the bonneville estates rockshelter rodent fauna and changes in late pleistocene middle holocene climates and biogeography in the northern bonneville basin usa abstract excavations at bonneville estates rockshelter nevada recovered rodent remains from stratified deposits spanning the past ca 12 500 14c yr bp 14 800 cal yr bp specimens from horizons dating to the late pleistocene and early holocene include species adapted to montane and moist and cool habitats including yellow bellied marmot marmota flaviventris and bushy tailed woodrat neotoma cinerea shortly after 9000 14c bp 10 200 cal yr bp these mammals became locally extinct or nearly so taxonomic diversity declined and the region became dominated by desert woodrats neotoma lepida and other species well adapted to xeric low elevation settings the timing and nature of changes in the bonneville estates rodent fauna are similar to records reported from nearby homestead and camels back caves and provide corroborative data on terminal pleistocene early holocene environments and mammalian responses to middle holocene desertification moreover the presence of northern pocket gopher thomomys talpoides at bonneville estates adds to a sparse regional record for that species and similar to homestead cave it appears that the ca 9500 14c yr bp 10 800 cal yr bp replacement of the northern pocket gopher by botta s pocket gopher in the great salt lake desert vicinity was also in response to climate change

age distribution and stratigraphy of glacier peak tephra in eastern washington and western montana united states tephra layers from williams lake fen wildcat lake and east wenatchee washington and kearns basin lost trail pass sheep mountain bog and marys frog pond montana were analyzed by electron mi

sedimentological processes in a scarp controlled rocky shoreline to upper continental slope environment as revealed by unusual sedimentary features in the neogene coquimbo formation north central chile abstract exceptionally good outcrops of miocene to pliocene deposits in the vicinity of submarine paleozoic basement scarps at carrizalillo north of la serena reveal a wealth of sedimentary features not commonly observed the most proximal facies consist of rock fall and coarse grained debris flow deposits directly abutting the basement wall from which they originated angular basement clasts are mixed with well rounded cobbles which probably formed as a basal gravel on a wave cut platform at the beginning of marine flooding subsequently accumulated at the scarp edge and were incorporated into the debris when the latter collapsed the poor sorting inverse grading and protruding cobbles and boulders are classical debris flow features with good clast imbrication indicating a laminar shearing action a medial facies is represented by secondary channels running parallel to the major scarp about 1 km downslope of the first locality in the largest channel megaflutes at the base indicate the passage of highly turbulent nondepositing flows eroding the soft silty substrate in the deepest central part of the channel a pebbly coquina shows horizontal and trough cross stratification with most of the bivalves oriented convex side up meter scale rip up clasts of the underlying siltstone are also present indicating turbulent flow with a density sufficiently high to retard settling the coquina is interpreted as a detachment deposit resulting from a hydroplaning debris flow along the central part of the channel where the velocity and rate of pore pressure decay were highest this deposit is overlain by fining upward massive to horizontally stratified sandstone very similar in texture and composition to the matrix of the debris flow suggesting its formation by surface transformation and elutriation of the latter along the channel margin a basal centimeter scale sandstone layer is virtually unaffected by the megaflute topography and clearly represents a subsequent event it is interpreted as a basal shear carpet driven by the overlying debris flow within the shear carpet a basal friction zone and an overlying collision zone containing a higher concentration of shell hash can be distinguished the overlying debris flow deposit is represented by massive coquina with scattered angular to rounded basement clasts it contains disarticulated bivalves oriented with their concave side up indicating large scale upward fluid escape during deposition a smaller secondary channel shows large rip up rafts of the underlying substrate some rafts appear to have been plucked from the substrate by a process of sand injection from an overriding high density sandy debris flow which probably originated during a tsunami such clasts can climb upward into a laminar flow by down current tilting and tumbling the most distal facies occurs below a second scarp oriented more or less parallel to the present coastline where finer grained turbidites onlap and backlap onto the stoss and lee sides of an obstacle formed by eroded boulder conglomerates the onlap deposits resemble inclined sandy macroforms recently described in submarine canyon settings they are interbedded with diatom containing volcanic ash beds with cross stratification dipping eastwards and containing deepwater microflora typical of continental upwelling zones

microbially induced sedimentary structures from the 1 64 ga chuanlinggou formation jixian north china abstract the present study documents abundant exceptionally preserved microbially induced sedimentary structures miss from the 1 64 ga chuanlinggou formation of the jixian area north china craton the chuanlinggou formation is dominated by black silty shale mudstone with fine sandstone of the lower part and was likely deposited in a relatively restricted shallow marine environment varying from fair weather wave action zone to below storm wave action zone both wrinkle structures and sand veins are very abundant in the lower and middle parts of the formation wrinkled layers are dark colored densely laminated and contain floating quartz grains and abundant mica grains both of which are aligned parallel to bedding plane such an arrangement pattern is attributed to the microbe s binding and trapping of miss sem imaging also shows that sticky networks interwoven by filamentous extracellular polymer substances eps and biofilms with distinct pores are very pronounced in clay matrix of wrinkled layers providing direct evidence of microbial activities during the formation of wrinkle structures in addition the circularly arranged quartz grains forming hollow cavities and vertical channels of quartz grains beneath the laminated layers are unique to the wrinkle structures showing initial forming stage of the sand veins sand veins similar to fills of sand cracks are usually preserved in silty shales and occasionally occur beneath the winkled surfaces they were formed due to methane degassing of decay of microbial mats and biofilms abundant nano particles of various epss isolated nanoglobules paired nanoglobules dumbbell shaped nanoglobules and polyhedron aggregates are detected in clay matrix close to sand veins indicating microbial participation in the formation of sand veins wide spatial distribution broadened environmental inhabitation and extremely high abundance and bed surface density of the misss indicate proliferation of miss forming microbial mats in mesoproterozoic times

hydraulic behavior of collapsible compacted gneiss soil the hydraulic behavior of a residual gneiss soil compacted at conditions that produce collapsible characteristics was studied using a triaxial permeameter system that allows independent control of net stresses and matric suction wetting paths under differing but constant loads were utilized to reflect field conditions associated with a collapsing soil earth fill dam the experimental results showed that different stress paths produce different amounts of volumetric collapse and distinct variations in the coefficient of permeability which at relatively high matric suctions was mainly affected by the increase in degree of saturation however as the soil approached saturation the coefficient of permeability became dependent on void ratio and net mean stress with the saturated coefficient of permeability being reduced at larger amounts of collapse the results also suggested that entrapped air in the soil voids may produce a significant reduction in the coefficient of permeability a constitutive relationship for the coefficient of permeability that takes net mean stress changes into account was proposed based on best fit analyses

