an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

interregional correlation of disconformities in upper cretaceous strata western interior seaway biostratigraphic and sequence stratigraphic evidence for eustatic change comment in their recent publication walaszczyk et al 2014 made a number of claims about regressive transgressive disconformities in uppermost turonian and lower coniacian upper cretaceous strata of the western interior foreland basin of north america they postulated that two of the disconformities are synchronous extending over a distance of 1650 km along the length of the cretaceous western interior seaway from horseshoe dam alberta canada on the northwestern margin of the basin to pueblo colorado united states near its center they proposed that the disconformities are not just intracontinental but also intercontinental lastly they extended two of the surfaces from north america into central europe and postulated that oscillations in relative sea level with some unknown element of eustatic control were responsible for their formation

imaging 3 d fracture networks around boreholes a new method has been developed for building and visualizing three dimensional 3 d subsurface natural fracture networks in rocks surrounding boreholes using image logs such as cast emi fmi fms rosi and others the method correlates fracture patterns with different stages of fracture network development for individual sets of fractures and extrapolates fracture density and connectivity from one dimension 1 d in boreholes to 3 d in the surrounding rocks the application of this work is 3 d visualizations of fracture distributions in volumes close to the boreholes for well planning reservoir scale fracture model building reservoir flow simulation and hydraulic fracture control

scaling and connectivity of joint systems in sandstones from western norway abstract the scaling properties of a joint system in devonian sandstones in western norway have been investigated using seven maps covering areas from 18 to 720 m across which were generated by mapping in the field and from low level aerial photography taken from different heights each map represent a scale window on the fracture population bounded by resolution at small scales and the sample size at large scales a power law relationship between fracture trace length and critical observation height maximum height at which a trace can be identified is derived and used to create a statistical model for the resolution effects the model indicates that a continuous smooth curve without a straight line segment on a log log cumulative frequency distribution plot does not necessarily rule out a power law as the underlying population distribution together the maps indicate a powerlaw trace length distribution with an exponent of 2 1 this power law may be valid over four or more orders of magnitude with natural lower cut off of around 1 m the exponent is significantly different from 2 0 strictly selfsimilar case and is reflected in a decrease in the abundance of fractures with length comparable to map size as map scale decreases the fracture trace length distribution results in a decrease in apparent connectivity with decreasing scale high resolution large scale maps are well connected while the lowest resolution map smallest scale is unconnected fractures in the smallest scale map are however connected by small fractures below the limit of resolution represented by the largest scale map the variation in apparent connectivity with scale has implications for fluid flow when fractures are open to fluid flow the scaling properties of apparent connectivity imply that beyond a certain scale the size of fracture controlling flow will be scale independent in this fracture system this appears to occur in sample areas of around 300 m across

surfaces with a long history the aptian top shu aiba formation unconformity sultanate of oman discontinuity surfaces in shallow marine carbonate successions may represent significant time gaps in the geological record of ancient epeiric neritic seas understanding the hidden geological information contained in major discontinuities is thus of key significance in palaeo environmental analysis sequence stratigraphy reconstructions of sea level change and basin evolution in the present paper the aptian top lower shu aiba formation discontinuity in the sultanate of oman is taken as a prominent example of a regionally extensive 100 000 km2 surface with a long up to 10 myr and complex geological history the top shu aiba discontinuity formed on the topographically elevated domain of the oman platform and represents in essence the late aptian time interval coeval carbonates in the intrashelf bab basin and oceanic rim indicate forced regression and sequence wise gradual down stepping available regional sedimentological sequence stratigraphic petrographic palaeontological and geochemical evidence from outcrops and cored wells in oman is summarized in part complemented by new data and reviewed in a process oriented context in the field the discontinuity is expressed as a low relief stained surface with evidence for a marine hardground stage being dominant indistinct features that indicate a transient meteoric precursor stage isotope shifts meteoric cements circumgranular cracks etc are present but their interpretation requires careful and detailed work this feature is remarkable as a series of relative sea level falls with amplitudes of up to several tens of metres from the early to late aptian boundary to the end of the aptian are reported from the middle east and elsewhere despite the palaeogeographic position of the study area in the tropical climate zone evidence of deep cutting karst features characteristic for many long term exposure surfaces worldwide is scarce acknowledging the fact that the modern world offers no genuine analogues for the lower aptian carbonate system in oman morphological similarities between actualistic wave eroded coastal terraces and the top shu aiba discontinuity are discussed critically this discussion may imply that during an exposure time of several million years the top shu aiba discontinuity experienced repeated stages of shallow flooding and emergence with each transgression removing portions of the underlying rock record the data shown here exemplify the complexity of hiatal surfaces in epeiric neritic carbonates and may serve as a case example for other major discontinuities

