the role of the calcium carbonate calcium phosphate switch in the mineralization of soft bodied fossils authigenic minerals play an important role in the preservation of most soft bodied fossils the greatest detail is preserved in apatite calcium phosphate but its precipitation is usually inhibited by the high concentrations of hco 3 in aqueous settings nonetheless investigations of soft bodied biotas have revealed very early authigenic calcite crystal bundles in close association with phosphatized soft tissues this demonstrates that the geochemical controls on soft tissue mineralization are dynamic and act on a very local scale direct comparisons with experimental results permit the conditions of fossilization to be inferred

bioturbation in burgess shale type lagerstatten case study of trace fossil body fossil association from the kaili biota cambrian series 3 guizhou china abstract cruziana gordia planolites rusophycus and trichophycus are common ichnological elements of the kaili biota new discoveries based on the examination of 323 specimens include eldoniids echinoderms trilobites monoplacophorans and non biomineralizing arthropods that are associated with trace fossils based on the observed effects of bioturbation on the preservation of five different animal groups it is clear that infaunal scavengers deposit feeders were periodically active on the kaili sea floor and were able to reach historic layers yielding exceptionally preserved fossils in general the average level of infaunal activity is absent to moderate ichnofabric index i i 1 to 3 in the kaili substrate by contrast the phycodes beds are completely disturbed by infaunal activity i i 5 observed burrow diameter ranges from diminutive 0 2 mm to normal up to 4 2 mm computed tomography allows us to visualize the precise geometry of the trace fossil body fossil association in three dimensions we concluded that although some kaili infaunal animals could bore through the biomineralized echinoderms they did not appear to have scavenged upon these echinoderms based on our three dimensional reconstruction furthermore kaili burrowers can reach the historic layers containing exceptionally preserved fossils without altering soft tissue preservation on the other hand we used conventional techniques to reveal that one burrow is filled with fecal pellets 100 200 m at its terminal end because most burrows are filled with yellow brown coarse sediment and because there is no compositional difference between the fecal pellets and the surrounding coarse sediment within the burrow the origin of the yellow brown coarse sediment is interpreted here as parautochthonous and or autochthonous and as a result of sediment reworking by deposit or suspension feeders the relative scarcity of soft part preservation in the kaili biota compared to the older chengjiang biota and the younger burgess shale biota may be the result of post burial bio disturbance due to the relatively high intensity of local bioturbation it is plausible that oxygenation in deeper sediments facilitated by bioturbation allowed carcasses in the kaili biota to undergo a more extensive period of normal decay prior to final burial than in other cambrian konservat lagerstatten

evolutionary paleoecology of the earliest echinoderms helicoplacoids and the cambrian substrate revolution bioturbation in neritic siliciclastic settings during the proterozoic phanerozoic transition increased in depth and intensity causing a change in substrates from the matgrounds characteristic of the proterozoic to the mixgrounds characteristic of the phanerozoic this change in bioturbation increased the water content of surficial layers of sediment and blurred the sediment water interface leading to the first appearance of a mixed layer development of a mixed layer throughout neritic environments would have had a strong impact on any benthic metazoans particularly sessile suspension feeders that were well adapted for survival on relatively unbioturbated proterozoic substrates the impact of this substrate transition on benthic metazoans has been termed the cambrian substrate revolution the unusual early cambrian helicoplacoid echinoderms were well adapted for survival on typical proterozoic style substrates the examination of new helicoplacoid specimens collected during this study combined with extensive study of the rocks in which they are preserved indicate that helicoplacoids lived as sediment stickers on a muddy substrate that underwent only low to moderate levels of strictly horizontal bioturbation and did not have a mixed layer the significant increase of bioturbation through the cambrian in neritic siliciclastic settings is likely to have led to the extinction of the helicoplacoids other similarly adapted sessile suspension feeding echinoderms may have also been driven to extinction by the effects of the cambrian substrate revolution the co existence during the cambrian of organisms adapted to the variety of substrates characteristic of this transitional period may also have contributed to the high degree of perceived morphological disparity during the cambrian explosion

small shelly fossils from the basal emigrant formation cambrian uppermost dyeran stage of split mountain nevada a latest early cambrian fauna of helcionelloid molluscs and small shelly fossils from the basal emigrant formation of nevada is described the fauna is the first of its kind to be described from trilobite bearing strata in the great basin and is well preserved but of limited diversity at the specific level the assemblage is largely endemic but it contains several genera with global distribution in the lower and middle cambrian costipelagiella nevadense n sp in the fauna is the oldest representative of the widespread but little known genus costipelagiella horn 1964 two additional new taxa are described anabarella chelata n sp and parkula esmeraldina n sp

