carbonate deposition physical limnology and environmentally controlled chert formation in paleocene eocene lake flagstaff central utah abstract lake flagstaff paleocene eocene of central utah owed its existence large size shallowness and low clastic content to its tectonic setting but the climate controlled its mostly autochthonous sediments during the first and most humid of the three lake phases the lake was fresh calcareous large and highly productive with abundant vegetation and snails the first deposits were limestones with gradually increasing detrital dolomite eroded from lake marginal carbonate mudflats that were undergoing penecontemporaneous dolomitization continuous fluctuation in lake level produced many secondary dewatering and pedogenic paludine fabrics the lake developed into a playa lake during the very arid second phase becoming restricted in area and fauna the water was saline and alkaline and twice became a gypsum precipitating brine frequent exposure of the lake beds resulted in much calichification and in rapid and complete dolomitization under the intermediate climate of the third phase the lake reexpanded and freshened snails returned and many limestones escaped dolomitization each phase defines a member of the flagstaff formation chert absent in the oldest beds increases up section the lowest chert forms minor small spheres and linings in voids near the top of the lowest member suggesting limited silica input and post dolomitization precipitation in areas of greatest groundwater movement the base of the middle member contains horizons of atextural chert mudcrack fillings and nodules that appear to have been an inorganically precipitated gel most of the middle member however contains abundant chert nodules that replaced limestone prior to dolomitization the nodules grew prior to burial some even prior to mudcrack formation by the movement of dissolved silica to areas of relatively low ph in the upper member chert is even more prevalent entire thin beds were pervasively but incompletely silicified prior to dolomitization probably by vertical evaporative pumping of siliceous groundwater moving under mudflats toward the lake

waterholes and their significance in the anastomosing channel system of cooper creek australia abstract cooper creek has developed a very extensive system of anastomosing channels a distinctive feature of which is the preponderance of waterholes which are readily identified as deepened and widened reaches of channel with more or less permanent water they are widely distributed over the floodplain but tend to decrease in number downstream possibly as a result of transmission losses which reduce erosive potential and to develop preferentially towards the west which has implications for the long term relocation of the system classification of waterholes according to degree of lateral restriction and flow status reveals only muted contrasts in waterhole form between the various types the one clear distinction is the unexpectedly low width length ratio of the most restricted dune flanked type its squat form being attributable to erodible banks and limited downstream confinement that waterholes have developed in abundance along cooper creek appears to be related to the presence of a more easily eroded sand sheet at depths of only 2 9 m below cohesive surface sediments sediment splays at their downstream ends indicate that waterholes can be maintained by the present regime but whether they were formed by that or a prior regime is a matter of debate some degree of inheritance cannot be discounted but a contemporary origin is favoured in view of the fact that most waterholes are located at points of flow convergence by focusing erosional energy when the floodplain is extremely broad waterholes play a significant role not only in maintaining existing channel lines but also in promoting the development of new ones as the invasion of a dune field testifies

the shoreline distribution and degradation of tilapia carcasses salton sea california taphonomic implications abstract the salton sea is a hypersaline closed lake system in southern california usa episodic fish kills led to bloating and floating fish bodies that were driven onto the shoreline by wind shear the documented taphonomic destruction of the stranded fish carcasses includes the distribution of the fish parts after desiccation and disarticulation mainly by wave induced transport with possible minor component of wind transport on the upper shoreface carcass decay is divided into five taphonomic categories 1 through 5 category 1 represents whole pliable fish recently washed onto the shoreline while category 5 incorporates longer term destruction into ultimately single isolated skeletal elements high water strand line deposits are delineated by the presence of categories 3 through 5 mixtures the general trend in 2012 was observed to be considerable bone disarticulation away from the shoreline because categories 1 and 2 were present in the swash zone the influx of fresh fish carcasses recharged the shoreline during 2013 the absence of new 1 and 2 categories arriving to the shoreline enhanced wave action to further break down categories 3 and 4 ultimately into category 5 in addition isolated bone elements segregate according to density differences typically on low gradient beaches wave and wave induced current action coupled with beach topography controls distribution of the various fish bones as an actualistic model the salton sea implies that shore parallel complete to partial fish carcass concentrations are more shoreward and isolated skeletal elements more distal

impressions of algal mats from the middle proterozoic belt supergroup northwestern montana u s a irregular low relief bedding plane markings which probably represent impressions of thin wrinkled algal mats have recently been detected in mudstones from the 1100 m y old snowslip formation belt supergroup glacier national park montana algal mat impressions are rarely reported from ancient strata yet algal mats are common in certain modern environments originating primarily in moist settings and in relatively quiescent shallow water settings such structures may be of some value in interpreting ancient depositional environments

diastasis cracks mechanically generated synaeresis like cracks in upper cambrian shallow water oolite and ribbon carbonates upper cambrian limestones and dolostones of western newfoundland canada display conspicuous synsedimentary mud cracks cracks occur in carbonate mudstone interbedded with ooid and peloid grainstone unwashed oolite and ribbon rock lithofacies the traditional interpretation is that these are desiccation cracks the weight of evidence supports an alternative e explanation cracks resulted from the differential mechanical behaviour under stress of stiff mud interlayered with loose ooid peloid sand the processes envisaged to cause such diastasis cracks may be applicabl e to a wide variety of both carbonate and terrigenous clastic deposits composed of interlayered sediments of contrasting material properties and may be a viable alternative to synaeresis

green river laminites does the playa lake model really invalidate the stratified lake model proponents of the playa lake model have proposed deposition of most of the green river formation microlaminated carbonates including oil shales in lakes that were not perennially stratified meromictic however there is a variety of evidence favoring a meromictic depositional environment 1 close similarity of much of the lamination to varves in modern meromictic lakes 2 evidence that hydrologic events favoring development of meromixis chemical stratification occurred prior to deposition of major accumulations of oil shale 3 mutually exclusive distribution of fossil nekton especially fish and normal lacustrine benthos including mollusks and 4 analogy with a quaternary playa that became a meromictic lake following increased inflow the playa lake model is untenable for the typical fish bearing kerogen rich microlaminated sediments these laminites were probably deposited in a large ectogenic meromictic lake a chemically stratified lake that formed when increased fresh water inflow drowned a saline playa complex

oxygen and hydrogen isotopes in the hydrologic cycle changes of the isotopic composition of water within the water cycle provide a recognizable signature relating such water to the different phases of the cycle the isotope fractionations that accompany the evaporation from the ocean and other surface waters and the reverse process of rain formation account for the most notable changes as a result meteoric waters are depleted in the heavy isotopic species of h and o relative to ocean waters whereas waters in evaporative systems such as lakes plants and soilwaters are relatively enriched during the passage through the aquifers the isotope composition of water is essentially a conservative property at ambient temperatures but at elevated temperatures interaction with the rock matrix may perturb the isotope composition these changes of the isotope composition in atmospheric waters surface water soil and groundwaters as well as in the biosphere are applied in the characterization of hydrological system as well as indicators of paleo climatological conditions in proxy materials in climatic archives such as ice lake sediments or organic materials

fish taphonomy and environmental inference in paleolimnology abstract the contribution of fish studies to palaeoecology generally takes the form of 1 inference from analogies in modern fish faunas and 2 fish taphonomy the pattern of death and dispersal of bones 1 modern fish faunas and associated organisms provide taxonomic ecological or functional analogues for interpretation of ancient limiting factors and behaviors these inferences presume taxonomic conservatism they also presume functional relationships between morphological form and feeding mode or habitat they become weak with increased geologic age or phyletic distance between ancient subject and modern anaogue 2 fish taphonomy may contribute information about limnology community composition life history mortality depositional environment and preservation taphonomic reconstruction of ecology and preservation depends on the applicability of analogous processes in modern ecology and l limnology in aquatic taphonomy temperature is the most important factor in determining the fate of a carcass above about 16 c depending on depth and pressure most carcasses are made buoyant by bacterial decay gases and are transported to the surface where they may decay further and fall piecemeal into deepwater environments or drift to beach environments where wave energy disarticulates abrades and scatters the bones below about 16 c most carcasses remain on the bottom until buried they may be disturbed by scavengers depending on oxygen concentration in the hypolimnion

taphonomic variations in eocene fish bearing varves at horsefly british columbia reveal 10 000 years of environmental change the eocene horsefly locality in british columbia has yielded many fossil fishes insects and plants its varved sediments make it ideal for study of temporal changes in environment and fish morphology several intervals of diatomaceous varves indicate a deep stratified lake setting earlier studies focused on morphological and taphonomic change during the 700 year h2 interval and morphological change during the 10 000 year h3 interval the present study uses taphonomy as an index for environmental change during the ten millennia represented by h3 comparing taphonomic changes with the morphologic changes found earlier the h3 interval records deposition in deep water indicated by dominance of the fish genera amyzon and eohiodon quiet water conditions are indicated by minimal fin disarticulation hypoxia at the time of fish death is confirmed by open mouths of most fish specimens while cool water on the lake floor prevented full flotation of fish carcasses water depth temperature and oxygenation fl

geomorphology within the interdisciplinary science of environmental flows article i nfo the field tradition in geomorphology informs beyond studying landforms by also providing a stage for understand ing how geomorphic elements influence the ecology of biota the intersection between fluvial geomorphology and riverine ecology represents an ideal confluence to examine the contribution of the geomorphic field tradition to en vironmental flows and show this area of riverine management as a research frontier for applied geomorphology environmental flows have consisted of a set of ecological based stream flow guidelines designed to inform sustain able water resource management that supports healthy riverine habitats and provides sufficient water supply for society geomorphological understanding is central to environmental flows because it is the interaction between flow form and substrate that influences habitat type condition availability and biotic use across space and time this relationship varies longitudinally laterally vertically overtime and across macro to mesoscale morphologies withintheriverine environment thegeomorphictemplateis therefore asintegralasthe flow wereviewedstudies where field evidence indicated that geomorphology impacts the effectiveness of environmental flow strategies and wemakethecasefortheneedtoincreasegeomorphic considerationsinenvironmental flows although flow iscom monly referred toas themaster variablein environmental flows geomorphologymediatestheeffectsof flow regime on ecological processes concepts and applications from this perspective on the role of geomorphology in riverine ecosystem research will inform the practice policy and implementation of environmental flows

