carbonate sedimentology of the early precambrian hamersley group of western australia abstract the early precambrian hamersley group of western australia contains both major and minor occurrences of well preserved carbonate sedimentary rock the carawine dolomite and the middle or paraburdoo member of the wittenoom formation are the two most extensive occurrences the carawine dolomite is restricted to the eastern part of the hamersley basin and contains abundant stromatolites oncolites and wave ripples as well as local occurrences of evaporite crystal pseudomorphs and oolitic to pisolitic textures these carbonate strata were deposited in a shallow water paleoenvironment herein referred to as the carawine platform in contrast the wittenoom formation is restricted to the centraland western parts of the hamersley basin and such shallow water features are entirely absent from its carbonate strata these strata consist largely of thinly laminated lutite but also include some thin carbonate turbidites the carbonate sedimentary rocks of the wittenoom formation as well as some in the carawine dolomite which display similar characteristics are therefore interpreted as sediments that were deposited off platform in deeper water paleoenvironments paleocurrent thickness and grain size trends of the carbonate turbidites indicate they were deposited by paleoflows moving south and west even though the carawine dolomite lies to the northeast of the wittenoom formation stratigraphic correlations using a newly recognized marker bed of probable impact origin suggest that the carbonate strata of the carawine dolomite are younger than the paraburdoo member of the wittenoom formation if true the carawine platform could not have been a source of sediment for most of the carbonate sedimentary rocks in the wittenoom formation but it may havebeen the sediment source for similar carbonate turbidites in younger formations such as the mt mcrae shale and the dales gorge member of the brockman iron formation this in turn suggests that carbonate sediments were accumulating in the shallower parts of the hamersley basin while some of the bifs were being deposited simultaneously in the deeper parts

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

constancy of silicate mineral weathering rate ratios between natural and experimental weathering implications for hydrologic control of differences in absolute rates abstract inverse models which apportion watershed effluxes geochemical mass balance over estimated mineral surface area give weathering rates for individual silicate minerals e g feldspar 1 3 orders of magnitude slower than laboratory rates comparisons of rates calculated from several recent watershed geochemical mass balance studies with experimentally determined rates reveal that the ratio of mineral weathering rates for a given silicate mineral pair determined in an internally consistent field study equals the ratio of rates for the same minerals in any internally consistent set of laboratory experimental data thus the coefficient which corrects the weathering rate for any mineral from a laboratory data set to a field setting is identical to the corresponding coefficient for any other mineral in the same data sets the correction factor linking experimental and natural rates must be independent of composition physical e g hydrologic controls rather than compositional or chemical controls cause the difference between weathering rates in nature and the laboratory because flow in natural weathering profiles is spatially heterogeneous not all of the potentially available surface in natural systems actually participates in reactions with pore fluids

late cambrian steptoean sedimentation and responses to sea level change along the northeastern laurentian margin insights from carbon isotope stratigraphy carbon isotopes are applied as tools for stratigraphic correlation of poorly fossiliferous upper cambrian carbonate strata in the northern u s appalachians upper cambrian steptoean marine carbonate rocks record a significant global positive carbon isotope excursion 13c 4 5 vienna peedee belemnite vpdb the timing of which is well documented in fossiliferous sections elsewhere the steptoean excursion peaks at a sea level lowstand that produced the sauk ii sauk iii sequence boundary on the north american craton in this study this excursion is documented for the first time in the northern u s appalachians in poorly exposed limestone debris flow and olistolith deposits interbedded within 20 m of continental slope shales of the schodack formation these deposits contain the only reported pre elvinia zone steptoean fauna in new york and record 13c values of up to 3 the slope carbonate sediment was mainly derived from the shelf margin and is mixed with common coarse grained silici clastic material these deposits reflect a seaward migration of the siliciclastic source area exposed craton suppressed carbonate platform sedimentation and shelf bypassing during the sauk ii sauk iii sea level fall nonfossiliferous dolostones and dolomitic marbles of the proposed carbonate platform correlatives the pine plains formation in southeastern new york and the stockbridge formation from western massachusetts also contain common coarse siliciclastics however sampled sections do not record elevated 13c values indicating that these strata are probably not of steptoean age this suggests that steptoean time is represented in the carbonate platform to slope succession of the northeastern present day laurentian margin by an extremely condensed stratigraphic interval or even a hiatus

carbonate platforms of passive extensional continental margins types characteristics and evolution abstract carbonate platforms of extensional margins may be grouped into several major categories homoclinal ramps have gentle slopes into deep water may have skeletal or ooid pellet sand shoal complexes that grade without break in slope into deep ramp nodular limestone and then into pelagic hemipelagic basin facies they generally lack significant slump and sediment gravity flow deposits in the deeper water facies distally steepened ramps differ from the above in having a marked increase in slope at the seaward edge of the deep ramp and abundant slumps slope breccias and turbidites however clasts of shallow platform margin facies are generally absent from breccias rimmed shelves have linear trends of shelf edge lime sands and reefs a marked increase in slope into deep water and foreslope and slope sands breccias with clasts of platform margin rocks and turbidites grading seaward into basin hemipelagic pelagic muds they may be divided into accretionary bypass and erosional margins isolated platforms are broad flat topped shallow platforms surrounded by deeper water few hundred meters to 4 km deep many are bypass margins but accretionary and erosional margins also occur finally incipiently to completely drowned or open platforms may develop by rapid submergence of ramps shelves or isolated platforms shallow platform margin facies are shifted landward and the earlier shallow water platform is covered with transgressive lags and deeper water blankets of hemipelagic or pelagic facies or open marine whole fossil wackestone the carbonate prisms commonly develop above a basal clastic phase ramps develop early and evolve into rimmed shelves however with drowning rimmed shelves may evolve up into ramps rimmed shelves may also develop into ramps where miogeoclinal faces prograde into filling marginal basins carbonate miogeocline deposition terminates when the shelf becomes a prograding clastic shelf or where it becomes part of a collisional orogen the various platform types may be recognized from continental margin sequences ranging from proterozoic to holocene in age

