The Subtle Thief: Selective Dissolution of Aragonite During Shallow Burial and the Implications for Carbonate Sedimentology
Published:January 01, 2008
V.Paul Wright, Lesley Cherns, 2008. "The Subtle Thief: Selective Dissolution of Aragonite During Shallow Burial and the Implications for Carbonate Sedimentology", Controls on Carbonate Platform and Reef Development, Jeff Lukasik, J.A. (Toni) Simo
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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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Controls on Carbonate Platform and Reef Development
Carbonate platforms and reefs emerge, grow and die in response to intrinsic and extrinsic mechanisms forced primarily by tectonics, oceanography, climate, ecology and eustasy. These mechanisms, or controls, create the physical, biological and chemical signals accountable for the myriad of carbonate depositional responses that, together, form the complex depositional systems present in the modern and ancient settings. If we are to fully comprehend these systems, it is critical to ascertain which controls ultimately govern the “life cycle” of carbonate platforms and reefs and understand how these signals are recorded and preserved. Deciphering which signals produce a dominant sedimentological response from the plethora of physical and biological information generated from superimposed regional to global-scale controls is critical to achieving this goal. With this understanding, it may be possible to extract common time- and space-independent depositional responses to specific mechanisms that may, ultimately, be used in a productive sense. Extensive research on a wide variety of carbonate platform and reefal systems in the past few decades has provided the foundation and understanding necessary to take carbonate research to a new level. With assistance from rapidly advancing computer software and an increasing use of cross-disciplinary integration, carbonate research is shifting from description and morphological analysis towards a science that is more focused on the assessment of process and genetic relationships. The aim of this special publication is to present a cross section of recent research that shows this evolution from a variety of perspectives and scales using examples distributed throughout the Phanerozoic.