellipsoid determined from field data this method has been applied to the strain data from deformed fragments in a succession of late triassic volcanic breccias abutting a large strike slip shear zone in north central british columbia the resulting position gradient tensor is then used to constrain the displacement across the shear zone suggesting 39 shortening normal to and dextral displacement of about 1700 m along the shear zone

isotopic composition of recent shark teeth as a proxy for environmental conditions abstract the o c and sr isotope compositions of teeth from ten species belonging to five families and three orders of sharks were measured to determine the influence of habitat diet and possible species specific fractionation effects on the isotopic composition of biogenic phosphate from fish the sharks were recently caught in subtropical waters off the kwazulu natal kzn coast of south africa as well as from cold waters in prince william sound pws alaska and victor bay vb nunavut canada 18 o values of tooth phosphate 18 o p range from 20 9 to 23 5 for the kzn sharks for most species the range in measured 18 o p values is about 0 6 but it may be as high as 1 1 for different teeth from a single shark dentine and enameloid within individual teeth have no apparent differences in 18 o p values the 18 o p values of the kzn shark teeth reflect the typical habitat of the studied species primarily the thermal structure of the water column off kzn at depths between 20 and 280 m the 18 o p values of teeth from different greenland sharks from vb and pacific sleeper sharks from pws are very homogeneous averaging 25 8 and 24 7 respectively these values appear to be in equilibrium with deep 500 m ocean waters in each case at temperatures of about 0 3 c or less there is little discernable evidence for species specific fractionation effects for the oxygen isotope composition of phosphate in the studied marine fish the oxygen isotope composition of carbonate in apatite averages about 9 1 higher than corresponding 18 o p values in agreement with equilibrium fractionation between carbonate and phosphate but with a large variance 1 1 5 18 o c values also vary by up to 1 between enameloid and dentine within single teeth but in a non systematic way differences in 13 c values between carbonate in enameloid and dentine is also large up to 8 but the 13 c values vary systematically enameloid is always enriched in 13 c compared to dentine and the 13 c content increases with developmental stage of the teeth 13 c values measured for enameloid 1 6 to 4 8 appear to approach equilibrium with dissolved inorganic carbon in seawater in contrast 13 c values for dentine range from 6 4 to 2 3 for kzn sharks and 9 0 to 10 8 for the cold water sleeper sharks and are compatible with a predominantly dietary carbon source the 87 sr 86 sr ratios of teeth from kzn sharks as well as those from pws and vb are uniform averaging 0 709167 sr content varies from 1270 to 2100 ppm a range that is similar to that in well preserved fossilized teeth seawater sr is thus clearly incorporated in vivo concentrations of sm and nd are in the ppb range and contrast the ppm range in fossilized teeth indicating a postmortem incorporation of rare earth elements in apatite of the teeth

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

energy partitioning during seismic slip in pseudotachylyte bearing faults gole larghe fault adamello italy thedeterminationoftheearthquakeenergybudgetremainsachallengingissueforearthscientists asunderstandingthepartitioningofenergyisa keytowardsthe understandingthe physicsofearthquakes here weestimatethe partitionofthe mechanical workdensity intoheatandsurfaceenergy energyrequiredtocreatenewfracturesurface duringseismicsliponalocationalongafault earthquakeenergypartitioningisdeterminedfromfield and microstructural analyses of a fault segment decorated by pseudotachylyte solidified friction induced melt produced during seismic slip exhumed from a depth of 10 km typical for earthquake hypocenters in the continental crust frictional heat per unit fault area estimated from the thickness of pseudotachylytes is 27 mj m 2 surface energy estimated from microcrack density inside clast i e cracked grains entrapped in the pseudotachylyte and in the fault wall rock ranges between 0 10 and 0 85 mj m 2 our estimates for the studied fault segment suggest that 97 99 of the energy was dissipated as heat during seismic slip we conclude that at 10 km depth less than 3 of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture 2008 elsevier b v all rights reserved

