Oolite Research Articles

Birth and demise of a Middle Jurassic isolated shallow-marine carbonate platform on a tilted fault block: Example from the Southern Iberian continental palaeomargin

Subbetic Middle Jurassic oolitic limestones of the Jabalcuz Formation crop out in San Cristóbal hill, near Jaén city (Andalucía, Spain), between hemipelagic limestone and marl successions. The Jabalcuz limestones range in facies from calcareous breccias and micritic limestones to white cross-bedded oolitic limestones. Recent erosion has exhumed a Jurassic isolated shallow-water carbonate platform on the San Cristóbal hill. This shallow platform developed on a tilted fault block. An almost continuous, laterally extensive outcrop reveals tectono-sedimentary features distinctive of block-tilting in the different margins of the fault block. The studied sections represent various palaeogeographic positions in the ancient shallow-water carbonate platform and basin transition. This exceptional outcrop allows to decipher the triggering mechanisms of the birth, evolution, and drowning of this Jurassic isolated shallow-water carbonate platform. Two shallowing-upward depositional sequences separated by flooding surfaces can be distinguished on two different sides of the fault block. In the southeastern part of the outcrop, proximal sections grade vertically from distal talus fault breccias, with bivalve and serpulid buildup intercalations, to white cross-bedded oolitic limestones defining the lowermost depositional sequence. Upwards, overlying a flooding surface, the second sequence with oolitic limestones prograding over micritic deposits is recorded. In the southwest, oolitic, peloidal, and more distal micritic facies alternate, with notable southeastern progradation of oolitic facies in the upper part of the section, which represents the upper depositional sequence. The top of this second depositional sequence is another flooding surface recorded by the sedimentation of marls with radiolarians from the overlying formation.In the northwestern outcrops, the two depositional sequences are also almost completely preserved and can be differentiated. A 100m-thick succession composed of a basal slumped unit of micritic and peloidal limestones overlain by cross-bedded oolitic limestones represents the lowermost sequence. The superposition of a newer slumped unit of micritic and peloidal limestones on the cross-bedded oolitic limestones defines the lower part of the uppermost depositional sequence. Finally, the central sections are less thick and comprise a facies succession consisting almost entirely of oolitic limestones.Locally, oolitic limestones often show cross-bedding and prograding clinoforms. The cross-bedding has centrifugal directions around the perimeter outcrops of San Cristóbal hill, whereas in the centre palaeocurrents are highly variable. The sense of the palaeoslopes as deduced from slumps also fits with a centrifugal pattern. Finally, in the southwestern outcrops, the demise of the carbonate platform is marked by backstepping oolitic facies, the presence of lumachelle facies, and onlapping hemipelagic facies.All the data point to the birth, evolution, and drowning of an isolated shallow-water carbonate platform that developed on a tilted fault block. The fault-block tilting controlled the development of talus breccias in the southeastern part and of slumps in the northwest-dipping hangingwall ramp. In the shallowest environments produced by the tilting (uppermost part of the fault block), a shallow-marine carbonate platform developed. Carbonate production (mainly oolitic) kept up with relative sea-level fluctuations and extended the platform at least to the northwest, southeast, and southwest based on observable data. Finally, tectonics and sea-level fluctuations drowned this carbonate platform.

Effective poroelastic coefficients of isotropic oolitic rocks with micro and meso porosities

The present work is devoted to the estimate of linear effective poroelastic properties of isotropic porous rocks characterized by an assemblage of porous grains (oolites), mesopores and solid grains. Examples of such type of microstructure may be found in oolitic limestones. Two distinct classes of pores are taken into account, micropores or intra oolitic pores and mesopores or inter oolitic pores. In the framework of Hashin Composite Sphere Assemblage (CSA, Hashin, 1962) and self-consistent models, a two step homogenization model is developed. At the first step, micropores are homogenized inside the oolites. At the second step, oolites, mesopores and solid grains are assembled by using the self consistent scheme. Levin’s theorem and transformation field analysis method are used to derive poroelastic coefficients (Biot coefficient and solid Biot modulus). Simple explicit formula are presented for effective poroelastic coefficients in the general case of double porosity media, under the assumption of spherical shape for all constituent particles and isotropic distribution. Finally comparisons between model and experimental data are presented for an oolitic limestone which includes micro-indentation results obtained at mesoscale and poromechanical results obtained at macroscale. Comparisons show that in the case of low macro stiffness, a degraded interfacial transition zone (ITZ) surrounding oolites, need to be introduced to fit the data

