structure of the vakhsh fold and thrust belt tadjik ssr geologic mapping on a landsat image base an enhanced landsat image of the northeastern tadjik depression in the soviet union was combined with field data to produce a 1 250 000 geologic map of the vakhsh fold and thrust belt and adjacent autochthon mapping of the relatively continuous geologic structure in this region first required recognizing marker beds and contacts at or near the resolution of the landsat sensor and then defining mappable units satellite image mapping was complemented by field study which was necessary in this recently deformed area both to verify the image mapping and to obtain more accurate structural dips deformation of the cretaceous and tertiary strata of the fold and thrust belt is in the western half of the mapped area conspicuously absent north of a buried basement fault that marks the hinge zone of the late mesozoic passive margin in the eastern half of the mapped area however the major thrusts displacing rocks northward have moved coherent sheets over the block fault these sheets now lie flat atop the autochthon to the north tectonically these observations indicate that 1 the crustal structure inherited from the mesozoic extensional phase has strongly influenced the late cenozoic pattern of deformation 2 the thrust sheets that are displaced over the paleo hinge zone actively load the basement rocks to the north and 3 the development of the fold and thrust belt which is markedly asymmetric has included the progressive overlapping of thrusts the later thrusts apparently formed internal to the older thrusts and subsequently overrode them

relationships of rock cleavage fabrics to incremental and accumulated strain in the conococheague formation u s a abstract pressure solution coupled with twin gliding and recrystallization acted to form two geometrically distinct cleavages in the conococheague formation northwest virginia and west virginia limestone layers contain a penetrative cleavage sp formed by pervasive pressure solution coble creep with twin gliding in more highly deformed zones dolomite layers contain a spaced solution cleavage ss formed by pressure solution also with twin gliding in highly deformed zones recrystallization textures occur in highly deformed zones of limestones and dolomites incremental strain shows that layering was initially inclined as much as 30 to shortening and that the deformation was locally non coaxial as viewed by the deforming material on the fold limbs spaced cleavage zones are curved and closely match the initial and final orientations of incremental elongation penetrative cleavage parallels the elongation axis of accumulated strain measured using deformed ooids pressure solution surfaces in dolomites concentrate insoluble materials deformation together with twin gliding and recrystallization are greatest in the hinge zones of folds and least on shallowly dipping limbs of asymmetric folds the deformation mechanism path of calcite and dolomite are similar changing from pressure solution to twin gliding with recrystallization as strain rate strain energy density increases

development of cleavage in limestones of a fold thrust belt in eastern new york abstract tectonic cleavage has developed in lower devonian limestones of the hudson valley fold thrust belt in new york state morphology and distribution of cleavage in these limestones is controlled by the amount of clay quartz matrix present and by strain only limestones with greater than 10 clay quartz matrix developed widespread cleavage x ray diffraction analyses indicate that the clay matrix was altered during deformation the width of the 001 illite peak in cleaved lime wackestone is less than that in uncleaved lime wackestone from the same stratigraphic level a minimum of 10 clay is necessary to provide interconnectivity between sites of dissolution and the free fluid system preliminary analyses of bulk chemistry indicate that calcite is removed from the local rock system during cleavage development supporting proposals that circulation of fluid through the rock plays a major role in the development of cleavage textural evidence suggests that both pressure solution and free face dissolution contribute to the removal of ions at grain boundaries cross cutting relations indicate that cleavage was initiated early during the development of the fold thrust belt but continued to develop during the late stages of folding

microstructures deformation mechanisms and strain patterns in a vertical profile inner appalachian fold thrust belt alabama a core from the american anniston no 1 well drilled in the pell city thrust sheet calhoun county alabama provides an excellent scientific opportunity to study in a vertical profile the deformation mechanisms and strain patterns associated with large scale structures the core contains stratigraphic units from cambrian to mississippian in age and two major thrust faults a detailed structural analysis revealed two deformation episodes a pre orogenic deformation and alleghanian orogenic deformation in the pre orogenic deformation synsedimentary folds and growth faults are the characteristic early structures and normal faults formed in lithifield rocks later during alleghanian deformation earlier fractures are overprinted by later s1 penetrative structures in limestone shale and siltstone within thrust sheets s1 is solution cleavage dolomites in the thrust sheets were deformed by fracturing and no penetrative cleavages formed in major fault zones s1 mylonitic foliation formed in limestone shale and siltstone fault related dolomites were deformed cataclastically and no s surfaces formed strain magnitude increases towards major thrust faults in both the hanging walls and footwalls for the typical fault configuration in the core with limestone dolomite in the hanging wall and shale siltstone in the footwall strain is mainly caused by pressure solution and cataclasis in the hanging wall and by plastic deformation in the footwall

