Rb-Sr geochronology of Vendian shales,the Staraya Rechka Formation,Anabar Massif,northern Siberia

Fine-grained clayey subfractions (SF) with particle sizes of 1–2, 0.6–1.0, 0.3–0.6, 0.2–0.3, 0.1–0.2, and <0.1 μm were extracted from shales of the Vendian Staraya Rechka Formation in the Anabar Massif and studied by XRD and Rb-Sr methods. All the clayey subfractions are represented by illite with high crystallinity indices, which are characteristic of the low-temperature diagenesis/catagenesis zone and grow with the decrease of the particle size. The Rb-Sr systematics in clayey subfractions combined with mineralogical data provide grounds for the conclusion that illite from clayey rocks of the Staraya Rechka Formation was forming during two periods: approximately 560 and 391–413 Ma ago. The first illite generation was likely formed in the course of lithostatic subsidence of the Staraya Rechka sediments and the second one, during the Devonian lithogenesis stage. It is assumed that age of the first generation (∼560 Ma) is close to that of the Staraya Rechka Formation. This inference is consistent with biostratigraphic, chemostratigraphic, and geochronological data obtained for both rocks of the Anabar Massif and Vendian sediments from other regions of Siberia.     

Evaluation of levels of antibiotic resistance in groundwater-derived <Emphasis Type="Italic">E. coli</Emphasis> isolates in the Midwest of Ireland and elucidation of potential predictors of resistance

Antibiotic-resistant (pathogenic and non-pathogenic) organisms and genes are now acknowledged as significant emerging aquatic contaminants with potentially adverse human and ecological health impacts, and thus require monitoring. This study is the first to investigate levels of resistance among Irish groundwater (private wells) samples; Escherichia coli isolates were examined against a panel of commonly prescribed human and veterinary therapeutic antibiotics, followed by determination of the causative factors of resistance. Overall, 42 confirmed E. coli isolates were recovered from a groundwater-sampling cohort. Resistance to the human panel of antibiotics was moderate; nine (21.4%) E. coli isolates demonstrated resistance to one or more human antibiotics. Conversely, extremely high levels of resistance to veterinary antibiotics were found, with all isolates presenting resistance to one or more veterinary antibiotics. Particularly high levels of resistance (93%) were found with respect to the aminoglycoside class of antibiotics. Results of statistical analysis indicate a significant association between the presence of human (multiple) antibiotic resistance (p?=?0.002–0.011) and both septic tank density and the presence of vulnerable sub-populations (<5 years). For the veterinary antibiotics, results point to a significant relationship (p?=?<0.001) between livestock (cattle) density and the prevalence of multiple antibiotic resistant E. coli. Groundwater continues to be an important resource in Ireland, particularly in rural areas; thus, results of this preliminary study offer a valuable insight into the prevalence of antibiotic resistance in the hydrogeological environment and establish a need for further research with a larger geological diversity.     

Mantle and crustal processes in the magmatism of the Campania region: inferences from mineralogy, geochemistry, and Sr–Nd–O isotopes of young hybrid volcanics of the Ischia island (South Italy)

Ischia, one active volcano of the Phlegraean Volcanic District, prone to very high risk, is dominated by a caldera formed 55 ka BP, followed by resurgence of the collapsed area. Over the past 3 ka, the activity extruded evolved potassic magmas; only a few low-energy explosive events were fed by less evolved magmas. A geochemical and Sr–Nd–O isotope investigation has been performed on minerals and glass from products of three of such eruptions, Molara, Vateliero, and Cava Nocelle (<2.6 ka BP). Data document strong mineralogical, geochemical, and isotopic heterogeneities likely resulting from mingling/mixing processes among mafic and felsic magmas that already fed the Ischia volcanism in the past. Detailed study on the most mafic magma has permitted to investigate its origin. The mantle sector below Ischia underwent subduction processes that modified its pristine chemical, isotopic, and redox conditions by addition of ≤1 % of sediment fluids/melts. Similar processes occurred from Southeast to Northwest along the Apennine compressive margin, with addition of up to 2.5 % of sediment-derived material. This is shown by volcanics with poorly variable, typical δ¹⁸O mantle values, and ⁸⁷Sr/⁸⁶Sr progressively increasing toward typical continental crust values. Multiple partial melting of this modified mantle generated distinct primary magmas that occasionally assimilated continental crust, acquiring more ¹⁸O than ⁸⁷Sr. At Ischia, 7 % of Hercynian granodiorite assimilation produced isotopically distinct, K-basaltic to latitic magmas. A SW–NE regional tectonic structure gave these magmas coming from large depth the opportunity to mingle/mix with felsic magmas stagnating in shallower reservoirs, eventually triggering explosive eruptions.     

