the effect of salt crust on the thermal conductivity of one sample of fluvial particulate materials under martian atmospheric pressures 1 a line heat source apparatus was used to measure thermal conductivities of a lightly cemented fluvial sediment salinity 1 1 g kg 1 and the same sample with the cement bonds almost completely disrupted under low pressure carbon dioxide atmospheres the thermal conductivities of the cemented sample were approximately 3 higher over the range of atmospheric pressures tested than the thermal conductivities of the same sample after the cement bonds were broken a thermal conductivity derived particle size was determined for each sample by comparing these thermal conductivity measurements to previous data that demonstrated the dependence of thermal conductivity on particle size actual particle size distributions were determined via physical separation through brass sieves when uncemented 87 of the particles were less than 125 m in diameter with 60 of the sample being less than 63 m in diameter as much as 35 of the cemented sample was composed of conglomerate particles with diameters greater than 500 m the thermal conductivities of the cemented sample were most similar to those of 500 m glass beads whereas the thermal conductivities of the uncemented sample were most similar to those of 75 m glass beads this study demonstrates that even a small amount of salt cement can significantly increase the thermal conductivity of particulate materials as predicted by thermal modeling estimates by previous investigators

chloride bearing materials in the southern highlands of mars chlorides commonly precipitate during the evaporation of surface water or groundwater and during volcanic outgassing spectrally distinct surface deposits consistent with chloride bearing materials have been identified and mapped using data from the 2001 mars odyssey thermal emission imaging system these deposits are found throughout regions of low albedo in the southern highlands of mars geomorphologic evidence from orbiting imagery reveals these deposits to be light toned relative to their surroundings and to be polygonally fractured the deposits are small

seismic and aseismic weakening effects in transtension field and microstructural observations on the mechanics and architecture of a large fault zone in se tibet

observations of highly correlated near simultaneous magnetic field perturbations at contraposed ground stations a merged data set from canadian auroral network for the open program unified study canopus and magnetometers ionospheric radars all sky cameras large experiment miracle magnetometer stations is used to study variations observed at widely separated locations three years of 10 s data are analyzed using canonical correlation techniques to determine the temporal offset of similar fluctuations observed at pairs of sites nearly simultaneous 10 min delay correlated episodes occur more often roughly 10 of the time when sites are in the dawn dusk sectors and less often 5 for noon midnight configurations

damped regional scale stress inversions methodology and examples for southern california and the coalinga aftershock sequence 1 we present a new focal mechanism stress inversion technique to produce regional scale models of stress orientation containing the minimum complexity necessary to fit the data current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea this procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor to remove these artifacts while retaining any stress variations that are strongly required by the data we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas this method is conceptually similar to other geophysical inverse techniques that incorporate damping such as seismic tomography in checkerboard tests the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion while resolving sharper true stress rotations than a simple smoothed model or a moving window inversion we show an example of a spatially damped stress field for southern california the methodology can also be used to study temporal stress changes and an example for the coalinga california aftershock sequence is shown we recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field

lake deposits of moderate salinity as sensitive indicators of lake level fluctuations example from the upper rotliegend saline lake middle late permian northeast germany abstract the rotliegend saline lake periodically covered wide areas of the southern permian basin in northwest europe during the permian the sedimentology mineralogy and geochemistry of lake deposits were studied to document very high frequency lake level fluctuations and to evaluate their triggers increased precipitation and marine ingressions into the basin resulted in lake extension increased run off is documented by intercalated fluvial deposits in low salinity deposits of the lake because lake deposits reflect mainly deposition in relatively wet climate phases they are not correlatable to halite deposits in other basin areas decreased precipitation is followed by shrinkage of the lake desiccation at its margins and higher lake salinity due to concentration of the brine carbonate and anhydrite contents of lake deposits increased considerably before the areas fell dry but halite is not preserved in the study area falling lake level is also reflected by the occurrence of wave ripples reflecting decreased water depth and finally by desiccation and formation of evaporite crusts not only the mineralogical content but also the colour of lake claystones changes with varying salinity anhydrite and carbonate free red claystones were replaced by violet to green and grey anhydritic and calcareous claystone or marls with increasing salinity the amount of boron adsorbed on illite also corresponds to changes in salinity and can therefore be used as a palaeosalinity indicator rare earth element concentrations within lake deposits do not reflect variations in salinity but different palaeogeographical settings marine ingressions into the lake are neither reflected by the amount of boron adsorbed onto illite nor by rare earth element contents of the lake deposits highly saline deposits are partly characterised by intensive deformation which can be interpreted as seismites or dissolution breccias

exceptionally preserved microbially induced sedimentary structures from the ediacaran post glacial successions in the kimberley region northwestern australia abstract a set of exceptionally preserved microbially induced sedimentary structures miss is described from the post glacial yurabi formation of late ediacaran age in the kimberley region northwestern australia these miss comprise oriented grains bamboo leaf like cracks polygonal cracks worm like cracks sinuous cracks gas domes pyrite concentrated laminae and micrite laminae most of the yurabi miss are morphologically comparable with their ancient and modern counterparts micrometre or nannometre scale bacteria or biofilm like inorganic objects are detected from most miss and are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization oriented grains indirectly support microbial control on their accumulation both pyrite conformable laminae and micrite laminae suggest degradation and decay of original microbial mats upon diagenesis sinuous cracks were likely generated in a soft sediment deformation process whereas other sand cracks bamboo leaf like cracks worm like cracks polygonal cracks could have formed from sediment surface layer microbial organics shrinkage upon desiccation gas domes may have formed as the result of anoxic redox reactions and being filled with gases and sediments transported from below two proxies bedding plane coverage percentage and accumulative thickness of single miss bearing beds are developed to semi quantitatively evaluate miss abundance on bedding plane and vertical outcrop respectively the yurabi miss have substratum preference to fine sandstone facies and intertidal settings the yurabi formation yields the most abundant and diverse post glacial miss assemblages during the late ediacaran worldwide both kimberley and global fossil records indicate that miss may have proliferated in shallow marine ecosystems soon after the retreat of ediacaran gaskiers glaciation during late neoproterozoic

a simple graphical method for estimating the components of the fault slip vector abstract a simple calculation of the components of the total slip vector d on a fault plane allows the relationships between the magnitudes of the three slip components of d the lateral horizontal displacement l the transversal horizontal displacement t and the vertical offset v to be determined the contribution of each slip component to the total slip can be plotted jointly in a ternary diagram assuming a unit length of the vector modulus and a suitable normalization for d each component equals the magnitude of d at the vertices of the diagram hence it is possible to estimate the percentage contribution of each slip component to the total movement of a fault or a set of faults the dip of the fault surface and the rake of the slickenlines are the input data required for displaying l t and v relationships in these diagrams this information may be useful in the analysis of movement geometry for different fault populations and in the determination of d by measuring just one of the fault slip components such as vertical slip associated with a fault scarp

