dark slope streaks on mars are aqueous processes involved 1 concentrations of dark slope streaks occur in the equatorial latitudes of mars mostly where magmatic driven activity dominates the geologic record although originally ascribed to wet debris flows all the most recent published hypotheses concerning these features focus on processes which disturb a brighter dusty mantle to expose a darker substrate these mechanisms invoke dry mass wasting or eolian processes excluding a role for water in light of the geographic geologic and morphologic considerations and the new information provided from the mars orbital camera and the mars orbital data altimeter we reexamine fluvial processes as a viable explanation for some of the dark slope streaks in our opinion two contrasting processes for the formation of dark slope streaks dust avalanching and spring discharge represent endpoints on a continuum of progenitors it may be that some of these features result from dry mass wasting or eolian processes some from fluvial processes and some from a mechanism s not yet conceived a spring discharge origin for the formation of the dark slope streaks has profound implications including mars having limited but currently active fluvial processes acting upon its surface as well as near surface aquifers

fluid dynamical implications of anastomosing slope streaks on mars 1 the mars global surveyor mission has imaged slope streaks some of which have formed in periods as short as 109 days these features are one of the most currently active surface processes on mars some slope streaks have flow like morphologic characteristics which include anastomosing patterns influenced by small topographic barriers in order to understand what processes gave rise to these specific features we applied viscoplastic flow numerical modeling techniques to simulated martian surfaces we simulate martian surfaces with observed slope streaks by using mars orbiter laser altimeter measurements to obtain large scale slope measurements and a photoclinometry technique on mars orbiter camera images to obtain meter scale topographic information our numerical simulations of slow moving plastic flows show that a fluid rheology and a short formation period are necessary to explain these features we estimate that the typical values of bulk viscosity and bulk yield strength are less than 10 pa s and less than 10 pa respectively the fluid rheology can be explained by a water related flow with a solid content less than about 20 an alternative explanation is a dry grain flow with extremely low cohesion and friction angle supported by dispersive pressure or a lubricant such as electric conditions of particles the continuous nature of anastomosing slope streaks that originate from point sources is best explained by continuous discharges of material or lubricant in this case the estimated flow rate is less than several cubic meters per second and the flow duration is estimated to be less than a day

the pre quaternary history of fire abstract although evidence for land vegetation comes from the silurian and maybe even earlier the first record of fossil charcoal fusain is from the late devonian for this period there are only one or two isolated records not until the early carboniferous is there a record of extensive charcoal deposits mainly preserved in near shore clastic sediments which provide evidence of significant and widespread wildfires by the late carboniferous charcoal was common or abundant in a wide range of facies including tropical wetland peats wildfire played an important role in shaping the environment at this time the latest palaeozoic and early mesozoic records of charcoal are fewer whereas important deposits of late mesozoic age are found worldwide the occurrence of charcoal at the cretaceous tertiary boundary has been highlighted as evidence for a global fire following a meteorite impact but this interpretation is questionable charcoal has been widely reported from tertiary sediments and its appearance in the quaternary and recent is not solely as a result of human impact through the past 400 million years there have been major changes in atmospheric oxygen levels that affected fire intensity and frequency fire systems thus have a long history and their impact on shaping the environment is assessed

aperiodic accumulation of cyclic peritidal carbonate tabulation of thickness data on nearly 3000 proterozoic and paleozoic peritidal carbonate cycles indicates that metre scale facies associations exhibit exponential thickness frequency distributions because carbonate deposition occurs during infilling of available space between sea level and the surface of the preceding cycle and because the rate of generation of accommodation space is ultimately determined by rates of platform subsidence thicknesses of individual cycles must record the duration of time since deposition of underlying units exponential thickness distributions therefore require either that upward shoaling carbonates record aperiodic accumulation or that any periodic forcing manifest during sedimentation has been masked by the vagarious nature of depositional processes such a conclusion is contrary to interpretation of such carbonate units as originating from high frequency eustatic change in addition exponential thickness distributions and sequence thickness structures are replicated when assuming a random probability of carbonate deposition under conditions of constant subsidence the nature of cycle thickness distributions therefore invalidates virtually any endeavor to derive an average depositional period from mean cycle thicknesses and refutes the use of such estimates as proxy records of past sea level oscillation frequency whether they are related to milankovitch band climate forcing or to any other periodic process

first report of cisuralian early permian charcoal layers within a coal bed from baode north china with reference to global wildfire distribution abstract fossil charcoal is reported for the first time from a cisuralian coal bed of the shanxi formation in the qiaotou section baode shanxi north china based on anatomical characteristics these charcoal fragments consist of coniferous or cordaitalean xylem unidentified primary xylem and cordaitalean and possible fern leaves these charcoal fragments represent the evidence of palaeowildfire taking place in tropical peat swamps during the cisuralian in cathaysia the palaeowildfire is most likely to be a surface fire and burning litter and shrubby vegetation fire frequency for this early permian peat swamp might have been on the order of 176 294 588 1429 years close to modern values compared with modern analogues the north china block during the cisuralian was probably wet in general but could be occasionally seasonally dry for short time intervals previous charcoal and inertinite records moreover indicate that palaeowildfires were globally common during the cisuralian overall more wildfire evidence was found in the artinskian kungurian than the asselian sakmarian except in the euramerican realm probably due to more suitable regional climate vegetation to fuel fires and taphonomic circumstances

observations and experiments on the origin and formation of inertinite group macerals the inertinite group macerals include fusinite semifusinite inertodetrinite macrinite micrinite and funginite and secretinite which together replace sclerotinite the macrolithotype fusain comprises fusinite and semifusinite and is now widely accepted as charcoal formed by wildfire activity however alternative origins for fusinite and semifusinite are still claimed this paper considers the use of the terms pyrofusinite degradofusinite rank fusinite and primary fusinite misleading while the definitions of the terms funginite and secretinite are also considered problematic observations made on modern wildfire derived and volcanogenic charcoal assemblages using reflectance and scanning electron microscopy together with experimental charcoalification studies demonstrate that most if not all inertinite macerals have acquired their optical and physical characteristics through the action of elevated temperatures the criteria for the identification of charcoals produced by wildfire and volcanic activity are outlined and the role of the petrographic nomenclature system is discussed

development of an equatorial carbonate platform across the triassic jurassic boundary and links to global palaeoenvironmental changes musandam peninsula uae oman abstract the triassic jurassic boundary is marked by one of the big five mass extinctions of the phanerozoic this boundary event was accompanied by several carbon cycle perturbations potentially induced by the opening of the central atlantic and associated volcanism and accompanied by an ocean acidification event continuous carbonate successions covering this interval of environmental change are however rare here data from a shallow marine equatorial mixed carbonate siliciclastic succession is presented that was studied on a regional scale four sections that are 48 km apart were examined on the musandam peninsula united arab emirates and sultanate of oman the system was analysed for its sedimentology vertical and lateral facies changes and stable carbon and oxygen isotopes strontium isotope analysis was used to determine the position of the triassic jurassic boundary horizon the studied ramp experienced an episode of demise during the late triassic followed by a restricted microbialite dominated ramp containing large amounts of siliciclastic facies during the latest triassic the diverse carbonate factory revived and flourished across the triassic jurassic boundary no clear evidence for a biocalcification crisis or an ocean acidification event across the triassic jurassic boundary is visible lateral facies heterogeneities can be observed across the studied interval attributed to hydrodynamic activity including tropical storms crossing the extensive shelf area although evidence for synsedimentary tectonic activity is present the vertical stacking pattern is largely controlled by changes in relative sea level the refined chronostratigraphy accompanied by the detailed environment of deposition analysis allows for a refinement of the regional palaeogeography the neritic equatorial carbonate ramp has archived a negative carbon isotope excursion preceding the triassic jurassic boundary that has also been reported from other study sites the lack of evidence for a biocalcification crisis across the equatorial triassic jurassic boundary indicates that the tethys did not experience a distinct global acidification event

observations on the nature and origin of fusain abstract evidence for a wildfire origin of fusain is examined charcoal produced by natural fires and artificial charring resembles fossil fusain both in physical size and shape and in optical reflectance artificially charred leaves and naturally burnt wood are illustrated using the sem reflectance studies on modern charcoals suggest that much semifusinite may be produced by pyrolysis the ecological implications of a wildfire origin of fusain are discussed and it is concluded that fires have been a feature of terrestrial ecosystems from at least the late devonian

sequence and isotope stratigraphy of late triassic distal periplatform limestones from the northern calcareous alps kalberstein quarry berchtesgaden hallstatt zone the kalberstein quarry at berchtesgaden exposes carnian norian deeper water hallstatt limestones conodont biostratigraphy microfacies and stable isotopes of bulk carbonate matrix were investigated the biostratigraphic results demonstrate a complete succession from the latest carnian tuvalian 3 i to the late norian sevatian 2 as expected from the periplatform setting of the hallstatt zone calculated mass accumulation rates conform partly to prograding sequences observed on the contemporary dachstein platform however discrepancies exist mainly for the middle norian pointing to an incomplete knowledge of the platform sequences the sequence stratigraphic framework based on platform data should be complemented with data from the periplatform hallstatt zone diagenetic alteration of the limestones from kalberstein quarry is low with a conodont alteration index cai 1 0 throughout the section oxygen isotope values ranging from 1 2 to 0 1 vpdb point to stabilization and cementation at very shallow burial depths in contact with seawater in a deeper water environment carbon isotope values display a clear stratigraphic trend with a rapid increase from 3 6 to 4 1 vpdb during the basal norian lacian 1 high values up to 4 2 during the lacian 2 and a slow decline starting in lacian 3 to 2 6 at the end of the norian sevatian 1 2 these trends are best explained by variations in the global organic carbon carbonate burial ratio with maximum organic carbon burial during the middle lacian

charcoal in the silurian as evidence for the earliest wildfire rare basal pridoli plant fossils which resemble the rhyniophytoid hollandophyton colliculum and have exceptional three dimensional cellular anatomy are preserved as charcoal as such these fossils from ludford lane in the welsh borders are evidence of the earliest recorded wildfire and are the first documented from before the devonian the fossils represent the charred remains of a low growing low diversity in situ rhyniophytoid or cryptospore bearing plant vegetation charred during a low temperature fire

