A review of the Tagus river tufa deposits (central Spain): age and palaeoenvironmental record

Abstract

Here we determined the aminostratigraphy and aminochronology of tufa deposits located in central Spain associated w i t h the Tagus river and some o f its tributaries (the Henares, Dulce, Cifuentes, Ruguilla, Trabaque, Escabas and Guadiela rivers). W e used aspartic acid and glutamic acid racemization ratios obtained from the ostracod Herpetocypris reptans. Tufa accumulations were found to be of different origins; those in t h e Henares, Cifuentes and Ruguilla rivers are of paludal origin, w h i l e those in t h e Dulce and Tagus rivers are o f fluvial origin. A generally g o o d correspondence was found b e t w e e n the age o f the deposits and the position of the terraces above the current thalweg. However, the geomorphological evolution of the Henares, Cifuentes and Ruguilla rivers (infilling of pre-existing valleys) has produced deposits of distinct ages at the same elevation above the current river thalweg, and sometimes, older tufas are located b e l ow younger ones. We distinguished eight main tufa-deposition episodes. These occurred predominantly during even Marine Isotopic Stages (MIS), at 4 0 6 ± 90 (MIS 11), 2 6 4 ± 68 (MIS 7e), 189 ± 4 0 (MIS 7a), 130 ± 27 (MIS 6- 5e), 101 ± 2 5 (MIS 5c), 3 2 ± 10 (MIS 3), 1 4 ± 4 (MIS 1), a n d 6 ± 2 (MIS l ) k a . These results are in agreement w i t h the dating of similar deposits from nearby areas and other zones of S p a i n a n d Europe. The tufa stable-isotope compositions were similar to other examples in central and southern Spain a n d their plot falls in the same field as other lowland European stream tufas. O x y g e n stable isotopes were influenced mainly b y temperature a n d rainfall. The <51 3C values indicated a major effect o f soil-derived carbon rather t h a n carbon from the catchment area, but moderated in each tributary b y evaporation, flow regime and biological effects (photosynthesis).