Abstract Genetic and diagenetic processes of travertine were examined at Futamata hot spring, where both active and inactive (subfossil and fossil) travertines are present. Geochemical and geomicrobiological analyses of active travertines reveal that abiotic process of CaCO3 precipitation is predominant. Photosynthetic inhibition of CaCO3 precipitation occurs at the upstream, while the cyanobacterial population is low in the downstream, resulting in photosynthesis-induced CaCO3 precipitation only in the midstream. Nonetheless, microorganisms have an effect upon depositional fabrics, and filamentous cyanobacteria possessing non-acidic sheaths contribute to the particle trapping/binding and the generation of pore space. Both active and inactive travertines are mainly composed of calcite; however, active travertine in the up-/midstream also contains some aragonite due to high rates of CO2 degassing. Active and subfossil travertines are characterized by domal topography, and relatively high flow rates are assumed due to the dominance of slope facies. On the other hand, fossil travertines are characterized by fissure-ridge topography and relatively low flow rates are assumed due to the dominance of crest and marsh facies. The elemental composition of travertines primarily reflects their constituent minerals, and the active travertines consisting of both aragonite and calcite show higher Sr, Ba, Na, and K contents, whereas travertines consisting solely of calcite show higher Mg and Mn contents. Due to elevated Mn content, bright cathode luminescence is exhibited by the primary calcite of active travertines. Most fossil travertines have experienced prominent diagenetic alteration in the vadose zone and are commonly cemented and recrystallized. In addition to meteoric water, percolating hot spring water was also involved in the diagenetic process. Combined with the results of U–Th dating, our results suggest that the formation of fissure-ridge travertines at Futamata hot spring began approximately 20 thousand years ago (ka) via fault activity, which terminated at around 7 ka and the domal travertines were formed by hot spring water discharging from several vents.

中文翻译：

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日本二俣温泉石灰华的成因与成岩作用

摘要 在 Futamata 温泉检查了钙华的遗传和成岩过程，其中存在活动和非活动（亚化石和化石）钙华。活性石灰华的地球化学和地球微生物学分析表明，CaCO3 沉淀的非生物过程占主导地位。光合作用抑制 CaCO3 沉淀发生在上游，而下游蓝藻数量较少，导致光合作用诱导的 CaCO3 沉淀仅发生在中游。尽管如此，微生物对沉积织物有影响，并且具有非酸性鞘的丝状蓝藻有助于颗粒捕获/结合和孔隙空间的产生。活性和非活性钙华均主要由方解石组成；然而，由于二氧化碳脱气率高，上游/中游的活性石灰华也含有一些文石。活动和亚化石石灰华以穹窿地形为特征，由于斜坡相的优势，假定流速相对较高。另一方面，化石石灰华的特征是裂隙脊地形，并且由于嵴和沼泽相的优势，假设流速相对较低。钙华的元素组成主要反映其组成矿物，文石和方解石共同组成的活性钙华具有较高的Sr、Ba、Na和K含量，而仅由方解石组成的钙华具有较高的Mg和Mn含量。由于锰含量升高，活性石灰华的原生方解石显示出明亮的阴极发光。大多数石灰华化石在包气带中经历了显着的成岩作用，通常被胶结和再结晶。除了大气水外，渗透的温泉水也参与了成岩过程。结合U-Th测年结果，我们的结果表明，二俣温泉裂隙脊石灰华的形成大约在2万年前（ka）通过断层活动开始，在7 ka左右终止，形成了穹窿石灰华由几个喷口排出的温泉水。