antarctic dry valleys microclimate zonation variable geomorphic processes and implications for assessing climate change on mars the antarctic dry valleys adv are generally classified as a hyper arid cold polar desert the region has long been considered an important terrestrial analog for mars because of its generally cold and dry climate and because it contains a suite of landforms at macro meso and microscales that closely resemble those occurring on the martian surface the extreme hyperaridity of both mars and the adv has focused attention on the importance of salts and brines on soil development phase transitions from liquid water to water ice and ultimately on process geomorphology and landscape evolution at a range of scales on both planets the adv can be subdivided into three microclimate zones a coastal thaw zone an inland mixed zone and a stable upland zone zones are defined on the basis of summertime measurements of atmospheric temperature soil moisture and relative humidity subtle variations in these climate parameters result in considerable differences in the distribution and morphology of 1 macroscale features e g slopes and gullies 2 mesoscale features e g polygons including ice wedge sand wedge and sublimation type polygons as well as viscous flow features including solifluction lobes gelifluction lobes and debris covered glaciers and 3 microscale features e g rock weathering processes features including salt weathering wind erosion and surface pitting equilibrium landforms are those features that formed in balance with environmental conditions within fixed microclimate zones some equilibrium landforms such as sublimation polygons indicate the presence of extensive near surface ice identification of similar landforms on mars may also provide a basis for detecting the location of shallow ice landforms that today appear in disequilibrium with local microclimate conditions in the adv signify past and or ongoing shifts in climate zonation understanding these shifts is assisting in the documentation of the climate record for the adv a similar type of landform analysis can be applied to the surface of mars where analogous microclimates and equilibrium landforms occur 1 in a variety of local environments 2 in different latitudinal bands and 3 in units of different ages documenting the nature and evolution of the adv microclimate zones and their associated geomorphic processes is helping to provide a quantitative framework for assessing the evolution of climate on mars

the origin of high frequency platform carbonate cycles and third order sequences lower ordovician el paso gp west texas constraints from outcrop data and stratigraphic modeling abstract the passive margin succession of the diablo platform lower ordovician west texas is represented by the second order sauk c supersequence set consisting of a basal transgressive clastic unit the bliss sandstone above the breakup unconformity marking the second order basal lowstand transgressive phase overlain by 750 m of drift related shallow marine platform carbonates the el paso group recording the second order highstand due to late paleozoic structuring of the gondwanan passive margin present exposures in texas are in an updip shelf position and lack internal stratal geometries across depositional strike so sequences and systems tracts are identified solely by the vertical stacking patterns of depositional subfacies and higher frequency fifth order cycles accommodation plots fischer plots of high frequency cycles gauge systematic shifts in third order accommodation of two complete third order sequences each about 2 m y long and 60 140 m thick within the el paso group this is expressed in the vertical succession of cycle types systematic changes in cycle thickness and variations in subfacies as revealed by histograms of subfacies types tied to fischer plots a complete el paso shelf sequence contains a thin lowstand systems tract of quartz arenite a thick transgressive systems tract dominated by upward thickening thrombolitic subtidal cycles and a highstand systems tract marked by dolomitic thinning upward peritidal cycles containing quartz sand the el paso third order depositional sequences have been correlated by biostrat graphy and cycle stacking pattern from the franklin mountains southeast to the diablo arch northeast into the ardmore basin and thence to the appalachian basin hence the third order sequences appear to be eustatic based on biostratigraphic correlation of accommodation plots around the periphery of gondwana time series analyses suggest that a strict allocyclic milankovitch driven glacio eustatic mechanism alone is insufficient to account for the higher frequency fifth order and lower frequency third order accommodation cycles we used a two dimensional forward computer simulation to compare allocyclic and autocyclic models for high frequency cycles the allocyclic simulation superimposes a deterministic milankovitch glacio eustatic driver on a lower frequency third order accommodation cycle and generates a two dimensional synthetic cross section composed of high frequency peritidal and subtidal cycles stacked into third order sequences the autocyclic simulation is generated by a ginsburg autocyclic mechanism for high frequency cyclicity triggered by third order accommodation changes the autocyclic simulation quantitatively replicates an autocyclic mechanism for fifth order cycle development linked to onshore sediment transport and seaward progradation of tidal flats the two dimensional internal facies architecture of a third order sequence and the high frequency cycle stacking patterns are simulated in both scenarios important differences in patterns of cycles and subfacies stacking in the simulations shed light on the interpretation of the diablo platform cycles and sequences as an alternative or a supplement to autocyclicity or milankovitch forced glacio eustasy we have studied stochastic models for driving high frequency changes in relative sea level these intriguing results maintain essentially all the features observed in the rock record our smoothed sto hastic simulations suggest that the cycle problem is much more complex than presently realized

hypautochthonous allochthonous coal deposition in the permian south african witbank basin no 2 seam a combined approach using sedimentology coal petrology and palaeontology abstract a suite of techniques including coal petrology micropalynology mesofossil analysis and macroscopic appearance has been used to examine the early permian south african witbank basin no 2 seam from a sample locality near ogies this coal appears to be similar in its palynological and petrographic composition to other coals of this interval from this basin however its accumulation appears to have been largely hypautochthonous or allochthonous evidenced by erosive contacts small scale cross laminations and fine lenticular bodies being recognised within the coal seam profile this ex situ deposition probably in part relates to frequent wildfire activity which may have promoted subsequent run off and erosion and led to the numerous mineral rich horizons observed in the sample seam profile in addition to the sedimentological characters described above the petrology of the seam and its mesofossils most particularly megaspores from a lycopsid parent vegetation indicate saturated peat forming conditions however examination of charred mesofossil fragments indicates periods of low humidity and even drying of the peat itself rendering it liable to combustion these contradictory characters may indicate seasonality and suggest a coldness of the climate at least for part of the year that could account for the retardation of peat decay during these drier intervals these characters can be reconciled with deposition during an interglacial phase as the dwyka glaciation terminates as has previously been proposed for the witbank basin no 2 seam

hirise observations of slope streaks on mars 1 images from the high resolution imaging science experiment have revealed new details on the morphologic and topographic characteristics of slope streaks on mars over 1500 hirise images were analyzed with 78 unique image sites having slope streaks images with low sun illumination reveal that dark slope streaks have topographic relief where streaked surfaces are lower than their surroundings slope streaks often initiate below localized features such as rock outcrops individual boulders and impact craters they are also abundant in great numbers within the blast zones of small young impact craters 10 50 m in diameter these observations suggest that slope streaks can be triggered by localized disturbances such as rockfalls and impact blasts seismic activity from external e g impacts or internal forces could also trigger slope streaks the topographic relief and triggering mechanisms of slope streaks seem to best fit models that involve dry dust avalanches martian slope streaks and meters thick avalanche scars are part of a continuum of active mass wasting features at meter to sub meter scales

on the fundamental difference between coal rank and coal type abstract this article addresses the fundamental difference between coal rank and coal type while theoretically settled long ago as being different aspects of coal systems science the two concepts are still often confounded in recent years this has resulted in the publication of several works stating that coal type changes with coal rank coal type refers solely to coals depositional origin and the maceral mineral admixture resulting from that origin coal types typically fall in to two categories humic coals developed from peat and sapropelic coals developed from organic mud either type may be allocthonous or autochthonous and within types further refinement of depositional environment can be made coal rank refers to the changes in geochemistry and resultant changes in reflectance caused by increasing thermal maturity of the coal thus it provides an overprint of maturity on existing coal types with proper techniques such as use of crossed polars and etching maceral forms can be differentiated even at high ranks and the original coal type determined

petrology and chemistry of permian coals from the parana basin 1 santa terezinha leao butia and candiota coalfields rio grande do sul brazil the current paper presents results on petrological and geochemical coal seam characterization in permian coal bearing strata from the parana basin southern brazil sequence stratigraphic analysis shows that peat accumulation in permian time was closely linked to transgressive regressive cycles with peat accumulation occurring in a predominantly back barrier lagoonal setting coal petrographic analysis indicates subbituminous coals at candiota and leao butia and high volatile bituminous coals at santa terezinha where locally the coal seams are thermally altered by volcanic intrusions petrographic composition is highly variable with seams at candiota and santa terezinha frequently enriched in inertinite chemical analyses indicate that all coals are mineral matter rich mean 49 09 wt with sio2 and al2o3 dominating as determined by icp aes quartz is also the predominant mineral detected by x ray diffraction where it is associated with feldspar kaolinite and hematite and iron rich carbonates the results from scanning electron microscopy are broadly consistent with the bulk chemical and mineralogical analysis quartz and clays are common in all samples analyzed other minerals observed were amongst others carbonates calcite siderite ankerite pyrite monazite kaolinite barite sphalerite rutile and quartz of volcanic origin the distribution of trace elements is well within the range typical for coal basins of other areas despite the fact that the parana basin coals are very high in ash yields the average concentrations for elements of environmental concern as b be cd co cr cu hg li mn mo ni pb sb se tl u v zn are similar to or less than the mean values for u s coal however considered on an equal energy basis parana basin coals will produce in combustion 5 to 10 times the amount of most elements compared to an equal weight us coal concentrations of major and trace elements such as fe b and s appear to be controlled by depositional setting with increasing values in coal seams overlain by brackish marine strata hierarchical cluster analysis identified three groups of major minerals and seven groups of trace elements based on similarity levels on a regional scale the coalfields can be separated by the differences in rank candiota and leao butia versus santa terezinha and by applying discriminant analysis based on 4 trace elements li as sr sb highest rb and sr values occur at candiota and are linked to syngenetic volcanism of the area whereas high y and sr values at santa terezinha can be related to the frequent diabase intrusions in that area