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

microbial mat control on siliciclastic precambrian sequence stratigraphic architecture examples from india abstract an attempt has been made to understand within a cause and effect framework the sequence building pattern in proterozoic time that witnessed non uniformiteranean microbial mat growth and epeiric sea development marine or marginal marine successions in three neoproterozoic formations the sonia sandstone in western india and the sirbu shale and upper bhander sandstone in central india have been examined here for this purpose the strikingly common feature of all three formations is vertical stacking of highstand systems tracts without intervention of any significant transgressive deposits in one instance only the transgressive systems tract is represented by a thin granular transgressive lag and in all other cases the evidence of transgression is simply marked by the presence of marine flooding surfaces the absence of transgressive strata relates to the low sea floor gradients which facilitated rapid transgressions combined with a generally low sediment supply aggradation under normal regressive highstand conditions in spite of the low sediment supply was promoted by the prolific growth of microbial mats which reduced the effects of wave and current reworking by organic binding of clastic particles

engineering geology of basaltic residual soil in leiqiong southern china the physical mechanical chemical mineralogical and microstructural properties of basaltic residual soil obtained from leiqiong area in southern china were examined emphasis was placed on the influences of minerals oxides and the soil fabric on engineering geological characteristics particularly on strength and deformation properties distinctive properties such as high strength and low compressibility relative to high void ratios high liquid limits and low natural densities were explained the soil fabric with the cement bond formed by iron oxides was considered as the main factor that caused to peculiar mechanical behavior whereas mineralogy and climate processes also played important roles under the influence of repeated cycle of alternate wetting and drying the residual soil generated a large collapsible deformation upon soaking and its strength significantly decreased because of the derogation of cement bond the formation of microcracks and the weakening of microstructure failure zones

influence of compaction procedure on the mechanical behaviour of an unsaturated compacted clay part 1 wetting and isotropic compression the influence of compaction pressure compaction water content and type of compaction static or dynamic on subsequent soil behaviour during wetting and isotropic loading has been investigated by conducting controlled suction tests on samples of unsaturated compacted speswhite kaolin the results are interpreted within the context of an elastoplastic framework for unsaturated soils to examine which compaction induced effects can be explained simply by variation in the initial state of the soil and which require that soils produced by different compaction procedures are modelled as fundamentally different materials the compaction pressure influences initial state by affecting the initial position of the yield surface but it also influences to a limited degree the positions of the normal compression lines for different values of suction the compaction water content influences the initial suction but also has a significant influence greater than does compaction pressure on the positions of the nor

tectono sedimentary evolution of the mesoproterozoic basins in the southern yan liao and mianchi queshan areas insights from stratigraphic pattern and detrital zircon geochronology the widespread mesoproterozoic successions around the world have recorded the breakup of the ancient supercontinent columbia in the north china craton ncc the mesoproterozoic basins in the yan liao and southern ncc are the important evidence to study the nature and evolution of the mesoproterozoic basins in this study we scrutinized the stratigraphic pattern and detrital zircon u pb geochronology in the southern yan liao and mianchi queshan areas in the southern ncc to investigate the evolutionary relationship between the mesoproterozoic basins in the north and south of ncc detrital zircons from the mesoproterozoic sequence in the southern yan liao areas showed monotonous source with age peak at ca 2500 ma corresponding well with the ages of the neoarchean complex in the central ncc however the mesoproterozoic sequence in the mianchi queshan areas which is represented by the ruyang group exhibited significantly different characteristics with influx of much younger zircons the southern yan liao and mianchi queshan areas showed distinct similarity in the stratigraphic pattern reflected by the mesoproterozoic successions in these two areas being both bracketed by two sequence boundaries and further divided into two sequences under a uniform sea level change the mesoproterozoic strata in these two areas probably possessed a correlative relationship in the stratigraphic patterns and basin evolutionary history

subaqueous shrinkage cracks in the devonian of scotland reinterpreted abundant lenticular straight to curving cracks on bedding planes are commonly interpreted as subaqueously formed shrinkage cracks syneresis cracks the two most influential examples being those in the green river formation picard 1966 and the devonian orcadian basin of scotland donovan and foster 1972 cracked surfaces in the orcadian basin deposits show all gradations between lenticular cracks and well developed polygons of subaerial origin some lenticular cracks are inferred to have formed during subaerial desiccation many of the simplest lenticular cracks also have the shapes of gypsum crystals and originated as pseudomorphs the gypsum crystals were often important in providing nuclei for later desiccation cracks more complex crack patterns of incipient to fully formed desiccation polygons have arisen from desiccation of surfaces containing gypsum crystals or pseudomorphs resulting from gypsum crystal dissolution cracks of all types are preserved by sand infills introduced by wind transport across dried up lake floors reassessment of the literature reporting subaqueous cracks in rocks shows that many of these cracks are likely to have originated in a similar way partly as gypsum crystals and partly by limited subaerial desiccation the remaining examples have either already been reinterpreted in other ways or are insufficiently documented to rule out a subaerial origin there is no clear evidence for subaqueously formed cracks being preserved in rocks

an insight into the role of hydraulic history on the volume changes of anisotropic clayey soils 1 volume changes of natural and compacted soils induced by changes in their water content have many practical implications in the service life of earth dams river and canal embankments and waste disposal facilities an insight into the overall strain response of a clayey soil upon gradual wetting and drying is provided here experimental data coming from oedometer and isotropic tests under suction and net stress control are presented for a compacted clay with an initial anisotropic fabric highlighting the relevant role played by the hydraulic path on collapse swelling and shrinkage strains irreversible strains could be observed after wetting drying paths and the subsequent drying wetting cycle both stress and hydraulic histories play a role in the evolution of the directional fabric of clayey soils the experimental data could be reproduced with a rather simple elastic plastic constitutive model with a mixed isotropic rotational hardening previously conceived for saturated soils the model is extended to unsaturated conditions by substituting the saturated effective stress with a measure of the average stress acting on the soil skeleton and by introducing generalized hardening rules governed by both plastic strains and degree of saturation coupling between the mechanical and the hydraulic behavior is provided by the water retention curve in which degree of saturation is adopted as a useful measure of the soil water content

