Fluid transport by solitary waves along growing faults: A field example from the South Eugene Island Basin, Gulf of Mexico

The Red Fault system is one of the main growth faults found in the South Eugene Island Basin, a salt withdrawal minibasin located offshore Louisiana, in the Gulf of Mexico. This fault system corresponds to a lateral boundary between fluid overpressured compartments. In addition, there is a set of observations indicating that the Red Fault system exhibits rapid episodic migration of fluids. This fault represents an example of preferential pathway for the upward episodic migration of overpressured hydrocarbons from deep, heavily pressured, compartments on time scales of years. The migrations of fluids into active growing faults could take the form of propagating surges (solitary waves) that propagate upward along the fault planes in a wave-like manner at km/yr. Solitary waves represent a very efficient mechanism for the upward transport of fluids along growth faults in sedimentary basins generating its own permeability. In addition, this mechanism is compatible with the fact that the fault plane is observed to sustain a static pore fluid pressure difference between its two sides. The propagation of solitary waves in active growth faults appears as a fundamental mechanism to understand the nature of upward fast migration of fluids along active growth faults in compartimentalized sedimentary basins.     

Dynamics of a confined lava flow on Kilauea volcano,Hawaii

This paper presents a new method of analysing lava flow deposits which allows the velocity, discharge rate and rheological properties of channelled moving lavas to be calculated. The theory is applied to a lava flow which was erupted on Kilauea in July 1974. This flow came from a line of fissures on the edge of the caldera and was confined to a pre-existing gully within 50 m of leaving the vent. The lava drained onto the floor of the caldera when the activity stopped, but left wall and floor deposits which showed that the lava banked up as it flowed around each of the bends. Field surveys established the radius of curvature of each bend and the associated lava levels, and these data, together with related field and laboratory measurements, are used to study the rheology of the lava. The results show the flow to have been fast moving but still laminar, with a mean velocity of just over 8 m s^–1; the lava had a low or negligible yield strength and viscosities in the range 85–140 Pa s. An extension of the basic method is considered, and the possibility of supercritical flow discussed.     

Hydrogeochemical evolution of Ordovician limestone groundwater in Yanzhou,North China

Major‐ion compositions of groundwater are employed in this study of the water–rock interactions and hydrogeochemical evolution within a carbonate aquifer system. The groundwater samples were collected from boreholes or underground tunnels in the Ordovician limestone of Yanzhou Coalfield where catastrophic groundwater inflows can be hazardous to mining and impact use of the groundwater as a water supply. The concentration of total dissolved solid (TDS) ranged from 961 to 3555 mg/l and indicates moderately to highly mineralized water. The main water‐type of the middle Ordovician limestone groundwater is Ca‐Mg‐SO₄, with SO₄^2‐ ranging from 537 to 2297 mg/l, and average values of Ca²⁺ and Mg²⁺ of 455.7 and 116.6 mg/l, respectively. The water samples were supersaturated with respect to calcite and dolomite and undersaturated or saturated with respect to gypsum. Along the general flow direction, deduced from increases of TDS and Cl^‐, the main water–rock interactions that caused hydrogeochemical evolution of the groundwater within the aquifer were the dissolution of gypsum, the precipitation of calcite, the dissolution or precipitation of dolomite, and ion exchange. Ion exchange is the major cause for the lower mole concentration of Ca²⁺ than that of SO₄^2‐. The groundwater level of Ordovician aquifer is much higher than that of C‐P coal‐bearing aquifers, so the potential flow direction is upward, and the pyrite in coal is not a possible source of sulfate; additional data on the stable sulfur and oxygen isotopic composition of the sulfate may be helpful to identify its origin. Although ion exchange probably accounts for the higher mole concentration of Na⁺ than that of Cl^‐, the dissolution of aluminosilicate cannot be ruled out. The data evaluation methods and results of this study could be useful in other areas to understand flow paths in aquifers and to provide information needed to identify the origin of groundwater. Copyright © 2012 John Wiley & Sons, Ltd.     

