paleostress reconstruction from calcite twin and fault slip data using the multiple inverse method in the east walanae fault zone implications for the neogene contraction in south sulawesi indonesia abstract a new approach for paleostress analysis using the multiple inverse method with calcite twin data including untwinned e plane was performed in the east walanae fault ewf zone in south sulawesi indonesia application of untwinned e plane data of calcite grain to constrain paleostress determination is the first attempt for this method stress states caused by the collision of the south east margin of sundaland with the australian microcontinents during the pliocene were successfully detected from a combination of calcite twin data and fault slip data this pliocene ne sw to e w directed maximum compression activated the ewf as a reverse fault with a dextral component of slip with pervasive development of secondary structures in the narrow zone between bone mountain and walanae depression

critical shear stress for mechanical twinning of jadeite an experimental study coarse grained natural jadeitite samples from myanmar were experimentally deformed in a griggs type solid medium apparatus at strain rates of 2 10 5 and 5 10 6 s 1 and temperatures of 900 and 1000 c the microfabrics of the deformed samples are investigated by scanning electron microscopy sem using the electron backscatter diffraction ebsd technique the critical shear stress for twinning in the 100 001 system is derived from the orientation distribution of jadeite crystals with and without mechanical twins the results indicate a homogeneous stress field within the sample and a critical shear stress of 150 25 mpa which compares well to that determined by kolle and blacic j geophys res 87 1982 4019 for mechanical twinning of other clinopyroxenes with the critical shear stress known mechanical twinning of jadeite can be used as a paleopiezometer for high stress tectonic environments

calcite twin widths and intensities as metamorphic indicators in natural low temperature deformation of limestone abstract twins in naturally deformed coarse grained limestones of the northern subalpine chain france show a direct relationship of twin width and intensity number of twins per mm to the peak metamorphism under diagenetic and anchimetamorphic conditions the transition from dominant thin twinning to dominant thick twinning occurs between a mean vitrinite reflectance ro of 1 60 and 2 60 or temperatures of between 150 and 200 c below the transition temperature increasing strain is apparently accommodated by adding new twins and above the transition temperature increasing strain is accommodated by twin widening similar transitions from thin to thick twinning with increasing metamorphism are also present in the helvetic alps the prealps and the central appalachian valley and ridge province these data for naturally deformed limestones support the interpretation from experimental studies of a temperature effect on twin width and intensity and indicate that the twinning in the northern subalpine chain occurred at or near peak metamorphism

stress tensor determination from the study of e twins in calcite a linear programming method abstract a new method for the determination of the stress tensor from calcite e twin lamellae has been discovered all e planes twinned and untwinned are taken into account to enable derivation of tensor characteristics the basic assumption is that the resolved shear stress a linear function of the unknown stress tensor components is greater respectively lower than the critical resolved shear stress for the twinned respectively untwinned planes the relevant inequality constraints can be solved using linear programming algorithms the application to experimental carrara marble and natural samples a goniatite from morocco has come up against one major difficulty polyphase deformation thus before applying this method it is necessary to operate some selection of the data one procedure based upon linear programming is proposed the results are consistent with those expected both for the experimental and natural cases for the carrara marble an estimate of the critical resolved shear stress t c for twinning gave a value around 300 400 bar the method can give in principle the stress tensor orientation and the relative magnitude of principal stresses simultaneously

the influence of grain size and grain size distribution on methods for estimating paleostresses from twinning in carbonates abstract this study examines the relative differential stresses around a minor thrust fault within the mountain city window tennessee u s a the fault zone developed within dolomite rocks and deformation took place by twinning fracturing pressure solution and the development of fine grained deformation zones grain size reduction is observed from undeformed wall rock to the center of the fault zone and occurred by dynamic recrystallization methods to determine paleostresses in naturally deformed rocks from twinning assume a single coaxial strain inducing event the recrystallization within the center of the fault zone removed the effects of earlier deformation so that the twinning more closely reflects a single coaxial deformation event late in the fault history two methods were used to estimate the relative differential stresses across the fault zone and the results show opposite trends towards the center of the fault zone the different results may be partially explained by the influence of grain size as only one of these methods considers the influence of grain size in addition the grainsize data from this fault zone demonstrate that the tendency for a grain size class to be twinned depends on the grain size distribution the grain size distribution may result in grain to grain stress concentrations that induce twinning thus grain size distribution should also be considered to achieve more accurate estimates of paleostresses

wuchiapingian early lopingian permian global brachiopod palaeobiogeography a quantitative approach abstract a global presence absence database of 212 wuchiapingian early lopingian permian brachiopod genera from 30 stations is analysed by cluster analysis nonmetric multidimensional scaling and minimum spanning tree to document the global palaeobiogeographical patterns five core groups are revealed by the quantitative analysis and interpreted as representing five marine biotic provinces they are the cathaysian tropical western tethyan tropical himalayan warm temperate austrazean cold temperate and greenland svalbard provinces cold temperate the cathaysian province is composed of many isolated or semi isolated islands situated in the palaeotethys whereas the other four provinces occurred mainly on the continental shelves of pangea the western tethyan province along the western coast of the palaeotethys the himalayan province on the northern margin of gondwanaland the austrazean province along the southeastern margin of gondwanaland and the greenland svalbard province on the northern margin of pangea in addition nonmetric multidimensional scaling helped to identify key biogeographic determinants latitude related thermal gradient appears to have accounted for most of the variance in the data geographic distance and ocean circulation may have also played a major but subordinate role in the delineation and or enhancement of some of the provinces comparison with early and middle permian global marine provincialism indicates that marine biotic provinces had significantly reduced during the lopingian late permian in the lead up to the end permian mass extinction

echinoid distribution in the cenomanian an analytical study in biogeography abstract faunal lists of cenomanian echinoids from sixteen geographical regions within europe north and south america africa and the middle east are compiled and subjected to quantitative analysis after revision 177 species and 78 genera are accepted species richness corrected for sampling bias shows no latitudinal variation in alpha diversity however beta diversity shows an apparent decline in temperate palaeolatitudes possibly due to a decrease in habitat diversity distributional patterns are best interpreted as a mosaic of overlapping geographical ranges and not as a pattern of discrete provinces distance matrix clustering parsimony analysis of endemism and cladistic vicariance analysis are all applied to the data specific and generic data produce slightly different topologies with charente maritime and portugal switching affinities this correlates with the development of oceanic rifting in the bay of biscay an event so closely predating the cenomanian that it is reflected in species but not generic data patterns of area relationships generally reflect proximity of regions palaeogeographically as expected both latitudinal and longitudinal gradational faunal changes are identified evidence though not conclusive suggests that atlantic and tethyan elements were by this time already differentiated south atlantic echinoid faunas show closest relationship to the texas region not with north africa

microbial dolomite crusts from the carbonate platform off western india the occurrence of late pleistocene dolomite crusts that occur at 64 m depth on the carbonate platform off western india is documented dolomite is the most predominant mineral in the crusts in thin section the crust consists of dolomitized microlaminae interspersed with detrital particles under scanning electron microscopy these laminae are made up of tubular filaments or cellular structures of probable cyanobacterial origin dolomite crystals encrust or overgrow the surfaces of the microbial filaments and or cells progressive mineralization obliterates their morphology well preserved microbial mats sulphide minerals pyrrhotite and marcasite and the stable isotope composition of dolomite in the crusts indicate hypersaline and anoxic conditions during dolomite formation the crusts are similar to dolomite stromatolites and biogeochemical processes related to decaying microbial mats under anoxic conditions probably played an important role in dolomite precipitation the dolomite is therefore primary and or very early diagenetic in origin the dolomite crusts are interpreted to be a composite of microbial dolomite overprinted by early burial organic dolomite the results of this study suggest that a microbial model for dolomite formation may be relevant for the origin of ancient massive dolomites in marine successions characterized by cryptalgal laminites the age of the crusts further suggests that the platform was situated at shallow subtidal depths during the last glacial maximum

strength characteristics of the r f and c slip systems in calcite abstract numerical modelling of crystallographic preferred orientation or texture development in plastically deformed materials requires specification of all potential slip and twinning systems and their relative strengths or critical resolved shear stresses crrs it is widely believed that the most important intracrystalline deformation systems in calcite are twinning on e 1 018 40 4 1 slip on r 10 1 4 2 021 and slip on f 1 012 2 2 01 the superscripted signs indicating slip sense it is these systems which have been used in modelling texture development in calcite polycrystals to date however modelling has been limited by insufficient and partly conflicting data on the relative strengths of the various slip and twinning systems in calcite deformation experiments on calcite single crystals performed by us in recent years taken together provide new data for a more complete and consistent quantification of the strength properties of the calcite glide systems in our experiments single crystals of calcite were compressed in both the 4041 and 2243 orientations at temperatures and constant strain rates in the range 300 800 c and 3 10 4 3 10 8 s 1 respectively the stress strain curves obtained mostly show two yield points slip line analysis shows that these yield points are related to the onset of macroscopically observable slip first on an r 2 021 system and then on an f 10 1 1 or c a system the latter two systems dominate at higher temperature 600 c at strain rate 3 10 5 s 1 and have not been taken into account in any texture modelling so far with increasing absolute temperature tabs calculated crss values c for the r f and c systems decrease in a manner which can be described by empirical power law functions of the type c a tabs b where b r 2 021 and f 10 1 1 systems the yield stresses for r 2 021 and f 10 1 1 slip were found to be rather insensitive to strain rate with conventional power law stress exponents 12 comparing the present results with previous data we conclude that two regimes of slip system activity exist namely a low temperature regime involving e twinning slip on r 2 021 and on f 2 2 01 positive direction not reported and a high temperature regime with r 2 021 f 10 1 1 and c a slip this slip system transition occurs at t 400 c at strain rate 10 4 10 5 s 1 and is expected to be associated with one or more texture transitions the results point to a clear need for renewed texture modelling of calcite polycrystals