inversion of field data in fault tectonics to obtain the regional stress i single phase fault populations a new method of computing the stress tensor summary we attempt a general definition of the inverse problem of computing the components of the regional stress tensor from a set of field data including the measurements of the strike and dip of several faults and the directions and senses of relative motion along these faults as indicated by slickenslides in previous treatments of this problem no experimental errors could be taken into account except those in measuring the pitch of slickenslides thus errors in the orientation of the fault strike and dip which have considerable practical importance were neglected in our work all experimental errors in the field measurements are taken into account so that the agreement between the computed stress tensor and the set of field measurements can be rigorously checked

unconfined alluvial flow processes recognition and interpretation of their deposits and the significance for palaeogeographic reconstruction abstract palaeogeographic interpretation of the sedimentary rock record depends on correct recognition from the preserved evidence of the processes responsible for transporting and depositing the sediment this in turn depends on robust knowledge transfer from previous workers and the successful exchange of ideas between workers requires consistent use of a well defined vocabulary we have identified serious breakdowns in all these interpretation steps in the case of terrestrial unconfined flow and its deposits and these failures are leading to unreliable environmental and climatic interpretation this is significant because such alluvial deposits commonly form a majority of the rock record of continental environments working from the basic principles of geomorphology and fluid dynamics we have undertaken a wide ranging analysis of the nature of out of channel flow and from this make predictions about the characteristics of its deposits we identify the range of possible locations and conditions that lead to the development of unconfined flow review the processes operating in each case and examine the range of lithological features that can be produced by these processes this allows us to evaluate the reliability of the criteria claimed for identification of out of channel flow deposits and examine how our new insights might alter palaeoclimatic and palaeogeographic reconstructions published previously by others the sedimentary record of unconfined flows is much more diverse and complex than usually portrayed the received wisdom that the record of unconfined flow consists solely of upwards fining thin beds produced from shallow waning flows is shown to be flawed a wide range of lithofacies are possible and the variation in both flow steadiness and uniformity needs to be taken into account the previously published criteria for recognition of flows of this type are not diagnostic of process or location unconfined flow deposits cannot reliably be identified from grain size or bed thickness similar lithofacies may develop in a wide range of geomorphic and climatic settings because the deposits solely reflect the local flow conditions and sediment availability we recommend that the terms sandflat and sheetflood should not be used in sedimentological accounts because there is no longer a safe informal usage for either contradictory application of these terms and lack of robust definitions is leading to significant misunderstanding of palaeogeography and process our analysis should improve reconstruction of past terrestrial environments because it reveals more clearly the true variety of possibilities for the occurrence of unconfined flow and the resultant deposits enhanced understanding of the inherent uncertainties and realisation of the wider range of plausible alternative explanations should help resolve apparent contradictions with independent indicators of climate or geographic position

tectonic evolution of the northern oman mountains part of the strait of hormuz syntaxis new structural and paleothermal analyses and u pb dating of synkinematic calcite

investigation of the near infrared spectral character of putative martian chloride deposits 1 putative chloride salt deposits observed throughout the southern highlands of mars by the compact reconnaissance imaging spectrometer for mars crism display featureless red slopes in near infrared ratio spectra it is hypothesized that the admixture of anhydrous chlorides or unoxidized sulfides with silicate rocks or minerals could imitate this spectral behavior three different sets of spectra were collected 1 simple mixtures of halite with labradorite and flood basalt at multiple concentrations 2 halite crusts formed on both labradorite and flood basalt and 3 simple mixtures of 25 and 50 wt acid washed pyrite with labradorite and flood basalt in all three instances multiple grain sizes were used to evaluate the effect of particle size on spectral results spectra of the mixtures and crusts were divided by pure labradorite and flood basalt spectra of the same grain size to produce ratio spectra comparable to the crism ratio spectra our study rules out pyrite as a possible component of these deposits whereas flood basalt mixtures with halite reproduced the observed red slope under some conditions this allows us to place some broad constraints on halite proportions and the effective grain sizes of these deposits

microbial influence on the accumulation of precambrian aeolian deposits neoproterozoic venkatpur sandstone formation southern india abstract in many presently active aeolian systems processes of sediment erosion transport and deposition are markedly influenced by vegetation which acts as an important sediment stabilising agent current sedimentary models for hyperarid continental settings devoid of vegetation and with adequate sand supply and wind force envisage intense aeolian activity resulting in the construction of extensive aeolian sand seas ergs during the proterozoic the earth s surface was devoid of vegetation yet ergs are not so common in proterozoic continental successions high water table levels and erosional reworking by fluvial or marine processes are recognised as possible factors that restricted accumulation and preservation of extensive proterozoic aeolian systems by contrast proterozoic biotic communities have traditionally been considered largely incapable of markedly influencing clastic sedimentary processes in continental settings however since it is now known that bacteria have colonised parts of the continental earth s surface since the palaeoarchean a question arises as to whether such organisms might have exercised some control on aeolian processes via substrate stabilisation the neoproterozoic venkatpur sandstone formation maximum age 709 ma is an aeolian depositional unit comprising small isolated barchanoid and transverse dunes and dry and damp sand sheet palaeoenvironments water table influenced aeolian sand sheet deposits composed of thin sand layers that alternate with a suite of microbially induced sedimentary structures miss provide evidence for fossilised bacteria these strata record the interaction between microbial mats and aeolian depositional processes which enabled the construction and accumulation of sand deposits as microbial mats stabilised and provided plasticity to the depositional accumulation surface they protected underlying i e accumulated aeolian deposits from possible wind erosion reducing the possibility that these stored deposits could be recycled as lagged input to a downwind aeolian system the stabilising influence of the microbial mats enabled the accumulation of the aeolian deposits resulted in a marked decrease in the availability of sand for aeolian transport and hindered construction and accumulation of large aeolian bedforms this depositional model highlights the significance of the microbial mats for controlling the depositional processes in precambrian aeolian dominated environment probably this model may be applied to other pre vegetated earth continental environments