coupling of diffusional mass transport and deformation in a tight rock abstract simple governing equations coupling diffusional transport at a macroscopic scale and deformation in a tight rock are formulated the deformation alone is described by a linear viscous rheology several deformations of geological interest are analyzed including the folding of an embedded layer a basic feature is the length scale dependence of diffusional effects interpretation of natural structures permits the estimation of parameters governing the diffusional transport and rate of deformation

hillslope runoff processes and models abstract hillslope hydrology is concerned with the partition of precipitation as it passes through the vegetation and soil between overland flow and subsurface flow flow follows routes which attenuate and delay the flow to different extents so that a knowledge of the relevant mechanisms is important in the 1960s and 1970s hillslope hydrology developed as a distinct topic through the application of new field observations to develop a generation of physically based forecasting models in its short history theory has continually been overturned by field observation thus the current tendency particularly among temperate zone hydrologists to dismiss all hortonian overland flow as a myth is now being corrected by a number of significant field studies which reveal the great range in both climatic and hillslope conditions some recent models have generally attempted to simplify the processes acting for example including only vertical unsaturated flow and lateral saturated flows others explicitly forecast partial or contributing areas with hindsight the most complete and distributed models have generally shown little forecasting advantage over simpler approaches perhaps trending towards reliable models which can run on desk top microcomputers the variety now being recognised in hillslope hydrological responses should also lead to models which take account of more complex interactions even if initially with a less secure physical and mathematical basis than the richards equation in particular there is a need to respond to the variety of climatic responses and to spatial variability on and beneath the surface including the role of seepage macropores and pipes which call into question whether the hillside can be treated as a darcian flow system

compound tectonic fabrics in singly folded rocks from southwest virginia u s a abstract a compound tectonic fabric is associated with folded and faulted calcareous mudrock in the foreland fold and thrust belt of the appalachian orogen two approximately coplanar spaced cleavages evolved during one episode of folding an earlier close spaced 40 spacing domainal microfabric is overprinted by and transitional with a wider spaced 2 3 cm spacing spaced disjunctive cleavage development of the spaced cleavage from the domainal microfabric is considered due to a change in dominant deformation mode from controlled grain boundary sliding to pressure solution factors which determine whether single or compound cleavage fabrics develop in singly folded rocks may relate to the timing of cleavage forming deformation increments relative to metamorphic dehydration reactions at low metamorphic grade anchimetamorphism to low greenschist facies it is proposed that grain alignment cleavage will develop when reactions are concomitant with deformation whereas a spaced cleavage will develop when reactions are inhibited or have gone to completion compound tectonic fabrics result when reactions either undergo completion or are initiated during the period of cleavage formation there are three distinct geometrical associations of compound fabrics and folds these associations are determined by the relative timing of formation of the various cleavages with respect to the folding

high latitude eurasian paleoenvironments introduction and synthesis abstract this special issue developed partly from the open pages conference held in moscow in may 2002 the dominant theme of the present collection of articles is the late pleistocene and holocene paleoenvironmental history of northern eurasia from the white to the black sea and from the estonia to the kurile islands here we briefly summarize the available paleorecords from the fsu territory covering the last 1500 years a number of records allow one to distinguish the climatic pattern of the 9th 13th centuries from earlier and later colder conditions in the kola peninsula urals taymir russian plain caucasus and east siberia the 10th 12th centuries were also slightly warmer in the far east kurile islands the warming of the 14th century in several regions including the russian plain altai and central asia was at least as intense as the earlier one at ca 1 kyr before present or even warmer the available data for this time period remain controversial in the arid area of central asia records from the caspian sea area suggest moderate temperature and relatively high humidity in the first half of the millenium whereas in the tien shan mountains the beginning of the millenium seems to have been warm and dry various line of evidence suggest a climatic deterioration in the second half of the last millenium throughout the fsu including the european part siberia the caucasus the mountains of the central asia the far east and the arctic archipelagoes