fracture zones constrained by neutral surfaces in a fault related fold insights from the kelasu tectonic zone kuqa depression abstract stress variation associated with folding is one of the controlling factors in the development of tectonic fractures however little attention has been paid to the influence of neutral surfaces during folding on fracture distribution in a fault related fold in this study we take the cretaceous bashijiqike formation in the kuqa depression as an example and analyze the distribution of tectonic fractures in fault related folds by core observation and logging data analysis three fracture zones are identified in a fault related fold a tensile zone a transition zone and a compressive zone which may be constrained by two neutral surfaces of fold well correlation reveals that the tensile zone and the transition zone reach the maximum thickness at the fold hinge and get thinner in the fold limbs a 2d viscoelastic stress field model of a fault related fold was constructed to further investigate the mechanism of fracturing statistical and numerical analysis reveal that the tensile zone and the transition zone become thicker with decreasing interlimb angle stress variation associated with folding is the first level of control over the general pattern of fracture distribution while faulting is a secondary control over the development of local fractures in a fault related fold

a scale independent approach to fracture intensity and average spacing measurement fracture intensity the number of fractures per unit length along a sample line is an important attribute of fracture systems that can be problematic to establish in the subsurface lack of adequate constraints on fracture intensity may limit the economic exploitation of fractured reservoirs because intensity describes the abundance of fractures potentially available for fluid flow and the probability of encountering fractures in a borehole traditional methods of fracture intensity measurement are inadequate because they ignore the wide spectrum of fracture sizes found in many fracture systems and the consequent scale dependence of fracture intensity an alternative approach makes use of fracture size distributions which allow more meaningful comparisons between different locations and allow microfractures in subsurface samples to be used for fracture intensity measurement comparisons are more meaningful because sampling artifacts can be recognized and avoided and because common thresholds of fracture size can be enforced for counting in different locations additionally quantification of the fracture size distribution provides a mechanism for evaluation of uncertainties estimates of fracture intensity using this approach for two carbonate beds in the sierra madre oriental mexico illustrate how size cognizant measurements cast new light on widely accepted interpretation of geologic controls of fracture intensity

characterization and interpretation of discontinuity surfaces in a jurassic ramp setting high atlas morocco discontinuity surfaces are widely recognized but often poorly understood features of epeiric carbonate settings in sedimentary systems these features often represent hiatus surfaces below biostratigraphic resolution and may represent a considerable portion of the time contained in the sediment record from an applied perspective discontinuities may represent horizontal flow barriers and result in reservoir compartmentalization here a total of 80 condensed surfaces s1 firmgrounds s2 and hardgrounds s3 from a jurassic middle and upper bajocian assoul formation ramp setting of the high atlas in morocco are carefully documented with respect to their morphology their secondary impregnation by fe and mn oxides and phosphates and their palaeoecological record a statistical frequency distribution of two surfaces of the s1 type 1 1 surfaces of the s2 type and 0 4 surfaces of the s3 type per 10 section metres is observed along a 220 m long carbonate succession based on two stratigraphically and spatially separated study windows and correlative sections the stratigraphic frequency distribution the lateral extent and the nature of facies change across discontinuities are documented in a quantitative manner specific features of the study site include the considerable stratigraphic thickness of the assoul formation and the conspicuous absence of subaerial exposure related features based on the data presented here firmground and hardground surfaces are best interpreted as maximum regression related features relative sea level lowstand results in a lowered wave base and wave orbitals and currents result in sea floor omission and lithification care must be taken to avoid overly simplistic interpretations as differences in bathymetry and carbonate facies result in marked changes in discontinuity characteristics in proximal distal transects the data shown here are of significance for those concerned with the interpretation of shoal water carbonate environments and are instrumental in the building of more realistic carbonate reservoir flow models

ichnology of a subaqueously prograding clastic wedge late pliocene morne l enfer formation fullarton trinidad implications for recognition of autogenic erosional surfaces and delineation of stress factors on irregular echinoids abstract the morne l enfer formation outcrops near fullarton trinidad expose an erosional surface between the shelf deposits below and a prograding clastic wedge of the late pliocene paleo orinoco system above the surface exhibits similarities as well as dissimilarities with examples of regressive surfaces of marine erosion rsmes in wave influenced shelf settings and also with incised valleys inherited from fluvial incision of shelf during a forced regression episode however detailed ichnological studies reveal that the surface is a subaqueous autogenically controlled erosional surface on a shelf dominated by the hyperpycnal and hypopycnal discharges with transient wave influence integration of ichnological and sedimentological characteristics also suggests complicated interrelationships among different stress factors affecting the infauna in different subenvironments especially the irregular echinoids the delta prograded subaqueously through autogenically establishing its lobe on the open shelf without stratigraphically significant erosional removal of sediments in the subaqueously prograding clastic wedge the fluvial influence pertains high stress conditions not only for the adult infauna but also for their larvae within the water column especially in and near the subaqueous distributary channels