chemical diagenesis of a multicomponent carbonate system 2 stable isotopes abstract this study examines the oxygen and carbon isotopic distribution in the brachiopods crinoids rugose corals and matrix cement from the mississippian burlington limestone iowa and missouri and the silurian read bay formation arctic canada the isotopic data can be reconciled with textural and trace element observations only if the 18o content of ancient oceans differed from that of the present oceans this postulated secular variation in the 18o content of seawater requires a separate evaluation of the mississippian and silurian carbonate components examination of the 18o content of the least altered low mg calcite fossil components of the two formations suggests that the 18o of mississippian seawater was on average about 1 5 lighter and that of silurian seawater was about 5 5 lighter than the 18o of present day ocean water the average diagenetic shift in 18o for the read bay formation which stabilized in a partly closed diagenetic phreatic meteoric system is about 1 for the original low mg calcite and about 2 for the original high mg calcite and aragonite components conversely for the burlington limestone which stabilized in an open diagenetic phreatic meteoric system the average diagenetic shift in 18o is about 3 for the original low mg calcite and about 4 f r the original high mg calcite components the 13c values of the originally low mg calcite or high mg calcite with less than 7 mole mgco3 brachiopods and rugose corals the originally high mg calcite crinoids and the originally aragonite lime mud of the burlington limestone and read bay formation are bimodally distributed this bimodal 13c distribution is independent of geologic age inferred original mineralogy of the component degree of diagenetic alteration and the type of diagenetic meteoric system with components from both the read bay formation and burlington limestone contributing to both 13c groups the mode of the light 13c group is 0 25 and for the heavy 13c group it is 3 25 pdb both 13c groups also show a decrease in 13c of about 1 with increasing diagenetic alteration stabilization

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

conodont alteration and tectonothermal evolution of a diagenetic unit in the iberian variscan belt ponga cuera unit nw spain tectonothermal analysis of a mainly carbonate unit located in the external part of the variscan orogen in nw spain is dealt with using the conodont colour alteration index cai and the study of textures of these microfossils the kubler index of the illite ki is used as a complementary method the area is characterized by a great uniformity in the cai values which in most cases are

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

fish tooth δ18o revising late cretaceous meridional upper ocean water temperature gradients the oxygen isotope composition of fossil fi sh teeth a paleo upper ocean temperature proxy exceptionally resistant to diagenetic alteration provides new insight on the evolution of the low to middlelatitude thermal gradient between the middle cretaceous climatic optimum and the cooler latest cretaceous period the new middle cretaceous low to middle latitude thermal gradient agrees with that previously inferred from planktonic foraminifera 18o recovered from deep sea drilling project and ocean drilling program drilling sites although the isotopic temperatures derived from 18o of fish teeth are uniformly higher by 3 4 c in contrast our new latest cretaceous thermal gradient is markedly steeper than those previously published for this period fish tooth 18o data demonstrate that low to middle latitude thermal gradients of the middle cretaceous climatic optimum and of the cooler latest cretaceous are similar to the modern one despite a cooling of 7 c between the two periods our new results imply that no drastic changes in meridional heat transport are required to explain the late cretaceous climate based on climate models such a cooling without any change in the low to middle latitude thermal gradient supports an atmospheric co2 decrease as the primary driver of the climatic evolution recorded during the late cretaceous

growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting 1 to understand how frictional melting affects fault instability we performed a series of high velocity friction experiments on gabbro at slip rates of 0 85 1 49 m s 1 at normal stresses of 1 2 2 4 mpa and with displacements up to 124 m experiments have revealed two stages of slip weakening one following the initial slip and the other immediately after the second peak friction the first weakening is associated with flash heating and the second weakening is due to the formation and growth of a molten layer along a simulated fault the two stages of weakening are separated by a marked strengthening regime in which melt patches grow into a thin continuous molten layer at the second peak friction the frictional coefficient decays exponentially from 0 8 1 1 to 0 6 during the second weakening the host rocks are separated completely by a molten layer during this weakening so that the shear resistance is determined by the gross viscosity and shear strain rate of the molten layer melt viscosity increases notably soon after a molten layer forms however a fault weakens despite the increase in melt viscosity and the second weakening is caused by the growth of molten layer resulting in the reduction in shear strain rate of the molten layer very thin melt cannot be squeezed out easily from a fault zone so that the rate of melting would be the most critical factor in controlling the slip weakening distance effect of frictional melting on fault motion can be predicted by solving a stefan problem dealing with moving host rock molten zone boundaries

conodont apatite δ88 86sr and δ44 40ca compositions and implications for the evolution of palaeozoic to early mesozoic seawater abstract we present high precision tims double spike stable isotope measurements of both 44 40 ca and 88 86 sr together with radiogenic 87 sr 86 sr ratios determined from conodont apatite these data represent five intervals ranging from the early ordovician to late triassic the conodont 44 40 ca values relative to nist 915a range from 0 47 to 0 15 with an apparent shift to more positive values between the early silurian and late devonian early carboniferous similar to the brachiopod based marine 44 40 ca record farkas et al 2007a we calculated a 44 40 ca seawater bio apatite fractionation factor of about 1 9 which allowed us to reconstruct a palaeo seawater 44 40 ca record from bio apatites despite a slightly positive offset of about 0 2 to 0 5 the 44 40 ca record obtained from bio apatites is consistent with the previously reported 44 40 ca seawater record inferred from carbonates we find that unlike the carbonate 44 40 ca records the 88 86 sr measurements from conodont apatite show unexpectedly large variations up to 1 with ratios ranging from 0 6 to 0 3 these reconnaissance data reveal a reasonable correlation between 88 86 sr and radiogenic 87 sr 86 sr r 2 0 60 n 13 p 0 002 suggesting that the controls from differential weathering regimes and or continental crustal compositions buffered ancient seawater compositions