Effect of Different Types of Coarse Aggregates on Strength of Concrete

Different types of coarse aggregates have distinguished petrological, petrographical and mineralogical and local characteristics, thus, their effects on concrete strength development are quite significant, various and unpredictable. So, the laboratory investigation on the concrete mixtures using local aggregates becomes very necessary before used in engineering practice. This paper carried out the evaluation of two types of coarse aggregates constantly used in Florida, including Miami Oolite limestone and Georgia granite, on their effects on the developments of compressive strength, splitting tensile strength and elastic modulus of concrete with time. And the prediction models based on ACI and Cario-Lew are evaluated and modified. The investigation results indicate that the concrete mixtures with Georgia granite aggregate tends to develop lower strength than those with Miami Oolite aggregate. And the modified models give better prediction on strength development of the concrete mixtures with aggregates often used in Florida.

New data on the structure of the sedimentary section on the Ita Mai Tai Guyot (Magellan Seamounts, Pacific Ocean)

The geological-prospecting investigations carried out by scientists from the Yuzhmorgeologiya State Scientific Center in the eastern segment of the Magellan Seamounts of the Pacific during the cruise of the R/V Gelendzhik in 2003–2010 brought new data on the topography of the Ita Mai Tai Guyot and its Lower Cretaceous-Pleistocene sedimentary section. The guyot is characterized by its complex irregular morphology with angular outlines being complicated by numerous relief mesoforms: spurs, scarps, and volcanic cones and domes. It is shown that the sedimentary cover was formed during a long period. The analysis of the organic macro- and microfaunal remains from the sedimentary rocks made it possible to define transgressive phases in the guyot’s development: the Albian-Cenomanian, the Late Campanian-Maastrichtian, and the late Paleocene-early Eocene. The oolitic limestone sequence recovered by DSDP Hole 202 is determined to be the Albian in age. Based on the original and published data, the geological development of the guyot was analyzed in comparison with other similar structures of the Magellan Seamounts.

Girvanella-coated grains from Cambrian oolitic limestone

Oolites from the Cambrian carbonate sequences of China were analyzed using standard petrographic methods. Thin-section examination reveals that Girvanella, probably representing calcified sheath of a filamentous cyanobacterium, is well preserved in carbonate grains with little diagenetic alterations. The carbonate grains preserved with Girvanella may constitute an independent category here, since Girvanella was previously rarely known in carbonate grains, especially in ooids. According to the microstructures, these carbonate grains can be divided into two types: Girvanella oncoids are ooid-sized grains composed entirely of a meshwork of Girvanella coating a poorly defined nucleus; Girvanella ooids in samples can be further subdivided into two types, Girvanella-core ooids and Girvanella-cortex ooids, according to the microstructures and the distribution of Girvanella in the ooids. Girvanella-core ooids are characterized by a well-defined Girvanella nucleus, which was probably a rounded fragment of the former cyanobacterial buildup. Girvanella-cortex ooids, in contrast, are characterized by the alternations of Girvanella laminae and the micrite laminae. Observations of this study provide direct evidence that microbes, most likely cyanobacteria, were involved in the formation of coated carbonate grains and influenced their microstructures.

Estimation of the damage of a porous limestone using continuous wave velocity measurements during uniaxial creep tests

The damage of an oolitic limestone during quasi-instantaneous compressive tests and multi-step creep tests was studied using an experimental device which enabled the simultaneous and continuous measurement of strains and elastic wave velocities under mechanical loading and controlled hydrous conditions. The simultaneous measurements of five elastic wave velocities (3 P-waves and 2 S-waves) in different directions of propagation and polarisation allowed us to assess the acoustic tensor at any time during loading and thus continuously monitor the evolution of rock damage. The general trend observed in the experimental results was the strong influence of hydrous conditions on both the quasi-instantaneous and time dependent behaviour of this rock. As traditionally observed in the quasi-instantaneous behaviour of quasi-brittle rocks under deviatoric loading, typical anisotropic straining was observed, confirmed by the anisotropy of the wave velocity measured in axial and lateral directions. However, after full unloading, even if a decrease in all waves’s velocities and dynamic elastic moduli was observed, the quasi-isotropy of waves’s velocities was recovered. This recovery after unloading cycle was observed until stress levels close to the peak (i.e., failure) stress. A comparison of laboratory results with numerical predictions from micromechanical models showed that these observations could not be explained by traditional crack propagation theories and that other mechanisms of crack growth must therefore be considered. These trends were also observed during the loading/unloading stages between each creep step with one notable difference, namely that the anisotropy developed during the creep stage was not recovered during the full unloading. A combination of crack growth and crack nucleation combined with a mechanism of progressive crack sliding and closure seems to explain these unusual results. The nucleation of cracks is mostly related to fast loading while the crack propagation is mostly due to subcritical growth of favourable oriented cracks.