the temporal relationship between joints and faults abstract examples are presented of three temporal relationships between joints and faults joints that pre date faults joints that are precursors to or synchronous with faults and joints that post date faults emphasis is placed on strike slip faults in carbonate beds but other examples are used general rules are given for identifying the three temporal relationships between joints and faults joints that formed before faults can be dilated sheared or affected by pressure solution during faulting depending on their orientation in relation to the applied stress system faulted joints can preserve some original geometry of a joint pattern with pinnate joints or veins commonly developing where faulted joints interact joints formed synchronously with faults reflect the same stress system that caused the faulting and tend to increase in frequency toward faults in contrast joints that pre or post date faults tend not to increase in frequency towards the fault joints that post date a fault may cut across or abut the fault and fault related veins without being displaced by the fault they may also lack dilation near the fault even if the fault has associated veins joints formed either syn or post faulting may curve into the fault indicating stress perturbation around the fault different joint patterns may exist across the fault because of mechanical variations geometric features may therefore be used in the field to identify the temporal relationships between faults and joints especially where early joints affect or control fault development or where the distribution of late joints are influenced by faults

stratigraphic controls on vertical fracture patterns in silurian dolomite northeastern wisconsin vertical opening mode fractures are mapped on quarry walls to assess the stratigraphic controls on fracture patterns in the relatively undeformed silurian dolomite of northeastern wisconsin our two stage study uses maps of vertical fractures to assess the effectiveness of various types of stratigraphic horizons e g organic partings or cycle bounding mud horizons in terminating opening mode fractures first the mechanical stratigraphy of the exposures is interpreted from the observed fracture pattern both visual inspection and a newly developed quantitative method are employed to identify effective mechanical interfaces the two methods show similar results confirming the validity of qualitative visual inspection the second stage of our study stochastically predicts mechanical stratigraphy and subsequent fracture pattern from empirical relationships between the observed sedimentary stratigraphy and the interpreted mechanical stratigraphy for example 63 of cycle bounding mud horizons within the inner middle and middle shelf facies associations serve as mechanical interfaces these empirical percentages are input to a monte carlo analysis of 50 stochastic realizations of mechanical stratigraphy comparisons of the stochastically predicted and interpreted mechanical stratigraphy yield errors ranging from 13 to 33 this method yields far better results than assuming that all stratigraphic horizons act as mechanical interfaces the methodology presented in this article demonstrates an improved prediction of fracture pattern within relatively undeformed strata from both complete characterization of sedimentary stratigraphy and understanding mechanical controls on fracturing

mechanism for joint saturation in mechanically layered rocks an example from southern israel abstract over 700 joint spacings were measured along a 190 m scanline within a single limestone bed of the turonian gerofit formation southern israel by investigating joints belonging to a single systematic set confined to a bed of uniform thickness one can factor out the major influences of bed thickness lithology and mechanical properties on joint set development joint spacing distributions and fracture spacing ratios fsr vary dramatically along the length of the scanline and correlate directly with throughgoing fracture zones belonging to the same tectonic stress regime regions cross cut by fracture zones display narrower median joint spacings fsr of 1 3 and unimodal joint spacing distributions where fracture zones are absent joint spacings have wider medians fsr of 0 8 and multimodal distributions because fracture zones most likely represent areas of high strain and laboratory experiments demonstrate a systematic decrease in fracture spacing with increasing strain regions of the bed cross cut by fracture zones are likely at a more advanced stage of joint set development and hence closer to saturation than other regions joint saturation in the gerofit formation may be achieved by a shift in scale from single layer to multi layer jointing as the development of throughgoing joints prevents the formation of additional bedding confined joints

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

two dimensional simulation of controls of fracture parameters on fracture connectivity two dimensional fracture simulation is conducted to analyze the controls of different fracture parameters variations in fracture orientation density and length on fracture network connectivity three different scenarios which are commonly encountered in natural fracture systems are analyzed 1 a single fracture set 2 two fracture sets with one primary through going set and 3 two fracture sets with approximately equal parameters the modeling reveals that certain parameters are more dominant in controlling the connectivity for each of the settings for a single set of fractures increases in length and dispersion and a decrease in spacing all result in higher fracture parallel connectivity but the decrease in spacing is the most important in increasing fracture normal connectivity especially where the dispersion in fracture strike is very low simulations of two sets of fractures reveal that the density length and angle between the two sets are important factors in producing complete connectivity in cases where one set of fractures is a systematic throughgoing set a critical combination of length of the second set and the angle between the two sets results in complete connectivity where both sets of fractures have varying length and density the influence of increasing density of one set has a great effect on connectivity when the other set is short and a more subtle to insignificant change when the other set is long the network also shows higher connectivity with increasing angles up to 90 between the two sets

