Travertine versus Calcareous tufa: distinctive petrologic features and stable isotopes signatures
Travertine versus Calcareous tufa: distinctive petrologic features and stable isotopes signatures
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石灰华与钙质凝灰岩：独特的岩石学特征和稳定的同位素特征
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发表时间：
2008
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通讯作者：
E. Capezzuoli
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作者：
A. Gandin;E. Capezzuoli
： A. Gandin和E. Capezzuoli，石灰华与钙质凝灰岩的岩石学特征和稳定同位素特征。（它的发行号0394-3356,2007）。陆相灰岩主要由富含碳酸盐的水沉积而成方解石壳，它们来源于热液源的温热水（石灰华）或岩溶源的冷水（钙质凝灰岩）。这两组固结碳酸盐在不同的地貌环境中，如冷水泉和河流山谷，或在温泉出现的环境中积极形成。这些岩石的化石遗迹经常在钙质地区以及没有暴露碳酸盐岩的地区被发现。然而，当与补给源的联系不明显时，对其成因起源的认识往往是不确定的，因为具体的岩相的定义尚未完全确定。通过对钙质凝灰岩和钙华岩相的详细分析，以及对现有地球化学资料的详细阐述，表明其岩石学特征和稳定同位素特征反映了不同的沉积环境条件，这反映了补给水体的物理化学性质，虽然主要是大气来源，但经历了不同的循环/补给历史。石灰华是层状良好的致密石灰岩，在热系统的近端由特殊的结晶壳组成，而在远端由细菌/蓝藻层积岩组成，通常与薄结晶壳、钙化气泡透镜和纸薄筏有关。在该体系中，碳酸盐沉积主要来源于新兴的过饱和水的强烈脱气和蒸发，同时伴随着排水网络的快速降温。石灰华矿物含量来源于深部地热/热液
: A. Gandin & E. Capezzuoli, Travertine versus Calcareous tufa: distinctive petrologic features and stable isotopes signatures . (IT ISSN 0394-3356, 2007). Terrestrial limestones, mainly deposited as calcite crusts by carbonate-rich waters flowing in subaerial settings, originate from warm- to-hot waters of hydrothermal provenance (travertines) or from cool waters of karstic derivation (calcareous tufa). The two groups of concretionary carbonates are actively forming in different geomorphologic settings such as cool-water springs and fluvial valleys, or in the surroundings of the emergence of thermal springs. Fossil remains of these rocks are frequently found in calcareous areas as well as in areas where carbonate rocks are not exposed. However the recognition on the field of their genetic derivation when connections with the feeding source are no more evident, is often uncertain since the definition of the specific litofacies are not yet completely elu-cidated. The detailed analysis of the lithofacies of calcareous tufa and travertines as well as the critical elaboration of existing geochemical data, shows that the petrologic features and stable isotopic signatures reflect the contrasting environmental conditions of deposition deriving from physico-chemical properties of the feeding waters that, although mostly of meteoric provenance, experienced different circulation/recharge history. Travertines are well bedded, often finely laminated compact limestones, composed in the proximal part of the thermal system by peculiar crystalline crusts and in the distal part by bacterial/cyanobacterial laminites often associated with thin crystalline crusts, len-ses of calcified-bubbles and paper-thin rafts. In this system the carbonate deposition mainly derives from intense outgassing of the emerging supersaturated waters, and evaporation, concomitant with the rapid drop in temperature along the drainage network. Travertine mineral content originates in deep geothermal/hydrothermal