Conodont dating of the Middle Ordovician breccia cap-rock limestone on Osmussaar Island, northwestern Estonia

Various mechanisms have hitherto been suggested to explain the formation of the Kundan (Middle Ordovician) Osmussaar Breccia in northwestern Estonia. Following the recent discovery of L-chondritic chromite in these peculiar, sand- penetrated strata, it seems plausible that the breccia is impact-related. Herein, the conodont faunas of three thin limestone intervals overlying the breccia at Osmussaar Island have been investigated, with the aim of establishing the age of the event in terms of the Baltoscandian conodont-based biostratigraphical scheme. Based on the presence of Microzarkodina ozarkodella, the limestone directly overlying the breccia is assigned to the M. ozarkodella Subzone of the Lenodus (Eoplacognathus?) pseudoplanus Zone. This is reinforced by means of a faunal shift between this sample interval and the subsequent one, which is directly comparable with a faunal shift in the Maekalda section, mainland Estonia. The middle, orthoceratite-yielding interval is assigned to the uppermost L. (E.?) pseudoplanus Zone (or, alternatively, the lowermost Eoplacognathus suecicus Zone), whereas the uppermost interval, an oolitic limestone, is referable to the E. foliaceus Subzone, corresponding to the lower part of the Lasnamagi Stage. These results support a connection between the Osmussaar event and the stratigraphic interval yielding abundant meteorites and/or high levels of L-type chromite in Sweden, as they both can be referred to the lower and/or middle part of the Kunda Stage. The minor difference in age between the first limestones deposited after the brecciation and the meteorite and L-chromite-yielding interval in Baltoscandia can be explained as caused by a period of non-deposition, seen as numerous hiatuses of various extent in the Kunda Stage in northwestern Estonia.

The problem of mechanical compatibility of natural building stones in restoration of monuments. Part I: Composite specimens

AbstractThe mechanical compatibility of natural building stones used in the restoration of ancient monuments as substitutes of the authentic material is studied in this short two-paper series. Attention is focused on the porous oolitic limestone of Kenchreae used in the erection of the monuments at the Epidaurean Asklepieion. In Part I experimental results are presented concerning the mechanical properties and constants of both the authentic (ancient and freshly quarried) material and the various stones proposed so far as possible substitutes. It is concluded that only the Kenchreae stone satisfactorily simulates the behaviour of the material used by ancient Greeks. The other types of stones have a substantially different character and their incorporation in the restoration should be treated with caution. In an effort to quantify the influence of the substitute stone on the authentic one, a series of experiments were carried out using composite specimens made from equal parts of authentic and substitute material with various inclination angles of the adhesion plane with respect to the load. It was concluded that the mechanical properties of the composite specimen are strongly affected by this angle and the dependence is not monotonous. In addition, strong strain discontinuities are recorded in the vicinity of the adhesion plane, which are responsible for the initiation of cracking in either of the two materials. It was pointed out that in some cases the incompatibility causes violation of the basic restoration principle concerning the protection of the ancient material. In this context certain geometrical configurations of the boundaries of the specimens are examined in Part II as a possible means of modifying the mechanical behaviour of the substitute stones, in order to make them as compatible as possible with the authentic material.