quantitative compositional analysis of a triassic carbonate platform southern alps italy abstract we have estimated abundance and distribution of automicrite marine cements and skeletal grains in the triassic sella massif an isolated platform flanked by steep 25 35 clinoforms 108 samples were taken at constant intervals from measured sections of the major zones of the platform edifice the platform top margin upper slope and lower slope in a first step carried out in the field and on hand specimen purely detrital deposits were separated from automicrite facies i e beds with automicrite cement filled primary vugs and admixtures of skeletal carbonate and lithoclasts in the second step samples with automicrite facies were thin sectioned and point counted the categories used for point counting were a automicrite b vugs and cement c microspar or neomorphic spar d skeletal grains and e internal sediments at the platform top 46 of samples are pure detrital deposits 27 consist of automicrite facies and 27 are too strongly altered by dolomitization to allow classification at the margin upper slope 68 of samples consist of automicrite facies 22 are pure detrital sediments and 10 are strongly altered at the lower slope 63 are detrital deposits 10 automicrite facies and 27 are extensively dolomitized the most important contributors to the automicrite facies are automicrite 41 on the platform top 29 on the margin upper slope 28 on the lower slope and early marine cement 35 on the platform top 48 on the margin upper slope 27 on the lower slope the amount of skeletal grains is less than 10 the automicrite facies stabilized the platform margin and upper slope automicrite abundant early marine cements and micro organisms such as tubiphytes formed a rigid framework thus substituting for the lack of a metazoan reef on the upper slopes the framework of automicrite facies stabilized the slope but intermittently the automicrite layers are frequently dissected by sediment filled fractures or are broken into clasts we assume that they slid on the layers of loose detritus bigger slides turned into rubbly debris flows that formed metre thick breccias at the lower slope and the proximal basin floor the planar shape and steep angle of the clinoforms indicate that the large scale geometry of the slope was not controlled by the automicrite but rather by non cohesive layers of sand and rubble piled up to the angle of repose the production mode of the sella is comparable of that of a mud mound factory this factory was highly productive in 1 ma the platform aggraded over 300 m and prograded over 2000 m in all directions

evolution of the stress field pattern in the south of the rhine graben from the eocene to the present a stress field evolution from the eocene to the present is proposed for the southern part of the rhine graben stress tensor determinations are supported by striated microfaults and calcite twin lamellae analyses both methods lead to the determination of 1 a an e w extension contemporaneous with the opening of the graben and 2 b a n s compressive event which may be related with alpine tectonics it is shown that a n s compressive event occurred prior to the oligocene extension a permutation between the 1 and 2 axes is proposed to explain the transition between compression and extension a 1 2 inversion during the oligocene is compatible with compression in the southern part of the rhine graben infilling horizontal 1 and extension vertical 1 more to the north during the miocene the jura emplacement corresponds to a n s compression in this area there is no significant variation of the 1 direction south of the rhine graben from the eocene to the late miocene the 1 direction only turns to a n140 direction during the pliocene or the quaternary

reef fabrics biotic crusts and syndepositional cements of the latemar reef margin middle triassic northern italy the latemar reef buildup of the central dolomites northern italy provides a rare opportunity to examine an in place middle triassic upper anisian to lower ladinian platform margin that is not strongly deformed or dolomitized the margin lies between the flat lying platform interior and steeply dipping foreslope clinoforms across this transition the depositional profile relates directly to a consistent lateral facies pattern 1 restricted biota grainstone of the platform interior 2 tubiphytes rich boundstone and 3 diverse biota grainstone that grades into 4 foreslope breccia beds the boundstone and diverse biota grainstone facies comprise the platform margin the boundstone facies consists of a framework of small 10 cm skeletal remains 10 by volume with associated biotic crusts internal sediments and syndepositional cements crusts and cements constitute most of the rock volume and created the boundstone fabric biotic crusts exhibit gravity defying geometries and range from a light grey structure grumeleuse rind to dark grey micritic laminae both cements and biotic crusts occur as redeposited talus in the foreslope talus deposits indicating a syndepositional origin the diverse biota grainstone facies primarily consists of skeletal peloidal grainstone with a diverse open marine biotic assemblage in contrast to the restricted biota grainstones of the platform interior that have a low diversity restricted marine biota metre scale hexacoral boundstone and centimetre scale sponge boundstone and microbial boundstone occur as isolated patches tens to hundreds of metres apart within the diverse biota grainstone facies the depositional profile facies zonation and biotic constituents all indicate that the latemar buildup had a shallow water reef margin in contrast to previous interpretations that these were upper slope reefs the syndepositional biotic crusts and inorganic cementation played key roles in stabilizing the boundstone fabric to form a wave resistant reef fabric

past climate and the role of ocean heat transport model simulations for the cretaceous a series of general circulation model experiments using global environmental and ecological simulation of interactive systems genesis were executed to evaluate the sensitivity of simulated mid cretaceous climate to small perturbations in ocean heat transport three experiments were performed 1 mixed layer ocean with no ocean heat transport zeroq 2 ocean heat transport specified as required for genesis to best match modern observations oneq and 3 doubled ocean heat transport twoq the oneq experiment represents an ocean heat transport which is actually about 15 of the values given by carissimo et al 1985 from modern observations as a sensitivity experiment these model simulations represent a doubling of the role of the ocean however relative to the observations they represent small perturbations to the total poleward heat transport in the model with the exception of the tropics no major changes in the structure of the general circulation of the atmosphere resulted from the modification of the ocean heat transport however relatively small increases in ocean heat transport resulted in a number of significant differences between simulations including tropical cooling polar warming weakened equator to pole surface temperature gradients weakened midlatitude jets decreased land sea pressure contrast and decreased midlatitude storminess the experiments indicate that changes in ocean heat transport which are well within the realm of possibility for earth history can have significant climatic impact although ocean heat transport may be a significant factor in explaining cretaceous polar warmth the changes specified in these experiments alone are not sufficient to explain the polar warmth of the cretaceous

late cretaceous cenozoic climatic variations of the northern antarctic peninsula new geochemical evidence and review aptian to pliocene time series of x ray fluorescence data from the antarctic peninsula are used to assess the degree of chemical weathering and maturity of sediments deposited prior and subsequent to the establishment of glaciation in west antarctica a continuous palaeoclimatic signal is inferred from comparing the results with previously published palaeotemperature and palaeobotanical data aptian cenomanian warm cool and santonian early paleocene warm cold cycles were followed by the global late paleocene early eocene climatic optimum subsequent steady decline in temperatures resulted in glacial conditions in the northern antarctic peninsula by early oligocene time under alternating cenozoic frigid cold climates and in sedimentary regimes dominated by physical weathering geochemical signatures were primarily indicative of provenance the development of cretaceous arboreal vegetation in the northern antarctic peninsula can be correlated with the major climatic cycles

regional shortening fabrics in eastern north america far field stress transmission from the appalachian ouachita orogenic belt paleozoic carbonates of cratonic eastern north america comprise the footwall of the appalachian ouachita fold and thrust belt and contain a layer parallel shortening lps fabric that is preserved by mechanically twinned calcite shortening directions are generally parallel to the appalachian ouachita thrust transport direction in carbonates of the thrust belt proper restored width 400 km and within carbonates up to 1700 km into the foreland giving a pre thrusting sedimentary prism 2100 km wide through which compressive orogenic stresses were transmitted the shortening strain magnitudes 6 and the inferred calcite twinning differential stress magnitudes 90 mpa decrease exponentially away from the orogenic front calcite twinning strain patterns in other adjacent tectonic provinces such as the grenville laramide keweenawan rift and newark basin are distinct from the twinning strains preserved in the cratonic paleozoic carbonates appalachian orogen far field stresses calcite microstructures

