Argillaceous Marls Research Articles

Geochemical and mineralogical proxies from the Messinian mudrocks (Catanzaro Basin, southern Italy): Paleoweathering and paleoclimate evolution during the onset of the Messinian salinity Crisis

The bulk mineralogy and geochemistry of mudrock samples from a representative section of the Calcare di Base Formation outcropping in the Catanzaro Basin (Calabria) were studied using X-Ray Diffraction and X-Ray Fluorescence techniques. Phyllosilicates are the main mineralogical constituents followed by quartz, calcite, feldspar, hematite and gypsum in the lower part of the studied succession, whereas calcite is the main mineralogical component in the upper part. The geochemical composition reveals that SiO2, Fe2O3, Al2O3, CaO and MgO are the most abundant oxides on average. The chemical weathering indices, such as the CIA (Chemical Index of Alteration) and its modifications, show low-medium values and thus suggest weak-moderate source area(s) weathering conditions, under a mainly dry/arid paleoclimate environment. The low kaolinite amounts confirm a low-moderate degree of weathering processes. The studied samples originate from an environment in which non-steady-state weathering conditions prevailed and active tectonism allows erosional processes. This trend suggests a paleoclimate characterized by persistent dry (arid) conditions alternating with relatively wet (humid) conditions. The studied mudrocks are characterized by recycling effects as recorded in the Al–Zr–Ti plot. The provenance of the studied samples is mainly related to a felsic source such as the rocks composing the Sila Massif.The composition of the studied samples was compared to that of similar samples from the Calcare di Base formation of the Rossano Basin to reconstruct the paleoclimate scenario of the Mediterranean area during the Messinian Salinity Crisis. The analogies between the mudrocks investigated in this work and the argillaceous marls from the Calcare di Base formation of the Rossano Basin suggest that they formed in the same (i) non-steady-state weathering and (ii) dry/arid paleoclimatic conditions. All the evidences allow to hypothesize that semi-closed basins, even if distant and not necessarily synchronous from each other, may have developed in a comparable way due to similar local climate condition, geochemistry of the body water and river run-off. The geochemical and mineralogical proxies from the mudrocks of the Calcare di Base Formation may open a new scenario for the understanding of paleoclimatic condition during the Messinian Salinity Crisis.

Physical properties and crystal structure of near end-member oxy-dravite from the Beluga occurrence, Nunavut territory, Canada

AbstractOxy-dravite, ideally Na(Al2Mg)(Al5Mg)(Si6O18)(BO3)3(OH)3(O), was found in a composition near its ideal end-member at the Beluga occurrence, Nunavut territory, Canada. It occurs in retrograde albite–muscovite–corundum–calcite domains in a calc-silicate rock. This uncommon oxy-dravite occurs as dark brown, equant to short-prismatic, idiomorphic crystals with vitreous lustre and up to ca. 4 × 3 cm in size. The oxy-dravite is optically uniaxial (–), with ω = 1.6453(5) and ɛ = 1.6074(18); its calculated density is 3.069 g.cm–3 with a compatibility index of 0.016. The Beluga oxy-dravite has trigonal symmetry, space group R3m with a = 15.9121(2) Å, c = 7.1788(10) Å, V = 1574.12(5) Å3 and Z = 3. The crystal structure was refined to R1 = 1.45 using 1613 unique reflections. The empirical crystal-chemical formula is X(Na0.88Ca0.08□0.03K0.01)Y(Al1.49Mg1.31Fe0.15Ti0.04Zn0.01)Z(Al5.42Mg0.58)T(Si5.84Al0.16O18)B(BO3)3V(OH2.95O0.05)W(O0.84OH0.01F0.15).Oxy-dravite in nature commonly occurs in a solid solution with foitite, schorl and oxy-schorl. At the Beluga occurrence, its minor contents of Al, vacancy [□], and Ca are most likely compensated by (□Al)(NaR2+)–1 and (CaMg)(NaAl)–1 exchanges of the oxy-magnesio-foitite and magnesio-lucchesiite components. The Beluga occurrence of oxy-dravite is characterised by an Mg-rich environment related to a metamorphic overprint of the original sedimentary sequence. This sequence of marine dolomitic argillaceous marl was influenced by (B,Cl)-rich fluids, probably proximally-derived from mineral breakdown reactions in the calc-silicate during the retrograde stage of metamorphism. The locality is a rare example of a tourmaline + corundum assemblage.

