bioturbation influence on reservoir quality a case study from the cretaceous ben nevis formation jeanne d arc basin offshore newfoundland canada the delineation ben nevis l 55 well located in the hebron ben nevis field offshore newfoundland targeted the cretaceous ben nevis formation in the petroleum rich jeanne d arc basin this case study focuses on the bioturbated net pay horizons and assesses the importance of animal sediment interactions in controlling the porosity and permeability of sandstone reservoir intervals our data reveal that bioturbation can either reduce permeability and porosity by as much as approximately 33 or enhance it by up to 600 dependent on burrow type and behavior of the trace making organism the net pay interval in the cored interval of ben nevis l 55 is characterized by ophiomorpha dominated ichnofabrics the action of bioturbators can be classified in terms of sediment mixing sediment cleaning sediment packing and pipe work building strategies bioturbation has the potential to 1 increase isotropy or uniformity of grain size by destroying sedimentary laminae through burrow homogenization or 2 decrease isotropy by selectively sorting grains into burrow lining and fill by grain size and through creation of open burrow systems filled with later sediments of differing character to the host sediment the petrophysical characteristics of the reservoir facies are highly dependent on trace fossil morphology presence or absence of burrow linings nature of burrow fills burrow size and bioturbation intensity mudstone rich facies and ichnofabrics containing mudstone filled and or lined burrows e g ophiomorpha and clusters of chondrites have the net effect of permeability reduction in contrast permeability enhancement is documented from muddy sandstone facies with clean sand filled burrows e g thalassinoides and clean sandstones with burrow mottled or diffuse to massive textures

magnetic mineralogy of pelagic limestones summary due to their extremely small size and low concentration the carriers of magnetization in limestones are usually identified through indirect rock magnetic methods this paper describes a method for extracting tiny ferromagnetic grains from consolidated calcareous rocks and summarizes a scanning electron microscope sem investigation of magnetic phases from several palaeomagnetically important pelagic limestones details of surface characteristics and elemental composition are readily accessible with the sem and complement normal rock magnetic experiments in giving a more complete assessment of the major ferromagnetic phases their origin and the timing and acquisition of magnetization the results confirm many indications of the indirect methods and introduce several important new features in addition to detrital titanomagnetite diagenetic titanohaematite and iron sulphides there is a significant contribution by authigenic microcrystalline haematite detrital cosmic spherules chromian spinels and skeletal titanomaghaemite

the role of event beds in the preservation of organic carbon in fine grained sediments analyses of the sedimentological processes operating during deposition of the whitby mudstone formation toarcian lower jurassic preserved in northeast england abstract geologists have recently observed that source rocks commonly contain a wide variety of microfabrics including diminutive ripples and burrows the existence of these fabrics challenges the assumption that persistent bottom water anoxia and low energy conditions are necessary prerequisites for enhanced organic carbon preservation in these units in order to enhance our understanding of the depositional and diagenetic processes responsible for organic carbon preservation in these strata the lower jurassic whitby mudstone formation which contains mudstones with up to 14 2 total organic carbon has been investigated using optical electron optical and geochemical methods four thinly bedded mudstone lithofacies were identified a silt bearing clay rich mudstones b clay rich mudstones c clay calcareous nannoplankton and organic carbon bearing mudstones and d cement rich mudstones internally individual beds are typically sharp based and normally graded they are either laminated partially bioturbated or homogenized where depositional fabrics are preserved pellets silt lags ripple lamination shell pavements wave enhanced sediment gravity flows of fluid mud and organo minerallic aggregates have been observed the presence of up to 14 2 toc in units that are sharp based and normally graded suggests that mass flows possibly generated by storms likely influenced sedimentation during deposition of these mudstones the abundant organo minerallic fabrics in these units indicates that at least some of the organic carbon was delivered to the seafloor as marine snow aggregates that likely formed in the water column following phytoplankton blooms homogenization of bed tops indicates that between sediment delivery episodes an infauna was able to colonize the seafloor implying that the bottom waters were at least partly oxygenated during these intervals these fabrics suggest that during deposition of the whitby mudstone formation organic carbon was being preferentially preserved below regions of high primary organic production the close association between sharp based graded beds and organo minerallic aggregates indicates that large volumes of organic carbon were delivered episodically to the seafloor and that conditions at the sediment water interface were episodically dynamic here organic carbon is likely to have been preferentially preserved because the frequency of depositional events was sufficiently high to minimize both oxidant diffusion into the sediment and organic carbon mineralization while bottom water anoxia may have developed during the phytoplankton blooms it was unlikely to have been persistent because the microfabrics present indicate that there was sufficient time and oxygen available for an infauna to disrupt the sediment between deposition events

re os systematics in chondrites and the fractionation of the platinum group elements in the early solar system we have investigated the re os system for samples of whole rock metal and sulfide from ordinary chondrites using closed system analytical techniques we found complete exchange between sample and tracer isotopes for silicate containing samples and obtained precise and reliable re os concentration measurements results on two group iva iron meteorites and on a silicate rich iron steinbach iva an are consistent with the iva ivb isochron and support the previous observation that iva ivb irons may be slightly older than iiab irons data on whole rock fragments and metal rich separates from the st severin chondrite ll6 show a large range in 1870re 188 os and in 187 os 188 os which makes possible in principle the determination of a re os internal isochron on a chondrite for the first time this re os fractionation may be due to partial melting of fenis and macroscopic redistribution of metal and sulfide the st severin data show a good correlation line on a 187 re 187 os evolution diagram if this is considered to represent an internal isochron it gives an age t 4 68 0 15 ae 187 re 1 64 10 11 a 1 and an initial 187 os 188 os 0 0 0953 0 0013 this age is in agreement with but slightly older than the more precise 187 re 187 os age for the iiab irons as well as for irons from other groups t 4 61 0 01 ae a st severin sulfide nodule has very low re and os concentrations and shows a young re os model age 2 3 ae indicating recent element remobilization whole rock and metal rich separates of h group chondrites h3 to h6 yield restricted ranges in 187 re 188 os 0 42 0 47 and 187 os 188 os 0 128 0 133 there is a systematic difference between re os in the metal extracted from a chondrite and the bulk chondrite this shows that there is a small but significant re os fractionation within subsystems contained in the chondrites from whole rock samples of h group chondrites we calculate a mean 187 re 188 os 0 423 0 007 and 187 os 188 os 0 12863 0 00046 which may characterize the evolution of an average chondritic reservoir for re os the ordinary chondrite data plot close to the iiab isochron although the deviations found are larger than found for the irons the re os chronometer in iron meteorites is apparently controlled by the re os fractionation due to fractional crystallization of liquid metal re os ages of iron meteorites give the time of crystallization of metal segregations and cores of early planetary bodies in contrast the behavior in ordinary chondrites while also dominated by the metal phases must reflect fractionation and transport on a local macroscopic scale within the chondrites between the metal phases after aggregation due to partial melting of fenis or represent variable re os fractionation of the metal phases prior to the accretion of the chondrites however for st severin we attribute the major re os fractionation to early heating of the meteorite above the fe fes eutectic we do not consider that the re os fractionation observed in other chondrites is due to the redistribution of re and os during chondrite metamorphism including shock but it may plausibly represent earlier stages of re os fractionation for the different feni metal constituents prior to accretion

an ichnological assemblage approach to reservoir heterogeneity assessment in bioturbated strata insights from the lower cretaceous viking formation alberta canada abstract facies scale trends in porosity and permeability are commonly mapped for reservoir models and flow simulation however these trends are too broad to capture bed and bed set heterogeneity and there is a need to up scale detailed bed scale observations especially in low permeability reservoir intervals here we utilize sedimentology and ichnology at the bed and bedset scale to constrain the range of porosity and permeability that can be expected within facies of the lower cretaceous viking formation of south central alberta canada three main facies were recognized representing deposition from the middle shoreface to the upper offshore amalgamated hummocky cross stratified sandstone facies facies s hcs consist of alternations between intensely bioturbated beds and sparsely bioturbated laminated beds trace fossil assemblages in bioturbated beds of facies s hcs are attributable to the archetypal skolithos ichnofacies and are morphologically characterized by vertical sand filled shafts vss bioturbated beds show poor reservoir properties max 10 porosity mean 85 1 md compared to laminated beds max 20 porosity mean 186 md bioturbated muddy sandstone facies facies s b represent trace fossil assemblages primarily attributable to the proximal expression of the cruziana ichnofacies four ichnological assemblages occur in varying proportions namely sediment churning assemblages sc horizontal sand filled tube assemblages hsf vss assemblages and mud filled lined or with spreiten mls assemblages ichnological assemblages containing horizontal max 30 porosity mean 1 28 md or vertical sand filled burrows max 10 porosity mean 2 2 md generally have better reservoir properties than laminated beds max 20 porosity mean 0 98 md conversely ichnological assemblages that consist of muddy trace fossils have lower porosity and permeability max 10 porosity mean 0 89 md highly bioturbated sediment churned fabrics have only slightly higher porosity and permeability overall max 15 porosity mean 1 29 md bioturbated sandy mudstone facies facies m b contain ichnofossils representing an archetypal expression of the cruziana ichnofacies four ichnological assemblages occur throughout facies m b that are similar to facies s b sc hsf vss and mls assemblages the sc max 15 porosity mean 21 67 md hsf max 20 porosity mean 3 79 md and vss max 25 porosity mean 7 35 md ichnological assemblages have similar or slightly lower values than the laminated beds max 20 porosity mean 10 7 md however mls assemblages have substantially lower reservoir quality max 10 porosity mean 0 66 md our results indicate that the most likely occurrence of good reservoir characteristics in bioturbated strata exists in sand filled ichnological assemblages this is especially true within the muddy upper offshore to lower shoreface where vertically oriented trace fossils can interconnect otherwise hydraulically isolated laminated sandstone beds this improves vertical fluid transmission the results of this work largely corroborate previous findings about ichnological impacts on reservoir properties unlike previous studies however we demonstrate that the characteristics of the ichnological assemblage such as burrow form and the nature of burrow fill also play an important role in determining reservoir characteristics it follows that not all bioturbated intervals attributed to the same facies should be treated equally when upscaling bed scale observations to the reservoir a range of possible permeability porosity values can be tested for model sensitivity and to help determine an appropriate representative elementary volume