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

a transtensional basin model for the organya basin central southern pyrenees based on magnetic fabric and brittle structures summary the purpose of this paper is to explain the kinematics of the inverted extensional organy basin centralsouthernpyrenees duringitsextensionalevolution thestudyoftheanisotropy of magnetic susceptibility ams and the study of brittle mesostructures are the instruments used to decipher the extensional kinematics separation of magnetic subfabrics analyses of ams at low temperature and anisotropy of the anhysteretic remanence aarm has been also done to properly interpret the obtained magnetic fabric data the combination of all magnetic fabric and brittle mesostructures analyses has provided new information to clarify thestructuralevolutionofthebasin whichsupportanewtectonicmodelfortheaptian albian basinal stage 20 sites for the magnetic fabric analysis were sampled in aptian lower albian marls the ams ellipsoids obtained at room temperature show their kmin axes perpendicular to bedding and kmax axes oriented nw se in 70 per cent of the samples n s in 15 per cent and ne sw in 15 per cent analyses of ams at low temperature show a better clustering of the axes of the magnetic ellipsoid pointing out that phyllosilicates constitute the carriers of the ams whereas the analyses of the aarm confirm the scattering of the ferromagnetic grains these results suggest that the obtained ams in the organy a basin was acquired during or shortly after deposition of the aptian lower albian marls without any subsequent overprint the direction of the magnetic lineation obtained from the ams at room and low temperatures agrees with the orientation of the stress axes obtained from the analysis of brittle mesostructures mainly faults and calcite filled tension gashes indicating its tectonic origin we interpret the orientation of the magnetic ellipsoids related to the transtensional movements linked to the formation of the organy a basin during the aptian albian interval which are consistent with the eastward displacement and rotation of iberia with respect to europe analysis oftensiongashesalsoindicatesamainnw seextensiondirection whereaspalaeostressanalysis of striated faults shows a more n s trending 3 the transtensional model proposed from magnetic fabric and brittle mesostructures for the organy a basin during the aptian albian is consistent with the creation of a strongly subsiding area south of the axial zone during the cretaceous and implies that rotation and separation of iberia respect to europe took place simultaneously

climatic and geochemical implications of archean pedogenic gypsum in the moodies group 3 2 ga barberton greenstone belt south africa abstract lithic sandstones of braided fluvial to supratidal facies in the paleoarchean moodies group 3 22 ga barberton greenstone belt south africa include several regionally traceable units with common to abundant in places rock forming nodular concretions of megaquartz pseudomorphs after gypsum barite and calcite concretionary accumulations are stratiform and commonly associated with aqueously reworked fine grained tuffaceous sediment of originally rhyodacitic composition and can grow to fist sized agglomerates in crusts tens of m in lateral extent weathering of tuffaceous material and feldspar delivered alkali cations such as ca ba and k while carbonates were likely supplied by silicate weathering of mafic to ultramafic volcanic rocks during exposure to a co2 rich atmosphere sulfate ions were partly delivered by oxidative pyrite dissolution which may have included microbial and abiotic disproportionation of volcanic s or so2 concretionary growth apparently took place under pedogenic to early diagenetic conditions within unconsolidated granular sediment in the vadose zone dominated by seasonal fluctuations of the groundwater level under evaporitic conditions the concretions likely represent the oldest terrestrial evaporites known to date and form part of the oldest known compound paleosols their formation and composition constrain the local occurrence of sulfate in the archean atmo and hydrosphere their interaction with the emerging biosphere archean weathering regime local climate and vadose zone hydrodynamics

dust sources in arid and semiarid china and southern mongolia impacts of geomorphological setting and surface materials abstract analysis of the geomorphological settings and surface materials in arid and semiarid china and southern mongolia revealed that the dominant dust sources are gobi deserts and alluvial fans adjacent to gobi deserts in the piedmonts of the kunlun qilian helan and gobi altai mountains these areas have persistent supplies of dust sized particles deposited by intermittent floods from the mountains and fine materials are also generated by weathering and aeolian processes acting on the coarse fractions of gobi surfaces clear spatial differences in mineral types and contents and in the salt contents of surface materials also strongly affected the intensity of dust emissions inconsistencies in monitoring simulation and calculation of dust emissions in previous studies of northern china and mongolia may have been caused by insufficiently detailed considerations of variations in the geomorphological setting where the geomorphological settings in these areas are not considered in sufficient detail deviations arise in the estimation and prediction of dust using current models although the present study did not quantify the persistence and replenishment of dust sources in the study area our conclusions about the importance of geomorphology can improve future studies of dust sources and controlling factors improve assessments of the effects of climate change on dust emissions and facilitate the interpretation of paleoclimate records

tertiary tectonic evolution of the external east carpathians romania abstract paleostress calculation and analysis of mesoscopic structures are integrated with depth interpreted geological profiles based on seismic studies and well correlation to derive a tertiary tectonic model for the east carpathians following early miocene and older orogenic phases the first tectonic event that affected the studied area is characterised by a wsw ene oriented shortening of middle miocene late burdigalian in age resulting deformations induced ene ward thrusting of tarcau and marginal units as well as the internal part of the subcarpathian nappe a second shortening event with an e w to wsw ene contraction direction took place in the late miocene sarmatian characterised by further foreland thrusting of the subcarpathian nappe and out of sequence deformation in the tarcau and marginal folds nappes along strike differences in deformation mechanisms are controlled by the friction coefficients along the main detachment layers by the lateral variations in the wedge thickness and by the involvement in the northern part of the thrusting system of the thick competent east european platform tear faulting occurred in both tectonic events the main resulting structure being the triangle zone developed south of the trotus valley the latest miocene latest sarmatian early pliocene is characterised by a strike slip stress field with nne ssw compression and wnw ese tension axis left lateral faults being dominant the last deformation which affected the studied area is characterised by nnw sse shortening during the pliocene major deformations taking place mainly in the sw most bending zone

synsedimentary dissolution pipes and the isolation of ancient bacteria and cellulose coarse clear halite from synsedimentary dissolution pipes in the permian salado formation in southeastern new mexico usa yielded viable halotolerant bacteria and well preserved cellulose believed to be permian in age here we show that geologic and hydrologic conditions have isolated these rocks since permian time pipes were dissolved most likely along cracks created by thermal contraction or desiccation and the boundaries of salt polygons saucers on exposed salado formation salt pan surfaces down to the level of the water brine table macropores developed at the brine level in some horizons as the water level rose coarse halite cemented the open space fluid inclusions millimeter scale trapped bacteria which were probably in a spore state as well as cellulose inclusion water from pipes in some cycles may have isotopic values reflecting permian meteoric water while other cycles may show evaporated permian seawater exposure surfaces are more prominent in the upper part of salado formation depositional cycles due to basin desiccation as indicated by cracks and dish shaped laminae clays were concentrated on many exposure surfaces by floods wind and dissolution dissolution pipes formed from these surfaces and a synsedimentary age is confirmed by undisturbed overlying halite beds salado formation halite has very low permeability 10 22 m 2 effectively preventing significant fluid flow and passage of fluids through the formation either to recrystallize salt or to introduce modern bacteria stratigraphic relationships halite textures fluid inclusion chemistry and hydraulic properties are all consistent with a synsedimentary origin of the dissolution pipes their crystals and the bacteria and cellulose recovered from the salado formation

