Fine-grained Mudstones Research Articles

Polar gigantism and remarkable taxonomic longevity in new palaeoscolecid worms from the Late Ordovician Tafilalt Lagerstätte of Morocco

ABSTRACT The Late Ordovician Tafilalt Biota of the Moroccan Anti-Atlas includes a diverse range of soft-bodied organisms, including palaeoscolecids, paropsonemid eldonioids, graptolites and cheloniellid arthropods, as well as a rich assemblage of mineralised taxa, among them conulariids, trilobites and echinoderms, often found as articulated skeletons. The new fossil locality, not far from the original Bou Nemrou site, has produced two new palaeoscolecid taxa, the new genus and species Anguiscolex africanus and the new species Wronascolex superstes. They are preserved as compression fossils in fine-grained mudstones, where the original phosphatic sclerites have been diagenetically substituted by pyrite and later weathered to iron oxides, giving them a characteristic rusty colour. This area of Gondwana was located adjacent to the Late Ordovician South Pole and both Anguiscolex africanus gen. et sp. nov. and Wronascolex superstes sp. nov. present a degree of polar gigantism, which has been suggested for other taxa in such high palaeolatitudes such as bryozoans, conulariids, trilobites and radiodonts. Lastly, the occurrence of Wronascolex extends the distribution of this typically Cambrian taxon into the Late Ordovician, indicating a total range for the genus exceeding 60 million years, more than any other palaeoscolecid genus described to date. urn:lsid:zoobank.org:pub:6FD5F086-FBC6-465C-B5B7-D29EF9A6B8FB

Side Resistance of Drilled Shafts in Weak Fine Grained Sedimentary Rock

Load transfer mechanism in side resistance of rock socketed drilled shafts has been studied for the past four decades using results of axial load tests and theoretical methods. Various models for prediction of side resistance have been proposed. Only few studies (e.g., Horvath et al. 1983; Rowe and Armitage 1987; Hassan et al. 1997, Miller 2003, Abu-Hejleh et al. 2003) have been completed on socket side resistance of drilled shafts in weathered and fractured fine-grained rock. These studies, however, were based on only a limited number of load test data. A survey of current predictive models has been conducted. This survey shows most of the current models include strong and intact rocks in their databases. Almost all of the current models use a power function to correlate side resistance of rock socket to rock unconfined compressive strength. A database of side resistance of large diameter drilled shafts in only weak fine-grained rocks, such as, weak shales, mudstones, and siltstones (i.e., Intermediate Geomaterial first introduced by O’Neil et al. 1996, Hassan et al. 1997, and O’Neill and Reese 1999) has been complied in this study. The range of weak rocks considered herein corresponds to an unconfined compressive strength of 0.48 to 4.8 MPa. Analysis of this database shows that a linear model best predicts the side resistance of drilled shafts in weak fine-grained sedimentary rocks.

Modified Standard Penetration Test for Illinois Weak Fine-Grained Rocks

Drilled shafts socketed in weak fine-grained rocks, such as, weak shales, mudstones, and siltstones, i.e., unconfined compressive strength (UCS) of 0.48 to 4.8 MPa (10 ksf to 100 ksf), are increasingly used to support structural loads from bridges and other transportation structures. The design of a drilled shaft requires knowledge of strength and compressibility parameters of the weak fine-grained rocks. However, the weathered nature and fragility of weak fine-grained rock limits recovery of intact core samples for laboratory triaxial compression testing. As a result, in situ tests are preferred to measure design parameters for weak fine-grained rocks. The standard penetration test (SPT) was modified and calibrated to assess the in situ UCSUCS and Young’s modulus of weak fine-grained rocks for design. This new procedure is termed the Modified SPT (MSPT) and uses the penetration rate (cm or inches per blow), not the sum of blow counts for the last 30 cm (12 inches) of penetration, to estimate UCS. A correlation between penetration rate and UCS was developed based on a subsurface investigation at twenty-one (21) weak fine-grained rock sites throughout Illinois. The proposed correlation can be used to foundation design parameters weak fine-grained rocks.

