Ostracode-based aminostratigraphy and aminochronology of a tufa system in central Spain

Abstract

In the Priego area, central Spain, extensive tufa deposits are located in three small tributaries located at the head of the 1000 km-long Tagus River. The deposits are originated after karst-origin running waters emerged from the confines of the canyons and expanded outward. Old tufa deposits of Priego are mainly present as terraced alluvial plain deposits where different autochthonous and allochthonous facies appear. Extraclastic deposits of quartzite and limestone clasts derived from Mesozoic rocks are interbedded with the tufa marking pulsatory high-flow periods. Using the geomorphologic analysis six terraced levels were differentiated and sampled for ostracode amino acid racemization analysis. D/ L ratios of aspartic acid and glutamic acid were used for dating purposes. Cluster analysis defined six aminozones (AM1–AM7) which were dated as follows: AM1: 407±12 ka oxygen isotope stages (OIS 11); AM2: 263±14 ka (OIS 7e); AM3: 181±17 ka (OIS 7a); AM4: 136±13 ka (OIS 5-6); AM5: 108±14 ka (OIS 5); AM7: 11±4 ka (OIS 1), indicating that tufa deposition took place during warm periods. Models of riverine and riverine-barrage tufa accumulation indicate that their maximum build-up took place between the canyon mouth and the point of depletion of dissolved CO 2, and this affected the elevation of the top of the deposits and their relative chronology.