deformation of mafic schists from subducted oceanic crust at high pressure and temperature conditions abstract we conducted triaxial deformation experiments using a griggs type solid pressure medium apparatus on two mafic schists that experienced different peak metamorphic conditions from the sambagawa metamorphic belt a greenschist and an epidote amphibole schist at a confining pressure of 1 gpa 400 c and strain rate of 10 5 1 s differential stresses for all mafic schists were higher than 1 gpa the greenschist samples were weaker than epidote amphibolite samples under all experimental conditions microstructures of recovered samples of greenschist indicate that deformation of mafic schist is accommodated by semi brittle deformation samples of the epidote amphibole schist deformed at 500 c show shear localization along a single fault oriented parallel to the foliation while mechanical data shows no rapid stress drop on the surface of the fault we observe the formation of slickensides with little gouge all sample types exhibit a high stress exponent n 15 and strain rate strengthening i e positive a b values frictional behavior that inhibits earthquake nucleation differential stress increased with increasing confining pressure while the friction coefficient decreased with increasing confining pressure and temperature greenschist and epidote amphibolite facies metamorphism typically occurs at hot subduction zones such as cascadia and southwest japan the lack of seismicity within the subducting oceanic crust at hot subduction zones could be explained by semi brittle deformation or frictional sliding with a positive a b during deformation of these types of metamorphic rocks weak and aseismic fault zones in subducting slabs might promote slab mantle decoupling at the corner of the mantle wedge and detachment and underplating of oceanic crust from the subducting slab to forearc crust

disappearing ink how pseudotachylytes are lost from the rock record abstract melt origin pseudotachylytes are the most widely accepted feature recording earthquake slip in the fault rock record however reports of pseudotachylytes are rare compared to the frequency and distribution of earthquakes in active faults suggesting melting occurs only under exceptional circumstances and therefore that pseudotachylytes are rarely formed in this paper we document the processes whereby pseudotachylytes are overprinted destroyed and otherwise removed from the rock record we present examples of recrystallized altered and cataclastically and crystal plastically deformed pseudotachylytes from a variety of ancient faults based on these observations we identify characteristics of pseudotachylytes that are resistant to change over geologic time and develop criteria to allow recognition of relict pseudotachylytes our results imply that pseudotachylytes are vastly under reported due to their vulnerability to destruction and the resulting difficulty in identification as a consequence the significance of frictional melting is underestimated the criteria we propose to distinguish relict pseudotachylytes can help to reconcile the observed frequency of earthquakes with the difficulty of demonstrating ancient seismic slip in the rock record

amorphous material formed by the mechanochemical effect in natural pseudotachylyte of crushing origin a case study of the iida matsukawa fault nagano prefecture central japan abstract pseudotachylytes from the iida matsukawa fault central japan iida pseudotachylytes are described down to the nanometer scale using high resolution electron microscopy scanning electron microscopy analyses of chemical compositions and mercury intrusion porosimetry the pseudotachylyte matrix chiefly consists of nanoscale particles and elongated submicron fragments with biotite composition amorphous material of several tens of nanometers in size is also observed despite the absence of melt textures lattice fringe images reveal that the amorphous phase coexists with lattice distortion in deformed biotite fragments that are several hundreds of nanometers in size the presence of these submicrostructures indicates that the amorphous material formed by mechanical stress during the comminution process that is via the mechanochemical effect we conclude that amorphous material does not always provide evidence of the rapid cooling of melt in pseudotachylyte the amorphous materials present in the iida pseudotachylyte resulted from the mechanochemical effect due to both shear stress and normal stress during the comminution process that accompanied fault motion

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

wear processes in rocks at slow to high slip rates abstract frictional wear experiments are performed on diorite granite and sandstone at sliding velocities of 0 004 0 27 m s under normal stresses of 0 21 6 3 mpa using a rotary shear apparatus to establish velocity dependent wear laws of rocks and to determine the partition of frictional work used for gouge generation power laws between normal shear stresses and steady state wear rate defined as thickness of gouge formed fault displacement account for our data for diorite and granite at low velocities and most experimental data on wear of rocks reported in the literature but an exponential law holds for wear of diorite at velocities greater than 0 11 m s and its wear rate increases dramatically at seismic slip rates a change from the power law to the exponential law seems to be caused by frictional heating and thermal fracturing both power and exponential laws can describe data for granite sandstones exhibit complex wear behavior possibly due to development of shiny slickenside surface that suppresses wear our data for diorite indicate that at the investigated normal stresses only 0 004 of frictional work is consumed for gouge formation at velocities less than 0 11 m s but this fraction increases markedly with increasing velocity energy partition for gouge formation is not constant and changes with velocity during earthquakes

