Dolocrete microcrystalline dolomite

Fig. 8F). Some dolocretes contain crusts of microcrystalline dolomite with collomorphic textures composed of alternating bands of dolomite and calcite (Fig. 8E). 

The EMP analyses revealed that dolomite and ankerite vary considerably in chemical composition, particularly in terms of Fe content (FeCOj = 0.3-36 mol%) (Table 1 Fig. 9). The microcrystalline dolomite rims and crusts in dolocrete, as well as the small rhombs replacing clays and occurring within mica in the sandstones, are relatively Fe poor to moderately ferroan (0.3-7.8% FeCOs) (Table 1 Fig. 9). However, both the small rhombs and the large blocky crystals in sandstones are zoned, with Fe increasing outwards to an ankeritic composition (Fig. lOE). Furthermore, the dolomites are slightly to moderately calcian ( 53-62 mol% CaCOj) (Table 1) and have relatively low Mn content (0.2-1.9 mol%). 

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