composition diagenesis and weathering of the sediments and basement of the callabonna sub basin central australia implications for landscape evolution abstract the evolution of the callabonna sub basin central australia is described in terms of sediment provenance stratigraphy sedimentology and postdepositional mineral and chemical alteration six mineral exploration drillholes in the mundi mundi plain were studied using a combination of qualitative and quantitative xrd pimatm portable infrared mineral analyzer xrf normative analysis and sem the sedimentary cover consists of 160 210 m of diagenetically modified fluvio lacustrine tertiary clay silt and sand comprising sandy mottled and gray clay units overlain by quaternary soil the basement consists of weathered proterozoic schist gneiss siltstone and shale quartz kaolinite smectite and muscovite are the dominant minerals within the sediments whereas the weathered bedrock contains quartz feldspar kaolinite illite and muscovite characteristic wavelength absorption features from pimatm show that the youngest sandy clay unit exhibits the lowest reflectance intensities because of its lower diagenetic maturity weathering of primary minerals within the basement produced an illite kaolinite rich saprolite whose clays exhibit strong reflectance intensities and well developed crystallinity the micromorphology of all secondary products reflects their environment of crystallization low porosity and anoxic conditions within the sediments resulted in poorly developed clays of variable textures colors and compositions conversely the weathered bedrock developed over protracted periods of in situ weathering resulting in better developed secondary products this study distinguishes between preburial weathering of the basement detrital mineralogy postdepositional alteration of the sedimentary cover and subsequent weathering of previously formed mineral assemblages this has widespread implications for paleotopographic weathering reconstitution and landscape evolution thus 1 the extent of weathering of basement relative to diagenesis and maturity of sediments and gradational nature of their unconformity suggests that most of the alteration of basement occurred prior to and was sustained after deposition of sediments and 2 morphotectonic evolution of the region controlled the composition of transported materials by changing the style and patterns of fluvial systems further influencing the distribution and preservation of sediments and weathered bedrock and hence regional landscape morphology

the middle late cambrian reef transition and related geological events a review and new view abstract the reefs of the middle late cambrian cambrian epoch 3 furongian have long been simply considered as microbialites that flourished in the aftermath of the archaeocyath extinction thorough review of the reefs in these periods shows however that the cambrian epoch 3 and the furongian actually yield different types of reefs the cambrian epoch 3 reefs are dominated by thrombolites and dendrolites largely constructed by the calcified microbes epiphyton and renalcis on the other hand the furongian reefs consist mainly of maze like maceriate reefs and columnar stromatolites the maceriate reefs most likely formed by siliceous sponges and calcified microbes including girvanella and tarthinia whereas the columnar stromatolites were mainly constructed by girvanella tarthinia and minor siliceous sponges other microbial reefs e g non columnar stromatolites persisted during the cambrian epoch 3 and the furongian mainly as small patch reefs or reefal crusts lithistid sponge microbial reefs initially formed in the cambrian epoch 3 and occurred throughout the furongian but occupied only a minor portion during these periods several geological events occurred across the boundary between the cambrian epoch 3 and the furongian including positive carbon and sulfur isotope excursions a eustatic sea level drop major faunal turnover of trilobites and diversification of new organisms the coincidence of these events and the transition in reefal fabrics suggest that reef ecosystems were significantly influenced by at least some of these events among the events it is likely that sea level change would have affected reefs although further studies are required in order to test whether and how the other events influenced the reef transition epiphyton and renalcis and thrombolites and dendrolites formed by them declined greatly most likely due to sea level fall and thus decreased in shallow marine habitat at the end of cambrian epoch 3 the cambrian epoch 3 thrombolites and dendrolites were gradually replaced by a sponge microbial association of the maze like maceriate reefs and the columnar stromatolites in the furongian coincident with a sea level rise

reef fabrics biotic crusts and syndepositional cements of the latemar reef margin middle triassic northern italy the latemar reef buildup of the central dolomites northern italy provides a rare opportunity to examine an in place middle triassic upper anisian to lower ladinian platform margin that is not strongly deformed or dolomitized the margin lies between the flat lying platform interior and steeply dipping foreslope clinoforms across this transition the depositional profile relates directly to a consistent lateral facies pattern 1 restricted biota grainstone of the platform interior 2 tubiphytes rich boundstone and 3 diverse biota grainstone that grades into 4 foreslope breccia beds the boundstone and diverse biota grainstone facies comprise the platform margin the boundstone facies consists of a framework of small 10 cm skeletal remains 10 by volume with associated biotic crusts internal sediments and syndepositional cements crusts and cements constitute most of the rock volume and created the boundstone fabric biotic crusts exhibit gravity defying geometries and range from a light grey structure grumeleuse rind to dark grey micritic laminae both cements and biotic crusts occur as redeposited talus in the foreslope talus deposits indicating a syndepositional origin the diverse biota grainstone facies primarily consists of skeletal peloidal grainstone with a diverse open marine biotic assemblage in contrast to the restricted biota grainstones of the platform interior that have a low diversity restricted marine biota metre scale hexacoral boundstone and centimetre scale sponge boundstone and microbial boundstone occur as isolated patches tens to hundreds of metres apart within the diverse biota grainstone facies the depositional profile facies zonation and biotic constituents all indicate that the latemar buildup had a shallow water reef margin in contrast to previous interpretations that these were upper slope reefs the syndepositional biotic crusts and inorganic cementation played key roles in stabilizing the boundstone fabric to form a wave resistant reef fabric

wishstone to watchtower amorphous alteration of plagioclase rich rocks in gusev crater mars previous observations by the spirit rover in gusev crater revealed a suite of rocks dubbed wishstone and watchtower class in which the parent lithology and daughter products of a distinctive style of aqueous alteration are evident results from spirit s miniature thermal emission spectrometer mini tes 2000 340 cm 1 were compromised by dust contamination of one of the instrument s mirrors for which a correction has since been developed now we have documented nearly 200 examples of rocks encompassing the span of alteration from wishstone class which spectrally resemble minimally altered plagioclase phyric basalt to the most altered watchtower class among them is a rock dubbed bruce that may be a previously unrecognized alteration spectral end member we employed factor analysis target transformation and linear least squares modeling to investigate the spectral characteristics and mineralogy of these rocks our results amplify those of a prior preliminary analysis showing that alteration produced a material resembling basaltic glass that masks the spectral features of plagioclase the association of this amorphous silicate component with a ferric iron nanophase oxide phase identified via spirit s mossbauer spectrometer is now clearly shown by our data further characterizing the distinctive mineralogic expression of the alteration these components and the absence of any recognizable secondary silicates or opaline silica may be an expression of alteration in the extreme aridity and cold of the martian environment similar mineralogic characteristics of soil measured with the chemin x ray diffraction instrument on the curiosity rover in gale crater may be an indication that this alteration process is widespread on mars

lateral moisture flow beneath a sandy hillslope without an apparent impeding layer part of a small drainage basin on the sevilleta national wildlife refuge about 25 km north of socorro nm was intensively instrumented with soil monitoring equipment to estimate natural ground water recharge soil moisture data were analysed with special attention to characterizing the influence of topography on the direction of vadose water flow paths in fine to medium aeolian sand moisture content data were obtained by the neutron scattering technique and hydraulic head data were obtained using tensiometers in addition tracer experiments were conducted on a sandy hillslope to delineate the flow paths of vadose water the results indicate that there is a strong lateral component to unsaturated flow on a hillslope even in the absence of apparent sublayers of much lower permeability darcian calculations estimate the long term steady deep flux beneath a concave location to be about 4 per cent of an assumed mean annual precipitation of 20 cm the deep soil water flux downward varied by several orders of magnitude during the 17 month period of record