carbonate rock characterization and modeling capillary pressure and permeability in multimodal rocks a look beyond sample specific heterogeneity carbonate rocks are known for their heterogeneity and petrophysical complexity this commonly leads to large uncertainties in reservoir models that are intended to predict fluid storage and fluid flow in this article focus is given to the characterization of pore systems at core plug scale to provide improved models for permeability and saturation prediction these methods fall under a wider rock typing workflow we examine the use of mercury air capillary pressure data for rock type definition and for predicting saturation and permeability we present new methods for modeling saturation in rocks with multimodal pore throat size distributions the methods bear similarity to those previously published but with some key differences mainly by relating the capillary pressure data to the pore systems representative for a rock type we also present a new method for relating permeability to pore throat sizes that is more versatile in that it can be employed for all types of pore throat size distributions unimodal or multimodal we demonstrate that a normalized pore throat radius parameter forms a straight line relationship with permeability over six orders of magnitude it appears to be a fundamental property for all pore systems so far examined the wider implication of the workflows presented is that they offer better integration between the methods used for saturation prediction and the methods used for permeability prediction something that is desirable for all subsurface studies

preservation of early cambrian animals of the chengjiang biota the chengjiang biota of yunnan china documents the earliest extensive radiation of the metazoa recorded in the fossil record gauging preservational bias is crucial in providing an assessment of the completeness of this biota and thereby elucidating whether it represents a comprehensive depiction of early cambrian life we here present a model to explain the nature of the exceptional preservation of the chengjiang biota and details of the decay process this study indicates that chengjiang fossils were preserved through two taphonomic pathways that may have captured tissues of distinct compositions and this finding should provide a foundation for the interpretation of chengjiang fossils many chengjiang fossils are preserved by pyrite later pseudomorphed by iron oxides the clay rich host sediment was deficient in organic carbon but replete in available fe and this composition ensured that a decaying carcass acted as a local substrate for fe and s reducing bacteria pyrite morphology probably reflects contrasts in the decay rate and hence the h 2 s production rate of different tissues in a carcass reactive rapidly decaying tissues would have quickly supplied h 2 s producing many pyrite nuclei resulting in framboidal habits more recalcitrant tissues would have produced h 2 s more slowly so that crystal growth operated on fewer nuclei resulting in larger euhedral pyrite crystals reflective films especially common on chengjiang arthropods represent the remains of degraded carbon

coupled two dimensional diagenetic and sedimentological modeling of carbonate platform evolution we have used a new coupled two dimensional diagenetic and sedimentological model to investigate the evolution of a simple aggrading carbonate platform subject to glacio eustatic sea level fluctuations the model employs variable hydrological zones internally defined from platform exposure and climate to provide a framework within which diagenetic processes are simulated at specified rates simulations show a clear stacked sequence of diagenetic zones which are readily recognizable because of their lateral continuity and distinct trends in diagenetic evolution from platform interior to margin however spatial associations between unconformity surfaces and underlying diagenetic zones that suggest causality are misleading the interaction between high amplitude sea level fluctuations and subsidence results in substantial overprinting and a complex diagenetic history that could not be unraveled by traditional stratigraphic and sedimentological methods

a new hypothesis for organic preservation of burgess shale taxa in the middle cambrian wheeler formation house range utah cambrian konservat lagerstatten are the most significant fossil deposits for our understanding of the initiation of phanerozoic life although many modes of preservation may occur these deposits most frequently contain nonmineralized fossils preserved in the form of kerogenized carbon films a rare yet important taphonomic pathway that has not previously been explained for any unit by a comprehensive model the middle cambrian wheeler formation of utah one of these lagerstatten contains abundant kerogenized preservation of nonmineralized tissues which occurs within a distinctive taphofacies that accumulated under the following conditions 1 domination of the siliciclastic fraction by clay sized particles 2 close proximity to a carbonate platform which resulted in mixed carbonate clay sediments 3 a well developed oxygen minimum precluding benthic colonization and burrowing and 4 relative proximity to oxic bottom waters facilitating transport of organisms from a habitable environment to one that favored their preservation we propose that preservation of nonmineralized tissues in the wheeler formation may have resulted from a combination of influences that reduced permeability and thus lowered oxidant flux which in turn may have restricted microbial decomposition of some nonmineralized tissues those influences include near bottom anoxia preventing sediment irrigation by restriction of bioturbation reducing conditions near the sediment water interface that may have acted to deflocculate aggregations of clay minerals resulting in low permeability face to face contacts early diagenetic pore occluding carbonate cements and an absence of coarse grains such as silt skeletonized microfossils fecal pellets or bioclasts this model may be applicable to kerogenized preservation of macrofossils in other fossil lagerstatten