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

water chemistry of lake quilotoa ecuador and assessment of natural hazards a geochemical survey carried out in november 1993 revealed that lake quilotoa was composed by a thin 14 m oxic epilimnion overlying a 200 m thick anoxic hypolimnion dissolved co2 concentrations reached 1000 mg kg in the lower stratum loss of co2 from epilimnetic waters followed by calcite precipitation and a consequent lowering in density was the apparent cause of the stratification the cl so4 and hco3 contents of lake quilotoa are intermediate between those of acid so4 cl crater lakes and those of neutral hco3 crater lakes indicating that lake quilotoa has a memory of the inflow and absorption of hc1 and s bearing volcanic magmatic gases the mg ca ratios of the lake waters are governed by dissolution of local volcanic rocks or magmas but k na ratios were likely modified by precipitation of alunite a typical mineral in acid so 4 cl crater lakes the constant concentrations of several conservative chemical species from lake surface to lake bottom suggest that physical chemical and biological processes did not have enough time after the last overturn to cause significant changes in the contents of these chemical species this lapse of time might be relatively large but it cannot be established on the basis of available data besides the lake may not be close to steady state mixing of lake quilotoa waters could presently be triggered by either cooling epilimnetic waters by 48c or providing heat to hypolimnetic waters or by seismic activity although quilotoa lake contains a huge amount of dissolved co2o 3 10 11 gu at present the risk of a dangerous limnic eruption seems to be nil even though some gas exsolution might occur if deep lake waters were brought to the surface carbon dioxide could build up to higher levels in deep waters than at present without any volcanic re awakening due to either a large inflow of relatively cool co 2 rich gases or possibly a long interval between overturns periodical geochemical surveys of lake quilotoa are therefore recommended q 2000 elsevier science b v all rights reserved

nearshore carbonate deposits in lake tanganyika an exceptionally wide variety of carbonate fades dominated by high magnesian calcite occurs along the littoral and shallow sublittoral zones 50 m of lake tanganyika in central africa these facies include exposed and submerged calcite cemented ridges of nearshore terrigenous sand ooid sand shoals and lithified oolite ridges chara meadows of bioturbated calcareous silts gastropod shell blankets and related coquinas and extensive thrombolitic microbial reefs though texturally and compositionally similar to many modern and ancient shallow water marine facies these deposits record carbonate deposition and cementation in a large tropical deep water lake of tectonic origin lithofacies along lake tanganyika represent the broadest spectrum of carbonate deposits yet reported from any modern lake and serve as important analogues for lacustrine carbonate sequences in the stratigraphic record

geochemistry of bazman thermal springs southeast iran abstract thermal springs of the bazman geothermal field 27 km south of the holocene bazman volcano caldera in makran continental margin se iran were studied for the first time new data on major components selected trace elements li rb cs ba sr fe al water isotopic composition h o and s chemical and isotopic 13c of co2 and ch4 3he 4he and 40ar 36ar composition of dissolved and bubbling gases from the hottest vents are presented four groups of springs with temperature range of 27 44 c discharge na cl waters with total dissolved solids tds of 800 to 7000 mg l from different aquifers composed of diverse type of rocks including granites and limestone only the hottest and most saline springs of the bazman field with low bicarbonate are close to equilibrium with surrounding rocks whereas the others discharge immature waters geothermometry based on sio2 concentrations na k and na k ca mg systems shows low equilibrium temperatures of up to 130 c consist with the temperatures estimated by alumino silicate minerals saturation indices the water isotopic composition 18o and d indicates meteoric origin with a small oxygen isotopic shift measured in the saline waters the 34s values of so4 indicate influence of gypsum and anhydrite dissolution from the host rock dissolved and free gases are n2 rich 95 vol with a high he content 0 5 vol a biogenic origin may be suggested for ch4 and co2 based on their carbon isotopic characteristics 62 and 13 vs v pdb respectively the r ra value of 0 5 indicates a contribution of about 6 of he from the mantle it is suggested that the bazman thermal waters are heated at considerable depth 4 5 km in a deep fault system most probably by the regional heat flow according to the local geothermal gradient

anaerobic oxidation of methane and sulfate reduction along the chilean continental margin anaerobic oxidation of methane aom and sulfate reduction sr were investigated in sediments of the chilean upwelling region at three stations between 800 and 3000 m water depth major goals of this study were to quantify and evaluate rates of aom and sr in a coastal marine upwelling system with high organic input to analyze the impact of aom on the methane budget and to determine the contribution of aom to sr within the sulfate methane transition zone smt furthermore we investigated the formation of authigenic carbonates correlated with aom we determined the vertical distribution of aom and sr activity methane sulfate sulfide ph total chlorins and a variety of other geochemical parameters depth integrated rates of aom within the smt were between 7 and 1124 mmol m 2 a 1 effectively removing methane below the sediment water interface single measurements revealed aom peaks of 2 to 51 nmol cm 3 d 1 with highest rates at the shallowest station 800 m the methane turnover was higher than in other diffusive systems of similar ocean depth this higher turnover was most likely due to elevated organic matter input in this upwelling region offering significant amounts of substrates for methanogenesis sr within the smt was mostly fuelled by methane aom led to the formation of isotopically light dic 13c 24 6 vpdb and of distinct layers of authigenic carbonates 13c 14 6 vpdb

lake level changes and hominin occupations in the arid turkana basin during volcanic closure of the omo river outflows to the indian ocean in the east african rift the western margin of lake turkana northern kenya exposes mio plio pleistocene lake sediments with dated volcanic horizons constraining basin dynamics at the astronomical time scale since the late pliocene coastal archaeological sites have formed within the lacustrine dynamics here lake levels are reconstructed from 2 4 to 1 7 ma using sedimentary facies and water depth controlled sediment association the lacustrine stratigraphy is measured with a total station and cyclostratigraphy is derived from tephrochronology the water depths are evaluated from paleochemical properties of lake sediments analyzed by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry our reconstruction highlights that lake turkana rose during 100 ka insolation eccentricity maxima periods in response to higher monsoonal inputs of the omo river however lake turkana also expanded through an insolation minimum at 2 17 1 95 ma this asynchronous lake phase coincides with volcanic closure of the omo river and lake turkana outflow sill to the east and the indian ocean an archaeological hiatus occurs during this endorheic lake phase and alkalinity increases at the beginning of the hiatus the lake rose again during insolation eccentricity maxima at 1 9 1 7 ma and a new outflow sill opened to the west and the nile basin hominin coastal occupations return during this exorheic freshwater lake phase

topographic control on distribution of modern microbially induced sedimentary structures miss a case study from texas coast abstract modern back barrier tidal flats of galveston island follets island and matagorda peninsula of the texas coast are dominated by mud to fine sand sized siliciclastic sediments and prolific microbial mats these microbial mats modify sediment behavior and result in a variety of microbially induced sedimentary structures miss common structures include knobby surfaces reticulated surfaces gas domes mat cracks sieve like surfaces erosional pockets wrinkles and mat chips in general mat thicknesses increase from 1 mm in the upper supratidal to 3 cm maximum in the lower supratidal and then decrease to 2 mm in the lower intertidal areas this same wedge shaped pattern is displayed by detailed measurements of mat thicknesses from the rims into the deeper centers of depressions pools on the supratidal flats measurements of 175 mat cracks show that height of the curled edges of the mat crack polygons increases with increase in mat thickness similarly measurements of 150 gas domes reveal that the size of the gas domes also increases with increasing thickness of the associated mats because mat thickness varies with elevation on the tidal flat curl height of the mat cracks and size of the gas domes are also related to elevation six zones were identified based on the occurrence of miss within the supratidal zone i to upper subtidal zone vi areas at the highest elevation knobby surfaces characterize zone i whereas zone ii is defined by reticulated surfaces along with reticulated surfaces gas domes and mat cracks characterize zone iii and zone iv respectively association of sieve like surfaces with mat cracks typifies zone v whereas mat deformation structures and sieve like surfaces define zone vi boundaries between the miss zones in general are parallel and related to tidal zones the distribution patterns of the miss zones are strongly controlled by local topography of the sediment surface because the degree of inundation is the primary controlling factor for the mat growth and resultant miss therefore distribution of the microbially induced sedimentary structures in siliciclastics along with the dimension of the mat cracks and gas domes can be potentially helpful in interpretation of topography of paleodepositional surfaces