determination of deviatoric stress tensors based on inversion of calcite twin data from experimentally deformed monophase samples part ii axial and triaxial stress experiments three samples of a bioclastic bajocian limestone from burgundy france were experimentally deformed under axial and triaxial conditions at 200 and 300 c in each sample a series of three mutually orthogonal thin sections were studied using a u stage the intracrystalline deformation of the calcite grains involved mainly twinning on the e planes precise measurement of the e twin lamellae combined with the etchecopar inverse method 1984 allowed the calculation of the four parameters of the reduced stress tensor responsible for the twinning as the principal differential stress values of the experimental deviatoric stress tensors were known the critical resolved shear stress crss values tau s for twinning on the e planes were then determined in each case at 200 c and 4 8 strain tau s is close to 15 mpa at 300 c and at 8 7 and 9 4 strain the calculated tau s values are close to 10 1 and 13 4 mpa respectively when compared with the data published by turner et al 1954 turner and heard 1965 and lacombe and laurent 1996 our results confirm that the crss values are more or less dependent on both the temperature and the bulk amount of strain consequences for the estimation of the actual principal differential stress values sigma 1 sigma 3 are described particularly for very weakly deformed cover rocks in the forelands of mountain chains

early rotation and late folding in the pennsylvania salient u s appalachians evidence from calcite twinning analysis of paleozoic carbonates calcite twinning analysis of paleozoic limestones from 42 sites reveals that the change in regional strike along the frontal edge of the pennsylvania salient is accompanied by an equal magnitude rotation of paleostress directions of up to 60 degrees the rotations recorded at 22 reliable sites show no discernible difference between sites with rocks of cambrian ordovician and silurian devonian age evidence for similarly fanned orientations is not present in foreland sites scatter in the data is attributed to grain scale rotations and compaction overprinting as demonstrated in prior studies and it was reduced by data cleaning methods as well as by the use of contouring and data averaging methods comparisons of paleostress directions within the belt reveal only minor rotations in the southwest region of the salient and the bulk of rotation is accommodated by the northern limb we hypothesize that these rotations resulted from convergence in the thrust wedge against a northerly bounding rigid basement block around pennsylvanian times this created a structural anisotropy in the evolving belt that guided the post rotational formation of folds in early permian times and produced the current pattern of the salient this model of decoupled thrusting rotation and folding explains a variety of previously conflicting observations in the area while offering a kinematically consistent scenario that may also apply to other curved orogenic belts

paleooceanography of the mesogean sea based on ostracods of the northern tunisian continental shelf between the late cretaceous and early paleogene a new method analysis used in the study of the el kef section north western tunisia led to the paleooceanographic reconstruction of the mesogean between late cretaceous and early paleogene several changes observed are in fact worthy of particular mention paleobathymetrically the area changed from an upper bathyal environment of about 400 m deep to an outer shelf domain of 100 50 m furthermore the oxygen minimum zone o m z became highly intense at a the cretaceous tertiary transition catastrophic event b the p1 p2 boundary intense thermic stratification and c between p4 and p6 very active paleoproductivity in this last episode the continental shelf environment was subjected to intense upwelling responsible for the formation of a prephosphatic environment at water sediment interface the paleooceanographic history of phosphates in the gafsa metlaoui basin is in fact in perfect stratigraphic and paleoenvironmental agreement with the paleobathymetric evolution of the kef region finally paleooceanographic communication between the mesogean and the north atlantic was at this period highly free because of lack of hydrologic relations between the north atlantic and the norwegian sea

from orientation to magnitudes in paleostress determinations using fault slip data abstract determinations of reduced stress tensors using fault slip data yield the orientation of principal stress axes and the ratio of the differences between principal stress magnitudes the use of rupture and friction laws allows determination of the two remaining unknowns that is the reconstruction of the complete stress tensor taking into account the depth of overburden brings an additional constraint the method is applied and discussed in the case of the hoover dam site western u s a where large data sets and rock mechanics information are available differences between intact sample and rock mass properties account for apparent disagreements between paleostress levels determined in similar tectonic environments pore pressure plays an important role where information about pore pressure is absent zero and hydrostatic pore pressure cases should be considered as limits

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

influence of stress temperature and strain on calcite twins constrained by deformation experiments abstract a series of low strain triaxial compression and high strain torsion experiments were performed on marble and limestone samples to examine the influence of stress temperature and strain on the evolution of twin density the percentage of grains with 1 2 or 3 twin sets and the twin width all parameters that have been suggested as either paleopiezometers or paleothermometers cylindrical and dog bone shaped samples were deformed in the semibrittle regime between 20 c and 350 c under confining pressures of 50 400 mpa and at strain rates of 10 4 10 6 s 1 the samples sustained shear stresses up to 280 mpa failing when deformed to shear strains 1 the mean width of calcite twins increased with both temperature and strain and thus measurement of twin width provides only a rough estimation of peak temperature unless additional constraints on deformation are known in carrara marble the twin density nl no of twins mm increased as the rock hardened with strain and was approximately related to the peak differential stress mpa by the relation 19 5 9 8 n l dislocation tangles occurred along twin boundaries resulting in a complicated cell structure which also evolved with stress as previously established the square root of dislocation density observed after quench also correlated with peak stress apparently both twin density and dislocation cell structure are important state variables for describing the strength of these rocks

fingerprinting stress stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding the case of the monte nero anticline in the apennines italy in this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold and thrust belt first we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion second we use our new approach to present a high resolution deformation and stress history that affected meso cenozoic limestone strata in the monte nero anticline during its late miocene pliocene growth in the umbria marche arcuate ridge northern apennines italy in this area an extensive stylolite joint vein network developed during layer parallel shortening lps as well as during and after folding stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during lps the stress regime oscillated between strike slip and compressional during lps before ultimately becoming strike slip again during late stage fold tightening our case study shows that high resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses beyond regional implications this study validates our approach as a new powerful toolbox to high resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques

postmagmatic tectonic evolution of the outer izu bonin forearc revealed by sediment basin structure and vein microstructure analysis implications for a 15 ma hiatus between pacific plate subduction initiation and forearc extension international ocean discovery program expedition 352 recovered sedimentary volcaniclastic successions and extensional structures faults and extensional veins that allow the reconstruction of the izu bonin forearc tectonic evolution using a combination of shipboard core data seismic reflection images and calcite vein microstructure analysis the oldest recorded biostratigraphic ages within fault bounded sedimentary basins late eocene to early oligocene imply a 15 ma hiatus between the formation of the igneous basement 52 to 50 ma and the onset of sedimentation at the upslope sites u1439 and u1442 extension led to the formation of asymmetric basins reflecting regional stretch of 16 19 at strain rates of 1 58 10 16 to 4 62 10 16 s 1 downslope site u1440 closer to the trench is characterized by a symmetric graben bounded by conjugate normal faults reflecting regional stretch of 55 at strain rates of 4 40 10 16 to 1 43 10 15 s 1 mean differential stresses are in the range of 70 90 mpa we infer that upper plate extension was triggered by incipient pacific plate rollback 15 ma after subduction initiation extension was accommodated by normal faulting with syntectonic sedimentation during late eocene to early oligocene times backarc extension was assisted by magmatism with related shikoku and parece vela basin spreading at 25 ma so that parts of the arc and rear arc and the west philippine backarc basin were dismembered from the forearc this was followed by slow rift to postrift sedimentation during the transition from forearc to arc rifting to spreading within the shikoku parece vela basin system

paleostress in cratonic north america implications for deformation of continental interiors compressive paleostresses as recorded by twinned calcite in carbonate rocks that cover cratonic northwestern north america are perpendicular to the orogenic front of the late cretaceous to early cenozoic sevier fold thrust belt inferred differential stresses decrease from 100 megapascals mpa at the orogenic front to 20 mpa up to 2000 kilometers inland new analyses near the late paleozoic appalachian front refine earlier results from the eastern midcontinent the appalachian and sevier stress data in north america9s continental interior are remarkably similar in spite of distinctly different tectonic properties this suggests that continental interior stresses are largely insensitive to tectonic characteristics of compressive plate margins and that far field stress transmission is filtered by deformation styles in mountain belts

a stress inversion procedure for polyphase calcite twin and fault slip data sets in rocks that are polydeformed an approach which separates faults prior to stress inversion is more appropriate the traditional stress inversion approach involving the concept of the best fit stress tensor e g a tensor which minimises the misfit between calculated and measured fault striae data often risks computing artificial stress tensors that are some form of average of mixed sets of real stress tensors a new approach is proposed in which fault data are pre processed to group the faults on the basis of their response to all possible orientations and magnitudes of applied stress a computer method is described which utilises cluster analysis based on the right dihedra method to divide dynamically mixed fault populations to monophase subsets this division is based on the ranked similarity coefficients of each fault pair from the raw data set the data clusters form dynamically homogeneous subsets which are used for the composite right dihedra solution this solution is re computed for the reduced stress tensor defined by the orientation of principal stress axes and the ratio of their magnitudes

an inverse problem in microtectonics for the determination of stress tensors from fault striation analysis abstract a method is proposed to compute some characteristics of a possible stress tensor related to striations measured in a given faulted area if several tectonic phases are responsible for the striations the method separates and determines the successive stress tensors the iterative algorithm consists of alternatively a sorting the data attributed to a tectonic phase and b computing the characteristics of the stress tensor of this phase the method is tested using an application to synthetic and actual data

