Experimental stabilization of carbonate sediments to calcite: Insights into the depositional and diagenetic controls on calcite microcrystal texture

• Published in: Earth and planetary science letters Vol. 538; p. 116235
• Main Authors: Hashim, Mohammed S., Kaczmarek, Stephen E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.05.2020
• Subjects: calcite crystal; carbonate diagenesis; experiment; stabilization; texture; experiment; stabilization; carbonate diagenesis; calcite crystal; texture
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2020.116235

•Aragonite sediments can be experimentally stabilized to calcite.•Experimental stabilization produces a wide variety of calcite microcrystal textures.•Experimental calcite textures are similar to those observed in the rock record.•Calcite textures are controlled by various depositional and diagenetic variables.•This study challenges existing hypotheses regarding the origin of calcite microtextures. Aragonite and high-magnesium calcite are abundant constituents of modern shallow marine carbonate sediments, but are rare in ancient carbonate rocks. Because these minerals are metastable, they tend to stabilize to microcrystalline calcite which is ubiquitous in most Phanerozoic marine and lacustrine limestones. Calcite microcrystals exhibit a range of textures that have been classified in terms of crystal size, morphology, and contact geometry. These textures have the potential to reveal information about the precursor sediments as well as the diagenetic conditions of stabilization, and thus may serve as a proxy for paleoenvironmental conditions. However, despite their ubiquity and importance, the origin of these textures is controversial. Hypotheses regarding the origin of calcite microcrystal textures typically involve inferences regarding the precursor depositional sediments, diagenetic conditions of stabilization, or diagenetic processes. Here, hundreds of laboratory experiments were conducted in which metastable carbonate sediments were stabilized to calcite. The goal of these experiments was to investigate the depositional and diagenetic controls on calcite microcrystal textures. The depositional variables investigated were precursor mineralogy, type, and size, and the diagenetic variables were temperature, fluid chemical composition, and fluid:solid ratio. Our results show that experimental stabilization of carbonate sediments produces calcite with a wide variety of textures depending on the various depositional and diagenetic parameters. These textures are remarkably similar to those commonly observed in the rock record. Calcite microcrystal morphology is controlled by fluid chemistry, fluid:solid ratio, and reactant type. Calcite microcrystal size is controlled by temperature, fluid chemistry, fluid:solid ratio, and reactant size. The degree to which calcite microcrystals are fitted together is controlled by reactant size and reactant microstructure. Our findings challenge most of the existing hypotheses regarding the origin of calcite microcrystal textures. We specifically show that textures that have been interpreted to indicate late diagenetic processes such as dissolution and cementation, may be the result of the early diagenetic processes of stabilization.