computer modeling the internal architecture of carbonate platforms a numerical computer model is described that calculates the internal architecture of carbonate platforms in response to varying values of carbonate production subaerial and submarine erosion sediment redeposition and sea level changes the computer generated sections closely resemble large scale outcrops and interpreted seismic profiles through carbonate platforms stillstand and transgressive sequences have prograding and downlapping platform geometries with lagoons developing in transgressive systems regressive sequences have downlapping clinoforms and erosional upper surfaces glacioeustatic scale cycles have a major control on platform geometry with erosional sequence boundaries developing during low stands and platform drowning occurring during transgressive periods lowstand downlapping wedges are minor features when compared with clastic systems and major progradation and downlap of slope deposits develop with transgressions and flooding of platform tops carbonate erosion rates are varied and have an important effect on the morphology of foodback surfaces which have a major control on platform top production the computer program contributes to the analysis of carbonate systems in two ways it gives a visual picture of the quantitative effects of the many parameters controlling carbonate geometries and it aids quantitative analysis of the architectures and time scales of ancient outcrop or seismic sequences

new eocrinoids from the burgess shale southern british columbia canada and the spence shale northern utah usa the family lyracystidae n fam and genus lyracystis n gen are proposed for the holotype and one paratype of the middle cambrian eocrinoid gogia radiata sprinkle the burgess shale arms from the same unit and many additional partial and more complete specimens of this eocrinoid collected from the burgess shale since 1975 a second species lyracystis reesei n gen and n sp is described from a single partly complete specimen from the similar aged spence shale of northern utah lyracystis has three wide v shaped arms bearing numerous long straight brachioles in the notch a partly organized theca having larger and smaller ridged plates with epispires and a very long multiplated stalk made up of rounded or spiny small plates lyracystis is the longest stalked suspension feeding echinoderm known from the middle cambrian the three remaining paratypes of gogia radiata and four new specimens with possible branched brachioles from the burgess shale are renamed gogia stephenensis n sp

settling strategy of stalked echinoderms from the kaili biota middle cambrian guizhou province south china abstract a total of 124 articulated echinoderms including sinoeocrinus lui n 30 s globus n 92 one indeterminate gogiid and one indeterminate edrioasteroid from the kaili formation middle cambrian eastern guizhou china was examined among them 73 of gogiid echinoderms are preserved attached to skeletal substrates suitable skeletal substrates for gogiid holdfasts in the kaili biota are organophosphatic brachiopods large trilobite fragments including cranidia free cheeks thoracic segments and pygidia hyoliths and scenella shells the high frequency of s globus attached to organophosphatic brachiopods is due to the high richness of organophosphatic brachiopods rather than a host specific association in the kaili biota however the possible discrimination against attachment to small trilobites such as pagetia requires further investigation based on 11 hand samples echinoderm population density epd varies from 0 3 to 4 5 echinoderms per 50 grind points 0 06 to 0 96 echinoderms per cm 2 depending on the percent coverage of skeletal debris crowding effect is evident when epd is approximately 0 32 echinoderms per cm 2 and the skeletal coverage is less than 20