Anisotropy of Magnetic Susceptibility Reveals Late Miocene Tectonic Activity in the Western Qaidam Basin

The western Qaidam Basin on the northeastern Tibetan Plateau located at the intersection between the Altyn Tagh Fault and the Kunlun Fault/Qimen Tagh Fault holds significant potential to reveal the tectonic process of these two faults as well as the evolution of the Qaidam Basin. In this paper, we conducted detailed anisotropy of magnetic susceptibility (AMS) records from Late Cenozoic sediments at the Qigequan section in the western Qaidam Basin to shed new light on the tectonic processes in this region. Based on the distribution of three principal axes of magnetic fabrics as well as magnetic fabric parameters, the AMS records can be divided into three parts. The lower part (∼6.9–4.6 Ma), mainly made of fine-grained mudstone and siltstone, exhibits three well-grouped principal axes with a NE-SW elongated Kmin axis as the embryonic tectonic magnetic fabric, suggesting constant NE-SW compressional strain. The middle part (∼4.6–3.0 Ma), characterized by mudstone, siltstone and sandstone, shows three less grouped principal axes and suggests a relatively weak and stable tectonic environment. The three principal axes of the upper part (∼2.4–0.4 Ma) is composed of sandstone and conglomerate of the Qigequan Formation, similar to the middle part, which was primarily attributed to the coarse lithology and not sensitive to tectonics since ∼2.6 Ma. The NE-SW compressional strain in the western Qaidam Basin is consistent with that in the northeastern basin, both of which are parallel to the upper crust movements revealed by the GPS, suggesting the dominant NE-SW compressional strain in the western and northern basins in the late Cenozoic. The decreasing magnitude of tectonic activities during ∼6.9–4.6 Ma indicates that the major geological units released most of the compressional strain in the western Qaidam Basin during tectonic activity that initiated in the early-late Miocene.

Taphonomy of a monodominantGryposaurussp. bonebed from the Oldman Formation (Campanian) of Alberta, Canada

A monodominant Gryposaurus sp. bonebed in the lower unit of the Campanian Oldman Formation of southern Alberta is the oldest hadrosauroid bonebed documented in the province and the first described from the formation. The sedimentology of the locality and the taphonomy of the hadrosaurid material indicates that the bonebed represents an assemblage of juvenile-sized individuals that were probably transported only a short distance from where they died to where they were finally deposited and preserved in a fine-grained mudstone within an overbank sequence. Histological examination of six limb elements confirms that all individuals are juveniles, with two age classes (<1 and <2 years of age at the time of death) that likely died in the same event. Bone microstructure data indicate that Gryposaurus experienced rapid growth over the 2-year life spans documented, equivalent to other Late Cretaceous hadrosaurids in North America. The parautochthonous nature of the bonebed, and the lack of small neonate (newborn) material and almost complete lack of large adult material, suggests that the bonebed represents a segregated group of juveniles. This group of immature individuals may have been an autonomous unit that had separated itself from a larger social grouping, possibly in an effort to increase their survivability.

Geochemical and sedimentary facies study – Implication for driving mechanisms of organic matter enrichment in the lower Silurian fine-grained mudstones in the Baltic Basin (W Lithuania)

More than 100 m-long core sections from Western Lithuania (Baltic Basin), presenting an almost continuous lower Silurian fine-grained siliciclastic organic matter-rich sedimentary record from Aeronian to Homerian, were investigated to evaluate the main forces governing the organic matter enrichment. The methods applied include organic and inorganic geochemistry, organic petrology, sedimentological and petrographic studies along with framboidal pyrite analysis, as well as analysis of stable nitrogen and organic carbon isotopes. The petrographic observations showed distinct mudstone diversity reflecting a variety of paleoenvironmental depositional conditions evolving against a backdrop of post-Ordovician climate, thus, sea level variations, and progressing development of foreland basin throughout the early Silurian. Reflectance measurements on vitrinite-like particles, supported by molecular organic geochemical and Rock-Eval data prove that kerogen from the studied section reached the oil window maturity stage. Rock-Eval pyrolysis, organic geochemical and petrographical as well as δ13Corg data clearly confirm the marine origin of the organic matter. Various geochemical proxies and sedimentary features indicate that in Aeronian a period of more humid climate favored enhanced nutrient input, which in turn intensified organic matter productivity resulting in large amounts of organic matter accumulation. Redox proxies (TOC/TS ratio, trace elements enrichment, molecular organic geochemical indices, framboidal pyrite analysis, TOC/P ratio) demonstrate a rather broad spectrum of bottom water oxygenation levels in the lower Silurian sediments accumulated under oxic - dysoxic – anoxic conditions interrupted by several episodes of euxinia. A highly condensed section of Aeronian black-grey mudstones manifests a very good organic matter preservation under sediment-starved and oxygen-depleted settings. Here, the oxygen-depleted water bottom conditions are well evidenced by low values of δ15N and δ13Corg pointing to the presence of diazotrophic N-fixing and chemoautotrophic organisms. The Sheinwoodian-Homerian section of monotonous grey calcareous mudstones evenly and moderately enriched in organic matter reflects the most steady environmental settings developed under more arid climate in comparison to Llandovery. Throughout the early Silurian sedimentation rates were overall low, although probably enhanced in Wenlock, and played a role in organic matter preservation. It was a critical factor during sedimentation of grey-greenish mudstone of the Telychian characterized by comparatively the lowest organic matter preservation efficiency. Variations in the intensity of the pycnocline, thus organic matter preservation, were probably controlled by climate-triggered sea level changes, although tectonically-driven paleoenvironmantal effects, bathymetry, and, at some point, intensified paleoproductivity inducing oxygen-restricted conditions, were likely contributing. Although MoEF/UEF ratios mainly indicate fully open marine settings during the entire early Silurian, Mo–TOC covariation clearly displays strict basinal restriction in the Aeronian. The profile of δ13Corg demonstrates six carbon isotope excursions along the lower Silurian section. The identified Late Aeronian and Early Sheinwoodian Carbon Isotope Excursions are linked to global sea-level changes, thus, changes in oceanic water circulation pattern. A high percentage of tiny pyrite framboids within the interval of Early Sheinwoodian CIE could reflect an increased pyrite burial under highly reducing conditions and might be associated with an Oceanic Anoxic Event. The three positive δ13Corg excursions within the Telychian seem to be related to an early diagenetic partial oxidation of organic matter.