determination of the tectonic evolution from fractures faults and calcite twins on the southwestern margin of the indochina block in polyphase tectonic zones integrating a study of fault and fracture with calcite twin analysis can determine the evolving paleostress magnitudes and principle stress directions that affected the area this paper presents the results of the analyses of fractures striated faults and calcite twins collected within the khao khwang fold thrust belt in central thailand se asia here we attempt to reconstruct the orientation of the principal stresses that developed during the tectonic evolution of this highly deformed polyphase orogen tectonic data were collected in the permian carbonates of the khao khad formation of the saraburi group and five successive tectonic stages are determined that are interpreted to have developed before during and after the triassic indosinian orogeny the first three stages predate the main deformation event the first stage is interpreted as a pre indosinian n s extensional stage the second stage described a n s strike slip and compressional regime largely perpendicular to the fold axes of the main structures while the third stage is associated with an e w compressional strike slip phase a further two stages took place after or during the main folding event and correspond to n s compression and to an e w composite strike slip contractional stage the latter which is interpreted to represent cenozoic deformation related to the india asia collision

middle late cretaceous climate of the southern high latitudes stable isotopic evidence for minimal equator to pole thermal gradients a detailed 18 o and 13 c stratigraphy has been generated from analysis of well preserved albian early maastrichtian foraminifera from deep sea drilling project dsdp sites 511 and 327 falkland plateau 58 s 62 s paleolatitude in the southern south atlantic and cenomanian and coniacian santonian foraminifera from dsdp site 258 naturaliste plateau 58 s paleolatitude in the southern indian ocean these results when combined with previously published maastrichtian stable isotope data from ocean drilling program odp site 690 weddell sea 65 s paleolatitude provide new insight into the climatic and oceanographic history of the southern high latitudes during middle late cretaceous time the planktonic foraminifer 18 o curves reveal a gradual warming of surface waters from the albian through the cenomanian followed by extremely warm surface waters from the turonian through the early campanian long term cooling of surface waters began in the late early campanian and continued through the end of the maastrichtian the benthic foraminifer 18 o record generally parallels changes in the oxygen isotopic curves defined by shallow dwelling planktonic foraminifera the vertical oxygen and carbon isotopic gradients were relatively low during the albian cenomanian high from the turonian early campanian and then low during the late campanian and maastrichtian foraminiferal oxygen isotopic data from published sources and this study are averaged for each site corrected for latitudinal changes in salinity based on modern day surface water values and plotted versus paleolatitude for the late albian coniacian santonian and late maastrichtian differences between lowand high latitude surface water paleotemperatures are estimated at 14 c during the late albian and late maastrichtian but the coniacian santonian reconstruction reveals only a 0 4 c latitudinal temperature gradient uncertainty regarding cretaceous salinity gradients and possible diagenetic alteration of 18 o values introduce error into our estimates of paleolatitudinal thermal gradients however apparent low equator to pole temperature differences could indicate much higher poleward heat transport than at present

residual stress measurements on a quartz vein a constraint on paleostress magnitude 1 the residual stress in a quartz vein from a metamorphic province is evaluated by an x ray diffraction technique diffraction analyses at multiple incident angles yield residual stress magnitudes for the specified directions on the plane parallel to the sample surface residual stress formation in the vein is found to be determined by the platy geometry with respect to the host rock the results indicate a compressive residual stress of 15 to 20 mpa parallel to the long axis of the vein the compressive stress magnitude parallel to the quartz vein is found to increase with sample temperature indicating that the quartz vein has a greater thermal expansion coefficient than that of the host rock a two dimensional model explaining residual stress formation in the vein in response to tectonic exhumation is proposed and the paleostress magnitude at the time of vein formation is estimated from the residual stress magnitude and fluid inclusion microthermometric data the quartz vein is concluded to have formed under a horizontal compressive stress of 550 660 mpa in the direction parallel to the long axis of the vein

elastic stress indication in elastically rebounded rock 1 it has long been believed impossible to estimate maximum paleo elastic stress in rocks because elastic strain disappears by elastic rebound when a rock is sampled plastic strain on the other hand leaves a permanent change in rocks even after stress is relaxed for example calcite records plastic strain as stress dependent intracrystalline deformation by mechanical twinning what happens if a rock contains a small amount of calcite bounded by silicate rich matrix is elastically loaded to answer this question we performed a series of triaxial compression tests of sandstones containing calcite particles under the elastic regime the statistical data show a good correlation between the density of calcite twins in elastically rebounded sandstone specimens and the maximum elastic stress applied to investigate in detail our experimental results we used the discrete element method dem to perform a numerical simulation of uni axial compression tests on sandstone our dem simulation shows the complex distribution of inter particle forces at each stress level however its statistical mean corresponds to the overall force load at the boundary this simulation result confirms that the statistically averaged calcite twin density can be regarded as a good stress indicator in real sandstones

determination of deviatoric stress tensors based on inversion of calcite twin data from experimentally deformed monophase samples preliminary results abstract following previous successful paleo stress determinations from numerically generated aggregates and naturally deformed samples preliminary results about stress reconstructions based on inversion of calcite twin data from experimentally deformed monophase samples are reported this new study carried out on samples of carrara marble and crinoidic limestone from eastern france provides a test of the validity of stress reconstructions using inverse methods which had not been properly calibrated before the percentages of correlated twins are discussed for each stress tesnor and the range of uncertainties on the determination of stress orientations and differential stress magnitudes is evaluated

synthetic slip plane the combination of a pair of twinned and untwinned e planes in a single calcite crystal application in dynamic analysis abstract this paper defines a synthetic slip plane as the linear combination of a pair of twinned and untwinned e planes in a single calcite crystal this auxiliary slip plane can be used together with the twinned e plane either to further constrain the extents of the compression and tension axes in graphic dynamic analysis or to better estimate the reduced stress in numerical dynamic analysis in this paper we proposed the novel method that solves for the reduced stress by maximizing the sum of the shear stress along the slip line on each twinned e plane or synthetic slip plane under the constraint of the 1 valued second stress invariant this new method yields an analytical solution of stress it is applied to a series of artificial examples without any measurement error generated under the prescribed stresses the estimated stresses are generally accurate and robust which illustrates the feasibility of this new method

on estimating the strength of calcite rocks under natural conditions abstract field studies of calcite mylonites often document microstructures produced by dislocation creep in contrast flow laws derived from experiments predict that calcite rocks should deform mostly by diffusion creep during tectonic processes to investigate this apparent discrepancy we compare stresses estimated by microstructural piezometers to those obtained by extrapolation of experimentally derived flow laws considering shear zones from different geological settings a clear trend is observed of increasing recrystallized grain size with increasing temperature however there is a large spread in grain size and associated stress because separate flow laws have been defined for various different marbles and limestones the strengths predicted for a given set of conditions differ significantly the stress estimates based on the piezometers and strength extrapolated from the various experimentally derived dislocation creep flow laws agree qualitatively but no single flow law predicts all the palaeostress estimates even if experimental data are disregarded the field observations are not consistent with a hypothetical law for coble creep they are consistent with a power law for dislocation creep but only if the material constants are different from those currently determined in laboratory experiments

empiricism and the biogeographical black box concepts and methods in marine palaeobiogeography abstract this paper reviews the concepts of palaeobiogeography in the wider context of biogeography as a whole and discusses the principal kinds of methods used in palaeobiogeography especially for reconstructing palaeogeography and geological history examples are mostly given from marine studies the emphasis is on the need for a more empirical approach especially in distinguishing between concepts of process and evidence of pattern and on the greater use of analytical methods biogeographical processes are very largely conjectural and are therefore envisaged collectively as a black box these processes can be grouped into three suites maintenance distributional change and origination according to a previously published scheme the variety of possible processes by which distributions arise can be expressed conceptually as alternative pathways through the black box empiricism in biogeography is hindered a by this synergism and b by the conflict between biogeography s different aims and the assumptions about processes embodied in these aims biogeography has conflicting geological and biological aims and there are six basic rationales with palaeobiogeographical equivalent applied to these aims 1 1 biogeographical raw data biogeographical patterns 2 2 biogeographical raw data biogeographical patterns biogeographical processes 3 3 biogeographical raw data biogeographical patterns biogeographical processes geological processes 4 4 biogeographical raw data biogeographical patterns assumption of biogeographical processes geological processes 5 5 biogeographical raw data biogeographical patterns assumption of geological processes biogeographical processes 6 6 biogeographical raw data biogeographical patterns assumption of geological processes biogeographical processes biological processes the different rationales especially their assumptions constrain the choice and quality of data used as well as choice of analytical method methods can be grouped according to the kinds of pattern they generate different kinds of pattern reflect different kinds of biogeographical process or black box pathway diversity of methodologies is therefore important because their results may provide complementary information critical appraisal of methods is not yet possible because there have been so few objective tests of them greater use of extrinsic criteria for assessing methods is advocated to supplement current emphasis on methodological theory in any case regardless of rigour in pattern analysis it is difficult to find satisfactory constraints for interpreting biogeographical patterns because the influence of geological processes on living systems is inadequately understood this particularly hinders use of distributions of organisms to reconstruct palaeogeography and geological history