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

palaeosols of the lower jurassic mishhor and ardon formations laterite derivative facies makhtesh ramon israel the lower jurassic sequence exposed at makhtesh ramon in the south western negev of israel comprises cyclic fluviatile sediments derived almost exclusively from the reworking of an older laterite terrain a succession of palaeosols having the characteristics of modern red brown earths has developed during periods of sub aerial exposure upon the fine grained overbank sediments a marked seasonal palaeoclimate with accompanying poor sub surface drainage conditions and some stagnation of ground water is reflected by the distribution and mottling patterns of the iron minerals with varying degrees of hydration precipitation of illuviated carbonate and sulphate minerals and the development of soil microrelief a complex history of pedogenesis and ground water alteration is shown by the rapid lateral facies change within this sequence into one dominated by high alumina flint clay and bauxite relict pedogenetic and sedimentological textural features of the combined palaeosol fluviatile sequence have been identified and mapped within the flint clay bauxite lithologies these features include irregular voids produced by solution of pedogenic sulphate nodules slickensided curviplanar surfaces of soil microrelief and depositional bedding the field relationships of these relicts indicate the overprinting of a younger chemical weathering event giving rise to the high alumina flint clay and bauxites the geometric shape of the upper bounding surface of the bauxite alteration zone is irregular and has an intrusive character with respect to the younger overlying unaltered sediments this together with abrupt changes in mottling patterns near the contact zone and subtle changes in mineralogy from a bauxitic assemblage at depth to one containing mixed layer clay minerals and carbonates nearer the contact leads to the conclusion that the later stages of chemical weathering occurred within a confined system where ground water movements were induced by intake of underlying aquifers

extreme events in the sedimentary record of maar lake pavin implications for natural hazards assessment in the french massif central a set of sedimentary cores high resolution swath bathymetry and subbottom profiler data provides new insights on sedimentary processes in meromictic maar lake pavin france three sedimentary environments i e littoral plateau and basin have been identified in the lake from sediment composition using bulk organic geochemistry and the analysis of hydroacoustic images various forms of rapidly deposited layers rdls have been identified and radiocarbon dated an up to date stratigraphy of sedimentary events matching coeval rdls across the lake is presented and illustrates a wide range of natural hazards linked to lake pavin during the last 2000 years in ad 600 a sudden lake outburst triggered a slump deposit along with a 9 m lake level drop that drove shifts in sedimentary organic matter composition outside the lake outburst flood deposits have been described downstream and provide sedimentary evidence for this event the lake level drop also favored the generation of gravity reworking processes as shown by 1 a regional earthquake triggered large slope failure on the plateau connected to a masswasting deposit in the basin dated to ad 1300 and 2 a succession of turbidites in ad 1825 and ad 1860 contemporaneous to two historic earthquakes suggesting that this lake is sensitive to earthquakes with a minimum epicentral intensity of v finally past observations of lake water color changes in ad 1783 and ad 1936 similar to reports in other meromictic lakes match iron rich deposits identified in maar lake sediments and suggest that lake pavin could have undergone limnic eruptions

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

recent channel adjustments in alluvial rivers of tuscany central italy drastic channel adjustments have affected the main alluvial rivers of tuscany central italy during the 20th century bed level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations changes in channel width were investigated by comparing available aerial photographs 1954 and 1993 98 bed incision represents the dominant type of vertical adjustment and is generalized along all the fluvial systems investigated the arno river system is the most affected by bed level lowering up to 9 m whereas lower incision generally less than 2 m is observed along the rivers of the southern part of the region human disturbances appear to be the dominant factors of adjustments the main phase of vertical change occurred during the period 1945 80 in concomitance with the phase of maximum sediment mining activity at the regional scale the second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel based on measurements of channel width conducted on aerial photographs 38 of the reaches analysed experienced a narrowing greater than 50 of the initial channel width the largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region a regional scheme of channel adjustments is derived based on initial channel morphology and on the amounts of incision and narrowing different styles of channel adjustments are described rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing in contrast sinuous meandering channels mainly adjusted vertically with a minor amount of narrowing copyright 2003 john wiley sons ltd

geochemical insight into differences in the physical structures and dynamics of two adjacent maar lakes at mt vulture volcano southern italy 1 we report on the first geochemical investigation of the monticchio maar lakes mt vulture volcano southern italy covering an annual cycle that aimed at understanding the characteristic features of the physical structures and dynamics of the two lakes we provide the first detailed description of the lakes based on high resolution conductivity temperature depth ctd profiles chemical and isotopic h and o compositions of the water and the amounts of dissolved gases e g he ar ch4 and co2 the combined data set reveals that the two lakes which are separated by less than 200 m exhibit different dynamics one is a meromictic lake where the waters are rich in biogenic and mantle derived gases while the other is a monomictic lake which exhibits complete turnover of the water in winter and the release of dissolved gases our data strongly suggest that the differences in the dynamics of the two lakes are due to different density profiles affected by dissolved solutes mainly fe which is strongly enriched in the deep water of the meromictic lake a conceptual model of water balance was constructed based on the correlation between the chemical composition of the water and the hydrogen isotopic signature gas rich groundwaters that feed both of the lakes and evaporation processes subsequently modify the water chemistry of the lakes our data highlight that no further potential hazardous accumulation of lethal gases is expected at the monticchio lakes nevertheless geochemical monitoring is needed to prevent the possibility of vigorous gas releases that have previously occurred in historical time

possible indicators of microbial mat deposits in shales and sandstones examples from the mid proterozoic belt supergroup montana u s a abstract it has been suspected for some time that microbial mats probably colonized sediment surfaces in many terrigenous clastic sedimentary environments during the proterozoic however domination of mat morphology by depositional processes post depositional compaction and poor potential for cellular preservation of mat building organisms make their positive identification a formidable challenge within terrigenous clastics of the mid proterozoic belt supergroup a variety of sedimentary structures and textural features have been observed that can be interpreted as the result of microbial colonization of sediment surfaces among these are a domal buildups resembling stromatolites in carbonates b cohesive behaviour of laminae during soft sediment deformation erosion and transport c wavy crinkly character of laminae d bed surfaces with pustular wrinkled appearance e rippled patches on otherwise smooth surfaces f laminae with mica enrichment and or randomly oriented micas g irregular curved wrinkled impressions on bedding planes h uparched laminae near mud cracks resembling growth ridges of polygonal stromatolites and i lamina specific distribution of certain early diagenetic minerals dolomite ferroan carbonates pyrite although in none of the described examples can it irrefutably be proven that they are microbial mat deposits the observed features are consistent with such an interpretation and should be considered indicators of possible microbial mat presence in other proterozoic sequences

chemical and isotopic compositions of minerals and waters from the campi flegrei volcanic system naples italy abstract based on their 34 s signature sulfate minerals and native sulfur around fumaroles and hot water pools from the campi flegrei volcanic area derive from supergenic oxidation of volcanic h 2 s their mean 34 s value 0 2 1 7 matches with that of fumarolic h 2 s at solfatara 0 3 0 3 as well as with the 34 s of 1 4 obtained for total sulfur in fresh trachyte from the area all 34 s values indicate a mostly deep seated origin for sulfur thermal waters were analysed for major and minor chemistry and for oxygen hydrogen and sulfur isotope compositions pools at pisciarelli are filled with evaporated meteoric water heated by rising magmatic gases the water 18 o 3 8 1 3 and 2 h 6 5 2 2 values in these steam heated waters are controlled by mixing and evaporation effects and the 34 s value of dissolved sulfate 1 3 0 3 basically agrees with supergenic oxidation of deep seated h 2 s as the major source of sulfur instead water from thermal springs and wells elsewhere in the campi flegrei appears to be a mixture between dilute meteoric and saline marine components the latter may be local seawater from the bay of pozzuoli the 18 o and 2 h values of waters sampled during 1993 1994 range from 5 6 to 0 3 and from 33 to 3 4 respectively the 34 s values of dissolved sulfate range between 0 1 and 19 5 in general sulfate is probably derived essentially from two sources both within the volcanic cover i e oxidation dissolution of pyrite and anhydrite and marine water an occasional source of water and sulfate is represented by magmatic gases which directly interact with shallow meteoric water as in the case of the hotel tennis well yielding steam heated water with 18 o 1 5 0 2 2 h 17 1 and 34 s 0 1

taphonomy of insects in carbonates and amber abstract the major taphonomic processes that control insect preservation in carbonate rocks limestones travertines and nodules are biological insect size and wingspan degree of decomposition presence of microbial mats predation and scavenging environmental water surface tension water temperature density and salinity current activity and diagenetic authigenic mineralisation flattening deformation carbonisation the major taphonomic processes that control the preservation of insects in fossil resins amber and copal are different but can be considered under the same headings biological presence of resin producers size and behaviour of insects environmental latitude climate seasonality resin viscosity effects of storms and fires soil composition and diagenetic resin composition insect dehydration pressure carbonisation thermal maturation reworking oxidation these taphonomic processes are geographically and temporally restricted and generate biases in the fossil record nevertheless where insects occur they may be abundant and very diverse taphonomic processes may impact on phylogenetic and palaeobiogeographic studies in determining the timing of the origin and extinction of insect groups and in identifying radiations and major extinctions taphonomic studies are an essential prerequisite to the reconstruction of fossil insect assemblages to interpreting the sedimentary and environmental conditions where insects lived and died and to the investigation of interactions between insects and other organisms