Conceptual model of fracture‐limited sea cliff erosion: Erosion of the seaward tilted flyschs of Socoa, Basque Country, France

AbstractSea cliff morphology and erosion rates are modulated by several factors, including rock control that reflects both lithology and rock structure. Erosion is anticipated to preferentially exploit ‘fractures’, broadly meant as any discontinuity in an otherwise continuous medium, where the rock mass is weakest. Unpicking the direct control of such fractures on the spatial and temporal pattern of erosion remains, however, challenging. To analyse how such fractures control erosion, we monitored the evolution of a 400 m‐long stretch of highly structured sedimentary cliffs in Socoa, Basque Country, France. The rock is known as the Socoa flysch formation. This formation combines decimetre‐thick turbidites composed of repeat triplets of medium to strong calcareous sandstone, laminated siltstones and argillaceous marls. The sequence plunges at 45° into the sea with a shore‐parallel strike. The cliffs are cross‐cut by two normal and reverse fault families, with 10–100 m alongshore spacing, with primary and secondary strata‐bound fractures perpendicular to the bedding, which combined delimit the cliff rock mass into discrete blocks that are exploited by the erosion process. Erosion, and sometimes plucking, of such beds and blocks on the cliff face was monitored using ground‐based structure‐from‐motion (SfM) photogrammetry, over the course of 5.7 years between 2011 and 2017. To compare with longer time change, cliff‐top retreat rate was assessed using SfM‐orthorectified archive aerial photographs spanning 1954–2008. We show that the 13,250 m2 cliff face released 4500 blocks exceeding 1.45 × 10−3 m3, removing a total volume of 170 m3. This equates to an average cliff erosion rate of 3.4 mm/year, which is slightly slower than the 54‐year‐long local cliff‐top retreat (10.8 ± 1.8 mm/year). The vertical distribution of erosion reflects the height of sea water inundation, where the maximum erosion intensity occurs ca. 2 m above high spring‐tide water level. Alongshore, the distribution of rockfall scars is concentrated along bed edges bounding cross‐cutting faults; the extent of block detachment is controlled by secondary tectonic joints, which may extend through several beds locally sharing similar mechanical strength; and rockfall depth is always a multiple of bed thickness. Over the longer term, we explain block detachment and resultant cliff collapse as a cycle. Erosion nucleates on readily exploitable fractures but elsewhere, the sea only meets defect‐free medium‐strong to strong rock slabs offering few morphological features for exploitation. Structurally delimited blocks are quarried, and with sufficient time, carve semi‐elliptic scars reaching progressively deeper strata to be eroded. Lateral propagation of erosion is directed along mechanical weaknesses in the bedding, and large episodic collapses affect the overhanging slabs via sliding on the weak marl beds. Collapse geometry is confined to one or several triplets of turbidite beds, but never reaches deeper into the cliff than the eroded depth at the foot. We contend that this fracture‐limited model of sea‐cliff erosion, inferred from the Socoa site dynamics and its peculiar sets of fractures, applies more broadly to other fractured cliff contexts, albeit with site‐specific geometries. The initiation of erosion, the propagation of incremental block release and the ultimate full failure of the cliff, have each been shown to be fundamentally directly controlled by structure, which remains a vital control in understanding how cliffed coasts have changed in the past and will change in the future.

Depositional setting and limiting factors of early Late Cretaceous glaucony formation: implications from Cenomanian glauconitic strata (Elbtal Group, Germany)

Cenomanian strata of the Elbtal Group (Saxony, eastern Germany) reflect a major global sea-level rise and contain, in certain intervals, a green authigenic clay mineral in abundance. Based on the integrated study of five new core sections, the environmental background and spatio-temporal patterns of these glauconitic strata are reconstructed and some general preconditions allegedly needed for glaucony formation are critically questioned. XRD analyses of green grains extracted from selected samples confirm their glauconitic mineralogy. Based on field observations as well as on the careful evaluation of litho- and microfacies, 12 glauconitc facies types (GFTs), broadly reflecting a proximal–distal gradient, have been identified, containing granular and matrix glaucony of exclusively intrasequential origin. When observed in stratigraphic succession, GFT-1 to GFT-12 commonly occur superimposed in transgressive cycles starting with the glauconitic basal conglomerates, followed up-section by glauconitic sandstones, sandy glauconitites, fine-grained, bioturbated, argillaceous and/or marly glauconitic sandstones; glauconitic argillaceous marls, glauconitic marlstones, and glauconitic calcareous nodules continue the retrogradational fining-upward trend. The vertical facies succession with upwards decreasing glaucony content demonstrates that the center of production and deposition of glaucony in the Cenomanian of Saxony was the nearshore zone. This time-transgressive glaucony depocenter tracks the regional onlap patterns of the Elbtal Group, shifting southeastwards during the Cenomanian 2nd-order sea-level rise. The substantial development of glaucony in the thick (60 m) uppermost Cenomanian Pennrich Formation, reflecting a tidal, shallow-marine, nearshore siliciclastic depositional system and temporally corresponding to only ~ 400 kyr, shows that glaucony formation occurred under wet, warm-temperate conditions, high accumulation rates and on rather short-term time scales. Our new integrated data thus indicate that environmental factors such as great water depth, cool temperatures, long time scales, and sediment starvation had no impact on early Late Cretaceous glaucony formation in Saxony, suggesting that the determining factors of ancient glaucony may be fundamentally different from recent conditions and revealing certain limitations of the uniformitarian approach.