frictional behavior of granite at low and high sliding velocities to study how the velocity dependence of steady state friction of granite varies as a function of sliding rate we slid initially bare surfaces of westerly granite at rates of from 0 001 m s 32 mm yr to over 3 mm s accumulating 376 mm of total displacement the normal stress was 50 mpa we find that the velocity dependence measured by a b changes from negative velocity weakening at 32 m s modeling of experimental data using a simple constitutive law shows that the magnitude of a the direct dependence of friction on velocity remains nearly constant at all rates up to at least 100 m s the increase in a b with velocity is due to a reduction in the magnitude of b our results are consistent with the view that a measures the deformation rate sensitivity of the fault zone material and that b measures the amount of change of some fault zone property

evolution of wear and friction along experimental faults we investigate the evolution of wear and friction along experimental faults composed of solid rock blocks this evolution is analyzed through shear experiments along five rock types and the experiments were conducted in a rotary apparatus at slip velocities of 0 002 0 97 m s slip distances from a few millimeters to tens of meters and normal stress of 0 25 6 9 mpa the wear and friction measurements and fault surface observations revealed three evolution phases a an initial stage slip distances 50 mm of wear by failure of isolated asperities associated with roughening of the fault surface b a running in stage of slip distances of 1 3 m with intense wear rate failure of many asperities and simultaneous reduction of the friction coefficient and wear rate and c a steady state stage that initiates when the fault surface is covered by a gouge layer and during which both wear rate and friction coefficient maintain quasi constant low levels while these evolution stages are clearly recognizable for experimental faults made from bare rock blocks our analysis suggests that natural faults bypass the first two stages and slip at gouge controlled steady state conditions

transient water adsorption on newly formed fault gouge and its relation to frictional heating determination of the amount of frictional heating on faults during slips provides insight into the mechanics of faulting fault slips cause frictional heating as well as production of gouge materials newly formed gouge is mechanochemically stimulated to gain a transient water adsorption ability we showed that the synthetic gouge from friction tests on rocks at a 1 mm s slip rate without frictional heating adsorbed a large amount of water comparable to that adsorbed by clay minerals the amount of adsorbed water decreased significantly with increasing slip rate to 100 mm s where the fault temperature increased above 400 c we confirmed there was no additional adsorption on the heated gouges after termination of the slip we conclude that the adsorption state can be considered a new indicator of a temperature rise of 400 c by frictional heating associated with recent near surface faulting

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

raman spectral elemental crystallinity and oxygen isotope variations in conodont apatite during diagenesis abstract conodont apatite has long been used in paleoenvironmental studies often with minimal evaluation of the influence of diagenesis on measured elemental and isotopic signals in this study we evaluate diagenetic influences on conodonts using an integrated set of analytical techniques a total of 92 points in 19 coniform conodonts from ordovician marine units of south china were analyzed by micro laser raman spectroscopy m lrs laser ablation inductively coupled plasma mass spectrometry la icp ms high resolution x ray microdiffraction hxrd and secondary ion mass spectrometry sims each conodont element was analyzed along its full length including the albid crown hyaline crown and basal body in either a whole specimen i e reflecting the composition of its outer layer or a split specimen i e reflecting the composition of its interior in the conodonts of this study the outer surfaces consist of hydroxyfluorapatite and the interiors of strontian hydroxyfluorapatite ionic substitutions resulted in characteristic raman spectral shifts in the position ss1 and width ss2 of the 1 po43 stretching band although multiple elements were enriched sr2 mg2 and depleted fe3 mn2 ca2 during diagenesis geochemical modeling constraints and known raman spectral patterns suggest that sr uptake was the dominant influence on diagenetic redshifts of ss1 all study specimens show lower ss2 values than modern bioapatite and synthetic apatite suggesting that band width decreases with time in ancient bioapatite possibly through an annealing process that produces larger more uniform crystal domains most specimens consist mainly of amorphous or poorly crystalline apatite which is inferred to represent the original microstructure of conodonts in a subset of specimens some tissues especially albid crown exhibit an increased degree of crystallinity developed through aggrading neomorphism however no systematic relationship was observed between crystallinity and raman spectral or elemental parameters oxygen isotopes show substantial variation within the conodont study specimens albid crown is on average 0 28 0 32 more depleted in 18o equivalent to 1 2 1 4 c higher temperatures than hyaline crown and basal body and the interiors of conodont elements are 1 08 0 37 more depleted in 18o equivalent to 3 0 6 4 c higher temperatures relative to their outer layers although albid crown is widely regarded as better preserved than other conodont tissue types its 18o depleted composition and greater development of secondary crystallinity suggest that in fact it may be the most strongly altered tissue type we conclude that raman spectral la elemental and hxrd microstructural data can provide useful information about the extent of diagenetic alteration of conodont elements and that such information should be taken into consideration in using conodont elemental and oxygen isotope data in paleoenvironmental studies