New data about tsunami evidence on Russia’s Pacific coast based on instrumental measurements for 2009–2010

Doklady Earth Sciences -     

Vertical distribution of organic compounds in the bottom sediments of two steppe lakes in Southern Siberia

New data on the distribution of organic compounds at different horizons (0–10, 30–40, and 70–80 cm) of bottom sediments of the fresh Fyrkal Lake (Republic of Khakaßsia) and the salt Lake Mormyshanskoe (Altai Territory) have been collected. The compositions of organic compounds in the sediments in the examined lakes has been found to differ considerably, though some parameters in their composition show changes in the same direction. The concentrations of triterpenoids of the groups of lupane, oleanane, and hopane in the sediments decrease with depth. An increase in the share of saturated compounds in the composition of steroids is accompanied by a decrease in the ratio of their isomers (5β/5α). Terrestrial vegetation dominates among organic matter sources, while, in Lake Fyrkal, the contributions of terrestrial plants and macrophytes are similar. The presence of thermally transformed steroids and triterpenoids throughout the vertical profile of sediments in Lake Mormyshanskoe may be an indication to a slight oil pollution of the water body.     

Slip Sequences in Laboratory Experiments Resulting from Inhomogeneous Shear as Analogs of Earthquakes Associated with a Fault Edge

Faults are intrinsically heterogeneous with common occurrences of jogs, edges and steps. We therefore explore experimentally and theoretically how fault edges may affect earthquake and slip dynamics. In the presented experiments and accompanying theoretical model, shear loads are applied to the edge of one of two flat blocks in frictional contact that form a fault analog. We show that slip occurs via a sequence of rapid rupture events that initiate from the loading edge and are arrested after propagating a finite distance. Each successive event extends the slip size, transfers the applied shear across the block, and causes progressively larger changes of the contact area along the contact surface. Resulting from this sequence of events, a hard asperity is dynamically formed near the loaded edge. The contact area beyond this asperity is largely reduced. These sequences of rapid events culminate in slow slip events that precede a major, unarrested slip event along the entire contact surface. We suggest that the 1998 M5.0 Sendai and 1995 off-Etorofu earthquake sequences may correspond to this scenario. Our work demonstrates, qualitatively, how the simplest deviation from uniform shear loading may significantly affect both earthquake nucleation processes and how fault complexity develops.     

Mineralogical-geochemical features of sulfide ores from the Broken Spur hydrothermal vent field

A representative collection of hydrothermal sediments was sampled practically from all the hydrothermal mounds of the Broken Spur hydrothermal vent field from the Mir manned submersibles during three cruises of R/V Akademik Mstislav Keldysh. Mineral associations characteristic of different morphological types of sulfide ores from hydrothermal pipes, plates, and diffusers are assessed. Particular attention is paid to the distribution of minor elements and their distribution patterns determined by the mineralogical zonation. The measured isotopic value of the sulfur in the sulfide minerals appeared to vary from 0.4 to 5.2‰, which indicates their similarity with the ores from the Snake Pit vent field and is related to the dilution of hot ore-bearing solutions by seawater and reduction of the water sulfate ions to H₂S with a heavy isotopic composition.