Climatic and tectonic significance of Late Pleistocene and Holocene tufa deposits in the Mijares River canyon, eastern Iberian Range, northeast Spain

The tufa deposits developed in the Mijares River canyon at the eastern sect or of the Iberian Range were studied by using geomorphological, stratigraph ic, micromorphological, mineralogical and chronological (U/Th and C-14) tec hniques. These tufas are located along a high-gradient river profile reach, with high water turbulence and mechanical outgassing, related to Quaternar y faulting activity upstream in the regional context of an extensional tect onic regime. Two stepped and terraced fluviatile tufa structures with large phytohermal barrage frameworks and smaller damned areas have been differen tiated. The first structure, Upper Pleistocene in age (from 200000 to 50000 years BP), is made up by two morphosedimentary units reaching 120 m in thi ckness, and the second one, Holocene in age (10000-5000 years BP), is 35 m in thickness. These structures record a more or less continuous tufa develo pment with a mean deposition rate ranging between 1 and 5 mm a(-1) as minim um. A preferential growth with high biological activity during warm and wet palaeoenvironmental stages (isotopic stages 7, 3 and 1) can be deduced. Th us, neotectonic activity controlled the location along the Mijares River as well as the large thickness of the tufa deposits, whereas warm climatic pe riods favoured intense tufa activity in the fluvial system. Copyright (C) 2 000 John Wiley & Sons, Ltd.