Characteristics and origins of ridges and troughs on the top of the Middle Miocene strata in the Beijiao Sag of the Qiongdongnan Basin, northern South China Sea

Sedimentary structures generated by (deepwater) bottom currents are of interest to geologists. Based on the root mean square, coherence attribute, and 3D representations, ridges and troughs are imaged for the first time using 3D high-resolution seismic data and confirmed by a well, YL19-1-1, in the Beijiao Sag of the Qiongdongnan Basin. Combined with 2D seismic profiles, we define the flow direction of bottom currents resulting in ridges and troughs. The results indicate that ridges and troughs occur on the top of the Middle Miocene strata and dominantly present wave-shaped structures. Their magnitudes decrease toward the upper and lower slopes. They extend for tens of kilometers, dominantly parallel to one another, with an evenly spaced distribution, some of which locally merge and bifurcate. They are aligned obliquely to the regional slope. The internal ridges are characterized by internal mounded reflections and/or parallel underlying-strata reflections. The presence of polygonal faults and weak to moderate amplitudes within the ridges and troughs suggests that they consist of fine-grained mudstones, as confirmed by the well YL19-1-1. High amplitudes filled within troughs are probably composed of coarse-grained turbidite materials, where polygonal faults are inhibited. Truncations and onlaps occur along the thalweg of a trough and are also clearly observed on the flanks of ridges and the walls of troughs. We infer that the troughs are a product of the erosion of bottom currents and the ridges are remnant underlying (sediment waves) strata as a result of the redeposition of eroded sediments. In addition, troughs are filled by turbidite materials with high amplitudes in the southwestern area of the 3D seismic survey, where ridges and troughs are a combined result of the early erosion by bottom currents and the later reworking by turbidity flows. We have developed conceptual schematic models to indicate the evolutionary history of the ridges and troughs. It provides new insights into the further understanding of the erosional and depositional impacts of bottom currents.

Petrographic, mineralogical and geochemical characterization of fine-grained rocks of the Pilmatué Member (Upper Valanginian-lower hauterivian) of the Neuquén Basin (Argentina): Implications for siliciclastic input, carbonate productivity and redox conditions

Petrographic, mineralogical and geochemical analyses of mixed siliciclastic-carbonate offshore deposits of the Pilmatué Member (Neuquén Basin) were carried out to define two scenarios for deposition: a confined ramp setting (CRS) and an open ramp setting (ORS). The CRS involves marly to carbonate-rich fine-grained mudstones, mostly laminated and non-bioturbated, enriched in redox proxies and depleted in rare earth elements (REE). The ORS comprises abundant siliciclastic-rich mudstones, mostly coarser-mudstones, depleted in redox proxies and with REE pattern similar to the PAAS. These variations are explained through fluctuations in carbonate productivity/terrigenous input, and changes in the circulation pattern of the basin. Within the CRS, high carbonate productivity would be favored due to the general greenhouse condition for the Early Cretaceous and the scarcity of terrigenous supply, related to the landward migration of the shoreline and low effectiveness of sediment distribution by marine currents. Furthermore, high organic matter productivity should lead to an oxygen-depletion close to the sediment-water interface. Instead, increasing sediment supply and dissolved oxygen in the ORS is related to shoreline progradation in the south and the consequent installation of across shelf flows that allowed vertical water circulation and the oxygen replenishment in benthic environment.