the timing of late pleistocene mammalian extinctions in north america more than 375 14c dates from 150 fossil sites in north america have been analyzed to evaluate the question of extinction of late pleistocene megafauna when critically evaluated no 14c ages for any extinct pleistocene genera are younger than 10 000 yr b p

microbially induced sedimentary structures a new category within the classification of primary sedimentary structures abstract cyanobacterial films and mats syndepositonally influence erosion deposition and deformation of sediments the biomass levels surface morphologies and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing growing microbial mats dredge grains from their substrate upwards whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle trap and bind suspended particles these and similar biotic physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures we distinguish structures on bedding planes leveled bedding surfaces wrinkle structures microbial mat chips erosional remnants and pockets multidirectional ripple marks and mat curls and internal bedding structures sponge pore fabrics gas domes fenestrae structures sinoidal laminae oriented grains benthic ooids biolaminites mat layer bound grain sizes we propose to place this group of microbially mediated structures as a fifth category bedding modified by microbial mats and biofilms in pettijohn and potter s 1964 existing classification of primary sedimentary structures

paleoproterozoic microbially induced sedimentary structures from lagoonal depositional settings in northern china abstract microbially induced sand cracks crack fills occur extensively on the top surface of fine sandstone beds of the paleoproterozoic zhaojiazhuang formation changcheng group 1 7 ga around the cangyan mountain hebei province northern china detailed field and microscopic petrographical evidence reveal that these sand cracks crack fills possibly resulted from dehydration and desiccation of microbial mats the age and peculiar morphology of these microbially induced sedimentary structures do not allow comparison with trace fossils or purely physical desiccation cracks the fine sandstone beds on the surfaces of which these microbially induced sedimentary structures formed were deposited in a lagoon brackish depositional setting marine to non marine transitional setting with episodic injection of marine water as such these microbially induced sedimentary structures suggest the colonization of the marine to non marine transitional settings in the paleoproterozoic period and that the search for evidence of early microbial life should be sought in the marine to non marine transitional settings these broad habitats suggest these microbes could have been eurytopic organisms capable of adapting to varying extents of salt and oxygen content variations like their modern counterparts

study of the water retention properties of a tropical soil some peculiarities of water retention in a tropical lateritic soil of clayey nature are presented and discussed the typical soil microstructure is shown through thin layer plates emphasizing soil microaggregation and pore distribution and their repercussion on the soil water retention curve and on hysteresis it is shown that the clayey soil has a behavior that to a large extent resembles sandy soil which is characterized by the relatively high saturated hydraulic conductivity low air entry value and small suction range at which water drainage takes place the severe weathering processes that originated this soil have produced an altered soil that seems to be homogeneous in terms of physical indices hydraulic conductivity and soil water retention characteristics up to 4 5 m in depth

meso neoproterozoic strata and target source rocks in the north china craton a review abstract along with the breakup of the supercontinent nuna and rodinia during the mesoproterozoic and neoproterozoic a series of sedimentary basins formed within or at the periphery of the ancient cratons under the regime of breakup of the supercontinent these basins underwent different evolutionary history hence formed different geological elements constituting the petroleum systems in this contribution the distribution and the stratigraphic successions of the meso neoproterozoic basins in the north china craton ncc were examined as well as the retrospective review for the mechanisms of the basin formation the synthesized geological and geochronological data support a long term extensional environment for the basins in the northern ncc the mesoproterozoic basins in the yanshan western liaoning yan liao and the zhaertai areas formed at the intracratonic position later than that in the bayan obo which possibly deposited in the continental margin the further efforts still need to be devoted to decipher the huge controversial around the tectonic nature of the basins in the southern ncc as well as their stratigraphic correlations with the basins in the north and central the distribution and organic geochemical characteristics of the mesoproterozoic source rock were also summarized three sets of source rock in the central ncc namely the chuanlinggou hongshuizhuang and xiamaling formations developed favorable geological and geochemical conditions for the generation of the hydrocarbon while in the south the cuizhuang formation was the only interval feasible for potential source rock the progress in seismic geophysics and borehole drilling suggested the existence of the mesoproterozoic beneath deep ordos basin this open a new window for the reconstruction of the mesoproterozoic paleogeography as well as the evaluation of the source potential of the mesoproterozoic basins in the north china craton

suction in compacted states examines the possible magnitude of suction in compacted states of clayey soils from the test results it is concluded that suction is zero in monotonically loaded unsaturated states this implies that suction in compacted states should be equal to the compaction stress itself however as data previously reported in literature have often shown suction is strongly related to the water content and not much affected by the compaction stress

possible biogenic structures from the lower cambrian strata in yunnan province south china microbially induced sedimentary structures miss are microbial traces in sandy deposits they have been formed by various modes of microbial behaviour in response to the prevailing physical dynamics in shallow marine environments since early archaean time an association of fossils phosphatic structures and grains stromatolites and microbial laminated levelling structures is documented from the zhongyicun member of lower cambrian strata in the baideng section dated close to 535 ma sem examination demonstrates that microbial laminated levelling structures are the result of the development of microbial mats composed of filamentous structures we propose that there was a short hiatus after the dolomite layer deposited when the dolomite layer was weathered to form centimetre scale valleys firstly and then microbes accumulated in these valleys and formed the microbial laminated levelling structures

human adaptation at the pleistocene holocene boundary in western canada 11 000 to 9000 bp abstract most of western canada was covered by ice until about 12 000 bp environments suitable for human habitation were established by about 11 500 bp the earliest known human occupations date to about 10 700 bp para glacial processes may have destroyed most early sites post glacial colonization occurred from the south only 14 archaeological sites contain radiocarbon dates earlier than 9000 bp the limited data from these sites suggest initial exploitation of big game in open environments until about 10 000 bp sites dating between 10 000 and 9000 bp are known mainly from the southern interior plains and document a continuation of bison hunting adaptive strategies in early boreal forests are still unknown

early jurassic microbial mats a potential response to reduced biotic activity in the aftermath of the end triassic mass extinction event wrinkle structures are microbially induced sedimentary structures miss formed by cyanobacteria and are common in pre cambrian and cambrian siltstones and sandstones but are otherwise rare in the phanerozoic geological record this paper reports the first discovery of mesozoic wrinkle structures from sweden these are preserved in fine grained and organic rich heterolithic strata of the lower jurassic hettangian hoganas formation in skane southern sweden the strata formed in a low energy shallow subtidal setting in the marginal parts of the danish rift basin palynological analyses of fine grained sandstones hosting the wrinkle structures show that the local terrestrial environment probably consisted of a wetland hosting ferns cypress and the extinct conifer family cheirolepidaceae palynostratigraphy indicates a hettangian age still within the floral recovery phase following the end triassic mass extinction event the finding of wrinkle structures is significant as the presence of microbial mats in the shallow subtidal zone in a deeper setting compared to where modern epibenthic microbial mats grow suggests decreased benthic biodiversity and suppressed grazing in shallow marine environments in the early aftermath of the end triassic mass extinction event

