Seasonal record from recent fluvial tufa deposits (Monasterio de Piedra, NE Spain): sedimentological and stable isotope data - Tufas and Speleothems: Unravelling the Microbial and Physical Controls - page 116

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

C. ARENAS*, C. OS ´ CAR, C. SANCHO, M. V ´ ZQUEZ-URBEZ,
L. AUQU ´ & G. PARDO
Department of Earth Science, University of Zaragoza, Calle Pedro Cerbuna 12,
E-50009 Zaragoza, Spain
*Corresponding author (e-mail: [e-mail])

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 fea-
tures of deposits from warm and cool periods had a variable pattern.
The sediment d 18 O 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 d 13 C composition had an irregular pattern, indicating that other
parameters than temperature intervened in the fluvial system.

The study of the short-term (seasonal) behaviour
pattern of active tufa system allows: (1) to
advance in the knowledge of the mechanical degas-
sing versus photosynthesis role in tufa deposition
processes; (2) to analyse the problems arisen from
correlating stable isotope composition of water
and derived tufaceous sediment; (3) to asses the
use of Quaternary tufa deposits for high-resolution
paleoclimate

(sedimentological and geochemical studies) along
with their environmental conditions. In addition,
both in the Park and in the surrounding areas, the
presence of many fossil tufa buildings proves the
high tufa sedimentation during some Quaternary
intervals until the present.
The aim of this contribution is to analyse seaso-
nal variations in sedimentological features recorded
on artificial substrates installed in different fluvial
subenvironments, and the significance of the
correlative carbon and oxygen stable isotope data
of sediment and water. The study is based on:
(1) monitoring of physical and hydrochemical
parameters, and characterization of the type of
substrates; (2) sedimentation rates measured season-
ally from tablets installed from August 1999 to
March 2003; (3) correlation of these thickness
values with the sedimentary record on cross-
sections of tablets once these were removed from
the field; and (4) textural and structural character-
istics and stable isotope composition of the several
seasonal intervals identified in the tablet records.
The study is focused on the analysis of the factors
that control present-day tufa sedimentation in the
Monasterio de Piedra Natural Park and aims to
obtain environmental and climatic information that

studies; and (4) to increase the

limited knowledge of present-day tufa activity

under different environmental conditions.
Understanding present-day dynamics of fluvial
tufa systems requires field monitoring of tufa sedi-
ment formation. Measurement of tufa deposition
rates and analysis of sediment, including both tex-
tural features and stable isotope composition, are
some of the most important parameters in order to
establish the characteristics of the tufa formation
process (Chafetz et al. 1991; Drysdale & Gilleson
1997; Lu et al. 2000; Matsuoka et al. 2001; Ihlenfeld
et al. 2003; Kano et al. 2004, 2007; Lojen et al.
2004; O'Brien et al. 2006; Shiraishi et al. 2008).
Due to the intense tufaceous activity observed, the
fluvial system within the Monasterio de Piedra
Natural Park is a highly suitable scenary to measure
sedimentation rates and to analyse the deposits