overlapping paleoichnology paleoecology and taphonomy analysis of tooth traces in a late pleistocene early holocene megafaunal assemblage of brazil and description of a new ichnotaxon in hard substrate abstract tooth traces are key evidence in vertebrate taphonomy paleoecology and paleoichnology they are product of feeding behavior of vertebrates and can also be evaluated in biostratinomic perspective regarding the quaternary fossil record of vertebrates in brazil the taphonomic paleoecological information of tooth traces has been underexplored recently features of this sort were identified in quaternary mammals fossils recovered from lajedo da escada caves state of rio grande do norte northeastern brazil consisting in an opportunity to unveil taphonomic paleoichnological and paleoecological aspects of the quaternary megafauna the ichnospecies machichnus bohemicus and m fatimae are recorded in the late pleistocene early holocene age the latter is a new ichnospecies of machichnus described herein the traces m fatimae and m bohemicus observed in glyptotherium sp were generated outside the cave by an adult individual of the large sized canid protocyon troglodytes during event of predation nonetheless m bohemicus recognized in eremotherium laurillardi and smilodon populator was generated by either a juvenile individual of p troglodytes or an adult of the small sized canid cerdocyon thous in a scavenging context outside the cave probably other tooth traces previously reported to the quaternary of brazil in the states of ceara and minas gerais can be assigned to machichnus

stress evolution during 3d single layer visco elastic buckle folding implications for the initiation of fractures abstract buckle folds of sedimentary strata commonly feature a variety of different fracture sets some fracture sets including outer arc tensile fractures and inner arc shear fractures at the fold hinge zones are well understood by the extensional and compressional strain stress pattern however other commonly observed fracture sets including tensile fractures parallel to the fold axis tensile fractures cutting through the limb extensional faults at the fold hinge and other shear fractures of various orientations in the fold limb fail to be intuitively explained by the strain stress regimes during the buckling process to obtain a better understanding of the conditions for the initiation of the various fractures sets associated with single layer cylindrical buckle folds a 3d finite element modeling approach using a maxwell visco elastic rheology is utilized the influences of three model parameters with significant influence on fracture initiation are considered burial depth viscosity and permeability it is concluded that these parameters are critical for the initiation of major fracture sets at the hinge zone with varying degrees the numerical simulation results further show that the buckling process fails to explain most of the fracture sets occurring in the limb unless the process of erosional unloading as a post fold phenomenon is considered for fracture sets that only develop under unrealistic boundary conditions the results demonstrate that their development is realistic for a perclinal fold geometry in summary a more thorough understanding of fractures sets associated with buckle folds is obtained based on the simulation of in situ stress conditions during the structural development of buckle folds

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

combining outcrop data and three dimensional structural models to characterize fractured reservoirs an example from wyoming combining a detailed outcrop characterization of fracture and fault occurrence with attributes from a three dimensional model of an anticlinally folded clastic reservoir body we determine which characteristics of the structural form and evolution are most closely related to the development of important reservoir scale structures our example reservoir body studied is the frontier formation 1 sandstone in oil mountain an asymmetric anticline on the western flank of casper arch in central wyoming the three dimensional model of the structure was constructed using an iterative scheme designed to maximize interpretation accuracy and precision the model was analyzed to determine the spatial variance in morphologic and kinematic attributes using a quantitative testing approach we found that the intensity of tectonically produced fractures is closely related spatially to rate of dip change and total curvature with the former having the strongest correlation this folding is a low strain process compared to tear faulting which has the strongest spatial correlation to larger strains the location and magnitude of these higher strain areas can be adequately predicted by three dimensional restoration and forward modeling of the upper bounding surface of the reservoir body we use these results to build a predictive model for fault and fracture distribution at oil mountain and to discuss how this approach can aid in the exploitation of analogous producing reservoirs