Integrated remote sensing and GIS for surface water development. Case study: Ras El Hekma area, northwestern coast of Egypt

The surface water development can help to address the growing demand for water resources and the effects of stormwater flooding on the local environment. The study area was chosen according to its special conditions where it represents one of the main headlands along the southern Mediterranean coast and receives amount of rainfall during the winter season. The main objective of this paper is to monitor and record data about the current surface water status as well as to have a systematic understanding of the water resources base in the study area, and this assessment will contribute in the exploitation of the surface water. The current research is integration between geomorphology, geology, remote sensing, and the applications of geographical information system. The total amount of annual rainfall and surface runoff are estimated (annual rainfall is 23.345 million m3 and surface runoff is 1.167 million m3). On the other hand, the surface runoff which has been resulted from one event (storm) is also estimated to be 483,000 m3/day. The present study introduce some recommendations; the cisterns should be established in the vicinities of the watersheds and on the downstream of the drainage basins to store water before draining to the sea, the dug should be in oolitic limestone to reduce drilling costs, the water reservoirs should be established to store large amount of surface water (from 2,000 to 3,000 m3). Dams are necessary to protect the agriculture activities from any flash hazard which is expected any time.

Protective effect of endolithic fungal hyphae on oolitic limestone buildings

This study presents characterizations of weathering forms of the same oolitic limestone from four quarries and eight monuments exposed on various environmental conditions focusing on the waterproofing effect of endolithic organic matter. Patinas were analyzed by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), capillarity coefficient through weathered and unweathered sides, gypsum content and porous network morphology by epoxy resin molding. Study of weathering forms on old quarries indicates that lichens colonization (Verrucaria nigrescens and Caloplaca aurantia) can fill the superficial porous network with a dense network of lichenised fungal hyphae. Capillary coefficient measurement on natural and calcinated samples showed that endolithic organic matter can waterproof the stone and could act as a sulfate contamination barrier. Similar endolithic organic layer due to ancient lichens growth are found on some antique monuments of the Nîmes downtown and could explain their well-preserved state, unlike decayed 19th century churches that were never colonized by lichens.

Influence of CO2on the long-term chemomechanical behavior of an oolitic limestone

[1] In order to study the long-term mechanical and petrographical evolutions of a carbonate rock (oolitic limestone) during storage of CO2, CO2 injection tests were performed in triaxial cells at temperature and mechanical stresses (isotropic and deviatoric) corresponding to the depth of the Dogger carbonate reservoirs of the Paris basin (∼800 m). We used a specific “flow-through” triaxial cell which allowed us to measure very low strain rates in both axial and lateral directions, while ensuring the sealing of the samples during the injection of CO2. Under isotropic loading, neither the dynamic percolation (i.e., flow-through tests) of dry supercritical/gaseous CO2, nor the diffusion of CO2, into initially saturated samples was shown to produce significant axial compaction and calcite dissolution. Indeed, even though the interstitial aqueous fluid becomes acidic, the progressive increase in dissolved species induces the H2O-CO2-calcite re-equilibrium. The dynamic injection of CO2-saturated solution induced significant axial compaction due to the dissolution of calcite at the sample/piston interface only under open flow conditions (i.e., the injected acidic solution is continuously renewed). Under closed flow conditions (i.e., acidic solution recirculation or no-flow conditions) which reproduce the physicochemical conditions of CO2 storage at the field scale better, the rapid H2O-CO2-calcite re-equilibrium inhibits calcite dissolution. Under deviatoric loading and closed conditions, the diffusion of CO2 induced a very small increase in the PSC (pressure solution creep) process which was stopped by the H2O-CO2-calcite re-equilibrium inside the sample. Therefore, a significant compaction of limestone samples was obtained only under open conditions and is mainly due to a purely chemical mechanism (calcite dissolution), while the contribution of the chemo-mechanical mechanism (PSC) was found to not be of any great importance. In the context of massive injection of CO2 at the field scale, if the reservoir can be considered as a closed system from a hydrodynamic point of view (i.e., the brine circulates in the aquifer but is not renewed by any groundwater), CO2 will not play a significant role in the chemistry of carbonate reservoirs due to the H2O-CO2-calcite re-equilibrium and will not induce reservoir compaction and affect its long-term storage capacity, whatever the stress state (isotropic or deviatoric).