corrigendum to the earliest phanerozoic carbonate hardground cambrian stage 5 series 3 implications to the paleoseawater chemistry and early adaptation of hardground fauna palaeogeogr palaeoclimatol palaeoecol 440 15 december 2015 172 179

applications of mineral surface chemistry to environmental problems environmental surface chemistry involves processes that occur at the interface between the regolith hydrosphere and atmosphere the more limited scope of the present review addresses natural and anthropogenically induced inorganic geochemical reactions between solutes in surface and ground waters and soil and aquifer substrates important surficial reactions include sorption ion exchange dissolution precipitation and heterogeneous oxidation reduction processes occurring at the solid aqueous interface recent research advances in this field have addressed both directly and indirectly societal issues related to water quality pollution biogeochemical cycling nutrient budgets and chemical weathering related to long term global climate change this review will include recent advances in the fundamental and theoretical understanding of these surficial processes breakthroughs in experimental and instrumental surface characterization and development of methodologies for field applications

platform and off platform carbonates of the upper cambrian of western maryland u s a upper cambrian carbonates in western maryland are comprised of platform facies conococheague limestone west of south mountain and basin facies frederick limestone east of south mountain conocheague platform carbonates contain interbedded non cyclic and cyclic facies non cyclic facies consist of cross stratified grainstones thrombolitic bioherms and graded thin bedded dolostones these were deposited in shallow subtidal shelf lagoons cyclic facies are composed of repeated sequences of cross stratified grainstone ribbon rock wavy prism cracked laminite and planar laminated dolostone the cyclic facies are shallowing upward cycles produced by lateral progradation of tidal flats over shallow nearshore subtidal environments cyclic and non cyclic facies are interbedded in the conococheague in a layer cake fashion but no higher order cyclicity can be found the frederick limestone is dominated by monotonously thick sequences of graded thin bedded limestones interbedded with massive peloidal grainstones and beds of breccia up to 10 m thick in the lower frederick the breccias contain transported megaclasts of epiphyton girvanella boundstones the basal frederick was deposited in a slope to basinal setting east of a rimmed shelf an epiphyton girvanella marginal reef along the shelf edge was the source of the blocks in the breccias the upper frederick limestone formed on a carbonate ramp

carbonate platform dominated by peloidal sands lower ordovician la silla formation of the eastern precordillera san juan argentina the lower ordovician la silla formation of the precordillera of west central argentina is part of the west facing early palaeozoic tropical carbonate platform succession that comprises the core of the cuyania terrane up to 360 m thick it is exposed in several thrust sheets over a distance of some 250 km along and across depositional strike over a palinspastically unrestored distance of about 35 km la silla formation is a strikingly pure limestone with subordinate finely crystalline dolomite and rare chert it accumulated on a more or less uniformly subsiding passive margin copious precipitation of microcrystalline calcite probably influenced by microbial activity to varying degrees led to the generation of peloids ooids and aggregates of these grains as well as small amounts of lime mud intraclasts stromatolites and thrombolites rare bioclasts are limited mostly to scattered gastropods and trilobite sclerites bioturbation is present locally the array of carbonate rock types is grouped into eight recurring lithofacies in order of decreasing abundance i peloidal grainstone ii laminated dolostone iii intraclastic rudstone iv microbial laminite v peloidal packstone vi ooidal grainstone vii thrombolite boundstone and viii mudstone these facies represent sediments that formed solely in a shallow subtidal marine environment with no evidence of restricted conditions hypersalinity or subaerial exposure no events of eustatic sea level change are recorded by far the dominant facies is grainstone composed of well sorted fine sand sized peloids and peloidal aggregates in homogeneous tabular to gently undulating medium to thick beds cross lamination is scarce clusters of sub metre sized microbial patch reefs developed sporadically the shallow platform is envisaged to have been covered by extensive peloidal sand flats and low relief banks and little lime mud was generated the setting was probably microtidal and may not have been affected by strong trade winds it was washed by frequent relatively gentle wave action but without experiencing powerful storms in the middle member anomalous lenses of intraclastic rudstone and laminated dolostone occur as graded beds overlying sharply downcut scoured surfaces up to 20 cm deep these are interpreted to indicate a phase when accretion was punctuated occasionally by tsunamis generated from rift faulting seaward of the platform margin the remarkably uniform peloidal grainstone composition over a broad area shows that given the appropriate combination of climate environmental and ecological factors large portions of some early palaeozoic platforms were dominated by grainy sediment and remained under well agitated conditions within fair weather wave base without distinct lateral facies differentiation or tidal flat aggradation

preferential flow in a sandy vadose zone 1 field observation abstract field experiments of water movement in the lower portion of an unsaturated zone i e vadose zone are far more difficult to conduct than those in the root zone thus our concept of the transport mechanism in the vadose zone is still primitive and mainly an extrapolation of our understanding of transport in the root zone recent results from field experiments conducted at the hancock agricultural research station indicated that water and solute applied uniformly to soil surfaces did not flow through the entire vadose zone by using dye tracing and profile excavation field experiments were conducted during the 1987 growing season to examine water flow patterns in the unsaturated zone of the central sand area of wisconsin csaw the results confirmed that preferential flow paths constitute the dominant flow pattern at this location water flowing through the root zone was funneled into concentrated flow paths that occupied only a small portion of the soil matrix in the vadose zone yet accounted for most of the transport the observed phenomena of preferential flow in a sandy vadose zone are discussed in this paper the mechanism and implications of preferential flow are presented in a companion paper

a unified model for characterisation and mechanical behaviour of rock fractures roughness and aperture are two important characteristic parameters of rock fractures it has been demonstrated by many authors that the knowledge of roughness does not directly lead to that of aperture and aperture is to be handled as a separate geometrical descriptor for determining normal deformability and flow response of a fracture the aperture distribution and the mechanical properties of the rock matrix are required when shearing of joints and fractures is considered roughness comes into play and affects the evolution of the aperture distribution the aperture distribution can be evaluated by knowing the correlation between the asperity profiles of the rock walls of a rock fracture thus the distributions of the contact area and void space determine the fracture dilation and hydraulics during shearing in this study a mathematical formulation of roughness and aperture of rock fractures is proposed both aperture and roughness are interpreted as scale dependent quantities and their statistical models are described by fractal theory the theoretical results are in very good agreement with experimental results and published data furthermore a constitutive model for the hydro mechanical behaviour of rock fractures is developed based on the new theoretical description of the geometry the model is based on a fractal island description of the contact areas and on an approach of micromechanics