the sliding scale mohr diagram abstract mohr diagrams for the position gradient tensor are a useful tool in problems of finite deformation for example to determine the angle between deformed lines and the angle of rotation of finite strain axes the conventional mohr diagram is less suitable however to visualise progressive deformation or deformation paths a sliding scale mohr diagram is introduced which serves this purpose better it consists of a mohr circle of fixed diameter and a mobile reference frame origin that maps the deformation path the sliding scale mohr diagram can be used as a visualisation tool for teaching purposes and for research on kinematics of progressive deformation

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

raman spectroscopy of fossil bioapatite a proxy for diagenetic alteration of the oxygen isotope composition abstract fossil bioapatite may yield biogeochemical signals of paleoenvironments captured by living organisms bioapatite may be diagenetically altered however with ions added or removed post mortem such change is typically assessed using destructive and demanding techniques here raman spectroscopy is used as a rapid and non destructive way to identify significant diagenetic alteration of fossil bioapatite we found spectral parameters of phosphate symmetric stretching 1 po43 to be very sensitive to variations in apatite chemistry particularly with respect to common diagenetic components co32 f sr2 the raman spectral parameters were subsequently applied to a set of modern biogenic and geologic magmatic apatite samples as potential endmembers for diagenetic alteration raman spectra were also collected from enamel and dentin respectively resistant vs alteration prone of fossil teeth phosphate oxygen isotopic values from the same enamel dentin samples were used as an index of alteration and provided definition of raman spectral parameters as relates to diagenetic alteration diagenetically altered samples were characterised by spectra with 1 po43 widths at half maximum height less than 13 0 cm 1 and 1 po43 band positions greater than 964 7 cm 1 raman spectroscopy is shown to have potential as a tool for pre screening fossil apatite samples before further analyses

reconstruction of deformation and flow parameters from deformed vein sets abstract in any homogeneously deformed material sets of material lines with a similar stretch history occupy sectors with a scale and orientation that depend on finite strain area change rate and vorticity of the parent flow if the size and shape of these material line sectors are known they can be used to determine the sense of shear and to calculate deformation and flow parameters even if actual stretches along material lines are unknown in rocks which have undergone near homogeneous deformation on a large scale the orientation of sets of boudinaged folded and folded boudinaged or boudinaged folded veins can be used for such calculations a general theoretical background to the problem is presented and a mohr circle construction to carry out the deformation and flow analysis is introduced among other statements the theory predicts that shortened or folded boudins must develop in non coaxial monophase deformation with considerable area change in the plane of observation or in polyphase deformation

characterization of fault roughness at various scales implications of three dimensional high resolution topography measurements accurate description of the topography of active fault surfaces represents an important geophysical issue because this topography is strongly related to the stress distribution along fault planes and therefore to processes implicated in earthquake nucleation propagation and arrest to date due to technical limitations studies of natural fault roughness either performed using laboratory of field profilometers were obtained mainly from 1 d profiles with the recent development of light detection and ranging lidar apparatus it is now possible to measure accurately the 3 d topography of rough surfaces with a comparable resolution in all directions both at field and laboratory scales in the present study we have investigated the scaling properties including possible anisotropy properties of several outcrops of two natural fault surfaces vuache strike slip fault france and magnola normal fault italy in limestones at the field scale digital elevation models of the fault roughness were obtained over surfaces of 0 25 m2 to 600 m2 with a height resolution ranging from 0 5 mm to 20 mm at the laboratory scale the 3 d geometry was measured on two slip planes using a laser profilometer with a spatial resolution of 20 m and a height resolution less than 1 m

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

revised phosphate water fractionation equation reassessing paleotemperatures derived from biogenic apatite oxygen isotopes of biogenic apatite have been widely used to reassess anomalous temperatures inferred from oxygen isotope ratios of ancient biogenic calcite more prone to diagenetic alteration however recent studies have highlighted that oxygen isotope ratios of biogenic apatite differ dependent on used analytical techniques this questions the applicability of the phosphate water fractionation equations established over 25 years ago using earlier analytical techniques to more recently acquired data in this work we present a new phosphate water oxygen isotope fractionation equation based on oxygen isotopes determined on fish raised in aquariums at controlled temperature and with monitored water oxygen isotope composition the new equation reveals a similar slope but an offset of about 2 to the earlier published equations this work has major implications for paleoclimatic reconstructions using oxygen isotopes of biogenic apatite since calculated temperatures have been underestimated by about 4 to 8 c depending on applied techniques and standardization of the analyses