cyclostratigraphic record of the triassic a critical examination high frequency fourth and fifth order cyclicity is a common feature of sedimentary sequencesinalldepositionalsettings whiletectonismandautocyclicprocessesare clearlyrespon sible for this cyclicity in some instances many cases are interpreted as resulting from orbitally forced variations in solar insolation at the milankovitch frequencies that is the precession and short and long eccentricity cycles at scales of tens of thousands to hundreds of thousands of years this forcing is presumed to have controlled sedimentation through periodic changes in climate or sea level examples of interpreted milankovitch frequency cyclicity occur throughout the triassic record and include much of the german triassic the alpine triassic and the newark supergroup of north america the cyclostratigraphy of these sections has been used as a tool for intrabasinal and interbasinal correlation and for chronostratigraphy these interpretations are not always without controversy however as conceptual arguments and radio isotopic age data have called some of these conclusions into question the stratigraphic record is inherently cyclical but the scale of this cyclicity varies in scale from the outcrop to the continental the largest scale or first order cycles are those that are truly continental in scope as they are thought to record changes in sea level caused by the operation of the wilson cycle at a scale of hundreds of millions of years prothero 1990 jacquin graciansky 1998 second order cycles corresponding to the sedimentary sequences of sloss 1963 last from tens of millions up to one hundred million years and are generally considered the result of long term trends in eustasy potentially in direct proportion to the activity of the mid ocean ridges the cause of the third order sea level cycles of millions of years duration is not well understood these cycles are often apparent at the basin scale and may be related to short term tectonic activity higher frequency fourth and fifth order cycles frequently are evident at the outcrop scale fourth order cycles include the classic cyclothems of the carboniferous e g heckel 1986 and have periods in the range of hundreds of thousands of years whilefifth order cyclesoperate at frequencies of tens of thousands of years these high frequency fourth and fifth order cycles are often referred to as milankovitch cycles due to the match of their interpretedperiodswiththecalculatedmilankovitch orbital frequences it is these high frequency cycles thatarethefocusofmuchmoderncyclostratigraphy and the record and application of these cycles in the triassic system is the focus of this chapter

mass movement slope streaks imaged by the mars orbiter camera narrow fan shaped dark streaks on steep martian slopes were originally observed in viking orbiter images but a definitive explanation was not possible because of resolution limitations pictures acquired by the mars orbiter camera moc aboard the mars global surveyor mgs spacecraft show innumerable examples of dark slope streaks distributed widely but not uniformly across the brighter equatorial regions as well as individual details of these features that were not visible in viking orbiter data dark slope streaks as well as much rarer bright slope streaks represent one of the most widespread and easily recognized styles of mass movement currently affecting the martian surface new dark streaks have formed since viking and even during the mgs mission confirming earlier suppositions that higher contrast dark streaks are younger and fade brighten with time the darkest slope streaks represent 10 contrast with surrounding slope materials no small outcrops supplying dark material or bright material for bright streaks have been found at streak apexes digitate downslope ends indicate slope streak formation involves a ground hugging flow subject to deflection by minor topographic obstacles the model we favor explains most dark slope streaks as scars from dust avalanches following oversteepening of air fall deposits this process is analogous to terrestrial avalanches of oversteepened dry loose snow which produce shallow avalanche scars with similar morphologies low angles of internal friction typically 10 30i for terrestrial loess and clay materials suggest that mass movement of low cohesion martian dusty air fall is possible on a wide range of gradients martian gravity presumed low density of the air fall deposits and thin unresolved by moc failed layer depths imply extremely low cohesive strength at time of failure consistent with expectations for an air fall deposit of dust particles as speed increases during a dust avalanche a growing fraction of the avalanching dust particles acquires sufficient kinetic energy to be lost to the atmosphere in suspension limiting the momentum of the descending avalanche front the equilibrium speed where rate of mass lost to the atmosphere is balanced by mass continually entrained as the avalanche front descends decreases with decreasing gradient this mechanism explains observations from moc images indicating slope streaks formed with little reserve kinetic energy for run outs on to valley floors and explains why large distal deposits of displaced material are not found at downslope streak ends the mass movement process of dark and bright slope streak formation through dust avalanches involves renewable sources of dust only leaving underlying slope materials unaffected areas where dark and bright slope streaks currently form and fade in cycles are closely correlated with low thermal inertia and probably represent regions where dust currently is accumulating not just residing

charcoal recognition taphonomy and uses in palaeoenvironmental analysis abstract charcoal predominantly the product of wildfires is abundant in many sedimentary rocks deposited in a wide range of environments from terrestrial to marine it also occurs in some volcanic rocks this paper outlines aspects of charcoal formation both natural and experimental and briefly considers the taphonomic processes leading to a final assemblage this is done using examples from recent fires and through experimentation the ways in which charcoal assemblages are recognized in the field and extraction in the laboratory are also considered methods of charcoal identification are presented the range of charcoalified plant organs that can be found is discussed and a wide range of study methods outlined including light microscopy dark field light microscopy reflectance microscopy scanning electron microscopy and synchrotron radiation x ray tomographic microscopy emphasis in this paper is on the study of macro and meso charcoal above180 m finally there is a consideration of the broad use of charcoal from plant evolution studies fire history studies vegetation studies anatomical studies climate and atmospheric studies and the wider importance of charcoal for the earth and biological sciences charcoal is information rich but yet is an under utilized resource

evidences for pre orogenic passive margin extension in a cretaceous fold and thrust belt on the basis of combined seismic and field data western transdanubian range hungary combined sedimentological and structural analysis was carried out in the field and on 2d seismic reflection profiles to recognize pre orogenic structures in a cretaceous fold and thrust belt detailed field observations were made in the keszthely hills western hungary while 2d seismic interpretation was carried out in the neighbouring zala basin as a result a fault controlled intraplatform basin system was identified by a detailed analysis of bounding faults and related outcropscale structures the norian rhaetian 227 201 3 ma synsedimentary faulting was associated with talus breccia formation small scale faulting and dyke formation in addition to slumping and other soft sediment deformations based on the distribution of talus breccia wnw ese trending map scale normal faults were identified in the keszthely hills which is in agreement with the directly observed outcrop scale synsedimentary faults on seismic sections similar wnw or nwtrending late triassic normal faults were identified based on thickness variations of the syn rift sediments and the presence of wedge shaped bodies of talus breccia normal faulting occurred already in the norian and extensional tectonics was active through the early and middle jurassic the late triassic grabens of the western transdanubian range could be correlated with those in western part of the southern alps and the bajuvaric nappe system of the northern calcareous alps these grabens were situated on the proximal adriatic margin and they represent the first sign of the alpine tethys rifting the locus of extension was laterally migrated westward towards the distal adriatic margin during early and middle jurassic

facies analysis of lofer cycles upper triassic in the argolis peninsula greece abstract the upper triassic carbonate sediments of argolis peninsula are part of the upper triassic lower jurassic extensive and thick neritic carbonate formations pantokrator facies that formed at the passive pelagonian margin and are considered as dachstein type platform carbonates facies analysis of the upper triassic lofer type lagoonal peritidal cycles in the dhidimi area proved that cycles although mostly incomplete were regressive shallowing upward the ideal elementary cyclothems are meter scale in thickness and begin with a subtidal bed member c represented by a peloidal dolostone with megalodonts wackestone or packstone being followed by a stromatolitic intertidal dolomitic mudstone and or fenestral intertidal dolomitic mudstone member b that is overlain by dolocrete terrestrial stromatolites or pisoidic dolomite or a supratidal soil conglomerate in red micritic matrix member a lofer cycle boundaries are defined at the erosional surfaces and accordingly the lofer cyclothems are unconformity bounded units due to common post depositional truncation of the subtidal and intertidal facies the supratidal members prevail being developed in places directly upon subaerial exposure surfaces erosionally reduced cyclothems peritidal layers are characterized by a well expressed lamination sheet cracks tepee structures fenestral pores and karst dissolution cavities the studied lagoonal peritidal cycles are considered to have been deposited in a tidal flat setting inner platform repeatedly exposed under subaerial conditions in the context of a broader tropical rimmed platform although the studied area was tectonically active due to rift activity and the autocyclic processes should also be taken in consideration the great lateral correlatability of cycles the facies shifting and the widespread erosion that resulted in superposition of supratidal pedogenic facies directly upon subtidal members subaerial erosional unconformity indicating a sea level drop reflect allocyclic control via high frequency eustatic sea level oscillation orbital forcing sediment deposition occurred during low stand system tract lst that probably continued also in the transgressive system tract tst and reflects an overall sea level fall under these conditions dissolution and cement precipitation episodes as well development of paleosols and karsts were triggered during a relatively less arid interval

eutectic brines on mars origin and possible relation to young seepage features abstract if the recently observed young gullies on mars represent seeps or outflows of aqueous fluid that fluid must be highly concentrated brine to be even moderately stable under current martian surface conditions such brines are to be expected in the megaregolith if an initial saline hydrosphere underwent evapoconcentration via water escape from the atmosphere evolved into subsurface cacl 2 enriched brines by chemical interaction with mafic rocks and then froze until eutectic compositions were reached although most such brines would tend to sink deep into the megaregolith they could be preserved locally at relatively high elevations as aquifers or frozen paleoaquifers perched between ground ice and crystalline salts

investigations of fusain transition fossils from the lower carboniferous comparisons with modern partially charred wood plant fossils showing vitrinite semifusinite fusinite transitions and permineralised semifusinite transitions were collected from lower carboniferous locations within the british isles several were obtained from east kirkton quarry bathgate scotland and one fusinite semifusinite vitrinite semifusinite fusinite transition fossil was collected at muckros head county donegal ireland the muckros head fossil was found in a limestone sea cliff face where it had been weathered proud of the rock matrix thus enabling a detailed examination and interpretation of the macroscopic appearance of the specimen the distinctive sandwich like cross section of the fossil is interpreted as being caused by the burial and coalification of a partially charred plant stem with recent exposure and weathering resulting in the loss of its shattered edges under s e m and reflected light microscopy non permineralised transition fossils are seen to grade from structureless vitrinite into compressed and bogen structured semifusinite and occasionally continue through to structured uncompressed fusinite with corresponding increases in reflectance these gradations parallel the reflectances seen in modern partially charred stems stable carbon isotopic analysis of the transition fossils c13 17 19 0 to 19 26 0 22 46 0 to 24 54 0 24 47 0 24 47 0 to 26 20 0 show a significant difference between the vitrinite and semifusinite fusinite with the semifusinite fusinite isotopically heavier the various techniques employed to investigate these transition fossils all indicate that they represent coalified partially charred stems correlation of the properties and characteristics of the semifusinite fusinite in transition fossils with the properties and characteristics of isolated semifusinite and fusinite fragments collected from rocks of the lower carboniferous through to the tertiary supports the view that most of these isolated fragments also represent fossil charred wood and charcoal

phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal varying concentrations of atmospheric oxygen have affected the development of animals and the role of wildfire in ecosystems reconstructions of past oxygen concentrations from fossil charcoal constrain atmospheric oxygenation over the past 400 million years variations of the earth s atmospheric oxygen concentration po2 are thought to be closely tied to the evolution of life with strong feedbacks between uni and multicellular life and oxygen1 2 on the geologic timescale po2 is regulated by the burial of organic carbon and sulphur as well as by weathering3 reconstructions of atmospheric o2 for the past 400 million years have therefore been based on geochemical models of carbon and sulphur cycling4 5 6 however these reconstructions vary widely4 5 6 7 8 9 10 particularly for the mesozoic and early cenozoic eras here we show that the abundance of charcoal in mire settings is controlled by po2 and use this proxy to reconstruct the concentration of atmospheric oxygen for the past 400 million years we estimate that po2 was continuously above 26 during the carboniferous and permian periods and that it declined abruptly around the time of the permian triassic mass extinction during the triassic and jurassic periods po2 fluctuated cyclically with amplitudes up to 10 and a frequency of 20 30 million years atmospheric oxygen concentrations have declined steadily from the middle of the cretaceous period to present day values of about 21 we conclude however that variation in po2 was not the main driver of the loss of faunal diversity during the permo triassic and triassic jurassic mass extinction events

high resolution subsurface water ice distributions on mars theoretical models predict that the depth at which water ice is stable in the subsurface of mars will vary due to local surface features such as rocks and slopes and the thermal inertia of the ground above the water so far measurements have been limited to overviews of the several hundred kilometre footprint covered by the ray spectrometer on board the mars odyssey spacecraft but joshua bandfield has now used the seasonal temperature response of the martian surface from odyssey s themis package to map water ice distribution at the sub kilometre scale the observations reveal significant regional and local water ice depth variability at potential landing sites for the mars phoenix mission due for launch later this year the phoenix lander s robotic arm will be able to dig up to half a metre or so into the soil to search for water ice and these results suggest that it may encounter considerable variation in the depth to the ice layer the seasonal temperature response of the martian surface is used to map local surface heterogeneities such as rocks slopes and thermal inertia of ground cover at subkilometre scale these observations show significant regional and local water ice depth variability and indicate that the depth to the water ice table is highly variable in the potential phoenix spacecraft landing ellipses theoretical models indicate that water ice is stable in the shallow subsurface depths of 1 2 m of mars at high latitudes1 2 3 4 5 6 7 these models have been mainly supported by the observed presence of large concentrations of hydrogen detected by the gamma ray spectrometer suite of instruments on the mars odyssey spacecraft8 9 10 the models and measurements are consistent with a water ice table that steadily increases in depth with decreasing latitude more detailed modelling has predicted that the depth at which water ice is stable can be highly variable owing to local surface heterogeneities such as rocks and slopes and the thermal inertia of the ground cover11 12 13 measurements have however been limited to the footprint several hundred kilometres of the gamma ray spectrometer suite preventing the observations from documenting more detailed water ice distributions here i show that by observing the seasonal temperature response of the martian surface with the thermal emission imaging system on the mars odyssey spacecraft14 it is possible to observe such heterogeneities at subkilometre scale these observations show significant regional and local water ice depth variability and in some cases support distributions in the subsurface predicted by atmospheric exchange and vapour diffusion models the presence of water ice where it follows the depth of stability under current climatic conditions implies an active martian water cycle that responds to orbit driven climate cycles15 16 17 several regions also have apparent deviations from the theoretical stability level indicating that additional factors influence the ice table depth the high resolution measurements show that the depth to the water ice table is highly variable within the potential phoenix spacecraft landing ellipses and is likely to be variable at scales that may be sampled by the spacecraft

depositional cycles composite sea level changes cycle stacking patterns and the hierarchy of stratigraphic forcing examples from alpine triassic platform carbonates carbonate platform deposits record a complex interplay of numerous geodynamic variables of which eustasy subsidence and sediment accumulation are prime factors in determining both the kilometer scale depositional sequence scale and meter scale depositional cycle scale stratigraphic packaging in this study we looked particularly at composite eustasy that is superimposed sea level fluctuations with different frequencies defined as orders and different amplitudes and the role it plays in the linkage between meter scale cyclic stratigraphy and kilometer scale sequence stratigraphy specifically we have investigated the relationship between low frequency third order 1 10 m y period depositional cycles and their component high frequency fourth 0 1 1 m y and fifth 0 01 0 1 m y order cycles through detailed stratigraphic analyses of alpine triassic platforms complemented by computer modeling on the basis of our results we suggest that in general there exists a hierarchy of stratigraphic forcing driven by composite eustasy that results in organized stacking patterns thickness subfacies character early diagenetic attributes of high frequency typically fourth and fifth order shallow water carbonate cycles dictated by low frequency third order relative sea level effects we suggest that systematic vertical changes in stacking patterns of high frequency cycles across a larger depositional sequence are due to systematic and predictable differences in depositional space available during the rising and falling stages of a relative third order sea level change we also suggest that these systematic variations in cycle stacking patterns will exist regardless of the mechanism responsible for generating the high frequency cycles be it an autocyclic or allocyclic mechanism this approach has major implications for the use of high frequency fourth and fifth order cycle characteristics to identify third order cycles in outcrops and cores of shallow water carbonates where stratigraphic control may be less than desirable this would constitute a valuable bridge between cyclic stratigraphy at the meter scale and sequence stratigraphy at the seismic scale we present two examples from triassic buildups of the alps the ladinian latemar buildup and the norian dolomia principale where a systematic succession of high frequency cycle stacking patterns and early diagenetic features exists within an overriding third order cycle sequence reflecting the interplay of short term high frequency fourth fifth order eustasy and long term low frequency third order eustasy in accordance with the hierarchy of stratigraphic forcing central to the interpretation of these examples is the demonstration that true eustatic rhythms are recorded in the high frequency cyclicity as verified by time series analyses and the use of fischer plots these examples can be modeled by computer under conditions of lag depth constrained sedimentation uniform subsidence and composite eustasy we also present two examples one from the alpine triassic the norian lofer cyclothems and one from the pleistocene of south florida that lack both a systematic succession of high frequency cycle stacking patterns and identifiable composite rhythms in the stratigraphic record despite the existence of composite high frequency eustasy in these examples we call upon 1 local tectonic forcing in the form of short term deviations in subsidence via faulting lofer example and 2 large differences in the relative amplitudes of different orders of high frequency sea level oscillations pleistocene example to explain the lack of composite rhythms and we present computer simulations to illustrate the concepts an understanding of composite relative sea level changes and the potential for a hierarchy of stratigraphic forcing provides the link between cyclostratigraphy and sequence stratigraphy and also has important implications regarding the stratigraphy of early diagenesis

improved general circulation models of the martian atmosphere from the surface to above 80 km we describe a set of two new generation general circulation models of the martian atmosphere derived from the models we originally developed in the early 1990s the two new models share the same physical parameterizations but use two complementary numerical methods to solve the atmospheric dynamic equations the vertical resolution near the surface has been refined and the vertical domain has been extended to above 80 km these changes are accompanied by the inclusion of state of the art parameterizations to better simulate the dynamical and physical processes near the surface boundary layer scheme subgrid scale topography parameterization etc and at high altitude gravity wave drag in addition radiative transfer calculations and the representation of polar processes have been significantly improved we present some examples of zonal mean fields from simulations using the model at several seasons one relatively novel aspect previously introduced by wilson 1997 is that around northern winter solstice the strong pole to pole diabatic forcing creates a quasi global angular momentum conserving hadley cell which has no terrestrial equivalent within such a cell the coriolis forces accelerate the winter meridional flow toward the pole and induce a strong warming of the middle polar atmosphere down to 25 km this winter polar warming had been observed but not properly modeled until recently in fact thermal inversions are generally predicted above one and often both poles around 60 70 km however the mars middle atmosphere above 40 km is found to be very model sensitive and thus difficult to simulate accurately in the absence of observations

anatomy of a cyclically packaged mesoproterozoic carbonate ramp in northern canada abstract carbonates in the upper member of the mesoproterozoic victor bay formation are dominated by lime mud and packaged in cycles of 20 50 m these thicknesses exceed those of classic shallowing upward cycles by almost a factor of 10 stratigraphic and sedimentological evidence suggests high amplitude high frequency glacio eustatic cyclicity and thus a cool global climate ca 1 2 ga the victor bay ramp is one of several late proterozoic carbonate platforms where the proportions of lime mud carbonate grains and microbialites are more typical of younger phanerozoic successions which followed the global waning of stromatolites facies distribution in the study area is compatible with deposition on a low energy microtidal distally steepened ramp outer ramp facies are hemipelagic lime mudstone shale carbonaceous rhythmite and debrites mid ramp facies are molar tooth limestone tempestite with microspar intraclast lags in a marine environment where stromatolitic and oolitic facies were otherwise rare large stromatolitic reefs developed at the mid ramp coeval with inner ramp facies of microspar grainstone intertidal dolomitic microbial laminite and supratidal evaporitic red shale deep subtidal outer ramp cycles occur in the southwestern part of the study area black dolomitic shale at the base is overlain by ribbon nodular and carbonaceous carbonate facies all of which exhibit signs of synsedimentary disruption cycles in the northeast are shallow subtidal and peritidal in character shallow subtidal cycles consist of basal deep water facies and an upper layer of subtidal molar tooth limestone tempestite interbedded with microspar calcarenite facies peritidal cycles are identical to shallow subtidal cycles except that they contain a cap of dolomitic tidal flat microbial laminite and rarely of red shale sabkha facies or of sandy polymictic conglomerate a transect along the wall of a valley extending 8 5 km perpendicular to depositional strike reveals progradation of inner ramp tidal flats over outer and mid ramp facies during shoaling the maximum basinward progradation of peritidal facies coincides with a zone of slope failure that may have promoted the development of the stromatolitic reefs the sea level history of the victor bay formation is represented by three hectometre scale sequences an initial flooding event resulted in deposition of the lower victor bay shale member upper member carbonate cycles were then deposited during highstand mid ramp slumping was followed by late highstand reef development the second sequence began with development of an inner ramp lowstand unconformity and a thick mid ramp lowstand wedge a second transgression promoted a more modest phase of reef development at the mid ramp and shallow water deposition continued inboard a third and final transgressive episode eventually led to flooding of the backstepping ramp overall consistent cycle thickness and absence of truncated cycles as well as the high rate and amount of creation of accommodation space suggest that the periodicity and amplitude of sea level fluctuation were relatively uniform and point to a eustatic rather than tectonic mechanism of relative sea level change high amplitude high frequency eustatic sea level change is characteristic of icehouse worlds in which short term large scale sea level fluctuations accompany rapidly changing ice volumes affected by milankovitch orbital forcing packaging of cyclic upper victor bay carbonates therefore supports the hypothesis of a late mesoproterozoic glacial period as proposed by previous workers

