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Abstract

Syndepositional aragonite dissolution at very shallow depths, above the lysocline, is a major process that affects carbonate deposition and skews the composition of carbonate sediments. Such dissolution is capable of altering sediment composition in many settings, and during microfacies analysis it is critical to be aware of this early, selective filtering by identifying taphonomic signatures. These effects are also capable of distorting the trophic composition of fossil biotas, potentially restricting the ability to identify nutrient levels and other controls. The evidence from widespread diagenetic limestones in shale (marl)-limestone rhythms supports the dissolution model, but the source of the precursor aragonite is unresolved; allochthonous aragonite mud is one possible source, but, especially during calcite- sea intervals, another possibility is from the autochthonous aragonitic fauna. Forward models for carbonate sedimentation will need to compensate for aragonite dissolution if realistic models are to be developed, but our knowledge of the environmental distribution and magnitude of aragonite dissolution is still woefully incomplete. Another major consequence of early aragonite loss is that the diagenetic potentials of many carbonate sediments have been changed, drastically reducing secondary porosity potentials long before they are affected by meteoric or burial processes.

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