fabric retentive non luminescent brachiopods as indicators of original delta 13 c and delta 18 o composition a test abstract fabric retentive non luminescent helderbergian brachiopods from open marine deposits analogous to brachiopods used in other studies to determine paleo oceanic stable isotopic composition exhibit depleted 13c values immediately below the erosional contact and more enriched values of 13c at greater stratigraphic distances below this surface in addition 13c values of these brachiopods display a marked shift across the erosional surface and values above it are essentially the same as those 30 m or more beneath the surface complementing these trends whole rock analyses metastable high agnesian calcite constituents echinoderms as well as early equant calcite cement also exhibit an increased depletion trend in 13c values as the helderberg oriskany contact is approached from below fabric retentive luminescent as well as obviously recrystallized brachiopods display stable isotopic values similar to those of fabric retentive non luminescent brachiopods thus best preserved fabric retentive non luminescent brachiopods exhibit values similar to obviously recrystallized brachiopods diagenetically altered metastable constituents echinoderms stable early meteoric cements and whole rock samples helderberg strata of new york state were affected by early meteoric diagenesis during a siegenian exposure event prior to deposition of the overlying marine oriskany sandstone meteoric diagenesis during this exposure gave rise to a characteristic carbon isotopic depletion trend approaching the helderberg oriskany contact all of the skeletal constituents underwent isotopic exchange during early diagenetic exposure to meteoric waters consequently the practice of using fabric retentive non luminescent brachiopods as indicators of their original chemistry and by extension paleo oceanic chemistry is questioned

efficient use of the velocity gradients tensor in flow modelling passchier c w 1987 efficient use of the velocity gradients tensor in flow modelling tectonophysm 136 159 163 for models of fabric development in rocks with vorticity as a variable parameter the choice of an unsuitable reference frame for instantaneous flow can hamper clear presentation of results the orientation of most fabric elements which develop in deforming rocks is attached to some principal direction of instantaneous flow syntaxial fibres crystallographic preferred orientation patterns steady state foliations and immobilised rigid objects seem to orient themselves in a fixed position relative to instantaneous stretching axes di while shape fabric elements and mica preferred orientation approach parallelism with the extensional apophysis i of the flow models for development of such fabric elements benefit from a choice of reference frame attached to either d or i

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

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

measurements of frictional heating in granite a large 150 150 40 cm granite sample sawn diagonally in half to simulate a fault was deformed in a biaxial rock press at normal stress up to 6 41 mpa displacements and local shear stress were monitored along the fault 200 40 cm temperature transients as large as 10 m c were recorded following stick slip events at distances of 0 2 to 1 0 cm from the fault and were related to stress displacement and total work the temperature measurements were used to calculate the heat generated on the fault during slip frictional heating was found to be 94 2 of the total work expended in each event implying a seismic efficiency of 4 8 when water was injected onto the fault both fractional stress drop and static frictional stress increased the efficiency of frictional heating was not lowered by the presence of water heat generated during deformation of a 0 15 cm thick layer of simulated gouge was also measured for sliding rates from 0 09 to 9 1 m s in these gouge experiments temperature rises were less than 0 1 c and were proportional to sliding rate

gouge formation by dynamic pulverization during earthquake rupture it is proposed here that fault gouge forms by rock pulverization within the tip region of a fast propagating earthquake due to the intensity of stress and rates of strain in this zone to examine this mechanism we calculate the deformation conditions of a dynamic shear fracture propagating close to the limiting rayleigh wave velocity the mechanical conditions close to the fracture tip are extreme tensile stresses approach 5 gpa volumetric strain rates exceed 105 s 1 and volumetric expansion alternates with volumetric contraction it is expected that a localized zone a few millimeters wide will be pulverized under these conditions this mechanism of dynamic gouge formation provides new insight to recent observations of the texture of gouge from the san andreas fault zone and from rupture zones in south african mines further as such extreme conditions develop only during fast propagating earthquakes presence or absence of pulverized gouge may serve as an indicator of earthquake propagation velocity

conodont sr ca and δ18o record seawater changes at the frasnian famennian boundary abstract the oxygen isotopic composition 18 o p and strontium calcium sr ca p ratios have been measured in late devonian conodonts palmatolepis sp from contemporaneous sections at coumiac france and m rirt morocco the sequences encompass two anoxic horizons the lower kellwasser lkw and upper kellwasser ukw events with the top of the ukw coinciding with the mass extinction at the frasnian famennian boundary the genus palmatolepis survived the faunal crisis but exhibited plastic responses to the environmental changes which are recorded in the evolution of shape during the anoxic events the present study demonstrates that shape 18 o p and sr ca p values of conodonts are correlated in both localities excluding diagenesis as the driving process for the measured 18 o p and sr ca p values the conodonts 18 o p and sr ca p values are correlated in both localities and distributed into either a pre crisis and crisis group using the relationships between the 18 o p and sr ca p values we estimate that the variation of the seawater sr ca ratio during the frasnian famennian mass extinction was of about 20 its initial value this drastic decrease of the seawater sr ca ratio is discussed in the light of the reef demise that occurred during the faunal crisis