extending the database of permian palaeo wildfire on gondwana charcoal remains from the rio do rasto formation parana basin middle permian rio grande do sul state brazil abstract macroscopic charcoal has been recovered from a bonebed from the barro alto outcrop middle permian guadalupian rio do rasto formation in the southernmost part of the parana basin brazil during this time a global biotic crisis was taking place and changes in the palaeofloristic composition can be observed records of palaeowildfires from the guadalupian period are scarce on a global scale in the parana basin low plant diversity compared to the entirety of gondwana persists and just a few plant bearing localities have so far been described from the northern part of the basin in the studied locality macroscopic charcoal could be detected in an outcropping bonebed and the occurrence of palaeo wildfires was confirmed besides representing the first palaeobotanical data for the guadalupian of the southern part of the parana basin the charcoal remains analyzed here are also a significant record of the local environmental conditions during the increase in aridity observed during the guadalupian and lopingian in gondwana this contributes to the understanding of regional changes that took place during this interval

a major fire event recorded in the mesofossils and petrology of the late permian lower whybrow coal seam sydney basin australia abstract petrographic and mesofossil analyses of plies from the late permian lower whybrow coal new south wales australia have revealed a significant fire event in both the swamp setting and the hinterland the fire event is characterised by a change in the maceral composition the seam during this interval being dominated by inertinite especially semifusinite following the fire event the mineral matter content of the coal increases this may be the result of increased run off and erosion in the hinterland due to destruction of vegetation this major fire event is also reflected in a change in the vegetation as represented by the mesofossil content of the seam prior to the fire event the seam contains abundant bisaccate taeniate pollen sporangia and seed like bodies of possible glossopterid affinity these are lost at the ply in which the fire event is recorded though seed like bodies become important again later the fire event also corresponds to a change in the megaspore content of the coal a new species appearing perhaps as a result of hydrological change following this major fire event a mineral rich ply was deposited which contains miospore masses of spores from fern like plants possibly representing a re colonisation event by rhizomorphs after vegetation death this evidence for a major fire and its implications for the origin of inertinites leads to the conclusion that throughout this and other permian gondwana coals fire was an integral part of the temperate mid high latitude southern hemisphere swamp ecosystem

time partitioning in cratonic carbonate rocks dissimilarity in relations between thickness duration and accumulation rate in holocene sections metre scale phanerozoic cycles and epoch interval phanerozoic sequences reflects variation in the distribution of depositional and hiatal time at different scales of observation modern accumulation rates are strongly dependent on duration of deposition lower rates correspond to longer durations phanerozoic cycle thicknesses are similar to those of holocene sections suggesting that both formed while filling similar amounts of accommodation space however accumulation rates of phanerozoic cycles and sequences are about two orders of magnitude less than in modern settings and they show neither strong dependence on duration of accumulation nor significant variation over phanerozoic time hence net accumulation is primarily controlled by regional subsidence rate these relations also allow for determination of that fraction of cycle period recorded as rock and that corresponding to hiatal time at intercycle boundaries depending on subsidence rate and amount of compaction most cratonic carbonate units accumulated over 3 to 30 of the time represented by sequences in which they occur

an investigation of wulantuga coal cretaceous inner mongolia macerals paleopathology of faunal and fungal invasions into wood and the recognizable clues for their activity coal macerals are the product of a complex series of decompositional and preservational pathways from living woody and herbaceous tissues to the variety of forms seen in coal the cretaceous wulantuga coal inner mongolia china offers an opportunity to observe a number of maceral forms resulting from these disparate pathways assemblages of coprolites within fusinite strongly suggest an origin related to arthropod ingestion and consequent in situ emplacement of the macrinitic coprolites within the damaged wood structure followed by combustion of the whole to achieve the observed reflectance

the flora of early permian coal measures from the parana basin in brazil a review abstract this paper presents an updated overview integrating both previous and newly published data on the most important floras found associated with early permian coal seams in the parana basin brazil these floras occur within the rio bonito formation and correspond to the gondwana glossopteris flora for this review five floras are selected in ascending stratigraphic order the sao joao do triunfo figueira quiteria morro do papaleo and irapua bed floras they are the best known floras of the basin in terms of taxonomic composition paleoecology and environments of deposition an early mid sakmarian to earliest artinskian age is indicated for the rio bonito formation based on absolute radiometric and relative biostratigraphic ages integration of available information about the selected floras allows evaluation of taphonomic and paleoecological factors to provide a more comprehensive understanding of the early permian floral record in the parana basin the variation observed in both the taxonomic composition of individual floras and in the frequency of occurrence of different plant groups is due to the broad range of environmental edaphic conditions that prevailed in the many different depositional settings represented in the rio bonito formation a more precise age determination obtained for the plant bearing deposits permits the establishment of a more confident correlation between the early permian floral succession in the parana basin and other early permian floral successions in other basins the sakmarian global warming favored the appearance of pecopterid and sphenopterid ferns amongst the spore producing plants and the glossopterids amongst the pollen producing plants

a distinct class of avalanche scars on mars we report observations of a set of surface features on mars that form a distinct class of avalanche scars these features have a horizontal scale of hundreds of meters but a depth scale of meters distinguishes them from the shallower features known as slope streaks the meters thick avalanche scars have escaped previous attention because of weak contrast between the interiors of the scarred regions and their surroundings often the most visible feature is a shadow cast by the trough wall a band 1 3 pixels wide in mars orbiter camera narrow angle images indicating maximum depths of 4 10 m we investigate the morphology of more than 500 such features slopes upon which the avalanches occur average about 27 impact craters are seen at the heads of some avalanche scars this subset exhibits statistically wider opening angles the scars span an estimated several ma in age those found so far occurred mainly in the olympus mons lower aureole we compare shapes of slope streaks to shapes of meters thick avalanches and the results support the notion that the two classes are distinct the newly discovered avalanches resemble some terrestrial flows of loose dry material such as dry snow and glass beads on the basis of these analogs we suggest a physical model

relation of eustasy to stacking patterns of meter scale carbonate cycles late cambrian u s a abstract an interbasinal study of late cambrian cyclic carbonate successions in the appalachian and cordilleran passive margins suggests that superimposed orders of eustasy controlled the development of large scale depositional sequences and the component peritidal to subtidal meter scale cycles that comprise them the focus of this paper is on the small scale cyclicity its probable control by milankovitch forced sea level oscillations and how stacking patterns of meter scale cycles can be used to define internal components of larger scale sequences and estimate variations in relative sea level fining upward peritidal cycles showing evidence of episodic emergence grade seaward into coarsening upward subtidal cycles which lack evidence of emergence and form a continuum across the cambrian carbonate platforms eustasy appears to exert the dominant control on the simultaneous development of peritidal and subtidal cycles on late cambrian carbonate platforms evidence for milankovitch forcing of glacio eustatic sea level oscillations is provided by a 4 1 bundling of fifth order meter scale cycles 96 ky within fourth order cycles spanning tens of meters 440 ky within the big horse member of the orr formation in the house range of utah the 4 1 bundling may manifest the short e centricity to long eccentricity ratio of the milankovitch astronomical rhythms systematic changes in the stacking patterns of meter scale cycles can be used in conjunction with fischer plots to define long term sea level cycles on fischer plots of peritidal cyclic successions long term relative sea level rises are characterized by thick subtidal dominated cycles with thin laminite caps long term relative sea level falls are defined by stacks of thin laminite dominated cycles that show brecciated cycle caps and quartz sands toward the relative sea level lowstand on fischer plots of dominantly subtidal cyclic successions long term sea level rise is characterized by storm dominated open marine carbonate cycles or thick deep ramp shale based cycles falling segments of the fischer plot are characterized by thin shallow subtidal cycles compos d of restricted lithofacies cycle stacking patterns parasequence sets provide the crucial link between the meter scale cycles parasequences and the larger scale sequences and their component systems tracts one and two dimensional models of peritidal and subtidal cycle development indicate that whereas peritidal cycle thickness is primarily controlled by accommodation space deeper subtidal cycle thickness is primarily controlled by sedimentation rate lithofacies within peritidal cycles reflect the sedimentologic response to fluctuations in sea level lithofacies within subtidal cycles may be related to fluctuations in the zones of fairweather and storm wave reworking that oscillated in harmony with sea level fluctuations and may have acted as a subtidal limit to upward aggradation the 2 d modelling illustrates how stacked peritidal to deep subtidal carbonate cycles with thicknesses compositions and stacking patterns similar to the late cambrian of north america can be generated by ilankovitch driven composite eustasy

field and modelling studies of cambrian carbonate cycles virginia appalachians reply abstract field studies coupled with computer modelling of carbonate cycles in the elbrook conococheague formations middle to upper cambrian in the appalachians have helped define the mechanisms of formation the sequence is up to 1 6 km thick and composed of cyclic peritidal carbonates these formed on an aggraded rimmed shelf on a mature passive continental margin the cycles 1 7 m thick have lower parts of subtidal intertidal carbonate and caps of dolomitic laminite containing minor quartz arenite shale and breccia sedimentation rates for these peritidal carbonate environments exceeded long term subsidence of the platform 0 01 to 0 1 m 1 000 yr thus the shelf stayed near to sea level i e was aggraded milankovitch 20 000 to 100 000 yr low amplitude sea level fluctuations few meters superimposed on 3rd order sea level fluctuation of 1 to 3 m y duration and less than 20 m amplitude caused periodic submergence of the gently sloping platform less than 0 02 m km slopes resulting in deposition of over 400 peritidal cycles in about 26 m y cycles that formed during 3rd order sea level rise are thick and limestone rich whereas those formed during 3rd order fall are thin quartzose and highly dolomitized the modelling suggests that fewer and thinner cycles formed during the long term falls compared to the rises reflecting decreased accommodation cycle frequency decreases into areas of lower subsidence rate open marine cycles typical of the outer shelf and cycles formed during 3rd order sea level rise contain digitate bioherms grainstone and ribbon carbonates in lower parts they reflect high subsidence rate and an open marine setting inner shelf cycles and cycles that formed during 3rd order sea level fall commonly are thrombolitic or have thin subtidal parts grainstone conglomerate or stromatolite and reflec the low subsidence rates interior areas of quaternary carbonate shelves are characterized by incipiently drowned facies and pinnacle reefs and are punctuated by soil caliche horizons and karst surface that reflect 100 m glacio eustatic sea level fluctuations in contrast many ancient shelves like the cambro ordovician shelf of the appalachians were flat topped and dominated by cyclic peritidal sequences lacking evidence of high amplitude sea level fluctuations such aggraded shelves may represent the typical state of mature carbonate shelves that formed in response to low amplitude milankovitch sea level fluctuations as opposed to the large scale fluctuations that typified the quaternary