geothermal convection in the tengiz carbonate platform kazakhstan reactive transport models of diagenesis and reservoir quality a fundamental challenge in carbonate reservoir characterization is predicting the spatial distribution of diagenesis we used a reactive transport model to investigate the viability of geothermal convection and associated patterns of diagenetic porosity modification in the tengiz isolated carbonate platform reservoir before burial forced convection generates significant calcite dissolution locally up to 45 toward the platform center minor calcite cementation up to 0 4 in the slope and moderate calcite dissolution and cementation up to 1 6 in serpukhovian boundstone convective cells the patterns and rates of diagenesis proved critically sensitive to specified vertical permeability after burial with 200 m 660 ft of salt modeled subsurface temperature contrasts drive platform scale free convection flow is hydraulically closed but significant dissolution up to 7 3 after 20 m y occurred in the serpukhovian and visean platform interior and minor cementation up to 0 7 occurred toward the margin a shale filled salt withdrawal basin 500 m 1640 ft deep significantly modifies the subsurface temperature distribution and free convective flow ascending groundwaters beneath the withdrawal basin created a zone of calcite dissolution up to 24 5 in 20 m y with a mushroom geometry and minor cementation up to 2 3 in 20 m y in the distal platform interior and margin rates of diagenesis are dramatically reduced with increasing overburden as compaction retards convective flow from a generic perspective free convection persists if the salt overburden is substituted with shale although flow is reversed resulting in a different distribution of diagenesis simulations of geothermal convection provide a physically viable model for the integration of direct diagenetic observations to augment predictions of reservoir quality in tengiz and other carbonate platform reservoirs

accommodation and sedimentary architecture of isolated icehouse carbonate platforms insights from forward modeling with carb3d abstract a fundamental control on the evolution of carbonate platforms is accommodation the space available for sediment deposition here we adopt a sensitivity analysis approach using the process based forward model carb3d to quantitatively investigate the sedimentary response of isolated carbonate platforms to individual accommodation drivers of eustasy subsidence and surface dissolution sediment production the mechanism invoked to fill accommodation is also investigated fourth order milankovich driven sea level cycles dominate icehouse carbonate sedimentology with 400 ky cycles modulating the effect of 100 ky cycles of comparable magnitude when both cycles are present both overwhelm higher frequency lower amplitude fifth order cycles which are rarely preserved on the platform top subsidence is a fundamental control on sedimentary stacking patterns sequence boundary frequency sbf and platform geometry with rapid subsidence increasing the preservation of platform top sequences most icehouse platforms are subject to extended periods of platform top exposure missed beats when the platform top remains emergent at a sea level maximum are common and create non milankovich sbfs furthermore during platform emergence surface lowering via surface dissolution also creates accommodation for the subsequent platform flooding event with surface dissolution rates in humid climates comparable to moderate rates of subsidence however accommodation generation by surface dissolution is self limiting in as much as accommodation generated by dissolution is rapidly refilled on flooding sediment production is a key control on unfilled accommodation which our simulations suggest is considerable on icehouse platforms increased shallow water 3 m depth sediment production enhances intra platform bathymetric relief between the margin and interior this is driven in large part by a higher sedimentation rate at the margin than in the interior platforms can be flooded to depths up to 45 m during marine transgressions and accommodation often remains unfilled there are two distinct phases of platform top sedimentation during the transgression and early highstand platform margins accumulate at a greater rate than interior sediments generating differential intra platform bathymetry subsequently accommodation in the interior fills by forced regression and progradation from the margins into the platform interior numerical forward models can augment our understanding of icehouse carbonate platform evolution by identifying the nature of the sedimentary response to individual controls they can thus contribute to improving characterization of carbonate reservoirs in icehouse platforms such as the large hydrocarbon fields in the north caspian and s e asia

pore system characterisation in heterogeneous carbonates an alternative approach to widely used rock typing methodologies abstract rock typing is used in carbonate reservoir characterisation to group petrophysically similar rocks for reservoir modelling purposes the focus is often upon bringing together samples with similar porosity permeability and capillary pressure to achieve this rock typing studies are usually conducted primarily on core plugs using routine core analysis data and thin sections however such an approach results in a tendency to focus on grouping samples with consistent petrophysical properties ignoring the geological controls on pore evolution this means that modelling rock types predicatively using 3d geocellular models is not easily accomplished furthermore where geological observations are made they tend to consider only depositional rock properties and not the effects of diagenesis in doing so a key control on the evolution of the carbonate pore network is ignored this paper addresses these issues using a giant carbonate reservoir in northern oman rock types were defined on the basis of pore geometry whilst retaining distinct geological descriptors the aim was to ensure that each rock type could be defined on the basis of both its petrophysical properties and behaviour during hydrocarbon recovery the results show that characterisation of pore heterogeneity is critical to the prediction of flow behaviour under reservoir conditions and that routine petrophysical parameters are often not good indicators of sweep efficiency