carboniferous climate teleconnections archived in coupled bioapatite δ18opo4 and 87sr 86sr records from the epicontinental donets basin ukraine abstract reconstructions of paleo seawater chemistry are largely inferred from biogenic records of epicontinental seas recent studies provide considerable evidence for large scale spatial and temporal variability in the environmental dynamics of these semi restricted seas that leads to the decoupling of epicontinental isotopic records from those of the open ocean we present conodont apatite 18 o po 4 and 87sr 86sr records spanning 24 myr of the late mississippian through pennsylvanian derived from the u pb calibrated cyclothemic succession of the donets basin eastern ukraine on a 2 to 6 myr scale systematic fluctuations in bioapatite 18 o po 4 and 87sr 86sr broadly follow major shifts in the donets onlap offlap history and inferred regional climate but are distinct from contemporaneous more open water 18 o po 4 and global seawater sr isotope trends a 1 to 6 offset in donets 18 o po 4 values from those of more open water conodonts and greater temporal variability in 18 o po 4 and 87sr 86sr records are interpreted to primarily record climatically driven changes in local environmental processes in the donets sea systematic isotopic shifts associated with myr scale sea level fluctuations however indicate an extrabasinal driver we propose a mechanistic link to glacioeustasy through a teleconnection between high latitude ice changes and atmospheric pco2 and regional monsoonal circulation in the donets region inferred large magnitude changes in donets seawater salinity and temperature not archived in the more open water or global contemporaneous records indicate a modification of the global climate signal in the epicontinental sea through amplification or dampening of the climate signal by local and regional environmental processes this finding of global climate change filtered through local processes has implications for the use of conodont 18 o po 4 and 87sr 86sr values as proxies of paleo seawater composition mean temperature and glacioeustasy

the spatial and temporal diversification of early palaeozoic vertebrates recent discoveries have dramatically altered traditional views of the stratigraphic distribution and phylogeny of early palaeozoic vertebrates and permit a reappraisal of biogeographic patterns and processes over the first 120 million years of vertebrate evolution stratigraphic calibration of the phylogenetic trees indicates that most of the pre silurian record can be inferred only through ghost ranges assessment of the available data suggests that this is due to a shift in ecological niches after the latest ordovician extinction event and a broadening of geographical range following the amalgamation of euramerica during the early silurian two major patterns are apparent in the bio geographic data firstly the majority of jawless fishes with dermoskeletal plated armour were highly endemic during cambrian ordovician time with arandaspids restricted to gondwana galeaspids to china and anatolepids astraspids and possibly heterostracans confined to laurentia these laurentian groups began to disperse to other continental blocks as the old red sandstone continent amalgamated through a series of tectonic collisions the second maj or pattern in contrast encompasses a number of microsquamous and naked jawed and jawless primitive vertebrates such as conodonts thelodonts placo derms chondrichthyans and acanthodians which dispersed rapidly and crossed oceanic barriers to attain cosmopolitan distributions although many have laurentian origins a clear difference in dispersal potential exists between these two types of fishes overall the development of biogeographic patterns in early palaeozoic vertebrates involved a complex interaction of dispersal vicariance and tectonic convergence

ophiolites as faithful records of the oxygen isotope ratio of ancient seawater the solund stavfjord ophiolite complex as a late ordovician example

analysis of deformation paths in shear zones the geometry of ductile shear zones can be used to solve problems of regional tectonics if the deformation path of material in the zones is sufficiently understood flow in many shear zones may have deviated from simple shear and consequently data on the final deformation state such as finite strain and volume change are insufficient for reconstruction of the deformation path even if flow parameters were constant during progressive deformation additional information on the flow vorticity number is also needed and can be obtained from fabric elements such as sets of folded boudinaged veins rotated porphyroblasts and blocked rigid objects mohr circle constructions are presented as a tool to calculate deformation parameters from fabric data to represent the deformation path graphically and to reconstruct flow parameters from the shape of this path if the vorticity number or the volume change rate changed during progressive deformation the deformation path can be partly reconstructed using sets of fabric elements which register mean and final values of these parameters

amorphous material in safod core samples san andreas fault evidence for crush origin pseudotachylytes 1 several types of amorphous material in ultracataclastic core samples recovered from 3194 m and 3294 m depth of the main bore hole of the san andreas fault observatory at depth are identified and described with transmission electron microscopy and scanning electron microscopy we observed 1 amorphous material on a slickenside surface 2 glassy bands contained in an ultracataclastic matrix and 3 amorphous rims surrounding quartz or feldspar clasts chemical analyses of the amorphous material reveal that silica content is slightly enriched or similar as in the adjacent matrix we suggest that all amorphous material was formed by comminution of clasts crush origin pseudotachylytes rather than by melting melt origin pseudotachylytes the observed amorphous phases may act as lubricating layers that reduce friction in the san andreas fault