role of matric suction in collapse of compacted clay soil this paper examines the influence of variations in matric suction on the collapse behavior of compacted bangalore clay soil the astm filter paper method measured the matric suctions of the compacted soil specimens the matric suction of the compacted clay soil specimens ranged between 50 and 8 000 kpa at the as compacted s r values of 90 and 35 comparison of the matric suction gravimetric water content relations of various compacted soils showed that the soil with a higher liquid limit has a higher matric suction at a given gravimetric water content variations in as compacted degrees of saturation at a constant relative compaction or variations in relative compaction at a constant as compacted degree of saturation notably affected the matric suction of the bangalore clay soil experimental results also showed that the influence of matric suction on the collapse behavior of this compacted clay soil greatly depended on the relative compaction of the specimens and the pressure at which they were inundated

microorganism mediated preservation of planolites a common trace fossil from the harkless formation cambrian of nevada usa specimens of planolites a tubular ichnofossil from the harkless formation cambrian of nevada are commonly rimmed by thin layers of limonite a probable pseudomorph after pyrite suggesting that bacterially induced biomineralization played a key role in the preservation of the burrows organic material secreted by a vermiform infaunal tracemaker is inferred to have formed the substrate for a biofilm that facilitated iron sulfide biomineralization by bacteria under localized anaerobic or dysaerobic conditions rapid microbially mediated biomineralization of mucus lined burrow walls is inferred to have promoted three dimensional preservation of burrows by strengthening them against sediment compaction and possibly providing sufficient support for burrows to allow time for sediment infill decomposition of organic materials in planolites also left evidence in sediment layers immediately above the burrows undulose sediment surfaces and small round pimpleform gas escape structures c 2011 elsevier b v all rights reserved less

environmental change recorded in sediments from the marmes rockshelter archaeological site southeastern washington state usa abstract the marmes rockshelter archaeological site in southeastern washington state contains a 11 kyr stratigraphic record that was excavated in the 1960s but only recently analyzed in detail we present the results of physical chemical and isotopic analyses of archived marmes sediments from rockshelter hillslope and floodplain locations multiple lines of evidence including eboulis production soil chemistry and 13c and 18o signatures in soil organic matter and calcium carbonate suggest that relatively cool moist conditions 10 600 to 9700 14c yr bp were followed by relatively warm and dry conditions as early as 9000 14c yr bp warm and dry conditions extended to the late holocene followed by a return to cooler and moister climate the limited range of 13c and 18o values in marmes paleosols suggests that the magnitude of moisture and temperature shifts was locally buffered in the lower snake river canyon but adequate to generate significant changes in sedimentation and soil formation possibly due to nonlinear geological and pedological processes these buffered canyon environments were well suited for establishing residential bases associated with foraging and logistical collecting strategies and may have minimized the influence of climate changes in food resource abundance

life on land in the proterozoic evidence from the torridonian rocks of northwest scotland the stoer group and diabaig formation of the torridonian succession in northwest scotland are late mesoproterozoic to early neoproterozoic ca 1200 1000 ma features preserved on the top surfaces of fine to medium grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures these include wrinkle structures remnants of apparent microbial crusts and indications of original cohesiveness and pliancy in sand sized sediment the surfaces on which the microbial structures formed were exposed subaerially abundant deep desiccation cracks and locally pedogenic structures in alluvial interfluve and lacustrine margin settings and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels thus these features indicate that earth9s biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the phanerozoic

microbial mats in the terrestrial lower triassic of north china and implications for the permian triassic mass extinction abstract evidence for microbial mats has been reported repeatedly from marine lower triassic rocks but scarcely mentioned in post mass extinction terrestrial facies here we report from the terrestrial lower triassic liujiagou formation in north china the presence of five kinds of microbially induced sedimentary structures miss or sedimentary surface textures including old elephant skin textures wrinkle structures palimpsest ripples manchuriophycus structures and sand cracks terrestrial microbial communities that produced these miss adapted not only to periodically desiccated conditions but also to the storm dominated palaeoenvironments in the liujiagou formation the permian triassic mass extinction ptme in north china is marked by the die off of plants disappearance of coal beds extinction of pareiasaurs among tetrapods decreased bioturbation levels and a dramatic change of sedimentary systems through the sunjiagou formation the sunjiagou formation recorded the turnover from an ever wet to a progressively drier and hotter climate and it spans the ptme in north china following this mass extinction miss became much more common and widespread suggesting that the mass extinction provided favourable biological and environmental conditions for the development of the miss in terrestrial ecosystems especially the decreased bioturbation intensity and grazing pressure associated with increased temperature and climatic drying in the upper part of the liujiagou formation and overlying heshanggou formation the disappearance of miss coupled with increased bioturbation might indicate an improvement of terrestrial ecosystems and the beginning of the triassic biotic recovery however as the investigation of miss in space and time through the geological record is in its early stages further geobiologic and geochemical studies as well as high precision isotopic dating from permian triassic terrestrial successions are needed to fully reveal the timing and pattern of the early triassic terrestrial ecosystem reconstruction

diagenetic xenotime age constraints on the sanjiaotang formation luoyu group southern margin of the north china craton implications for regional stratigraphic correlation and early evolution of eukaryotes abstract eukaryote fossil bearing ruyang and luoyu groups are extensively exposed along the southern margin of the north china craton but their age has long been a matter of controversy due to the absence of reliable radiometric dates by dating detrital zircons and diagenetic xenotimes from the sanjiaotang formation of the luoyu group this paper confirms that the ruyang and luoyu groups were deposited during the period of 1750 1400 ma the new age constraints suggest that the sanjiaotang formation is coeval with the xiamaling formation of the jixian group on the northern margin of the north china craton correlation of the luoyu group with the jixian group is thus indicated the ruyang and luoyu groups contain abundant fossils of eukaryotic organisms such as acritarch and macroalgae accordingly eukaryotic proliferation extends back to the mesoproterozoic consistent with results of molecular phylogenetic analysis that a rapid morphological diversification of eukaryotic organisms occurred prior to 1400 ma