taphonomy palaeoecological implications and colouration of cambrian gogiid echinoderms from guizhou province china based on rich material 381 specimens examined from two cambrian echinoderm faunas the early cambrian balang fauna and middle cambrian kaili fauna in guizhou province south china the taphonomy of gogiid echinoderms is described in detail and the preservation of stereomic microstructure and organic remains of cambrian gogiid echinoderms is reported here for the first time taphonomic considerations include entombment patterns decay sequences individual specific diagenetic histories unusual burial postures selective disarticulation patterns and postmortem elongation in particular five categories of gogiid entombment patterns are proposed to describe the multi directional orientations recorded at the burial time of articulated gogiids gogiid bearing slabs of guizhou material primarily 70 display the type 2 entombment pattern articulated gogiids preserved with fan shaped brachioles thus most guizhou gogiids were buried with brachioles preserved in feeding posture during obrution events balang gogiid faunas contain the oldest evidence of palaeoecological interactions among echinoderms and other indigenous taxa in addition to pre burial and post burial decay other potential causes for unusual disarticulation patterns exhibited by the gogiids from the lower cambrian balang formation include pre burial bio disturbance and post burial bioturbation based on ichnogenera including rusophycus and planolites chemical analyses reveal that carbon calcium manganese and iron are the major elements responsible for the variety of colours exhibited by guizhou gogiids three dimensional stereomic microstructure mean stereom pore size 8 4 8 7 m average trabecular thickness 4 5 4 6 m occurs on the external surfaces of thecal plates in two gogiid species stereom preservation in calcite suggests that the dissolution of calcareous echinoderm plates yielding characteristic mouldic preservation is sub recent after lithificaiton and exposure of gogiid bearing marine sedimentary successions on or near the land surface

modelling the permeability evolution of carbonate rocks abstract diagenesis is a major control on the distribution of porosity and permeability in carbonate rocks and therefore impacts fluid flow in the subsurface while changes in porosity can be directly related to diagenetic petrographic characteristics such as cement distribution and dissolution features quantifying how these textures relate to attendant changes in permeability is more challenging here we demonstrate for the first time how pore scale models representing typical carbonate sediments and their diagenetic histories can be used to quantify the evolution of petrophysical properties in carbonate rocks we generate 3d pore architecture models i e the spatial distribution of solid and pores from 2d binarized images representing the typical textural changes of carbonate sediments following hypothetical diagenetic pathways for each 3d rock model we extract the pore system and convert this into a network representation that allows flow properties to be calculated the resulting porosity and permeability evolution scenarios display several diagenetic tipping points where the decrease in permeability is dramatically larger than expected for the associated decrease in porosity the effects of diagenesis also alter the capillary entry pressures and relative permeabilities of the synthetic cases providing trends that can be applied to real rocks indeed values of porosity and absolute permeability derived from these synthetic 3d rock models are within the range of values measured from nature such diagenetic pathway models can be used to provide constraints on predicted flow behaviour during burial and or uplift scenarios using diagenetic back stripping of real carbonate rocks

a fuzzy logic approach for the estimation of facies from wire line logs a method based on fuzzy logic inference can be used to identify lithological and depositional facies from wire line logs fuzzy logic is inherently well suited to characterizing vague and imperfectly defined knowledge a situation encountered in most geological data it can thus yield models that are simpler and more robust than those based on crisp logic the method is simple easy to comprehend and robust it also generates several confidence measures that can be used to assess the quality of the analysis several enhancements including static and dynamic constraints are discussed the technique is tested here by applying it to predict the depositional facies of a cored well in a marine carbonate environment and comparing the output with the facies derived from core analysis the two show considerable agreement which indicates that this method can be an effective means of predicting the facies of uncored wells from their logs the method has advantages when contrasted with other techniques that rely on multivariate statistics and neural networks compared to those techniques this method is simpler easier to retrain more reproducible noniterative and more computer efficient

rise of echinoderms in the paleozoic evolutionary fauna significance of paleoenvironmental controls echinoderms were a major enduring component of paleozoic marine faunas beginning with the rapid diversification of crinoids and other classes in the early ordovician this diversification was triggered by increased availability of habitable areas accompanying sea level rise and changed sedimentation styles newly collected early ordovician echinoderms facilitate determination in detail of life modes and important adaptations during this transition interval substrate consistency and stability were crucial spatial limiting factors that resulted in heterogeneous distribution patterns for echinoderm classes crinoids were overwhelmingly large food groove suspension feeders with relatively open filtration fans attached by small discs to hard ground surfaces in shallow water they were preadapted for this life mode rhombiferans were mobile small food groove suspension feeders they lived on soft substrates at various depths several important crinoid clades underwent a second phase of diversification during the middle ordovician by developing holdfasts adapted to soft substrates and densely pinnulate arms with small food grooves leading to dominance of this class among paleozoic echinoderms our findings are in basic agreement with the overall onshore diversification pattern of most paleozoic benthic invertebrates but we argue for an extrinsic environmental control substrate availability for the observed echinoderm distribution