Distinct deep subsurface microbial communities in two sandstone units separated by a mudstone layer

Deep subsurface microbial communities are more abundant in coarse-grained sedimentary rocks such as sandstones than in fine-grained mudstones. The low porosity and low permeability of mudstones are believed to restrict microbial life. Then, it is expected that distinct, isolated microbial communities may form in sandstones separated by mudstones. In this context, the connectivity between microbial communities in different sandstone units can be investigated to infer evolutionary patterns of diversification in space-time, which may potentially contribute with relevant data for analyses of hydraulic connectivity and stratigraphic correlation. In this work, we used high throughput DNA sequencing of a ribosomal 16S gene fragment to characterize the prokaryotic communities found in Permian sandstone samples of the same core that are separated by one mudstone interval, in the Charqueadas coal field, Parana Basin (Southern Brazil). Our samples were collected at ∼300 m deep, in porous sandstones separated by a thick mudstone package. Differences in the bacterial community structure between samples were observed for the classified OTUs, from phylum to genus. Molecular biology might be further applied as a possible tool to help to understand the spatial and temporal distribution of depositional facies, and the efficiency of low permeability rocks to compartmentalize reservoirs. Ongoing studies aim to extend the present investigation into further analyses regarding lateral changes in microbial communities present in the same sandstone units.

DETECT - Quantifying the Risk of CO2 Leakage Along Fractures Using an Integrated Experimental, Multiscale Modelling and Monitoring Approach

To verify and demonstrate successful long-term geological CO2 storage to regulatory bodies and the public, it is critical to improve our understanding of the potential for CO2 migration from storage reservoirs along natural pathways. Currently, there are significant gaps in our understanding of multi-phase fluid migration in faulted and fractured caprocks. Caprocks are typically fine-grained mudstones, carbonates or evaporites, with low matrix permeability and high geochemical reactivity. Potential leakage rates depend on pressure gradients, fluid densities, viscosities and saturations, and the flow properties of the fracture networks. Fracture permeability is highly sensitive to fluid pressure and stress regime, and physical and chemical interactions taking place in the fracture network, including mineral dissolution and precipitation, swelling or shrinkage of clay minerals and hydro-mechanically driven fracture propagation. These combined effects can result in an increase or decrease in fracture permeability and network connectivity over different temporal and spatial scales. The highly coupled nature of these processes makes experimental parameterization and predictive modelling highly challenging, especially at the large temporal and spatial scales relevant to CO2 storage. Although some fundamental laboratory and modelling studies are available in the literature, an integrated study, involving a complete life cycle risk assessment of CO2 leakage through fractured caprocks is lacking. Risk analysis is further complicated by the fact that a leak can only be detected and quantified when geophysical or chemical monitoring tools are able to distinguish relevant changes in gas saturation, pressures or compositions compared to baseline levels. The DETECT research program, cofunded by the European Union and national governments as part the ACT initiative, intends to determine realistic flow rates across fractured and faulted mudstone caprocks, and aims to identify existing monitoring tools capable of detecting such fluid migration. For this purpose, the monitoring performance of state-of-the-art technologies will be compared with flow rate predictions from coupled hydro-mechanical flow and reactive transport simulations at single fracture, fracture network and reservoir-scales, which in turn have incorporated insights from a comprehensive laboratory study of stress and reactivity dependent fracture permeability. This improved understanding of the potential flow rates will feed into an integrated life cycle risk assessment using the established bowtie method to provide an overall picture of the natural paths via which CO2 leaks could occur from subsurface storage reservoirs. The bowtie model will be expanded to include quantitative risk assessment, with the goal of calculating the probability/likelihood of leakage across the caprock and estimating the risk reduction provided by monitoring.

DELTAIC AND SHELF DEPOSITIONAL PACKAGES OF THE GULANI MEMBER OF PINDIGA FORMATION, GONGOLA SUB-BASIN, NORTHERN BENUE TROUGH, N.E. NIGERIA

Stratigraphic and facies analysis of the Gulani Member of the Pindiga Formation in the Gongola Sub-basin of the Northern Benue Trough indicated that the lithostratigraphic architecture of the formation are characterized by three bioturbated lithologic units. These includes the lower succession of heterolithic units with fine grained sandstones and mudstone interbeds, passing into succession of medium-coarse grained sandstone with dominantly trough crossbeds and a upper succession of medium grained trough crossbedded sandstone and mudstone interbeds. Facies evaluation of these distinct succession indicated development of a corresponding pro-delta sands and clays, moving into delta front sands and then shelf sandstone and claystone respectively. Thus suggesting that the Gulani Member was generally formed in a coastal setting defined by river dominated deltaic setting and shelf depositional environment.

