Phanerozoic limestones are composed of low-Mg calcite microcrystals (i.e., micrite) that typically measure between 1 and 9 μm in diameter. These microcrystals, which host most of the microporosity in subsurface reservoirs, are characterized by a variety of microtextures. Despite the overwhelming consensus that calcite microcrystals are diagenetic, the origin of the various textures is widely debated. The most commonly reported texture is characterized by polyhedral and rounded calcite microcrystals, which are interpreted to form via partial dissolution of rhombic microcrystals during burial diagenesis. A proposed implication of this model is that dissolution during burial is responsible for significant porosity generation. This claim has been previously criticized based on mass-balance considerations and geochemical constrains. To explicitly test the dissolution model, a series of laboratory experiments were conducted whereby various types of calcites composed of rhombic and polyhedral microcrystals were partially dissolved under a constant degree of undersaturation, both near and far-from-equilibrium.Our results indicate that calcite crystals dissolved under far-from-equilibrium conditions develop rounded edges and corners, inter-crystal gulfs (narrow grooves or channels between adjacent crystals), and a few etch pits on crystal faces—observations consistent with the burial-dissolution hypothesis. Crystals dissolved under near-equilibrium conditions, in contrast, retain sharp edges and corners and develop ledges and pits—suggesting that dissolution occurs more selectively at high-energy sites. These observations support the longstanding understanding that far-from-equilibrium dissolution is transport-controlled, and near-equilibrium dissolution is surface-controlled. Our results also show that while the rhombic calcite crystals may develop rounded edges and corners when dissolved under far-from-equilibrium conditions the crystals themselves do not become spherical. By contrast, polyhedral crystals not only develop rounded edges and corners when dissolved under far-from-equilibrium conditions but become nearly spherical with continued dissolution. Collectively, these observations suggest that rounded calcite microcrystals more likely form from a precursor exhibiting an equant polyhedral texture, rather than from a euhedral rhombic precursor as previously proposed. Lastly, the observation that calcite crystals developed rounded edges and corners and inter-crystal gulfs after only 5% dissolution indicates that the presence of such features in natural limestones need not imply that significant porosity generation has occurred.

中文翻译：

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实验溶解过程中方解石微晶形态的演变

多生代石灰石由通常直径为1至9μm的低镁方解石微晶（即微晶石）组成。这些微晶具有地下储层中的大部分微孔，其特征是具有各种微纹理。尽管人们普遍认为方解石微晶是成岩作用的，但各种纹理的起源仍受到广泛争议。最常报告的纹理特征是多面体和圆形方解石微晶，这被认为是通过在埋藏成岩过程中菱形微晶的部分溶解而形成的。该模型的一个暗示含义是在埋藏期间的溶解会导致大量孔隙的产生。先前已根据质量平衡考虑因素和地球化学限制对这一说法提出了批评。为了明确测试溶出度模型，进行了一系列实验室实验，使由菱形和多面体微晶组成的各种方解石在恒定的不饱和状态下（接近和远离平衡）部分溶解。我们的结果表明方解石晶体在远离平衡的条件下溶解，会形成圆形的边缘和拐角，晶体间的缝隙（相邻晶体之间的狭窄凹槽或通道）以及晶体面上的一些蚀刻坑-观察结果与埋藏溶解假设相符。相反，在接近平衡的条件下溶解的晶体保留了锋利的边缘和角落，并形成了壁架和凹坑-这表明溶解在高能位点上发生的选择性更大。这些观察结果支持长期以来的认识，即远离平衡的溶出度受运输控制，而接近平衡的溶出度受表面控制。我们的结果还表明，尽管菱形方解石晶体在远离平衡条件下溶解时可能会形成倒圆的棱角，但晶体本身不会变成球形。相比之下，多面体晶体在远离平衡状态下溶解时不仅会形成圆角和圆角，而且在持续溶解下会变成接近球形。总体而言，这些观察结果表明，圆形方解石微晶更有可能由具有均等多面体织构的前体形成，而不是由先前提出的整面菱形前体形成。最后，