Age constraints on the Neoproterozoic Baikal Group from combined Sr isotopes and Pb–Pb dating of carbonates from the Baikal type section, southeastern Siberia

Depositional ages for the middle part of the Neoproterozoic sedimentary succession exposed along Lake Baikal in the southern margin of the Siberian Platform have been constrained by the application of Sr isotope chemostratigraphy and Pb–Pb dating of carbonate rocks. The thick siliciclastic–carbonate Baikal Group is the type section of the regional Siberian succession. Although many of the Baikal Group carbonate rocks have undergone pervasive dolomitization by mixed meteoric-marine fluids, oolitic limestones in the 800-m-thick carbonate member of the Uluntui Formation preserve primary textures and high Sr contents (up to 3200ppm), suggesting that aragonite might have been the original precursor. The 87Sr/86Sr in the least altered high-Sr limestones (Mg/Ca<0.08 and δ18O>−8‰ PDB) range within 0.70842–0.70876, values we interpret as representing the best proxy for coeval seawater. Stepwise dissolution using 0.5N HBr was applied to enrich samples in primary carbonate from the Uluntui Formation and nine data points from the five least altered, high-Sr limestones yielded a Pb–Pb isochron age of 560±30Ma with MSWD=0.6 and probability=0.8. This age matches that inferred from Sr isotope stratigraphy (580–550Ma) and further supports the inference that the Baikal paleobasin was connected to the contemporary oceans. Our Sr chemostratigraphy and Pb–Pb isochron age of the Uluntui limestones cast doubt on previously proposed correlations of the Baikal Group as late Mesoproterozoic to Cryogenian. Instead, the data indicate that the entire siliciclastic–carbonate succession of the Baikal Group was most likely deposited during the Ediacaran (or Vendian, of the Russian Stratigraphic Scale).

The Isle of Portland, Dorset, England

The Isle of Portland is one of the jewels in the crown of the ‘Jurassic Coast’ of Dorset, southern England. Thomas Hardy aptly described this limestone peninsula as the ‘Gibraltar of Wessex’, and used its stone quarries as the backdrop for one of his novels (The Well‐Beloved). Quarries then, as now, work the world‐famous Portland Stone—a Jurassic oolitic limestone—from which St Paul's Cathedral and many other well‐known buildings are constructed. Rocks exposed in the numerous disused quarries scattered across the isle, together with exposures in spectacular sea‐cliffs, paint a vivid picture of life and environments, ∼150 million years ago. In addition to Jurassic patch‐reefs, coastal sabhkas, fossil forests and dinosaur footprints found in the bedrock, more recent geological phenomena include two Quaternary raised beaches, solution caves filled with vertebrates, and massive coastal landslips. The aim of this article is to provide a field guide for those wishing to explore the geology of this little‐known region for themselves.

The sauropod dinosaur Cetiosaurus OWEN in the Bathonian (Middle Jurassic) of the Ardennes (NE France): insular, but not dwarf

A chevron bone from an Early Bathonian oolitic limestone in the Ardennes (NE France) is referred to the sauropod dinosaur Cetiosaurus Owen, previously known from the Middle Jurassic of England, on the basis of its rod-like distal end. This is the first well attested occurrence of Cetiosaurus in France. The presence of Cetiosaurus remains in the Bathonian of both Oxfordshire and the Ardennes is explainable by the fact that these regions were situated on the margin of the London-Brabant Massif land area, on which sauropod populations apparently lived. Contrary to the condition in other sauropods in insular environments, there is no evidence of dwarfism in Cetiosaurus from the London-Brabant Massif, probably because this emergent area was connected to the much larger Fenno-Scandian Shield.

Espectrorradiometria de reflectância de rochas carbonáticas na região do infravermelho de ondas curtas

This work aims to study the spectral behavior of carbonaceous rocks from Sete Lagoas Formation of Group Bambuí, in the region of Serra do Ramalho, state of Bahia. Measurements of reflectance in laboratory were made for sixteen samples of limestones and four dolomites in shortwave infrared (1300 to 2500 nm), using a spectroradiometer PIMA. The analysis of the spectra was accompanied by detailed observations of field, petrographic descriptions, chemical analysis of major compounds and organic matter content, to the following group of carbonate rocks: lime mudstone, calcarenites, oolitic limestone, argillaceous limestone, and dolomite. Based on spectral analysis it is observed that the position of the main absorption feature of ion CO3-2 in lime mudstone, argillaceous limestones and calcarenites has their peak centered on average 2336 nm while the oolitic limestone is centered on 2332 nm. The main differences between the features of the limestones are marked by increased depth of absorption features, with increasing particle size or the presence of clay and a decrease of absorption with the presence of organic matter. The dolomites have its main feature centered on average 2321 nm. Secondary absorptions bands occur near 2140 nm, 1930 nm, and 1430 nm. The presence of organic matter even in quantities of less than 0.1% cause reduction in the depth of absorption feature or even its almost total suppression for all rocks studied.