Preliminary Data of Fluvial Geomorphological Evolution and Its Link with Hazards and Human Impact: The Case of Peiros River, North Western Peloponnese, Greece

River channel dynamics are the result of the complex interaction between natural and human factors, at both local and regional scale. The study of river channel dynamics may be an important way to better understand the mechanisms that rule the functioning of fluvial systems, allowing predictions of its future evolution to be made and appropriate adaptation measures to be taken, remediating the risks related to the fluvial dynamics. The purpose of this study is to present specific aspects concerning the river channel dynamics of Peiros River, NW Peloponnese, Greece and to reveal the role of various control factors. Peiros, the longest river in Achaea, has sources at the NE part of the Erymanthos mountains flowing into Patras gulf. This study traces the various stages of geomorphological evolution of the low part of Peiros's river channel and enables us to study the links between human activity, local tectonics, morphology and fluvial dynamics. The study area belongs to the geotectonic zone of Gavrovo-Tripoli flysch, consisting mainly of medium-bedded fine-grained sandstones and mudstones and influenced by ENE and WNW trending faults aligned with the river flow. The spatial and temporal variability of sediment transport is controlled by various variables, including the natural features of the catchments and human activity. The latter is an important control factor for both the processes of sediment generation, transfer and accumulation and for channel dynamics. At the same time, these processes are responsible on short and long run for the alteration of the river channels, which entail negative environmental consequences. The study revealed restriction of sediment supply, coastal retreat, lateral erosion and migration of the rivers channel that complies with the local tectonics of the area, although major stream offsets are not created. The morphological changes although, are mainly attributed to human intervention factors, such as the construction of a dam and transversal bars that restricted the water flow and consequently the sediment supply. That factor combined with the climate change, had as result to drastically alter the morphology of the area. These morphological changes, except of loss of property and boundary problems, also made the area vulnerable to flush flood events. Structures close to the coast are exposed to more risk because of the measured coast retreat. No remediation measures have been taken, except the installation of rip-rap of limited length and one groin, in an attempt to slow down the coastal retreat and diminish wave action.

Proterozoic 40Ar/39Ar ages from cave deposits of the Malapa, Sterkfontein and Dinaledi fossil sites, Cradle of Humankind, South Africa

We have explored the use of 40 Ar / 39 Ar dating on Mn ooids and peloids, and fragments of indurated, extremely fine-grained mudstone occurring in cave sediments in the Cradle of Humankind (CoH) UNESCO world heritage site, to obtain ages of fossil-bearing cave sediments. Samples analysed were from the Malapa site (envisaged as a testing ground because it was previously dated with high precision by the uranium-lead method and paleomagnetism), the floor of the Dinaledi Chamber in Rising Star Cave, as well as boreholes 2 and 3 of the Sterkfontein Cave. The 40 Ar/ 39 Ar apparent ages of the dated samples turned out to be unrelated to cave formation processes, rendering the Malapa-based validation irrelevant. The results do, however, provide insight into aspects of the origin of the cave sediments and dated material. Most samples yielded disturbed 40 Ar/ 39 Ar spectra. The apparent pooled gas ages for the Mn ooids analysed from Malapa range between 476 ± 13 Ma and 1964 ± 13 Ma. Of 5 ooids from Sterkfontein, one yielded 1597 ± 13 Ma, while the rest range between 1960 ± 35 Ma and 2081 ± 13 Ma, the latter being a plateau age. Peloidal Mn nodules from Dinaledi Chamber samples yielded apparent ages between 1975 ± 9 Ma and 2096 ± 13 Ma. Indurated mudstone fragments were analysed from Sterkfontein and for 3 out of 4 samples, the apparent pooled gas ages range from 1970 ± 14 Ma to 2059 ± 13 Ma (one yielded 1623 ± 15 Ma). We conclude that ooids, peloids and indurated mudstone fragments are derived from higher levels in the Transvaal Supergroup stratigraphy, trapped in karst features over time as these were eroded, and finally washed into the caves.

Possible link between weak bottom simulating reflections and gas hydrate systems in fractures and macropores of fine-grained sediments: Results from the Hikurangi Margin, New Zealand