paleocene lakes of the central rocky mountains western united states abstract lacustrine environments are well developed in the paleocene to early eocene sedimentary sequences in the intermontane basins of the central rocky mountains the available evidence points toward a widespread episode of lake formation in the middle late paleocene torrejonian tiffanian followed by a second major period during the latest paleocene to early eocene clarkforkian wasatchian the earlier period of lake formation is dominated by relatively shallow although often areally extensive freshwater lakes associated with fluvial and paludal environments in basins in northern wyoming and montana a high clastic input prevailed thich mudstone often structureless marks the deep water facies of these lakes with tabular sandstone lenticular carbonate and lignite occurring along the fluviodeltaic margins farther south and west in colorado and wyoming alkaline lakes dominated by carbonate deposition were prevalent the appearance and disappearance of standing water in both northern and southern basins may be more closely controlled by tectonics than by climate most evidence points toward prevailing humid sub tropical conditions until the very end of the paleocene

taphonomic analysis of fish in rift lacustrine systems environmental indicators and implications for fish speciation abstract two rift basin lacustrine successions cacheuta and los rastros formations in the middle triassic of argentina were studied to test two different hypotheses 1 fish taphonomy is useful as an indicator of environmental conditions for these two paleolakes and 2 fish taphonomy is useful for understanding environmental effects on speciation the fish fossils are found in two lacustrine deposits as isolated and disarticulated scales and cranial bones clumps and stringers of scales articulated body segments and complete specimens four taphofacies are defined for cacheuta specimens ca a to ca d and three taphofacies are defined for los rastros fish assemblages lr a to lr c a principal components analysis was performed with the taphonomic features supporting the seven taphofacies defined a taphonomic model is proposed that characterizes a lacustrine deltaic environment developed in the rift basin and identifies three sub environments each one with its particular fossil assemblages the fish assemblages in the los rastros formation suggest that the fishes preserved in delta front and turbidity current deposits lr b and lr c taphofacies were allochthonous to the lake and probably inhabited the delta plains and affluent fluvial system in contrast the isolated fish remains preserved in open lake deposits lr a taphofacies likely represent both autochthonous and or allochthonous specimens in the cacheuta formation articulated and isolated fish remains preserved in open lake deposits ca a and ca d tafofacies might represent autochthonous lacustrine specimens based on the good preservation of the material the fish remains preserved in underflow and turbidity current deposits ca b and ca c taphofacies were allochthonous to the lake and probably inhabited the delta plain and affluent fluvial system the fish taphonomic study of two different rift basin lacustrine successions allows test of the two proposed hypotheses fish taphonomy was useful as an indicator of environmental conditions beacuse the differences in fish preservation allowed differentiation of the sub environments and reconstruction of the environmental conditions and dynamics of the rift lake basins also fish taphonomy was useful for understanding environmental effects on speciation by characterizing the environments and dynamics that promote the development of new fish species recognizing fish inhabited environments and identifying the generalist and specialist species

exploratory flow duct experiments on combined flow bed configurations and some implications for interpreting storm event stratification abstract experiments were conducted to define equilibrium combined flow bed configurations developed under a wide range of oscillatory uo and unidirectional uu velocity components with a constant oscillation period of 8 5 sec and median grain size of 0 09 mm in the range of flows studied uo 0 0 80 m sec uu 0 0 25 m sec the bed phases are no movement small 2d ripples small 3d ripples large 3d ripples and plane bed small 2d ripples are stable at low uo and uu by increasing either velocity component the plan view bed configuration becomes progressively less regular as small 3d ripples develop small 3d ripples are stable at low to moderate uo and a wide r nge of uu under purely oscillatory flow as uo increases beyond about 0 40 m sec large scale hummocky bed forms become stable when a unidirectional component is applied these bed forms quickly develop a downstream asymmetry and generally move in the direction of uu the dip angles of the lee flanks increase with increasing uu although they remain less than the angle of repose at high oscillatory velocities uo 0 70 0 80 m sec plane bed is the stable bed phase when uu 0 05 m sec much hummocky cross stratification shows a preferred dip direction of the coset laminae our experiments support the idea that such cross stratification is produced by combined flow the large 3d ripples produced at high oscillatory velocities and small to moderate unidirectional velocities would presumably generate what might be called anisotropic hummocky cross stratification if we had been able to aggrade the bed during the runs this would be the case even in dominantly oscillatory flow the experiments show that even a weak unidirectional current of several centimeters per second superimposed upon a strong oscillatory flow results in bed forms that move predominantly in a single direction and that leave sets of laminae that dip predominantly in that direction in runs at large uo the purely oscillatory large scale bed forms were quickly planed off as uu was increased from zero but a series of almost stationary gentle undulations on the bed surface persisted for indefinitely long times where the original topographic highs were situated even at the highest unidirectional flow investigated 0 25 m sec this suggests a possible origin for the gentle undulation observed in cretaceous parallel laminated shallow marine sandstones described by arnott 1987 1988 with spacings up to a few meters and heights not much more than a centimeter

geochemical monitoring of the thermal waters of the phlegraean fields abstract thermal waters from the phlegraean fields pf caldera area have been periodically sampled and analysed during the period 1990 1999 for major chemical constituents and chemico physical parameters to define the most useful variables for geochemical surveillance the variations observed in waters from different locations were compared with ground movements and microseismic events recorded at the time of observation the discontinuous monitoring of the hydrothermal system of the pf has given indications about the geochemical variations brought about by changes in the chemical and physical characteristics of the deep aquifers because of the complexity of the pf geothermal system in each sampling location different variations have been observed and then evaluated on the basis of the different kinds and degrees of deep fluid supply characterising waters sampled in the different zones in some cases a good correspondence between vertical soil movements and chemical changes in the waters has been observed in particular in pools and wells located around the solfatara crater interesting variations in some chemical parameters ph ammonia and or so 4 2 cl ratios have been recorded variations can be observed in all of the sampling locations but pools and wells located near the solfatara crater are the best sites for detecting changes occurring in the deep hydrothermal system and possibly in the activity of the underlying magma chamber

skeletal halites from the jurassic of massachusetts and their significance pseudomorphs after skeletal halite occur in a bed of lower jurassic lacustrine shale at holyoke massachusetts the pseudomorphs include pagoda types similar to those described by southgate and show dissolution furrows however the shales were deposited in a permanently subaqueous rather than an emergent environment and the pseudomorphs accordingly grew in brine saturated sediment evaporation to dryness is not therefore essential to the genesis of skeletal halite

time dependent co2 variations in lake albano associated with seismic activity lake albano alban hills volcanic complex central italy is located in a densely populated area near rome the deep lake waters have significant dissolved co2 concentrations probably related to sub lacustrine fluid discharges fed by a pressurized co2 rich reservoir the analytical results of geochemical surveys carried out in 1989 2010 highlight the episodes of co2 removal from the lake the total mass of dissolved co2 decreased from 5 8 107 kg in 1989 to 0 5 107 kg in 2010 following an exponential decreasing trend calculated values of both dissolved inorganic carbon and co2 concentrations along the vertical profile of the lake indicate that this decrease is caused by co2 release from the epilimnion at depth 9 m combined with 1 water circulation at depth 95 m and 2 co2 diffusion from the deeper lake layers according to this model lake albano was affected by a large co2 input that coincided with the last important seismic swarm at alban hills in 1989 suggesting an intimate relationship between the addition of deep originated co2 to the lake and seismic activity in the case of a co2 degassing event of an order of magnitude larger than the one that occurred in 1989 the deepest part of lake albano would become co2 saturated resulting in conditions compatible with the occurrence of a gas outburst these results reinforce the idea that a sudden co2 input into the lake may cause the release of a dense gas cloud presently representing the major volcanic threat for this densely populated area

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

paleolimnology and taphonomy of some fish deposits in fossil and uinta lakes of the eocene green river formation utah and wyoming abstract in four sections in the lacustrine eocene green river formation in utah lake uinta fish are preserved on carbonate mudflats along high energy carbonate shorelines in the littoral zone and in deeper profundal areas scattered bones and scales are found throughout dropped from disintegrating floating carcasses gar scales typify shallow water deposits partly due to habitat preference beach concentrations of greatly abraded bones and scales grade offshore into storm lag layers and lenses which grade to loosely packed horizons or patches of unworn remains littoral fish fossils range from dropped bones to good skeletons with much floating lifting and scavenging preservation improves away from the waterline not only into deep and cold profundal waters where the carcasses are protected from scavenging by anoxia and prevented from floating by temperature and pressure but also onto mudflats where stranding and burial of carcasses can also protect them a section through an isolated part of the green river formation in wyoming fossil lake also ranged from profundal to littoral with minor emergence dropped body parts were found throughout but preservation quality of the best specimens improved with presumed depth the beds with the best specimens seem to have accumulated at the bottom of a deep stratified warm monomictic lake our lake uinta sections were generally shallower and suggest more fluctuations in water level but this is not relevant to broad paleolimnological interpretations because they represent marginal zones which are necessarily more sensitive to changes in depth overall fish fossils are especially informative in deeper waters where sedimentary distinctions fail

dams and geomorphology research progress and future directions dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river these changes have been described for more than 50 years but process form relationships have only been advanced with the establishment of a conceptual framework during the 1970s and then the extension of monitoring data and advancement of remote sensing technologies particularly over the past 20 years this paper reviews these developments and identifies three influential themes i channel dynamics ii the role of riparian vegetation and iii channel change as the driver of ecological change changes can be rapid in semi arid regions but elsewhere relaxation periods may extend to millenia in these latter cases regime or steady state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales

comparison of historical and modern river surveys reveal changes to waterhole characteristics in an australian dryland river abstract human activities are known to impact the physical template of river channels these impacts can result from deliberate direct modifications as well as via indirect processes linked to broadscale landscape change this study examined changes in the physical template of the barwon darling river a dryland river in southeastern australia historical longitudinal profiles from the late 1800s were compared with contemporary profiles derived from high definition side scanning sonar comparisons focused on characterising waterhole features as they are a critical biophysical component of dryland rivers the use of historical data presented several challenges related to small sample size and suspected sampling bias in the historical survey however this study demonstrates that these issues are not insurmountable providing the limitations and uncertainties with the data are acknowledged and data analyses are limited to parameters that can distinguish genuine landscape change the findings revealed a dramatic change in the physical template of the barwon darling river over a 120 yr period waterhole depths and distances between waterholes have been altered significantly the magnitude and trajectory of change was found to be scale dependent with the greatest observable change aligned with the presence or absence of low level weirs waterholes influenced by low level weirs have increased in depth because of localised impoundment whilst the distance between deep waterholes 4 m in depth has declined substantially in contrast the maximum depths of waterholes located outside the influence of weir pools has declined by 1 6 m and the distance between deep waterholes has more than doubled in several reaches these declines are likely to be caused by sediment accumulation in waterholes associated with anthropogenic increases in sediment flux and a decline in the river s capacity to entrain and transport sediment throughout the system

flow and form in rehabilitation of large river ecosystems an example from the lower missouri river abstract on large intensively engineered rivers like the lower missouri the template of the physical habitat is determined by the nearly independent interaction of channel form and flow regime we evaluated the interaction between flow and form by modeling four combinations of modern and historical channel form and modern and historical flow regimes the analysis used shallow slow water shallow water habitat swh defined as depths between 0 and 1 5 m and current velocities between 0 and 0 75 m s as an indicator of habitat that has been lost on many intensively engineered rivers and one that is thought to be especially important in rearing of young fishes two dimensional hydrodynamic models for modern and historical channels of the lower missouri river at hermann missouri indicate substantial differences between the two channels in total availability and spatial characteristics of swh in the modern channel swh is maximized at extremely low flows and in overbank flows whereas the historical channel had substantially more swh at all discharges and swh increased with increasing discharge the historical channel form produced 3 7 times the swh area of the modern channel regardless of flow regime the effect of flow regime is evident in increased within year swh variability with the natural flow regime including significant seasonal peaks of swh associated with spring flooding comparison with other reaches along the lower missouri river indicates that a channel form is the dominant control of the availability of habitat even in reaches where the hydrograph is more intensively altered and b rehabilitation projects that move toward the historical condition can be successful in increasing topographic diversity and thereby decreasing sensitivity of the availability of habitat to flow regime the relative efficacy of managing flow and form in creating swh is useful information toward achieving socially acceptable rehabilitation of the ecosystem in large river systems

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

water and dissolved gas geochemistry at coatepeque ilopango and chanmico volcanic lakes el salvador central america abstract coatepeque on the e slope of santa ana volcano ilopango inside ilopango caldera and chanmico associated with san salvador volcano are volcanic lakes in el salvador showing a thermocline at a relatively shallow depth from 30 to 40 m from 20 to 40 m and from 5 to 15 m depth respectively and anoxic conditions below 33 24 and 4 m depth respectively the na cl composition of the coatepeque and ilopango lakes displaying tds values up to 1226 and 1216 mg l respectively is likely due to hydrothermal fluids that feed these two lakes as also confirmed by cl br molar ratios 650 high as b li and si contents and cl so42 ratio 1 the mg2 hco3 water composition of lake chanmico whose tds values were between 566 and 856 mg l suggests water rock interaction processes with mafic ultramafic rocks variably affected by serpentinization processes which produced high mg2 si and b concentrations waters at depth were characterized by the presence of co2 from an extra lacustrine source as suggested by 13c co2 values significantly less negative than those typically related to biogenic processes albeit this gas was found in smaller quantities when compared to those recorded in other meromictic lakes hosted in quiescent volcanic systems e g lake kivu in drc monticchio albano and averno lakes in italy hule and rio cuarto lakes in costa rica lake pavin in france the occurrence of ch4 whose concentrations in lake chanmico were up to two orders of magnitude higher than those recorded in coatepeque and ilopango lakes suggests bacterial methanogenesis

geochemical and biochemical evidence of lake overturn and fish kill at lake averno italy abstract lake averno is situated in the homonymous crater in the northwestern sector of the campi flegrei active volcanic system in campania region italy in february 2005 a fish kill event was observed in the lake prompting a geochemical survey to ascertain the possible cause in february 2005 a geochemical survey revealed that the lake water was unstratified chemically and isotopically presumably as a result of lake overturn this fish kill phenomenon was recorded at least two other times in the past in contrast to the february 2005 results data collected in october 2005 shows the lake averno to be stratified with an oxic epilimnion surface to 6 m and an anoxic hypolimnion 6 m to lake bottom at about 33 m chemical and isotopic compositions of lake averno waters suggest an origin by mixing of shallow waters with a na cl hydrothermal component coupled with an active evaporation process the isotopic composition of dissolved inorganic carbon as well as the composition of the non reactive dissolved gas species again supports the occurrence of this mixing process decreasing levels of so 4 and increasing levels of h 2 s and ch 4 contents in lake water with depth strongly suggests anaerobic bacterial processes are occurring through decomposition of organic matter under anoxic conditions in the sediment and in the water column sulfate reduction and methanogenesis processes coexist and play a pivotal role in the anaerobic environment of the lake averno the sulfate reducing bacterial activity has been estimated in the range of 14 22 mol m 2 day 1 total gas pressure of dissolved gases ranges between 800 and 1400 mbar well below the hydrostatic pressure throughout the water column excluding the possibility at least at the survey time of a limnic eruption vertical changes in the density of lake waters indicate that overturn may be triggered by cooling of epilimnetic waters below 7 c this is a possible phenomenon in winter periods if atmospheric temperatures remain frosty for enough time as occurred in february 2005 the bulk of these results strongly support the hypothesis that fish kill was caused by a series of events that began with the cooling of the epilimnetic waters with breaking of the thermal stratification followed by lake overturn and the rise of toxic levels of h 2 s from the reduced waters near the lake bottom

source processes of the thermal waters from the phlegraean fields naples italy by means of the study of selected minor and trace elements distribution abstract the geochemical characteristics of hydrothermal waters from the phlegraean fields p f naples italy were analysed for minor and trace elements selectively mobilised in hydrothermal systems such as b f hg as pb and tl the water samples collected from a shallow aquifer likely to be fed by deeper fluids showed various geochemical features resulting from the mixing of three components 1 surface waters of meteoric origin 2 hot deep waters deriving from water rock interaction and including deep waters of marine origin 3 magmatic fluids rising from the local magma chamber lying a few kilometres below the town of pozzuoli this setting although very complex provides a reliable means of studying the distribution of the investigated trace elements in particular within the phlegraean area high contents of b 0 1 48 mg l f 0 5 8 mg l as 16 6050 g l and hg 0 7 232 g l were observed the levels of thallium in the springs close to solfatara about 7 g l were in line with those normally recorded in hydrothermal areas whereas high levels of this element up to 23 3 g l were identified in other wells of the study area lead 1 3 to 29 1 g l appears to be anomalous with respect to its normal content in groundwater about 1 g l owing to the presence of high density brines at depth which enhance the solubility of pb in volcanic rocks under hydrothermal conditions the distribution of the investigated trace elements in the phlegraean fields thermal area is probably related to the different ascent pathways of the fluids clearly apart from the influence exerted by anomalous thermal conditions each element shows a different behaviour depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values which determine ion partitioning in gaseous phases based on geochemical evidences and on the distribution of minor and trace elements the source processes of the investigated hydrothermal waters were defined five main groups were identified 1 acid sulphate waters resulting from mixing of meteoric water with magmatic gases mainly h 2 s 2 high sulphate chloride waters from a deep reservoir located in the major upflow zone 3 waters associated with significant degassing of magmatic co 2 4 waters from a deep geothermal neutral chloride reservoir resulting from heating of marine water modified by water rock interaction processes 5 cold waters from the inner area influenced by low temperature water rock interaction processes

biological and sedimentary facies of australian salt lakes abstract four main types of salt lakes are recognized in australian 1 large playa lakes 2 small closed lakes or pans 3 crater lakes and 4 coastal lakes not connected to the sea basically all have an nacl chemistry biological and sedimentary facies characteristic of these salt lakes can be arranged into three basic groups which relate to particular phases in lake regimes these phases are 1 wet phases of ephemeral shallow lakes 2 dry lakes and 3 deep water lakes all elements of the salt lake biota with fossilizable remains are discussed with a detailed account of the palaeo ecological information they offer elements of the nonaquatic biota associated with salt lake sediments are also analysed sedimentary features of australian salt lakes pertinent to palaeoecology are discussed in the context of their association with the biota using numerous illustrations the distribution of the biota on lake floors for example its concentration in particular areas of the lake or its destruction during particular episodes such as lake filling and drying is mentioned in the context of recognizing different facies three major lake regime phases are presented with emphasis on the biological and sedimentary facies which characterize them the paper concludes with a brief discussion of the relevance of recognizing particular salt lake facies and changes in lake histories for the study of palaeoclimates and for mineral and oil exploration