palaeoecology and evolution of marine hard substrate communities abstract marine organisms have occupied hard substrates since the archaean shells rocks wood and sedimentary hardgrounds offer relatively stable habitats compared to unconsolidated sediments but the plants and animals which inhabit them must develop means to gain and defend this premium attachment space hard substrate communities are formed by organisms with a variety of strategies for adhering to and or excavating the substrates they inhabit while mobile grazers organically attached and even soft bodied organisms may leave evidence of their former presence in ancient hard substrate communities a superior fossil record is left by sessile encrusters with mineralised skeletons and by borers which leave trace fossils furthermore encrusters and borers are preserved in situ retaining their spatial relationships to one another and to the substrate spatial competition ecological succession oriented growth and differential utilisation of exposed vs hidden substrate surfaces can all be observed or inferred hard substrate communities are thus excellent systems with which to study community evolution over hundreds of millions of years here we review the research on modern and ancient hard substrate communities and point to some changes that have affected them over geological time scales such changes include a general increase in bioerosion of hard substrates particularly carbonate surfaces through the phanerozoic this is at least in part analogous to the infaunalisation trends seen in soft substrate communities encrusting forms show an increase in skeletalisation from the palaeozoic into the mesozoic and cenozoic which may be a response to increasing levels of predation hard substrate communities considering borers and encrusters together show a rough increase in tiering through the phanerozoic which again parallels trends seen in soft substrate communities this extensive review of the literature on living and fossil hard substrate organisms shows that many opportunities remain for large scale studies of trends through time at the community and clade levels palaeontologists will especially benefit by closer integration of their work with that of neontologists particularly in aspects of ecology such as larval recruitment competition and succession

derivation of parent fracture population statistics from trace length measurements of fractal fracture populations this note describes how to estimate the three dimensional fracture size distribution from trace length statistics

bivalve trace fossils in an early miocene discontinuity surface in patagonia argentina burrowing behavior and implications for ichnotaxonomy at the firmground hardground divide abstract ichnofossils developed in a firmground at the contact between the middle eocene lower miocene continental sarmiento formation and the lower miocene marine chenque formation in central eastern patagonia argentina are assigned to gastrochaenolites ornatus kelly and bromley kelly s r a bromley r g 1984 ichnological nomenclature of clavate borings palaeontology 27 793 807 and interpreted as dwelling structures of suspension feeding bivalves these record the activities of pholadids most likely belonging to the pholadinae bivalves are usually preserved as casts and external molds within the biogenic structures the details of the internal ornamentation in g ornatus allow identification of two sets of scratch patterns permitting comparison with the boring behavior of modern pholadids in terms of ichnotaxonomy when the same organism is able both to excavate and to bore and the excavation technique is identical to the mechanical perforation technique the same name should be used accordingly gastrochaenolites whilst more commonly assigned to bioerosion structures in hard substrates is herein regarded as available also for bivalve burrows in firm but unlithified substrates the firmground studied here represents a co planar surface of lowstand erosion and transgressive erosion that produced exhumation of deposits belonging to the sarmiento formation providing appropriate conditions for the development of the glossifungites ichnofacies differential erosion of the apertural necks the heterogeneity of the available casting material and the wide size range of ichnofossils suggest a complex history of colonization and erosion for this surface

bathymetry sediment texture and substrate cohesiveness their impact on modern glossifungites trace assemblages at willapa bay washington abstract glossifungites demarcated discontinuities have been demonstrated to have stratigraphic significance unfortunately their stratigraphic utility commonly eclipses the palaeoecological information derived from such surfaces this paper attempts to identify factors that influence the nature of trace assemblages observed in modern firmgrounds in particular it focuses on the causes of lateral variability and erosional topography inherent to glossifungites surfaces the extensive pleistocene database at willapa bay is used to test the interpretations striking heterogeneity in glossifungites assemblages is documented from modern firmgrounds at willapa bay this variability is related to intertidal zonation sediment texture the absolute firmness of the firmground and the presence or absence of a sediment veneer generally subtidal and lower to middle intertidal firmgrounds are colonized by crustaceans the upogebia association or the bivalve petricola the petricola association these surfaces are characteristically burrowed with thalassinoides and gastrochaenolites like traces the upper intertidal is dominated by the polydora association the burrows of which include diminutive diplocraterion and arenicolites like traces sandy and heterolithic substrates are avoided by burrowing crustaceans and polychaetes alike in contrast petricola is observed in muddy sandy mud and heterolithic substrates therefore where colonized sandier substrates are dominated by the clavate gastrochaenolites like burrows produced by these bivalves the absolute firmness of exhumed firmgrounds is quite variable the upogebia association is absent in substrates that exceed 10 9 pa polydora dominated assemblages are poorly developed in similar firmgrounds the petricola association however is well developed in relatively firm substrates finally the morphologic characteristics of exhumed modern firmgrounds show that the history of a glossifungites demarcated surface can be extremely dynamic firmground surfaces are exposed to an array of physico chemical conditions as they are exhumed colonized and pass into the geological record these surfaces are commonly re exhumed due to auto and allocyclic processes