Small amounts of free gas in interstitial sediment pores are known to significantly lower compressional (P-) wave velocity (Vp). This effect, combined with moderately elevated Vp from the presence of gas hydrates, is usually thought to be the cause for the often observed strong negative reflection coefficients of bottom simulating reflections (BSRs) at the base of gas hydrate stability (BGHS). At several locations however, weak BSRs have been observed, which are difficult to reconcile with a presence of gas in sediment pores. We here present a rock physics model for weak BSRs on the Hikurangi Margin east of New Zealand. Thin sections of a fine-grained mudstone sample from a submarine outcrop in the vicinity of a weak BSR show macroscopic porosity in the form of fractures and intrafossil macropores. We apply the Kuster-Toksöz theory to predict seismic velocities for a rock with water-saturated interstitial micropores and gas or hydrates in macroscopic pore space simulating fractures or compliant macropores. We match field observations of a weak BSR with a reflection coefficient of −0.016 with two end-member models; (1) rocks with gas hydrate-filled voids with a concentration of <4% of bulk sediment overlying water-filled voids, or (2) fully gas-saturated voids at a concentration of <2% beneath water-filled voids. A natural system is likely to consist of a combination of these end-members and of macroporosity filled with a mixture of water and gas or hydrate. Our results suggest weak BSRs may be caused by gas hydrate systems in fractures and macropores of fine-grained sediments with fully water-saturated interstitial pore space. Gas may be supplied into the macroscopic pore space by diffusion-driven short-range migration of methane generated within the gas hydrate stability field or, our favoured model based on additional geologic considerations, long-range advective migration from deeper sources along fractures.

The Importance of Siliceous Radiolarian-Bearing Mudstones in the Formation of Sediment-Hosted Zn-Pb ± Ba Mineralization in the Selwyn Basin, Yukon, Canada

Sediment-hosted massive sulfide (SHMS) mineralization occurred in three main episodes during the evolution of the Selwyn Basin, Yukon, and Northwest Territories, Canada. In the Macmillan Pass district (Tom and Jason deposits), the Upper Devonian strata of the Earn Group host the youngest, least deformed examples of SHMS mineralization. The Earn Group comprises gray to black, homogeneous mudstones, which have been deformed in the Cordilleran fold-and-thrust belt, are weathered and poorly exposed; this makes stratigraphic correlations and the recognition of prospective units very challenging. The host rock (siliceous mudstone) and mineralized intervals at the Tom and Jason Zn-Pb ± Ba deposits have been sampled from drill core. Major element chemistry and total organic carbon (TOC) data are presented for the host-rock samples from two drill holes (TYK-5, n = 18; 76-17, n = 19). All mudstones contain between 2 and 5 wt % TOC and 67 to 83 wt % SiO2. Subtle alteration, marked by potassium loss (K2O/Al2O3 50% radiolarians by volume) within the mineralized horizons and in barren, time equivalent strata, and therefore are a useful stratigraphic marker unit in otherwise homogeneous, featureless fine-grained mudstones. The presence of highly siliceous, carbonaceous mudstone units (with preserved radiolarians) suggests that in the Late Devonian there is a link between biological productivity in the water column, the resultant sedimentation, and the SHMS deposits. These biosiliceous lithologies may be particularly favorable host rocks to SHMS mineralization for the following reasons: (1) high porosities during early diagenesis preserve volume and enhance permeabilities in partially lithified sediments, which are important parameters for subseafloor replacement mineralization; (2) these units are rich in organic materials due to their deposition in productive settings, and have a high capacity for the generation of sulfide via sulfate reduction. Therefore, we suggest there is a link between times of high biological activity and productivity in oceans, sediments derived from those processes, and SHMS deposits.

PROFIL SEDYMENTOLOGICZNY PRZEDKELOWEJSKICH (JURAJSKICH) UTWORÓW SILIKOKLASTYCZNYCH W OTWORZE BADAWCZYM CIANOWICE 2 (OKOLICE KRAKOWA)

SEDIMENTOLOGICAL PROFILE OF THE PRE-CALLOVIAN (JURASSIC) SILICICLASTIC DEPOSITS IN THE CIANOWICE 2 BOREHOLE (NEAR KRAKOW, POLAND) Abstract. In the Cianowice 2 borehole (located in the vicinity of Krakow), straight on the erosional unconformity on the top of metamorphosed Neo-Proterozoic (Ediacaran) shales and below carbonate deposits of Callovian, 20 meters thick interval of siliciclastic rocks has been encountered. The siliciclastic rocks are composed of conglomerates, sandstones, mudstones and subordinate intercalations of coal, siderite and marls. Stratigraphical position of this interval can be inferred based on poorly-preserved miospore assemblage, spanning relatively long geological time (Jadwiga Ziaja, pers. comm. ) – it can represent either Early or Middle Jurassic, or both of those epochs, while the lowermost coarse-grained package can be even of an older, i.e . Triassic age. The interval was subdivided into 5 well-distinguished sedimentary successions, separated by bounding surfaces, mostly of erosional character – only succession 3 starts with sharp lithological contrast between sandy deposits and overlying mudstones, which reflects flooding and rapid retrogradation (either lacustrine or lagoonal). All these bounding surfaces (particularly bottoms of successions 1, 3 and 5) are of regional correlative significance-erosional bounding surfaces can represent sequence boundaries, while bottom of the succession 3 can represent correlative surface of a transgression. In each succession, except for the lowermost one, subordinate fining-upward cycles are dominating. They represent diminishing-upward energy of transport. The succession 1 is composed of breccia and conglomerates with chaotic structure, indicative of mudflow – dominated fans, possibly passing into alluvial fans and back to the mudflow fan again in the top. There is a marked lithological contrast (possibly connected also with considerable hiatus) between the coarse-grained deposits of succession 1 and following successions built of fine-grained sandstones, siltstones, mudstones and claystones. The succession 2 is composed of five fining-upward cycles, indicative of fluvial environment (fluvial plain), with traces of plant vegetation. The succession 3 is entirely composed of mudstones of lacustrine origin, with numerous traces of plant vegetation, siderite concretions and bands and coals at the top. Successions 4 i 5 again contain typical fining-upward fluvial cycles with traces of plant vegetation. The overall profile shows peneplanation of a landscape and continuous diminishing of energy of sedimentary processes up to the top of succession 3 marked with coals. Then, fluvial sedimentation returned. Regional comparison of the Cianowice 2 borehole with borehole Parkoszowice 58 BN, located some 40 km to NW tends to suggest the Early Jurassic (most probably Pliensbachian–Toarcian) age of the profile (the lowermost coarse-grained part can be of a Triassic age), but until more reliable biostratigraphical or chemostratigraphical evidences are obtained, these more detailed interpretations of stratigraphical division remain tentative.