geomorphology and late holocene morphogenesis of tchinguiz tepe hill old termez uzbekistan central asia tchinguiz tepe hill is the southernmost outcrop interrupted at the shores of the amu darya of the cenozoic sediments that form the baysuntau kugitangtau alignment the initiation points of the recent morphogenesis are the slopes and a pediment controlled structurally by the unequally weathered substrate the hill is covered by sediments of varying thickness on the south side which is exposed to dominant winds from the se and was occupied by humans at least during kushan times 1st and 2nd centuries ad its form is derived from two systems of natural processes slope and aeolian and an anthropic one which have operated under arid to semiarid conditions these processes have mobilized sands from the weathered substrate and from the afghan dunes and pebbles and gravels from early kushan time constructions such as the fortress of the tchingiz tepe hill slope wash processes have contributed materials which have evolved as slope aeolian sediment in the mantled pediment part of the aeolian sand has been re exported together with primary autochthonous sand outside the hill towards the north thus in tchinguiz tepe the current morphogenesis has slowed down considerably and is currently in dynamic equilibrium with a slow increase in sediments the carbonate crusts which are not very well developed have formed a complex host sediment anthropic morphogenetic action has modified the natural shape of the hill from the earliest times of occupation to the present day and has generated materials that are now incorporated in the slope wash and govern the current topography and the distribution of sediments from the wall of the fortress and other buildings

late holocene climatic and environmental changes in arid central asia abstract late holocene climate and environmental changes in arid central asia were analyzed using various paleoclimate archives such as ice cores tree rings lake sediments historical documents glacial fluctuations and archeological data over the last 2000 years arid central asia witnessed three humid periods from ad 0 410 650 890 and 1500 1820s dry periods occurred in 420 660 and in 900 1510s concerning temperature the most striking features are the existence of the medieval warm period mwp and the little ice age lia the mwp was recorded in the 9 12th centuries and was accompanied by an anomalously dry climate whereas the lia extended from the 15 18th centuries and was accompanied by pluvial conditions temperature and precipitation show significantly negative correlations on annual decadal and centennial timescales temperature was generally above average when dry climate conditions predominated on decadal to centennial timescales during the last 1000 years the coldest decades of the last millennium the period 1630 1650s matched with an anomalously wet episode the combination of paleoclimatic evidence clearly suggests that the combination of cold and wet climate condition during the lia was responsible for the strong glacial advances in several mountain systems of central asia

the loess sequence from remisowka northern boundary of the tien shan mountains kazakhstan part i luminescence dating abstract similar to the chinese loess the loess deposits surrounding the high mountain regions of central asia play an important role in understanding the climate and environmental change during the pleistocene in eurasia despite their thickness and widespread distribution the loess deposits in southeast kazakhstan have so far not been investigated in detail the remisowka loess palaeosol sequence is located in the vicinity of the north tien shan mountains at an altitude of 1070 m above sea level in the profile under study nine loess layers were distinguished intercalated by eight pedocomplexes and so indicating a similar cyclicity like the loess palaeosol sequences in central asia and china at the remisowka section 12 loess samples were taken to set up a more reliable chronological model for the section using a luminescence dating approach polymineral fine grains were investigated by infrared optically stimulated luminescence applying the multiple aliquot additive dose protocol preliminary fading experiments were carried out for one sample taken from the uppermost loess layer while the results of the uppermost layer are in agreement with geological age estimates and indicate a correlation to the late glacial age underestimation is very likely for the samples below the first weak palaeosol no significant age increase with depth was recognised the reason for this age underestimation is not yet fully understood but could be related to anomalous fading further methodological approaches are necessary as well as a combination of different chronometric techniques for improvement of the results

