AMINOSTRATIGRAPHY AND AMINOCHRONOLOGY OF A TUFA SYSTEM OF CENTRAL SPAIN

In the Central Part of Spain, extensive tufa deposits are located in two small tributaries located in the head of the 1000 km-long Tagus river. This deposits can be explained because of degassing processes that took place after the Ca(CO3H)2-saturated karst-origin running waters lost their confinement into canyons expanding over a flat Tertiary-age basin. Tufa usually appears as terraced alluvial plain deposits. Tufa deposits appear as autochthonous deposits: phytoherm framestone and boundstone; clastic deposits: phytoclastic, oncolitic, intraclastic, micritic tufa and peloidal tufa. Associated deposits are: paleosols s.l., speleothems, aeolian silts, gytja and sapropel. Extraclastic deposits made of quartzite and limestone clasts from Mesozoic-age rocks appear as beds of variable thickness. In spite of invertebrate remains, mainly gastropods and ostracodes, are abundant in all the beds uncemented fine sand and silt-sized beds are very favorable for fossil obtaining after washing and sieving. According to the geomorphological analysis seven terraced levels have been differentiated. All of them were sampled for ostracod recovery and amino acid racemization analysis in a GC, according to the Goofriend’s (1991) protocol. D/L ratios of aspartic acid and glutamic acid were used for dating purposes. After a cluster analysis of the obtained values five different aminozones (AZ1-AZ5) were identified. The obtained aminozones matched well for each river terrace system. For calibrated age calculation the algorithms defined by Ortiz et al. (in press) were used and the obtained results were as follows: AZ1: 407±12 ka; AZ2: 263±14 ka; AZ3: 181±17 ka; AZ4: 119±19 ka; AZ5: 11±4 ka.