Modes of occurrence of dolomite in some Arabian carbonate rocks

الملخص EN

-In Central Saudi Arabia, outcrops of the Upper Permian Khuff and Upper Jurassic Jubaila carbonate formations have been affected by widespread dolomitization and dedolomitization.

The latter replacement process is frequently associated with the development of rhombohedral pores.

Nine different modes of occurrence of dolomite were recognized in the examined rocks.

They are: (1) ferroan dolomite and iron oxide rhombohedra; (2) calcitized dolomite ; (3) leached dolomite rhombohedra ; (4) zoned dolomite ; (5) dark centered-clear rimmed dolomite ; (6) sucrosic dolomite ; (7) interlocking dolomite ; (8) crypto- and microcrystalline dolomite ; and (9) cement dolomite.

These modes are likely to have resulted from paragenetic and epigenetic changes in the texture and composition of dolomite crystals during their growth stages and later weathering respectively.

They possibly reflect as well differences between the physico-chemical environments of the penecontemporary and subsequent to burial dolomitization.

The former produced extremely fine-textured, iron-free, dolomite replacing lime mud matrix and/or calcarenite, whilst the latter formed coarser and zoned dolomite crystals indiscriminately replacing depositional carbonate constituents and sparry calcite cement.

Dolomite not only grew as replacement to calcium carbonate sediments and rocks, but also as pore-filling cement.