Intrinsic and extrinsic controls of spatial and temporal variations in modern fluvial tufa sedimentation: A thirteen‐year record from a semi‐arid environment

Abstract

Sedimentological and hydrochemical parameters of the River Piedra (northeast Spain) were monitored every six months (from 1999 to 2012) at 24 sites, at which tablets were installed all along the river. The river water is of HCO 3 -SO 4 -Ca type and is notably influenced by inputs from upstream karstic springs. Tufa deposition was first detected 8 km downstream of these springs and greatly increased from there, primarily along the steeper stretch (i.e. within the Monasterio de Piedra Natural Park); then, deposition decreased through the most downstream stretch, with smaller ground water inputs. The spatial evolution of the tufa thickness, with parallel variations of PWP (Plummer, Wigley, Parkhurst) rates, was thus determined by the river water pCO 2 which was controlled by ground water inputs and by the river bed slope. Five fluvial subenvironments and seven sedimentary facies were characterized. The water flow conditions are the primary factor responsible for the distinct deposition rates of facies, mainly through CO 2 -outgassing. Stromatolites and moss-tufa and alga-tufa had the highest rates, whereas loose tufa formed in slow-flowing water and tufa of spray areas had thinner deposition. A six-month pattern in the deposition rate was detected through thickness measurements. That pattern was parallel to the seasonal PWP rates. The increased deposition during warm periods (spring and summer; mean: 5Á08 mm) compared with cool periods (autumn and winter; mean: 2Á77 mm) is linked chiefly to temperature, which controlled the seasonal changes in the physico-chemical and biological processes; this finding is supported by a principal components analysis. Seasonal variations of insolation and day duration also contributed to such a deposition pattern. Large discharge events, which provoked erosion of tufa deposits and dilution of water, caused the reversal of the seasonal deposition rate pattern. Stromatolites are likely to preserve the most complete sedimentary record. Although tufas are a potentially sensitive record of climate-related parameters, erosion is an intrinsic process that may overwhelm the effects of such parameters. This issue should be considered in palaeoclimatic studies based on the tufa record, particularly in semi-arid conditions.Keywords Fluvial tufa facies, present hydrochemistry and deposition rate monitoring, sedimentary processes, semi-arid climate, Spain. INTRODUCTIONThe study of present-day tufa sedimentation in the fluvial environment has become a matter of great interest because of the ability of tufas to record environmental (for example, climatic and hydrological) changes at different time scales. The high-deposition rates of fluvial tufas (i.e. as much as 16 to 17Á5 mm yr À1 ; Pentecost, 1978; V azquez-Urbez et al., 2010) makes possible the short-term monitoring of physical, chemical and biological parameters, which allows the factors that control the tufa sedimentation to be analyzed. Most studies of present fluvial tufas deal with stable-isotope geochemistry Kawai et al., 2009;...

Geobody architecture, genesis and petrophysical characteristics of the Budakalász travertines, Buda Hills (Hungary)

“…Gradzinski et al, 2014), wedge-shaped valley fill travertines (e.g. Arenas et al, 2014;Huerta et al, 2016) and a mixed travertine-terrigenous system (Croci et al, 2016) have been reported. The overall geobody of the Budakalász travertines was described as a mound/fissure ridge complex (Scheuer and Schweitzer, 1985;Pentecost, 2005).…”

Factors Affecting Tufa Degradation in Jiuzhaigou National Nature Reserve, Sichuan, China

“…S PL and S PS 2 are located on the stream bed below the Panda Waterfall and in a depression on the Pearl Shoal with turbulent flow, respectively. High flow velocities and turbulence enhance CO 2 , which favors CaCO 3 precipitation at S PS 2 and S PL [6,15,34], and when the water velocity is greater than 120 cm·s −1 , variations in water velocity will not cause CaCO 3 deposition [7]. The faster the water flows, the higher CaCO 3 precipitation is within the threshold value (120 cm·s −1 ) of flow velocity at S PS 2 and S PL .…”

“…The NO3 − concentrations increased with water flow (from 0.73 mg·L −1 to 1.11 mg·L −1 ), and this may be interpreted as a consequence of nutrient accumulation in the streams. The highest Calcite is the main component of tufa [7], and tufa in Jiuzhaigou is no exception. Three ttufa samples were randomly selected for XRD (two samples) and EDS (one sample) analyses, respectively.…”

“…Therefore, fast flow below the hydrodynamic threshold probably was one cause of promoting the CaCO 3 deposition besides the hydrochemical parameters and biological factors considered in the following sections of this article. Calcite is the main component of tufa [7], and tufa in Jiuzhaigou is no exception. Three tufa samples were randomly selected for XRD (two samples) and EDS (one sample) analyses, respectively.…”

“…Foreign diatoms were included in the tufa mass, and hence, the tufa mass that was used to calculate the deposition rate was overestimated somewhat. Values of water depth and velocity refer to the ranges of the means at each site from field investigations and [7].…”