Shoreline changes along the southeastern coast of Martha's Vineyard, Massachusetts for the past 200 years

Shoreline changes since 1776, including two 30-yr periods separated by nearly 100 yr are documented from surveys, topographic maps, harbor charts, and aerial photographs for the southeastern corner of the island of Martha's Vineyard, Massachusetts (41°25′ N, 70°35′ W). From 1776 to 1969, a barrier beach has receded by more than 880 m, and average rate of 4.6 m/yr. A series of four detailed surveys from 1840 to 1886 document consistent shoreline retreat in this area of 3.1 m/yr.For the period 1938–1969, planimetry from aerial photographs and field observation indicate that more than 28 ha and nearly 3 × 10⁶ m³ of foreland composed of till have washed away. A house, located 200 m from the cliff edge of the foreland in 1938 was only 56 m from the cliff edge in July 1972.Violent storms were associated with the opening of the bay behind the barrier beach in nearly the same location in 1856, 1886, 1938, and 1954. Easterly migration of the opening results in rapid erosion of the southeastern corner of the island (Wasque Point) and eventual closing of the opening.Field observation of the 1954 opening indicates that the mechanism of failure of the barrier beach is primarily by storm tide-induced subsidence. Subsequently, strong (up to 1.2 mps) easterly currents cause migration of the opening to the east and closure within 15 yr.A summary review of evidence for changes in sea level in the past is suggested in partial explanation for the consistent shoreline retreat described in this paper.     

Methodological frameworks for the geography of organizations

In this paper, we present three methodological frameworks for the geographic study of organizations. These are situated within three meta-theoretical perspectives in human geography: spatial science, critical realism, and post-structuralism. Each framework offers a different theorization of organizations, and each prompts different research questions that can be used to guide their geographic study. The research questions we offer are general, and are pertinent to all types of organizations. To supplement the methodological contributions of this paper, we suggest how each of these frameworks might inform empirical investigations of Appalshop, a media arts organization located in Whitesburg, Kentucky.     

Cordierite-Cummingtonite Facies Rocks from the Gold Brick District, Colorado

The unusual association of cordierite and cummingtonite (? gedrite+ chlorite + biotite + ilmenite + plagioclase + quartz) definesa metamorphic facies within aluminous, low-Ca amphibolites fromthe Proterozoic rocks of the Gold Brick District, east of Gunnison,Colorado. More Fe-rich bulk chemistries in the same facies arecharacterized by assemblages consisting of cordierite+-gedrite+ garnet + chlorite + biotite + ilmenite + plagioclase + quartz,whereas more Mg-rich compositions are characterized by cordierite+ anthophyllite + chlorite + biotite + ilmenite ? plagioclase+ quartz. The assemblage gedrite 4- cummingtonite + chlorite+ biotite + ilmenite + plagioclase + quartz was also observed.Coexisting cordierite+ anthophyllite + cummingtonite was notobserved in any rocks, apparently because this assemblage isstable over only a very narrow range of bulk compositions. Metamorphosedpelitic rocks are more iron rich than the assemblage cordierite+ gedrite + garnet + chlorite + biotite + ilmenite + plagioclase+ quartz and consist of garnet ?cordierite ?staurolite ? chlorite? andalusite + biotite + ilmenite + plagioclase + quartz? microclineor muscovite. Mineral rim compositions from cordierite-bearing amphibolitesand metapelites determined by electron microprobe analysis showsystematic Fe/Mg partitioning and define assemblages that occupynon-overlapping regions of the compositional system SiO₂-TiO₂-Al₂O₃-MnO-FeO-MgO-CaO-Na₂O-K₂O-H₂Oas determined by algebraic and statistical methods developedby Braun & Stout (1975) and Fisher (1989). Graphical methods(projections) produced spurious overlaps not confirmed by themore rigorous algebraic tests. The spurious overlaps were generatedbecause standard projective analysis was not able simultaneouslyto account for the important effects of the components Na₂O,CaO, and MnO on the AFM topologies. The results of algebraicand statistical analysis are consistent with an equilibriumorigin at constant values of temperature and pressure. The cordierite-cummingtonite facies encompasses the relativelylow-pressure and moderate-temperature conditions associatedwith the stability field of andalusite. Garnet-biotite geothermo-metry,and garnet, aluminosilicate, silica, plagioclase (GASP) geobarometrysuggest that temperatures and pressures were nearly constantacross the study area at 550( ? 70) ?C and 3 kb, respectively,near the peak of metamorphism. Other geothermometers and geobarometers,and independent pressure and temperature estimates, are compatiblewith garnet-biotite thermometry and GASP geo-barometry. Gradientsin fO₂ or H₂O are not required to explain the compatibilityof these assemblages at constant T and P. Cordierite + cummingtonite-bearingrocks can apparently be derived from anthophyllite +garnet-bearingrocks by increasing temperature or decreasing pressure.     

Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska

A high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35–50 μm quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil’s Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr—much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values.     

