Meteoric Environment

There is an extensive literature that exists concerning carbonate diagenesis in the vadose and phreatic meteoric environmental settings (see e.g., Bathurst, 1975, 1980 James and Choquette, 1984 and Moore, 1989 for reviews). Much of this work has dealt with the stabilization of aragonite and magnesian calcite to calcite in the present meteoric diagenetic realm associated with Pleistocene limestones. As 

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Uranium is readily mobilized in the meteoric environment, principally as the highly soluble uranyl ion (U02 ) and its complexes, the most important of which are the stable carbonate complexes that form in typical groundwaters (pH > 5, pC02 = 10 bar) (Gascoyne 1992b Grenthe et al. 1992 see also Langmuir (1997) for review). Uranium is... 

Figure 7.15. Major settings and principal controls of meteoric diagenesis, and a schematic drawing of the meteoric environment. (After James and Choquette, 1984.)...

Figure 7.29. A scatter plot of 813C and 8180 values of Holocene and Pleistocene carbonate sediments. Open circle, unlithified bulk Holocene sediments + s, lithified bulk Holocene sediment closed circles, Pleistocene limestones altered by meteoric water. For Pleistocene limestones altered in the meteoric environment, temperate climate samples are represented by 8180 values more enriched than -5%o, whereas tropical climate samples have 8180 values more depleted than -5%o. The large depletion in 13C is because the sediment samples are primarily from vadose environments. (After Land, 1986.)...

Obviously there are major differences between the 13c content of Jamaican chalks altered in the vadose meteoric environment and that of Shatsky Rise limestones. However, as Land (1979b) pointed out, if chemical stabilization of the Jamaican chalks had occurred in the phreatic meteoric environment with little influence from soil CO2, Sr and 180 depletions would be observed with little change in 8l3C. The limestones formed would be more homogeneous and virtually indistinguishable geochemically from Shatsky Rise sediments. 

There is a need to investigate more examples of the stabilization of calcitic carbonates in the meteoric environment. 

Criteria for differentiating limestones that have undergone diagenesis in the meteoric environment from those that have been altered in the deep subsurface should be developed and extended. 

This review is organized as follows in Sec. 2, the large scale phenomenological physics of meteors is discussed, detailing observations as well as the respective current interpretations. Meteorites will not be discussed in this review. Studies of the chemical and physical processes associated with meteorites have been largely concerned with composition, phase transformations and entrapment of noble gases in the solid meteorites. The reader is referred to several reviews and textbooks on the subject.The elementary gas-phase molecular dynamics relevant to the meteor environment is discussed in Sec. 3, and will primarily focus on the hyperthermal nonequilibrium processes, in concert with the subject matter of this book. 

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