Spatial distribution of fallout and lithogenic radionuclides controlled by soil carbon and water erosion in an agroforestry South-Pyrenean catchment

The mineral composition of soils and weathering processes are known to control the natural radioactivity of soils but research on the influence of water erosion and of main soil properties in the spatial variability of lithogenic and fallout radionuclides remains little investigated in heterogeneous agroecosystems with complex landscape. An extensive study was conducted to determine the mass activities of fallout (137Cs, 210Pbex) and lithogenic radionuclides (238U, 226Ra, 232Th, 40K) an assess the main controls affecting their spatial variations in a representative 2.5 km2 Pre-Pyrenean catchment of north-eastern Spain. The complex agroforestry catchment holds two distinctive parent materials, Muschelkalk limestones and Keuper argillaceous marls, in which the variability of the main soil properties and soil erosion patterns are well characterised. A total of 228 soil samples have been measured by using a high-purity germanium detector. Lithological influence on the variability of radionuclides was investigated and our results indicate that there are strong significant differences between the mass activities of 137Cs, 210Pbex, 226Ra and 40K based on the two different parent materials. Positive correlations were found among the radioactivity contents of 232Th and 40K and the clay content. Total organic carbon (SOC) was also positively correlated with 137Cs, 210Pbex and 226Ra activities, whereas carbonate content and SIC were negatively correlated with the radionuclides with higher significance in soils on limestones.To gain knowledge on the spatial variability of the radionuclides within the landscape, maps of the distribution of radionuclides were generated by GIS interpolation tools of the entire set of measured activities and soil properties within a 100 × 100 m grid. The spatial patterns obtained, besides the variations of radionuclides along four selected transects, confirm the key role of water erosion in the mobilisation of fallout radionuclides, especially 137Cs, while lithogenic radionuclides were sensitive to physical processes in areas where soil loss was intense. This study not only filled the gap of radioactivity data in agroforestry systems with contrasting parent materials, but also shed light on the potential of radionuclides for tracking soil redistribution processes in fingerprints studies.

Correlation of upper Miocene–Pliocene Lake Pannon deposits across the Drava Basin, Croatia and Hungary

Upper Miocene to Pliocene (Pannonian) sediments of the Pannonian Basin System accumulated in the brackish Lake Pannon and the fluvial feeder systems, between 11.6-2.6 Ma. Their stratigraphic subdivision has been problematic for a long time due to the laterally prograding architecture of the basin fill and the historically independently evolving stratigraphic schemes of the neighbouring countries. We correlated the lithostratigraphic units of the Lake Pannon deposits between Hungary and Croatia in the Drava Basin, using lithological, sedimentological and palaeontological data from boreholes and outcrops, and seismic correlation. The Croatica and Medvedski breg formations in Croatia correspond to the Endrőd Fm. in Hungary, comprising shallow to deep water, open lacustrine, calcareous to argillaceous marls. The Andraševec fm. in Croatia corresponds to the Szolnok and Algyő Fms. in Hungary, consisting of sandstones and siltstones of turbidite systems and of clay marls deposited on the shelf-break slope. The Nova Gradiška fm. in Croatia is an equivalent of the Újfalu Fm. in Hungary, built up of a variety of lithologies, including sand, silt, clay and huminitic clay, deposited in deltaic environments. The Pluska fm. in Croatia corresponds to the Zagyva Fm. in Hungary, consisting of variegated clays, silts, sands and lignites, deposited in alluvial and fluvial environments. Coarse-grained (sand, gravel) basal layers are assigned to the Kálla and Békés Fms. and the Sveti Matej member of the Croatica fm. Coarse-grained intercalations within the deep-water marls belong to the Dorozsma Member of the Endrőd Fm. in Hungary, and to the Bačun member of the Medvedski breg fm. in Croatia. Sediment transport and lateral accretion of the shelf edge in the Drava Basin took place from the N, NW, and W, to the S, SE, and E, respectively. According to the biostratigraphic and chronostratigraphic analyses, the oldest shelf-break slopes in the Mura Basin are more than 8 Ma old, whereas the youngest ones in the southeasternmost part of the Drava Basin may be Pliocene in age (younger than 5.3 Ma). Thus, the 180 km long and at least 700 m deep Drava Basin was transformed into a fluvial plain during the last 3.5 million years of the Miocene.

