Microcrack networks in granite affected by a fault zone: Visualization by confocal laser scanning microscopy

Microcracks in the Cretaceous Ryoke-type granite in Japan were investigated by using deep drilling core samples collected in the Mizunami Underground Research Project of the Japan Nuclear Cycle Development Institute (JNC). The granite body suffered brittle deformation associated with Tertiary thrust movement. Based on core-scale and microscopic deformation features, the drill core from a depth of 300 to 700 m is divided into four domains, i.e. (A) undeformed granite, (B) granite intruded by cataclastic seams, (C) fractured granite in the fault damage zone, and (D) foliated cataclasite at the fault center. To characterize microcrack geometries in each domain, we employed the impregnation method using a low-viscous acrylic resin doped with fluorescent agents and captured the microcrack images by confocal laser scanning microscopy (CLSM). The CLSM image in the fault damage zone revealed anisotropic development of microcrack networks related to the fault movement. Both CLSM observation and porosity measurements reveal a drastic increase of micro-pores in the foliated cataclasite, possibly caused by fragmentation, and granulation and crack sealing in the fault zone.     

Deuterium in interstellar clouds

Increasing numbers of observations of deuterium ratios have revealed that all is not as it seemed in interstellar space. Tom Millar describes how fractionation theory has confirmed the importance of interstellar grains in cosmic chemistry.     

Determining rainy season onset and retreat over Nigeria from precipitation amount and number of rainy days

Summary This study assesses the relative efficiency of the use of rainfall amount and rainy days in the determination of rainfall onset and retreat dates in Nigeria based on rainfall data for the period 1961 to 2000. Daily rainfall data were sourced from the archives of the Nigerian Meteorological Services, Oshodi Lagos. The specific locations for which data were collected are: Ibadan, Ilorin, Kaduna and Kano. The method of percentage cumulative mean rainfall values was employed in the determination of the rainfall onset and retreat dates. The results obtained show that both rainfall amount and rainy days are equally effective in the determination of the mean rainfall onset and retreat dates in Nigeria. With regards to the rainfall onset and retreat dates of the individual years however, the method based on the rainy days is more effective than that based on rainfall amount, as the former yielded more realistic dates than the latter. It is thus recommended that studies investigating rainfall onset and retreat dates within a series of individual years in Nigeria, should be based on rainy days rather than rainfall amount.     

Population abundance and seasonal migration patterns indicated by commercial catch-per-unit-effort of hakes (Merluccius capensis and M. paradoxus) in the northern Benguela Current Large Marine Ecosystem

We developed generalised additive models (GAMs) to estimate standardised time-series of population abundance indices for assessment purposes and to infer ecological and behavioural information on northern Benguela hakes, Merluccius capensis and M. paradoxus, using haul-by-haul commercial trawl catch-rate data as proxies for hake densities. The modelling indicated that individual ship identifiers should be used rather than general vessel characteristics, such as vessel size. The final models explained 79% and 68% of the variability in the commercial catch rates of M. capensis and M. paradoxus, respectively. The spatial density patterns were consistent and confirmed existing knowledge about these species in the northern Benguela system. Furthermore, seasonal migration patterns were described for the first time and were found to correspond to the known spawning areas and seasons for M. capensis and M. paradoxus. Spatial density patterns were validated using the geostatistical modelling results of fisheries-independent trawl survey data. Improved understanding of the relationships between fleet dynamics and fish movement can be achieved by taking into consideration the present catch-rate model and spatial and seasonal distribution maps. We conclude that the yearly standardised CPUE time-series are problematic as proxies for total stock abundance because of spatial coverage issues. Consequently, such CPUE data should not be used for stock-size assessments and fisheries advice concerning northern Benguela hakes until this is solved. We generally recommend the exclusion of standardised CPUE time-series from stock assessments when important and changing parts of the stock distribution cannot be targeted by the fishery, such as due to closed areas or seasons.     

A refined model of the influence of orography on the mesoscale distribution of extreme precipitation

Abstract

This paper briefly summarizes the results of a four-year research project carried out for the Federal Ministry of Agriculture and Forestry in Vienna, Austria. The main objective was the development of a deterministic model for the estimation of the distribution of extreme precipitation in complex terrain. The orographic component of precipitation is conceptually divided into a part directly generated by dynamic uplift and a part originating from convective activity. The model for the first type of precipitation enhancement is based on the theory of linear two-dimensional air flow over mountains. A dynamically consistent flow field and explicit simulation of the seeder-feeder mechanism are the main improvements compared to an earlier version of this model (Haiden et al., 1990). The assessment of convective precipitation is based on a new parameterization using results of an analytical model of thermally induced upslope flow. A comparison of model results with observations shows reasonable agreement regarding the structure of the precipitation fields.     