quantitative filling model for continental extensional basins with applications to early mesozoic rifts of eastern north america in many half graben strata progressively onlap the hanging wall block of the basins indicating that both the basins and their depositional surface areas were growing in size through time based on these constraints we have constructed a quantitative model for the stratigraphic evolution of extensional basins with the simplifying assumptions of constant volume input of sediments and water per unit time as well as a uniform subsidence rate and a fixed outlet level the model predicts 1 a transition from fluvial to lacustrine deposition 2 systematically decreasing accumulation rates in lacustrine strata and 3 a rapid increase in lake depth after the onset of lacustrine deposition followed by a systematic decrease when parameterized for the early mesozoic basins of eastern north america the model s predictions match trends observed in late triassic age rocks significant deviations from the model s predictions occur in early jurassic age strata in which markedly higher accumulation rates and greater lake depths point to an increased extension rate that led to increased asymmetry in these half graben the model makes it possible to extract from the sedimentary record those events in the history of an extensional basin that are due solely to the filling of a basin growing in size through time and those that are due to changes in tectonics climate or sediment and water budgets

mantle co2 degassing at mt vulture volcano italy relationship between co2 outgassing of volcanoes and the time of their last eruption abstract mantle volatiles are mainly lost from the earth to the atmosphere through subaerial and submarine volcanism recent studies have shown that degassing of mantle volatiles also occurs from inactive volcanic areas and in tectonically active areas a new challenge in earth science is to quantify the mantle derived flux of volatiles e g co2 which is important for understanding such diverse issues as the evolution of the atmosphere the relationships between magma degassing and volcanic activity gas pressure and seismogenic processes and the hazards posed by volcanic lakes here we present a detailed study of mantle derived co2 budget from mt vulture volcano in the apennines italy whose latest eruption occurred 141 11 kyr ago the relationship between 13cco2 and total dissolved carbon at mt vulture volcano indicates that the emitted co2 is a mixture of a biogenic end member with an average 13cco2 of about 17 and a mantle derived co2 end member with 13cco2 values from 3 to 2 these values of mantle derived 13cco2 are in the range of those for gas emitted from active volcanoes in the mediterranean we calculated the contribution of individual components co2 in groundwater in lakes and from main pools to the total co2 budget in the area we used new measurements of water flow combined with literature data to calculate the co2 flux associated with groundwater and measured the gas flux from the main pools on the volcanic edifice finally we calculated the co2 flow in the lakes based on the gradient concentration and eddy diffusivity the total mantle derived co2 budget in the area is 4 85 10 8 mol yr 1 which is more than double previous estimates this is higher than those observed in younger volcanic systems elsewhere thereby supporting the existence of actively degassing mantle melts below mt vulture volcano a structural map highlights the tectonic control on co2 flow across the mt vulture volcanic edifice indeed the tectonic discontinuities that controlled the magma upwelling during the most recent volcanic activity are still the main active degassing structures the new estimate of co2 budget in the mt vulture area together with literature data on co2 budget from historically active and inactive italian volcanoes suggests a power law functional relationship between the age of the most recent volcanic eruption and both total discharged co2 r 2 0 73 and volcano size normalized co2 flux r 2 0 66 this relation is also valid by using data from worldwide volcanoes highlighting that deep degassing can occur over very long time too in turn the highlighted relation provides also an important tool to better evaluate the state of activity of a volcano whose last activity occurred far in time finally our study highlights that in the southern apennines an active degassing of mantle derived volatiles i e he co2 occurs indiscriminately from west to east this is in contrast to the central northern apennine which is characterized by a crustal radiogenic volatile contribution which increases eastward coupled to a decrease in deep co2 flux this difference between the two regions is probably due to lithospheric tears which control the upwelling of mantle melts their degassing and the transport of volatiles through the crust

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

controlled excavations in the pesciara and monte postale sites provide new insights about the palaeoecology and taphonomy of the fish assemblages of the eocene bolca konservat lagerstatte italy abstract the eocene konservat lagerstatte of bolca italy is famous for the abundance and exquisite preservation of its fossils although the bolca sites have provided one of the most studied ichthyofaunistic fossil assemblages of the world several aspects about the community structure and the biostratinomic processes that led to the accumulation of its fish remains have been neglected or underestimated in order to improve our knowledge concerning the palaeoecology and palaeoenvironment of bolca a quantitative palaeoecological and taphonomic analysis of the fish remains collected during controlled excavations at the pesciara and monte postale sites is presented herein the results of these analyses concur to suggest that these two sites have different speciose fish assemblages and different depositional contexts the high quality preservation of the fishes from the pesciara site has allowed for the species level identification of most of its specimens providing a good resolution of its palaeoecological spectrum the pesciara fish assemblage is defined by a sharp oligarchic structure clearly dominated by planktivorous taxa the taphonomic features confirm that the sediments were deposited in an intraplatform basin in which anoxic conditions at the bottom and the development of the biofilm acted as promoters of high quality fossil preservation on the other hand the moderate preservation quality of the fishes from monte postale does not allow for most of the specimens to be identified at the genus or species level making it difficult to interpret the ecological and trophic relationships within this assemblage nevertheless the abundance of marine and terrestrial plants coupled with the large number of invertebrates including abundant corals concur to suggest that the sediments of monte postale were likely deposited close to an emerged coastal area characterized by mangroves seagrass and coral reefs the prominent disgregation of fish skeletons coupled with the unimodal dispersion of the elements and bioturbations clearly indicate a high degree of disturbance in the monte postale palaeoenvironment suggesting at least periodic aerobic conditions at the bottom

the stable isotope geochemistry of volcanic lakes with examples from indonesia abstract stable isotope compositions d 18o and 34s of volcanic lake waters gas condensates and spring waters from indonesia italy japan and russia were measured the spring fluids and gas samples plot in a broad array between meteoric waters and local high temperature volcanic gas compositions the d and 18o data from volcanic lakes in east indonesia plot in a concave band ranging from local meteoric waters to evaporated fluids to waters heavier than local high temperature volcanic gases we investigated isotopic fractionation processes in volcanic lakes at elevated temperatures with simultaneous mixing of meteoric waters and volcanic gases an elevated lake water temperature gives enhanced kinetic isotope fractionation and changes in equilibrium fractionation factors providing relatively flat isotope evolution curves in 18o d diagrams a numerical simulation model is used to derive the timescales of isotopic evolution of crater lakes as a function of atmospheric parameters lake water temperature and fluxes of meteoric water volcanic gas input evaporation and seepage losses the same model is used to derive the flux magnitude of the keli mutu lakes in indonesia the calculated volcanic gas fluxes are of the same order as those derived from energy budget models or direct gas flux measurements in open craters several 100 m3 volcanic water day and indicate a water residence time of 1 2 decades the 34s data from the keli mutu lakes show a much wider range than those from gases and springs which is probably related to the precipitation of sulfur in these acid brine lakes the isotopic mass balance and s cl values suggest that about half of the sulfur input in the hottest keli mutu lake is converted into native sulfur

toward a model for open and closed basin deposition in ancient lacustrine sequences the newark supergroup triassic jurassic eastern north america abstract climate and tectonics have a profound influence on the lacustrine sedimentary record because they affect hydrologic systems in depositional basins lakes in hydrologically closed basins tend to fluctuate in depth producing transgressive regressive sequences sometimes associated with evaporites lakes in hydrologically open basins tend to have stable shorelines producing thick sedimentary deposits that lack transgressive regressive sequences and evaporites in addition some lakes fluctuate between open and closed producing transgressive regressive sequences in which deep water sediments were deposited when the lake was overflowing and shallow water sediments capped by subaerial exposure surfaces were deposited when the basin was closed lacustrine deposits in the northern part of the newark supergroup consist of cyclic transgressive regressive sequences locally containing evaporites they are interpreted as deposits of hydrologically closed basins which occasionally became open at lake high stand in the southern part of the newark supergroup many of the lacustrine sequences are thicker lack evaporites and some contain coal and siderite these features suggest deposition in hydrologically open basins fluvial paleocurrents in at least one southern basin suggest through flow and open basin deposition thin lacustrine sequences interpreted as perennial floodplain lake deposits are associated with these fluvial systems and may also indicate open basin conditions

taphonomy of lacustrine fish fossils of the parnaiba basin northeastern brazil spatial and causative relations of konservat lagerstatten in west gondwana during jurassic cretaceous abstract fossil bonanzas called konservat lagerstatten provide geological windows to the ecology of ancient life communities these deposits often occur as cluster of fossil localities with similar geographic locations geological ages and facies as the fossils were generally preserved during special periods and large scale events in earth history within environments with exceptional taphonomic conditions this work applied petrological and geochemical analyses to evaluate the taphonomic pathway of a konservat lagerstatten in the muzinho shale upper jurassic lower cretaceous of the parnaiba basin northeastern brazil these lacustrine deposits include interbedded limestones and fossiliferous black shales deposited in anoxic non euxinic and saline environment black shales contain articulated skeletons of fish fossils characterised by three dimensional preservation of the skeletal tissue the polytypical assemblage includes diverse ontogenetic stages and is concentrated in a specific stratigraphic level mass mortality was triggered by anoxia probably established by stratified water column high c flux and thermocline demise the specimens are encased in kerogen bearing siliciclastic laminae and cementstone microfacies both microbially induced the fossils were cemented by eodiagenetic poikilotopic calcite that filled the skeletal articulation including bone trabeculae and voids originally filled by bone marrow the short distance similar fossil assemblages ages and coincident palaeoenvironments suggest that muzinho shale parnaiba basin and crato formation araripe basin compose a cluster of exceptional preservation in west gondwana lava flows and outgassing related to the central atlantic magmatic province camp resulted in the subaereal exposure of volcanic plains acid rains and subsequent co2 greenhouse crisis camp magmatism was especially voluminous in northern brazilian basins enhancing nutrient rich waters and lacustrine eutrophication due to intensified chemical weathering in this area probably other konservat lagerstatten remain unreported in west gondwana despite similar causative events the individual taphonomic pathways of muzinho shale and crato formation are very different suggesting that in these cases local phenomena affected authigenesis and diagenesis