applications of twin analysis to studying meteorite impact structures abstract this paper describes a technique twin analysis of dolomite and calcite which was used to estimate the level of erosion of an impact crater if the age of impact is known the level of erosion gives the amount of sediments present at that time the estimate of the level of erosion and the presence or absence of tectonic strains in calcite constrains the age of impact this technique might also be useful in identifying deeply eroded impact structures twin analysis gives the greatest shortening direction e 1 tilt corrected e 1 directions converge at or above the present day surface if a shallow gas explosion or meteorite impact explains the structure rather than a deep gas or cryptovolcanic explosion the energy density recorded by twinning distinguishes an impact from a shallow gas explosion for structures 100 m diameter at serpent mound a well established impact structure e 1 directions converge at 1400 390 m 95 confidence interval of the mean above the present day structure and the sample closest to the center of the structure records an energy density of 1 7 10 7 j m 3 these results are consistent with previous studies showing that serpent mound is an impact e g r w carlton c koeberl m t baranoski g a schumacker discovery of microscopic evidence for shock metamorphism at the serpent mound structure south central ohio confirmation of an origin by impact earth and planet sci lett 162 1998 177 185 the level of erosion and other data suggests that serpent mound formed between 290 and 256 ma and was originally 8 5 to 11 km in diameter dolomite twinning is not observed at serpent mound suggesting that this technique may only be useful for studying larger more deeply eroded structures

paleomagnetic evidence for cenozoic block rotations in the tadjik depression central asia this paper presents results of a paleomagnetic study of oligo miocene red beds of the tadjik depression in central asia we sampled about 530 cores at 69 sites and six localities across the depression and along the western border of the pamirs samples were thermally demagnetized and high temperature components appear to predate folding of upper tertiary age throughout the depression paleomagnetic inclinations are consistent with those observed on the stable turan platform at the western margin of the depression however they are shallower by about 30 than the inclination predicted from the reference apparent polar wander path this appears to indicate a 23 difference in latitude which is incompatible with paleogeographic reconstructions for the tertiary a sound interpretation of this anomaly would require a better constrained tertiary paleomagnetic reference for asia inside the tadjik depression paleomagnetic declinations are all significantly rotated counterclockwise with respect to those measured on the turan platform the eastern part of the depression is a domain of large rotation 52 13 to 46 15 whereas smaller amounts of rotation have occurred in the western part 27 14 to 14 15 the similarity between tertiary and cretaceous data available for the area shows that rotations have occurred since the miocene little or no paleomagnetic rotations are observed in the ranges bordering the northern and western parts of the depression paleomagnetic and structural data suggest that block rotations in the tadjik depression are associated with indentation of the pamirs into stable asia at a larger scale observed rotations are compatible with a model of regional sinistral wrenching along a strip running from the gulf of oman to lake baikal

optical microstructure of partly recrystallized calcite in some naturally deformed marbles abstract deformed marbles from the mt lofty ranges south australia have microstructures characterized by deformed relics of calcite interspersed with much finer grained recrystallized calcite and with minor quartz and diopside the deformed calcite relics contain numerous subgrains and show abundant evidence of strain induced migration of twin and grain boundaries new calcite grains have nucleated and grown preferentially along twins especially at twin intersections at grain and kink like boundaries and apparently randomly inside deformed relics optical microstructural evidence suggests that dynamic syntectonic recrystallization has taken place along with some static recrystallization probable mechanisms for the initiation of recrystallization include bulge nucleation and subgrain nucleation

development of preferred orientation in plane strain deformed limestone experiment and theory carbonate rocks deform preferentially by twin gliding on e 01 18 and slip on r 10 14 and f 02 21 in polycrystalline aggregates strong textures develop we report on experimentally produced textures in triaxial plane strain geometry with orthorhombic symmetry at 200 c and 400 c pole figure of the experimentally deformed specimens are compared quantitatively with theoretical simulations based on the taylor theory using both slip and mechanical twinning as mechanisms agreement at low and high temperature is satisfactory and documents that models developed for f c c metals can be applied to low symmetry minerals provided that deformation mechanisms are known and that mechanical twinning is properly accounted for comparison with experimental results indicates that strain was nearly homogeneous at the conditions considered and the same may apply to many geological textures three texture types are described which are differentiated mainly by the relative importance of e twinning