co2 forced climate and vegetation instability during late paleozoic deglaciation the late paleozoic deglaciation is the vegetated earth9s only recorded icehouse to greenhouse transition yet the climate dynamics remain enigmatic by using the stable isotopic compositions of soil formed minerals fossil plant matter and shallow water brachiopods we estimated atmospheric partial pressure of carbon dioxide pco2 and tropical marine surface temperatures during this climate transition comparison to southern gondwanan glacial records documents covariance between inferred shifts in pco2 temperature and ice volume consistent with greenhouse gas forcing of climate major restructuring of paleotropical flora in western euramerica occurred in step with climate and pco2 shifts illustrating the biotic impact associated with past co2 forced turnover to a permanent ice free world

upper paleozoic charcoal remains from south america multiple evidences of fire events in the coal bearing strata of the parana basin brazil abstract the occurrence of macroscopic fossil charcoal in sediments has widely been accepted by the scientific community to be a direct indicator for the occurrence of paleowildfires for the upper paleozoic of the northern hemisphere records of macroscopic charcoal are relatively common on the other hand for the southern hemisphere only a few records have been described for this period for the parana basin in particular only a single occurrence of fossil charcoal has been described in detail so far in this study several occurrences are summarized for the lower permian rio bonito formation sakmarian artinskian based on this study it can be stated that macroscopic charcoal remains can be considered a common element throughout the lower permian coal bearing interval in the southern and southeastern margin of the parana basin the occurrence of fossil macroscopic charcoal remains in different late paleozoic mire related clastic deposits of the parana basin adds support to previous studies that have demonstrated the abundant presence of inertinite as a petrographic component of various coals in different coalfields in this particular basin these charcoal occurrences support previous hypotheses that proposed that paleowildfires should have been common during the early permian in the western gondwana realm

fossil charcoal as an indicator of palaeoatmospheric oxygen level charcoal results from incomplete combustion of plant material it is produced naturally by wildfire and being relatively tough and unbiodegradable it may be transported and incorporated into a variety of sedimentary environments wildfire requires adequate atmospheric oxygen for the combustion of plant fuel wood leaf litter fossil charcoal from the devonian onwards suggests that the oxygen level in the atmosphere has not fallen below 13 in this interval further the extreme flammability of even wet plant fuel at oxygen levels above 35 makes this the highest figure compatible with the occurrence of terrestrial vegetation

aureole deposits of the martian volcano olympus mons the aureole of grooved terrain that surrounds the large shield volcano olympus mons consists of several overlapping roughly circular sheets each 0 5 to 1 5 km thick the surfaces of these materials bear abundant curvilinear ridges and troughs 10 to 100 km long and 1 to 5 km wide which form anastomosing patterns that vary in length and width over the aureole the aureole is asymmetric to olympus mons extending almost 1000 km northwest from the center of the volcano but only 600 km southeast the lobate form of the deposits the pressure ridges on their surfaces and the deflection of aureole material around barriers indicate that the deposits were emplaced as viscous flows high resolution viking orbiter pictures show the aureole material to be unstratified and it is inferred to contain randomly distributed large dark blocks whose weathering products form dark streaks in the talus on the flanks of ridges a pyroclastic origin is proposed for the aureole the following sequence is suggested at least six great pyroclastic eruptions occurred prior to the construction olympus mons they formed very fluid ash flows that became viscous during late stages of emplacement and pressure ridges formed on the surfaces of the deposits before they finally came to rest the oldest and most extensive aureole deposit finely grooved terrain was considerably modified by erosion prior to being partly covered by later eruptions a positive gravity anomaly over the olympus mons area may define the site of a near surface magma chamber that was the source of the pyroclastic eruptions

the role of the wind transported dust in slope streaks activity evidence from the hrsc data abstract slope streaks are gravity driven albedo features observed on martian slopes since the viking missions the debated mechanism of formation could involve alternatively dry granular flow or wet mass wasting a systematic mapping of slope streaks from the high resolution stereo camera is presented in this paper two regions known for their slope streaks activity have been studied the first one is located close to cerberus lava flow and the second one is inside the olympus mons aureole the statistics of slope streaks shapes measured from orthorectified images confirm previous results from mars orbiter camera surveys preferential orientations of slope streaks are reported slope streaks occur preferentially on west facing slopes at latitudes lower than 30 n for olympus and on south west facing slopes for cerberus wind directions derived from a general circulation model during the dusty season correlate with these orientations furthermore west facing slopes at olympus have a thicker dust cover these observations indicate that slope streaks are dust avalanches controlled by the preferential accumulation of dust in the downstream side of the wind flow the paucity of slope streaks at high latitudes and their preferential orientation on south facing slopes have been presented as an evidence for a potential role of h 2 o phase transition in triggering or flow the potential role of h 2 o cannot be ruled out from our observations but the dust avalanche model together with the atmospheric circulation could potentially explain all observations the role of h 2 o might be limited to a stabilizing effect of dust deposits on northward facing slopes at intermediate latitudes 30 n 33 n and on all slopes further north

diffusion barriers at mars surface conditions salt crusts particle size mixtures and dust the diffusion coefficient of water vapor through porous media at mars like surface conditions is measured for a variety of complex particle size distributions and soil compositions micron sized dust simulants mixtures of sand and dust sized particles and salt encrusted sand are examined we find that while the value of the diffusion coefficient d can be reduced by up to a factor of 10 for heavily salt encrusted soils minimum observed d 0 4 0 04 cm 2 s 1 moderate amounts of salt only produce minor reductions in d mechanical packing of pure dust can lower d by a similar amount while mixtures of dust with sand sized particles produce at most a factor of 4 reduction we conclude that present day processes of aeolian redistribution moderate levels of salt encrustation and volatile loss from dirty ice would be inefficient at producing soil deposits and lags on mars that pose significant barriers to diffusion therefore subsurface ice deposits that are thermally unstable would not be protected against sublimative loss by such materials

the interpretation of cyclic successions of the middle and upper triassic of the northern and southern alps abstract theories regarding the formation of sedimentary cycles in the 3rd 4th and 5th order bands are reviewed with reference to the middle and upper triassic of the northern calcareous alps nca and southern alps milankovitch autocyclic and tectonic theories are discussed together with an evaluation of concepts of chaotic sedimentation and a case example from the nca concerning eustasy 3rd 4th and 5th order sea level fluctuations were probably a low amplitude low rate phenomenon caused by fluctuations in the volume of mountain glaciers and ocean water during the triassic the mid and late triassic was a non glacial interval in which polar regions may have been ice free so glacio eustasy can not be expected eustatic sea level variations in the 3rd 4th and 5th order bands seem to have left no useful imprint on cyclic successions in the region whatever record there may be is inextricably mixed with two other signals tectonic activity and autocycles the review shows how sedimentation in the triassic of the area was strongly influenced by tectonic activity this is as true for the middle and late triassic of the nca as it is for the southern alps tectonic activity may be responsible for large scale cyclicity 4th to 3rd order scale although seismogenic structures have yet to be identified and described in carbonate successions of the alps candidates do exist slumped and microfaulted layers in laminated sediments of the seefeld basin upper triassic nca have been described as the products of fault movements the sedimentary record from the nca and southern alps also leaves little doubt that autocyclic processes were important in all environments except perhaps the deep sediment starved basins most small scale platform cycles 5th order scale in the region can be related to autocyclic processes and in shallow basinal successions to events such as storms previous workers have not been consistent in their interpretation of cyclic successions in the area applying diverse theories to similar successions so far the steinplatte hochkonig platform with attached kossen basin is the only example interpreted with reference to tectonics and autocyclicity eustasy was probably not the most important factor in cycle generation in the triassic of the nca and southern alps such an approach could prove useful in future studies

a dominant tectonic signal in high frequency peritidal carbonate cycles a regional analysis of liassic platforms from western tethys abstract meter scale peritidal carbonate cycles are a common feature of the geological record but debate continues about what processes lead to their formation three conceptual models or a combination thereof are commonly invoked to explain cycle formation eustasy tectonics or autocyclicity these three models are tested with a large new dataset from different early jurassic plate margins from western tethys study of seven logged sections from spain italy greece tunisia morocco and gibraltar enables an analysis of the possible roles of local versus regional patterns and controls on cyclicity within a sinemurian time slice cycle types are diverse and include shallowing upward cycles parasequences but also deepening upward and diagenetic cycles high frequency sequences and subtidal cycles numbers of cycles per section and cycle stacking patterns within this time slice vary from section to section statistical tests runs tests time series and bundling all indicate random stacking of cycles within sections and an absence of any bundling of thicknesses or of facies trends assessment of cycle types by their occurrence and stacking patterns indicates little support for either eustasy or autocyclicity being the dominant cycle forming mechanism however the variability in numbers of cycles per section thickness variations of the sections cycle type variability and randomness of stacking patterns all favor a pulsed tectonic control for the creation and filling of accommodation space this conclusion is further supported by evidence that has largely arisen during the course of this study of syndepositional extensional tectonics in the sinemurian on these rifted tethyan margins although tectonics appears to be the dominant control superimposed eustasy and or autocyclic processes cannot be discounted