megablocks of calcified algae in the cow head breccia western newfoundland vestiges of a cambro ordovician platform margin slope and basin deposits in the cow head group of early paleozoic age contain a wide variety of carbonate clasts among the most common largest and most persistent middle middle cambrian to lower middle ordovician are blocks of fine grained white limestone the origin of these clasts is unknown as no limestones of similar lithology have been found in contemporaneous shallow water carbonate deposits anywhere in the northern appalachians petrographic study of these enigmatic limestones reveals that no matter what their age they are of similar composition calcified algae cement and fine grained sediment the predominant algae are epiphyton spp occurring as numerous masses of tiny shrublike and clumplike growths and girvanella spp developed as numerous thin strands and arcuate sheets renalcis spp and stromatolitic algae although locally common are not persistent the algae are surrounded by fibrous calcite cement interpreted to be synsedimentary while the numerous small cavities between algae are partly filled with geopetal marine sediment these blocks are interpreted to be redeposited fragments of reef mounds and buildups which grew along the shallow submerged margin of the north american craton during early paleozoic time these buildups are now probably buried beneath the allochthonous cow head strata the mounds were composed of calcareous algae because there were no large reef building metazoans during this time in geologic history recognition of similar clasts in analogous settings in the quebec and southern appalachians as well as in the cordillera suggests that this facies was both widespread and persistent for more than 70 m y

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

an aem tem study of weathering and diagenesis abert lake oregon i weathering reactions in the volcanics abstract abert lake in south central oregon provides a site suitable for the study of sequential weathering and diagenetic events in this first of two papers transmission electron microscopy was used to characterize the igneous mineralogy subsolidus alteration assemblage and the structural and chemical aspects of silicate weathering reactions that occur in the volcanic rocks basalts basaltic andesites and dacitic rhyolitic extrusive and pyroclastics that outcrop around the lake olivine and pyroxene replacement occurred topotactically whereas feldspar and glass alteration produced randomly oriented smectite in channels and cavities the tetrahedral octahedral and interlayer compositions of the weathering products largely dioctahedral smectites varied with primary mineral composition rock type and as the result of addition of elements released from adjacent reaction sites weathering of the highly evolved fe rich jug mountain complex at the north end of the lake produced a homogeneous smectite assemblage that contrasts with the heterogeneous smectite assemblage replacing the volcanics along the eastern margin of the lake the variability within and between the smectite assemblages highlights the microenvironmental diversity fluctuating redox conditions and variable solution chemistry associated with mineral weathering reactions in the surficial environment late stage exhalative and aqueous alteration of the volcanics redistributed many components and formed a variety of alkali and alkali earth carbonate chloride sulfate and fluoride minerals in vugs and cracks overall substantial mg si na ca and k are released by weathering reactions that include the almost complete destruction of the mg smectite that initially replaced olivine the leaching of these elements from the volcanics provides an important source of these constituents in the lake water the nature of subsequent diagenetic reactions resulting from the interaction between the materials transported to the lake and the solution will be described in part ii banfield et al 1991

direct observation of reactant product interfaces formed in natural weathering of exsolved defective amphibole to smectite evidence for episodic isovolumetric reactions involving structural inheritance abstract high resolution transmission electron microscopy hrtem and energy dispersive x ray microanalysis eds were employed to characterize grain boundary structures in naturally weathered amphibole our observations provide insights into the submicroscopic mineralogic controls on transport of solutions to and from reaction sites finely exsolved amphibole anthophyllite gedrite in outcropping slightly weathered gedrite gneiss transforms isovolumetrically to smectite stacking faults and exsolution lamellar boundaries focus weathering reactions whereas chain width defects decrease the susceptibility of the surrounding amphibole to alteration relatively al poor anthophyllite lamellae alter slightly more readily than those of al rich gedrite large quantites of mg fe si and al are removed from reaction sites however smectite compositions directly reflect

sequence stratigraphy and depositional facies of lower ordovician cyclic carbonate rocks southern missouri u s a abstract lower ordovician cyclic carbonate strata of southern missouri were deposited in a warm shallow epeiric sea on a fully aggraded carbonate platform sedimentological characteristics distinguish the jefferson city and cotter dolomites from the underlying gasconade and roubidoux formations mixed carbonate siliciclastic sedimentation characterizes the roubidoux formation with sandstones accounting for up to 60 of sedimentation the gasconade jefferson city and cotter dolomites exhibit an increased occurrence of chalcedonic chert nodules in very similar shape and texture to the gypsum and anhydrite nodules common on modern sabkha supratidal flats casts of halite and ghosts of gypsum laths also exist in the jefferson city and cotter strata but are rarely found in the underlying units facies analysis from drill cores and outcrop sections provides the basis for identifying two major meter scale cycle types type i cycles consist of algal stromatolites tidal flat laminites mechanical and algal ooid grainstones wavy peloidal wackestones and quartz sandstones interpreted as peritidal facies they are the dominant components of the roubidoux formation jefferson city dolomite and cotter dolomite type ii cycles consist mostly of subtidal facies such as strongly burrowed mudstone thrombolite boundstone and stromatolites type i cycles are thinner and represent highstand systems tracts whereas the thicker type ii cycles represent transgressive systems tracts and are dominant in the gasconade dolomite the cycle stacking patterns facies changes and the intrabasinal correlatability of fischer plots made from the widely spaced sections argue for a eustatic control on sea level fluctuation on the platform interbasinal correlation with other north american basins is possible using biostratigraphic information and comparison of fischer plots five missouri sequences correlate with those described for other regions the continent wide uniformity in cycle stacking patterns indicates a primarily eustatic control on lower ordovician meter scale cycle development regional tectonic and autocyclic controls probably account for general differences in sedimentation pattern among the correlated basins

microbialites of the neoproterozoic beck spring dolomite southern california ancient microbialites reflect interactions between microbial communities and environmental conditions however evaluating the relative roles of microbial community processes and environmental influences on microbialite morphology and internal fabric in the rock record can be challenging the neoproterozoic beck spring dolomite preserves diverse microbialites and thus provides an opportunity to explore the factors that influenced microbialite development locally stromatolitic thrombolitic and composite microbialites are abundant in subtidal to upper intertidal carbonates in the beck spring dolomite thrombolitic and composite microbialites have not been recognized previously in this unit but compose much of the newly defined thrombolitic member stratigraphic relationships demonstrate that these three types of microbialites formed in close spatial and temporal association in subtidal to intertidal environments the relative proportions and distributions of stromatolitic and thrombolitic microbialites vary with depositional environment stromatolitic microbialites dominate in deeper intertidal to subtidal facies whereas thrombolitic textures are more abundant in upper intertidal facies composite microbialites composed of intermingled clotted and laminated textures formed in all environments but are most abundant in intertidal facies the broad environmental distribution of stromatolitic thrombolitic and composite microbialites and the intermingling of textures suggest that laminated and clotted textures reflect diverse microbial community morphologies rather than environmental variations furthermore the ca 750 ma age of thrombolitic microbialites in the beck spring dolomite requires that they formed without the influence of calcimicrobes or metazoans colonizing and grazing the microbial mat surface thus these thrombolites provide further evidence that the biostratigraphic distribution of thrombolites cannot be uniquely attributed to evolution of calcifying and grazing organisms in the earliest cambrian and that older microbial communities were capable of producing clotted textures

