Original paper

Holocene Tufa changes in response to human impact on environments: Upper Ebro Basin. Northern Spain

Amuchastegui, María José González; Serrano, Enrique


The environmental changes that took place with the passing of the Pleistocene to the Holocene produced optimal conditions for sedimentation of tufa build-ups in all Mediterranean and Atlantic transitional environments where calcareous rocks are representative. In the Upper Ebro Basin (Iberian Peninsula) tufas shaped valleys and slopes, however, the Holocene was not a period of continuous carbonate sedimentation in these areas. Geomorphological and lithostratigraphic analyses of Holocene tufas and associated deposits in four secondary valleys of the Upper Ebro with tufa systems (Purón, Molinar, Tubilla and Sedano) allowed three morphogenic tufa stages to be defined: two were stages of tufa deposition and the other was an erosion period with a strong incision event. This paper provides an overview of the archaeological, chronological and palaeoenvironmental data of the Upper Ebro Basin, and once climate and vegetation changes, human occupation and tufa evolution have been analyzed, the natural changes are not found to be synchronic with tufa morphodynamics. Although environmental conditions did not undergo great changes, tufa dynamics went through profound changes during the Holocene in response to intense human usage. Four main stages related to the human-climate sequence can be differentiated. The first period was an erosive crisis at a time of very low human pressure related to the 8.2 Abrupt Change. The second was concentrated in the Atlantic period between 6.5 and 5.5 ka, when an increase in human activity coinciding with the expansion of megalithism and cattle farming led to deforestation and short moderate environmental changes. The third stage was characterized by tufa erosion and began immediately after the Millennium of Change (4.2–3.2 ka), coinciding with intense occupation of the land and profound human changes. Finally, a tufa sedimentation stage has taken place over the last two millennia, which has been interpreted as a response to the re-balancing of the geosystem. The close connection between human occupation and the evolution of the tufas permits us to establish a human-climate sequence with three distinct phases in places particularly favourable to human settlement.


spainupper ebro basintufa depositsholocenehuman impact