Where dolomite and calcite cements occur together, calcite is commonly the younger. This is true of cements that fill both primary (intergranular and intraskeletal) and secondary (vug and vein) pores. Rarely there is an alternation of cement types, but where this occurs, dolomite is still usually the penultimate, and calcite the ultimate.

In primary pores, the most likely unidirectional process producing the sequence, dolomite-calcite, is a change from marine to freshwater phreatic conditions through a lowering of sea level, elevation of the land, or increase in freshwater head.

In secondary pores, fluid inclusion studies of epigenetic dolomite-calcite show the dolomite to be both hotter and saltier than the associated younger calcite. Therefore, this sequence most likely records precipitation concomitant with erosional unloading, which should both reduce the geothermal environment and promote a freshening of the water.

End_of_Article - Last_Page 780------------