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

barnett shale gas production fort worth basin issues and discussion newark east barnett shale field fort worth basin texas is currently the most productive gas field in texas in terms of daily production and is growing at an annual rate of more than 10 however despite the fact that the barnett play has been studied intensely by very capable geologists and engineers from several companies over a period of many years there continues to be several misunderstandings concerning fundamental factors controlling the success of the barnett play of north texas barnett gas production is poorer in areas near faults and structural flexures anticlines and synclines fractures which are most abundant in these structural settings are detrimental to barnett production open natural fractures are rare in the barnett and have little or nothing to do with barnett productivity in areas where barnett shale is thermally mature with respect to gas generation it is slightly overpressured about 0 52 psi ft 11 76 kpa m limestone beds within the barnett formation are the product of debris flows that originated on a carbonate shelf to the north of the present basin center it appears that the barnett can be used as an exploration model for other basins especially analogous basins of the ouachita trend the history of the development of the barnett reservoir in north texas provides an excellent example of how persistence can lead to success in nonconventional gas plays

magnetic fabrics of the south dabashan belt at the north margin of south china constraint on the origin of the arcuate trace of chengkou fault abstract the south dabashan belt at the northern margin of the south china block is a typical arcuate shaped orogenic belt in western china its formation and evolution are important for understanding the collisional orogeny and intracontinental deformation in the south qinling orogen and its foreland basin anisotropy of magnetic susceptibility ams can provide fabric patterns which can be used to discuss the strain of the south dabashan belt rock magnetism reveals that paramagnetic minerals dominate magnetic susceptibility and some ferromagnetic minerals also exist magnetic fabrics of triassic and jurassic strata are essentially type ii fabric with well developed magnetic lineation further they rarely show sedimentary fabric indicating the early stage of the deformation processes magnetic fabrics show that early horizontal shortening strain is characterised by a radial pattern in the south dabashan belt our results indicate that the chengkou fault initially formed as a normal fault with arcuate shape during the opening of the mianlue ocean and has a controlling effect on the formation of the curved fold and thrust belt then the later shortening strain overprints the previous deformation but barely changes the curvature of the chengkou fault

evidence for the presence of 53mn in the early solar system chromium isotopic anomalies appear to be widespread in the allende inclusions clear anomalies are shown in the 53cr 52cr isotopic ratio deviations from the terrestrial value are correlated with the mn cr ratios indicating that 53mn half life t 3 7 106y existed at the time of formation of the meteorite inclusions the initial 53cr 52cr in the inclusions is lower than the terrestrial value recent results have shown that chromium isotopic anomalies are frequent on the 54cr isotope birck and allegre 1984 at the same time our results suggested the possibility of some anomalies on the 53cr isotope which can be produced by the decay of 53mn the present article presents improved precision measurements on the same inclusions of the allende meteorite and an extension of the measurements to mineral separates these results are the first evidence for live 53mn in the early solar system noted 53mn in the following

comment on interplay of deformation and magmatism in the pangong transpressional zone eastern ladakh india implications for remobilization of the trans himalayan magmatic arc and initiation of the karakoram fault by k sen b k mukherjee and a s collins journal of structural geology 62 2014 13 24

quantitative correlation of texture and magnetic anisotropy of compacted calcite muscovite aggregates abstract deformation of carbonate rocks leads to crystallographic preferred orientations cpos of calcite which in turn generates an anisotropy of magnetic susceptibility ams the use of the diamagnetic anisotropy which arises from the preferential orientation of calcite for texture characterization is usually hindered by 1 the weakness of the anisotropy and 2 overlapping contributions from paramagnetic and ferromagnetic minerals to the ams in this study the diamagnetic paramagnetic and ferromagnetic sub fabrics of synthetic calcite muscovite samples have been separated using high field torque measurements the cpo of calcite and muscovite has been determined by neutron diffraction and the magnetic sub fabrics are compared to the ams that was re calculated from the cpo the isolated diamagnetic sub fabric shows a good correlation with the calcite texture for calcite concentrations above 70 the paramagnetic sub fabric is shown to be a reliable texture parameter for muscovite even at a concentration of 5 the results demonstrate the capability of the ams method as a texture parameter in impure carbonate rocks

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

traces in the dark sedimentary processes and facies gradients in the upper shale member of the upper devonian lower mississippian bakken formation williston basin north dakota u s a abstract black organic rich rocks of the upper shale member of the upper devonian lower mississippian bakken formation a world class petroleum source rock in the williston basin of the united states and canada contain a diverse suite of mudstone lithofacies that were deposited in distinct facies belts the succession consists of three discrete facies associations fas these comprise 1 siliceous mudstones 2 quartz and carbonate bearing laminated mudstones and 3 macrofossil debris bearing massive mudstones these fas were deposited in three facies belts that reflect proximal to distal relationships in this mudstone system the macrofossil debris bearing massive mudstones fa 3 occur in the proximal facies belt and contain erosion surfaces some with overlying conodont and phosphate lithoclast lag deposits mudstones with abundant millimeter scale siltstone laminae showing irregular lateral thickness changes and shell debris in the medial facies belt quartz and carbonate bearing laminated mudstones dominate exhibiting sub millimeter thick siltstone layers with variable lateral thicknesses and localized mudstone ripples in the distal siliceous mudstone facies belt radiolarites radiolarian bearing mudstones and quartz and carbonate bearing laminated mudstones dominate overall total organic carbon toc contents range between about 3 and 10 wt with a general proximal to distal decrease in toc content abundant evidence of bioturbation exists in all fas and the lithological and toc variations are paralleled by changes in burrowing style and trace fossil abundance while two horizontal traces and two types of fecal strings are recognized in the proximal facies belt only a single horizontal trace fossil and one type of fecal string characterize mudstones in the distal facies belt radiolarites intercalated into the most distal mudstones are devoid of traces and fecal strings bedload transport processes likely caused by storm induced turbidity currents were active across all facies belts suspended sediment settling from near the ocean surface however most likely played a role in the deposition of some of the mudstones and was probably responsible for deposition of the radiolarites the distribution pattern of high toc sediments in proximal and lower toc deposits in some distal facies is interpreted as a function of higher accumulation rates during radiolarian depositional events leading to a decrease in suspension derived organic carbon in radiolarite laminae the presence of burrows in all fas and nearly all facies in the upper bakken shale member indicates that dysoxic conditions prevailed during its deposition this study shows that in intracratonic high toc mudstone successions such as the upper bakken shale member bed load processes most likely dominated sedimentation and conditions promoted a thriving infaunal benthic community as such deposition of the upper bakken shale member through dynamic processes in an overall dysoxic environment represents an alternative to conventional anoxic depositional models for world class source rocks

geological controls on matrix permeability of devonian gas shales in the horn river and liard basins northeastern british columbia canada abstract controls of matrix permeability are investigated for devonian gas shales from the horn river and liard basins in northeastern british columbia canada mineralogy is varied with high carbonate high quartz and moderate quartz carbonate and clay rich strata quartz content varies between 2 and 73 carbonate varies between 1 and 93 and clay varies between 3 and 33 the toc content ranges between 0 3 and 6 wt and porosity varies between about 1 and 7 for horn river basin samples quartz is mainly biogenic in origin derived from radiolarians toc content increases with the quartz content suggesting the toc and quartz both are derived from siliceous phytoplankton a positive relationship between porosity and quartz content is due to the positive relationship between quartz and toc matrix permeability parallel to bedding varies between 7 5e 02 and 7 1e 07 md at an effective stress of 15 mpa variation in permeability is due to a complex combination of factors that includes origin and distribution of minerals pore size distribution and fabric mercury intrusion capillary curves indicate that the higher matrix permeability values 2e 03 md occurs in samples that contain interconnected pore apertures greater than 16 m even when these samples may contain less macropores than low permeability samples the fabric of high permeability samples can be either isotropic or anisotropic however permeability of anisotropic samples is more sensitive to changes in effective stress than isotropic samples more highly anisotropic samples contain moderate amounts of quartz carbonate and in some clay high permeability samples that contain a more balanced ratio between micro meso and macroporosity would not only have faster flow rates but also greater access to sorbed gas within the microporosity compared to samples that lack mesopores several muskwa samples compared to evie and besa river samples contain higher quartz moderate clay and high toc content coupled with high permeability less sensitivity to effective stress and balanced ratios between micro meso and macroporosity would be a lower exploration risk due a greater propensity to fracture the ability to produce and store hydrocarbons due to higher toc contents and greater communication between macropores and micropores in the organic and clay fractions