morphogenesis and facies relationships of thrombolites and siliciclastic stromatolites in a cambrian tidal sequence elat area southern israel abstract thrombolites and siliciclastic stromatolites occur within the lower cambrian marine timna formation in the elat area southern israel this rock succession consists of four consecutive stratal suites which together represent a transgressive regressive cycle within a peritidal depositional system the thrombolites are associated with the sea ingression stage and occur as a series of massive bedded strata with laminoid fenestral layers and with a microclotted peloidal fabric of the micritic material sem eds study of the clotted and peloidal micrite reveals a calcitic framework of pitted polygonally shaped units 2 m wide together with a few groups of compressed large hollow structures these forms are interpreted as the possible remnants of bacterial decomposers and of coccoid dominated mat forming unicells respectively the intimate structural connection between the carbonate fraction and the microbe structures suggest in situ carbonate production through bacterial decay of the cyanobacterial material during its self burial with carbonate precipitating as solid phases on vacant extracellular envelopes the siliciclastic stromatolites developed during seashore progradation and now occur as rare laterally linked columnar forms within channelled cross stratified sandstones at the top of the timna succession they are finely laminated with a low to moderate degree of inheritance of the laminae and are partly burrowed by skolithos textures and the geometry of the siliciclastic stromatolites suggest that they were formed through binding of transported quartz sand sized particles by bottom dwelling filamentous microorganisms sediment production and the growth pattern of the two structures within the timna sequence seem to have been regulated by different microbial assemblages which shifted in response to changes in environmental factors through time and space the differential distribution of the two buildups in the sedimentary sequence reflects the difference in balance between the biological attributes of the two biotas and the physical environment pitted architectures such as those displayed by the timna thrombolites could be an ontogenetic fingerprint of microbially constructed rocks which might help to recognize them in the fossil record when other evidence is lacking

lateritic weathering of pyroxenites at niquelandia goias brazil the supergene behavior of nickel two typical lateritic weathering profiles jacuba ahd angiquinho from the niquelandia ni deposits brazil were studied in order to establish the petrological relationship between the supergene ni products and the parental pyroxenes frbm the base to the top of the profiles pyroxenes are replaced by goethite and kaolinite through a series of transitional ni bearing phyllosilicates the mineralogy and the chemical composition especially the ni content of these clay minerals depends on the degree of fracturing and serpentinization of the pyroxenite and the location of the pyroxenite with respect to neighboring dunite within the jacuba profile smectite and pimelite pseudomorphs after pyroxene are especially ni rich and in fact are the most ni enriched clay minerals now known in lateritic weathering profiles

stratigraphic restriction of stromatolites in a middle and upper ordovician foreland platform succession ottawa embayment eastern ontario stromatolites are abundant and widely distributed within two narrow stratigraphic intervals in middle darriwilian and upper lower turinian ordovician strata of the laurentian foreland interior in the ottawa embayment eastern ontario these lithostratigraphic markers coincide with rapid tectonically driven flooding of the foreland interior and may identify an opportunistic microbial response to nutrient loading with shallow peritidal subtidal marine reworking of terrestrial or nutrient rich coastal systems the remaining chatfieldian edenian foreland platform succession represents deeper water deposition in response to elevated subsidence rates along the laurentian margin stromatolites are absent in this higher energy setting but microbial calcite is preserved as coccoid like microencrustations on skeletal debris stromatolites of darriwilian age are dolomitic occur in the carillon formation and are part of a regional 200 km onlap of peritidal sediment during onset of taconic orogenesis

analysis of aperture evolution in a rock joint using a complex network approach a complex network approach to characterize a rough fracture is developed some metric spaces similarity measurements between apertures profiles are set up and a general evolutionary network in two directions parallel and perpendicular to the shear direction is constructed evaluation of the network shows the connectivity degree distribution of edges of network after a transition step falls into a stable state that coincides with a gaussian distribution based on this event and real observations of the complex network changes an algorithm is proposed in which evolution of a network is accomplished using preferential and random attachments of edges while the number of nodes is fixed evolution of clustering coefficients and number of edges display similar patterns observed in shear stress hydraulic conductivity and dilation changes which can be engaged to estimate shear strength distribution of asperities distinguishing the contact profiles and their changes despite the former case disclosed growing networks which can shed light on the details of changes within intra topology of profiles

an isotopic study of a fluvial lacustrine sequence the plio pleistocene koobi fora sequence east africa stable isotopic analyses of plio pleistocene and modern sediments in the fluvial lacustrine system occupying the turkana basin east africa provide constraints on the paleoenvironmental and diagenetic histories of the pliocene through the recent sediments in the basin the 13c values for carbonates in lacustrine sediments range from 15 to 22 relative to pdb depending on the varying proportions of co2 from the atmospheric reservoir and from various metabolic sources the 18o values of carbonates in lacustrine sediments indicate that the isotopic composition of paleolake water varied by over 10 from the pliocene to the present the 13c values for pedogenic carbonates record paleoccologic variations and suggest that c4 plants did not become well established in the preserved depositional parts of the basin until about 1 8 myr ago the 18o values pedogenic carbonates suggest a range of over 10 for the isotopic composition of soil water during this interval they also suggest a period of major climatic instability from about 3 4 to 3 1 myr and at about 1 8 myr together the 13c and 18o values of pedogenic carbonates indicate that the present conditions are as arid and hot as any that had prevailed during deposition of these plio pleistocene sediments