MIDDLE MIOCENE DROWNED RAMP IN THE VICINITY OF MARIJA BISTRICA (NORTHERN CROATIA)

Fossiliferous Middle Miocene deposits from the surroundings of Marija Bistrica (north-east of Zagreb) transgressively overly older pre-Cenozoic bedrocks. Fossils from shallow marine environments are in most cases preserved as bioclasts, while deep marine calcareous oozes characterize the pelagic marls. The age of the transgressive sequence is estimated on the basis of planktic biota from marls (foraminifera, nannoplankton and pteropods) as the Badenian NN5 Nannozone. The following palaeoenvironments can be distinguished or presumed on the basis of biota and sedimentary features: (1) beach characterized by polymictic conglomerates with rhodolith-rich carbonate matrix ; (2) oyster banks, recognized from secondarily found oyster clusters ; (3) lagoons marked with compact bioclastic deposits and rhodolith-halimeda assemblage ; (4) patch-reefs recognized from the surrounding bioclastic deposits ; (5) shallow subtidal maerl beds preserved as loose bioclastic deposits and (6) distal slope argillaceous marls with pelagic biota. Palaeoenvironmental analyses indicate rapid drowning, most probably corresponding to the transgression during the Middle Badenian TB 2.4 3rd order transgressive-regressive sequence.

Landslide: Mineralogical and Physical Investigation

In order to construct a road bed foundation, if land has moved, on an area with old landslides, there is a high chance of it moving again. The investigation was made in a region with hilly relief, in which the parent materials of soils are argillaceous marls of Pliocene age. Because the slope is scarped and the versant has been cut, the soil mass slide favoured of the particle-size distribution dominated by heavy clay. With a reiteratedly percolative moisture regime, the soil material is saturated in water fora long period (700-800 mm precipitation/year), and that can increase the slope mass, thereby increasing the driving forces. In a soil profile situated on the top of the hill, with landslide for about 40 m length of the road, disturbed and undisturbed soil samples were analysed physic-chemical and mineralogical. For the heavy and light minerals from the sand fraction a polarized light analyser is used, and for clay minerals X-ray, differential thermal and infrared absorption method are used. The particle-size distribution in the soil profile is dominated by the clay fraction, which reached 53.2% in the ABt horizon and 63.0% in the Bt horizon (67-93 cm depth). The structure of the light minerals, consists of quartz (41-58%); feldspar (10.16-18.10%); muscovite (14.10-26.04). The heavy minerals are oxides (2.61-15.26%), hornblende (0.58-2.87%) and biotite (0.51-2.68%). It must be mentioned the presence of the metamorphic minerals, with the source of the Poiana Rusca mountains. These minerals are epidote (1.01-1.86%), disthene (0.70-1.86%), staurolite (0.73-2.46%) and sillimanite (0.35-0.45%). The clay minerals, inherited from the parent material or formed during the soil-forming process are dominated by smectite, which represent (71-85%) from the total clay minerals, illite 10-21%, and Kaolinite, 4-12%. Rheological properties, like plastic index (53.8%), activity index (1.01%) and consistency index (0.99-1.00%) show that the shrinkage – swelling processes are active, and provoke landslide. We propose some technical measures for decreasing the driving force and increasing the resisting forces on the slope, such as: drainage net with track ditch and inspection chamber, driven pile a 10 m depth, and so on.

Origin Of Scapolite-Hosted Sapphire (Corundum) Near Kimmirut, Baffin Island, Nunavut, Canada