benthic cyanobacteria and their influence on the sedimentary dynamics of peritidal depositional systems siliciclastic evaporitic salty and evaporitic carbonatic abstract peritidal sedimentary systems are widely colonized by benthic cyanobacteria that form biofilms and microbial mats the bacterial communities interfere with physical and chemical sedimentary dynamics which is documented by the formation of microbially induced sedimentary structures miss the structures form a new fifth category in the existing classification of primary sedimentary structures siliciclastic depositional systems are dominated by physical dynamics by biostabilization cyanobacteria shelter their substrata against erosion during periods of intensive hydraulic reworking or they permit flexible deformation of sandy sediments during low hydrodynamic disturbance the bacteria enhance deposition of sediments by baffling trapping and binding such biotic physical interference is recorded by miss such as erosional remnants and pockets or planar stromatolites chemical depositional systems include i evaporitic salty environments characterized by evaporation and dissolution and ii evaporitic carbonatic environments that include evaporation dissolution and in situ lithification of organic matter here cyanobacterial mats experience periodical desiccation or evaporation of crystals and mat related structures such as petees and polygonal patterns of cracks are formed cyanobacteria and heterotrophic bacteria provide a chemical microenvironment that supports in situ lithification of organic matter in thin sections carbonate precipitates as ooids or lines of decaying filaments are visible miss occur in modern and ancient depositional systems they record i biological abilities of benthic cyanobacteria to cope with sedimentary dynamics and ii paleoclimate and paleoenvironmental conditions during earth history similar structures are also expected in extraterrestrial paleo environments

determination of geomechanical properties and collapse potential of a caliche by in situ and laboratory tests working in complex grounds have always been difficult for engineering geologists because of the heterogenous nature of such geo materials which results in different behaviors under stresses the caliches outcropping in the adana basin and its close vicinity are selected as the study material because of their highly complex nature and also understanding their mechanical behaviour and collapse potential is too difficult although their aerial extent is large in the region for this reason investigation of the collapse potential and mechanical behaviour of the caliches by applying new approaches besides the conventional in situ and laboratory tests is the purpose of the study the study includes five main stages such as measurements of caliche profiles in situ tests plate loading sampling shooting photographs for photoanalyses and laboratory studies four different levels such as hard pan silty sandy layer gravelly blocky layer and clayey level are described for the caliches employed the hard pan level is a weak rock with an average uniaxial compressive strength of 11 89 mpa while the others have typical soil characteristics a series of plate loading tests are applied on the blocky gravelly level of the caliche to determine the modulus of elasticity the modulus of elasticity and the allowable bearing capacity are determined between 28 6 65 3 and 1 5 2 0 mpa respectively to determine the grain size distribution curve in addition to sieve analyses a photoanalysis technique is also applied and a combination procedure between the results from both sieve analyses and photoanalyses is introduced and the grain size curves for the blocky gravelly level of the caliche are obtained according to the results of collapse potential index tests performed on the samples collected from 20 locations of the study area the soft pan level of the caliche has slight to moderate degree of collapse indices in the final stage various simple and statistically meaningful empirical equations are proposed for the indirect determination of the collapse index by employing simple paramateres

mid wisconsinan vertebrates and their environment from january cave alberta canada abstract january cave in the rocky mountains of southwestern alberta has yielded vertebrate remains from a coprocenosis of mid wisconsinan age taphonomic analysis indicates accumulation by raptors mostly owls and mammalian carnivores the vertebrate record together with pollen analysis indicates that cool dry conditions prevailed in an extensive tundra like environment with prairie elements in the valleys below thirty four mammalian taxa have been recovered from january cave today some of these species e g lemmus sibiricus and dicrostonyx torquatus do not coexist with others e g cynomys sp mustela nigripes vulpes velox and lagurus curtatus therefore the january cave local fauna represents a nonanalog mammalian community characteristic of the late pleistocene it suggests that the region enjoyed an equable climate with reduced climatic extremes but still cool further supporting a mid wisconsinan age estimate for the fauna it is the first major small vertebrate fauna of its age to be reported from alberta

microbially induced sedimentary structures from the mesoproterozoic huangqikou formation helan mountain region northern china abstract seven types of microbially induced sedimentary structures miss wrinkle structures levelled ripple marks organic carbonaceous laminae microsequences polygonal sand cracks polygonal sand crack fills and gas domes are documented from the mesoproterozoic huangqikou formation of the helan mountain region western part of north china facies analysis suggests that the miss hosting rocks were deposited in a supertidal to intertidal setting both wrinkle structures and gas domes are morphologically different from those previously documented from other ancient siliciclastic rocks but probably formed by the same microbially mediated process as those published elsewhere other miss resemble their ancient and modern counterparts in both morphology and size the presence of carbonaceous laminae coupled with laser raman and carbon isotopic data 25 0 5 indicates a biogenic origin of the wrinkle structures the absence of intercalating mudstone layers as well as different lithologic composition between polygonal sand cracks crack fills and host rock indicate that both the polygonal sand cracks and polygonal sand crack fills likely resulted from dehydration and desiccation of organic rich microbial mats the biogenicity of gas domes is supported by the different lithologic composition between infillings and wall

proliferation of miss forming microbial mats after the late neoproterozoic glaciations evidence from the kimberley region nw australia abstract a total of 20 morphological types of microbially induced sedimentary structures miss are recognized from the late neoproterozoic tillite bearing successions of the kimberley northwestern australia which include alpha petees triradiate cracks multidirectional linear ridges millimeter ripples erosional remnants and pockets and so on of these triradiate cracks multidirectional linear ridges and millimeter ripples are reported for the first time from the neoproterozoic worldwide most kimberley miss are morphologically comparable with their ancient and present day counterparts whose biogenicity have been well demonstrated in the kimberley during the interglacial period miss have colonization preference to relatively coarse sandy substrates ranford formation and their abundance decreased towards the younger strata throssell shale in contrast miss abundance increased from the older strata yurabi formation towards the younger strata flat rock formation during the postglacial period however overall both miss abundance and bedding plane coverage percentage increased from the marinoan younger marinoan gaskiers interglacial successions to younger marinoan gaskiers postglacial successions indicating a proliferation of microbial mats after the younger marinoan gaskiers glaciation the increase of microbial mats could have ameliorated marine biogeochemical conditions and ecosystems and thus laid the foundation for the rise of ediacaran biota in australian basins

