排序方式: 共有3条查询结果,搜索用时 0 毫秒
1
1.
《Sedimentology》2018,65(5):1482-1503
Subsurface granitic environments are scarce and poorly investigated. A multi‐disciplinary approach was used to characterize the abundant moonmilk deposits and associated microbial communities coating the granite walls of the 16th Century Paranhos spring water tunnel in Porto city (north‐west Portugal). It is possible that this study is the first record of moonmilk in an urban subsurface granitic environment. The morphology and texture, mineralogical composition, stable isotope composition and microbial diversity of moonmilk deposits have been studied to infer the processes of moonmilk formation. These whitish secondary mineral deposits are composed of very fine needle‐fibre calcite crystals with different morphologies and density. Calcified filaments of fungal hyphae or bacteria were distinguished by field emission scanning electron microscopy. Stable isotope analysis revealed a meteoric origin of the needle‐fibre calcite, with an important contribution of atmospheric CO 2, soil respiration and from weathering of Ca‐bearing minerals. The DNA ‐based analyses revealed the presence of micro‐organisms related to urban contamination, including Actinobacteria, mainly represented by Pseudonocardia hispaniensis , Thaumarchaeota and Ascomycota, dominated by Cladosporium . This microbial composition is consistent with groundwater pollution and contamination sources of the overlying urban area, including garages, petrol stations and wastewater pipeline leakage, showing that the Paranhos tunnel is greatly perturbed by anthropogenic activities. Whether the identified micro‐organisms are involved in the formation of the needle‐fibre calcite or not is difficult to demonstrate, but this study evidenced both abiotic and biogenic genesis for the calcite moonmilk in this subsurface granitic environment. 相似文献
2.
3.
Moonmilk represents a conspicuous but controversially discussed precipitate of cave settings. Here, new electron backscatter diffraction microscopic and petrographic evidence on the origin of moonmilk calcite is presented. Calcite fibres in a moonmilk mat from the walls of an active cave (Tunnel‐Cave) in Devonian massive limestones in the northern part of the Rhenish Massif (Germany) show orientations of the crystallographic c‐axis independent of the morphological fibre orientation. This observation and the morphology of the fibres are in agreement with microbially induced, as opposed to abiogenic, calcite precipitation. Carbon‐isotope data are higher (1·9 to 3·3‰) than those commonly measured regionally in speleothem calcite (stalagmites, stalactites and flowstones), an observation attributed to kinetic effects. In combination, these findings add independent evidence to the complex interplay of inorganic and bio‐induced carbonate precipitation in cave environments. 相似文献
1