Gem-quality corundum (sapphire) occurs in scapolite-rich calc-silicate rock hosted in marble of the Lake Harbour Group near Kimmirut, southern Baffin Island. A deposit of blue and colorless gem corundum (Beluga occurrence) is compared to a similar calc-silicate pod generally lacking corundum but containing nepheline (Bowhead occurrence) and located 170 m to the SSW. Corundum formation was made possible by three equally important sequential metamorphic reactions: (1) formation of nepheline, diopside, and K-feldspar (inferred) at granulite facies peak metamorphic conditions; (2) partial retrograde replacement of the peak assemblage by phlogopite, oligoclase, calcite, and scapolite (Me-50-Me-67) as a result of CO2-, H2O-, Cl-, F-bearing fluid influx at 1782.5 +/- 3.7 Ma (P-T 720 degrees C, 6.2 kbar); and (3) retrograde breakdown of scapolite + nepheline (with CO2-and H2O-bearing fluid) to form albite, muscovite, corundum, and calcite. Late, low-temperature zeolite mineralization is common in corundum-bearing zones. Based on thermodynamic models, the corundum-forming reaction only occurs in a 100 degrees C window with an upper limit determined by scapolite-nepheline stability, and a lower limit determined by the formation of Al-silicate rather than corundum. The protolith is inferred to be dolomitic argillaceous marl with no evidence to suggest the initial presence of evaporites. The enrichment of trace metals V and Cr, and the depletion of Co, Ni, and Mn, suggest reducing diagenetic conditions in the initial sediment. Beluga calc-silicate rock is strongly depleted in REE. Oxy-dravite delta B-11 (+3.9 +/- 0.7%) is consistent with a marine boron source. The oxygen isotope composition of corundum (delta O-18(VSMOW) = 16.4 +/- 0.1%) is comparable to that of corundum in marble or desilicated pegmatite associated with marble.

A Gerecse pannóniai puhatestűi és lelőhelyeik: rétegtan, őskörnyezet és fejlődéstörténet

A Gerecse földtani térképezése során a Magyar Földtani és Geofizikai Intézet geológusai új, vagy régen feledésbe merült és részletesen soha nem dokumentált pannóniai feltárásokat azonosítottak a hegység északi előterében, az onnan dél felé felnyúló völgyekben, és a hegység belsejében is. Az ezekből begyűjtött puhatestű fauna (kiegészítve a már korábban ismert tatai puhatestű faunával és régebbi gyűjteményi anyagokkal) és a feltárásokban megfigyelhető szedimentológiai jellemzők alapján a pannóniai rétegsor itt is, mint az egész Dunántúli-középhegység északnyugati peremén, egyetlen transzgresszív-regresszív ciklusból áll. A ciklus transzgresszív szárnyát a tatai téglagyári feltárásokban a vékony transzgresszív bázisrétegre települő Száki Formáció kékesszürke agyagja és az abban megőrződött mély szublitorális fauna, míg a Gerecse központi részén, a tardosi Vályus-kút környékén, 375 méter tengerszint feletti magasságban a lignites agyaggal kezdődő rétegsor fedőjében települő, szintén mély szublitorális puhatestűeket tartalmazó agyag képviseli. A dunaszentmiklósi Iván halála-völgyben valószínűleg egy szökőár hozta létre a kréta fekü anyagából képződött konglomerátumot, homokos mátrixában tömegesen megjelenő zárt (két teknős) pannóniai kagylóhéjakkal. Az üledékciklus regresszív szárnyát az Újfalui Formáció képződményei adják; ezek legjobb feltárásai a Gerecse északi előterében, a Neszmély környéki völgyekben (Nyáraska-völgy, Disznós-kúti-völgy, Csekendi-völgy) és Süttő környékén találhatók. A formációt felépítő felfelé sekélyedő, néhány méter vastag ciklusok faunája a kagylók uralta sekély szublitorális együttesekből, a csigák magas diverzitásával jellemzett litorális faunákból és végül mocsári puhatestű együttesekből áll. Gyűjteményi anyagokban előfordulnak folyóvízi fajok is. A transzgresszív szárny a Congeria czjzeki zóna felső részébe tartozik, míg a regresszív szárny a Lymnocardium ponticum zóna része; a teljes ciklus képződésének kora 9,4–8,7 millió év lehetett. A fáciesek elterjedése alapján a transzgresszió már tagolt térszínen játszódott le, majd az üledékképződéssel egyidejűleg is folyt a terület vetődéses deformációja, de a tatai és vályus-kúti rétegsorok közötti nagy magasságbeli különbség csak további vetőmozgásokkal, a Gerecse utólagos kiemelkedése nyomán jöhetett létre.

Predictions of the highest potential transmissivity of fractures in fault zones from rock rheology: Preliminary results

AbstractFracture transmissivity in a fault zone is a significant parameter when solving certain geoscientific and geotechnical problems. However, the transmissivities are difficult to predict quantitatively owing to the complexity of in situ conditions such as the apertures of fractures. This study analyzes extensive data sets on flow anomalies (transmissive zones) detected from fluid/flow logs of boreholes in fault zones in the light of rock rheology, fracture mineralization/dissolution, and fracture orientation at six sites, namely Horonobe (Japan; siliceous mudstone), Wellenberg (Switzerland; argillaceous marl), Forsmark (Sweden; granite/granodiorite), Olkiluoto (Finland; gneiss), Northern Switzerland (granite/gneiss), and Sellafield (UK; volcaniclastic rocks and sandstone). The flow anomalies are correlated to fractures in fault zones. The data sets show that the transmissivities of the flow anomalies are strongly controlled by the ductility index, defined as the effective mean stress normalized to the tensile strength of the intact rock. An empirically derived power law relationship exists between the transmissivity and the ductility index, allowing predictions of the highest potential transmissivities of fractures in possible fault zones with maximum errors of about 2 orders of magnitude, due to the inevitable heterogeneity of a fault zone. The actual transmissivities may be further reduced by mineral precipitation in the fractures, or increased by mineral dissolution. Fracture orientation has no discernable influence on the transmissivity. The results may prove helpful for understanding and predicting the long‐term transport properties of fault zones in the upper crust.

