Tufa Research Articles

Tufa sedimentation in changing hydrological conditions: the River Mesa (Spain)

The processes controlling tufa deposition along the River Mesa (NE Spain) were studied from April 2003 to September 2009, based on six-monthly monitoring of physical and chemical parameters of the river water and sedimentological characteristics, including deposition rates on tablets. With a mean annual discharge around 1.5m3/s, the sedimentation rate (mean 2mm/yr) recorded important spatial, seasonal and interannual variations. The river waters are of the calcium bicarbonate type. In this study, three distinct river stretches were distinguished based on the steady groundwater inputs, some of low-thermal nature. Groundwater discharges controlled the water chemical composition, and some sedimentation features too. At each stretch, an increase in pCO2 and conductivity was measured around the spring sites. Decreasing trends in conductivity or alkalinity with high enough saturation values with respect to calcite were only clearly observed in the intermediate stretch, which had higher tufa deposition rates than the other two. Tufa deposition rates were higher in cool (autumn+winter) than in warm (spring+summer) periods. In some low-rainfall warm periods, tufa deposition was inhibited or limited due to the low flow –mainly from groundwater inputs– and to the dryness of some river sites, which indeed favoured erosion during flooding. A decrease in yearly deposition rates from April 2006 onwards paralleled an important reduction in the river discharge. Groundwater inputs, drought periods and flood events should therefore be considered to understand fluvial tufa sedimentation in semi-arid conditions.

Holocene aggradation/erosion of a tufa dam at Triponzo (central Italy.)

Holocene aggradation/erosion of a tufa dam at Triponzo (central Italy.)

Microbial fabric formation in spring mounds ("microbialites") of alkaline salt lakes in the Badain Jaran sand sea, PR China

The large sandy desert of Badain Jaran Shamo, Inner Mongolia, has several salt lakes located among megadunes with crests as high as 400 m. Most of the lakes are hypo- to hypersaline and alkaline, with pH values between 8.5 and 10. Because of their reef-like aragonitic pinnacles rising from the lake floor, Lake Nuoertu and Lake Huhejaran have been investigated in detail. The porous limestones of the tufa pinnacles ("spring mounds") result from a hydrochemically forced, exopolymer-mediated calcification of cyano-bacteria-dominated microbial mats at sublacustrine springs. The development of their enigmatic fabrics is documented for the first time. Sickle-cell-like and bubble-shaped fabrics reflect successive mineralization during degradation, shrinkage of the organic mucus, and gas formation by bacteria. Fossil analogues are known from the Pleistocene and Miocene (Riescrater lake), but older non-marine, Phanerozoic examples are expected. To the extent that these textures are associated exclusively with alkaline environments, they can be used to test the hypothesis of an alkaline ocean early in Earth history.

Two Mechanisms of Tufa Formation in the Cement Grouting Tunnels at Wujiangdu Hydropower Station of Guizhou

Wujiangdu Hydropower Station of Guizhou is one of the biggest hydroelectric projects built in karst areas of China. It has a dam 165 m high, with a capacity of 630,000 kW. Its electric energy production is 3.34 billion kW-·h/a. Since its launching in 1979, the station has contributed a lot to the economy in Southwest China.

Tufa dam

Tufa dam