the preservation potential of environmentally diagnostic sedimentary structures from a coastal sabkha abstract the abu dhabi sabkha constitutes the landward portion of the shallow sloping carbonate ramp situated on the northwestern coast of the united arab emirates uae the sabkha in this region is composed of a complex assortment of carbonate organic and evaporitic facies that constitute a regressive sabkha sequence the surface features of the sabkha can be grouped into distinct laterally continuous facies associations that are directly correlatable with elevation above present day sea level previous investigations have suggested the employment of the abu dhabi sabkha as a modern depositional analogue to ancient carbonate evaporite formations however a quantitative analysis of the relationship between sabkha surface and subsurface characteristics has not previously been undertaken this study describes in detail the sedimentary structures and textures seen at the sabkha surface and compares them to the holocene age facies retained in the shallow subsurface of the 36 sedimentary structures observed at the sabkha surface only seven 19 are still identifiable in the early burial realm the majority of the surface structures were lost during early burial as a result of microbial mat decomposition destructive evaporite precipitation and compaction the loss of diagnostic sedimentary features during early burial as a result of fabric destructive processes has considerable implications for the recognition and interpretation of ancient sabkha sequences documenting these processes from a range of modern sedimentary environments will aid in the identification of those diagnostic features that may be reliably employed during paleoenvironmental reconstructions

saline pan deposits from the 1 8 ga makgabeng formation waterberg group south africa abstract interbedded medium to fine grained sandstones and mudstones which occur within an 800 m thick areally extensive aeolian dune and interdune deposit of the 1 8 ga makgabeng formation waterberg group south africa are interpreted as saline pan deposits few examples of saline pan deposits have been documented from the precambrian rock record most of those described have been assigned to alkaline saline and playa lake settings seven saline pan facies are recognized in the makgabeng formation a strongly asymmetrical ripples b inversely graded laminations c slightly asymmetrical ripples d symmetrical ripples e massive sandstone f horizontal lamination and g massive graded mudstone these facies are interpreted respectively as current ripple wind ripple combined flow ripple wave ripple suspension e and g and upper plane bed deposits f xrd analysis of saline pan mudstones from drill core south of the study area indicates the presence of trace amounts of anhydrite and gypsum additional evidence for evaporite deposition includes evaporite pseudomorphs in the underlying dune deposits and distinctive structures linked to efflorescent salt crust development stacking of facies reflects fluctuations 10 s to 100 s of years in the hydrologic regime of the saline pan whereas the efflorescent crusts are consistent with shorter period months or years flooding and desiccation cycles maximum saline pan depths and geographic extent are recorded by thick graded mudstone facies g near the base of the deposit indicating a time of possible climatic amelioration and saline pan expansion followed by semiarid to arid conditions reflected in the overlying dune deposits

climatic versus halokinetic control on sedimentation in a dryland fluvial succession fluvial systems and their preserved stratigraphic expression as the fill of evolving basins are controlled by multiple factors which can vary both spatially and temporally including prevailing climate sediment provenance localized changes in the rates of creation and infill of accommodation in response to subsidence and diversion by surface topographic features in basins that develop in response to halokinesis mobilized salt tends to be displaced by sediment loading to create a series of rapidly subsiding mini basins each separated by growing salt walls the style and pattern of fluvial sedimentation governs the rate at which accommodation becomes filled whereas the rate of growth of basin bounding salt walls governs whether an emergent surface topography will develop that has the potential to divert and modify fluvial drainage pathways and thereby dictate the resultant fluvial stratigraphic architecture discerning the relative roles played by halokinesis and other factors such as climate driven variations in the rate and style of sediment supply is far from straightforward diverse stratigraphic architectures present in temporally equivalent neighbouring salt walled mini basins demonstrate the effectiveness of topographically elevated salt walls as agents that partition and guide fluvial pathways and thereby control the loci of accumulation of fluvial successions in evolving mini basins drainage pathways can be focused into a single mini basin to preserve a sand prone fill style whilst leaving adjoining basins relatively sand starved by contrast over the evolutionary history of a suite of salt walled mini basins region wide changes in fluvial style can be shown to have been driven by changes in palaeoclimate and sediment delivery style the triassic moenkopi formation of the south western usa represents the preserved expression of a dryland fluvial system that accumulated across a broad low relief alluvial plain in a regressive continental to paralic setting within south eastern utah the moenkopi formation accumulated in a series of actively subsiding salt walled mini basins ongoing evolution of which exerted a significant control on the style of drainage and resultant pattern of stratigraphic accumulation drainage pathways developed axial parallel to salt walls resulting in compartmentalized accumulation of strata whereby neighbouring mini basins record significant variations in sedimentary style at the same stratigraphic level despite the complexities created by halokinetic controls the signature of climate driven sediment delivery can be deciphered from the preserved succession by comparison with the stratigraphic expression of part of the system that accumulated beyond the influence of halokinesis and this approach can be used to demonstrate regional variations in climate controlled styles of sediment delivery

biosedimentary and geochemical constraints on the precipitation of mineral crusts in shallow sulphate lakes abstract seasonal desiccation of mg2 na ca2 so42 cl saline lakes in la mancha central spain that host microbial mats led to the precipitation of hydrated na mg sulphates and gypsum sulphates precipitated in the submerged conditions form extensive biolaminites whilst in marginal areas they produce thin crusts sedimentological mineralogical petrographic and high resolution textural studies reveal that the crusts were formed within the benthic microbial mats that thrive at salinities ranging from 160 to 340 g l 1 the minerals of the crusts are primary bloedite na2mg so4 2 4h2o epsomite mgso4 7h2o gypsum caso4 2h2o and mirabilite na2so4 10h2o as well as secondary hexahydrite mgso4 6h2o and thenardite na2so4 primary bloedite crystals which form the framework of surficial and submerged crusts are seen to nucleate subaqueously and grow incorporatively within the matgrounds displacive and incorporative epsomite grows on previous bloedite crystals and also on the ground mirabilite is precipitated rapidly at the brine air interface over bloedite and epsomite hexahydrite and thenardite are formed due to dehydration of epsomite and mirabilite respectively hydrochemical modeling with phreeqc indicated that evaporitic biolaminites are forming from brines undersaturated with respect to bloedite epsomite and mirabilite which suggests that the microorganisms contribute to the heterogeneous nucleation of the sulphates in the microbial mats unlike carbonates the influence of microbes on the growth and morphology of complicated double salts such as bloedite has not been documented previously and provides a new perspective on the formation of hydrated sulphate minerals that are common on earth as well as other planets