ichnology and sedimentology of a mud dominated deltaic coast upper cretaceous alderson member lea park fm western canada abstract current depositional models largely promote the perception that all open coastal distal sea proximal land gradients are reflected by upward coarsening grain size trends and that shoreline deposits are represented by prominent sand bodies although commonly the case significant departures from this model may occur when the availability of coarser sediment calibers sand sized and larger is limited this is especially true where alongshore sediment transport influenced depositional systems are associated with rivers that supply abundant suspended sediments underestimating the role of grain size segregation may lead to misinterpretations of energy levels and water depths especially in some shale dominated sedimentary units the upper cretaceous alderson member lea park fm is an up to 180 m thick gas charged shale unit that we interpret as an ancient analogue for modern offshore and mud dominated deltaic coasts sedimentological and ichnological data collected from 27 cores indicate that much of the sediment volume of the alderson member was deposited in relatively shallow water under the influence of tidal and wave processes in a deltaic coastal setting characteristic features reflecting these depositional affinities include 1 increased proportions of terrestrially derived organic matter 2 indications of thixotropic to soupy substrates e g fluid mud coupled with rapid depositional rates 3 an impoverished ichnological signal planolites dominated suites 4 micro laminated shale 5 shale on shale erosional contacts 6 scour and fill structures and 7 intervals of low angle cross stratification the interpretation of relatively shallow water settings is also supported by recurring root bearing horizons glossifungites ichnofacies demarcated transgressive surfaces of erosion and conglomeratic surfaces at particular stratigraphic levels the deposits are interpreted to include offshore subaqueous deltas muddy shoreface and or tidal flat and aggradational muddy coastal plain chenier plain sub environments the results of this study improve our knowledge of ichnological and sedimentological characteristics of shallow marine shale units and are potentially useful for recognition of similar nearshore mud prone deposits elsewhere

ethology of the trace fossil chondrites form function and environment abstract the behaviour of the iconic ichnogenus chondrites is re evaluated based on review of existing literature and analysis of novel data macroscopic thin section and esem edx observations ct scans and resin peels of modern analogues computer controlled serial grinding morphometric analysis and theoretical morphology the bedding plane expression of chondrites is well constrained by morphometry 1 the angle of dichotomy formed by a pair of adjacent branches is typically between 30 and 56 interquartile range mean 47 2 branching order is between 1 and 9 3 branches are on average nine times longer than wide in the third dimension downward branching is dominant but bundled shafts and upward branching may be present the size of chondrites increased markedly from the late jurassic to the late cretaceous suggesting that the tracemakers became larger and larger microfabric analysis of chondrites shows active fill or alternatively passive fill of empty tunnels by currents or clay percolation a new mechanism proposed herein the tracemakers built chondrites to obtain food 1 vermiform deposit feeders produced chondrites for searching for food in the sediment fodinichnion 2 asymbiotic bivalves built chondrites for cultivating and directly ingesting bacteria agrichnion 3 chemosymbiotic bivalves produced chondrites to provide symbionts with chemical agents chondrites was modified through the life of the tracemaker or it represented a part of the producer s lifespan chondrites and its modern tracemaker s is associated with a range of marine settings including well oxygenated dysoxic and space limited nucleocave environments as such chondrites is regarded as an extremotolerant ichnotaxon

organism sediment interactions in shale hydrocarbon reservoir facies three dimensional reconstruction of complex ichnofabric geometries and pore networks abstract the lithological and mineralogical characteristics of mudstones and siltstones and their stress strain behavior at the meter to nanometer scale can play a critical role in the exploitation of unconventional shale reservoirs shale fabrics that result from bioturbation can produce extensive interconnected networks of biologically redistributed sediment grains within reservoir mudstone facies the presence of biologically generated heterogeneities may substantially affect reservoir stimulation and thus production from shale facies this study presents volumetric evaluation of ichnofabrics dominated by phycosiphon like and aff chondrites and provides insights into the impact of trace fossils on the rheological and petrophysical characteristics of mudstones it is calculated that in addition to creating significant volumes of silty clay poor zones of enhanced porosity and permeability trace fossils create interpenetrating frameworks of brittle material that reduce communication distances from the low permeability matrix to the higher permeability silt rich burrows reducing communication distances to less than 1 cm increases the potential for diffusive transport of hydrocarbon molecules from the tight matrix to the wellbore connected volumes this is because shale ichnofabrics create abundant fracture prone planes of weakness and increase the surface area of the interface between the hydrocarbon rich matrix and porous burrow fills thereby promoting fluid exchange understanding of the three dimensional characteristics of ichnofabrics may form the basis of future modeling of fracture spacing and complexity that is critical to shale gas reservoir characterization

magnetic fabrics and petrofabrics their orientation distributions and anisotropies abstract magnetic fabric and other petrofabric anisotropies may be described by second rank tensors represented by ellipsoids for a homogeneous petrofabric that is adequately sampled a stereoplot of the orientation distribution of the tensors principal axes maximum intermediate and minimum should show three orthogonal concentrations the concentrations form some combination of shapes from circular clusters through partial girdles to full girdles the concentrations elliptical eccentricities are constrained by the symmetry of the sample orientation distribution i e l l s l s etc as well as the individual sample anisotropies the mean orientations of principal axes must be orthogonal just as with individual sample tensors this requires tensor statistics for their calculation jelinek 1978 furthermore elliptical confidence cones for the means should parallel principal planes preserving overall orthorhombic symmetry however in practice sub orthorhombic symmetry may arise from unrepresentative sampling but it may also be a useful indicator of multiple or heterogeneous petrofabrics in the case of magnetic fabrics the wide range in average susceptibility values and variation in magnetic mineralogy permit small numbers of high susceptibility samples to deflect the orientation of the tensor mean away from the majority of samples normalizing the samples by their bulk susceptibility overcomes this but the orientation of high susceptibility outliers may signify an event or subfabric of importance that we should not discard therefore stereoplots of both normalized and non normalized orientation distributions should be compared preferably also identifying the outliers it is important to distinguish the shape of the orientation distribution ellipsoid from the shape of the individual magnetic fabric ellipsoids the qualitative l s nomenclature is best replaced by tj where tj 1 oblate tj 1 prolate jelinek 1981 invariably the orientation distribution is described by an ellipsoid whose shape is more spherical than that of the individual sample anisotropy ellipsoids because the latter have scattered orientations furthermore the shape of the orientation distribution ellipsoid need bear no relation to the shape of individual sample ellipsoid anisotropies the concepts are illustrated with 1119 measurements of anisotropy of magnetic susceptibility ams from seven areas and with 188 measurements of anisotropy of anhysteretic remanence aarm from two areas

magnetic susceptibility as a tool to study deformed calcite with variable impurity content 1 a set of calcite mylonites were systematically sampled along the basal shear zone of the morcles nappe located in the southwestern swiss alps to investigate the relationship among crystallographic preferred orientation cpo chemistry and anisotropy of magnetic susceptibility ams second phase minerals are 10 vol of the rock the substitution of trace impurities for ca in the calcite crystal lattice in particular fe mn mg and sr varies among the samples with total values ranging from 1450 190 ppm in the most pure sample to 2450 320 ppm for the most impure sample fe shows the largest variation among the sample group and varies by a factor of nearly four from the purest 230 30 ppm to the most impure sample 840 110 ppm all samples have negative bulk susceptibility and the concentration of ferromagnetic in a broad sense phases is very low a correlation is identified between trace element chemistry cpo of calcite and the magnetic susceptibility the bulk susceptibility and the ams vary systematically with fe and mn elemental concentration in the matrix calcite and this variation is apparent for the entire length of the shear zone a simple model that takes into account the cpo and trace element chemistry is used to explain the resulting bulk susceptibility and ams calcite mylonites and marbles from other locations fit the model indicative of a general relationship between cpo chemistry and ams in calcites where second phase minerals are sparse for lithologies that are dominated magnetically by calcite with a deficiency of secondary phases magnetic susceptibility can be used to rapidly screen rock samples for the variation of paramagnetic trace elements fe and mn and cpo which can then be used for detailed microfabric studies

methods and applications of magnetic anisotropy a special issue in recognition of the career of graham j borradaile methods and applications of magnetic anisotropy a special issue in recognition of the career of graham j borradaile

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

the influence of deformation mechanisms on magnetic fabrics in weakly deformed rocks abstract magnetic fabrics of weakly deformed rocks are not simply correlated with the principal finite strain directions depositional magnetic fabrics persist at 30 shortening where the rocks are deformed by particulate flow grain boundary sliding rocks with a spaced stylolitic cleavage believed to be formed by pressure solution and shortened by 20 50 have maximum susceptibility parallel to the intersection of cleavage and bedding this type of magnetic fabric is attributed to the interference of a depositional magnetic fabric between cleavage surfaces with a tectonic magnetic fabric in the cleavage surfaces

biogenic magnetite as a primary remanence carrier in limestone deposits abstract studies on the microbial communities and magnetic phases of samples collected from carbonate oozes at sugarloaf key fl u s a and calcareous laminated sediments from laguna figueroa baja california mexico have revealed the existence of magnetotactic bacteria and ultrafine grained single domain magnetite in both environments magnetotactic bacteria were identified by light and electron microscopy the single domain magnetite was detected by coercivity spectra analysis with a squid magnetometer and examined under the transmission electron microscope the similarity in terms of size and shape between the single domain magnetite found in these sediments and the magnetite observed in the bacterial magnetosome from enriched cultures indicates the ultrafine grained magnetite in these two marine environments was biologically formed these results combined with the common occurrences of ultrafine grained magnetite in limestone deposits detected rock magnetically suggest biogenic magnetite may be present and contribute to the magnetic remanence in these rocks several cambrian limestone samples separately collected from siberia china and kazakhstan were examined for the presence of bacterial magnetite samples from the lower cambrian sinskian formation at siberia platform were found to contain both a large amount of apparently bacterial magnetite particles and a very stable primary magnetic component post cambrian diagenesis does not seem to affect the microgranulometry of these apparently bacterial magnetite crystals or the magnetic remanence carried by them assessing the potential role of biogenic magnetite as a primary remanence carrier in other phanerozoic limestone deposits ought to be further pursued