the origin of the fumaroles of la solfatara campi flegrei south italy abstract the analysis of gaseous compositions from solfatara campi flegrei south italy fumaroles since the early 1980s clearly reveals a double thermobarometric signature a first signature at temperatures of about 360 c was inferred by methane based chemical isotopic geoindicators and by the h2 ar geothermometer these high temperatures close to the critical point of water are representative of a deep zone where magmatic gases flash the hydrothermal liquid forming a gas plume a second signature was found to be at around 200 240 c at these temperatures the kinetically fast reactive species h2 and co re equilibrate in a pure vapor phase during the rise of the plume a combination of these observations with an original interpretation of the oxygen isotopic composition of the two dominant species i e h2o and co2 shed light on the origin of fumarolic fluids by showing that effluents are mixture between fluids degassed from a magma body and the vapor generated at about 360 c by the vaporization of hydrothermal liquids a typical andesitic water type d 20 18o 10 and a co2 rich composition x co 2 0 4 has been inferred for the magmatic fluids while for the hydrothermal component a meteoric origin and a co2 fugacity fixed by fluid rock reaction at high temperatures have been estimated in the time the fraction of magmatic fluids in the fumaroles increased up to 0 5 at each seismic and ground uplift crisis bradyseism which occurred at campi flegrei suggesting that bradyseismic crises are triggered by periodic injections of co2 rich magmatic fluids at the bottom of the hydrothermal system

paleontology of proterozoic shales and mudstones examples from the belt supergroup chuar group and pahrump group western usa abstract proterozoic black shales and other fine grained siliciclastic rocks contain a variety of fossils these fossils are illustrated by examples from three proterozoic units in the western usa the belt supergroup middle proterozoic the chuar group late proterozoic and the upper pahrump group late proterozoic a variety of microfossils and megafossils occur in the belt supergroup western montana acritarchs and filamentous microfossils are moderately well preserved in sub greenschist facies black shale in the little belt mountains the biologic affinity of the acritarchs is uncertain they could represent the vegetative or encystment stage of eukaryotic algae or the outer envelope of colonial coccoid cyanobacteria most of the filaments in these shales are of a size and morphology that is consistent with prokaryotic affinities however rare 20 and 40 m wide filaments could be either prokaryotic or eukaryotic higher grade sub greenschist facies dark gray to black mudstones in glacier national park contain poorly preserved acritarchs and spheroidal and filamentous pseudomicrofossils they are of interest because they provide information useful for distinguishing authentic microfossils from pseudofossils in mudstones and shales that have undergone substantial burial metamorphism several authentic megafossils occur in lower belt shales in the little belt and big belt mountains montana one of these is the carbonaceous compression beltina danai which could represent either fragments of a microbial mat or fragments of a sheet like megascopic alga the megafossil grypania spiralis has the form of a coiled ribbon and tentatively is interpreted as a megascopic alga green to purple mudstones and muddy sandstones in the lower belt supergroup in glacier national park contain markings that resemble a string of beads they are interpreted as megafossils that may have eukaryotic algal affinities black shales in the late proterozoic kwagunt formation chuar group grand canyon arizona contain a variety of acritarchs and filamentous microfossils of special interest is the vase shaped microfossil melanocyrillium which is interpreted as the sporangium of a eukaryotic and probably megascopic alga melanocyrillium also occurs in black mudstone in the late proterozoic pahrump group southeastern california

impact des ecosystemes microbiens sur la sedimentation impact of microbial ecosystems on sedimentation abstract the microbial communities which often give rise to the fine lamination in sediments are very diverse both in species composition e g phototrophic and chemotrophic bacteria fungi algae and metabolism e g oxygenic and anoxygenic photosynthesis organic and inorganic chemosynthesis anaerobic and aerobic respiration organic and inorganic fermentation these microbial ecosystems have separated for more than 3 5 ga 3500 m y they intervene in the biostructuration of sediments by active mineral deposition particle trapping and sediment stabilisation they build bioconstructions stromatolites oncolites oolites and microbial bioherms further they are active in a number of biogeochemical biomineralisation processes including phosphatogenesis carbonate genesis and the formation of iron ore and sulfur deposits and petroleum and kerogen they are also active agents in the biocorrosion and bioerosion of sedimentary rocks under marine and terrestrial conditions since they have an enormous capacity for proliferation microbial laminated communities invade new habitats practically instantaneously where suitable energy sources and gradients for electron flow are available in addition such microbial systems are excellent and sensitive paleoecological indicators in order to study their impact on sedimentation and fossilisation a close collaboration between geologists and microbiologists is needed only in this way can the nature of fossil microbial ecosystems and the metabolisms that were at work be recognized and reconstructed

in channel geomorphic complexity the key to the dynamics of organic matter in large dryland rivers abstract large rivers are often considered to retain less organic material than smaller streams primarily because of a decrease in retentive structures from our observations on the barwon darling river a semi arid river in southeastern australia we suggest that geomorphic complexity plays a fundamental role in the retention of organic matter the barwon darling river has a complex river channel cross section with large inset benches being a prominent morphological feature within the channel the importance of geomorphic complexity for retaining organic material is likely to be significant in dryland rivers these rivers spend extended periods at low flow with infrequent large floods that inundate the floodplain they do however experience more frequent within channel floods that inundate in channel bench features in channel geomorphic complexity and its ability to retain organic material therefore means that although the dominant lateral movements of organic material will still occur during large overbank flows smaller pulse inputs will occur with each in channel rise and fall in water level in dryland rivers where large overbank flows may only occur every seven or more years these small pulse inputs of organic material may well be vital for the integrity of the system this paper describes the contemporary complexity of a channel in a regulated and an unregulated reach of the barwon darling and compares this with cross sections surveyed in 1886 we show that flow regulation has greatly reduced channel complexity we estimate the potential organic matter input to each bench level within the channel using data collected under near natural riparian conditions and measure the contemporary organic loads within the channel of the regulated and unregulated reach this modelling suggests that the development of water resources has reduced the complexity of the channel in the regulated reach resulting in a potential decrease in the retention of organic matter in this region of the river the importance of this organic matter to the aquatic food web of the barwon darling river is also demonstrated

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

taphonomy of lacustrine shoreline fish part conglomerates in the late triassic age lockatong formation collegeville pennsylvania usa toward the recognition of catastrophic fish kills in the rock record abstract fish parts bones and scale elements preserved in sandstones and conglomerates characterize an uncommon type of lacustrine strandline setting identified in the triassic lockatong formation of the newark supergroup the triassic fish part sandstones and conglomerates are composed of disarticulated skeletal remains and formed during the lake expansion phase diverse mudstone clast types derived from the underlying lowstand playa deposits integrated into the younger transgressive shoreline sequence that contains disarticulated fish parts we propose that the salton sea california usa is a modern hypersaline lacustrine environmental analog for the deposition of fish remains on the salton sea high wind events cause mass fish kills forming a modern shoreline dominated by barnacles and fish remains using modern day observations from fish kills in the salton sea california usa we suggest that the following taphonomic scenario mass kills of triassic fish species took place during deposition of the lacustrine lockatong formation high wind events caused overturning of the lake waters either depleting oxygen or toxically poisoning the fish after death bacterial decomposition bloated the fish by generated gas in tissues causing the fish carcasses to float the decomposing fish carcasses were driven shoreward by wind and wave action and deposited on the shoreline and possibly scavenged by phytosaurs following soft tissue decay the disarticulated remains were reworked into normally graded beds composed of intraclasts and fish part elements the intermixing of intraformational clasts and fish parts reflects the impact of storms on the lacustrine shoreline during the expansion phase of the van houten cycle short period milankovich frequency cycles that consist of three recorded phases of lake rise to fall recorded in various facies stackings

the stratigraphy and paleoenvironment of a lycoptera bed site in eastern inner mongolia china correlation with the fossiliferous lower cretaceous strata in western liaoning abstract the stratigraphy and the fossil assemblage of a lower cretaceous lycoptera bed of the xinganling group in naketa arongqi area inner mongolia china are described and the paleoenvironment is discussed as it relates to the jehol biota the naketa fossil bed belongs to the lower part of volcanic sedimentary jiufengshan formation and preserves a typical eel eosestheria ephemeropsis trisetalis lycoptera davidi faunal assemblage which indicates a strong affiliation to the jehol biota of western liaoning china the fossil bed was deposited in a shallow to semi deep lacustrine setting with occurrence of oil shale facies and this is different from the lycoptera bed of the yixian formation and more similar to the overlying jiufotang formation in western liaoning a layer of volcanic tuffite within the fossil bed is dated as 121 6 0 47 ma using the zircon u pb isotopic dating method this age is contemporary with the age of the base of jehol biota producing jiufotang formation in western liaoning thereby supporting the biostratigraphic correlation however the genus lycoptera is almost entirely absent in western liaoning with only one species in the jiufotang formation where the dominant fish genus is jinanichthys therefore lycoptera in the great xing an mountain areas appears to have a longer record than in western liaoning which likely indicates that the fish fauna changed earlier in western liaoning and this observation supports the hypothesis that the yanliao area was the diversification center of some cretaceous new groups in ne asia preliminary analysis of the taphonomy and the geology indicates that the mass mortality of fish at the naketa site may not be related to volcanism additional taphonomic investigations would allow a better understanding of the early cretaceous aquatic paleoecology and paleoenvironment in the volcanic rifting regions the great xing an mountain area is a new opportunity for expanding the research on the jehol biota beyond the core localities in western liaoning