cold stage formation of calcrete nodules in the chinese loess plateau evidence from u series dating and stable isotope analysis this pilot study shows that some calcrete nodules from the base of palaeosols in the chinese loess sequences can be dated by u series isochron methods the ages obtained suggest that the nodules did not form during interglacial climate stages rather they formed either during interglacial glacial transitions or glacial climate stages thus the nodules appear not to have formed contemporaneously with the soils beneath which they immediately lie but significantly post date them post pedogenic injection of carbonate into stratigraphically lower horizons is therefore identified this finding contradicts previous assumptions regarding the timing of nodule formation carbon and oxygen isotope analyses of the nodules identify isotopic compositions which independently suggest that climatic conditions cooler and possibly drier than at present prevailed at the time of nodule formation

the role of abiotic factors in the cambrian substrate revolution a review from the benthic community replacements of west gondwana abstract the cambrian substrate revolution refers to a substantial and rapid change to the nature of marine sedimentary substrates in the early cambrian and is widely interpreted as a biologically driven event a direct response to evolutionary innovations in metazoan burrowing and the development of new shelly faunas however abiotic factors such as tectonic and climatic evolution also had the potential to restructure cambrian substrates and are here shown to be more plausible drivers of change in the benthic faunas of western gondwana the western mediterranean region underwent a southward drift during cambrian times which drove a switch from subtropical carbonates to temperate siliciclastic substrates with short term episodes of temperate carbonate productivity as a result microbial and shelly carbonates disappeared diachronously in a stepwise manner across the lower middle cambrian boundary interval archaeocyathan microbial reefs were replaced by chancelloriid eocrinoid spiculate sponge meadows in which the stepwise immigration of new echinoderm taxa was primarily controlled by extensional tectonic events first recorded in rifting settings and later in passive margin platforms availability of new kinds of substrate was thus the primary factor that controlled where and when evolutionary innovations in benthic strategies arose examples of this include the early cambrian colonization of phosphatic hardgrounds and thrombolite crusts by chancelloriids archaeocyathan and spiculate sponges and the exploitation by benthos to the increasingly widespread availability of shelly grounds and carbonate firmgrounds by early diagenetic cementation a microbial mat epifaunal antagonistic relationship is demonstrated for echinoderm pelmatozoans based on the non overlapping palaeogeographic distributions of microbial reefs and mats versus mud sticker pelmatozoans cambrian benthic communities thus evolved in parallel with substrates in response to abiotic factors rather than being the primary drivers of substrate change

taphonomy of cystoids echinodermata diploporita from the napoleon quarry of southeastern indiana usa the lower silurian massie formation as an atypical lagerstatte abstract diploporites like most pelmatozoan echinoderms are characterized by complex multi element skeletons prone to complete disarticulation if left exposed for extended periods of time consequently preservation of abundant articulated diploporite thecae is rare and generally restricted to environments where rapid burial events could catastrophically entomb individuals one such environment is represented by the lower portion of the wenlock age massie formation at the new point stone quarry near napoleon southeastern indiana which we recognize as a konservat lagerstatte yet taphonomic evidence does not support live burial diploporites holocystites spp are dominantly preserved as intact thecae without any portions of brachioles and with damage plate shifting and plate loss plate jumbling on one side post mortem encrustation is common but epibionts are typically present on the well preserved sides of thecae geopetal sediment fill of thecae shows that the well preserved side commonly faced upward following burial this taphonomic state is paradoxical as burial of live diploporites would have resulted in preservation of complete individuals with no encrusters and only compaction induced damage rapid burial of diploporites following a short interval of exposure would have resulted in preservation similar to observed patterns but with encrusters and geopetal infills indicating that the poorly preserved side faced up and burial after extended exposure would have resulted in thorough disarticulation of thecae rather a variable and in some cases complex taphonomic history is suggested for diploporites from the napoleon quarry with at least some individuals having experienced one or more brief episodes of exhumation prior to final burial early diagenetic cementation of initial theca filling sediment is the most likely mechanism for keeping thecae intact during subsequent exposure