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

importance of rock properties on the producibility of gas shales abstract as the development of unconventional gas resources has progressed the heterogeneity and complexity of shales as gas and oil reservoirs have become apparent the production histories from shales both within a sequence of interbedded strata and from adjacent wells commonly exhibit inexplicable variations and predictions from numerical modeling are rarely accurate as a result of the variability in the reservoir and rock parameters of gas shales the complex interaction between the shale properties and the producibility of the reservoir is seldom apparent one of the most difficult parameters to quantify is the fabric this study compares the relative importance of the fabric parameters of gas shales on their producibility using a commercial numerical simulator and field and laboratory determined rock properties the fabric parameters include the stress dependent fracture permeability which controls the gas transport through the fracture network as well as the effective fracture spacing which controls the path length for gas transport through the matrix and the stress dependent matrix permeability which controls the gas transport through the matrix the results of the numerical simulations show that for a wide range of stress dependent fracture permeabilities stress dependent matrix permeabilities and fracture spacings the productivity of a gas shale reservoir is limited by inefficient gas transport through the matrix the matrix permeability below which gas production is subeconomic is not a specific value but varies with the effective fracture spacing and with fracture permeability the matrix permeability and effective fracture spacing have a greater impact on the producibility of strata with larger fracture permeabilities the influence of the effective fracture spacing on production is greater than the influence of the matrix permeability the lower production associated with a large fracture spacing or a small matrix permeability can be offset by a large matrix permeability or a small fracture spacing the production simulations also show the strong dependence on the geomechanical properties of the rock which affect how the gas transport through the matrix and fractures changes with stress the influence of the geomechanical properties on the producibility depends on whether the production is limited by the gas transport through the matrix when the fabric parameters result in a matrix independent production small fracture spacing large matrix permeability small fracture permeability the production is solely controlled by the stress dependent fracture permeability with larger initial fracture permeability larger young s modulus and larger poisson s ratio resulting in higher production in this case young s modulus is much more influential than the poisson s ratio when the fabric parameters result in a matrix limited production the rock mechanics parameter which relates the exponential decline of matrix permeability with effective stress has the strongest influence on the producibility the influence of poisson s ratio on producibility not only varies with the fabric parameters but also with the young s modulus and when the production is matrix limited a smaller poisson s ratio results in a higher production for all cases except when both and young s modulus are small

faeces clay minerals and reservoir potential by controlled experiments that simulate marine conditions it is shown that accelerated weathering and mineral authigenesis occur during the combined process of digestion ingestion and excretion of sediment by worms previously characterized synthetic mud composed of finely ground low grade metamorphic slate dominated by highly crystalline chlorite and muscovite was unchanged in control tanks over a 20 week time scale but was significantly different in faecal samples from an experimental tank populated with the annelid arenicola marina chlorite was preferentially destroyed during digestion and both chlorite and muscovite underwent peak broadening with a skew developing towards higher lattice spacings neoformed minerals with very high d spacings and a mineral with 0 75 nm basal lattice spacing possibly berthierine were detected in the cast samples it is postulated that the lowered ph microenvironment in the guts of organisms may accelerate mineral dissolution and precipitation processes during ingestion these results show that macrobiotic activity significantly accelerates weathering and mineral degradation along with mineral authigenesis neoformed minerals produced in this way would be likely to form the precursors of diagenetic clay mineral cements and thus have an impact on sandstone reservoir quality

inverse magnetic fabric in carbonate bearing rocks abstract the observation of a magnetic susceptibility ellipsoid whose maximum axis corresponds to the minimum axis of petrofabric pole of bedding or schistosity is referred to as an inverse magnetic fabric the investigation of the magnetic properties of some ferroan carbonate monocrystals and paramagnetic limestones demonstrates that c axis preferred orientation of paramagnetic carbonates results in a maximum susceptibility parallel to the flattening direction inverse magnetic fabrics due to magnetite are also encountered in weakly deformed limestones a mineralogical model based on the property of single domain grains to have a zero susceptibility parallel to their long axis is proposed however more complex cases are also encountered

182w and 187re 187os systematics of iron meteorites chronology for melting differentiation and crystallization in asteroids w isotopic compositions measured by n tims in five iron meteorite groups are used in conjunction with 187re 187os isotopic data to constrain the timing of metal segregation and crystallization respectively in the iron meteorite parent bodies fractionation of the parent isotope 182hf half life 9 2 ma from the daughter 182w likely occurred during segregation of metal from silicate in the iron meteorite parent bodies if w isotopic equilibrium was achieved between silicate and metal during metal segregation then the w isotopic compositions in the irons should record the timing of this event samples were taken from the five largest iron meteorite groups including the four magmatic groups iiab iiiab iva and ivb and the nonmagmatic iab iiicd group together these groups comprise approximately 90 by weight of iron meteorites classified so far with the exception of the iva group the groups have well defined 187re 187os isochron ages which are interpreted as the time of crystallization of the metal of their parent bodies within each magmatic group samples that crystallized both early and late in the sequence of each core were analyzed to evaluate possible evolution of the w isotopic composition during crystallization all the samples examined display very similar w values within a narrow range of compositions between 5 1 and 3 1 witzation began less than a few percent of additional metal was segregated to the cores moreover the average w values for the five groups have no resolvable difference ranging from 4 08 0 69 iva to 3 30 0 15 iab iiicd these data indicate that all of the iron meteorite parent bodies underwent metal segregation within 5 ma of each other apparently independent of their composition size and time of crystallization of the metal in all groups except the iiiab group there is a resolvable time interval between the timing of metal segregation as constrained by the w isotopic data and the initiation of core crystallization as given by the re os isotopic systematics

bioturbational structures record environmental changes in the upwelling area off vietnam south china sea for the last 150 000 years the sediments in the upwelling area off central vietnam are totally bioturbated and display a low diverse assemblage of bioturbational structures during interglacial times marine isotope stage mis 1 5a 5c 5e summer monsoon leads to pronounced upwelling and seasonally pulsed arrival of organic matter on the seafloor these deposits are characterized by a 4 tier bioturbated zone with zoophycos zoophycos producers used this seasonal food source and show a cache behavioral strategy during glacial periods upwelling was weak and oxygenation of bottom water decreased as evidenced by bioturbational structures that show a decrease in size penetration depth and diversity enlarged freshwater influx during glacial times fuelled primary production and led to estuarine circulation the resultant oxygen minimum layer favored an increased deposition of organic matter that in turn affected sediment properties during mis 2 and 5b oxygenation was probably a little lower than today during mis 3 and 5d chondrites like burrows point to a stronger oxygen deficiency during mis 4 bottom water oxygenation was even lower and only biodeformational structures occur in soft sediment rich in benthic food based on these findings an ichnofabric model for food rich fairly soft deposits experiencing oxygen deficiency is suggested having biodeformational structures as low oxygen end member

ichnofabrics and their roles in the modification of petrophysical properties a case study of the ordovician majiagou formation northwest henan province china abstract the carbonate rocks of the ordovician majiagou formation from the northwestern part of henan province and their diverse trace fossils provide an outcrop analogue for bioturbated low porosity and low permeability carbonate reservoirs three ichnofabrics can be defined based on the ichnotaxonomy ichnodiversities individual abundances and overall bioturbation indices the balanoglossites ichnofabric represented medium to relatively high energy sedimentary environments such as intertidal zone and subtidal shoals in the carbonate platform the planolites ichnofabric suggested relatively low energy protected sedimentary environments such as lagoons in a restricted carbonate platform but also occurs in the deeper water depressions in the open carbonate platform the chondrites ichnofabric characterized low energy and reduced oxygen conditions with burrows penetrating below a shallow redox interface in deeper water settings that include the distal slope as well as local depressions in the open carbonate platform our analysis suggests that the modifications of petrophysical parameters are controlled or influenced by the ichnofabric characteristics burrow architecture burrow cross cutting relationship degree of bioturbation and burrow connectivity the permeability contrast between burrow fills and matrix and the dolomitization of burrow fills the micritic host sediments have negligible porosity and permeability the bioturbated sediments have significant differences in fabric texture porosity and permeability the burrow fills are very commonly dolomitised each of the burrow types can enhance reservoir properties but the greatest differences are associated with the balanoglossites ichnofabric in which porosity and permeability can reach over 2 and 70 md preliminary stratigraphic studies indicate that reservoir potential in the subsurface will be linked to an understanding of the distribution of shoal and intertidal facies as well as their associated balanoglossites ichnofabrics