The distributions of, and relationship between, He and nitrate in eddies

We present and discuss the distribution of ³He and its relationship to nutrients in two eddies (cyclone C1 and anticyclone A4) with a view towards examining eddy-related mechanisms whereby nutrients are transported from the upper 200–300 m into the euphotic zone of the Sargasso Sea. The different behavior of these tracers in the euphotic zone results in changes in their distributions and relationships that may provide important clues as to the nature of physical and biological processes involved.The cyclonic eddy (C1) is characterized by substantial ³He excesses within the euphotic zone. The distribution of this excess ³He is strongly suggestive of both past and recent ongoing deep-water injection into the euphotic zone. Crude mass balance calculations suggest that an average of approximately 1.4±0.7 mol m⁻² of nitrate has been introduced into the euphotic zone of eddy C1, consistent with the integrated apparent oxygen utilization anomaly in the aphotic zone below. The ³He–NO₃ relationship within the eddy deviates substantially from the linear thermocline trend, suggestive of incomplete drawdown of nutrients and/or substantial mixing between euphotic and aphotic zone waters.Anticyclone (A4) displays a simpler ³He–NO₃ relationship, but is relatively impoverished in euphotic zone excess ³He. We suggest that because of the relatively strong upwelling and lateral divergence of water the residence time of upwelled ³He is relatively short within the euphotic zone of this eddy. An estimate of the recently upwelled nutrient inventory, based on the excess ³He observed in A4's lower euphotic zone, is stoichiometrically consistent with the oxygen maximum observed in the euphotic zone.     

Transport of stable isotopes: I: Development of a kinetic continuum theory for stable isotope transport

Equations are developed describing migration of stable isotopes via a fluid phase infiltrating porous media. The formalism of continuum fluid mechanics is used to deal with the problem of microscopic inhomogeneity. Provision is made explicitly for local equilibrium exchange of isotopes between minerals and fluids as well as for kinetic control of isotopic exchange. Changing characteristic parameters of transport systems such as porosity, permeability, and changes in modal proportions of minerals due to precipitation or dissolution are taken into account.The kinetic continuum theory (KCIT) is used to show how to deduce the dominant mechanism of mass transport in metasomatic rocks. Determination of the transport mechanism requires data on the spatial distribution of the reaction progress of exchange reactions between minerals and fluids involving at least two stable isotope systems such as ¹³C-¹²C and ¹⁸O-¹⁶O, for example. It is concluded that a combination of field and laboratory measurements of two or more stable isotope systems can be used to place constraints not only on the mechanism of transport but also on the magnitude of fluid fluxes, the identity of fluid sources, and the molecular species composition of fluids.Variables used C number of chemical components - D _i,j hydrodynamic dispersion tensor [m²/s] - D _i ^j diffusion coefficient matrix [m²/s] - D ^* apparent diffusion coefficient, includes sorption, dispersion, porosity and tortuosity [m²/s] - F number of degrees of freedom (variance) - f _i ^j mass or number of isotope j in fluid species i - g acceleration due to gravity [m/s²] - flow [m³/m² s] - j isotope species - j chemical element - k coefficient defined in Eq. 17 - K permeability of porous media [m²], [darcy] - L _ij phenomenological diffusion coefficient matrix [mol²/j m s] - m number of fluid species - n number of isotope exchange vectors - p number of phases - P pressure [Pa] - P ^* hydrological pressure potential [Pa] - R ^j ratio of concentration of rare to common isotope of element j - r number of restrictions imposed on system - s _i ^j mass or number of isotope j in one mole of mineral phase i - t time [s] - V volume [m³] - X _i number of moles of fluid species i in unit fluid volume - X _l number of moles of mineral l in unit volume - X _l ^j mole fraction of isotope j in one mole mineral l - X ^* mole fraction with respect to the whole system - z space coordinate [m] - z transformed space coordinate - z ^* location of an infiltration front [m] - _x–y ^j fractionation factor between two phases, x, y, for isotope j - porosity - fluid viscosity [Ns/m²] - fraction of porosity accessible to a specific mass transport mechanism - chemical potential [j/mole] - stoichiometric reaction coefficient - normalized reaction progress variable - mass, specific mass [gr/cm] - tortuosity - fluid velocity [m/s] - c common isotope - init initial - j isotope species - r rare isotope - tot sum of common and rare isotope - dif diffusive - disp dispersive - eq mineral composition in equilibrium with initial infiltration concentration of the fluid - f fluid - inf infiltrative - r rock, without fluid phase - samp sample - std standard - sys system - tot fluid and rock