Espectrorradiometria de reflectância de rochas carbonáticas na região do infravermelho de ondas curtas

This work aims to study the spectral behavior of carbonaceous rocks from Sete Lagoas Formation of Group Bambui, in the region of Serra do Ramalho, state of Bahia. Measurements of laboratory reflectance were made for sixteen samples of limestones and four dolomites in shortwave infrared (1.3 to 2.5 mm), using a spectroradiometer PIMA. The analysis of the spectra was accompanied by detailed observations of field, petrographic descriptions, chemical analysis of major compounds and organic matter content, to the following group of carbonate rocks: lime mudstone, calcarenites, oolitic limestone, argillaceous limestone, and dolomite. Based on spectral analysis we observe that the position of the main feature of ion absorption CO 3 -2 in lime mudstone, argillaceous limestones and calcarenites has their peak centered on average 2.336 micrometres while the oolitic limestone is centered on 2.332 micrometers. The main differences between the features of the limestones are marked by increased depth of absorption features, with increasing particle size or the presence of clay and a decrease of absorption with the presence of organic matter. The dolomites have its main feature centered on average 2.321 micrometers. Secondary absorptions bands occur near 2,14 µm, 1,93 µm, and 1,43µm. The presence of organic matter even in quantities of less than 0.1% showed a reduction in the depth of absorption feature or even his masquerading for all rocks studied.

Microbial carbonates and corals on the marginal French Jura platform (Late Oxfordian, Molinges section)

Molinges was located on an Upper Jurassic ramp system of low-energy regime that developed at the southern margin of the French Jura platform. The sedimentary succession is characterized by the transition from a mixed siliciclastic-carbonate to a carbonate depositional setting that occurred during a long-term shallowing-upward trend. The disappearance of siliciclastics is explained by a climatic change, from humid and cold to drier and warmer conditions, previously identified in Late Oxfordian adjacent basins. The base of the section shows marl-limestone alternations of outer ramp. In its middle part, the section displays oncolitic marls, coral-microbialite beds and oncolitic limestones that deposited in a mid ramp position. Finally, the upper section part is made of oolitic limestones of inner ramp. In outer- to mid-ramp settings submitted to terrigenous inputs, the stacking pattern of deposits and facies evolution allow the identification of elementary, small-, medium-, and large-scale sequences. Small amplitudes of sea-level variations probably controlled rapid shifts of facies belts and reef window occurrences. In small-scale sequences, the coral beds developed during periods of sea-level rise. The decreasing rate of sea-level rise is marked by the downramp shift of the oncolitic limestone belt that led to the demise of coral-microbialite beds. These bioconstructions are mainly represented by thin biostromes in which corals never reach great sizes. The coral assemblages mainly include the genera Enallhelia, Dimorpharaea, Thamnasteria, and some solitary forms (Montlivaltia and Epistreptophyllum). They suggest relatively low-mesotrophic conditions in marine waters during the edification of the primary framework. Relatively cold water temperatures and periods of more elevated nutrient contents are probably responsible of the reduced coral development and the formation of a large amount of microbialites.

Estimation of the damage of a porous limestone from continuous (P- and S-) wave velocity measurements under uniaxial loading and different hydrous conditions

SUMMARY The damage of a porous rock (Euville oolitic limestone) was studied through uniaxial stresscyclingtests.Anexperimentaldevice,allowingthesimultaneousandcontinuousmeasurement of strains (in two perpendicular directions) and five elastic wave hree P waves and two S waves) velocities in two different directions under fully controlled hydrous conditions, was developed for the work presented in this paper. Hence, the damage was monitored in a really precise and continuous way through the evolution of dynamic and static elastic moduli. The evolutions of wave velocities and elastic moduli, which reproduce very remarkably the shape of the stress–strains curves, showed that the limestone, initially isotropic, became progressively anisotropic during uniaxial loading due to microcrack damage. Indeed, even if the creation of microcracks is probably scattered and isotropic before the coalescence of microcracks,asshowninpaststudies,pre-existingmicrocracksandpenny-shapedporeswhich are perpendicular (or almost perpendicular) to the uniaxial stress direction closed, whereas axially-oriented microcracks opened. The anisotropy of the damage is completely reversible but some of the damage is irreversible. VP(90◦), which cannot record the opening of these microcracks, started to decrease just before the macroscopic failure of the sample and can detect, therefore, very precisely the macroscopic failure of the material. The influence of water on the strength and deformation of the Euville limestone was analysed by considering both the hydromechanical and physio-chemical (‘Rehbinder effect’, intergranular pressure solution and subcritical cracking) effects of water.