palaeostress estimation using calcite twinning experimental calibration and application to nature abstract by means of high temperature deformation experiments on calcite rocks of different grain sizes we have established the relationships between differential stress and twinning incidence twin density and volume fraction and the way that these relationships depend on grain size both twinning incidence and volume fraction increase with grain size at a constant level of differential stress log twin density is proportional to stress but is independent of grain size at a given grain size volume fraction of twinning increases non linearly with differential stress twinning activity measured by twinning incidence increases linearly with stress the behaviour of each of these parameters is independent of temperature strain and strain rate these relationships can be used as a basis for the estimation of palaeostress values in naturally deformed calcite rocks this is illustrated by a study of twinning activity in limestones close to thrust faults in the cantabrian zone of the variscan orogenic belt in northwestern spain high peak differential stresses were measured ranging from 150 to 250 mpa using the turner dynamic analysis technique however it is clear that shear stresses resolved parallel to the fault planes were very low the attainment of high stress differences when the resistance to faulting was low is attributed either to bending forces induced during the motion of the non planar surfaces relative to each other or to the stress peak being attained prior to the localization of deformation onto the fault surfaces

biostratigraphic and radiometric age data question the milankovitch characteristics of the latemar cycles southern alps italy the combination of age diagnostic fossils in platform carbonates geometrical relationships with coeval basinal successions and single zircon u pb ages from volcaniclastic layers in basinal deposits constrain the age of a cyclic succession in the interior of the latemar platform to a narrow time span in the middle triassic with a duration shorter than 5 m y precession induced milankovitch band sea level oscillations are therefore excluded as controls for most of the 600 platform cycles reported from latemar statistical evaluation and graphic space time analyses of cycle stacking patterns alone may therefore not allow an unambiguous recognition of milankovitch frequencies in ancient platform carbonates

paleostress magnitudes associated with development of mountain belts insights from tectonic analyses of calcite twins in the taiwan foothills determinations of stress magnitudes based on inversion of calcite twin data from fault related folds in the taiwan foothills show a decrease of differential stresses during synfolding erosion and exhumation suggesting that paleodepth of burial largely controlled the levels of differential stresses sustained by rocks regional frictional conditions linked to shallow and or deep decollement tectonics probably also influenced stress magnitudes combination of the twin inversion technique with fracture analysis and rock mechanics data provides first order estimates of principal stress values related to the major pleistocene shortening event in taiwan these stress estimates are compared to previous stress estimates in fold thrust belts and to available data on differential stress magnitudes in foreland and hinterland domains of orogens at the scale of an entire orogenic system the most striking point is a decrease of differential stresses from the hinterland toward the foreland this decrease not only reflects tectonic stress attenuation away from the plate boundary but also suggests a major control by the depth of deformation differential stresses estimated from natural deformation consequently provide an independent support to the depth dependent strength and the frictional behavior of the upper continental crust deduced from laboratory experiments and stress measurements in deep boreholes

inversion of calcite twin data paleostress reconstruction and multiphase weak deformation in cratonic interior evidence from the proterozoic cuddapah basin india abstract paleostress orientations from mechanically twinned calcite in carbonate rocks and veins in the neighborhood of large faults were investigated to comment on the nature of weak upper crustal stresses affecting sedimentary successions within the proterozoic cuddapah basin india application of turner s p b t method and spang s numerical dynamic analysis on cuddapah samples provided paleostress orientations comparable to those derived from fault slip inversion results from the neighborhood of e w faults cutting through the paleoproterozoic papaghni and chitravati groups and the neoproterozoic kurnool group in the western cuddapah basin reveal existence of multiple deformation events 1 ne sw 3 in strike slip to extensional regime along with an additional event having nw se 3 for lower cuddapah samples 2 compressional transpressional event with ese wnw or nne ssw 1 mainly from younger kurnool samples integrating results from calcite twin data inversion fault slip analysis and regional geology we propose that late mesoproterozoic crustal extension led to initial opening of the kurnool sub basin subsequently influenced by weak compressional deformation the dynamic analysis of calcite twins thus constrains the stress regimes influencing basin initiation in the southern indian cratonic interior and subsequent basin inversion in relation to craton margin mobile belts and plausible global tectonic events in the proterozoic

recent and future trends in paleopiezometry in the diagenetic domain insights into the tectonic paleostress and burial depth history of fold and thrust belts and sedimentary basins paleopiezometry provides an access to the past stress magnitude key to better understand the behaviour of the earth s crust over long period of time this contribution presents a review of some paleopiezometric techniques that can be used in the diagenetic domain in fold and thrust belts and sedimentary basins calcite twinning and stylolite roughness techniques have been selected and are presented through a critical description of their methodologies along with approaches to further reconstruct the complete effective stress tensor major geological lessons learned over the past decades from published studies are summarized and discussed along with a way forward to potential breakthroughs

using neutron diffraction to examine the onset of mechanical twinning in calcite rocks experimental calibration of the calcite twin piezometer is complicated by the difficulty of establishing the stresses at which the twins observed in the final deformation microstructures actually formed in principle this difficulty may be circumvented if the deformation experiments are performed in a polychromatic neutron beam line because this allows the elastic strain and hence stress in differently oriented grains to be simultaneously monitored from diffraction patterns collected as the experiment is proceeding to test this idea small strain 0 3 uniaxial compression experiments have been performed on carrara marble grain size 150 m and solnhofen limestone 5 m at temperatures of 20 600 c using the engin x instrument at the isis neutron facility uk at the lowest temperatures 25 c carrara 200 c solnhofen the deformation response was purely elastic up to the greatest stresses applied 60 mpa carrara 175 mpa solnhofen the sign of the calcite elastic stiffness component c14 is confirmed to be positive when the obverse setting of the calcite rhombohedral lattice in hexagonal axes is used in the carrara marble samples deformed at higher temperatures elastic twinning was initiated at small stresses 15 mpa in grains oriented such that the schmid factor for twinning was positive on more than one e twin system at greater stresses 65 mpa at 200 c decreasing to 41 mpa at 500 c there was an abrupt onset of permanent twinning in grains with large schmid factors for twinning on any one e twin system no twinning was observed in the solnhofen limestone samples deformed at 200 or 400 c at applied stresses of 180 mpa these results highlight the potential of this approach for detecting the onset of twinning and provide through experiments on samples with different microstructures a strategy for systematically investigating the effects of microstructural variables on crystallographically controlled inelastic processes

paleobiogeography of campanian maastrichtian foraminifera in the southern high latitudes abstract distributions of planktonic and benthic foraminifera have revealed antarctic land sea distributions oceanic surface gyre configurations and changes in the configurations of the tethyan transitional and austral realms during campanian maastrichtian time poleward changes in the diversity of total and keeled planktonic species of the southern hemisphere are compared for the early and late campanian and early and late maastrichtian latitudinal diversity gradients were weakest during the early campanian and more pronounced during the late campanian and maastrichtian shallow marine seaways within west antarctica are suggested by similarity of late cretaceous nearshore benthic and open ocean planktonic assemblages from southern high latitude land and drill sites and by the occurrence of recycle cretaceous marine microfossils from antarctic interior and continental margin localities development of a major water mass boundary between cool surface waters south of about 50 s paleolatitude and warmer surface waters to the north in the south atlantic and indian ocean may have caused biogeographic isolation of austral realm assemblages during late campanian and early maastrichtian time several planktonic foraminifera show significant diachroneity in their latitudinal distributions magnetobiostratigraphic data suggest that abathomphalus mayaroensis migrated from high to low latitudes whereas pseudotextularia elegans globigerinelloides subcarinatus globotruncanella citae globotruncanella petaloidea globotruncana bulloides and globotruncana subcircumnodifer made time transgressive poleward migrations the distribution of a mayaroensis is in agreement with isotopic evidence for late maastrichtian climatic cooling while that of p elegans correlates with a latest maastrichtian warming event about 66 8 66 6 ma delayed first occurrences of the other taxa cannot be explained by paleoclimatic factors alone variations in global eustatic sea level and orogeny between southern south america and west antarctica may have also influenced the taxonomic composition of southern high latitude foraminiferal assemblages

calcite twins from microveins as indicators of deformation history abstract in order to investigate whether the evidence of the deformation history is preserved in the microvein calcite twinning microstructures several families of calcite veins have been studied from weakly deformed mesozoic limestones of the western iberian chain eastern iberian peninsula the maximum shortening directions established with this method correspond to the previously established paleostress evolution of this chain the reconstructed stress regimes evolve from predominantly compressional four compressional episodes with the maximum shortening direction oriented successively nw se n s ne sw and e w to extensional the established orientations of maximum shortening axes are consistent with the directions of paleostrains that have been independently deduced from stylolites and fault striations in the same region moreover the results clearly show that the e twins record some paleostress orientations that are not registered in the studied area by fault population analysis in this sense the e twins record older paleostress orientations than the small faults probably because the faults were reactivated several times and the twins were not modified since their formation the calculated values of twin strains 1 differential stress magnitudes 62 mpa and the existence of type i twins formed below 200 c confirm that this region was slightly deformed under low p t conditions