Paleo-redox boundaries in fractured granite

At the Earth’s surface, Fe(II) often oxidises and forms insoluble Fe(III)-(oxyhydr)oxides, whose particle size and structure depend on solution composition and temperature during formation and afterwards. Bacterial processes and exposure to reducing environments reduces them again, releasing dissolved iron to the groundwater. During such cycling, the Fe isotopes fractionate to an extent that is expected to depend on temperature. In this study, we report on the use of Fe-oxides as paleo-redox indicators, using their structure, morphology and Fe-composition as a clue for formation conditions. In samples taken from ∼120 m drill cores in granite from SE Sweden, X-ray amorphous, superparamagnetic, nanometre-sized Fe-oxides are confined to fractures of the upper ∼50 m, whereas well-crystalline Fe-oxides, with particle sizes typical for soils, occur down to ∼110 m. We also identified hematite with a particle size of 100 nm, similar to hematite of hydrothermal origin. The Fe isotope composition of the fine-grained Fe-oxides (−1‰ < δ⁵⁶Fe < 1‰, IRMM-14 referenced) scatter significantly compared to the distribution previously observed for hydrothermal material (−0.26‰ < δ⁵⁶Fe < 0.12‰) and they are dominantly heavier than Fe-bearing silicates from fractures (−0.56‰ < δ⁵⁶Fe < −0.35‰). This is consistent with formation by low-temperature weathering, where Fe-silicates dissolve, Fe(II) oxidises and Fe(III)-oxides precipitate. The X-ray amorphous, nanometre-sized nature of near-surface Fe-oxides suggests recent formation. The deeper situated, well-crystalline Fe-oxides are more mature and we interpret that they record earlier oxidising events. They exist in fractures that are not significantly altered, indicating formation during periods of oxidation. Our results show that oxygenated water may reach depths of ∼110 m in fractured granite. The absence of natural, low-temperature Fe-oxides from deeper drill cores suggests that oxygenated waters do not readily penetrate beyond about 100 m and suggests that radioactive waste repositories located at a depth of ∼500 m should be well-protected from oxygenated waters.     

Pressure-temperature cartography of Fe-S-Si immiscible system

Multi-anvil press experiments were performed using a single cell assembly containing six different compositions. This set-up allows a careful sampling of the miscibility gap for given P-T conditions. Shrinking of the miscibility gap in the Fe-S-Si system has been studied from 4 to 12 GPa up to 2200 K, demonstrating a stable immiscible zone up to 4 GPa and 2200 K and its closure at higher pressures. Presence of both S and Si in the Earth’s core is suggested by chondritic models. Therefore, its composition is inherited from processes at pressures higher than 4 GPa. This evolution of the Fe-S-Si miscibility gap is linked with the change in the local short-range order in Fe and Fe-S liquids. Our results indicate that core formation under reducing conditions would be affected by immiscibility for planetesimals up to size of the Moon. Furthermore, due to the difference in wetting properties between the two immiscible liquid phases, the S-rich metal phase would control the chemical exchange between liquid metals and silicates during early differentiation in planetesimals.     

Pure compound and sediment elutriate embryo larval assay of winter flounder from the Hudson/Raritan Estuary and Long Island Sound

Winter flounder (Pseudopleuronectes americanus), a demersal egg layer, is at risk from dioxins and metals in the sediments of the Hudson/Raritan Estuary (the Estuary). The effects of tetrachlorodibenzo-p-dioxin (TCDD), mercuric chloride and sediment elutriates on the embryos of winter flounder from four sites in the Estuary, and a reference site: Long Island Sound (LI) were examined. Embryos were exposed from 2 days after fertilization until 2 days post hatch. TCDD absorption by embryos/larvae ranged from 13 to 44%, with an average 23.4%. One experiment, with the LI population showed a LD₅₀ of 1.8 pg/larva (2.6 ng/g) and LD₁₀ of 0.9 pg/larva (1.4 ng/g). Major observed lesions included pericardial edema (PE), and spinal lesions (SL). Background lesion occurrence in controls was 0.31 lesions/individual, and 0.27 major lesions/individual. NOELs were observed for PE 0.3–0.5 pg/larva, and SL 1.4–9.0 pg/larva. PE and SL are good indicators of low and high dose effects of TCDD in winter flounder, respectively. With mercuric chloride all populations showed 50% mortality at 100 μg/l, and 50% lesions at 25–50 μg/l. Three of seven sediment elutriates collected from the Estuary were acutely toxic. Site-specific variability in sediment toxicity and breeding stock sensitivity to known contaminants was observed. Future studies should incorporate metamorphosis from larva to juvenile. (USEPA:CR825437, NIEHS:ES07148).     