primary structure influence on compositional banding in psammites examples from the puncoviscana formation north central argentina abstract we investigate the influence of sedimentary structures in development of foliations in banded psammites and pelites in the meta turbiditic pampean belt eastern sierras pampeanas northwest argentina these anchizone to upper greenschist facies rocks were exhumed from near surface to mid crustal levels and preserve sedimentary structures and gradual changes in tectonic fabrics and microstructures primary variations in clay content affected the degree of development of a compaction related pressure solution cleavage s p resulting in enhancement of the original sedimentary banding the resulting compositional banding was overprinted by a tectonic cleavage s 1 related to mid cambrian chevron folding in banded sandstones pressure solution and mica growth that define s p and s 1 foliations are increasingly better developed in phyllosilicate rich domains with increasing structural depth and metamorphic grade clay rich laminae in the protolith acted as the locus for mica nucleation and growth favoring dissolution of quartz up to 42 causing passive concentration of mica pressure solution thus produced banded sandstones with a spaced bedding parallel s p cleavage in shallower sections and compositionally banded psammites and schists at depth these observations demonstrate that formation of compositional banding does not require tectonic transposition of an older planar fabric similar processes may produce compositional banding in a wide range of meta sedimentary rocks

germanium silicon as a flow path tracer application to the rio icacos watershed 1 we use dissolved silicon together with its geochemical twin germanium for the first time as a hydrologic tracer to study water delivery to the stream during storm events in the rio icacos watershed puerto rico ge and si were measured on base flow stormflow springwater and soil water samples compositions of all of these waters appear to reflect varying contributions from three components which we attribute to solutes released from bedrock weathering groundwater from short term soil water interaction quick soil water and longer term soil water interaction matrix soil water base flow stream waters have high si and moderate ge ge si ratio 0 29 mol mol consistent with a predominantly bedrock weathering source as indicated by their similarity with water sampled from springs emerging from the saprolite bedrock boundary on a hillslope landslide scar during storm events there is a shift toward more dilute compositions but higher ge si ratios similar to those measured on water samples from temporary depression storage and overland flow quick soil water geochemical mass balance shows that 80 90 of the stream chemistry can be explained by mixing groundwater with this quick soil water composition which we infer to reflect new water traveling as shallow throughflow stream water 18o values decrease to more negative values typical of precipitation supporting rapid delivery of rainwater to the stream channel during stormflow the third component with a ge rich composition characteristic of soil matrix water sampled by tension lysimeters is required to explain higher stream water ge si ratios measured during hydrograph recession we infer from this an additional slower and less dominant pathway for delivery of soil water to the stream channel

least squares restoration of tertiary thrust sheets in map view tajik depression central asia the tajik depression located west of the pamirs and south of the tien shan is a compressional intermontane basin bounded by basement overthrusts and filled with mesozoic and cenozoic sediments the internal structure is typical of a thin skinned tbld and thrust belt kinematic data available in the literature suggest that indentation of the pamirs into asia durino the cenozoic collision of india and asia has been accommodated in various ways within the depression including westward extrusion thickening combined with wrenching along n s tblds and thrusts and counterclockwise rotations these various detbrmation processes can be analyzed and quantified by reconstruction of the predeformed state of the depression however the combina tion of thrusting wrenching and block rotations implies a nonplane deformation which cannot be restored properly using balanced cross sections alone we have therefore developed a numerical method for restoration of stratigraphic surfaces designed for regions of nonplane compressional tectonics the deformed region is represented in map view as a mosaic of fault bounded blocks overlapping each other along the faults blocks are separately unfolded and then numerically packed together by least squares minimization of overlaps yielding fields of finite horizontal translations and rotations about vertical axes to analyze the deformation postdating the collision of india and asia we have restored a stratigraphic surface at the base of the cenozoic first in order to test the numerical method we restored a map that had previously been restored by a purely manual method restoration of a second map drawn from newly available subsurface data leads to geometrical inconsistencies overlaps and gaps which cannot be reduced remain in the restored state after correction of these inconsistencies restoration yields a complex mode of deformation for the depression individual thrust slices have undergone counterclockwise rotations about verti cal axes the magnitudes increasing from west to east up to a maximum of 40 o near the pamirs horizontal shortening is 150 km 35 in the center of the depression and 240 km 85 in the northeastern part between the pamirs and the tien shan strike slip motions commonly not revealed by balancing cross sections are associated with thrusting on faults striking n s inde pendent paleomagnetic data and slip directions on small scale faults provide positive checks on the results of our restoration