sedimentary facies and depositional environments of early mesozoic newark supergroup basins eastern north america abstract the early mesozoic newark supergroup consists of continental sedimentary rocks and basalt flows that occupy a ne trending belt of elongate basins exposed in eastern north america the basins were filled over a period of 30 40 m y spanning the late triassic to early jurassic prior to the opening of the north atlantic ocean the sedimentary rocks are here divided into four principal lithofacies the alluvial fan facies includes deposits dominated by 1 debris flows 2 shallow braided streams 3 deeper braided streams with trough crossbeds or 4 intense bioturbation or hyperconcentrated flows tabular unstratified muddy sandstone the fluvial facies include deposits of 1 shallow ephemeral braided streams 2 deeper flashflooding braided streams with poor sorting and crossbeds 3 perennial braided rivers 4 meandering rivers 5 meandering streams with high suspended loads 6 overbank areas or local flood plain lakes or 7 local streams and or colluvium the lacustrine facies includes deposits of 1 deep perennial lakes 2 shallow perennial lakes 3 shallow ephemeral lakes 4 playa dry mudflats 5 salt encrusted saline mudflats or 6 vegetated mudflats the lake margin clastic facies includes deposits of 1 birdfoot deltas 2 stacked gilbert type deltas 3 sheet deltas 4 wave reworked alluvial fans or 5 wave sorted sand sheets coal deposits are present in the lake margin clastic and the lacustrine facies of carnian age late triassic only in basins of south central virginia and north and south carolina eolian deposits are known only from the basins in nova scotia and connecticut evaporites and their pseudomorphs occur mainly in the northern basins as deposits of saline soils and less commonly of saline lakes and some evaporite and alkaline minerals present in the mesozoic rocks may be a result of later diagenesis these relationships suggest climatic variations across paleolatitudes more humid to the south where coal beds are preserved and more arid in the north where evaporites and eolian deposits are common fluctuations in paleoclimate that caused lake levels to rise and fall in hydrologically closed basins are preserved as lacustrine cycles of various scales including major shifts in the late triassic from a wet carnian to an arid norian in contrast fluvial deposits were mainly formed in response to the tectonic evolution of the basins but to some extent also reflect climatic changes the newark supergroup illustrates the complexity of rift basin sedimentation and the problems that may arise from using a single modern analog for sedimentary deposition spanning millions of years it also shows that a tremendous wealth of depositional climatic and tectonic information is preserved in ancient rift basin deposits which can be recovered if the depositional processes of modern rift basin deposits are understood

estuarine biofilm patterns modern analogues for precambrian self organization this field and laboratory study examines whether regularly patterned biofilms on present day intertidal flats are equivalent to microbially induced bedforms found in geological records dating back to the onset of life on earth algal mats of filamentous vaucheria species functionally similar to microbial biofilms cover the topographic highs of regularly spaced ridge runnel bedforms as regular patterning is typically associated with self organization processes indicators of self organization are tested and found to support this hypothesis the measurements suggest that biofilm induced sediment trapping and biostabilization enhance bedform relief strength and multi year persistence this demonstrates the importance of primitive organisms for sedimentary landscape development algal covered ridges consist of wavy crinkly laminated sedimentary deposits that resemble the layered structure of fossil stromatolites and microbially induced sedimentary structures in addition to layering both the morphological pattern and the suggested formation mechanism of the recent bedforms are strikingly similar to microbialite strata found in rock records from the precambrian onwards this implies that self organization was an important morphological process in times when biofilms were the predominant sessile ecosystem these findings furthermore emphasize that self organization dynamics such as critical transitions invoking ecosystem emergence or collapse might have been captured in fossil microbialites influencing their laminae this notion may be important for paleoenvironmental reconstructions based on such strata

mineral control of arsenic content in thermal waters from volcano hosted hydrothermal systems insights from island of ischia and phlegrean fields campanian volcanic province italy this paper documents arsenic concentrations in 157 groundwater samples from the island of ischia and the phlegrean fields two of the most active volcano hosted hydrothermal systems from the campanian volcanic province southern italy in an attempt to identify the environmental conditions and mineral solution reactions governing arsenic aqueous cycling on ischia and in the phlegrean fields groundwaters range in composition from nacl brines which we interpret as the surface discharge of deep reservoir fluids to shallow depth circulating fluids the latter ranging from acid sulphate steam heated to hypothermal cold bicarbonate groundwaters arsenic concentrations range from 1 6 to 6900 g l 1 and from 2 6 to 3800 g l 1 in the phlegrean fields and on ischia respectively they increase with increasing water temperature and chlorine contents and in the sequence bicarbonate groundwatersbsteam heated groundwatersbnacl brines according to thermochemical modeling we propose that high as concentrations in nacl brines form after prolonged water rock interactions at reservoir t fo2 and fh2s conditions and under the buffering action of an arsenopyrite pyrite pyrrhotite rock assemblage on their ascent toward the surface nacl brines become diluted by as depleted meteoric derived bicarbonate groundwaters giving rise to hybrid water types with intermediate to low as contents steam heated groundwaters give their intermediate to high as concentrations to extensive rock leaching promoted by interaction with as bearing hydrothermal steam 2005 elsevier b v all rights reserved

depositional subenvironments in an arid closed basin the wilkins peak member of the green river formation eocene wyoming u s a the wilkins peak member of the green river formation is a non marine dolomitic deposit that formed in an arid hydrologically closed basin a transect from the margin to the centre of the wilkins peak basin was examined in outcrop exposures in the south eastern corner of the basin and was supplemented with published core descriptions the rocks were divided into seven facies based upon lithology layering style and sedimentary fabrics 1 af facies quartzose conglomerates and sandstones representing sandy alluvial fans coming from the uinta mountains 2 sf facies quartzose peloidal dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans 3 dm facies irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat 4 el facies dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds 5 pl facies finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes 6 sm facies trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology these represent a central salt pan and the surrounding saline mudflat 7 as facies arkosic sandstones siltstones and mudstones which represent braided river and more basinal deltaic plain deposits the five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations there are at least forty 3 4 m thick cycles in the wilkins peak and one large scale cycle comprising the whole member which mimics the facies changes of the smaller cycles this is compatible with the transitions of the wilkins peak member to the tipton and laney members as climatic responses and not shifts in drainage the sheet flood sandstones actively aggrading subaerial mudflats and bedded evaporites of the wilkins peak are apparently unique within the green river formation they reflect the unusual provenance and hydrology of the wilkins peak and suggest chemical and sedimentary models established for the other green river members will not be applicable

sheet flow deposits of graded beds and mudstones on an alluvial sandflat playa system upper triassic blomidon redbeds st mary s bay nova scotia the 400 m of blomidon redbeds accumulated in a semi arid rift valley in the subtropics at st mary s bay these redbeds are 64 sandy mudstone playa mudflats 25 graded beds sandflats at the toes of alluvial fans 10 fissile claystone playa lakes and 1 channel sandstone stream channels flash floods in mountains south of the valley flowed down alluvial fans to spread out to the north east as sheet flows on sandflats and playa mudflats deceleration of the sheet flows deposited graded beds 2 83 cm in thickness on the sandflats and thin layers of mud on the playas nine sequences consisting of arrangements of six lithologies compose 90 of the graded beds in order of decreasing abundance these are ripple cross laminated siltstone horizontally laminated mudstone fining upward ripple cross laminated siltstone ripple cross laminated sandstone horizontally laminated mudstone cross bedded sandstone horizontally laminated mudstone ripple cross laminated sandstone ripple cross laminated siltstone rippledrift cross laminated siltstone horizontally laminated mudstone fining upward ripple drift cross laminated siltstone cross bedded sandstone ripple cross laminated siltstone and cross bedded sandstone ripple cross laminated siltstone horizontally laminated mudstone the sheet flows perhaps up to 1 m in depth had a high concentration of suspended load deposition was dominantly during lower flow regime conditions and moderate to rapid flow deceleration there are 32 thinning and fining up cycles where a sandflat package of graded beds is transitionally followed by a playa package of sandy mudstone the cycles range in thickness from 1 3 to 13 3 m averaging 4 6 m each cycle is initiated by avulsion to a new active channel network on a fan gradual abandonment of the channel network produces the thinning and fining up cycle the cycles are grouped in three 60 70 m fining up megacycles upwards within each megacycle the packages of sandy mudstone compose a progressively larger proportion of the cycles each megacycle evidently was initiated by a brief period of tectonic movement on the border faults that produced greater relief of the highlands relative to the valley floor subsequent erosion gradually lowered the relief to yield a fining up megacycle