Stratigraphy, composition and provenance of argillaceous marls from the Calcare di Base Formation, Rossano Basin (northeastern Calabria)

AbstractThe Calcare di Base Formation is a part of the Rossano Basin characterizing the Foreland Basin System of northeastern Calabria. Messinian argillaceous marls from the Calcare di Base Formation have been studied to characterize the sedimentary evolution of this formation during the post-orogenic phases of the Calabria–Peloritani Arc. The mineralogical assemblage of the argillaceous marls is dominated by phyllosilicates (illite, chlorite, illite/smectite mixed layers and traces of kaolinite), carbonate minerals (calcite, aragonite and dolomite), quartz and traces of feldspars (both K-feldspars and plagioclase), gypsum and celestine. The palaeoweathering index records changes at the source, reflecting variations in the tectonic regime as shown in the A–CN–K plot, where the studied samples describe a trend typical of a source area in which active tectonism allows erosion of all zones within weathering profiles developed on source rocks. The studied samples are derived from an environment in which non-steady-state weathering conditions prevailed. This trend could record deformational events that affected the Mediterranean area during the Miocene. The Th/Sc versus Zr/Sc ratios and Al–Zr–Ti plot suggest that the samples likely record a recycling effect from their basement rocks. The geochemical proxies of these samples suggest a provenance from a mainly felsic source. The Messinian argillaceous marls record that deposition probably occurred in a semi-closed marine environment mainly subject to hypersalinity with local episodes of meteoric water influx, during a period characterized by persistent dry and warm/arid conditions alternating with relatively wet conditions.

Heterogeneous rock mass classification by means of the geological strength index: the San Mauro formation (Cilento, Italy)

This paper describes an application of the geological strength index (GSI) method to the San Mauro formation, which is characterized by sandstones alternating with argillaceous marls. The Sandstone/Pelite (S/P) ratio and structural complexity were determined. Geo-structural and geo-mechanical surveys were undertaken in situ and rock samples were tested in the laboratory. A map of the S/P ratio was produced showing the bedrock divided in four classes. Three ranges of GSI values were identified. The values of the intact UCS and of the constant m i were appropriately reduced to reflect the variable presence of sandstone compared with the pelitic fraction. A “weighted average” of the intact strength properties of the hard and weak layers was adopted. The values for the intact materials were reduced from 20 to 60% depending on the GSI categories of the heterogeneous rock mass. In this way, seven classes of rock masses characterized by different values of GSI, reduced UCS and m i values were identified.

Analysis of small-scale heterogeneity in clastic rocks by using computerized X-ray tomography (CT)

The aim of this study is to recognize the basic clastic rock types on the basis of Hounsfield Units (HUs) by using statistical methods (hypothesis tests, distribution fitting, and confidence intervals). How does this recognition depend on depositional history of samples tested? Does the numerical pattern of HUs obtained from small-scale analyzing of some particular sedimentary structures coincide to the textural expectations of those sedimentary structures? Are the HU values provided by the CT measurements capable of evidencing micro-cycles belonging to a particular depositional history? For testing the numerical recognition, we analyze macroscopically homogeneous argillaceous marl, siltstone and fine sandstone samples with similar depositional background, age, and degree of diagenesis. The preliminary research shows that the Hounsfield Units can identify different sedimentary rocks considerably well. There are significant differences among the confidence intervals belonging to the different rock types. However, there also have been some slight overlaps among them. For analyzing the effects of the depositional processes in case of a particular rock type, samples from channel sandstone, distributary mouth-bar, massive (structureless) sandstone from a delta-fed turbidity fan, and channel sandstone with traction carpet origin from a delta-fed turbidity fan (all coming from Pannonian basin filling series) are used. The results prove again the significant differences in the terms of both confidence intervals and distribution-types; however, some overlapping also occurs.

