Geologic formations, continental

There are four candidate geologic isolation environments the sea floor, ice sheets, deep continental geologic formations, and shallow continental geologic formations. In waste manage-... 

INTERNATIONAL ATOMIC ENERGY AGENCY, Concepts and Examples of Safety Analyses for Radioactive Waste Repositories in Continental Geological Formations, Safety Series No. 58, IAEA, Vienna (1983). 

Arsenic is ubiquitous in nature and is found in detectable concentrations in all environmental matrices. The occurrence of As in the continental crust of Earth is usually given as 1.5 to 2.0 mg/1. The distribution of arsenic in nature is extremely variable, showing little correlation with geological formation, climate, or soil. Numerous minerals, rocks, sediments and soils contain arsenic partly as constituent of sulfide minerals or complex sulfides of metal cations and partly as a constituent retained by soils and/or sediments in occluded or adsorbed forms. The latter is manifested primarily by the adsorption or occlusion of As on hydrous A1 and Fe oxides, but these are not necessarily the only source. Arsenic is also adsorbed on clay colloid, is bound to organic matter and may form slightly water soluble compounds with Al, Fe, Ca and Mg in the soil matrix. Some of the more common minerals in soils are arsenopyrite (FeAsS), Orpiment (AsgSg) etc. 

From the outset exploration activity has been focused on the crystalline and continental volcanosedimentary formations of the Alps, Sardinia and Calabria and the alkaline Quaternary volcanics of central Italy. Uranium occurrences have been found in all these geological settings (Fig. 1), numerous mineralized showings and the Novazza and Val Vedello deposits occurring in the volcanosedimentary formations of the post-Hercynian basins of the Alpine range. 

Conditions of rock weathering, sediment formation and therefore geochemical processes as a whole were different in the geological past (Veizer, 1973) oxygen and carbon dioxide partial pressures were different and there were more basic rocks available for weathering. The Precambrian sediments of the Canadian and Scottish shields are discussed by J. G. Holland and Lambert (1973) in relation to the composition of the continental crust. 

The chemistry of the present-day continental crust is the frame of reference anchoring any discussion of secular evolution of crustal composition, or the processes of its formation. In this chapter we build on the considerable efforts of a number of scientists to develop an integrated geological and geophysical model for the continental crust (see Chapter 3.01 for a detailed treatment of the methodologies employed to infer crustal compositions). 

Kramers, J. Tolstikhin, I. 1997. Two terrestrial lead isotope paradoxes, forward transport modelling, core formation and the history of the continental crust. Chemical Geology, 139, 75-110. 

Bryant, R.G., Sellwood, B.W., Millington, A.C. Drake, N.A. (1994) Marine-like potash evaporite formation on a continental playa case study from Chott el Djerid, southern Tunisia. Sedimentary Geology 90, 269-291. 

Despite the current popularity of the polyphenol theory, a completely satisfactory scheme for the occurrence of humic and fulvic acids in diverse geologic environments has yet to be established. In practice, all pathways may be operative, but not to the same extent in all environments or in the same order of importance. A lignin pathway may-predominate in wet sediments, such as peats and swamps. The drastic conditions existing in soils under a harsh continental climate (e.g., some Mollisols) may favor humus synthesis by sugar-amine condensation. The disappearance of amino acids from buried sediments has been attributed to the formation of brown nitrogenous polyelectrolytes by reaction with reducing sugars (Stevenson, 1974). 

Alternative views of early Archaean mantle evolution require that mantle depletion started as early as ca. 4.5 Ga (see compilation in Rollinson, 1993). These models imply significant mantle Sm-Nd fractionation in the very early Archaean and have major implications for the differentiation of the early Earth. One such study is that of Bennett et al. (1993) who measured very high eNd values (+3.5 to +4.5) in 3.81 Ga Amitsoq gneiss samples. Collerson et al. (1991) also calculated an isochron eNd value of +3.0 for 3.8 Ga-old peridotites from northern Labrador. The extreme deviation from CHUR early in Earth history (Fig. 3.27) was interpreted by Bennett et al. (1993) as evidence for an extreme and very early fractionation of the Earth s mantle relative to CHUR. Such an event implies the formation of extensive continental crust prior to 3.8 Ga, for which there is no independent geological evidence. This apparent paradox and the claim for very early extensive mantle differentiation led to a detailed reexamination of the Bennett... 

Bjornerud, M.G. and Austrheim, H., 2004. Inhibited eclogite formation the key to the rapid growth of strong and buoyant Archaean continental crust. Geology, 32, 765-8. 

Nikiel, a. M. Manor, J. S. 1999. Spatial variations in formation water salinities. South Pelto and South Timbalier areas, eastern Louisiana continental shelf Transactions of the Gulf Coast Association of Geological Societies, 49, 396-403. 

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