karst dissolution along fracture corridors in an anticline hinge jandaira formation brazil implications for reservoir quality abstract folded fractured and karstified structures have been recognized in several carbonate reservoirs however they are rarely fully identified from seismic or well data and have been poorly described the present study investigates the geological and structural controls that regional anticlines may exert on solution enlarged fracture corridors and epigenic karst concentrations in folded fractured carbonate units we performed regional mapping based on 106 2d seismic lines 51 well logs unmanned aerial vehicle uav imagery of four major outcrop sites i ii iii and iv and field investigations to parameterize fracture and karstic features density spacing length and aperture the study area is potiguar basin brazil where we identified the gentle ne trending apodi fold 10 km wide and 20 km long the fold formed along an inverted extensional fault during the latest miocene quaternary stress field and the envelope of the meandering trend of the apodi river coincides with the ne trending fold axis the fracture pattern in the fold hinge zone consists of two orthogonal syn folding fracture sets a ne sw striking hinge parallel set and an orthogonal nw se striking set these fractures and superposed karstification are mostly concentrated in the hinge zone along fracture corridors in an area 1 5 km wide and 20 km long we conclude that fracture corridors in anticline hinges are likely sites to have high fracture densities and wide apertures these corridors provide reservoir spaces that are favorable for the formation of karst cavities with significant increases in permeability and porosity along the fracture sets these features act as important fluid pathways and storage areas where matrix porosity is low the findings can be used for first order prediction in karstified carbonate reservoirs

structural controls of fracture orientations intensity and connectivity teton anticline sawtooth range montana the teton anticline is a multiple hinge anticline containing fractured mississippian devonian carbonates in the frontal part of the sawtooth range in montana the structure serves as a good surface analog for fracture patterns and connectivities within subsurface folded carbonate reservoirs the primary fracture sets are longitudinal and transverse relative to the axis of the fold although two additional oblique sets are also present the length and density of the longitudinal fracture sets are strongly controlled by position relative to multiple hinges the transverse fractures are related to changes in fold plunge and exhibit less variation in fracture density fracture connectivity is dependent on the number of fracture sets their orientations and dispersions and the densities of the fracture sets the connectivity is measured using two parameters the fractional connected area fca which represents the fraction of the total sample area that is connected by fractures and the distribution of clusters of different sizes in any given area because the longitudinal fractures represent the dominant fracture set and also show the most variation with structural position the fracture connectivity as measured by both the fcas and the distribution of cluster sizes is greater in the vicinity of the fold hinges the results and approaches used in the study have some important implications for subsurface folded fractured carbonate reservoirs the analysis of sparsely distributed fracture data from wells must be integrated with an understanding of the controls of the macroscopic structure on fracture parameters to effectively simulate fracture patterns and connectivities around subsurface structures

bivalve bioerosion in cretaceous neogene amber around the globe with implications for the ichnogenera teredolites and apectoichnus abstract amber samples with bivalve borings from six localities around the world ranging in age from hauterivian to miocene have been studied the possible assignment to teredolites or gastrochaenolites is discussed considering the type of substrate as an ichnotaxobase it is proposed to regard amber or similar resins as a variant of xylic substrates and to maintain the separation between the two ichnogenera and their different paleoecological implications the amber borings are assigned to teredolites clavatus leymerie 1842 and apectoichnus longissimus kelly and bromley 1984 respectively the presence of bioglyphs in a few borings suggests a mechanical production process with pholadid bivalves such as martesia preserved inside many of the samples representing the producer in general the amber producing trees mostly grew along a forested coastline where they were occasionally flooded by seawater or even transported from rivers into the sea and later deposited

analog modeling of divergent and convergent transfer zones in listric normal fault systems transfer zones are common features in passive margins such as the gulf of mexico where deformation between adjacent listric normal faults is accommodated by the formation of complex secondary fault systems two common types of transfer zones are 1 convergent with the main faults dipping toward each other and 2 divergent with the main faults dipping away from each other analog clay models are developed for both convergent and divergent transfer zones with the faults approaching each other offset by 90 and overlapping each other during extension the structures initiate as symmetric grabens and later transform into asymmetric half grabens the main fault and associated synthetic faults form a narrow zone of deformation whereas the antithetic faults develop into a broader zone constituting evenly spaced discrete fault segments orientations lengths densities and sizes of connected fault clusters vary with the type of transfer zone structural position relative to the fault offsets and total extension the experiments show that the antithetic faults in convergent transfer zones and synthetic faults in divergent transfer zones tend to be more consistent in orientation and connect easily synthetic faults in convergent transfer zones and antithetic faults in divergent transfer zones change orientation along strike toward the transfer zone fault connectivity in approaching transfer zones is generally higher than in normal offset or overlapping configurations the analog models provide important insights on the geometry of fault patterns and possible fluid migration pathways within transfer zones