proliferation of miss related microbial mats following the end permian mass extinction in the northern paleo tethys evidence from southern qilianshan region western china as a consequence of the end permian mass extinction microbes proliferated in the post extinction shallow marine ecosystems in which they grew as various microbially induced sedimentary structures misss in siliciclastic settings this paper reports for the first time the discovery of abundant misss from the lowest triassic sandstones of shallow water margin origin in the zhihema sections of the southern qilianshan region west china the sandstones are characterized by well developed cross beddings and ripple marks and a claraia dominated bivalve assemblage of middle late griesbachian age these sedimentary structures together with the bivalves suggest a high energy peritidal zone of a shoreface setting in a clastic shallow sea environment seven types of misss are recognized and described here pictograph like sand cracks crack fills polygonal sand crack fills erosional remnants multidirectional linear grooves sinuous crack fills fusiform sand cracks crack fills and leveled ripple marks most of the newly found misss are morphologically comparable with their ancient and modern counterparts detailed optical microscope and scanning electron microscope sem analyses reveal that thin clayey laminae and filamentous mica grains are aligned parallel to bedding plane and that the matrix supported quartz grains overall are oriented both of which are interpreted to indicate biogenic origin the biogenic origin of these misss is reinforced by the presence of copious putative nanoglobules and filamentous biofilm like organic objects in the interspaces of clay minerals in laminated layers these nanometer scale objects are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization the presence of misss on the northern margins of paleo tethys indicates that the post extinction microbial mats had expanded their distributions from low latitude to moderate high latitude regions moreover unlike some previously reported microbial mats that contain very rare body and trace fossils the southern qilianshan misss were found in association with abundant vertical burrows and bivalves suggesting that the miss forming microbial mats may have served as oases for trace making organisms and opportunistic bivalves to flourish in shallow marine habitats immediately after the end permian mass extinction

late pleistocene and holocene vertebrates and palaeoenvironments from charlie lake cave northeast british columbia excavations outside charlie lake cave peace river district british columbia revealed deposits dating from 10 700 bp to the present the earliest fauna 10 700 10 000 bp was deposited when the newly deglaciated landscape was largely unforested and included bison bison sp ground squirrel spermophilus sp a large hare lepus sp snowshoe hare lepus americanus and a variety of birds including the cliff swallow hirundo pyrrhonota by 10 000 bp snowshoe hare lepus americanus was the most numerous mammal indicating the development of forested conditions by 9000 bp the fauna resembled the modern peace river fauna prior to european settlement typical of a largely forested landscape with wetland areas indicated by aquatic avian species subsequent holocene climatic fluctuations are not evident in the faunal record

climatic implications of latest pleistocene and earliest holocene mammalian sympatries in eastern washington state usa abstract for more than fifty years it has been known that mammalian faunas of late pleistocene age are taxonomically unique and lack modern analogs it has long been thought that nonanalog mammalian faunas are limited in north america to areas east of the rocky mountains and that late pleistocene mammalian faunas in the west were modern in taxonomic composition a late pleistocene fauna from marmes rockshelter in southeastern washington state has no modern analog and defines an area of maximum sympatry that indicates significantly cooler summers than are found in the area today an earliest holocene fauna from marmes rockshelter defines an area of maximum sympatry including the site area but contains a single tentatively identified taxon that may indicate slightly cooler than modern summers

paleoecological and biogeographical implications of late pleistocene noble marten martes americana nobilis in eastern washington state usa a mandible identified as noble marten martes americana nobilis recovered from sediments dating to 11 800 cal yr bp and a humerus identified as m a cf nobilis recovered from sediments dating from 13 100 to 12 500 cal yr bp at the marmes rockshelter archaeological site in southeastern washington represent the first record of this taxon in the state mammalian taxa associated with the marmes rockshelter noble marten represent a diversity of open mesic habitats corroborating earlier analyses of other records of the noble marten in the western united states and exemplify how paleozoologists determine the ecology and environmental predilections of extinct taxa the recovery site represents the topographically lowest record of this species in western north america and the farthest north record in the united states future research should examine known late quaternary martes spp remains from british columbia and alberta to fill in the 2200 km geographic gap in the known distribution of this taxon between a record in the northern yukon and those in the western united states and to refine our knowledge of noble marten paleoecology

a framework for the behaviour of unsaturated expansive clays the paper presents a framework for describing the mechanical behaviour of unsaturated expansive clays it is an extension of an existing formulation developed for unsaturated soils of low activity the extended framework is based on the distinction within the material of a microstructural level where the basic swelling of the active minerals takes place and a macrostructural level responsible for major structural rearrangements by adopting simple assumptions concerning the coupling between the two levels it is possible to reproduce major features of the behaviour of unsaturated expansive clays some selected qualitative comparisons between model predictions and experimental results reported in the literature are presented despite the simplified hypotheses made a very encouraging agreement is obtained key words capillarity clay model unsaturation suction expansive soils

diagenetic xenotime dating to constrain the initial depositional time of the yan liao rift abstract in the mesoproterozoic and neoproterozoic the north china craton ncc underwent long lived sedimentation with minor volcanism in the yan liao rift forming the mesoproterozoic changcheng jixian and qingbaikou groups in sequence the basal boundary age of the lower changcheng group indicates the initial time of the ncc as a stable cratonic block and can be used to make correlations among several representative basins worldwide recent studies have debated the initial depositional time of the changcheng system which is the key to understanding the proterozoic tectonic evolution of the ncc this study documented the xenotime and monazite from the lowermost changzhougou and chuanlinggou formations of the changcheng group the monazite grains from the chuanlinggou formation yielded u pb ages between 1810 ma and 2500 ma which are comparable to the detrital zircon u pb ages in the same formation indicating their detrital origin xenotime mostly occurs as overgrowths on the detrital zircon grains supporting a post depositional origin the low u content of the changzhougou formation s xenotimes indicates a hydrothermal origin its peak age of 1570 15 ma may indicate a hydrothermal event the xenotime from the chuanlinggou formation is characterized by a high u content and a ree pattern with a nonexistent or weak negative eu anomaly and a higher gd yb ratio implying a diagenetic origin these xenotime overgrowths yielded a wide age variation even on a single grain due to prolonged xenotime precipitation the oldest population of 1716 3 ma is interpreted as the minimum depositional age of the chuanlinggou formation the lowest boundary of the changchengian system must be older than 1716 ma this work demonstrates that diagenetic xenotime could better constrain the depositional time however extensive systematic research is required especially with higher spatial resolution and more diagenetic xenotime grains