Life in the sublittoral zone of long-lived Lake Pannon: paleontological analysis of the Upper Miocene Szák Formation, Hungary

Life and depositional environments in the sublittoral zone of Lake Pannon, a large, brackish Paratethyan lake from the Late Miocene, were reconstructed from fossils and facies of the Szák Formation. This formation is exposed in several, roughly coeval (9.4–8.9 Ma) outcrops, located along strike of the paleo-shelf-break in northwestern Hungary. The silty argillaceous marl of the formation was deposited below storm wave base, at 20–30 to 80–90 m water depth. The abundance of benthic organisms indicates that the bottom water was usually well oxygenated. Interstitial dysoxia, however, may have occurred immediately below the sediment–water interface, as evidenced by occasional preservation of trace fossils such as Diplocraterion. The fauna comprised endemic mollusks, including brackish cockles of the subfamily Lymnocardiinae, dreissenid mussels (Congeria), and highly adapted, uniquely large-sized deep-water pulmonate snails (planorbids and lymnaeids). Ostracods were dominated by endemic species and, in some cases, endemic genera of candonids, leptocytherids, cypridids, and loxoconchids. Fish remnants include a sciaenid otolith and the oldest skeletal occurrence of Perca in Europe. The phytoplankton comprised exclusively endemic coccolithophorids, mostly endemic dinoflagellates (prevailingly Spiniferites), and cosmopolitan green algae. The Late Miocene fauna and flora of Lake Pannon were in many ways similar to the modern Caspian biota, and in particular cases can be regarded as its precursor.

Minor changes in surface-water fertility across the oceanic anoxic event 1d (latest Albian, SE France) evidenced by calcareous nannofossils

The latest Albian sediments deposited in the Vocontian basin in south-eastern France record the oceanic anoxic event (OAE) 1d, locally named the Breistroffer interval. They are represented by argillaceous marls and marls, containing organic matter (total organic carbon varying from 0.8 to 1%). Changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance, ichnofossil assemblage, and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the OAE 1d sediments in this area. The pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic/benthic, and of allochthonous origin from carbonate platforms. The enrichment in organic carbon within the Breistroffer interval is weak and not associated with high surface-water productivity. The organic matter is mainly terrigenous. Its record is due to (1) a good preservation under dysoxic conditions within the sediments, and (2) a weak input of allochthonous carbonates. Eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances. Distinctive patterns in nannofossil assemblages and macrofauna abundances within the Breistroffer interval are also recognized, reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate.

Derivation and application of a geologic dataset for flow modelling by discrete fracture networks in low-permeability argillaceous rocks

Argillaceous rock formations are targets of exploration for radioactive waste disposal sites in several countries. Groundwater flow in most indurated argillaceous rocks is very limited and occurs (if at all) mainly in brittle discontinuities, such as faults. On the basis of surface observations, core logging and hydraulic measurements in boreholes penetrating an argillaceous marl formation in the Swiss Alps, the relationships between internal fault architecture, larger-scale arrangement of the fault network and fault transmissivity are explored. Only a fraction of all faults observed in the cores correlates with water inflow points into the boreholes, and this is taken as evidence of variable transmissivity within each fault. Such flow channeling is also supported by geologic evidence. Stochastic discrete fracture network models are used for the upscaling of measured fault transmissivities, namely for the calculation of effective hydraulic conductivities ( K eff) of model cubes with lengths of side of 50–500 m. Input data to these models include size, spacing, orientation, heterogeneity (flow channeling) and transmissivity of the faults. Fault size is not well known, but a sensitivity analysis shows that even the extreme assumption of infinite size yields K eff only less than 1 order of magnitude higher when compared to the base case. The effect of different arrangements of flow channels within each fault is also explored but has no appreciable effect on K eff. It is concluded that calculated values for K eff are robust because those input parameters that are least adequately known have only limited effects on the model results.

Climatic control of fluvial‐lacustrine cyclicity in the Cretaceous Cordilleran Foreland Basin, western United States

ABSTRACTTectono‐stratigraphic models of foredeep sedimentation have generally presumed a direct link between changing rates of tectonism and concomitant sedimentological response as manifested by change in thickness, composition or depositional environment of sediment accumulating in adjacent basins. Lacustrine limestone units within the early Cretaceous fluvial/lacustrine Gannett Group of western Wyoming exhibit systematic variation in several geochemical proxies of relative rates of precipitation and evaporation, indicating that lakewater chemistry was controlled by variation in regional climate.Change in proportion of allochthonous terrigenous clastic vs. autochthonous carbonate deposition, as well as carbonate Mg/Ca ratio and stable isotopic composition, occurs at two scales. Metre‐scale alternation of micritic limestone and argillaceous marl is accompanied by mineralogical and isotopic variation within individual beds, indicating preferential carbonate accumulation during intervals of decreased regional meteoric precipitation relative to lake‐surface evaporation. Limestone deposition began during intervals of maximum aridity, and decreased as increased meteoric precipitation‐driven flux of terrigenous clastic sediment overwhelmed sites of carbonate accumulation. Similar upsection variation in limestone mineralogy and isotopic composition at a scale of tens of metres reflects the multiple processes of long‐term increase in meteoric precipitation and lakewater freshening prior to influx of terrigenous sediment, across‐basin fluvial‐deltaic progradation, and renewed accumulation of riverine terrigenous units. Such trends suggest that formation‐scale alternation between fluvial clastic and lacustrine carbonate deposition was controlled by climate change.