the application of ichnology to palaeoenvironmental and stratigraphic analysis it has been increasingly realized by sedimentologists in the petroleum industry and academia that integration of ichnological information into sedimentological models and vice versa is one of the main means by which we can improve our understanding of ancient depositional environments this volume aims to provide an analytical review of the ichnology of all major depositional environments and the use of ichnology in biostratigraphic and sequence stratigraphic analysis as well as highly refined palaeoenvironmental studies the remit of the book is achieved through a combination of review articles and novel research papers that outline methodologies and protocols for improving our understanding of ancient palaeoenvironments trace fossils from microscopic borings to dinosaur footprints are considered the comprehensive coverage of ancient depositional environments means that the book will be of use as a course text for undergraduates as well as an invaluable reference text for all students of ichnology whether they are ichnologists sedimentologists or petroleum geologists by trade

control of cambrian evaporites on fracturing in fault related anticlines in the zagros fold and thrust belt orientation and distribution of fractures in the oligocene early miocene asmari formation a major reservoir rock of the zagros petroleum system were investigated in two anticlines of the zagros fold and thrust belt the sim and kuh e asmari anticlines developed in the areas of the zagros characterized by the occurrence and absence of cambrian evaporites at the bottom of the stratigraphic pile respectively the aim was to outline major differences in terms of fracture spacing and saturation organic matter maturity and clay minerals based geothermometers suggest that the depth of deformation for the top of the asmari formation in the kuh e asmari anticline was in the range of 1 5 2 7 km assuming a geothermal gradient of 22 5 c km the asmari formation in the sim anticline probably experienced a slightly deeper sedimentary burial maximum 3 km with a geothermal gradient of 20 c km the spacing of fractures is generally 2 3 times larger i e strain accommodated by fracturing is smaller in the sim anticline than in the kuh e asmari anticline this is consistent with regional geological studies analogue and numerical models that suggest that thrust faults geometry and related folds are markedly different in the absence or presence of a weak decollement evaporites the larger spacing in the sim anticline is also consistent with higher temperature predicted for the asmari formation in this area by contrast the orientation of fractures with respect to the fold axes is the same in both anticlines the fracture systems are rather immature in both anticlines the amount and density of fractures in the twofolds are controlled by regional occurrence absence of salt and probably different burial rather than local features fold geometry

natural ventilation of an enclosure containing two buoyancy sources this paper describes experiments and theoretical modelling of a naturally ventilated enclosure containing two point sources of buoyancy previous work on the flow and stratification that develop in a space owing to the presence of a single source of buoyancy has been extended to cover two sources of positive or negative buoyancy in an attempt to produce more realistic models of practical problems examples include naturally ventilated buildings and industrial or medical processes involving dispersal of contaminants by air currents the experimental technique involves the use of a water filled enclosure with salt solution injected at two points these sources of negative buoyancy form turbulent plumes within the enclosure two sources of unequal strength are found to produce a vertical density profile consisting of three distinct fully mixed layers the paper describes a theoretical model that successfully predicts the depths and densities of these layers the positions of the interfaces between the three layers were found to be a function only of the effective area a of the enclosure openings the height of the enclosure h and the ratio of the strengths of the two sources of buoyancy b 1 b 2 the behaviour of a system with one source of positive buoyancy at the lower boundary and one of negative buoyancy at the upper boundary of the enclosure is also examined this case has particular relevance to the prediction of thermal stratification in rooms with both cold and warm surfaces present again the height of the interfaces is dependent only on the geometry of the enclosure and the source strength ratio three distinct types of flow pattern are predicted and observed

use of curved scanlines and boreholes to predict fracture frequencies abstract we advance the method of hudson and priest journal of rock mechanics and mining sciences geomechanics abstracts 20 1983 73 89 to develop a method for a curved scanline to be used to predict the numbers of fractures that would be observed in any direction when sampling along a scanline the probability of intersecting a fracture is influenced by the relative orientations of the fracture and of the scanline at that location this sampling bias can be minimised by the use of the terzaghi correction w cos 1 where is the angle between the scanline and the normal to the fracture these corrected frequencies are used to simulate fracture frequencies for all other orientations by doubly correcting the data modelled fracture frequency is contoured on a graph of simulated scanline plunge against simulated scanline azimuth this method is based upon the assumption that the data collected along the scanline is representative of the fracture population when the terzaghi correction has been applied a graph of cumulative frequency of fractures against distance along a scanline provides a simple method for determining whether the scanline crosses differently fractured areas frequencies are corrected for dip strike and both dip and strike with data from homogeneously fractured areas plotting as straight lines these frequencies can be normalised for ease of comparison