Insight into the development of a carbonate platform through a multi-disciplinary approach: a case study from the Upper Devonian slope deposits of Mount Freikofel (Carnic Alps, Austria/Italy)

The development and behavior of million year-scaled depositional sequences recorded within Palaeozoic carbonate platform has remained poorly examined. Therefore, the understanding of palaeoenvironmental changes that occur in geological past is still limited. We herein undertake a multi-disciplinary approach (sedimentology, conodont biostratigraphy, magnetic susceptibility (MS), and geochemistry) of a long-term succession in the Carnic Alps, which offers new insights into the peculiar evolution of one of the best example of Palaeozoic carbonate platform in Europe. The Freikofel section, located in the central part of the Carnic Alps, represents an outstanding succession in a fore-reef setting, extending from the Latest Givetian (indet. falsiovalis conodont zones) to the Early Famennian (Lower crepida conodont zone). Sedimentological analysis allowed to propose a sedimentary model dominated by distal slope and fore-reef-slope deposits. The most distal setting is characterized by an autochthonous pelagic sedimentation showing local occurrence of thin-bedded turbiditic deposits. In the fore-reef slope, in a more proximal setting, there is an accumulation of various autochthonous and allochthonous fine- to coarse-grained sediments originated from the interplay of gravity-flow currents derived from the shallow-water and deepwater area. The temporal evolution of microfacies in the Freikofel section evolves in two main steps corresponding to the Freikofel (Unit 1) and the Pal (Unit 2) limestones. Distal slope to fore-reef lithologies and associate changes are from base to top of the section: (U1) thick bedded litho- and bioclastic breccia beds with local fining upward sequence and fine-grained mudstone intercalations corresponding, in the fore-reef setting, to the dismantlement of the Eifelian–Frasnian carbonate platform during the Early to Late Frasnian time (falsiovalis to rhenana superzones) with one of the causes being the Late Givetian major rift pulse; (U2) occurrence of thin-bedded red nodular and cephalopod-bearing limestones with local lithoclastic grainstone intercalations corresponding to a significant deepening of the area and the progressive withdrawal of sedimentary influxes toward the basin, in relation with Late Frasnian sea-level rise. MS and geochemical analyses were also performed along the Freikofel section and demonstrate the inherent parallel link existing between variation in MS values and proxy for terrestrial input. Interpretation of MS in terms of palaeoenvironmental processes reflects that even though distality remains the major parameter influencing MS values, carbonate production and water agitation also play an important role.