Katoite, a new member of the Ca3Al2(SiO4)3-Ca3Al2(OH)12 series and a new nomenclature for the hydrogrossular group of minerals

The new mineral katoite, Ca3Al2(SiO4)(OH)8, occurs in Pietramassa near Montalto di Castro (Viterbo, Italy), associated with many other hydrated calcium silicates and aluminates in the vugs of a phonolite which effused through argillaceous marls of Pliocene age. Microprobe and TG analyses yielded the empirical formula Ca2.96(Al1.85Mg0.01)(Si0.69S0.11)O2.93(OH)9.07 ; X-ray study showed it to be cubic, Ia3d with a 12.358(2) Å. Physical properties (thermal behaviour, refractive index, infrared spectrum, and X-ray powder diffraction) are consistent with its chemical composition and with its pertinence to the solid solution series Ca3Al2Si3O12 (grossular) and Ca3Al2(OH)]2 (synthetic phase) with an approximate content of 27 % of the former and 73 % of the latter. This makes it the first natural compound of the series with a grossular content lower than 50 % and confirms the existence, also in nature, of a complete series with a SiO4 ⇌ (OH)4 isomorphous replacement within the grossular structure. By analogy with other isomorphous mineral series, two names, hibschite and katoite, are appropriate to represent the two solid solution fields with more and less than 50 % Si in the tetrahedra, respectively. The name hydrogrossular remains applicable as a group name for members of the whole series with an appreciable OH content but otherwise undetermined SiO4/(OH)4 ratio. The paragenetic sequence found in nature and laboratory experiments reported in earlier literature, indicate for katoite a crystallization temperature of approximately 300 °C with a relatively high water vapour pressure and a limited Si supply.

Ostracode Biostratigraphy and Paleoecology of Upper Taylor Group (Campian, Upper Cretaeous) in Central Texas: ABSTRACT

The upper Taylor Group in Travis and Williamson Counties, Texas, is lithologically monotonous, consisting of an argillaceous marl (Pecan Gap Formation) grading upward into a calcareous claystone (Bergstrom Formation), with no identifiable lithologic breaks in 142 m (466 ft). Outcrops more than 1-2 m (3.3-6.6 ft) thick are few, and existing biostratigraphic zonations for this interval are generalized. To examine the potential of Ostracoda for biostratigraphic subdivision of this interval, six outcrops totaling 64 m (210 ft) of exposed section were sampled at 1.5-m (5-ft) intervals. Fifty-four species of Ostracoda were identified and their stratigraphic ranges plotted. Species diversity and equitability trend lines and triangular diagrams of proportional family composition provide a basis for paleoecologic interpretation. Three distinct assemblages of ostracodas are found in these samples, and they can be assigned to interval zones proposed by E. M. Brouwers and J. E. Hazel in 1982, which had not previously been extended to central Texas. The Pecan Gap assemblage is characterized by Cythereis caudata and Limburgina verricula and belongs to the Limburgina verricula Zone. The lower to upper assemblage is characterized by Cytheromorpha unifossula, and it contains species common to both the Limburgina verricula and the Escharacytheridea pinochii Zones. Cytherelloidea crafti and Xestoleberis ovata characterize the uppermost assemblage, which falls within the Escharacytheridea pinochii Zone, although the nominal species is absent. Depositionally, the upper Taylor is a single genetic unit. The gradational nature of faunal changes and a lack of nonrandom events in the diversity and equitability trends suggest that the first and last appearances of species should approximate evolutionary events, giving maximum chronostratigraphic significance to this biozonation scheme and offering hope for eventual refinement. The composition of these assemblages indicates deposition in a low-energy environment deeper than 75 m (246 ft). The name Neylandville, defined by paleontologic rather than by lithologic criteria, should not be used in central Texas and possibly elsewhere. Instead, the name Bergstrom should encompass the entire genetic package of claystones between the Pecan Gap Formation and the Navarro Group. End_of_Article - Last_Page 1210------------