molecular indicators of palaeosalinity and depositional environment of small scale basins within carbonate platforms the late triassic hauptdolomite wiestalstausee section near hallein northern calcareous alps austria abstract microfacies and biomarker analyses are used to determine the environmental conditions during deposition of marly dolomicrites from the hauptdolomite wiestalstausee section near hallein salzburg austria part of the late triassic hauptdolomite dachstein carbonate platform of the northern calcareous alps phytoplankton and photosynthetic bacteria are considered to be the major primary producers of the organic matter in these immature 0 5 equivalent vitrinite reflectance carbonate rich rocks contributions from vascular plants are suggested from the n alkane distribution pattern and high content of c 29 steranes enhanced microbial activity in the depositional environment is proposed on the basis of the hopanoid content the occurrence of aryl isoprenoids probably derived from carotenoids of the photosynthetic green sulfur bacteria chlorobiaceae indicates the presence of free h 2 s in the bottom water mesohaline conditions in the upper part of the water column are deduced from the presence of dimethylated and trimethylated 2 methyl 2 tridecylchromans mttcs co variation in the distribution of mttcs and pristane phytane ratio and the concentration of a c 16 aryl isoprenoid argue for photic zone anoxia due to salinity stratification the biomarker composition points to a high productivity marine environment with limited water exchange and a stratified water column confirmed by microfacies analysis a small scale basin formed within the restricted inner lagoonal area of the hauptdolomite dachstein carbonate platform through erosion by currents followed by a sea level rise is considered the most appropriate depositional environment of the dolomicrites of the wiestalstausee section

a new look at sedimentation rates and the completeness of the stratigraphic record several recent papers have suggested that completeness of stratigraphic sections can be estimated by using the ratio of long term sedimentation rates to short term rates we show that the median short term sedimentation rates used in these papers are erroneous and are mostly an artifact arising from improper data manipulation to demonstrate the artificial character of short term median rates we have generated a series of plots assuming a constant sedimentation rate with fixed variance and defined limits of measurement precision these plots demonstrate that increasing variance in the time required to deposit sediments will result in spuriously high short term median sedimentation rates a new method for calculating median sedimentation rates which eliminates the problem of spurious median rates is then applied to make an improved estimate of expected completeness recalculated median values show that sedimentation rates for pelagic sediments are close to identical for both short term and long term tim

the genesis of lofer cycles of the dachstein limestone northern calcareous alps austria peritidal carbonate platform lofer cycles have been regarded as a record of sea level oscillations driven by variations in the earth s orbit fresh analysis of a newly measured 700 m thick section from the steinernes meer is presented here estimation of stratigraphic completeness indicates that this sequence is only 0 75 9 5 complete strongly suggesting that milankovitch patterns are not preserved analysis of cycle thickness frequency distributions reveals an exponential pattern strongly suggestive of aperiodic random deposition rather than periodic deposition in response to orbital forcing evidence for the importance of autocyclic processes e g lateral migration of inter to supratidal mudbanks and subtidal areas and syn sedimentary tectonic downfaulting events within this already active late triassic extensional zone is presented

periodicity of mesoscale phanerozoic sedimentary cycles and the role of milankovitch orbital modulation data on more than 200 mesoscale sedimentary cycles indicate that phanerozoic cycle periods are randomly distributed with respect to the four major milankovitch orbital parameters except late mississippian through late pennsylvanian cycles which show positive clustering about the 413 000 yr eccentricity period cycle periods calculated from average thicknesses and accumulation rates are strongly dependent on the former correlation coefficient 0 802 but relatively independent of the latter correlation coefficient 0 360 hence calculated period is largely a function of average cycle thickness and milankovitch range periods will be preferentially calculated for cycles with average thicknesses between 1 m and 20 m regardless of actual causes of cyclicity for individual cyclic sequences arguments for milankovitch control based solely on average period are unfounded comparison of short term holocene sedimentation rates and long term phanerozoic accumulation rates for cyclic peritidal and delta

episodic fire runoff and deposition at the palaeocene eocene boundary qualitative and quantitative coal petrological analyses have been undertaken on the laminated lignite at the base of the cobham lignite bed from scalers hill kent england the maximum negative carbon isotope excursion which marks the beginning of the palaeocene eocene thermal maximum petm occurs near the top of the laminated lignite the lignite contains inertinite a petrographic term used to describe charcoal the laminated lignite has inertinite rich and inertinite poor layers indicative of episodic fires and post fire erosion charcoal clasts are derived from living or recently senesced plants and are dominated by the leaf stalks of herbaceous ferns and wood fragments from flowering plants the charcoal assemblage reflects a low diversity flora possibly adapted to disturbance by fire derived from a source vegetation subjected to seasonal surface wildfires the environmental conditions leading up to and across the onset of the petm are therefore interpreted as incorporating a persistent fire regime with episodic wildfires followed by rainfall and runoff events abundant charcoal indicates near modern oxygen levels whereas the absence of charred peat in this area calls into question previous suggestions that burning of palaeocene peats might have contributed to the short lived negative carbon isotope excursion at the palaeocene eocene boundary

evidence of widespread wildfires in coal seams from the middle jurassic of northwest china and its impact on paleoclimate abstract today wildfire is an important disturbance in many continental ecosystems and it is assumed that with ongoing climate changes the frequencies and impacts of wildfires will increase in many regions one way to obtain information about the potential long term influences of wildfires on ecosystems and the climate system itself is to study palaeo wildfires a total of 140 jurassic samples including 122 coal samples and 18 rock samples from roof and floor of coal seams were collected from 4 coalfields in northwestern china the samples were analyzed by macropetrography microscopy scanning electron microscopy gas chromatography and gas chromatography mass spectrometry to study the evidences of wildfires and their impact on the paleoclimate high contents of pyrogenic inertinites charcoal natural char and natural coke particles observed in the samples which indicate that widespread wildfire events occurred in the early middle jurassic in all over northwestern china additionally high molecular weight polycyclic aromatic hydrocarbons were detected in the coal samples these aromatic compounds were formed under high temperature and provide further evidence of wildfires according to a carbon emission model for modern forest fires the total carbon and gas emissions from wildfires in peat swamps of the middle jurassic in northwest china were calculated by the data from 21 575 coal samples of number of 1567 drill core samples the total carbon released from peat swamp forest wildfires was at least 1207 gt corresponding to emissions of co2 co and ch4 of 1926 gt 163 gt and 8 8 gt respectively the huge amount of co2 released by forest fires in the peat swamp systems of the middle jurassic in northwestern china alone was equivalent to 64 20 of the total co2 in the atmosphere at present 3000gt the large amounts of greenhouse gases released by wildfires must have led to long term changes in the atmospheric composition and have caused global warming which could have the reason of affected the paleoclimate

subsurface ice on mars with rough topography high latitude ground ice on mars discovered by the gamma ray spectrometer suite is thought to be thermally stable owing to the presence of vapor in the martian atmosphere however local slopes can alter surface and subsurface temperatures substantially and hence allow ground ice to persist at locations where it would otherwise be unstable global statistics of the topography of mars are computed processed and extrapolated to derive a description of surface roughness on spatial scales to which ground ice should be sensitive this slope distribution is convolved with a new thermal model for the dependence of subsurface ice on slope to produce a prediction of the global ice distribution that includes the effect of topographic roughness in the highest latitudes slopes reduce the amount of buried ice while in lower latitudes the ice fraction increases widening the geographic boundary of the ice table at the high latitudes where ice is stable beneath horizontal ground the estimated reduction of ice is small compared to the existing ice volume areas in the midlatitudes with high surface roughness that have previously been predicted to be ice free are predicted to contain quantities of ice that may be detectable at present and accessible in the future slopes cause ground ice to be stable to latitudes of about 25 degrees in both hemispheres including for example areas within the northern olympus mons aureole deposits hecates tholus and hellas basin ice is unstable at equatorial latitudes even when accounting for surface slopes

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

slope streaks on mars a new wet mechanism slope steaks are one of the most intriguing modern phenomena observed on mars they have been mostly interpreted as some specific type of granular flow we propose another mechanism for slope streak formation on mars it involves natural seasonal formation of a modest amount of highly concentrated chloride brines within a seasonal thermal skin and runaway propagation of percolation fronts given the current state of knowledge of temperature regimes and the composition and structure of the surface layer in the slope streak regions this mechanism is consistent with the observational constraints it requires an assumption that a significant part of the observed chlorine to be in form of calcium and ferric chloride and a small part of the observed hydrogen to be in form of water ice this wet mechanism has a number of appealing advantages in comparison to the widely accepted dry granular flow mechanism potential tests for the wet mechanism include better modeling of the temperature regime and observations of the seasonality of streak formation

sedimentology carbon isotope stratigraphy and micropalaeontology of the rhaetian zlambach formation implications for the dachstein carbonate platform development northern calcareous alps austria abstract middle to late rhaetian toe of slope to basin deposits zlambach formation of the northern calcareous alps in the tethyan realm have been studied with respect to depositional palaeoenvironments and chemo and sequence stratigraphy using high resolution stable isotope and x ray fluorescence measurements microfacies and microfossil analysis our results show that the zlambach formation represents a regressive transgressive succession which includes one 3rd order and two 4th order depositional sequences as well as several subordinate sedimentary cycles reflecting variations of calciturbidite input from the dachstein platform due to minor sea level fluctuations we present the first high resolution 13ccarb record for the middle and upper rhaetian interval of the west tethyan open marine realm the data show in contrast to earlier suggestions that growth and progradation of the dachstein carbonate platform margin was continuous until the early choristoceras marshi ammonoid zone upper rhaetian in the late c marshi zone the hallstatt basin was affected by significant environmental perturbations as recorded by a 1 0 ccarb negative excursion followed by a 1 3 positive excursion and contemporaneous fluctuations in benthic microfossil abundance and diversity the occurrence of comparable carbon isotope excursions in the late c marshi zone of intraplatform basinal deposits of the northern calcareous alps suggests that these perturbations were of a higher significance than previously thought these isotope excursions could be related to regional ecologic changes such as the late rhaetian termination of the dachstein platform margin growth