the tectonic development of the hellenic arc and the sea of crete a synthesis abstract we use field analyses together with interpretation of aerial photographs orbital imagery and sea beam data to define more accurately the geometry of fault systems in the hellenic arc the tectonics of the area are dominated by extensional processes related to normal faulting we then use sea beam data previous oceanographic studies and extrapolation of field analyses on surrounding islands to describe the fault pattern of the cretan sea basin which is found consistent with the land fault pattern the mechanisms of the late neogene and quaternary deformation of the central and southern aegean region are analysed in terms of stress trajectories as revealed by field studies of fault populations we then examine the subsidence of the sea of crete in terms of a model of uniform stretching of the lithosphere the opening of the sea of crete was cylindrical and did not result in bending of crete this leads us to modify the southern portion of an earlier kinematic reconstruction of aegea in agreement with recent paleomagnetic results the implications of the opening of the sea of crete on the tectonic evolution of the straits to the west and east of crete are discussed finally the uplift of the outer arc is explained by underplating due to subduction

late permian non marine marine transitional profiles in the central southern permian basin northern germany the transition from rotliegend to zechstein within the southern permian basin is one from continental desert to a marine environment during the upper rotliegend ii a huge playa lake existed there this lake was temporarily influenced by precursors of the zechstein transgression therefore the mega playa evolved into a sabkha system one of these early marine ingressions is known from an outcrop in schleswig holstein laminated silt and claystones deposited within a standing water body are intercalated in siltstones of a salt flat environment the lake sediments are characterised by high frequency cyclicity shown by the sedimentary record and also by palaeontological data the section contains fresh water as well as brackish marine and marine fauna climatically forced cycles interact with marine incursions after the zechstein transgression had flooded the basin completely sedimentation was controlled by sea level fluctuations two sections in the southern north sea and in schleswig holstein are presented in this paper cyclicities with different frequencies controlled the sedimentation of the kupferschiefer t1 and the werra carbonate ca1 sediments of the north sea sequence were deposited within a shallow bay at the margin of an elevation therefore the high frequency cyclicity became obvious within the sedimentary patterns and in the faunal content

holocene activity and seismogenic capability of intraplate thrusts insights from the pampean ranges argentina abstract trench excavations across the el molino fault in the southeastern pampean ranges of central western argentina have revealed a deformation zone composed of opposite verging thrusts that deform a succession of holocene sediments the west verging thrusts place precambrian basement over holocene proximal scarp derived deposits whereas the east verging thrusts form an east directed fault propagation fold that deforms colluvium fluvial and aeolian deposits ages for exposed fault related deposits range from 7 1 0 4 to 0 3 ka evidence of surface deformation suggests multiple rupture events with related scarp derived deposits and a minimum of three surface ruptures younger than 7 1 0 4 ka the last rupture event being younger than 1 ka shortening rates of 0 7 0 2 mm a are near one order of magnitude higher than those estimated for the faults bounding neighboring crustal blocks and are considered high for this intraplate setting these ground rupturing crustal earthquakes are estimated to be of magnitude mw 7 0 a significant discrepancy with the magnitudes mw

coeval versus reciprocal mixed carbonate siliciclastic deposition middle devonian baltic basin eastern europe implications from the regional tectonic development the middle devonian narva succession in the baltic basin represents a significant turnaround in the history of the basin the detailed study of core and outcrop sections and the three dimensional correlations across the baltic basin reveal a carbonate dominated mixed retrogressive succession overlain by a siliciclastic dominated progradational succession the palaeogeographic reconstructions show how the shallow tide influenced basin expanded from south west to north east and later during the transgression also to the north south and east the transgressive portion of the basin fill is dominated by carbonate rich sabkha and supratidal to intertidal deposits on the basin margins and subtidal carbonates in the basin centre siliciclastic material was derived by tidal currents and storm waves from the south west through a tidal inlet and flood tidal delta complex this initial transgressive phase is characterized by the lack of subsidence or even episodic uplifts in the northern north western part of the basin margin shown by convergence of timelines and the thin 30 m transgressive succession in contrast on the southern margin the facies associations stack vertically into a 70 to 80 m thick succession indicating significantly higher subsidence rates the upper part of the transgressive phase indicates subsidence across the whole basin the upper progradational portion of the basin fill is dominated by coarse siliciclastic tide influenced deltaic deposits that rapidly prograded from north west to south east this detailed study on the narva succession shows that siliciclastic and carbonate deposition was coeval and that mixing occurred at different temporal and spatial scales the mixing was controlled by grain size volume and location of siliciclastic input rather than relative sea level changes as suggested in widely used reciprocal mixing models it is suggested that the forebulge of the scandinavian caledonian fold and thrust belt migrated to the north western margin of the baltic basin during the earliest eifelian as indicated by the lack of subsidence and probable uplift in the northern north western margin during the early transgressive phase the forebulge migration ceased although the forebulge had already started to subside during the later stages of the transgressive phase the deltaic progradation is interpreted to be associated with the orogenic collapse and uplift in the scandinavian caledonides that caused the erosion of the foreland basin fill and the coarse sediment transport into the baltic basin

