Dolocrete phreatic

Sources of Ca and Mg for calcrete and dolocrete are uncertain, but are often believed to be windblown dust. Calcium and Mg may also be derived from pyroclastic material (Bestland Retallack, 1993) and oceanic aerosols (Quade et al., 1995). These sources are also relevant to phreatic carbonates. In some cases the groundwater may bring ions... 

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... 

In this paper the terms dolocrete and calcrete are used to indicate sediments extensively cemented by displacive dolomite and calcite under conditions ranging from the soil horizon to shallow phreatic. Conversely, we use the expression carbonate cement in sandstones where is no evidence of displacive, near-surface precipitation. Kaolin is used as a... 

---