Quantitative Carbonate Diagenesis: Natural laboratories versus experimental work
Ruhr University Bochum, Germany
Diagenesis refers to all processes that affect a given carbonate sediment or mineral after its deposition or precipitation. Exceptions include weathering and tectonism. Diagenesis is the single most significant obstacle to those concerned with environmental data archived in the stratigraphic record of planet Earth and its bearing on the evolution of life. In this presentation, I review the potential and pitfalls of field and experimental approaches to early marine and burial carbonate diagenesis. The focus is on physical, geochemical, and microbiogeological processes and their impact on the isotope geochemical, elemental, and petrographic properties of biogenic and abiogenic aragonite and calcite. A proximal-to-distal transect across the intertidal sabkha and lagoon of Abu Dhabi serves as case example to discuss non-conventional early marine lithification models and the bearing of fluid geochemistry on aragonite cement morphology. Experimental work explores the significance of internal versus external fluid reservoirs during aragonite-to-calcite neomorphism and recrystallization and discusses the concepts of small-scale fluid and rock buffered systems. Recrystallization experiments using coral aragonite document the significance of reactive surfaces and the dominance of fluid Mg:Ca ratios on diagenetic processes. In combination, data discussed here critically re-evaluate textbook-type paradigms in carbonate diagenesis and shed light on previously less often considered processes and products.