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Seasonal record from recent fluvial tufa deposits (Monasterio de Piedra, NE Spain): sedimentological and stable isotope data

Abstract Physical and hydrochemical parameters and sedimentation rates were monitored twice a year from August 1999 to March 2003 at the Monasterio de Piedra area (NE Spain). Different tufa facies related to distinct fluvial subenvironments were characterized and the isotopic composition of water was analysed seasonally. Sedimentary features (thickness, texture and structure) and stable isotope composition of the seasonal record on tablets were analysed. The seasonal intervals were identified from six-monthly thickness measurements on tablets. Sedimentation rates had a strong seasonal pattern with higher values in warm periods than in cool ones, although erosive events and sporadic, warmer-than-normal climate conditions altered it. Three main types of fluvial facies were studied in detail: dense, stromatolitic tufa; dense to porous, massive tufa; and spongy, moss- and alga-bearing, crudely laminated tufa. Textural features of deposits from warm and cool periods had a variable pattern. The sediment δ18O composition showed a rhythmic variation, with higher values in cool periods and lower in warm ones, caused by the fractionation due to seasonal temperature variations. The calculated temperatures for a theoretical equilibrium precipitation accord with the actual measured temperatures. The sediment δ13C composition had an irregular pattern, indicating that other parameters than temperature intervened in the fluvial system.