quantification of carbonate ramp sedimentation and progradation rates for the late holocene abu dhabi shoreline abstract we utilize new radiocarbon dates and detailed sedimentological logging of the abu dhabi sabkha to produce the first well constrained internally consistent rates for late holocene carbonate ramp sediment accumulation and progradation for the southern shore of the persian gulf these data are applied to test the hypothesis that in low angle carbonate ramp systems ramp geometry is the primary control on sedimentation and progradation rates and therefore estimates acquired from other depositional environments cannot be applied to low angle carbonate ramp systems average calculated progradation rates of 0 75 m yr are higher than progradation rates proposed for other late holocene and recent carbonate settings a relationship that is explained by the lack of accommodation space in the low angle laterally extensive ramp system in the sedimentary record such relatively high progradation rates would produce laterally extensive lithologically uniform units with little or no evidence of progradational features and would appear to be largely contemporaneous across their extent the total average sediment accumulation rate of 0 029 cm yr is lower than those proposed from most other late holocene to recent shallow water carbonate depositional environments again a relationship interpreted to result from the limited accommodation space of low angle carbonate ramp systems calculated sediment accumulation rates show little variation over the past 1 400 years yet the calculated progradation rates exhibit a sharp decline from a maximum of 1 03 m yr before 677 946 cal bp to 0 70 m yr afterwards this is interpreted to reflect a rise in relative sea level or distal steepening of the ramp system applying the progradation rates proposed in this paper the lagoon system in the study area would be completely infilled in less than 4 000 years calculated sediment accumulation rates for syndepositional and early postdepositional interstitial displacive evaporite formation are higher than those for carbonate and microbial mat intervals continued precipitation of evaporite minerals during burial would result in a further increase in their relative contribution to the sediment pile conversely compaction particularly of microbial mat intervals will result in a decrease in apparent sediment accumulation rates for non evaporite intervals these processes need to be considered when modeling the basin evolution of mixed evaporite carbonate sequences in the stratigraphic record during calculation of sedimentation rates it is important to consider both a correction for compaction and a correction for evaporite formation

synsedimentary brecciation in the eifelian middle devonian baltic basin sudden catastrophe or diagenetic collapse the eifelian sedimentary record in the epeiric baltic basin contains an extensive brecciated interval known as the narva breccia during recent decades the origin of this breccia has been attributed to 1 palaeoseismicity 2 extraterrestrial impact event or 3 diagenetic collapse our studies show the presence of two different breccia types that form 11 stratigraphic horizons and contain several laterally and stratigraphically unrelated breccias the occurrence of type 1 and type 2 breccias together with carbonate sabkha and carbonate inter to supratidal tidal flat deposits on the basin margins indicates synsedimentary brecciation formed in a sabkha environment type 2 breccia could also originate from wave cycling loading

an example of stress tensor distribution deduced from the aftershocks of the november 23 1980 southern italy earthquake abstract the total inversion algorithm tarantola and valette 1982 is applied to a set of focal mechanisms corresponding to the aftershocks of the southern italy november 23 1980 earthquake m s 6 9 and the elements of several stress tensors are computed the obtained complex distribution of stress for this region is analyzed and two zones around the main event corresponding to areas of tension and compression distributed at different depths are delimited a stress tensor was sought for a third region corresponding to events which occurred along the strike of the main event and with magnitudes greater than 2 2 but with ambiguous results

characterizing the ionospheric current pattern response to southward and northward imf turnings with dynamical supermag correlation networks we characterize the response of the quiet time no substorms or storms large scale ionospheric transient equivalent currents to north south and south north imf turnings by using a dynamical network of ground based magnetometers canonical correlation between all pairs of supermag magnetometer stations in the northern hemisphere magnetic latitude mlat 50 82 is used to establish the extent of near simultaneous magnetic response between regions of magnetic local time mlat parameters and maps that describe spatial temporal correlation are used to characterize the system and its response to the turnings aggregated over several hundred events we find that regions that experience large increases in correlation post turning coincide with typical locations of a two cell convection system and are influenced by the interplanetary magnetic field by the time between the turnings reaching the magnetopause and a network response is found to be 8 10 min and correlation in the dayside occurs 2 8 min before that in the nightside

unusually well preserved casts of halite crystals a case from the upper frasnian of northern lithuania abstract upper frasnian carbonate siliciclastics of the stipinai formation northern lithuania comprise a bed of calcareous silty arenite with casts of halite crystals including hopper crystals unusually well preserved casts occur on the lower surface of the bed while poorly preserved casts are present on the upper bedding surface the casts originated as the result of the dissolution of halite crystals which grew in the sediment the dissolution took place during early stages of diagenesis when host sediment was soft unstable cavities after crystal dissolution were filled by overlying sediment forming their casts the collapsing sediment form sink hole deformation structures which disturb wave ripple cross lamination from the upper part of the bed dewatering pipe structures are also present the casts and accompanying sink hole and dewatering pipes are classified as the postdepositional deformation structures caused by haloturbation

slip vectors and fault mechanics in the makran accretionary wedge southwest pakistan the makran is a broadly east west trending arcuate accretionary wedge currently forming where the oceanic floor of the gulf of oman is being subducted north northeastward beneath the south asian margin two traverses across the makran coast ranges extending about 80 km inland from the coastline which lies about 100 km north of the wedge front show that the structure of this region is dominated by large back rotated south directed thrust faults and associated folds related structures include duplexes fault gouge containing reidel shears and melange along fault zones these structures are cut by later north directed backthrusts out of sequence south directed thrusts and apparently conjugate sets of nne trending sinistral and nw trending dextral strike slip faults slip vectors were determined from slickenlines fiber lineations gouge fabrics and riedel shears vectors from early thrusts and bedding parallel slip surfaces corrected for tectonic rotation form a broad south directed concentration lying between the normal to the regional strike varying from 160 to 180 and the present plate convergence vector 200 locally the concentration is bimodal this pattern may represent the interaction between plate forces and body forces in the accretionary wedge the late thrusts have widely variable slip vectors and stair step off the early thrusts they overlap in orientation and slip vector with gently dipping sinistral strike slip faults suggesting that they also stair step in plan off the latter the steep strike slip faults represent the final tectonic stage involving minor n s shortening and longitudinal extension these three stages probably occurred in sequence in any one area but migrated diachronously southward as the wedge grew

evidence for the exsolution of cl rich fluids in martian magmas apatite petrogenesis in the enriched lherzolitic shergottite northwest africa 7755 abstract martian meteorite northwest africa 7755 is a new example of an enriched lherzolitic shergottite containing some of the coarsest grained apatite yet identified in shergottite meteorites their size has permitted detailed observations of volatile distributions within single grains we have demonstrated that some apatites have been invaded by shock melts which act to devolatilize parts of grains resulting in significant cl enrichment in the adjacent regions the extent of chemical heterogeneity within single grains must be carefully considered in other shergottites so that the effects of secondary modification of apatites are well constrained prior to interpreting the volatile contents and primary magmatic processes apatite grains unaffected by shock melts are oh f enriched and cl poor f 50 cl 14 oh 36 relative to interstitial apatites reported in other shergottites the volatile compositions are similar to interstitial apatites reported in terrestrial mafic intrusions such apatites in terrestrial intrusions are argued to have formed after significant cl loss due to the exsolution and migration of cl rich brines calculated relative f 2 cl 2 and h 2 o fugacities for nwa 7755 apatites show a trend of degassing rather than fractionation noted in previous studies indeed we interpret the volatile contents of apatites analyzed in the cumulate shergottite nwa 7755 to represent snapshots of the evolving late stage residual liquid during exsolution of a cl rich brine this fluid phase has subsequently been lost from an open magma system migrating upward through the cumulate sequence enriching residual liquids in cl alternatively it formed a hydrothermal system in the martian crust surrounding the intrusion furthermore by comparison with terrestrial examples we suggest that the late stage evolution of volatile bearing phases in nwa 7755 is similar to that of comparable terrestrial mafic rocks primary cumulus apatites are f rich whereas interstitial apatites may be either cl rich forming as a result of modification through the interaction with cl rich brines or oh f rich forming from a magma having exsolved or degassed a cl rich fluid phase

