Earth Sciences

ABSTRACT The sealing efficiency of shale layers is studied through the hydraulic parameters which are required for sustaining overpressure during geologically significant periods. Assuming a 1D sedimentary complex composed of a sealing layer overlying a permeable one, we give approximate solutions for the dissipation of a given initial overpressure. The time constant for relaxation involves the thickness, hydraulic conductivity and specific storage of the seal and also those of the permeable layer. The values of the various hydraulic parameters are discussed. It is argued first that the specific storage corresponding to plastic deformation during burial compaction is larger than the one which would correspond to elastic deformation. When taking into account (i) plausible values for specific storage of the upper shale layer and (ii) the storage effect of the lower permeable layer, it is found that a shale layer of several tens of m with an hydraulic conductivity of the order of 10-15 ms-1 maintains overpressure for 1 Myr. For such hydraulic parameter values, in the absence of on-going pressuring forces, initial overpressures would decay with a time constant (corresponding to a decrease by a factor e ∼, 2.7) of 1 Myr. This is interpreted as supporting a dynamic origin for observed abnormal pressures.

ABSTRACT Mareschal's (1976) work is extended to the case of a heterogeneous superficial layer represented by a rectangular island surrounded by a 1-km deep ocean in order to investigate the problem of time lags expected in magnetic variations recorded over a laterally heterogeneous region. A Y-component perpendicular to the source field polarization is found, in contrast to the results of Mareschal. Using simple model sources to test the responses of various model earths to complex sources, lateral heterogeneities in the upper layer are not found to render the representation of the induced field by that of a perfect conductor more invalid than it is in the case of a normally layered earth.

ABSTRACT Natural hydrofracturing caused by overpressure plays an important role in geopressure evolution and hydrocarbon migration in petroliferous basins. Its mechanism is quite well understood in the case of artificial hydraulic fracturing triggered by high-pressure fluid injection in a well. This is not so for natural hydraulic fracturing which is assumed to initiate as micro-cracks with large influence on the permeability of the medium. The mechanism of natural hydraulic cracking, triggered by increasing pore pressure during geological periods, is studied using a fracturing model coupled to the physical processes occurring during basin evolution. In this model, the hydraulic cracking threshold is assumed to lie between the classical failure limit and the beginning of dilatancy. Fluid pressure evolution is calculated iteratively in order to allow dynamic adjustment of permeability so that the fracturing limit is always preserved. The increase of permeability is interpreted on the basis of equivalent fractures. It is found that fracturing is very efficient to keep a stress level at the rock’s hydraulic cracking limit: a fracture permeability one order of magnitude larger than the intrinsic permeability of the rock would be enough. Observations reported from actual basins and model results strongly suggest that natural hydraulic cracking occurs continuously to keep the pressure at the fracturing limit under relaxed stress conditions.

ABSTRACT In the Earth's crust the temperature is largely controlled by heat conduction. However, under some circumstances, the thermal state is disturbed by advection of heat associated with groundwater flow. The corresponding thermal disturbance depends on the water flow velocity (modulus and direction) and therefore thermal data may be used to constrain the pattern of natural fluid flow. In this paper, some models of thermal disturbance induced by convective heat transfer are presented. They are based on the assumption that the water flow is concentrated in thin permeable structures such as aquifer or fault zones. The steady-state and transient thermal effects associated with such scenarios are computed using a somewhat idealized model which depends on a small number of parameters: flow rate, time, aquifer geometry and thermal parameters of surrounding rocks. In order to extract the conductive and convective components of heat transfer from temperature data and to estimate the corresponding fluid flow rate, it is first necessary to estimate the thermal conductivity field. The problem of the estimation of thermal conductivity in clay-rich rocks, based on laboratory and in-situ measurements, is emphasized. Then a method is proposed for the inversion of temperature data in terms of fluid flow. Vertical and lateral variations of thermal conductivity are taken into account and the fluid flow is assumed to be concentrated on a specified surface (2-D quasi-horizontal pattern). Thermal effects of the flow are simulated by a distribution of surface heat production which can be calculated and then inverted in terms of horizontal fluid flow pattern.