simulation of three dimensional flow of immiscible fluids within and below the unsaturated zone this paper presents a two phase flow model based on a three dimensional finite difference formulation as three dimensional simulations can require substantial computer effort a numerical technique that takes advantage of vector and parallel processing computer architecture is developed the model is posed in terms of water saturation and nonwetting fluid pressure it uses three phase capillary pressure and relative permeability relationships to permit simulation within or below the unsaturated zone a modified formulation of slice successive overtaxation an iterative matrix solution technique is introduced this technique is designed to use parallel processing capabilities of new computers the model is applied to immiscible fluid flow at two chemical waste landfills near niagara falls new york at both sites denser than water nonaqueous liquids napls are present in the groundwater regimes in relatively large quantities the model applications address several technical concerns at the two sites including the effectiveness of clay as a geologic barrier to napl migration owing to capillary pressure forces the three dimensional aspects of dense napl flow and the sensitivity of napl recovery in pumping wells due to various hydrogeologic and fluid properties the results of the applications show that 1 even under a downward hydraulic gradient natural differences in capillary pressure relationships for different lithologies can prevent downward migration of napl 2 without any lithologic capillary barrier an upward hydraulic gradient induced by a de watering system can prevent downward migration of napl 3 napl recovery at wells is sensitive to relative permeability a relationship that requires field calibration in many settings and 4 the three dimensional aspects of two phase flow and hydrogeologic heterogeneity require explicit treatment in many settings

a random field model for surface roughness and aperture of rock fractures present constitutive models for rock fracture behaviour require information concerning the fracture geometry on which the mechanical and hydraulic properties of the rock mass are greatly dependent in this paper measurements of rock fracture surfaces and aperture using a 3 d laser scanning technique are reported in order to check the validity of a fractal model for fracture geometry this formulation incorporates fractal descriptions of roughness angularity and aperture fractal patterns can be persistent if an increasing increment implies an increase in the next increment or anti persistent if increasing increments follows decreasing increments persistence and anti persistence are recognised as descriptors of the geometrical complexity of roughness and aperture the analysis of the data also shows that the fractal models apply until stationarity occurs for sufficiently large samples which behave as random variables these sample sizes are defined as stationarity thresholds of roughness and aperture moreover the study of the cross correlation between the asperity height and aperture provides the link between fracture roughness and aperture geometry a theoretical model of fracture aperture during shearing is developed and successfully compared with experimental and numerical studies reported in the literature

reactant product textures volume relations and implications for major element mobility during natural weathering of hornblende tallulah falls formation georgia blue ridge u s a natural weathering of hornblende from the tallulah falls formation georgia u s a takes place under thoroughly leached oxidizing conditions at the earliest stage of weathering corrosion of hornblende forms denticulated terminations with only minimal porosity apparent within the partially pseudomorphic kaolin group weathering product or between it and the reactant mineral isovolumetric replacement of hornblende by kaolin group clay or precursor products implies inheritance of parent mineral silica tetrahedra by the weathering products and largely immobile behavior of si during early weathering aluminum normally considered immobile or minimally mobile during weathering must be imported into early stage weathering products more advanced weathering of hornblende forms denticulated terminations separated from the earlier formed products by a large continuous peripheral void porosity is much more conspicuous at this stage late stage ferruginous products precipitate from fe mobilized in solution dissolved fe to form the late stage goethite can be entirely derived from the parent hornblende requiring only short transport distances for aqueous fe between the source parent mineral and the location of product precipitation textural and volumetric relationships between naturally weathered hornblende and its partially pseudomorphic weathering products suggest structurally controlled immobility of much parent mineral si and considerable mobilization of al at early stages of weathering but at more advanced stages of weathering the textural and volumetric relationships are consistent with immobility of al and fe and leaching of substantial si and all base cations

subsurface water flow simulated for hillslopes with spatially dependent soil hydraulic characteristics water flow through hillslopes consisting of five soil layers with varying spatial dependence in hydraulic characteristics in the lateral plane was simulated by solving richards equation in three dimensions under varying rainfall intensities and for two complexities of terrain by concepts of similar media the variability in soil hydraulic characteristics was expressed by a single dimensionless parameter the scaling factor the moments of log normally distributed were set as mean 1 0 and standard deviation 1 0 four cases of spatial dependence of in the lateral plane were selected for simulation using exponential variogram functions ranging in spatial structure from radom no spatial dependence to large dependence large correlation lengths the simulations showed that the rates of subsurface flow from the 30 hillslope during and following rainfall were significantly enhanced with an increase in spatial dependence subsurface drainage was also increased with increases in rainfall intensity and slope complexity for hillslopes the relative effect of spatial dependence in soil hydraulic characteristics was smaller with 30 horizontal pitching than without pitching hillslopes with a random distribution of hydraulic characteristics provided greater opportunity for soil units with differing water capacities to interact than in cases with spatially correlated distributions this greater interaction is associated with a greater lag in subsurface flow generation these studies illustrate some of the expected effects of spatial dependence of soil hydraulic characteristics on the integrated hydrologic response of land areas

hydrologic mechanisms governing fluid flow in a partially saturated fractured porous medium in contrast to the saturated zone within which fluid moves rapidly along fractures the fractures with apertures large relative to the size of matrix pores will desaturate first during the drainage process and the bulk of fluid flow would be through interconnected pores in the matrix within a partially drained fracture the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture the residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small normal to the fracture surfaces the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block a general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions results are obtained from an aperture distribution model for fracture saturation hydraulic conductivity and effective matrix fracture flow areas as functions of pressure the effects of distortion of flow paths by the air pockets are taken into account by a phase separation constriction factor in a generalized cubic law for fracture flow under a partially saturated condition the reduction of matrix fracture flow area is taken into account by summing the aperture distribution function to a saturation cutoff aperture which is inversely proportional to the suction head drainage from a column of fractured tuff is simulated using available parameters for the densely welded tuff of the topopah spring member at yucca mountain southern nevada the column is bounded by discrete vertical fractures and dissected by horizontal fractures with the fracture spacings determined by the frequencies and orientations of fractured cores the fraction of fracture surfaces with coatings is assumed to correspond to the fraction of in situ fracture contact area the characteristic curves for the matrix are based on laboratory measurements of tuff samples from the cases simulated for the fractured porous columns with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties however the quasi steady changes of the fluid flow of a partially saturated fractured porous system could be approximately simulated without taking the fractures into account