suspected microbial mat related crack like sedimentary structures in the palaeoproterozoic magaliesberg formation sandstones south africa abstract the occurrence of patchy preservation of ripples and of palimpsest ripples on many sandstone bed surfaces of the c 2 1 ga magaliesberg formation pretoria group transvaal supergroup south africa suggests that microbial mats grew within the upper parts of sandy deposits of the braid deltaic tidally controlled epeiric marine coastline palaeoenvironment inferred for this stratigraphic unit recently limited occurrences of petee ridges cracked sand layers elephant skin textures wrinkle structures and manchuriophycus like cracks have been found substantiating the envisaged role for microbial mats binding sandy sediment and providing cohesion during active sedimentation by fluvial and tidal processes ripple marks associated with most of these biogenic sedimentary structures enable evaluation of genetic processes for the ripples currents waves wind as well as estimation of wave heights and water depths cf tanner w f 1967 ripple mark indices and their uses sedimentology 9 89 104 tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 the petee ridges are interpreted as reflecting spring low tidal desiccation which cracked the mats followed by disruption of sand beneath the mat due to loading from incoming tides or subsequent deposits slightly sinuous sand cracks on ripple crests are related to a similar combination of low tidal desiccation and formation of wind ripples with subsequent high tides providing the deeper water conditions and larger wave heights calculated from the tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 formula synaeresis cracking is inferred for both elephant skin cracks and manchuriophycus structures these inferred suspect microbial sedimentary structures when studied in relation to data derived from associated ripples thus enable better estimation of depositional conditions within the magaliesberg palaeoenvironment and indicate minimum epeiric tidal ranges of c 112 cm in general these structures are found associated with evidence for shallower water and higher energy conditions which probably protected the microbial mats from degradation by heterotrophic bacteria through fast burial a possible association of such mat related structures with epeiric marine or passive margin coastline conditions may be pertinent for much of the precambrian clastic record

subaqueous shrinkage cracks in the sheepbed mudstone implications for early fluid diagenesis gale crater mars the sheepbed mudstone yellowknife bay formation gale crater represents an ancient lakebed now exhumed and exposed on the martian surface the mudstone has four diagenetic textures including a suite of early diagenetic nodules hollow nodules and raised ridges and later diagenetic light toned veins that crosscut those features in this study we describe the distribution and characteristics of the raised ridges a network of short spindle shaped cracks that crosscut bedding do not form polygonal networks and contain two to four layers of isopachous erosion resistant cement the cracks have a clustered distribution within the sheepbed member and transition laterally into concentrations of nodules and hollow nodules suggesting that these features formed penecontemporaneously because of the erosion resistant nature of the crack fills their three dimensional structure can be observed cracks that transition from subvertical to subhorizontal orientations suggest that the cracks formed within the sediment rather than at the surface this observation and comparison to terrestrial analogs indicate that these are syneresis cracks cracks that formed subaqueously syneresis cracks form by salinity changes that cause sediment contraction mechanical shaking of sediment or gas production within the sediment examination of diagenetic features within the sheepbed mudstone favors a gas production mechanism which has been shown to create a variety of diagenetic morphologies comparable to the raised ridges and hollow nodules the crack morphology and the isopachous layered cement fill show that the cracks were filled in the phreatic zone and that the sheepbed mudstone remained fluid saturated after deposition and through early burial and lithification

stable isotope variations in the neoproterozoic beck spring dolomite and mesoproterozoic mescal limestone paleokarst implications for life on land in the precambrian proterozoic karst events lowered 13c values by as much as 11 for the 800 ma beck spring dolomite california and as much as 8 5 for the 1 1 ga mescal limestone central arizona relative to the originally deposited carbonate the 13c changes are attributed to input of 13c depleted organic co2 derived from photosynthetic organisms that colonized the ancient land surface the large isotopic shift and its presence at two separate localities suggest that proterozoic karst surfaces were colonized by significant photosynthetic communities with phytomasses possibly approaching those of today

tufted microbial cyanobacterial mats from the proterozoic stoer group scotland upward thinning stellate and polygonal carbonate structures are described and compared to modern and ancient stromatolites although tufted microbial mats are common in modern settings they have rarely been described from ancient rocks owing to their poor preservation potential the preservation of these from the stoer group is due to early replacement by calcite before their original tufted relief could be obliterated by compaction associated limestones with some similar features are interpreted as flat to mamillated microbial mats

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

skeleton of extinct north american sea mink mustela macrodon abstract mustela macrodon extinct sea mink is known only from prehistoric and historic native american shell middens dating less than 5100 years old along coastal islands of the gulf of maine northeastern north america the species is distinct from all known extant subspecies of m vison american mink but still belongs to the north american subgenus vison metric comparisons between m macrodon and five subspecies of m vison using skull mandible humerus radius femur and tibia skeletal elements show that m macrodon is larger in overall size and robustness and is proportionately larger in the dental region many habitat related parallels exist between coastal island mink of the gulf of maine and those of the alexander archipelago southeastern alaska where the overall largest living subspecies of mink is found m v nesolestes

diverse microbially induced sedimentary structures from 1 ga lakes of the diabaig formation torridon group northwest scotland abstract the siliciclastic lacustrine rocks of the 1000 ma diabaig formation northwest scotland contain a remarkable diversity of macroscopic structures on bedding planes that can be compared with various kinds of microbially induced sedimentary structures miss field sedimentological investigations combined with laboratory analysis of bedding planes and petrographic study of thin sections have allowed us to characterise a range of depositional environments and document the spectrum of biological structures miss are reported from frequently subaerial environments through commonly submerged facies and down to permanently sub wavebase settings palaeoenvironmental conditions water depth exposure hydrodynamic energy control the distribution of miss within these facies this demonstrates that mat forming microbial communities were arguably well adapted to low light levels or periodic exposure some miss from the diabaig formation are typical of precambrian microbial mats including reticulate fabrics and old elephant skin textures in addition to these a number of new and unusual fabrics of putative microbial origin are described including linear arrays of ridges and grooves cf arumberia and discoidal structures that are comparable with younger ediacaran fossils such as beltanelliformis these observations indicate that benthic microbial ecosystems were thriving in freshwater lake systems 1000 ma and indicate how microbially induced sedimentary structures may be applied as facies indicators for proterozoic lacustrine environments the discovery of structures closely resembling ediacaran fossils cf beltanelliformis also serves to highlight the difficulty of interpreting simple discoidal bedding plane structures as metazoan fossils