sapropel burn down and ichnological response to late quaternary sapropel formation in two 400 ky records from the eastern mediterranean sea two approximately 400 ky long sedimentary records from the eastern mediterranean sea were used to study the factors determining why some sapropels are more or less completely erased while others are preserved x ray radiographs bulk density organic carbon content fe al and mn al ratios were used to reconstruct initial thickness and burn down ratios of sapropels s1 to s11 the results show that at the low sedimentation rate open ocean settings studied initial carbon content of the sapropel as well as post sapropel sedimentation rate and carbon flux have had only limited influence on the preservation of sapropels in contrast the regional position relative to the deep water source controlling bottom water current intensity and bottom water oxygenation played a major role in the preservation of the sapropels furthermore orbitally controlled variations in the intensity of subsequent summer insolation maxima also seem to play an important role in the preservation potential of sapropel layers subsequent strong insolation maxima resulting in thick sapropels tend to act as a lid preventing further burn down of the older sapropels below the long and well dated records also offer an opportunity to study the response of the benthic fauna to the drastic environmental changes related to the formation of sapropels the sediment in the two cores is generally characterized by mottled burrows with only scarce occurrences of distinct trace fossils such as scolicia thalassinoides chondrites and trichichnus the meager ichnofauna is attributed to the well oxygenated and warm bottom waters in an oligotrophic environment typical for non sapropel times the sparse ichnofauna and the lack of tiered ichnocoenosis render existing models of bioturbational response to changes in bottom water oxygenation unsuitable for this kind of environments however observations on individual traces support earlier studies that suggest that the trace fossils trichichnus and chondrites are the result of chemosymbiotic activities that benefit from reducing conditions in the pore water and that the producers of scolicia have a preference for well oxygenated conditions and sandy substrates c 2006 elsevier b v all rights reserved

effect of phycosiphoniform burrows on shale hydrocarbon reservoir quality unconventional gas tight gas coalbed methane and shale gas has become an increasingly significant source of energy economic production from such low permeability reservoirs relies upon identifying regions of the reservoir that will yield the highest gas production rates currently available gas recovery technologies are highly dependent on the fracturability of the reservoir zones of enhanced brittleness and permeability within shale gas reservoir horizons are a prerequisite for successful shale gas recovery such brittle zones are directly linked with increased quartz and or carbonate content within the mudstone in mudstones with high clay mineral content quartz may be concentrated and redistributed as a result of burrowing activities of infaunal organisms high quality porosity and permeability zones in shale petroleum reservoirs may be present in the form of silty and sandy tortuous strips of selectively concentrated grains of quartz that constitute burrow halos grain selective burrows therefore can improve reservoir capacity permeability and fracturability and thus control the storativity of the shale petroleum reservoir this study presents three dimensional reconstructions of three different types of phycosiphon like burrows and investigates the possible fluid flow paths caused by the ichnofabric the volumetric approach to the bioturbation generated by phycosiphoniform burrow makers used herein shows that the volume of sediment that becomes more porous and more permeable media within such bioturbated interval can range from 13 to 26 of the total volume the quartzose strips of sediment caused by bioturbation are highly tortuous and interconnected vertically and horizontally thereby increasing both horizontal and vertical permeability additionally the quartz frameworks created by the burrows may locally increase fracturability within otherwise nonbrittle mudstones

integrated stratigraphy of the kimmeridge clay formation upper jurassic based on exposures and boreholes in south dorset uk for the purposes of a high resolution multi disciplinary study of the upper jurassic kimmeridge clay formation two boreholes were drilled at swanworth quarry and one at metherhills south dorset uk together the cores represent the first complete section through the entire formation close to the type section we present graphic logs that record the stratigraphy of the cores and outline the complementary geophysical and analytical data sets gamma ray magnetic sus ceptibility total organic carbon carbonate 13 c org of particular note are the new borehole data from the lowermost part of the formation which does not crop out in the type area detailed logs are available for download from the kimmeridge drilling project web site at http kimmeridge earth ox ac uk of further interest is a mid eudoxus zone positive shift in the 13c org record a feature that is also registered in tethyan carbonate successions suggesting that it is a regional event and may therefore be useful for correlation the lithostratigraphy of the cores has been precisely correlated with the nearby cliff section which has also been examined and re described magnetic susceptibility and spectral gamma ray measurements were made at a regular spacing through the succession and facili tate core to exposure correlation the strata of the exposure and core have been subdivided into four main mudrock lithological types a medium dark dark grey marl b medium dark dark grey greenish black shale c dark grey olive black laminated shale d greyish black brownish black mudstone the sections also contain subordinate amounts of siltstone limestone and dolostone comparison of the type section with the cores reveals slight lithological variation and notable thick ness differences between the coeval strata the proximity of the boreholes and different parts of the type section to the purbeck isle of wight disturbance is proposed as a likely control on the thickness changes

integrating depositional models ichnology and sequence stratigraphy in reservoir characterization the middle member of the devonian carboniferous bakken formation of subsurface southeastern saskatchewan revisited the upper devonian lower carboniferous bakken formation is a widespread siliciclastic unit in the subsurface of the williston basin that is subdivided into three members lower and upper organic rich shale members and a dolomitic silty and sandy middle member although the unit has become one of the most active oil plays in north america and numerous sedimentologic studies have been made no consensus about the depositional environments of the middle member has been achieved previous studies suggested several depositional and sequence stratigraphic scenarios including lowstand offshore shoreface normal regressive offshore shoreface incised estuary and falling stage shoreface complexes for the middle member we propose a new depositional and sequence stratigraphic model and compare it with some previous interpretations this new model includes a basal transgressive systems tract tst embracing shelf deposits a highstand systems tract comprising shelf to lower shoreface environments and an upper tst encompassing a brackish water embayment complex and offshore to shelf settings petrophysical characterization of the sedimentary facies reveals that bay mouth cross stratified fine grained sandstone flaser bedded very fine grained sandstone formed in wave dominated tidal flats offshore transition highly bioturbated interbedded very fine grained sandstone and siltstone and tidal flat very fine grained sandstone with common mud drapes possess the best reservoir qualities recognition of a restricted embayment within the bakken middle member has major implications for both exploration and production embayment facies with good reservoir quality constitute good oil prospects in localized areas whereas fully marine facies may represent good oil prospects of more regional extent

magnetic fabrics of the morcles nappe complex abstract anisotropy of magnetic susceptibility ams measured with high fields at ambient and low temperatures 77 k has been used to separate ferromagnetic sensu lato paramagnetic and diamagnetic sub fabrics for deformed limestones located in a nappe structure from southwest switzerland the magnetic fabrics are dominantly controlled by paramagnetic and diamagnetic minerals and ferromagnetic minerals contribute significantly only at two of the eight study locations separation of the magnetic sub fabrics is possible in the root zone and overturned limb of the morcles nappe which contains a high ratio of diamagnetic matrix calcite to paramagnetic secondary phases each of the sub fabrics displays a relationship with structural cleavage and the crystallographic preferred orientation cpo of calcite in the root zone and overturned limb the maximum axis of the paramagnetic ams ellipsoid kmax lies close to the pole to cleavage with the intermediate kint and minimum kmin axes near the cleavage plane conversely the diamagnetic kmin lies close to the pole to cleavage with kmax and kint axes near the cleavage plane slight offsets in the poles to cleavage and in the principal ams directions are observed they are interpreted to be the consequence of a second phase deformation event affecting only the cpo but not the macroscopic structural elements the diamagnetic sub fabric reflects the cpo of calcite produced through recrystallization during nappe deformation iron rich calcite appears to control the paramagnetic sub fabric susceptibility ellipsoids approach oblate shapes for the diamagnetic sub fabric with the most extreme shapes reaching susceptibility differences k kmax kmin close to that of single crystal calcite whereas the paramagnetic sub fabric is represented mainly by prolate shape ellipsoids the low field ams ellipsoids show mixed oblate and prolate shapes without consistency within or between sites it is evident that when the magnetic sub fabrics of the root zone and overturned limb are separated their individual shapes and distribution of principal directions mirror the developed cpo

mudstone lithofacies in the kimmeridge clay formation wessex basin southern england implications for the origin and controls of the distribution of mudstones abstract lithofacies analysis has been undertaken on a suite of apparently monotonous organic rich mudstones from the upper jurassic kimmeridge clay formation kcf in the wessex basin southern england using a combination of hand specimen description whole rock geochemistry optical petrography and electron optical petrography five lithofacies have been identified these are clay rich mudstones silt rich mudstones nannoplankton rich mudstones laminated mudstones and concretionary carbonates these facies can be distinguished from one another on the basis of physical sedimentary structures and the relative proportions of allochthonous autochthonous and diagenetic components in each all five of the kcf lithofacies studied were deposited in a marine shelf environment below fair weather wave base but in relatively shallow water close to storm wave base deposition occurred in regions where sand and other coarse clastic allochthonous debris were not being supplied and the bottom waters varied from oxic to anoxic the main factors influencing the development of the five facies were distance from source area primary productivity bottom water anoxia absolute bathymetry clastic dilution and local sediment accumulation rates specifically the clay rich mudstones were deposited in regions farthest down the sediment transport paths commonly in areas by passed by the main sediment supply and beneath surface waters of relatively low primary productivity in contrast the silt rich mudstones were deposited in more proximal areas closer to the source of the sediment in regions where surface productivity and sediment accumulation rates were much higher the nannoplankton rich mudstones accumulated beneath regions where productivity in the surface water layers was fairly high dominated by coccolithophoroid production and the supply of clastic sediment was insufficient to significantly dilute the autochthonous fraction of the sediment unlike the other facies laminated mudstones were deposited in areas where the bottom waters were anoxic surface productivity was enhanced and local sediment accumulation rates were high the concretionary carbonates were precipitated by diagenetic processes in areas where sediment accumulation rates were very low these facies descriptions have enabled a detailed sedimentological study of the kimmeridge clay formation to relate depositional and diagenetic processes directly to the facies present thereby allowing classical facies analyses to be undertaken on apparently homogeneous mudstone successions

