Early studies suggested that the vast majority of this calcite is not of primary origin but rather formed due to dedolomitization [4, 5].
Dedolomitization or dolomite calcitisation describes the replacement process of dolomite by calcite .
Several conditions have to be met for dedolomitization to take place.
In the thin section some dolomite rhomb show zoning, filling showing dedolomitization
in upper part.
Low [delta][sup.13]C values, accompanied by variable [delta][sup.18]O signatures in two analysed limestone interbeds (Marinova 3 and 4), indicate dedolomitization origin of these rocks.
Dissolution of precursor dolomite may also provide a source of [Ca.sub.2+] for late diagenetic calcite fillings and dedolomitization processes.
Mechanism of dedolomitization
and expansion of dolomitic rocks, Cement and Concrete Research 23(6): 1397-1408.
Historical correlations between discharge and concentrations of specific ions are considered as evidence of active diagenesis, specifically dedolomitization, in rock units of the Blanco River.
Since that time, rocks in the aquifer underwent several major near-surface diagenetic changes, including extensive dedolomitization. In this process, freshwater flushing replaces gypsum and magnesium in dolomitic rocks with calcite.
In addition to the processes of dedolomitization
, evaporite dissolution, and ion exchange (see Bea et al.
When dolomite is present (and consequently [Ca.sup.2+] and [Mg.sup.2+]), dedolomitization occurs: dolomite transforms into calcite.
When calcite is absent in the primary minerals, calcite is still precipitated in the system, due to the increase in [Ca.sup.2+] supplied by dolomite dissolution (dedolomitization) mentioned above.