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

effects of changing water content and atmospheric pressure on radon flux from surfaces of five soil types a computer code rn3d was used to study the effects of varying the water content of five homogeneous soil types clay silt loam sand and gravel and atmospheric pressure on the transport of radon from soil surfaces temperature 20 c and radium content were assumed to be the same for all soils surface fluxes and soil pore space concentrations were computed for steady state diffusion only steady state diffusion with steady pressure gradients and sinusoidal e g diurnal changes in atmospheric pressure pressure gradients drive advective radon transport a steady state pressure gradient of 0 5 pa m enhanced the total radon surface flux over the diffusive flux from 0 01 for clay to 1000 for gravel at 0 saturation at 90 saturation the enhancements were one tenth as much the degree of enhancement was approximately proportional to the gradient along the soil column a net enhancement of surface flux over steady diffusive flux up to 6 for sinusoidal surface pressure changes was observed for all five soil types the study reveals that radon flux is affected as much by varying soil water content as by varying soil type

carbonate deposition and sequence stratigraphy of the terminal cambrian grand cycle in the southern appalachians u s a abstract the cessation of shale and carbonate deposition of the conasauga group grand cycles middle to upper cambrian and the establishment of the widespread peritidal carbonate deposition of the knox group upper cambrian to lower ordovician represent a prominent change in sedimentation along the early paleozoic passive continental margin in the southern appalachians to evaluate the causes for this change this study focuses on the maynardville formation which is the uppermost carbonate unit of the conasauga group the maynardville consists of 1 a lower subtidal facies succession which is underlain by the nolichucky shale and resembles the rest of the conasauga group carbonate deposits and 2 an upper peritidal facies succession which is conformably overlain by similar peritidal deposits of the copper ridge dolomite knox group deposition of shale and subtidal carbonate took place in deep ramp nolichucky to shallow ramp subtidal shoal and lagoonal settings lower maynardville the carbonate ramp was westward sloping toward the conasauga intrashelf shale basin to the east the ramp was linked to a broad semiarid carbonate tidal flat encompassing a variety of peritidal environments upper maynardville and copper ridge the maynardville is a shallowing upward succession that formed by carbonate platform aggradation and basinward progradation the transition between the maynardville and the copper ridge dolomite is within a conformable peritidal carbonate succession that contains common siliciclastic sand size detritus this interval is interpreted as a sequence boundary correlative with the craton wide late steptoean dresbachian franconian or sauk ii sauk iii unconformity the change from a conasauga to a knox depositional style may be related to distinct stages in passive margin evolution the end of grand cycle deposition in the early late cambrian is coincident with the cessation of tectonic activity along extensional features an intracratonic graben and other fault systems and marks the transition into a mature passive margin setting the mature margin was characterized by decreased rates of thermal subsidence which coupled with the infilling of the conasauga intrashelf basin favored shallow water carbonate deposition the final stabilization of the margin is reflected in the deposition of the thick peritidal carbonate strata of the knox group

cambrian series 3 carbonate platform of korea dominated by microbial sponge reefs abstract metazoans have been considered as negligible components of cambrian series 3 and furongian microbial dominated reefs in contrast to their presence in earlier terreneuvian cambrian series 2 microbial archaeocyath reefs however recent discoveries of sponges in cambrian series 3 furongian reefs of australia china iran usa and korea have raised question regarding their contribution in terms of carbonate platform development which have never been assessed this study examines cambrian series 3 deposits of the daegi formation korea to elucidate this question the 100 m thick middle part of the daegi formation is dominated by boundstone facies which occupies 45 of the study interval as well as bioclastic wackestone to packstone bioclastic grainstone and ooid packstone to grainstone facies the daegi reefs are primarily thrombolitic in composition with 90 n 26 29 of the reefs containing an average of 9 sponges in aerial percentage calculated from thin sections lithistid sponges composed of peloidal fabrics some desma spicules and spicule networks commonly occupy the interstitial space in microbial clusters are encrusted by mesoclots and epiphyton and are surrounded by micrite subordinate non lithistid demosponges occur within clusters of microbial elements the middle daegi formation can be largely subdivided into shoal environment dominated by grainstone to packstone facies and shallow subtidal platform interior environment located behind shoal with wackestone to packstone facies the microbial sponge reefs mainly developed around platform interior as patch reefs the current study indicates that metazoans in the form of lithistid and non lithistid demosponges are nearly ubiquitously incorporated in daegi reefs and contributed greatly to the formation of microbial sponge reefs as well as carbonate platform during the time study of these microbial sponge reefs and their distribution within the carbonate platform may help us to understand how carbonate sedimentary environments responded to the extinction of archaeocyaths

transgressive oversized radial ooid facies in the late jurassic adriatic platform interior low energy precipitates from highly supersaturated hypersaline waters dark gray oolitic units characterized by oversized ooids with primary radial calcite fabrics occur in the interior of the late jurassic late tithonian adriatic platform a large mesozoic tethyan isolated platform in croatia they differ from open marine platform margin ooid grainstones in their dark color cerebroid outlines broken and recoated grains abundant inclusions highly restricted biota and lack of cross stratifithey have been interpreted as being of vadose origin vadoids at tops of upward shallowing parasequences however detailed sections show that most oolitic units occur at bases of precessional parasequences overlying erosional surfaces on fenestral carbonates the oolitic units are similar to quiet water ooids that form today in low energy settings they developed in an arid climate during initial transgression of supratidal fl ats along lowenergy shores seaward of tidal fl ats and along the margins of restricted lagoons and intertidal ponds superimposed fenestral fabrics meniscus micrite cements and grain breakage occurred as they aggraded to high tide level and were subjected to wetting and drying thermal expansion and contraction and wind transport they migrated landward with transgression forming extensive sheets and were overlain by subtidal lagoonal facies that shallow up into fenestral carbonates these distinctive facies may have been overlooked in the geological record or their geological distribution requires juxtaposition of calcite seas high calcite supersaturation states arid climate and presence of fl at topped carbonate platforms in a greenhouse world

microbial laminite versus rooted and burrowed caps on peritidal cycles salinity control on parasequence development early cretaceous isolated carbonate platform croatia some parasequences in the interior of the early cretaceous isolated carbonate platform croatia which formed under a greenhouse climate lack the typical regressive tidal flat laminites instead these bioturbated emergent parasequences have burrowed and rooted upper parts capped with thin greenish paleo sols and are reminiscent of triassic lofer cycles we propose that the bioturbated cycle tops reflect coastal salinities that are normal marine brackish or metahaline whereas the transgressive rare and abundant regressive tidal flat laminites formed under hypersaline coastal waters thus these features may be used to track gross salinity changes of coastal waters on the platform through time in addi tion we suggest ways to evaluate whether the salinity changes relate to hypersaline embay ments on the platform or changes in the cli mate at the parasequence scale we propose that the bioturbated emer gent parasequences could have formed under semiarid conditions seaward of subtle shallow embayments on the platform con temporaneously in the bayheads micro bial laminites developed these would require time equivalent updip and downdip laminate capped and bioturbated emer gence capped parasequences however the para sequences could also have been con trolled by climate changes the laminite capped parasequences could have resulted from salinity increase with shallowing of the platform interior under semiarid condi tions stable climate in contrast the bio turbated emergence capped parasequences could have formed during times of more humid climate punctuating the overall semi arid climate the humid phase would have favored brackish to normal marine salinities in the coastal zone along with macrophytes and intense animal and plant bioturbation which would suppress development of lami nite caps thus these parasequences provide a means of tracking gross salinity of coastal waters and if climate induced then they have implications for fluctuating climates in greenhouse worlds