paleomagnetic dating of fracturing using breccia veins in durness group carbonates nw scotland abstract a paleomagnetic study of red fault related breccia veins in the cambro ordovician durness group in nw scotland was conducted to determine the time of brecciation the origin of the veins and the nature and timing of associated fluid related diagenetic alteration the veins contain brecciated fragments of the host durness group and strike either east west or north south clasts of breccia cemented by calcite suggest multiple brecciation events the host durness limestone is a gray dolomite and contains a devonian chemical remanent magnetization crm that resides in magnetite the veins contain magnetizations that reside in hematite and are interpreted as crms the breccias in north south veins contain a triassic crm whereas the veins with east west strikes contain a jurassic crm authigenic hematite is common in the breccias along growth planes in the calcite cements the two crms within the veins are interpreted as dating two separate brecciation and fluid flow events that precipitated authigenic hematite the brecciation and fluid flow events are interpreted to be related to extension in the mesozoic which is consistent with the extensional history of the northern atlantic margins

chondrites a trace fossil indicator of anoxia in sediments the trace fossil chondrites a highly branched burrow system of unknown endobenthic deposit feeders occurs in all types of sediment including those deposited under anaerobic conditions in some cases such as the jurassic posidonienschiefer formation of germany chondrites occurs in black laminated carbonaceous sediment that was deposited in chemically reducing conditions in other cases such as numerous oxic clastic and carbonate units throughout the geologic column chondrites typically represents the last trace fossil in a biotutbation sequence this indicates that the burrow system was produced deep within the sediment in the anaerobic zone below the surficial oxidized zone that was characterized by freely circulating and oxidizing pore waters

evidence for high energy events and shallow water deposition in the chattanooga shale devonian central tennessee usa abstract the upper devonian chattanooga shale of central tennessee a classical black shale was deposited in an epicontinental setting west of the appalachian foredeep its finely laminated and highly carbonaceous nature is commonly interpreted to indicate deposition in comparatively deep and stagnant water interbeds of bioturbated greenish gray shale indicating oxygenated bottom waters are commonly ascribed to pycnocline fluctuations however laminated fine sand and silt and hummocky cross stratification hcs at the base of some of these beds indicates interaction of storm waves with the seabed and suggests that greenish gray shale beds are post storm mud drapes other interesting features are inclined undulose erosion surfaces that are conformably overlain by shale beds sets of inclined shale beds that suggest low angle cross bedding and clearly and uniformly developed alignment of clay particles magnetic fabric studies these observations show that the seabed was at times subject to prolonged erosion by bottom currents erosion surfaces agitation and reworking by storm waves hcs and greenish gray shale beds and sediment transport by long lived bottom currents particle alignment the epicontinental sea setting and the presence of hcs and other storm produced features suggest a relatively shallow water depth possibly only a few tens of meters together with abundant evidence of variably strong bottom currents and bioturbation of black and gray shale beds this suggests that abundant planktonic organic matter production rather than stagnant bottom waters are the primary cause for black shale formation

orthogonal switching of ams axes during type 2 fold interference insights from integrated x ray computed tomography ams and 3d petrography abstract we applied x ray computed microtomography ct in combination with anisotropy of magnetic susceptibility ams analysis to study metamorphic rock fabrics in an oriented drill core sample of pyrite pyrrhotite quartz mica schist the sample is extracted from the paleoproterozoic martimo metasedimentary belt of northern finland the ct resolves the spatial distribution shape and orientation of 25 920 pyrrhotite and 153 pyrite grains localized in mm thick metapelitic laminae together with microstructural analysis the ct allows us to interpret the prolate symmetry of the ams ellipsoid and its relationship to the deformation history ams of the sample is controlled by pyrrhotite porphyroblasts that grew syntectonically during d1 in subhorizontal microlithons the short and intermediate axes k3 and k2 of the ams ellipsoid interchanged positions during a subsequent deformation d2 that intensely crenulated s1 and deformed pyrrhotite while the long axes k1 maintained a constant position parallel to the maximum stretching direction however it is likely that all the three ams axes switched similar to the three principal axes of the shape ellipsoid of pyrite porphyroblasts from d1 to d2 the superposition of d1 and d2 produced a type 2 fold interference pattern

anisotropy of diamagnetic susceptibility in thassos marble a comparison between measured and modeled data abstract a study of shear zones within the calcite marble complex of the island of thassos greece shows that the low field anisotropy of magnetic susceptibility ams technique can be successfully applied to diamagnetic rocks for characterizing rock fabrics the strain path involves both an early pure shear stage and a simple shear overprint that is documented by a transition from triaxial neutral to uniaxial prolate shapes of ams ellipsoids the maximum susceptibility is oriented perpendicular to the rock foliation reflecting the preferred orientation of calcite c axes in the protolith as well as in the mylonites for three samples that represent different types of calcite fabrics the ams was recalculated from neutron and electron backscatter diffraction textural data a comparison of the measured and modeled data shows a good coincidence for the orientation of the principal ams axes and for the recalculated anisotropy data both measured and modeled data sets reflect the change from neutral to distinct prolate ellipsoids during progressive deformation

magnetic fabrics in the basal ice of a surge type glacier 1 anisotropy of magnetic susceptibility ams has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments here we present results from debris rich basal glacier ice to examine deformation associated with glacier motion basal ice samples were collected from tunabreen a polythermal surge type glacier in svalbard the magnetic fabrics recorded show strong correlation with structures within the ice such as sheath folds and macroscopic stretching lineations thermomagnetic low temperature susceptibility varying field susceptibility and isothermal remanent magnetism acquisition experiments reveal that the debris rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier an up glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation the results suggest that ams can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed

ichnology of a late devonian early carboniferous low energy seaway the bakken formation of subsurface saskatchewan canada assessing paleoenvironmental controls and biotic responses abstract in spite of the high interest on the late devonian early carboniferous bakken formation as one of the most important oil plays in north america and the numerous studies carried out in this unit no ichnologic analysis has been presented yet based on conventional sedimentologic data previous studies of the bakken interpreted the unit as formed entirely under open marine conditions however integration of ichnology has been key to the identification of not only open marine but also brackish water marginal marine conditions based on the geometry of the sedimentary bodies and the sequence stratigraphic framework the brackish water interval is interpreted as an embayment with limited or intermittent connection to the open sea salinity oxygen content and storms are regarded as the most important environmental parameters that controlled the distribution and nature of the trace fossils in the bakken formation sparse bioturbation relatively low ichnodiversity and the impoverished cruziana ichnofacies characterize the marginal marine deposits suggesting stressful brackish water conditions marine deposits from the middle member in contrast are highly bioturbated with a moderate ichnodiversity and the distal cruziana ichnofacies that flourished during fully marine well oxygenated conditions there is only a slight difference between the total ichnodiversity of the open marine interval ten ichnogenera and that of the brackish water interval seven ichnogenera ichnodiversity should not be considered at face value and isolated from other aspects when evaluating stress levels in order to detect a brackish water signal lack of bioturbation in the black shale of the lower and upper members resulted from anoxic conditions the passage from anoxic lower member to well oxygenated conditions middle member was gradational as is revealed by the occurrence of oxygen deficient trace fossils at the top of the lower member finally the contrasting styles in tempestite preservation in upper offshore deposits from the lower and upper open marine intervals is attributed to variations in the intensity and frequency of storm during deposition of the highstand and transgressive deposits

sequential colonization of muddy turbidites in the eocene beloveža formation carpathians poland abstract a 100 350 m thick succession of centimeter thick fine grained turbidites form the lower mud dominated part of a prograding deep sea fan in the eocene belove a formation in the carpathian mountains of poland these strata contain over 50 ichnotaxa only six of which are common phycosiphon nereites chondrites scolicia halopoa ophiomorpha polished slabs and examination of cross cutting relationships show that post event colonization was sequential using modern analogues it can be shown that the colonization of different depth levels in the sediment at different times reflects changing geochemical conditions especially the re adjustment and re establishment of the redox boundary modern analogues allow an assessment of the timing of each colonization phase the phycosiphon producers entered first and occupied the well oxygenated muds 5 40 mm below the sediment surface as the redox boundary reformed nereites producers entered and probably utilized microbial matter just above the redox boundary about 15 30 mm below the sediment surface subsequently chondrites producers penetrated down to the oxygen deficient layers of the event bed or even deeper levels the halopoa producers entered with phycosiphon but reworked coarser layers contemporaneously with this sequential colonization deep permanent bioturbators which were unaffected by the event cross cut the post depositional suite the variability of the resultant ichnofabrics can be attributed in part to a patchy distribution of the benthos and the relative frequency of turbidite events five ichnofabrics which reflect the successive colonization episodes are recognized each was modified by elements of the permanent infauna

anisotropy of magnetic susceptibility measurement schemes the precision of ams determination is enhanced by measuring susceptibility in directions with a uniform orientation distribution that include the four body diagonals some standard 10 5 cm samples with mean susceptibility 100 si possess too few magnetic grains for reliable petrofabric interpretation whatever the measurement strategy we should only interpret their ams if they pass fabric homogeneity tests