taphonomy and depositional circumstances of exceptionally preserved fossils from the kinzers formation cambrian southeastern pennsylvania abstract the emigsville member of the kinzers formation cambrian southeastern pennsylvania is a deposit of exceptional preservation containing three main lithofacies that were part of a mixed siliciclastic carbonate debris fan developed seaward of a carbonate shelf along the appalachian margin of laurentia fossils were exceptionally preserved in a shelf environment subject to tempestite deposition most remains are fragmentary which emphasizes the importance of predation as a taphonomic process where emigsville sediments were deposited remains are preserved mostly as organic carbon films pyrite crusts and aluminosilicate films these preservation styles apparently depended upon the development of microbial consortia in isolated microenvironments and some of the microbes were autolithified sedimentary and biological evidence suggests that anoxia salinity fluctuations and sedimentary obrution played relatively minor roles in the emigsville member of the kinzers formation the abundance of exceptionally preserved remains suggests that exceptional sedimentary conditions were not necessary in the cambrian in order for exceptional preservation to occur the abundance of predation evidence in a deposit of exceptional preservation reinforces the concept that predation was the primary taphonomic filter during cambrian time

quantification of pore structure and its effect on sonic velocity and permeability in carbonates carbonate rocks commonly contain a variety of pore types that can vary in size over several orders of magnitude traditional pore type classifications describe these pore structures but are inadequate for correlations to the rock s physical properties we introduce a digital image analysis dia method that produces quantitative pore space parameters which can be linked to physical properties in carbonates in particular sonic velocity and permeability the dia parameters derived from thin sections capture two dimensional pore size domsize roundness aspect ratio ar and pore network complexity poa comparing these dia parameters to porosity permeability and p wave velocity shows that in addition to porosity the combined effect of microporosity the pore network complexity and pore size of the macropores is most influential for the acoustic behavior combining these parameters with porosity improves the coefficient of determination r2 velocity estimates from 0 542 to 0 840 the analysis shows that samples with large simple pores and a small amount of microporosity display higher acoustic velocity at a given porosity than samples with small complicated pores estimates of permeability from porosity alone are very ineffective r2 0 143 but can be improved when pore geometry information poa r2 0 415 and domsize r2 0 383 are incorporated furthermore results from the correlation of dia parameters to acoustic data reveal that 1 intergrain and or intercrystalline and separate vug porosity cannot always be separated using sonic logs 2 p wave velocity is not solely controlled by the percentage of spherical porosity and 3 quantitative pore geometry characteristics can be estimated from acoustic data and used to improve permeability estimates

diagenesis and crystal caskets echinoderm mg calcite transformation dry canyon new mexico u s a abstract the stereom of living echinus esculentus skeletons is composed of mg calcite interambulacral plates 6 mole mgco3 spines 4 mole mgco3 and is compared with the stereom of pennsylvanian echinoderms from the holder formation dry canyon some dry canyon echinoderms had their pore system 55 volume filled by magnesian ferroan calcite cement before the stereom transformed type 1 into small 20 m diameter in ossicles that underwent type 2 transformation indicates ionic transfer over tens of microns the margins of some type 2 ossicles set in a clay matrix are fe rich and contain barite crystals the fe2 and ba2 were transferred from the surrounding clay hundreds of microns into these ossicles type 1 transformation was catalyzed by internal water from the stereom the presence of a ferroan calcite crystal casket confined alteration to the skeletal mg calcite type 2 transformation involved both stereom and pore filling mg calcite cement the unstable dolomite crystals formed by both transformation processes were protected from further change by the crystal caskets in which they are encased the transformation of dry canyon echinoderms was probably triggered or accelerated by rising temperature caused by burial the bulk composition of stereom that has undergone type 1 transformation can be used as a proxy for the original major element chemistry of echinoderm skeletons minor amounts of mg calcite cement that occur in dry canon type 1 ossicles indicate the chemistry of porewater close to the sediment water interface fossil echinoderms are preserved in many ways and it is suggested that their textural variations can be used to map the distribution of diagenetic reactions the stereom is destroyed in most fossil echinoderms and even in those where the stereom shape is preserved its internal structure is changed echinoderm mg calcite does not transform with perfect textural preservation