Chronology of geomorphological changes in a cantabrian mountain valley over the last 20,000 years.

Abstract

This is an in-depth study of a mixed deposit of terrace and alluvial fan in a valley of the Cantabrian Mountains that aims to characterize environmental conditions during the period following the Last Glacial Maximum (LGM) at the end of the Pleistocene and the entire Holocene, including human influence to the present day. In this perspective, the lithostratigraphy of different layers was described, the granulometric analysis performed in situ and in the laboratory, the organic bulk sediment dated by radiocarbon and weight, and other empirical studies, such as paleomagnetism were performed. The results reveal a temporal sequence of deposition from around 19.4 ky BP to the present showing different sedimentary environments. Paleoclimatical scientific literature in sorrounding areas complemented the interpretation of the results e.g. pleistocene glaciers, speleothems, palynology and geomorphology. We conclude a completely diferent evolution of studied section between Late-Pleistocene and Holocene. Bottom layers, composed of coarse boulders, are interpreted in the context of a second glacial push after the Local Last Glacial Maximum under conditions of torrentiality. In the upper layers, in the Holocene, there was an increase in sedimentation from slopes through alluvial and colluvial cones, and rivers lost their capacity to transport these sediments. Important environmental changes in the Middle Holocene, 5.5 ky BP, were detected with possible evidence of human action. A decrease from that moment in the deposited sediment caliber was verified.