Paleogeographic regionalization of Triassic seas based on conodontophorids

Geographic differentiation of conodontophorids between northern and southern latitudes commenced in the Triassic since the early Induan. Cosmopolitan long-lived genera of predominantly smooth morphotypes without sculpturing were characteristic of high-latitude basins of the Panboreal Superrealm. Since the early Olenekian until the Carnian inclusive, this superrealm consisted of the Siberian Realm that extended over Northeast Asia and the Canada-Svalbard Realm that included the Svalbard Archipelago and northern regions of Canada. Throughout the Triassic period, conodontophorids characteristic of the Tethys-Panthalassa Superrealm spanning the Tethys and low-latitude zones of the Pacific were highly endemic, very diverse in taxonomic aspect, having well-developed sculpturing and tempos of morphological transformations. Distinctions between the Early-Middle Triassic conodontophorids from northern and southern zones were not as great as afterward, and their impoverished assemblages from southern Tethyan basins were close in some respects to the Boreal ones. Their habitat basins of that time can be grouped into the Mediterranean-Pacific and India-Pakistan realms. Hence, the extent of geographic differentiation of conodontophorids was not constant and gradually grew, as their taxonomic diversity was reducing in northern basins but relatively increasing in southern ones. The Panboreal e Tethys-Panthalassa superrealms of conodontophorids, which are most clearly recognizable, are close to first-rank paleobiochores (superrealms) established earlier for ammonoids and bivalve mollusks. Main factor that controlled geographic differentiation of Triassic conodontophorids was climatic zoning. Initially lower diversity of southern Tethyan assemblages points probably to relatively cooler water regime in the peri-Gondwanan part of the Tethys. The established patterns in geographic distribution of conodontophorids characterize most likely the real trend of their differentiation and evolution, i.e., the distribution area contraction prior to complete extinction at the end of the Triassic     

Iron(III) accumulations in inland saline waterways,Hunter Valley,Australia: Mineralogy,micromorphology and pore-water geochemistry

Discharge of Fe(II)-rich groundwaters into surface-waters results in the accumulation of Fe(III)-minerals in salinized sand-bed waterways of the Hunter Valley, Australia. The objective of this study was to characterise the mineralogy, micromorphology and pore-water geochemistry of these Fe(III) accumulations. Pore-waters had a circumneutral pH (6.2–7.2), were sub-oxic to oxic (Eh 59–453 mV), and had dissolved Fe(II) concentrations up to 81.6 mg L⁻¹. X-ray diffraction (XRD) on natural and acid-ammonium-oxalate (AAO) extracted samples indicated a dominance of 2-line ferrihydrite in most samples, with lesser amounts of goethite, lepidocrocite, quartz, and alumino-silicate clays. The majority of Fe in the samples was bound in the AAO extractable fraction (Fe^Ox) relative to the Na-dithionite extractable fraction (Fe^Di), with generally high Fe^Ox:Fe^Di ratios (0.52–0.92). The presence of nano-crystalline 2-line ferrihydrite (Fe₅HO₃·4H₂O) with lesser amounts of goethite (α-FeOOH) was confirmed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX), and transmission electron microscopy (TEM) coupled with selected area electron diffraction (SAED). In addition, it was found that lepidocrocite (γ-FeOOH), which occurred as nanoparticles as little as ∼5 lattice spacings thick perpendicular to the (0 2 0) lattice plane, was also present in the studied Fe(III) deposits. Overall, the results highlight the complex variability in the crystallinity and particle-size of Fe(III)-minerals which form via oxidation of Fe(II)-rich groundwaters in sand-bed streams. This variability may be attributed to: (1) divergent precipitation conditions influencing the Fe(II) oxidation rate and the associated supply and hydrolysis of the Fe(III) ion, (2) the effect of interfering compounds, and (3) the influence of bacteria, especially Leptothrix ochracea.