structural and microstructural evolution of the rattlesnake mountain anticline wyoming usa new insights into the sevier and laramide orogenic stress build up in the bighorn basin the rocky mountains in western us provide among the best examples of thick skinned tectonics following a period of thin skinned tectonics related to the sevier orogeny the compressional reactivation of basement faults gave birth to the so called laramide uplifts arches the bighorn basin located in wyoming is therefore a key place to study the transition from thin to thick skinned tectonics in orogenic forelands especially in terms of microstructural and stress strain evolution our study focuses on a classic laramide structure the rattlesnake mountain anticline rma wyoming usa a basement cored anticline located in the western part of the bighorn basin stress and strain evolution analysis in folded sedimentary layers and underlying faulted basement rocks were performed on the basis of combined analyses of fractures fault slip data and calcite twinning paleopiezometry most of the fractures are related to three main tectonic events the sevier thin skinned contraction the laramide thick skinned contraction and the basin and range extension serial balanced cross sections of rma and displacement profiles suggest that all thrust faults were coeval evidencing strain distribution in the basement during faulting the comparison of rma with another structure located in the eastern edge of the bighorn basin i e the sheep mountain anticline sma allows to propose a conceptual model for the geometric and kinematic evolution of laramide related basement cored anticlines finally the stress evolution is reconstructed at both the fold scale and the basin scale we show that the evolution of stress trends and magnitudes was quite similar in both structures rma and sma during laramide times thick skinned tectonics in spite of different stress regimes during sevier thin skinned tectonics and post laramide times stress trends and fracture patterns were different in these two structures these results suggest that the distance to the orogenic front influenced the fracture patterns but not the foreland stress magnitudes which were likely controlled by the structural style

hydrothermal venting within a coral reef ecosystem ambitle island papua new guinea shallow water 5 10 m hydrothermal venting in a nearshore coral reef environment at ambitle island in the tabar feni island arc east of papua new guinea occurs as focused discharge of boiling fluid from discrete ports 10 15 cm in diameter and as dispersed discharge of diffuse bubble streams that issue through the sandy mixed carbonate volcaniclastic sea floor abiotic aragonite and microcrystalline ferroan low mg calcite interlaminated with fe oxyhydroxides are the prominent hydrothermal precipitates geochemical attributes of aragonite 18o 13c and fluid inclusions suggest that cements formed from a solution with salinities 5 at temperatures of 100 c with probable contribution of hydrothermal co2 sr isotope ratios in abiotic hydrothermal aragonite 0 704 15 are similar to those in island arc basalt and denote considerable subsurface water rock interaction of meteoric water derived from the adjacent volcanic island the sr isotope ratio of a coral sample 0 707 46 collected adjacent to a vent portal suggests coral growth within a mixed seawater hydrothermal environment

marine ostracode provincialism in the late cretaceous of the tethyan realm and the austral province abstract a synthetic analysis based on previous and new data allows the recognition of four main palaeobiogeographic units palaeobioprovinces for the late cretaceous of the tethyan realm and austral province of the south temperate realm south european north central american afro arabian and austral bioprovinces another unit the dinaro hellenic subprovince is located between the south european and the afro arabian bioprovinces special emphasis is given to the spatial and temporal distribution of ostracode assemblages at the specific level and selected key genera within several geographic zones from the tethys north central america southern europe northern africa and the middle east to eastern africa india south africa and australia several factors are responsible for these palaeobiogeographic distributions provincialism and their evolution the position and extension of continental margins oceanic surface current patterns paleobathymetry eustatic sea level changes paleolatitudes and their influence on paleoclimates other parameters are the biology physiology and ecology of the ostracodes therefore ostracode provincialism has a high potential for further paleogeographic inferences such as global tectonic reconstructions

nature and evolution of middle triassic carbonate buildups in the dolomites italy during the middle triassic an evolution from carbonate bank to buildup highly elevated in respect of the adjacent basins is observed in the alps the dolomites in the southern alps italy are here considered as an example during the anisian subtidal banks of the upper serla fm with rare peritidal cycles show only a limited biologic density and diversity with the late anisian contrin fm a gradual development of binding and framework building communities can be observed the sinking of wide areas of the contrin carbonate bank into anoxic conditions plattenkalke fm allowed the birth of isolated buildups their increased carbonate production due to a greater diversity and density of organisms was able to keep up with the rate of subsidence the latemar buildup with additional data for the slope taken from mt coldai civetta and sass da putia is used to illustrate the main character of a lower ladinian buildup the restricted platform sediments display peritidal cycles prevalent in the subtidal portion is dasycladacean packstone grainstone associated with gastropods ammonoids and blue green algae in the supratidal portion desiccation and tepee structures are present scleractinian and sphinctozoan frameworks are rare on the upper part of the slope which is bound predominantly by encrusting organisms mainly blue green algae porifers and tubiphytes the prevailing sediments on the upper part of the slope are bindstones whilst packstones and rudstones are in the lower part of the slope the latter carbonates were cemented early under submarine conditions mostly by isopachous palisade cement polyphasic internal sediments with phreatic vadose influence are present and can in the middle lower part of the slope replace most of the original sediment

sea level changes versus hydrothermal diagenesis origin of triassic carbonate platform cycles in the dolomites italy abstract the triassic platform carbonate cycles of the dolomites best developed and studied at the latemar have been considered key examples for the documentation of eustatic sea level changes the cycles appear to reflect a low energy lagoonal environment which is however difficult to reconcile with the small platforms lacking marginal energy barriers in a tropical stormy climate an alternative interpretation to eustatically controlled cyclicity and repeated subaerial exposure is provided by diagenesis in a hydrothermal field elevated heat flow 0 2 ma before the onset of the mafic igneous activity triggered the circulation of diagenetic fluids with a composition similar to seawater by intermittent opening of fractures through some platforms this caused tepee formation by precipitation of displacive cement pendant cement and pisolite formation and favoured cyanobacterial mat formation and their early dolomitization the abundance of cycles correlates with that of the somewhat younger volcanic dikes crosscutting some platforms diffuse venting or seeping in the upper unconsolidated sediment layers explains the stratiform occurrence of the diagenetic features and alternation with normal marine deposition in deep but photic water at the wave base

marine faunal realms of the mesozoic review and revision under the new guidelines for biogeographic classification and nomenclature consensus among the friends of paleobiogeography produced tentative guidelines to the classification and nomenclature of marine biogeographic units i e biochores based on these loose rules the present paper is a critical review of all published mesozoic marine realms subrealms and superrealms formerly called climatic belts biochores are defined by the overall endemism within geographic and time envelopes that include choro and chrono types without consideration of facies or climate the hierarchy of ranks or tiers is superrealm realm subrealm province subprovince only ranks in italics are obligatory region is informal these ranks scale with endemism geographic range and persistence in time biochores are named geographically following nomenclatural guidelines not strict rules of synonymy and homonymy with priority beginning with uhlig s paper of 1911 uhlig s two climatic belts are tentatively accepted as optional top ranking superrealms for times of exceptional global endemism available names for them are euroboreal or panboreal new and tethys panthalassa the validity of the 29 existing names for realm group biochores realms subrealms and superrealms in the marine mesozoic is discussed 19 names are rejected for a variety of reasons including synonymy homonymy and usefulness the most important realm group biochores are arctic and boreal atlantic in the boreal euroboreal realm or superrealm and tethyan mediterran caucasian indo pacific jurassic early cretaceous and austral middle late cretaceous in the tethys panthalassa superrealm