rates of development of tafoni in the moenkopi and kaibab formations in meteor crater and on the colorado plateau northeastern arizona tafoni are pits formed by non uniform weathering in otherwise uniform rock two equations have been proposed for the rate of development of tafoni both based on 2000 year old outcrops from the coast of japan we have taken tafoni measurements from the meteor crater arizona and vicinity that extend the equations back at least 50 000 years as reported in earlier studies we found pit depth to be the best tafone parameter to measure the size of the pit decreases significantly with increasing inclination of the rock surface however the size of the pit can vary greatly for other reasons in some cases the measurements are statistically significantly different between two stations taken from contiguous areas of similar inclination and aspect in an apparently homogeneous bed it is clear however that over tens of thousands of years tafoni enlarge significantly our data are generally log normal and all are markedly heteroscedastic the 1991 equation proposed by matsukura and matsuoka does not fit our data the 1996 equation proposed by sunamura provides a better fit we propose a sigmoidal equation d b1 e b2 b3 t where d is the depth t is the age and b1 b2 and b3 vary with lithology this new equation fits our data far better than the earlier published equations copyright 2002 john wiley sons ltd

glacial interglacial cycles in arid regions of northern eurasia abstract considering evolution of arid environments in northern eurasia through the glaciation interglacial cycle the author adheres to the opinion as stated by i p gerasimov according to the latter pluvial stages in arid regions correspond to glaciations in the arcto boreal zone while xerothermal stages are synchronous to interglacials there are new paleofloristic evidence obtained in support of this opinion in particular it has been inferred from pollen spectra that during pluvial stages boreal flora including forest species penetrated into the caspian lowland turanian plain and to the black sea coast i e the regions of dry steppes and deserts at present at the xerothermal stages the typical steppe and desert landscapes of arid zone were restored

calcite fabrics in a natural shear environment the helvetic nappes of western switzerland the aim of this contribution is to describe and interpret the crystallographic orientations and microstructures of calcite in the upper jurassic limestones of the helvetic nappes between the mont blanc and aar massifs over a distance along strike of about 180 km the c axis preferred orientation pattern which could be inferred is regionally very constant the c axis point maxima are everywhere subperpendicular to the regional strike of the chain there is an obliquity between the orientation of the macroscopically dominant cleavage and the microscopically visible long axes of individual grains the c axis maxima in most specimens are parallel to the axis of shortening of the microscopic grain shape fabric this fabric geometry indicates either continuous shear deformation or alternatively a two stage deformation history the obliquity of the grain shape fabric may be due to the fact that the flattening plane of the individual grains reflects only the last increment of a continuous shear process or it may represent a later finite deformation which has led to the formation of a regionally developed second cleavage there is a systematic relationship between the direction of these late shear movements and the main overthrust direction as given by the finite strain pattern this suggests that the microfabric of the rocks was acquired during a progressive rotation with time of the main overthrust direction the observed pattern of preferred orientation has been correlated by several authors with intracrystalline deformation mechanisms a combination of slip on r and twinning on e however the e twinning observed in the specimens investigated is younger than the development of the crystallographic fabric a new method for stress determination from e twinning is proposed

kinematics of underthrusting in the paleozoic antler foreland basin field mapping and structural analysis of paleozoic rocks in the northern roberts mountains in central nevada reveal that fine grained siliciclastic strata deposited early in the history of the antler foreland basin underthrust and underplated as two discrete fault bound packets to the roberts mountains allochthon as it encroached upon the north american continental shelf underplating also resulted in the intercalation of north american outer shelf slope strata between the two foreland basin packets as the basal detachment of the roberts mountains allochthon stepped downward in the sedimentary section deformation of foreland basin and outer shelf slope strata was in response to ese in layer shortening accompanied by top ese layer parallel shear within 10 m of fault surfaces along which underplating and underthrusting occurred stratal disruption fold tightness and asymmetry and cleavage development near the lower and upper bounding faults are greater than in the center of underthrust packages indicat