distribution of palaeosols and deposits in the temporal evolution of a semiarid fluvial distributary system bauru group upper cretaceous se brazil abstract the stratigraphic and sedimentological knowledge of the bauru group upper cretaceous se brazil is still generally insufficient and controversial a sedimentological and palaeopedological study allowed to interpret the south eastern portion of the bauru group according to the model of a fluvial distributary system this work has two objectives 1 to include palaeosols in the interpretation of a fluvial distributary system and 2 to give detailed information on the sedimentological and stratigraphic features of the se portion of the bauru group in order to support biostratigraphical taphonomic and palaeoecological studies in the south eastern portion of the bauru group three genetic stratigraphic units were described and interpreted here informally called lower intermediate and upper units the lower unit is constituted of muddy sandstone salt flat deposits and sandstone sheet deltas deposits and is interpreted as a basinal part of a fluvial distributary system the intermediate unit is formed of very fine to fine grained sandstone filled ribbon channel and sandy sheet shaped beds suggesting a distal or medial portion of a fluvial distributary system the upper unit does not match with the present models of the fluvial distributary system because mostly constituted of moderately developed well drained medium to fine grained sandstone palaeosols which testify pauses of sedimentation to the order of 104 years preserved features of sedimentary structures suggest that the parent material was formed by occasional catastrophic unconfined flows this unit may represent the most distal portion of a fluvial distributary system generated by retrogradation of the alluvial system due to aridification of the climate the upper unit may be interpreted also as proximal portion of fluvial distributary system if considering the coarser grained and the well drained palaeosols however the absence of channel deposits makes this interpretation unconvincing

temperature seasonality control on modern halite layers in the dead sea in situ observations layered halite sequences are found in deep basins throughout the geological record however analogs for such sequences are commonly studied in shallow environments here we studied active precipitation of halite layers from the only modern analog for deep halite precipitating basins the hypersaline dead sea in situ observations in the dead sea link seasonal thermohaline stratification halite saturation and the characteristics of the actively forming halite layers the spatiotemporal evolution of halite precipitation in the dead sea was characterized by means of monthly observations of 1 lake thermohaline stratification temperature salinity and density 2 degree of halite saturation and 3 textural evolution of the active halite deposits we present the observed relationships between the textural characteristics of layered halite deposits i e grain size consolidation and roughness and the degree of saturation which in turn reflects the limnology and hydroclimatology the lake floor is divided into two principal environments a deep hypolimnetic lake floor and a shallow epilimnetic lake floor in the deeper hypolimnetic lake floor halite continuously precipitates with seasonal variations 1 during summer consolidated coarse halite crystals form rough surfaces under slight supersaturation 2 during winter unconsolidated fine halite crystals form smooth lake floor deposits under high supersaturation these observations support interpretations of the seasonal alternation of halite crystallization mechanisms the shallow epilimnetic lake floor is highly influenced by the seasonal temperature variations and by intensive summer dissolution of part of the previous year s halite deposit which results in thin sequences with annual unconformities this emphasizes the control of temperature seasonality on the characteristics of the precipitated halite layers in addition precipitation of halite on the hypolimnetic floor at the expense of the dissolution of the epilimnetic floor results in lateral focusing and thickening of halite deposits in the deeper part of the basin and thinning of the deposits in shallow marginal basins

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

network analysis of geomagnetic substorms using the supermag database of ground based magnetometer stations the overall morphology and dynamics of magnetospheric substorms is well established in terms of the observed qualitative auroral features seen in ground based magnetometers this paper focuses on the quantitative characterization of substorm dynamics captured by ground based magnetometer stations we present the first analysis of substorms using dynamical networks obtained from the full available set of ground based magnetometer observations in the northern hemisphere the stations are connected in the network when the correlation between the vector magnetometer time series from pairs of stations within a running time window exceeds a threshold dimensionless parameters can then be obtained that characterize the network and by extension the spatiotemporal dynamics of the substorm under observation we analyze four isolated substorm test cases as well as a steady magnetic convection smc event and a day in which no substorms occur these test case substorms are found to give a consistent characteristic network response at onset in terms of their spatial correlation such responses are differentiable from responses to the smc event and nonsubstorm times we present a method to optimize network parametrization with respect to the different individual station responses the spatial inhomogeneity of stations in the northern hemisphere and the choice of correlation window sizes our results suggest that dynamical network analysis has potential to quantitatively categorize substorms dimensionless parameters can then be obtained that characterise the network and by extension the spatio temporal dynamics of the substorm un der observation we analyse four isolated substorm test cases as well as a steady magnetic convection smc event and a day in which no substorms occur these test case substorms are found to give a consistent characteristic net work response at onset in terms of their spatial correlation such responses are differentiable from responses to the smc event and non substorm times we present a method to optimise network parametrisation with respect to the different individual station responses the spatial inhomogeneity of stations in the northern hemisphere and the choice of correlation window sizes our results suggest that dynamical network analysis has potential to quantitatively categorise substorms

taphonomic controls on animal tracks at saline alkaline lake bogoria kenya rift valley impact of salt efflorescence and clay mineralogy abstract the morphologies of subaerial vertebrate tracks and invertebrate traces in surficial sediments can be used in paleoenvironmental reconstructions by providing details about the initial substrate conditions e g water content and any changes experienced during trace preservation a qualitative field study was undertaken to identify the factors affecting track taphonomy in saline lake margin environments supported by experiments to isolate selected factors that modify track morphology and substrate characteristics flamingo tracks ubiquitous around saline alkaline lake bogoria in the kenya rift were the focus of field study although other vertebrate tracks and surficial invertebrate trails and tunnels were also considered a complex and interacting set of environmental factors were identified such as the effect of lake level fluctuations on substrate grain size and capillary evaporation several factors affect the early taphonomic modification destruction stabilization and or cementation of tracks and their associated substrates the laboratory experiments tested the effects of pore water salinity clay mineralogy e g swelling or non swelling clays drying method e g solar radiation or wind and wetting and drying cycles on tracks these data were supported by statistical analyses of impression depth and planimetric area the results show that track morphology in smectitic substrates is altered rapidly by wetting and drying particularly if the substrates contain saline pore waters but morphology is less affected in non swelling clays the degree of morphologic alteration and or resistance to wetting and drying varies with the rate of substrate drying and the type of the resulting salt efflorescence e g interstitial vs surficial crust these short term process related taphonomic effects help to explain the morphologic variants of tracks in lake marginal settings and provide insights into the preserved distribution patterns of subaerial ichnofossil assemblages