pore types in the barnett and woodford gas shales contribution to understanding gas storage and migration pathways in fine grained rocks the identification of organoporosity microscale and nanoscale pores within organic matter in shales its importance to storage and perhaps transfer of gas molecules through shales and methods for gathering three dimensional images of the pores such as by argon ion milling and or field emission scanning electron microscopy have all been well documented and discussed for unconventional gas shales however other types of pores exist within shales that can be important to storage and migration of gas and oil and other technologies are available for their identification and imaging the different pore types found in the barnett and woodford shales are described and classified in this article scanning electron microscopy revealed the presence of porous floccules in both the barnett and woodford shales which appear similar to laboratory produced floccules and to those in other ancient shales published experimental and observational studies indicate that floccules are hydraulically equivalent to coarser grains and are transported by traction processes current induced microsedimentary structures and textures within the barnett and woodford shales as well as the preserved floccules suggest such processes were active during transport and deposition pore spaces between the floccules are open and can provide storage space as well as permeability pathways for gas molecules through the shales pores are also found within organic matter that occurs both as discrete particles and as adsorbed coatings around clay grains in the shale they are referred to here as organopores porous fecal pellets are also common in the barnett shale preserved fossil fragments such as organic walled spores and inorganic sponge spicules have hollow central chambers which may remain partially or completely open even after burial intraparticle pores occur between grains of various minerals e g pyrite framboids microchannels within shale matrix which may be the bounding surfaces of scours or microsedimentary structures may also provide permeability pathways for hydrocarbon migration mircrofractures are also common and their initiation might be related to mineral crystal structure when present in sufficient quantity these pore types offer potential gas and oil molecule storage spaces and permeability pathways through the shales

biogenically enhanced reservoir properties in the medicine hat gas field alberta canada abstract spot minipermeametry and micro ct analytical techniques were employed to evaluate the effect s of bioturbation on porosity and permeability distributions in reservoir facies of the highly prolific medicine hat gas field of alberta canada this study focuses on five cm scale samples that occur at different stratigraphic positions and intersect discrete bioturbated horizons within the medicine hat member spot minipermeability results demonstrate that permeability in bioturbated sandstones is up to two orders of magnitude greater than those of the muddy matrix thus corresponding to a dual porosity fluid flow system graphing bioturbation intensity versus measured permeability indicates that burrows are well connected horizontally and provide flow conduits micro ct models reveal that burrowed sandstones are isolated and planiform in character rare interpenetrations from vertically oriented trace fossils serve to interconnect these hydraulically isolated strata results show that bioturbated sandstones possess reservoir properties comparable to those associated with laminated sandstones yielding an anisotropic porous medium understanding the impact of trace fossils on porosity permeability distributions in the medicine hat gas field can be used to identify potential reservoir from previously interpreted non reservoir rock and ultimately improve reserve estimations

inverse magnetic fabric in deformed limestones of the morcles nappe switzerland anisotropy of magnetic susceptibility ams was measured at 15 sites in deformed helvetic limestones of the morcles nappe in western switzerland inverse magnetic fabrics characterized by axes of maximum susceptibility subperpendicular to bedding or cleavage were observed at four sites in the root zone of the nappe acquisition and thermal demagnetization of isothermal remanent magnetization show that the ferromagnetic mineralogy is dominated by pyrrhotite with various proportions of magnetite hematite and goethite the matrix minerals were studied in thin section with a staining technique to distinguish different carbonates by x ray texture goniometry and by microprobe analysis observations of ams at room and liquid nitrogen temperatures and of the temperature dependence of bulk susceptibility lead to the conclusion that the inverse fabrics result from a paramagnetic component due to fe2 ions in the calcite matrix

origin of fracture porosity example from altamont field utah the occurrence of natural fracture systems in subsurface rock can be predicted if careful evaluation is made of the geologic processes that affect sedimentary strata during their cycle of burial diagenesis uplift and erosional unloading variations in the state of stress within rock arise for example from changes in temperature pore pressure weight of overburden or tectonic loading hence geologic processes acting on a sedimentary unit should be analyzed for their several contributions to the state of stress and this information used to compute a stress history from this stress history predictions may be made as to when in the burial cycle to expect fracture joint formation what type of fractures extension or shear may occur and which geologic factors are most favorable to development of fractures a stress history is computed for strata of the naturally fractured altamont oil field in utah s uinta basin calculations suggest that fractures formed in extension that the well cemented rocks are those most likely to be fractured that fractures began to develop only after strata were buried to great depth and that the fracture system continued to develop as strata were uplifted and denuded of overburden geologic evidence on fracture genesis and development is in accord with the stress history prediction stress history can be useful in evaluating a sedimentary basin for naturally fractured reservoir exploration plays

anisotropy of magnetic susceptibility ams and diamagnetic fabrics in the durness limestone nw scotland anisotropy of magnetic susceptibility ams and diamagnetic fabrics in the durness limestone nw scotland

petroleum geology of the giant elm coulee field williston basin the elm coulee field of the williston basin is a giant oil discovery in the middle bakken formation devonian mississippian discovered in 2000 horizontal drilling began in the field in 2000 and to date more than 600 wells have been drilled the estimated ultimate recovery for the field is more than 200 million bbl of oil 31 8 million m3 the bakken formation in the field area consists of three members 1 upper shale 2 middle silty dolostone and 3 lower siltstone the total bakken interval ranges in thickness from 10 to 50 ft 3 1 to 15 3 m over the field area the upper shale is dark gray to black hard siliceous slightly calcareous pyritic and fissile the shale consists of dark organic kerogen minor clay silt size quartz and some calcite and dolomite the kerogen consists mainly of amorphous material and the organic material is distributed evenly throughout the shale interval not concentrated in laminations or lenses the upper shale ranges in thickness from 6 to 10 ft 1 8 to 3 1 m over the field area the middle member consists of a silty dolostone and ranges in thickness from 10 to 40 ft 3 1 to 12 2 m the lower member in the elm coulee field consists of brownish gray argillaceous organic rich siltstone burrowing and brachiopod fragments are common in the lower member this facies is equivalent to the lower bakken black shale facies on the northern side of the field and is interpreted to be an updip landward equivalent to the deeper water black shale facies the lower member ranges in thickness from 2 to 6 ft 0 61 to 1 8 m based on the abundance of fossil content and amount of burrowing the members of the bakken formation are interpreted to have been deposited under aerobic middle member common burrows and rare fossils dsyaerobic lower member common fossils and lesser amount of burrows and anaerobic conditions upper member rare fossils and burrows the main reservoir in elm coulee field is the middle member which has low matrix porosity and permeability and is found at depths of 8500 to 10 500 ft 2593 to 3203 m the current field limits cover approximately 450 mi2 1165 km2 the middle bakken porosities range from 3 to 9 and permeabilities average 0 04 md overall the reservoir quality in the middle bakken improves upward as the amount of clay matrix decreases the middle bakken is interpreted to be a dolomitized carbonate shoal deposit based on subsurface mapping and dolomite lithology the main production is interpreted to come from matrix permeability in the field area occasional vertical and horizontal fractures are noted in cores the vertical pay ranges in thickness from 8 to 14 ft 2 4 to 4 3 m the bakken is slightly overpressured with a pressure gradient of 0 53 psi ft 0 02 kpa m horizontal wells are drilled on 640 to 1280 ac 259 to 518 4 ha spacing units long single laterals dual laterals and trilaterals have all been drilled in the field the horizontal intervals are sand gel and water fracture stimulated initial production ranges from 200 to 1900 bopd 31 8 to 302 1 m3 day initial potential rates for vertical wells are generally less than 100 bopd 15 9 m3 day the upper bakken shale probably also contributes to the overall production in the field the exact contribution is unknown but estimated to be less than 20 of the total production the elm coulee field illustrates that the bakken petroleum system has enormous potential for future oil discoveries in the williston basin

life in near anoxic conditions a case study of the ichnology and infaunal ecology of silurian graptolitic black shales from sardinia italy abstract a trace fossil assemblage from the silurian llandovery black shales of the genna muxerru formation is reported for the first time the ichnofossil record is abundant well preserved and comprises alcyonidiopsis cochlichnus phymatoderma planolites large morphotype planolites rough morphotype and a small chondritid sedimentological and ichnological evidence indicates that the bioturbated black shales were deposited in outer shelf or deeper settings with severe depletion in oxygen the seafloor provided a high food supply for the infauna the palaeoenvironment of the genna muxerru formation is an ancient analogue of modern oxygen minimum zones burrow fills are apparently massive in macroscopic view whereas observations under the petrographic and stereoscopic microscope show that a lifestyle dominated i e that of pellet filling sediment feeders as such the genna muxerru formation provides not only a new ethologic reference for low oxygen settings but also a methodological benchmark for ichnological analysis of black shales bioturbation in black shales may be commoner than expected but its recognition requires microscopic observation

single domain particles in rocks and magnetic fabric analysis magnetic susceptibility anisotropy is commonly used as a guide for determining stress and flow axes in rocks and for assessing the suitability of anisotropic rocks for palaeomagnetic purposes we have recently demonstrated however in laboratory produced samples that as theoretically expected susceptibility anisotropy is dependent on particle size multidomain particles of magnetite or similar strongly magnetic particles with shape anisotropy exhibit a maximum susceptibility parallel to their easy remanent magnetization axes whereas uniaxial single domain particles exhibit a maximum susceptibility perpendicular to their easy magnetization axes hence susceptibility anisotropy does not yield an unambiguous determination of particle alignment in rocks independent of domain state by demonstrating uniaxial single domain anisotropy characteristics for the first time in a rock specimen we show here that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro or ferrimagnetic particles in rocks in particular apparently foliated rocks can actually be lineated and vice versa moreover rocks with low anisotropy of susceptibility can have a much higher anisotropy of remanence remanence anisotropy methods are shown to give unambiguous determinations of the degree and type of alignment

