Abstract

Shallow subtidal and peritidal carbonates in the lower Lost Burro Formation have been pervasively dolomitized. Evidence for late diagenetic burial dolomitization consists of very coarse crystallinity, zebroid structure, healed microfractures, “local” limestone-dolomite facies relations, transection of bedding by dolomite tongues and fronts, truncated and relict stylolites, oxygen-isotope data, and a “net fabric.” The latter consists of seams of replacement dolomite (concentrated along stylolites and microfractures) that enclose remnants of micrite in which are disseminated large, baroque, cross-shaped dolomite crystals. The presence of a relict net fabric in dolomite immediately across a sharp dolomite front strongly suggests that a large mass of dolomite resulted from replacement in the burial environment as contrasted with late diagenetic neomorphism of earlier dolomite, a process that may also be significant. It is proposed that Mg2+ ions were delivered by water moving along stylolites and now-healed microfractures. The significance of late diagenetic burial dolomitization in the geologic record has been underestimated. There are fewer thermodynamic and kinetic constraints for dolomitization in the burial environment. Also, it is premature to conclude that this environment is too tight to permit sufficient water circulation for dolomitization.

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