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

cretaceous and early tertiary climates of antarctica evidence from fossil wood abstract fossil wood is abundant in cretaceous and early tertiary sediments of the northern antarctic peninsula region the wood represents the remains of vegetation that once grew in high palaeolatitudes when the polar regions were warmer during former greenhouse climates fossil wood is a unique data store of palaeoclimate information analyses of growth rings and anatomical characters in fossil wood provide important information about temperature rainfall seasonality and climate trends for this time period in antarctica climate signals from fossil wood supported by sedimentary and geochemical evidence indicate a trend of cool climates during the early cretaceous followed by peak warmth during the coniacian to early campanian narrower growth rings suggest that the climate cooled during the maastrichtian and palaeocene cool wet and possibly seasonal climates prevailed at this time with tentatively estimated mean annual temperatures mats falling from 7 c to 4 8 c respectively determined from dicotyledonous dicot wood anatomy the late palaeocene early eocene was once again warm with estimated mats of 7 15 c from dicot wood analysis but conditions subsequently deteriorated through the latter part of the eocene when cold seasonal climates developed ultimately leading to the onset of cenozoic ice sheets and the elimination of vegetation from most of antarctica

reliability of selected procedures of stress inversion and data separation for inhomogeneous populations of calcite twins and striated faults insights from numerical experiments in the course of numerical experiments selected algorithms for stress tensor inversion and separation of heterogeneous populations of calcite twins and striated faults were tested artificial data sets were created in a manner simulating natural processes they were composed of data dynamically compatible with one or two stress tensors and chaotic noise imitating natural imperfections for calcite twins the classical inversion procedure is considered valid with restrictions regarding a high proportion of chaotic data when shape ratio of the stress tensor is poorly constrained the algorithm of etchecopar 1984 fide tourneret and laurent in tectonophysics 180 287 302 1990 devised originally for calcite twins has been modified and applied to fault slip data facilitating a rejection of incompatible outliers two main classes of data separation procedures were tested separation contemporary with inversion and separation prior to inversion utilising hierarchical clustering the separation contemporary with inversion performs moderately but often fails with complex calcite twin sets the performance of hierarchical clustering is high but only with a 1 orientation as a similarity criterion the new strategy introduced in this contribution for fault slip data the hierarchical clustering with the right dihedra construction as the similarity criterion nemcok et al 1999 is satisfactory additionally a new approach is proposed for fault slip data utilising principles of the classical algorithm for heterogeneous populations of calcite twins validated algorithms for striated faults were successfully applied to a natural data set from the holy cross mts central poland

inversion of polyphase calcite twin data for deviatoric stress tensors 2 application to the huangling dome northern south china abstract the north trending huangling dome located on the northern margin of the reactivated yangtze platform provides an appropriate place to understand the complexity of intraplate deformation of the south china continent since the early mesozoic in this study palaeostress analysis using calcite twins was carried out to address the deformation mechanism of the dome poorly understood at present ten limestone samples and three marble samples were collected from the platform cover on the eastern and western flanks and the core basement measured under the universal stage and inverted for stress analysis using our recently proposed method all the stress estimates for the samples were classified into two layer parallel shortening lps subsets and two non lps subsets they represent nw se compression ne sw compression n s compression and n s or e w extension respectively in correspondence to principal tectonic events since the early mesozoic they do not verify existing explanations about the genesis of the dome for example extrusion induced e w compression and differential uplift related e w extension a new formation model was therefore proposed under the nearly n s compression the dome initiates as an e w trending brachy anticline and owing to basement inheritance and variation of regional shortening gains the current configuration

joint analyses of calcite twins and fault slips as a key for deciphering polyphase tectonics burgundy as a case study abstract determination of regional paleostresses based on calcite twin analysis has been successfully applied for the first time in the burgundy platform france paleostress tensors obtained with this method are internally consistent along the profile studied moreover the same directions of paleostresses are independently inferred from fault striation analysis the results clearly show that the late mesozoic cenozoic evolution of the area has involved polyphase deformation including 1 1 nne ssw extension probably late mesozoic in age 2 2 n s compression related to a major orogenic event in the pyrenees and provence late eocene in age 3 3 e w extension related to the oligocene rifting event the rhine saone rift system 4 4 wnw ese compression related to the late miocene westward thrusting of jura calcite twin and striated fault analyses are two complementary tools for paleostress determination their combined application will allow accurate mapping of paleostress trajectories in intraplate tectonics setting moreover calcite twins can allow stress and paleostress determination when macroscopic features are not observable which is often the case in very weakly deformed areas and in drill holes

global cretaceous paleogeography international geologic correlation program project 191 abstract five global cretaceous paleogeographic maps within a plate tectonic framework are illustrated based on the ten contributions in this special volume

multivariate data analysis in palaeoecology and palaeobiogeography a review abstract palaeoecologists and palaeobiogeographers are often confronted with large multivariate data sets from which fossil communities assemblages or associations or faunal provinces are to be recognized the complex multidimensional nature of these data sets the recognition of the enormous variation of communities and environments both in space and time and the difficulties of dealing with these problems by the human mind justify the use of multivariate statistical methods in palaeoecology and palaeobiogeography concepts and basic procedures of several commonly used multivariated statistical methods of palaeoecology and palaeobiogeography are reviewed in the wider context of quantitative community ecology and biogeography basic assumptions about data structure and theoretical and practical limitations are discussed the emphasis is on evaluation of binary similarity coefficients and two multivariate approaches cluster analysis and ordination thirty nine binary similarity coefficients are evaluated against nine criteria jaccard s coefficient of community is found most suitable as a similarity measure between samples under the conditions tested algorithmic procedures of cluster analysis especially the agglomerative hierarchical cluster analysis techniques and indirect ordinations particularly polar ordination principal component analysis principal coordinate analysis correspondence analysis detrended correspondence analysis and nonmetric multidimensional scaling are outlined and their applicability to palaeoecological and palaeobiogeographical data is discussed where the data are appropriate an integration of cluster analysis and ordination is suggested to be applied to the same data

intraplate paleostresses reconstructed with calcite twinning and faulting improved method and application to the eastern paris basin lorraine france this study deals with the reconstruction of intraplate paleostresses calcite twinning inversion provides paleostress directions and differential values even in poorly outcropping areas however existing methods are not well adapted to multiphase deformation cases and the calculation of stress values provides unreliable estimates modifications were brought to a calcite twinning inverse method and to the processing of results in a new twin data separation process the whole set of data is used to calculate each tensor the variability of yield stress value for twinning with strain hardening is taken into consideration a first order yield stress calcite grain size dependence function has been established with a sample showing various grain sizes this modified method of calcite twinning inversion was applied in the eastern paris basin lorraine france in this platform area measured fractures are preferentially trending ne sw and nw se at all scales the meso cenozoic paleostress succession reconstructed with fault slips is complex jurassic sedimentation occurred during the tethys rifting a mainly strike slip phase with r1 successively striking nnw and nne is attributed to the tertiary pyrenean orogenesis and is followed by wnw extension in the oligocene after local ene compression wnw compression was probably due to the alpine late miocene collision the calcite twinning inversion has confirmed these tectonic events and their succession order and the directions of stress axes were specified using grain size and strain rate sensitive yield stress values the differential stresses can be estimated with an uncertainty of few mpa they range between 20 and 30 mpa depending on the tectonic event the oligocene paleodepths of the sampled calcite estimated using differential stress values are structurally sensible thus the original calcite twinning inverse method has been improved complex paleostress successions such as in platform areas may be deciphered by combination with fault slip inversion even if additional improvement is possible this calcite twinning inverse method opens new ways to determine stress distributions in tectonic plates d 2004 published by elsevier b v

cretaceous tectonic evolution of the sava klepa massif republic of north macedonia results from calcite twin based automated paleostress analysis abstract the sava klepa massif represents an approximately 5 2 km sized fault bounded block of dominantly basaltic rocks located within the sava zone an important suture zone between the eurasian europe and gondwana adria continental plates in the balkans its nature and tectonic evolution is controversial it is either interpreted as a remnant of the youngest tethyan oceanic realm left behind after the main closure in the late jurassic or as the delimiter of a diffuse tectonic boundary between adria and europe which had already collided in the late jurassic and was dominantly controlled by transtensional tectonics during cretaceous times in order to strengthen one or the other model we concentrate on the sava klepa massif enclosing paleozoic basement rocks which mainly consist of a layered sequence of metamorphic marbles and mica schists the metamorphic basement shows deformation structures clearly related to the klepa event our results are based on paleostress and paleostrain analysis of twinned calcite from deformed marbles and field observations microstructural analysis and 40ar 39ar dating of white mica paleostress and paleostrain analysis was enhanced by using an automated fabric analyser microscope and developing the herein presented freeware standalone windows executable pact software paleostress analysis with calcite twins our results support the hypothesis that the sava klepa massif was formed during transtension as a pull apart basin in the late cretaceous this could have happened either after the collision of the european and adriatic plates or along a transtentional zone in the fore arc region during subduction of the last tethyan oceanic lithosphere

palaeostress magnitudes in the khao khwang fold thrust belt new insights into the tectonic evolution of the indosinian orogeny in central thailand using the khao khwang fold thrust belt in central thailand as case study we handled data from calcite twinning analysis in order to propose the quantification of the effective principal palaeostresses magnitudes since the onset of the early stages of the indosinian orogeny we also combined the differential stress estimates from mechanically induced calcite twins with geochronological data in order to constrain the timing of the palaeoburial depth and subsequent uplift by folding within the khao khwang fold thrust belt the proposed mechanical scenario is based on the time constrained kinematic sequence of fracturing faulting and folding in the strata of the carbonate formations of the saraburi group cross checking the data on the palaeostress orientations regimes and differential stress magnitudes with rock mechanics analysis we provided data on the principal stress magnitudes for each tectonic stage that developed during the indosinian orogeny further 40ar 39ar and u pb geochronological data allowed to place reliable constraints on the amount and rate of vertical uplift of the carbonate formations of the saraburi group