wetting induced volume changes in compacted silty clays and high plasticity clays wetting induced deformations of compacted fine grained soils are of particular interest in earthworks engineering where embankment design needs to take into account potential future water content

wetting induced compression of compacted oklahoma soils the wetting induced compression of compacted oklahoma soils was investigated one dimensional oedometer tests were conducted on 22 oklahoma soils that encompassed relative compaction and moisture contents within typical embankment specifications results show that factors directly related to the fines composition can be used for preliminary estimation of collapse potential statistical analysis of the oedometer test data indicates that variables having the most impact on collapse index were compaction moisture content dry unit weight plasticity index and clay size fraction charts were developed to facilitate the estimation of collapse settlement of fills for different conditions including fill height moisture content and soil type three case histories involving embankments that experienced significant settlement are presented for comparison the comparison shows a reasonable agreement between predictions and field estimates of collapse settlement at the embankment centerlines the limited evidence suggests that predictions based on one dimensional assumptions may underestimate actual settlements possibly due to the two dimensional nature of embankments

mat related sedimentary structures in neoproterozoic peritidal passive margin deposits of the west african craton anti atlas morocco abstract proterozoic inliers in the central anti atlas mountains expose predominantly siliciclastic sedimentary successions deposited in peritidal zones along the neoproterozoic continental margin of the west african craton wac the low grade metamorphic and modestly deformed sediments contain a wealth of sedimentary structures related to the former presence and activities of microbial mats and respective physicobiological processes the well preserved structures include wrinkle structures erosion marks microbial sand chips spindle shaped and subcircular microbial shrinkage cracks and possibly gas domes and cabbage head structures thin sections exhibit mat fragments and dispersed grains of hematite limonite after pyrite in fine grained quartzitic storm deposits post storm layers frequently consist of matrix supported sand sized to silt sized grains and are overlain by argillaceous veneers including isolated silt sized grains and black carbonaceous laminae the muddy veneers are considered to represent compacted stacks of microbial mats biolaminites which colonized and biostabilized storm and post storm layers and thus prevented them from eroding in the absence of grazing and burrowing organisms and at suitable depositional and hydrodynamic conditions it may be expected that proterozoic microbial mats extensively grew from the supratidal to the intertidal zones and occasionally e g behind protective barriers in the subtidal zone and beyond mat related structures however need specific conditions for their formation and preservation wrinkle structures erosion marks and microbial sand chips require tractional currents and soon deposition and burial respectively such conditions are preferably met in intertidal and supratidal zones spindle shaped and subcircular cracks require mat shrinkage due to either desiccation or syneresis crack propagation implies progressive shrinkage while superposition of crack generations indicates repeated alternation between mat exposure and flooding respective conditions prevail in the upper intertidal zone gas domes and cabbage head structures are related to the production of gas from decaying organic material beneath a sealing cohesive mat they may be some of the first features formed during genesis of petee structures in the intertidal to lower supratidal zones mat related structures may serve as sensitive facies indicators once their modes of formation are revealed

a proposal of structural models for colluvial and lateritic soil profile from southwestern brazil on the basis of their collapsible behavior abstract this paper aims to propose structural models for understanding the collapsibility of a colluvial and lateritic soil by conducting oedometric tests with controlled suction executed in laboratory the undisturbed soil samples submitted to experiments were collected by opening a trial pit in experimental field for soil mechanics and foundations situated at the state university of campinas sao paulo brazil the soil samples were characterized by means of standard geotechnical tests chemical and mineralogical tests and mercury intrusion porosimetry oedometric tests with controlled suction showed the influence of matric suction on the compressibility of the soil samples it was also observed that the higher the values of matric suction the higher the laboratory collapse potential cp the mineralogical chemical tests indicated the presence of oxides and hydroxides of iron in the samples compounds usually associated with cementation the presence of mineral such as kaolinite gibbsite hematite and goethite was also observed the impregnated thin layer plates of the soil samples as well as the grain size distribution curves and mercury intrusion porosimetry indicated the presence of a structure formed by microaggregates structural models for soil collapse were proposed basing on the results obtained there were behavioral differences in each soil sample collected at different depths the behavior of the sample collected at a 1 5 m depth was basically influenced by matric suction as for the samples collected at 4 5 m and 6 5 m besides being both influenced by matric suction they were also influenced by the presence of cementing agents samples collected at 4 5 m and by the presence of more angular grains of quartz samples collected at 6 5 m

terminal pleistocene change in mammal communities in southeastern washington state usa abstract small mammal communities in western north america experienced declines in taxonomic richness across the late pleistocene to holocene transition pht a recent natural global warming event one community also experienced a decline in evenness and others replaced one species with a congener variability in response of small mammal communities to pht warming is apparent at the presently arid and xeric marmes site in the columbia basin of southeastern washington state megafauna were absent by about 13 000 cal yr bp evenness of small mammals declined about 11 700 cal yr bp and again about 11 400 cal yr bp whereas richness declined about 11 400 cal bp regional faunal turnover was however minimal among small bodied taxa local mammal communities are depauperate as a result of megafaunal extinctions and subsequent decreases in small mammal richness and evenness the latter chronologically corresponds with a decrease in primary productivity driven by increasing warmth and aridity more faunas must be studied in order to fully document the range of variability in the responses of mammalian communities to pht warming documentation of patterns in those responses will facilitate understanding and enhance predictive accuracy with respect to responses of mammalian communities to modern global warming

spatial and temporal distribution of microbially induced sedimentary structures a case study from siliciclastic storm deposits of the 2 9 ga witwatersrand supergroup south africa abstract microbially induced sedimentary structures miss arise from the interaction of microbial mats with the physical sedimentary dynamics of shallow marine settings the structures occur in siliciclastic deposits of paleo archean age to modern where they record biostabilization and baffling trapping and binding of photoautotrophic microbenthos in the brixton formation witwatersrand supergroup south africa erosional remnants and pockets wrinkle structures and oscillation cracks include carbon and pyrite rich filament like textures that resemble modern trichomes of cyanobacteria c isotope ratios of 22 0 1 indicate potential photoautotrophy the miss occur at the turning points of regression transgression and are restricted to a specific sedimentary facies characterized by 2 20 cm thick fine sandstone beds predominantly composed of quartz the sandstone beds display ripple marks which record moderate hydraulic reworking this spatial and temporal distribution of miss in the brixton formation is consistent with occurrences of those structures in comparable environments throughout earth history