Shale Holds Huge Potential for Researchers at Universities

A simple question, “Can you tell us about shale?” has spawned growing research programs at universities around the globe. In less than five years, industry-supported university research has played a key role in defining the structure and elements in shale. The work in a group of laboratories at the University of Oklahoma (OU) in Norman, Oklahoma, is an example of the competitive drive to understand these challenging rocks. Now the goal is to explain the inner workings of these rocks and use that understanding to find more oil and gas and produce it far more efficiently. “The whole thing started with the question: Can you tell us about shale? It is leading into so many interesting areas,” said Chandra Rai, who along with Carl Sondergeld has led the OU lab at the Mewbourne School of Petroleum and Geological Engineering. The pair and a longtime lab manager moved into academia in 1999 when BP donated its petrophysics lab to the university. At the time, shale exploration was often still seen as little more than an interesting experiment by Mitchell Energy Company in the Barnett Shale around Fort Worth, Texas. During the following decade: The lab—renamed the Integrated Core Characterization Center—moved to OU’s main campus in Norman. Devon Energy bought Mitchell Energy and showed that drilling horizontal wells could significantly increase shale gas production. The industry mobilized to tap the enormous potential in unconventional reservoirs. In 2004, Devon’s shale exploration team started seeking more outside advice. “When we began to look at it, we realized we had some big questions about shale,” said Jeff Hall, vice president of exploration at Devon. On the list were: How does oil and gas move through the rocks to the wellbore? How can we better complete wells in this reservoir? There are big differences in production from well to well. Why is that? Devon’s shale research led it down a meandering path. It started with a geophysical study that morphed into a geological study that raised engineering questions. Hall said, “We began to realize it is more complicated.” To begin with, researchers had to find tools capable of looking into the structure of these extremely fine-grained mudstones. When they did, it was clear the name shale covered a variety of things. “People started with the idea that all shales were all the same,” Sondergeld said. “It is amazing when you see the microstructure how different they are.” Other companies and universities followed a similar path into shale research. The size of the resource, and the work needed to go after it, are both huge. From the start, the research indicated how unconventional shale reservoirs really are. As the list of questions grew, so did the range of experts involved.

Cenozoic sediments in the southern Tarim Basin: implications for the uplift of northern Tibet and evolution of the Taklimakan Desert

Abstract Cenozoic sedimentary successions along the southern margin of the Tarim Basin, western China, reach up to 10 km in thickness. The two studied sections, the Yecheng and Aertashi, comprise c . 4.5 km and c . 7.0 km of clastic sedimentary rocks respectively. The base of the Yecheng section has been dated palaeomagnetically to be about 8 Ma. Age control of the Aertashi section is based on 87 Sr/ 86 Sr measurements (for the basal marine bed), together with magnetostratigraphy and regional stratigraphic correlation. The lower part of each section is mainly composed of fine-grained mudstone and fine sandstone, which makes up the Wuqian Group (Miocene). The palaeoenvironment is low-energy, meandering and braided streams. The middle part is composed of red mudstone, sandstone with thin conglomerate beds, which make up the Artux Formation (Pliocene). The palaeoenvironment is a distal- to mid-fan environment. The uppermost part of the section, known as the Xiyu Formation (Plio-Pleistocene), consists of cobble and boulder conglomerate intercalated with massive siltstone lenses, which formed as proximal alluvial fan and aeolian deposits. Neogene red beds passing upward into upward-coarsening conglomerate and debris-flow deposits record the change in palaeoslope related to uplift of the northern margin of Tibetan Plateau. The formation of aeolian dunes at c . 8 Ma, and underlying playa lake deposits (as at Aertashi), may indicate an arid, enclosed basin in the southern Tarim after this time. Sedimentological characteristics, together with grain size distribution and geochemistry of siltstone bands in the Xiyu and Artux Formations, point to an aeolian origin. This indicates that the Taklimakan Desert and the regional climate regime may have been fully developed by the Early Pliocene. The onset of aeolian sedimentation in the southern Tarim Basin coincided with uplift of the northern Tibetan Plateau, as inferred from the lithofacies change. Tibetan Plateau uplift resulted in the shift of sedimentary environments northwards into the southern Tarim Basin, and could well have triggered the onset of full aridity in the Taklimakan region as a whole.

Small-volume U–Pb zircon geochronology by laser ablation-multicollector-ICP-MS

U–Pb zircon geochronology is hampered by problems acquiring meaningful geologic ages on zoned grains that retain isotope signatures from multiple growth or thermal events. We present a new method using laser ablation-multicollector-inductively coupled plasma-mass spectrometry to overcome complications associated with intricately zoned zircon crystals through in situ sampling of zircon volumes as small as 12–14 µm in diameter by 4–5 µm in depth (< 3 ng of zircon). Using Channeltron multipliers to monitor Pb intensities in conjunction with a total ion counting method and errors calculated as function of the number of counts, the small-volume technique reproduced published ages on eight Mesoproterozoic–Cretaceous secondary zircon standards precise and accurate within 2%, and an age ∼ 1 Ma too young on a Oligocene-aged grain. Two initial applications of the small-volume technique — the detrital zircon provenance of fine-grained mudstones and shales and the creation of zircon U–Pb age maps to investigate the detrital and metamorphic history of a granulite-facies paragneiss — demonstrate the utility of this technique to a variety of geologic problems and confirm the viability of laser ablation-multicollector-inductively coupled plasma-mass spectrometry as a tool for high spatial resolution U–Pb geochronology.