Although anaerobic lagoons are used globally for livestock waste treatment, their detailed microbial cycling ofN is only beginning to become understood. Within this cycling, nitrification can be performed by organisms that produce the enzyme ammonia monooxygenase. For denitrification, the reduction of nitrite to nitric oxide can be catalyzed by two forms of nitrite reductases, and N,O can be reduced by nitrous oxide reductase encoded by the gene nosZ The objectives of this investigation were to (i) quantify the abundance of the amoA, nirK, nirS, and nosZ genes; (ii) evaluate the influence of environmental conditions on their abundances; and (iii) evaluate their abundance relative to denitrification enzyme activity (DEA). Samples were analyzed via real-time quantitative polymerase chain reaction and collected from eight typical, commercial anaerobic, swine wastewater lagoons located in the Carolinas. The four genes assayed in this study were present in all eight lagoons. Their abundances relative to total bacterial populations were 0.04% (amoA), 1.33% (nirS), 5.29% (nirK), and 0.27% (nosZ). When compared with lagoon chemical characteristics, amoA and nirK correlated with several measured variables. Neither nirS nor nosZ correlated with any measured environmental variables. Although no gene measured in this study correlated with actual or potential DEA, nosZ copy numbers did correlate with the disparity between actual and potential DEA. Phylogenetic analysis ofnosZdid not reveal any correlations to DEA rates. As with other investigations, analyses of these genes provide useful insight while revealing the underlying greater complexity of N cycling within swine waste lagoons.

ABSTRACT Ostracoda from a 25 m thick exposure in sediments of the upper Karewa formation indicate lacustrine conditions in the Kashmir intermontane basin during the Middle to Late Pleistocene. The Middle to Late Pleistocene age is established on the basis of lithostratigraphy and confirmed by two thermoluminescence age determinations at the top of the section. The ostracod assemblages show that the lake water remained fresh or, at most, was very slightly saline, throughout the period represented by the section. Nearly all ostracod taxa identified from the sediments are cold stenothermal forms and they include inhabitants of the littoral and profundal domain as well as running waters and springs. The Ostracoda present within the section indicate that during deposition of the upper Karewa sediments a large, but fairly shallow, well-oxygenated open-basin freshwater lake existed in that central part of the Kashmir Basin. Although the sequences suggest changes in water depth may have occurred, lacustrine conditions were otherwise largely unchanged over the period represented by the section, up until the demise of the lake during the early part of the Late Pleistocene.

We have employed a light-absorbing electrically conductive polymer as a matrix to determine the molecular mass of small organic molecules using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. This method, which is in contrast to the usual MALDI strategy for matrix selection in which a small molecule matrix is used with a high molecular mass analyte, addresses the problem of matrix interference which limits the usefulness of MALDI-TOF for small molecule analysis. Use of negative ion mode offers advantages for this application. Using this approach, we have obtained clean molecular ion mass spectra of small organic molecules in the mass range 100-300 Da.

The characteristic isotopic abundance patterns of transition metals are useful in identifying species seen in mass spectra of compounds containing these metals. Examples of such analysis for ruthenium and osmium complexes, of special interest because of their potential for optoelectronic ...

Soltzberg, LJ, Hendrickson, E., McLaughlin, A., Newsky, S., Saikin, C. and Trieu, M.(2009), Metal contamination in matrix-assisted laser desorption/ionization samples prepared with the 'vortex'solvent-free method. Rapid Communications in Mass Spectrometry, 23: 462– ...

Abstract Arctic charr and European whitefish are common species in northern Europe, but have a parapatric distribution pattern and rarely coexist in substantial densities within the same lake. Whitefish is considered to be the strongest competitor, usually causing ...