equatorial and midlatitude distribution of chlorine measured by mars odyssey grs 1 the 2001 mars odyssey gamma ray spectrometer grs has made the first measurement of the equatorial and midlatitude distribution of cl at the near surface of mars a mean concentration value of 0 49 wt cl has been determined from a grand sum of grs spectra collected over the planet excluding high latitude regions cl is significantly enriched within the upper few tens of centimeters of the surface relative to the martian meteorites and estimates for the bulk composition of the planet however cl is not homogeneously distributed and varies by a factor of 4 even after smoothing of data with a 10 arc radius filter several contiguous geographically large 20 regions of high and low cl concentrations are present in particular a region centered over the medusae fossae formation west of tharsis shows significantly elevated cl a large region north of syrtis major extending into utopia planitia in the northern hemisphere shows the lowest cl concentrations on the basis of hierarchical multivariate correlations cl is positively associated with h while negatively associated with si and thermal inertia we discuss four possible geologic mechanisms aeolian volcanic aqueous and hydrothermal that may have affected the cl distribution seen by grs while some of the distribution may be due to cl rich dust deposits transported by aeolian processes this mechanism does not appear to account for all of the observed variability we propose that reactions with volcanic exhalations may have been important for enriching cl in medusae fossae formation material

paleobotanical and palynological analysis of faxinal coalfield lower permian rio bonito formation parana basin rio grande do sul brazil abstract the sedimentary section exposed at the faxinal coalfield bears abundant plant fossil remains distributed within a tonstein level interlayered in a section mainly comprised by siltstones and coal deposits of the rio bonito formation lower permian parana basin brazil this contribution presents a paleobotanical taxonomic updating of this coalfield based on an in depth revision of available data as well as the direct analysis from material deposited in paleontological collections published and unpublished according to this reevaluation the faxinal coalfield bears 15 paleobotanical taxa comprised mainly by leaves of glossopteridales composing a typical coal forming flora new palynological results from this section are derived from five associated levels which revealed distinct assemblages comprising 30 taxa of spores 21 of pollen grains and 3 related to algae elements the associations are compatible with the glossopteris rhodeopteridium zone and with the protohaploxypinus goraiensis subzone base of the vittatina costabilis zone related to the cisuralian lower permian late sakmarian early artinskian stratigraphical considerations are given based on comparison with other neighboring sections as well as with a regional erosion surface recognized in this outcrop

orbitally forced lofer cycles in the dachstein limestone of the julian alps northeastern italy lofer cyclothems of the upper triassic dachstein limestone of the julian alps northeastern italy are the focus of a new sedimentological cyclostratigraphic study a 112 cycle long field section reveals that the meter scale basic cycle shallows upward from subtidal megalodont bearing subfacies to intertidal laminites capped by a paleosol subfacies time series analysis of a correlative grayscale scan of a high resolution field photograph shows that a 166 m thick succession of lofer cycles has time frequency characteristics consistent with earth s precession index suggesting that the lofer cycles were generated by eustatic sea level oscillations that were forced by milankovitch cycles

charcoalified logs as evidence of hypautochthonous autochthonous wildfire events in a peat forming environment from the permian of southern parana basin brazil abstract evidences of paleowildfires from the upper coal seam s from the faxinal coalfield have been analyzed through petrographic fluorescence and scanning electron microscopy sem specifically at the base 1 and top 2 boundaries of an interlayered tonstein bed and revealed recurrent charcoal deposition in the peat forming environment an unusual accumulation of adjacent large sized 21 8 13 4 cm and larger charred logs occurs throughout the coal seam area 1 6 km 2 beneath the tonstein bed boundary 1 reflecting an extensive wildfire event in hypautochthonous autochthonous conditions the logs display a semifusinite vitrinite semifusinite sandwich like structure sensu jones et al 1993 indicating burning in growth position and reflectance measurements below 1 ro suggest that this was a low temperature fire dryness in the peatland during the fire event was clearly detected by altered fluorescence of spores and algae corroborating previous studies the paleoecological setting can be characterized as a swamp forest based on the presence of pollen clusters and organs observed under fluorescent light and on the identification under sem of the morphogenus agathoxylon hartig as a single wood type reflecting the dominance of arborescent gymnosperms glossopterids in the peatland homogenized cell walls observed under sem ratified the recognition of the material as charcoal the reestablishment of regular conditions of peat deposition following the major fire episode is represented by alternate bands of vitrinite and semifusinite in both boundaries 1 and 2 suggesting an oscillation from dry to wet conditions in the climate pattern and the occurrence of wildfires as common and systemic events fire ignition activity and spread in the peat forming environment resulted from a combination of lightning strikes dryness fuel abundance and high atmospheric oxygen levels

the diversification of paleozoic fire systems and fluctuations in atmospheric oxygen concentration by comparing silurian through end permian 250 million years myr charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long term variations in fire occurrence and fire system diversification are related to fluctuations in late paleozoic atmospheric oxygen concentration charcoal a proxy for fire occurs in the fossil record from the late silurian 420 myr to the present its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13 to 35 the fire window herein we observe that as predicted atmospheric oxygen levels rise from 13 in the late devonian to 30 in the late permian so too fires progressively occur in an increasing diversity of ecosystems sequentially data of note include the occurrence of charcoal in the late silurian early devonian indicating the burning of a diminutive dominantly rhyniophytoid vegetation an apparent paucity of charcoal in the middle to late devonian that coincides with a predicted atmospheric oxygen low and the subsequent diversification of fire systems throughout the remainder of the late paleozoic first fires become widespread during the early mississippian they then become commonplace in mire systems in the middle mississippian in the pennsylvanian they are first recorded in upland settings and finally based on coal petrology become extremely important in many permian mire settings these trends conform well to changes in atmospheric oxygen concentration as predicted by modeling and indicate oxygen levels are a significant control on long term fire occurrence

mass movement within a slope streak on mars 1 slope streaks on mars represent a currently active geological process various theories for slope streak formation have suggested that slope streaks form by disturbing only a thin surface veneer or by staining of the surface preserving pre existing topography within the streak theories also vary as to whether the formation mechanism requires the presence of water or another liquid we present observations of a slope streak that reveal topographic mounds within the streak these mounds do not continue outside the streak and we suggest that they formed with or immediately after the slope streak we use estimates of the total volume of mounds in this particular streak compared with the estimated excavation volume to extrapolate to a global sediment transport rate from slope streak formation if this slope streak is typical then this calculated rate is greater than estimates of the total volume of material transported by dust storms each year

shrimp u pb zircon dating and palynology of bentonitic layers from the permian irati formation parana basin brazil abstract this paper presents the first shrimp zircon age data from bentonitic ash fall layers intercalated with the irati sedimentary rocks as well as palynofossils retrieved from the petrobras six mine parana state southern brazil the permian irati formation is one the most important oil source horizons within the parana basin and consists mainly of siltstones gray claystones as well as organic rich claystones intercalated with limestones zircon morphology based on cathodoluminescence images includes two different populations a dominant population of euhedral prismatic elongate to acicular grains which are most likely related to an ash fall volcanism and a population of rounded to large prismatic grains that were interpreted as detrital grains shrimp analysis performed on the euhedral and prismatic grains revealed an age of ca 278 4 2 2 ma 7 points with 95 confidence interpreted as the crystallization age of the volcanic eruption based on this new dating the irati formation should be placed on the lower permian cisuralian artinskian in age modifying substantially the traditional ages previously attributed to this unit the palynofossils from this level include key species of the lueckisporites virkkiae zone such as l virkkiae l densicorpus l stenotaeniatus weylandites lucifer alisporites splendens typical species of this zone also occur in african and other south american argentina permian strata allowing stratigraphical correlations the origin of the ash falls is not clearly defined it may be related either to calc alkaline arc magmatism associated to the sanrafaelica orogeny 275 and 250 ma or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern gondwana at ca 278 my the dating of this unit is significative to calibrate biostratigraphic schemes along the parana basin as well as equivalent zones in gondwana areas mainly in its occidental portion

the presence and stability of ground ice in the southern hemisphere of mars abstract we calculate new estimates of ground ice stability and the depth distribution of the ice table the depth boundary between ice free soil above and ice cemented soil below and compare these theoretical estimates of the distribution of ground ice with the observed distribution of leakage neutrons measured by the neutron spectrometer instrument of the mars odyssey spacecraft s gamma ray spectrometer instrument suite our calculated ground ice distribution contains improvements over previous work in that we include the effects of the high thermal conductivity of ice cemented soil at and below the ice table we include the surface elevation dependence of the near surface atmospheric humidity and we utilize new high resolution maps of thermal inertia albedo and elevation from mars global surveyor observations results indicate that ground ice should be about 5 times shallower than in previous predictions while results are dependent on the atmospheric humidity depths are generally between a few millimeters and a few meters with typical values of a few centimeters results are also geographically similar to previous predictions with differences due to the higher resolution of thermal inertia and the inclusion of elevation effects on humidity comparison with the measured epithermal neutron count rates in the southern hemisphere indicate that the geographic distribution of the count rate is best correlated with ground ice in equilibrium with 10 to 20 pr m precipitable micrometers column abundance of atmospheric water assuming a uniform distribution with co2 however given the uncertainties 5 to 30 pr m also may be viable this water abundance represents a longer term average over 100 to 1000 yr there is a high degree of correlation between the depth of the ice table and the epithermal count rate that agrees remarkably well with predicted count rates as a function of ice table depth these results indicate that ground ice in the upper meter of the martian soil is in diffusive equilibrium with the atmosphere since ground ice in this depth zone is expected to undergo saturation desiccation cycles with orbital variations this ice should be younger than about 500 kyr and was emplaced under similar cold and dry climate conditions of today remaining differences between the predicted depths of the ice table and those inferred from the neutron data are likely to be due to subpixel heterogeneity in the martian surface including the presence of rocks slopes and patches of soil with varying thermophysical properties

slope streak formation and dust deposition rates on mars 1 the mars orbiter camera moc has imaged sometimes repeatedly mass movements known as slope streaks which are abundant in the dust covered regions on mars they are among the few known examples of contemporary surface changes a survey of 173 collocated image pairs indicates that these features are currently forming at a high rate of 7 per existing streak per martian year either there is a complete turnover within a few decades or the streak population is currently increasing rapidly large spatial as well as possible temporal variations in the formation rate are obtained from these data streaks do not appear to fade over time periods comparable to their inverse formation rate of 28 years as seen by analysis of viking orbiter images containing streaks that are still visible in moc images gradual or stochastic variations in dust deposition may be needed to explain observations of changes in the formation rate and its current imbalance with the fading rate