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41.
Knowing little about how porosity and permeability are distributed at depth, we commonly develop models of groundwater by treating the subsurface as a homogeneous black box even though porosity and permeability vary with depth. One reason for this depth variation is that infiltrating meteoric water reacts with minerals to affect porosity in localized zones called reaction fronts. We are beginning to learn to map and model these fronts beneath headwater catchments and show how they are distributed. The subsurface landscapes defined by these fronts lie subparallel to the soil-air interface but with lower relief. They can be situated above, below, or at the water table. These subsurface landscapes of reaction are important because porosity developed from weathering can control subsurface water storage. In addition, porosity often changes at the weathering fronts, and when this affects permeability significantly, the front can act like a valve that re-orients water flowing through the subsurface. We explore controls on the positions of reaction fronts under headwater landscapes by accounting for the timescales of erosion, chemical equilibration, and solute transport. One strong control on the landscape of subsurface reaction is the land surface geometry, which is in turn a function of the erosion rate. In addition, the reaction fronts, like the water table, are strongly affected by the lithology and water infiltration rate. We hypothesize that relationships among the land surface, reaction fronts, and the water table are controlled by feedbacks that can push landscapes towards an ‘ideal hill’. In this steady state, reaction-front valves partition water volumes into shallow and deep flowpaths. These flows dissolve low- and high-solubility minerals, respectively, allowing their reaction fronts to advance at the erosion rate. This conceptualization could inform better models of subsurface porosity and permeability, replacing the black box. 相似文献
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B.L. Nikitenko B.N. Shurygin V.G. Knyazev S.V. Meledina O.S. Dzyuba N.K. Lebedeva E.B. Peshchevitskaya L.A. Glinskikh A.A. Goryacheva S.N. Khafaeva 《Russian Geology and Geophysics》2013,54(8):808-837
Recent integrated studies of Mesozoic reference sections of the Anabar area (northern Middle Siberia, Laptev Sea coast) and the reinterpretation of all the previous data on a modern stratigraphic basis permit considerable improvement of the bio- and lithostratigraphic division and facies zoning of Jurassic and Cretaceous sediments in the region. Analysis of abundant paleontological data allows the development or considerable improvement of zonal scales for ammonites, belemnites, bivalves, foraminifers, ostracods, dinocysts, and terrestrial palynomorphs from several Jurassic and Cretaceous intervals. All the zonal scales have been calibrated against one another and against regional ammonite scale. Reference levels of different scales useful for interregional correlation have been defined and substantiated based on the analysis of lateral distribution of fossils in different regions of the Northern Hemisphere. It provides the possibilities to propose and consider parallel zonal scales within the Boreal zonal standard for the Jurassic and Cretaceous periods. A combination of these scales forms an integrated biostratigraphic basis for a detailed division of Boreal-type sediments regardless of the place of their formation and for the comparison with the international stratigraphic standard as far as a possible use of a set of reference levels for correlation. 相似文献
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L. Ya. Aranovich N. S. Bortnikov S. A. Bushmin O. V. Vikent’eva E. O. Dubinina V. M. Kozlovskii Yu. M. Lebedeva 《Petrology》2009,17(4):389-409
This paper considers petrogenetic processes related to the influence of fluid flows on rocks in regional deformation zones at different depth levels within the Earth’s crust. It was shown that silica mobility could be important for eclogites developing after (meta)gabbroids: in the absence of quartz, the main eclogitic minerals, garnet and omphacite, are stabilized to significantly lower pressures compared with the quartz-saturated system. Based on petrological data and the analysis of oxygen isotope distribution in coexisting minerals from the hypersthene-sillimanite Mg-Al-Si granulites of Palenyi Island (Por’ya Guba of the Lapland granulite belt), it was concluded that these rocks were formed at high temperature and pressure (approximately 900°C and 10 kbar) under the influence of an external fluid. The influence of the fluid flow had to be rather short and spatially nonuniform. 相似文献
47.
S. V. Lebedeva I. V. Zemlyanov A. A. Lomonosov 《Russian Meteorology and Hydrology》2018,43(10):655-663
The results of studying the hydrological regime ofthe Volga-Akhtuba floodplain based on the joint analysis of observation and hydrodynamic modeling data are presented. The calculated hydrological characteristics are compared with observational data. The areas and boundaries of zones flooded by the water flow from the Akhtuba and Volga rivers are estimated. The efficiency of water engineering activities aimed at the improvement of flooding conditions is analyzed for the most problematic part of the Volga-Akhtuba floodplain. 相似文献
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The paper discusses a method for the statistical evaluation of the vertical current velocity componentV
z(z) using data provided by profilers. The calculation of theV
z(z) profiles involves the determination of the root-mean-square deviation of the error of determination of the vetical current
velocity component at each level and the RMS deviation of the sample statistical variability of this quantity's estimates.
ProfilesV
z(z) have been computed for the north-western Black Sea using three surveys, with the involvement of an OLT profiler. The computations
have shownV
z(z) to have a two-layer structure, with zero being crossed in the main pycnocline. Such structure of the current velocity
vertical component is consistent with the hydrodynamic model of the field of currents induced by buoyancy fluxes through the
lateral boundaries of the basin. The availability of the zero values of the vertical current velocity in the pycnocline yields
a tool for gaining insight into the mechanism controlling the emergence of the oxic/anoxic interface and areas with sharp
vertical gradients of chemical and hydro-optical characteristics.
Translated by Vladimir A. Puchkin. 相似文献
50.
Nosova A. A. Lebedeva N. M. Sazonova L. V. Voznyak A. A. 《Doklady Earth Sciences》2022,505(2):517-523
Doklady Earth Sciences - Evidence for liquid immiscibility between Fe-rich and Si-rich silicate melts in ferrobasalt of the Ladoga Graben in the Baltic Shield belonging to the Mesoproterozoic... 相似文献