inversion of calcite twin data for paleostress orientations and magnitudes a new technique tested and calibrated on numerically generated and natural data abstract the inversion of calcite twin data is a powerful tool to reconstruct paleostresses sustained by carbonate rocks during their geological history following etchecopar s 1984 pioneering work this study presents a new technique for the inversion of calcite twin data that reconstructs the 5 parameters of the deviatoric stress tensors from both monophase and polyphase twin datasets the uncertainties in the parameters of the stress tensors reconstructed by this new technique are evaluated on numerically generated datasets the technique not only reliably defines the 5 parameters of the deviatoric stress tensor but also reliably separates very close superimposed stress tensors 30 of difference in maximum principal stress orientation or switch between 3 and 2 axes the technique is further shown to be robust to sampling bias and to slight variability in the critical resolved shear stress due to our still incomplete knowledge of the evolution of the critical resolved shear stress with grain size our results show that it is recommended to analyze twin data subsets of homogeneous grain size to minimize possible errors mainly those concerning differential stress values the methodological uncertainty in principal stress orientations is about 10 it is about 0 1 for the stress ratio for differential stresses the uncertainty is lower than 30 applying the technique to vein samples within mesozoic limestones from the monte nero anticline northern apennines italy demonstrates its ability to reliably detect and separate tectonically significant paleostress orientations and magnitudes from naturally deformed polyphase samples hence to fingerprint the regional paleostresses of interest in tectonic studies

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

global campanian upper cretaceous ostracod palaeobiogeography abstract the distribution of 218 campanian marine ostracod genera from 38 geographical areas was used for a quantitative palaeobiogeographical analysis the data were analysed using multivariate statistical methods ordination methods and parsimony analysis of endemicity these methods resulted in distinct geographical area groupings of the studied regions with these groupings seven palaeobiogeographical units based on campanian ostracod occurrences are distinguished the composition of the area groupings and the distribution of the palaeobiogeographical units are discussed their development and spatial distribution are broadly controlled by campanian palaeoclimates partly modified by palaeogeographical conditions

bivalve provinces in the proto atlantic and along the southern margin of the tethys in the jurassic abstract using multivariate methods the distribution pattern of jurassic bivalve genera and subgenera within the proto atlantic and along the southern margin of the tethys is analysed based on an extensive literature survey and examination of field collections four bivalve provinces are recognised within the proto atlantic 1 the boreal bivalve province in the north 2 the northern transitional province 3 the southern transitional province and 4 the mediterranean bivalve province the former two provinces are assigned to the boreal faunal realm the latter two to the tethyan faunal realm the southwestern margin of the tethys belongs to the mediterranean bivalve province the southeastern margin to the ethiopian bivalve province the latter is only poorly defined by bivalve genera subgenera in particular its northern boundary is blurred with the arabian region occupying an intermediate position between the mediterranean and the ethiopian bivalve provinces province boundaries based on bivalves do not always coincide with those based on ammonites the reason for this is probably different modes of life ammonites as a rule being active swimmers and bivalves being substrate related and subjected to passive dispersal during the larval stage diversity is not suitable to characterize bivalve provinces due to differences in outcrop size preservation potential and sampling history and due to differences in the degree of environmental heterogeneity within and between regions migration patterns of jurassic bivalves either reflect changes in the climatic condition e g the northward spread of tethyan taxa in the late early jurassic and middle jurassic in the course of amelioration of the climate or prevailing current patterns the origin of faunal provinciality is thought to be complex and a result of the interplay of several factors the importance of which varied throughout the jurassic

biogeography of circum mediterranean miocene pliocene rodents a revision using factor analysis and parsimony analysis of endemicity abstract the biogeographic relationships of north african miocene pliocene rodent faunas are assessed using two different methods factor analysis and parsimony analysis of endemicity the mediterranean basin is a true biogeographic province within it north africa makes up a sub province of its own only slightly closer to the ibero occitanian sub province than to the eastern mediterranean one these three sub provinces retain their permanency over time localities within them being clustered according to their geological age rather than by geographic location the miocene pliocene is a period of strong but transitory similarity between the north and south while there is a steady trend toward homogenisation of the northern mediterranean most of the exchanges occur through france between the eastern mediterranean and eastern spain and between the latter area and the rest of iberia and north africa while there are very few trans mediterranean and southern longitudinal exchanges

inversion of polyphase calcite twin data for deviatoric stress tensors 1 a novel numerical approach abstract a new inversion method is developed in this paper to estimate deviatoric stress tensors from a certain population of polyphase calcite twins it is both to minimize the number of the common incompatible twinned and untwinned e planes and to maximize the sum of the resolved shear stresses along the compatible twinned e planes under each reduced stress the genetic algorithm is employed to resolve this optimization problem a series of two phase equally mixed artificial datasets generated under the prescribed stresses were taken to demonstrate the feasibility of this method results indicate a strong tendency to have an increasing accuracy of reduced stress with the ascent of the prescribed maximum differential stress the difference between the prescribed stresses and the number of twinned calcite crystals respectively what is more the maximum differential stress becomes sufficiently large to permit an accurate estimate of reduced stress even though the prescribed stresses are intermediately similar to each other however the method assumes a constant critical resolved shear stress value to rescale the stress tensors and does not consider the influence on the critical resolved shear stress value of strain hardening grain size and temperature it takes an enormous amount of time in calculation

determining deviatoric stress tensors from calcite twins applications to monophased synthetic and natural polycrystals theoretically calcite twins analysis makes possible the full determination of the deviatoric stress tensor responsible for the formation of the twin lamellae that is the orientations of the principal stress axes and the three differential stress values i j may be calculated assuming conditions of constant resolved shear stress for twinning inverse method using nonlinear regression and robust estimation is proposed applications to monophased synthetic polycrystals that are generated numerically by solving the direct problem and to a natural sample from the quercy southwest of france have given good results comparison with the first method proposed by turner 1953 modified by nissen 1964 for principal stress orientations and by jamison and spang 1976 for differential stress values clearly emphasizes the considerable interest of this new method

late mesozoic and cenozoic stratigraphy and geological history of the south atlantic high latitudes abstract the complex analysis of various organic remains in upper mesozoic and cenozoic deposits of the southwest atlantic legs 36 40 71 and piston cores has led to a reliable subdivision of the sedimentary cover in its high latitudinal part planktonic foraminifers and calcareous nannoplankton dominate the biostratigraphy of the cretaceous and paleogene from the oligocene the leading role in the subdivision of sediments gradually passed to siliceous microfossils that provided an extremely detailed stratigraphy in the late cenozoic the history of oceanic subsidence sedimentation hiatuses and ccd fluctuations within the falkland plateau have been reconstructed on the basis of the biostratigraphic scheme obtained an attempt to trace cretaceous and cenozoic relative climatic fluctuations according to the changing in planktonic foraminiferal assemblages has been made oceanic and continental data combined have specified some aspects in the geological evolution of the high latitude south atlantic basin from its opening to date this paper emphasizes the importance of the circum antarctic current in paleoclimatic and sedimentational changes as well as the onset of the antarctic cover glaciation

stress and strain patterns kinematics and deformation mechanisms in a basement cored anticline sheep mountain anticline wyoming 1 in order to characterize and compare the stress strain record prior to during and just after folding at the macroscopic and the microscopic scales and to provide insights into stress levels sustained by folded rocks we investigate the relationship between the stress strain distribution in folded strata derived from fractures striated microfaults and calcite twins and the development of the laramide basement cored sheep mountain anticline wyoming tectonic data were mainly collected in lower carboniferous to permian carbonates and sandstones in both rock matrix and veins calcite twins recorded three different tectonic stages the first stage is a pre laramide sevier layer parallel shortening lps parallel to fold axis the second one is a laramide lps perpendicular to the fold axis and the third stage corresponds to laramide late fold tightening with compression also perpendicular to the fold axis stress and strain orientations and regimes at the microscale agree with the polyphase stress evolution revealed by populations of fractures and striated microfaults testifying for the homogeneity of stress record at different scales through time calcite twin analysis additionally reveals significant variations of differential stress magnitudes between fold limbs our results especially point to an increase of differential stress magnitudes related to laramide lps from the backlimb to the forelimb of the fold possibly in relation with motion of an underlying basement thrust fault that likely induced stress concentrations at its upper tip this result is confirmed by a simple numerical model beyond regional implications this study highlights the potential of calcite twin analyses to yield a representative quantitative picture of stress and strain patterns related to folding

determination of principal stress magnitudes using calcite twins and rock mechanics data abstract this paper proposes a new method for determining principal stress magnitudes based on the use of the deviatoric stress tensor determined from computer inversion of calcite twin data additional evaluation of the vertical stress weight of overburden or of the mean stress is enough to calculate the complete stress tensor we emphasize that the best reasoning consists of combining calcite twin analysis with rock mechanics data failure friction criteria because the determination of the six parameters of the absolute stress tensor is overconstrained