Experimental stabilization of carbonate sediments to calcite: Insights into the depositional and diagenetic controls on calcite microcrystal texture
Experimental stabilization of carbonate sediments to calcite: Insights into the depositional and diagenetic controls on calcite microcrystal texture
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DOI：
10.1016/j.epsl.2020.116235
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发表时间：
2020-05-15
影响因子：
5.3
通讯作者：
Kaczmarek, Stephen E.
中科院分区：
文献类型：
--
作者：
Hashim, Mohammed S.;Kaczmarek, Stephen E.
文石和高镁方解石是现代浅海碳酸盐沉积物中丰富的成分，但在古代碳酸盐岩中却很少见。由于这些矿物是亚稳定的，它们往往会稳定为微晶方解石，微晶方解石在大多数显生宙海洋和湖相石灰岩中普遍存在。方解石微晶表现出一系列的纹理，这些纹理根据晶体尺寸、形态和接触几何形状进行分类。这些纹理有可能揭示有关前体沉积物以及稳定成岩条件的信息，因此可以作为古环境条件的代表。然而，尽管它们无处不在且重要，但这些纹理的起源仍存在争议。关于方解石微晶结构起源的假设通常涉及关于前体沉积沉积物、稳定成岩条件或成岩过程的推论。在这里，进行了数百项实验室实验，将亚稳态碳酸盐沉积物稳定为方解石。这些实验的目的是研究方解石微晶结构的沉积和成岩控制。研究的沉积变量是前驱矿物学、类型和尺寸，成岩变量是温度、流体化学成分和液固比。我们的结果表明，碳酸盐沉积物的实验稳定产生了具有多种纹理的方解石，具体取决于各种沉积和成岩参数。这些纹理与岩石记录中常见的纹理非常相似。方解石微晶形态由流体化学、流体：固体比例和反应物类型控制。方解石微晶尺寸由温度、流体化学、流体：固体比例和反应物尺寸控制。方解石微晶体装配在一起的程度由反应物尺寸和反应物微观结构控制。我们的发现挑战了大多数有关方解石微晶结构起源的现有假设。我们特别表明，被解释为表明晚期成岩过程（例如溶解和胶结作用）的纹理可能是早期成岩稳定过程的结果。 (C) 2020 Elsevier B.V. 保留所有权利。
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. (C) 2020 Elsevier B.V. All rights reserved.