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

seismic slip recorded in tourmaline fault mirrors from elba island italy abstract this paper reports the first example of fault mirrors developed in an unusual protolith consisting of tourmaline crystals with interstitial goethite the deformation mechanisms active in the fault zone have been investigated from the outcrop to the nanoscale aiming to identify possible traces of frictional heating at seismic slip rate as observed for other fault mirrors in different protoliths the investigation revealed the superposition of two main deformational stages the first was dominated by brittle processes and produced a cataclastic ultracataclastic principal slip zone a few mm thick the second was associated with seismic slip and produced a sharp discontinuity the principal slip surface within the cataclastic ultracataclastic zone the mirror like coating a few microns thick occurs on the principal slip surface and is characterized by 1 absence of interstitial goethite 2 occurrence of truncated tourmaline crystals 3 highly variable grain size from 200 m to 200 nm 4 tourmaline close packing with interlobate grain boundaries and 5 tourmaline random crystallographic orientation micro and nanostructural investigations indicate the occurrence of thermally activated processes involving both interstitial goethite and tourmaline in particular close to the principal slip surface goethite is completely decomposed and produced an amorphous porous material with local topotactic recrystallization of hematite tourmaline clasts are typically characterized by strongly lobate boundaries indicative of reaction and partial decomposition at grain boundaries tem observations revealed the occurrence of tourmaline nanograins a few tens of nm in size characterized by rounded shape and fading amorphous boundaries that cannot be obtained by brittle processes lastly the peculiar interlobate microstructure of the mirror surface is interpreted as the result of grain boundary recrystallization processes taking place by deformation at high t conditions our results show that tourmaline fault mirrors recorded localized high t processes triggered by frictional heating and can be therefore considered as reliable traces of ancient earthquakes

the use of mohr circles to describe non coaxial progressive deformation abstract mohr circles are useful in strain analysis but are also potentially powerful tools to translate geological fabric data into tensors describing the deformation and to reconstruct flow parameters this paper shows how mohr circles can be used to visualize the effects of variable flow parameters such as stretching rate volume change rate and vorticity number on parameters of cumulative deformation as described by the position gradient tensor a mean vorticity number is introduced as a deformation parameter besides finite cumulative strain and volume change

experimental investigations on dating the last earthquake event using osl signals of quartz from fault gouges abstract obtaining a reliable age of the latest seismic slip event along an active fault is important for seismic hazard assessment here we observe changes in the optically stimulated luminescence osl signal of quartz crystals due to frictional heating in artificial fault gouges comprising a mixture of quartz grains and ca bentonite powder the fault gouge was deformed using a high velocity rotary shear apparatus at room temperature and room humidity at a seismic slip rate of 1 31 m s 1 intense slip localization occurred along a very thin layer 300 m thick within the simulated fault zones 1 mm thick the estimated temperature of the slip localized layer sll increased by 475 c from frictional heating the quartz osl signals of the gouges were fully reset most noticeably for the sll in contrast there was rare slip localization at subseismic slip rates 0 06 0 001 m s 1 for which the estimated temperature rise in the sll was 120 c hence the quartz osl signal was not reset under this condition the results suggest that quartz osl dating can be used to constrain the age of the latest seismic event in natural quartz bearing fault zones where a sll occurs

mechanisms of fault mirror formation and fault healing in carbonate rocks abstract the development of smooth mirror like surfaces provides insight into the mechanical behaviour of crustal faults during the seismic cycle to determine the thermo chemical mechanisms of fault mirror formation we investigated carbonate fault systems in seismically active areas of central greece using multi scale electron microscopy combined with raman and electron energy loss spectroscopy we show that fault mirror surfaces do not always develop from nanogranular volumes the microstructural observations indicate that decarbonation is the transformation process that leads to the formation of smooth surface coatings in the faults studied here piercement structures on top of the fault surfaces indicate calcite decarbonation producing co2 and lime cao lime subsequently reacts to portlandite ca oh 2 under hydrous conditions nanoscale imaging and electron diffraction reveal a thin coating of a non crystalline material sporadically mixed with nano clay forming a complex composite material that smooths the slip surface spectroscopic analyses reveal that the thin coating is non crystalline carbon we suggest that ordering hybridisation of amorphous carbon led to the formation of partly hybridised amorphous carbon but did not reach full graphitisation calcite nanograins 100 nm and new nanograins formed by back reaction secondary nanograins