fractal analysis of fractures in rocks the cantor s dust method abstract the cantor s dust method of fractal analysis has been used to describe the regularity of fracture patterns in geological materials seen on a two dimensional surface this linear method of analysis is well adapted to a determination of two dimensional phenomena the determination of the fractal dimension d indicates that it varies regularly as a function of the orientation of the analysis direction this is taken to indicate that there is a relation unexplained as yet between the regularity of the fracture pattern and the forces which produced it the use of the cantor s dust method on naturally fractured materials ranging in dimension from 3 mm to 45 m in maximum dimension indicates the fractal nature of the fractures found in natural materials the analysis method can also be used to identify local variations in the stress field which caused failure such as the fractures in a feldspar compared to those in the host granite etc the method appears to be a sensitive descriptive measure of the failure patterns in rocks

multibend fault bend folding this paper shows how slightly complex but angular fault shapes with only a few bends lead to broadly curved and or highly complex folds a common perception exists that simple angular fold geometries are a necessary consequence of the normal assumptions of fault bend fold theory namely angular fault bends straight faults and flexural slip to the contrary it is shown here that exact application of these low level assumptions produces great complexity from simple fault shapes this complexity is caused by the combination of 1 generation of new axial surfaces by displacement of hangingwall cut offs past successive fault bends and 2 fragmentation of axial surfaces by mutual interference the result is entwined arrays of fold axial surfaces that produce quasi curved and or complex folds from discrete angular fault bends fold complexity grows in a highly non linear way in the most extreme case the number of fold axial surface segments grows as the fourth power of the number of fault bends this paper presents examples of the immense variety of complex fold geometries that are thus generated 0 1997 elsevier science ltd all rights reserved

substrate controlled ichnofacies along a marine sequence boundary the intra valanginian discontinuity in central neuquen basin argentina abstract the intra valanginian discontinuity in the neuquen basin argentina marks a dramatic sea level fall within lower cretaceous strata and can be mapped for tens of kilometers both along depositional strike and dip in the proximal region of the lowstand configuration the subaerial segment of the sequence boundary is demarcated by alluvial conglomerates basal mulichinco formation onto deep marine black shales vaca muerta formation in the distal marine realm the time equivalent marine sequence boundary separates black shales and marls beneath from shallow marine carbonate deposits above this paper documents and discusses substrate controlled trace fossils demarcating the marine sequence boundary across more than 30 km in a proximal distal transect in order to shed light onto processes affecting the sea floor during the generation biogenic modification and preservation of this regionally extensive omission surface the downdip expression of the marine sequence boundary is well exposed across a 20 km long strike oriented outcrop everywhere in this region the discontinuity is demarcated by robust thalassinoides with well defined walls and circular cross sections suggesting that the marly substrate was relatively firm during excavation the burrow system is filled with bioclasts of echinoids and bivalves not present in underlying strata up to pebble size intraclasts that were eroded from the underlying succession and authigenic minerals glauconite phosphates this trace fossil suite illustrates the glossifungites ichnofacies the updip expression of the marine sequence boundary in the study area was recorded in a cored well located about 20 km from the outcrops as in the distal region a first generation of passively filled thalassinoides excavated into a firm marly substrate is attributed to the glossifungites ichnofacies however this suite is cross cut at the top by gastrochaenolites and other unidentified borings bored intraclasts also occur above the omission surface this trace fossil suite represents the trypanites ichnofacies the intra valanginian discontinuity records a complex history after the onset of the dramatic sea level fall extensive erosion and exhumation of previous sediments as well as early cementation combined to produce different types of substrates during the generation of the omission surface firmgrounds and hardgrounds colonization of firm substrates probably started firstly in proximal regions when relative sea level was still falling during early transgression firmgrounds were occupied in distal regions and borers colonized the hardgrounds developed in proximal regions thus the surface demarcates a composite surface involving a sequence boundary plus a transgressive surface draped in turn by a mixing of sediments suggesting siliciclastic starvation the generation and preservation of the features associated with the intra valanginian discontinuity are thought to result from the combination of a ramp type pre existing morphology coupled with a high amplitude sea level fall and a relatively deep marine setting prior to the formation of the omission surface

appraisal of fracture sampling methods and a new workflow to characterise heterogeneous fracture networks at outcrop abstract characterising fractures at outcrop for use as analogues to fractured reservoirs can use several methods four important fracture data collection methods are linear scanline sampling areal sampling window sampling and circular scanline sampling in regions of homogeneous fracture networks these methods are adequate to characterise fracture patterns for use as outcrop analogues however where fractures are heterogeneous it is more difficult to characterise fracture networks and a different approach is needed we develop a workflow for fracture data collection in a region of heterogeneous fractures in a fold and thrust belt which we believe has applicability to a wide variety of fracture networks in different tectonic settings we use an augmented circular scanline method along with areal sampling to collect a range of fracture attribute data including orientation length aperture spatial distribution and intensity this augmented circular scanline method more than halves the time taken for data collection provides accurate unbiased data that is representative of local fracture network attributes and involves data collection of a wider range of fracture attributes than other sampling techniques alone