finite element analysis of multiphase immiscible flow through soils a finite element model is developed for multiphase flow through soil involving three immiscible fluids namely air water and a nonaqueous phase liquid napl a variational method is employed for the finite element formulation corresponding to the coupled differential equations governing flow in a three fluid phase porous medium system with constant air phase pressure constitutive relationships for fluid conductivities and saturations as functions of fluid pressures which are derived in a companion paper by j c parker et al this issue and which may be calibrated from two phase laboratory measurements are employed in the finite element program the solution procedure uses backward time integration with iteration by a modified picard method to handle the nonlinear properties laboratory experiments involving water displacement from soil columns by p cymene a benzene derivative hydrocarbon under constant pressure were simulated by the finite element program to validate the numerical model and formulation for constitutive properties transient water outflow predicted using independently measured saturation capillary head data agreed with observed outflow data within the limits of precision of the predictions as estimated by a first order taylor series approximation considering parameter uncertainty due to experimental reproducability and constitutive model accuracy two dimensional simulations are presented for a hypothetical field case involving introduction of napl near the soil surface due to leakage from an underground storage tank subsequent transport of napl in the variably saturated vadose and groundwater zones is analyzed

cryptalgal metazoan bioherms of early ordovician age in the st george group western newfoundland bioherms are common in the st george group a sequence of shallow water carbonate rocks deposited on the western continental shelf of iapetus ocean they range from small heads and metre sized mounds to extensive banks and complexes many metres thick and hundreds of metres in lateral extent the cores of these bioherms are principally composed of thrombolites unlaminated branching columnar stromatolites structures quite distinct from laminated stromatolites which are common in intertidal beds associated with thrombolites is a diverse fauna of burrowing invertebrates trilobites nautiloids pelmatozoans brachiopods gastropods rostroconchs and archaeoscyphiid sponges on the basis of framework building components three main bioherm types are distinguished 1 thrombolite mounds 2 thrombolite lichenaria or sponge mounds and 3 thrombolite lichenaria renalcis reef complexes the framework of the last is the most complex with abundant cavities and a demonstrably uneven growth surface of thrombolites corals and free standing renalcis heads walls and roofs some cavities were active sediment conduits while others were protected their roofs draped with renalcis and their walls coated by cryptalgal laminites these bioherms possess the attributes of shallow water ecologic reefs they span a critical time gap in the development of reefs the transition period from algal dominated bioherms of the precambrian and cambrian to the metazoan dominated bioherms of the middle ordovician and remaining phanerozoic

an aem tem study of weathering and diagenesis abert lake oregon ii diagenetic modification of the sedimentary assemblage abstract this paper compares the mineralogy and chemistry of clay minerals in sediments from various depths and positions in abert lake and surrounding playa with those of the weathered materials entering the lake in order to reveal the nature and extent of post depositional mineralogical modification analytical electron microscope aem data from individual clay particles reveal that each sample is comprised of a highly inhomogeneous smectite assemblage the thin clay flakes commonly less than 10 nm wide display a complete range in octahedral sheet compositions from nearly dioctahedral to nearly trioctahedral the very abundant mg rich lake smectites with an estimated composition k 0 29 al 0 23 mg 2 16 fe 0 30 si 3 80 al 0 20 o 10 oh 2 are not formed by weathering this confirms the importance of diagenetic mg uptake lattice fringe imaging failed to reveal distinct brucite like or vermiculite like layers suggesting that interstratifications of this type are rare or absent siliceous coatings on clay particles identified by silica excess in smectite analyses seem to favor topotactic overgrowth of stevensite rather than addition of brucite like layers to the dioctahedral nuclei the growth of k stevensite dilutes the al content of the crystal and thus the increasing diagenetic modification reduces rather than supplements its illite component smectite compositions within individual samples were highly variable yet source related characteristics such as the abundance of fe rich smectite were apparent little evidence for systematic k or mg enrichment with depth was identified in samples from depths of down to 16 feet below the sediment water interface the most magnesian assemblages are associated both with weathering sources of mg rich smectite and playa environments subjected to repeated wetting and drying cycles thus the observations suggest that clay compositions primarily reflect changes in lake levels brine composition and source characteristics rather than time and depth compaction effects other diagenetic reactions in the sediment include recrystallization of na rich silica gel and diatom fragments abundant submicron sized untwinned euhedral crystals of k feldspar are interpreted to be authigenic in origin

mixed siliciclastic carbonate upward deepening cycles of the upper cambrian inner detrital belt of laurentia abstract high resolution sedimentological and biostratigraphic data recently recovered from upper cambrian strata in the northern rocky mountain and central appalachian regions reveal that meter scale cycles of very different character developed synchronously during deposition of the basal subzones of the ibexian series in both the carbonate facies belt and the distal part of the inner detrital mixed siliciclastic carbonate facies belt of the laurentian paleocontinent a typical mixed siliciclastic carbonate cycle in the snowy range formation of wyoming and montana consists of the following lithofacies in ascending order shale shale with very thin grainstone interbeds grainstone with subordinate thin shale interbeds flat pebble conglomerate and in some cycles thrombolitic bioherms internal transitions between the constituent lithofacies are mostly gradational but cycle boundaries are sharp with shale directly overlying flat pebble conglomerate and or thrombolitic boundstone we postulate that these mixed siliciclastic carbonate cycles developed in response to different depositional dynamics than meter scale cycles developed in carbonate belt facies specifically cycles in the carbonate belt were produced largely by temporal variation in accommodation space and associated filling of that space through progradation of the carbonate system and aggradation to sea level in contrast cyclic deposition within the inner detrital belt was controlled by variations in terrigenous sediment input and resulting effects on carbonate productivity in this case enhanced delivery of siliciclastic mud by rivers was triggered by regression and or a shift to more humid climatic conditions an upward increase of carbonate in the main part of the cycles reflects enhanced carbonate production in response to the reduction of terrigenous clay supply during shoreline retreat widespread cementation of fine grainstone substrates led to deposition of extensive beds of flat pebble conglomerate possibly in association with elevated sea surface temperatures and enhanced storm intensity thrombolites formed at times of maximum transgression as microbial communities thrived in the absence of turbidity colonizing the irregular surfaces of flat pebble conglomerate beds we thus interpret these wholly subtidal cycles to record full changes in paleobathymetry with the bulk of the cycles recording upward deepening rather than shoaling associated with regression comparison with age equivalent shoaling cycles of the conococheague formation of the carbonate belt of the appalachian mountains highlights the different depositional dynamics in the mixed siliciclastic carbonate systems and underscores the peril in extrapolation of depositional models derived from carbonate systems to mixed systems regardless of age or paleogeographic setting