climate variability in the aral sea basin central asia during the late holocene based on vegetation changes high resolution pollen analyses 50 yr from sediment cores retrieved at chernyshov bay in the nw large aral sea record shifts in vegetational development from subdesertic to steppe vegetation in the aral sea basin during the late holocene using pollen data to quantify climatic parameters we reconstruct and date for the first time significant changes in moisture conditions in central asia during the past 2000 yr cold and arid conditions prevailed between ca ad 0 and 400 ad 900 and 1150 and ad 1500 and 1650 with the extension of xeric vegetation dominated by steppe elements these intervals are characterized by low winter and summer mean temperatures and low mean annual precipitation pmm 250 mm yr conversely the most suitable climate conditions occurred between ca ad 400 and 900 and ad 1150 and 1450 when steppe vegetation was enriched by plants requiring moister conditions pmm 250 500 mm yr and some trees developed our results are fairly consistent with other late holocene records from the eastern mediterranean region and the middle east showing that regional rainfall in central asia is predominantly controlled by the eastern mediterranean cyclonic system when the north atlantic oscillation nao is in a negative phase

orientation history and rheology in slates kodiak and afognak islands alaska abstract theoretical and experimental studies have shown that slates have a roughly parabolic yield curve in and space where is the orientation of cleavage relative to the maximum compressive stress is the orientation of cleavage relative to the incremental shortening direction and is the deviatoric stress deformation mechanisms that operate in low grade rocks such as diffusive mass transfer in a grain boundary fluid dislocation creep and frictional grain boundary sliding may have stress strain rate relationships that depend on during a progressive strain history and may vary as a function of the strain path thus the sequence of dominant deformation mechanisms as well as the stress strain history may depend on the orientation history or variations in as strain accumulates in the kodiak formation a slate belt in southwest alaska the orientation history and deformation mechanisms were evaluated using incremental strain indicators and microstructures there are four successive textural events 1 development of a slaty cleavage s2 with antitaxial growth of fibrous quartz and mica in pressure shadows fi2 2 static growth of siderite and chlorite porphyroblasts 3 10 70 rotation of porphyroblasts relative to s2 with growth of curved syntaxial siderite fibers and 4 antitaxial growth of fibrous quartz and micas with local development of a crenulation cleavage s3 cumulative incremental strain and progressive finite strain histories were determined in 23 samples from syntectonic fibers and orientation histories were reconstructed from information provided by cumulative incremental strain histories textural and strain analyses indicate that 1 the strain history of nearly all samples can be approximated by two coaxial strain accumulations separated by a rigid rotation 2 development of crenulation cleavages was dependent on the orientation history and the magnitude of the early strain accumulation i e the degree of mica alignment at the completion of d2 3 unstable behavior or buckling occurred when suggesting that the angle of internal friction was close to 0 i e basal slip in micas may have been more important than frictional grain boundary sliding and 4 diffusive mass transfer was accompanied by anisotropic plastic deformation so the orientation history could be used to reconstruct the history

strain partitioning in the helvetic thrust belt of eastern switzerland from the leading edge to the internal zone abstract the strain and strain partitioning in the helvetic thrust belt are analysed in order to determine their variation across the belt from the external thin skinned portion to the internal thick skinned portion and in order to begin the detailed mechanical analysis of the entire fold and thrust belt coarse grained limestones of jurassic and cretaceous age were chosen for analysis because they can be traced from the external to the internal zones the strain within a bed is partitioned into three components transgranular pressure solution microfaults veins twinning granular and intragranular exclusive of twinning crystal plasticity associated with recrystallization transgranular strain was very important in the early history of the helvetic nappes giving way to twinning at a later stage under tectonic burial twinning strain was early in the infrahelvetic complex giving way to intracrystalline deformation at the later stage of burial the transition from transgranular to intragranular dominated strain occurred at a vitrinite reflectance value of 3 5 significantly below the greenschist grade of metamorphism in a large scale fold at the leading edge of the helvetic nappes transgranular strains were associated with the buckling stage of the fold and twinning occurred during fold tightening in more internal parts of the helvetic nappes twinning strains are also late with regard to transgranular strains but here their pattern corresponds to the regional finite strain pattern in the internal zone the infrahelvetic complex twinning seems to have been an early event and records an initial layer parallel shortening followed by regional internal deformation with intragranular strains