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Phreatic zone diagenesis

Unlike marine sediments, where early diagenesis typically occurs entirely within the phreatic (saturated) zone, early diagenetic alterations in terrestrial sediments occur in both vadose (unsaturated) and phreatic zones. Furthermore, in terrestrial... [Pg.27]

Carbonate cements are often among the dominant components of diagenesis and hence are of decisive importance in determining the reservoir quality of sandstone sequences. Despite this, the timing, the geochemical conditions of precipitation and dissolution, as well as the source and fate of these cements are not fully understood. In continental and near-shore sediments, cements commonly precipitate as calcretes and dolocretes in the vadose and phreatic zones, and attain a variety of mineral-ogical, textural and distribution patterns as well as elemental and isotopic compositions. These cements form lenses and layers of densely cemented... [Pg.53]

Because the bulk of the limestone volume of Bermuda has spent most of its existence in the vadose zone, much of the limestone mass shows the imprint of vadose diagenesis, and progressive depletion in 13C with increasing age. However, limestones older than 125,000 years have spent more time in the phreatic meteoric zone. These limestones are more extensively altered by freshwater and freshwater-seawater mixtures. Their relatively light 813C values, however, imply alteration in a relatively open system in which soil carbon dioxide, depleted in 13C because of oxidation of organic matter, was an important source of carbon for replacement reactions. [Pg.344]


See other pages where Phreatic zone diagenesis is mentioned: [Pg.316]    [Pg.337]    [Pg.352]    [Pg.353]    [Pg.361]    [Pg.433]    [Pg.28]    [Pg.317]    [Pg.321]    [Pg.346]    [Pg.355]    [Pg.357]    [Pg.363]   
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Diagenesis

Phreatic zone

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