Geochimica et Cosmochimica Acta ( IF 5 ) Pub Date : 2021-04-16 , DOI: 10.1016/j.gca.2021.04.010 Ramon Mercedes-Martín , Mike Rogerson , Tim J. Prior , Alexander T. Brasier , John J.G. Reijmer , Ian Billing , Anna Matthews , Tracy Love , Scott Lepley , Martyn Pedley
Ancient and recent terrestrial carbonate-precipitating systems are characterised by a heterogeneous array of deposits volumetrically dominated by calcite. In these environments, calcite precipitates display an extraordinary morphological diversity, from single crystal rhombohedral prisms, to blocky crystalline encrustations, or spherulitic to dendritic aggregates. Despite many decades of thorough descriptive and interpretative work on these fabrics, relating calcite micro-morphology with sedimentary hydrogeochemical conditions remains a challenge. Environmental interpretations have been hampered by the fact that calcite morphogenesis results from the complex interaction between different physico-chemical parameters which often act simultaneously (e.g., carbonate mineral supersaturation, Mg/Ca ratio of the parental fluid, organic and inorganic additives). To try to experimentally address the sedimentological causes of calcite morphogenesis, an experimental approach yielding a first attempt at a calcite growth-form phase diagram is presented here. The initial aim was to account for the carbonate products experimentally nucleated in alkaline, saline lake settings. These are the result of at least two competing calcite precipitation ‘driving forces’ that affect morphogenesis: the calcite supersaturation level of the parental fluid, and the concentration of microbial-derived organic molecules (alginic acid). A key finding of this study is that common naturally-occurring calcite products such as calcite floating rafts, rhombohedral prismatic forms, di-pyramid calcite crystals, spherulitic calcite grains, or vertically stacked spheroidal calcite aggregates, can be related to specific hydrogeochemical contexts, and their physical transitions pinpointed in a phase diagram. By exploring binary or ternary responses to forcing in morphological phase-space, links between calcite growth forms and (palaeo)environmental conditions can be determined. This provides a truly process-oriented means of navigating questions around carbonate precipitate morphogenesis for the future.
中文翻译:
走向陆地碳酸盐的形态图:评估碳酸盐过饱和和藻酸对方解石沉淀形态的影响
古代和最近的陆地碳酸盐沉淀系统的特征是方解石在体积上占主导地位的非均质沉积物阵列。在这些环境中,方解石沉淀物表现出非凡的形态多样性,从单晶菱面体棱镜到块状晶体结壳,或从球状到树枝状聚集体。尽管数十年来在这些织物上进行了详尽的描述和解释工作,但方解石的微观形态与沉积水文地球化学条件的关联仍然是一个挑战。由于方解石形态发生是由于经常同时起作用的不同理化参数之间复杂的相互作用所致(例如,碳酸盐矿物过饱和,母体液的Mg / Ca比,有机和无机添加剂)。为了尝试通过实验解决方解石形态发生的沉积学原因,此处介绍了一种尝试方解石生长形式相图的实验方法。最初的目的是要说明在碱性盐湖环境中实验成核的碳酸盐产品。这是至少两个相互竞争的方解石沉淀“驱动力”影响形态发生的结果:父母流体的方解石过饱和水平和微生物衍生的有机分子(海藻酸)的浓度。这项研究的关键发现是常见的天然方解石产品,例如方解石浮筏,菱形方柱形,双金字塔方解石晶体,球状方解石晶粒或垂直堆积的球状方解石骨料,可能与特定的水文地球化学环境有关,并且它们的物理转变在相图中精确指出。通过探索对形态相空间中强迫的二元或三元响应,可以确定方解石生长形式与(古)环境条件之间的联系。这提供了一种真正面向过程的方法,可用于将来解决碳酸盐沉淀物形态发生方面的问题。