determination of stresses from heterogeneous focal mechanism data an adaptation of the multiple inverse method abstract a new method is proposed to separate stresses from earthquake focal mechanism data double couple component of focal mechanisms from spatially or temporarily varying state of stress the underlying multiple inverse method was originally devised for geological fault slip data but we have adapted its resampling scheme to focal mechanism data to cope with the nodal planes ambiguity problem the stresses compatible with a dataset are recognized as the clusters of reduced stress tensors the clusters are identified with the k means clustering the uncertainty of the stresses are evaluated from the spread of the clusters the technique is shown to successfully determine valid stresses from simulated data we have also applied the technique to natural data from southwestern japan

surface and subsurface sedimentary structures produced by salt crusts the growth and subsequent dissolution of salts on or within sediment may alter sedimentary structures and textures to such an extent that it is difficult to identify the depositional origin of that sediment and as a result the sediment may be misinterpreted to help to overcome such problems with investigating ancient successions results are presented from a comprehensive study of the morphology and fabrics of three large areas of modern salt flats in se arabia the sabkhat matti inland region and the at taf coastal region both in the emirate of abu dhabi and the umm as samim region in oman these salt flats are affected by tidal marine alluvial and aeolian depositional processes and include both clastic and carbonate dominated surficial sediments the efflorescent and precipitated salt crusts in these areas can be grouped into two main types thick crusts with high relief 10 cm and a polygonal or blocky morphology or thin crusts with low relief 10 cm and a polygonal or blister like appearance the thin crusts may assume the surface morphology of underlying features such as ripples or biogenic mats a variety of small scale textures were observed pustular growths hair like spikes and irregular wrinkles evolution of these crusts over time results in a variety of distinctive sedimentary fabrics produced by salt growth sediment deformation salt solution sediment collapse sediment aggradation and compound mixtures of these processes salt crust processes produce features that may be confused with aeolian adhesion structures an example from the lower triassic ormskirk sandstone formation of the irish sea basin demonstrates how this knowledge of modern environments improves the interpretation of the rock record a distinctive wavy laminated facies in this formation had previously been interpreted as the product of fluvial sheetfloods modified by soft sediment deformation and bioturbation close inspection of laminations seen in core reveals many of the same sedimentary fabrics seen in se arabia associated with salt crusts this facies is the product of salt growth on aeolian sediment and is not of fluvial origin

the response of high latitude convection to a sudden southward imf turning we describe the response of the high latitude convection to a sudden southward turning of the imf in this event bz recorded at the wind satellite switched from 6 nt to 6 nt in 2 minutes and effects in the ionosphere were observed by the superdarn hf radars in the vicinity of noon mlt the convection switched suddenly 2 min from sunward to antisunward with the velocity change reaching magnitudes as great as 1500 m s in about 6 minutes surprisingly the responses at the other mlts distributed from noon to midnight began at virtually the same time meridional flows near 22 mlt were observed to reverse direction in about 4 minutes with the velocity change reaching magnitudes as great as 750 m s in about 8 minutes this example shows that the convection can respond to a sudden imf change practically simultaneously 2 min over the entire high latitude zone and reconfigure from a pattern characteristic of bz to one characteristic of bz in a very short 2 4 min time

remote sensing and in situ mineralogic survey of the chilean salars an analog to mars evaporate deposits abstract the identification and characterization of hydrated minerals within ancient aqueous environments on mars are high priorities for determining the past habitability of the planet few studies however have focused on characterizing the entire mineral assemblage even though it could aide our understanding of past environments in this study we use both spaceborne and field vnir spectroscopy analyses to study the mineralogy of various salt flats salars of the northern region of chile as an analog for martian evaporites these data are then compared to laboratory based raman and xrd analyses for a complete overview on mineral assemblages central core and marginal zones within the salars are easily distinguished on the landsat 8 band color composites these areas host different mineral assemblages that often result in different landscapes the lower elevation salar de atacama located in the andean pre depression is characterized by a unique thick halite crust at its center whereas various assemblages of calcium sulfates gypsum bassanite anhydrite and sodium sulfates mirabilite thenardite blodite glauberite borates ulexite pinnoite al fe clays and carbonates calcite aragonite were found at its margin sulfates form the main crust of the andean salars to the east although various compositions are observed these compositions appear controlled by the type of feeder brine ca so4 or mixed a result of the local geology among other factors sulfate crusts were found to be generally thin

mesoproterozoic erg and sand sheet system architecture and controlling factors galho do miguel formation se brazil abstract aeolian systems of the precambrian time were established in different palaeoclimatic and palaeogeographic conditions than the present different morphologies of dunes draas as linear oblique and star forms are widespread in the recent aeolian systems however the ancient aeolian deposits are rarely interpreted as these types of bedforms and usually referred to as transverse dunes the nature and complexity of bedform morphology in precambrian aeolian systems as well as the factors that allow the construction accumulation and preservation of these environments are still not well defined extensive exposures of galho do miguel formation in southeastern brazil represent a mesoproterozoic erg succession and exhibit a distinct facies architecture which contributed to the understanding of these deposits three architectural elements were identified i tangential cross stratified sandstone with superimposed trough cross bedded sandstone ii planar laminated sandstone and iii extensive flat bedded sandstone dominated by wrinkly laminae these elements are organized into three succession groups representative of simple transverse dune oblique compound draa and sand sheet systems the simple to compound dune draa system corresponds to the most central parts of the erg associated with a higher sediment availability and lower water table level conversely the sand sheet system occurs under low sediment availability and higher water table level in the marginal portions of the erg precambrian climatic oscillations may have changed the aeolian system morphology allowing the alternation of simple and complex aeolian dunes resulting in high frequency changes in sand sheet system and the remobilization of previously accumulated sediments over large geographic areas

the polygonal surface structures in the dalangtan playa qaidam basin nw china controlling factors for their formation and implications for analogous martian landforms