Factors controlling present-day tufa dynamics in the Monasterio de Piedra Natural Park (Iberian Range, Spain): depositional environmental settings, sedimentation rates and hydrochemistry

Abstract

The tufa record and hydrochemical characteristics of the River Piedra in the Monasterio de Piedra Natural Park (NE Spain) were studied for 6 years. The mean discharge of this river was 1.22 m 3 /s. The water was supersaturated with calcium carbonate. The HCO 3 -, Ca 2? and TDIC concentrations decreased along the 0.5-km-long studied stretch, whereas the calcite SI showed no systematic downstream or seasonal variation over the same stretch. Several sedimentary subenvironments exist in which four broad types of tufa facies form: (1) Dense laminated tufa (stromatolites), (2) Dense to porous, massive tufa, (3) Porous, coarsely laminated tufa with bryophytes and algae, and (4) Dense, hard, laminated deposits in caves. The halfyearly period thickness and weight of sediment accumulated on 14 tablets installed in several subenvironments showed that the deposition rate was greater in fast flowing river areas and in stepped waterfalls, and lower in slow flowing or standing river areas and in spray and splash areas. Mechanical CO 2 outgassing is the main factor controlling calcite precipitation on the river bed and in waterfalls, but this process does not explain the seasonal changes in depositional rates. The deposition rates showed a halfyearly period pattern recorded in all fluvial subenvironments persistent over time (5.26 mm, 0.86 g/cm 2 in warm periods; 2.26 mm, 0.13 g/cm 2 in cool periods). Mass balance calculations showed higher calcite mass values in warm (21.58 mg/L) than in cool (13.68 mg/L) periods. This biannual variation is mainly attributed to the seasonal differences in temperature that caused changes in inorganic calcite precipitation rate and in biomass and the correlative photosynthetic activity. Tufa sedimentation was therefore controlled by both physicochemical and biological processes. The results of this study may help test depositional rates and their environmental controls and thus assess the climatic and hydrological significance of ancient tufas in semi-arid conditions, in particular in the Quaternary.

Current tufa sedimentation in a high discharge river: A comparison with other synchronous tufa records in the Iberian Range (Spain)

“…Positive six-month values represent deposition but may also involve erosion during the corresponding six-month period and later deposition surpassing the latest measured six-month accumulation height (see Fig. 13 in Vázquez-Urbez et al, 2010). In the present work, the spring and summer months represent the warm period, while the autumn and winter months represent the cool period.…”

“…Approximately a week after their removal, the tablets were placed back in their original position until the next six-month period. The differences in sediment height (mean of measurements at 50 points per tablet) between consecutive measuring times represented the six-month sedimentation rates at each site (a detailed description can be found in Vázquez-Urbez et al, 2010). Negative six-month values represent erosion during the corresponding sixmonth period, which may affect older deposits.…”

“…Studies on modern carbonate sedimentation in the fluvial environment have proven the ability of tufas and associated deposits to record diverse environmental information at different time scales (Drysdale and Gillieson, 1997;Kano et al, 2003;Shiraishi et al, 2008;Vázquez-Urbez et al, 2010). The short-term periodic monitoring of physical, chemical and biological parameters and high-resolution analysis of associated deposits, both in natural and laboratory contexts, are facilitated by the generally high deposition rates (Pentecost, 1978;Gradziński, 2010;Arenas et al, 2014).…”

Review of tufa deposition and palaeohydrological conditions in the White Peak, Derbyshire, UK: implications for Quaternary landscape evolution

“…Supersaturation with respect to calcium carbonate is critical, as is the potential for significant outgassing of carbon dioxide to overcome the kinetic resistance to calcium carbonate precipitation (Lorah and Herman, 1988). This may occur as a consequence of physical water agitation (Chen et al, 2004;Lorah and Herman, 1988;Vázquez-Urbez et al 2010), or biological uptake of carbon dioxide (Pentecost, 1999). Irrespective of the degassing process, biological mediation in the form of microparticulate trapping is significant in binding the sediment and providing a substrate for growth, as illustrated in Figure 6.…”

Fluvial diffluence episodes reflected in the Pleistocene tufa deposits of the River Piedra (Iberian Range, NE Spain)

“…Of special note in the NE of the Iberian Peninsula are the valleys of the Rivers Piedra and Mesa (in the central Iberian Range) where spectacular tufa edifices are found (Léranoz et al, 1987;Arenas et al, 2004;Vázquez-Urbez, 2008;Sancho et al, in press-b). These systems are currently functional (Arenas et al, 2004Vázquez-Urbez et al, 2010), providing an opportunity to study them from a hydrochemical, geochemical, sedimentological, or biological standpoint.…”