Tafonomia de biválvios em calcários oolíticos da formação Teresina (Bacia do Paraná, Permiano Médio, Prudentópolis, PR)

Herein, it is presented the first detailed taphonomic study on bivalve mollusk shells preserved in the oolitic limestones of the Teresina Formation (probably Kungurian-Roadian, Lower-Middle Permian) in the eastern margin of the Parana basin. The selected beds are located in two quarries (informally named PRU 1 and PRU 2) in Prudentopolis municipality (Center-South Parana State), and positioned approximately in the middle of the formation and probably in the Pinzonella illusa Zone. The PRU 1 limestone (~30 cm thick), which is partially silicified and intercalated with predominantly pelitic rocks, is classified as a bivalve oolitic grainstone. The basal contact is erosive and the top shows symmetrical ripple marks, which are draped by shale with mud cracks. There are two fining-upwards successions characterized by dense to dispersed packing of the shells, which are usually disarticulated, randomly oriented (many nested/stacked) and mixed with some pelitic intraclasts. Microhummocky cross-stratification occurs a little below the top of the bed. The PRU2 bed is classified as ooid-bivalve rudstone (~5 cm thick), where all shells are disarticulated and fragmented, showing dense packing. The bivalves probably inhabited a muddy substrate and were mixed (as parautochtonous and allochthonous bioclasts) with ooids during high-energy storm events, including posterior shell displacement as a result of bioturbation. Thus, the calcareous beds represent amalgamated proximal tempestites with a complex taphonomic history, strong temporal/spatial mixing of bioclasts and limited paleoecological resolution. They are a typical example of shell beds generated in a huge epeiric sea, which was not necessarily connected to the ocean and where very low depositional-slope gradient, very slow subsidence and minimum sediment accommodation space caused frequent sediment reworking by storm related processes.

An integrated study of the petrophysical properties of carbonate rocks from the “Oolithe Blanche” formation in the Paris Basin

Petrophysical properties were measured on oolitic limestone from the Oolithe Blanche formation (middle Jurassic) in the Paris Basin. Eighteen oriented blocks were collected from three outcrops regarding of the three main facies, oolitic shoal facies, tide dominated facies and prograding oolitic facies. We investigated the relationship between both compressional wave and electrical conductivity with different petrophysical properties such as porosity (water porosity and mercury porosity), permeability and capillarity imbibition. These have led us to relate the variations of petrophysical properties to several microstructural parameters, among them the microporous structure is the most important. Concerning P wave velocities, the general trend observed is as expected a decrease of velocities as the porosity increases but with a significant fluctuation of velocities for a given value of porosity. We have used two distinct effective medium approximations to describe the velocity variations: the self-consistent (SC) approximation and the cemented contact theory (CCT) but no unique model can simply explain our velocity behaviours. The main parameter that controls the P wave velocities is the distribution of microporosity inside oolites: for samples with velocities higher than 4 km/s the microporosity is mainly located in the rim of the ooids while for samples with velocity lower than 4 km/s the microporosity is homogeneous across the ooids. Acoustical fabrics, which are controlled by the facies, indicate that sedimentary textural components such as the amount of cement and arrangement of elements within the oolitic limestones (bioclasts, pellets and ooids) and their degree of connectivity may have some influences on the acoustic velocities. In contrast with acoustic properties, the electrical conductivity data are not so clustered by facies indicating that transport properties are more influenced by microstructural heterogeneities. One single Archie's law can well account for all the data sets but these sets also show a large range of tortuosity factor related to the microporosity arrangement inside oolites. Some good predictive permeability modeling were found using mercury injection spectra. Our investigations reveal that, the best way for fluids to flow is to pass through the microporosity in the oolites, and that permeability depends mainly of the connectivity of the ooids, which is certainly related to the facies.