Surficial environments

Lead and Zinc in the Surficial Environment, Third International Geochemical Exploration Symposium, Toronto, Canada, 1970. 

Lead Isotopes as Monitors of Anthropogenic and Natural Sources Affecting the Surficial Environment... 

In order to solve the problem of missing calcium oxalate accumulation, the first question to ask is whether or not the mineral is stable, i.e. is calcium oxalate able to spontaneously oxidize when in contact with the atmosphere If this is the case, the explanation is simple all the oxalate produced is rapidly oxidized as CO2, and therefore can be neither accumulated in the surficial environment nor in the fossil record. This assumes that the transformation of oxalate into CO2 must be complete and rapid in normal conditions, i.e. at 25 °C (298.15 K) and a pressure of 1 atm. This complete oxalate oxidation in solution is given by the following reaction ... 

Figure 6. Geochemical analysis of Fe and Mn extractions from the four main cave sediment layers as compared to different surficial environments. A. Fe results for die cave sequence. B. Fe results for the surficial environments. C. Mn results for the cave sequence. D. Mn results for die surficial environments.

The scavenging effects of clays, organic debris and hydrous oxides outweigh the dissolution of Ra by chloride in the surficial environment. As a result there is a net deficit of Ra in stream waters entering the oceans, even though the water in the oceans contains an excess of Ra (Cochran, 1979). 

Disequilibrium in the U decay series has been studied for many years and is observed in almost all surficial environments. Rosholt (1959) measured U, Pa,... 

We may conclude from the above that U is the most mobile element in the U decay series in the surficial environment. Its removal from one site and deposition in another leads to radioactive disequilibrium over time spans of several half-lives of the respective daughter products. Concomitantly, decay and growth of daughter products, depending on the abundance of the parent, tend to re-establish equilibrium, given sufficient time. 

Dyck, W., 1974. Geochemical studies in the surficial environment of the Beaverlodge area, Saskatchewan. Geol. Survey Canada, Paper 74-32, 30 pp. 

Dyck, W., 1978. The mobility and concentration of uranium and its decay products in temperate surficial environments. In Short Course in Uranium Deposits, Min. Assoc. Canada, pp. 57-100. 

Levinson, A.A. and Coetzee, G.L., 1978. Implications of disequilibrium in exploration for uranium ores in the surficial environment using radiometric techniques - a review. Min. Sci. Eng., 10 19-27. 

In addition to carbonate precipitation, the introduction ofC02-fixing organisms into the surficial environment must have a paramount impact on the terrestrial carbon cycle... 

Despite the complexities and variations in surficial environments of precipitation, vadose zone cements in arid environments have a number of distinctive characteristics. 

Each individual flux in the two preceding equations is a function of combinations of environmental factors. These factors, and the coupling between the chemical and macroscopic transport processes in the surficial environment, will be discussed in the subsequent sections of this chapter. The discussion will focus on the coupling between the chemical, hydrological, and physical processes and will deal with the global average fluxes of water, solid and dissolved materials that are products of the three interaeting classes of forces and processes... 

It is, however, simpler to consider for the totality of chemical kinetic and transport processes that operate on different physical and time scales in the surficial environment three main classes of driving forces—physical, hydro-logical, and chemical—and responses to these forces in various physical, hydrological, and biogeochemical processes. This is illustrated schematically in Table 1, which gives a matrix of 3 x 3 couplings between physical, hydrological, and chemical forces and their environmental effects as far as these concern transport. 

A relatively modest portion of Figures 1 and 2 represents the range of conditions to which soils and surficial sediments are exposed. As will be noted later, the Eh values of soils and sediments range from +800 to —250 mv., but +600 to 0 mv. is the more general range. A pH range of 4 to 10 brackets all but the most extreme surficial environments. This area is hash marked in Figures 1 and 2. 

Molybdenum (Mo) is an essential element for many plants and animals (Newton and Otsuka, 1980). Because of its chemical properties. Mo readily provides sites for reactions and catalysis in biochemical systems (Haight and Boston, 1973). It is therefore important to understand the processes that control the distribution, speciation, and behavior of Mo in the surficial environment. These processes will affect the bioavailability of Mo and ultimately its passage into the food chain. 

Concentrations of Mo in water and soil solutions are generally lower under acid conditions than under near-neutral or alkaline conditions (Moore and Patrick, 1991). This behavior of Mo in the surficial environment is related mainly to its tendency to form dissolved anionic species. The availability of Mo to plants is largely dependent on soil pH, in that the availability of Mo in soils is greatest under alkaline conditions and least under acidic conditions. 

The ionic radius of U is very similar to that of tetravalent Th, and to those of many rare-earth ions (Table 2). This fact determines the occurrence of both Th and U in many rare earth bearing minerals. In the surficial environment, however, U is readily oxidized to U, which forms UOi , uranyl ion. ... 

Yapp, C. (2001). Rusty relics of Earth history iron (111) oxides, isotopes and surficial environments, Anna. Rev. Earth Planet. Sci. 29, 165-199. 

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