lateral variability in shallow marine ichnofabrics implications for the ichnofabric analysis method ichnological analysis commonly undertaken both in the field and in core studies is generally carried out in vertical logged successions this work documents the results of a detailed ichnofabric study of two highly bioturbated sandstone beds separated by a mudstone within the thick lower jurassic succession of the yorkshire coast uk the two sandstone beds contain relicts of hummocky cross stratification and rare bioclasts of bivalves and belemnites bioturbation of the beds is intense and the diversity of trace fossils is considerable trace fossils present include teichichnus rectus teichichnus isp a thalassinoides isp palaeophycus heberti diplocraterion parallelum rhizocorallium rosselia socialis schaubcylindrichnus isp chondrites isp planolites isp and phycosiphon incertum ichnofabrics were studied at 5 m intervals parallel to the modern cliff line which is parallel to the inferred jurassic palaeo coastline the results demonstrate that there is considerable patchiness to ichnofabric even in a comparatively simple depositional setting such as a storm influenced shelf this observation is in line with studies of the modern sea floor the implications of patchiness in ichnofabric are broad ranging but most importantly suggest that caution is needed in the use of ichnofabric analysis for intra regional correlations

ichnological analysis the common ground between ichnofacies workers and ichnofabric analysts abstract this work compares the approaches taken by the two schools of applied ichnology ichnofacies and ichnofabric analysts and proposes an integrated approach for future improvement there are many similarities between the two approaches which mainly differ in the resolution at which ichnological analysis is undertaken ichnofabric work is by necessity performed on a bed by bed basis and interpreted at a scale consistent with that of the sedimentologist s facies ichnofacies studies in contrast seldom report bed by bed changes in ichnological content instead highlighting bedset to facies association scale changes in ichnology through comparison with summary models of ichnological trends this work highlights the fact that workers from both schools utilize the same tools with slightly different emphases to reach their ichnological conclusions contention between the two schools has in recent years centred upon which is the better method for studying trace fossils an artificial construct that detracts from the fact that both are extremely useful to sedimentological and palaeoenvironmental studies ichnofabric analysis is in addition a highly effective means of documenting bioturbated sedimentary fabrics as the basis for petrophysical studies ichnofacies and ichnofabric analysts use the same toolbox of ichnological methods to determine ancient palaeoenvironments the scale of observation is generally different but the results closely comparable the recognition of key stratal surfaces on ichnological grounds is also possible with both methodologies ichnofacies analysts look to recognise glossifungites ichnofacies firmgrounds in offshore mudstones ichnofabric studies would look to recognise overprinting of fabrics created by groups of organisms from different palaeoenvironments but associated with the same key surface it is proposed that the terms ichnofacies method and ichnofabric analysis are abandoned in favour of a neutral ichnological analysis method encompassing the approaches and terminology of both to produce a unified scientifically rigorous user friendly methodology

use of low cost multistripe laser triangulation mlt scanning technology for three dimensional quantitative paleoichnological and neoichnological studies abstract the purpose of this paper is to test the application of a new low cost 2995 00 us multistripe laser triangulation mlt scanner and three dimensional 3d software for semiquantitative and quantitative analyses of ichnofossils and modern traces the goal of this research is to improve on existing analytical techniques and apply new methods to 3d digital models of ichnofossils and modern traces objectives are to 1 provide researchers with new ways to develop and test hypotheses quantitatively in the fields of paleoichnology neoichnology sedimentology and soil science and 2 discuss uses advantages and limitations of mlt technology related to ichnology we scanned and created digital models of a variety of mostly continental ichnofossils and modern terrestrial traces produced by invertebrates and vertebrates visual methods applied include making uniformly colored specimen surfaces stereo pairs anaglyph stereo images animations and cross sections quantitative methods applied include measuring distances tortuosity indices and angles and producing contour maps of tracks two of the most useful properties measurable from digital models are surface area sa and volume v these are used rarely in ichnology because they are difficult to measure with traditional methods we use sa to calculate area exploited and introduce a method of quantifying surface roughness adapted from research on soil surfaces we measure v of burrows tracks and coprolites as well as introduce a new measure termed volume exploited we hypothesize that different tracemakers make burrows with characteristic v to sa ratios this is partially supported by statistical tests of previously published data we also use v to sa ratios to determine relative compactness a metric adapted from building physics digital models ensure perpetuity of specimens because they preserve 3d data that can be used to make physical copies placed in museums and disseminated easily to researchers and educational institutions of all levels data from digital models can be used to interpret ichnocoenoses bioturbation rates and pedogenic properties and processes in soils and paleosols note that mlt scanning digitizes only surfaces of objects so it is best suited for exogenic traces and casts of endogenic traces

reverse engineering mother nature shale sedimentology from an experimental perspective abstract experimental study of the sedimentology of shales can take a variety of forms at its simplest one can experiment with suspensions in a glass jar and try to understand their settling behavior or one can manipulate mud in a tank or bucket to gain insights into its rheology this approach was championed over a century ago by sorby and the insights gained can be quite profound more recently tank and settling tube experiments of animal sediment interactions compaction behavior and sediment unmixing via re suspension have proven to be highly informative in spite of their simplicity flumes can be used to obtain quantitative information about depositional and erosional parameters and to generate fundamental bedforms in flume experiments however it is of critical importance that the flume be designed in a way that flocculated materials move under shear stress conditions that would be reasonable in natural environments although much flume work on muds has been conducted by hydraulic engineers the transfer of that knowledge to sedimentology is hampered by the fact that engineers and sedimentologists are interested in different though not mutually exclusive products from such experiments engineers and hydrologists are commonly concerned with quantifying fluid flow properties whereas sedimentogists are particularly interested in the sedimentary products that result from a variety of flow conditions recent sedimentologically oriented flume studies have shown that muds can form deposits at flow velocities and shear stresses that would suffice to transport and deposit medium grained sand mud suspensions are prone to flocculation and the resulting floccules travel in bedload and form ripples that accrete into beds the latter finding suggests that many laminated shales were deposited from currents rather than by settling from slow moving or still water there are many other sedimentary features in shales that can potentially be reproduced in flume studies and in the future serve to provide a quantitative basis for shale sedimentology

a comparison of the effectiveness of clast based finite strain analysis techniques to ams in sandstones from the sevier thrust belt wyoming abstract geological strain analysis of sedimentary rocks is commonly carried out using clast based techniques which rely on assumptions regarding clast shapes and orientations as well as distances between clast centres to evaluate the accuracy of these methods in low strain regimes we have compared strain analysis estimates to the anisotropy of magnetic susceptibility ams in sandstone samples from the wyoming salient the cordilleran mountain belt of north america is one of the world s classic foreland fold and thrust belts the sevier belt represents the thin skinned front of this orogenic event characterized by thrust faults and folds that shortened and translated sequences of devonian to cretaceous strata eastward deformation increases westward providing an ideal laboratory and geological setting to explore the potential correlation of anisotropy of magnetic susceptibility ams to clast based strain analyses studies attempting to define the relationship between ams and finite strain have been in vogue since the link between layer parallel shortening and ams was first established this relationship despite proven strong correlations between the ams tensors and tectonic directions is generally complicated by competing sub fabrics as well as the various magnetic anisotropy properties of the minerals contributing to the ams fabric even with these complications we conclude that ams is much more sensitive to incipient tectonic fabrics than clast based methods

miocene heterozoan carbonate systems from the western atlantic equatorial margin in south america the pirabas formation abstract outcrops of neogene carbonates of the north brazilian platform occur exclusively along the equatorial coast and represent some of the few existing examples of neogene carbonate systems of the atlantic coast of south america the pirabas formation early middle miocene is the northernmost part of this platform although onshore mainly consists of small and scattered outcrops it considerably extends in the subsurface keeping record of relevant geological and paleontological episodes of tropical south american history intending to improve the knowledge of south american carbonate and providing a solid basis for future comparisons between the pirabas basin and other largely subsurface cenozoic basins this research investigates the aricuru outcrops by combining a standard petrographical and paleontological approach with advanced microct analyses the aricuru area is characterized by mixed siliciclastic carbonate sand sized deposits which probably deposited after the early miocene according to the palynological assemblage the bioclastic fraction of the rock is dominated by benthic foraminifera mostly soritids amphisteginids small rotaliids and small miliolids typical of marginal marine environments bryozoans calcareous algae halimeda echinoderms and mollusks the abundant siliciclastic fraction together with the taxonomic composition of the foraminiferal echinodermal crustacean ichnofossil and fish assemblages indicates deposition in a tropical coastal environment featuring both protected and more exposed sectors the carbonate system probably developed under abundant nutrient supply which fostered heterotroph suspension feeders over hermatypic corals the demise of this system was most likely caused by a growth in siliciclastic input due to increased rainfall in the coastal area the sedimentary evolution of the pirabas formation is similar to the one of the foz do amazonas basin and fits well with the general evolutionary trend of cenozoic carbonate factories of the region indicating the potential of the pirabas subsurface record for understanding other cenozoic basins their paleoenvironmental significance and their potential as oil gas and water reservoirs