Holocene aeolian development in Central Spain; chronology, regional correlations and causal processes

Abstract

Extensive areas in the southern part of the Duero Tertiary Basin (Central Spain) are covered by aeolian sands. Presently, the aeolian system is relict but in its origin and development it can be described as a “wet aeolian system”. Climatic and environmental changes during the Holocene are typified by alternating humid and arid periods. These are recorded in the sedimentary record as either organic-rich sandy palaeosols or clean aeolian sand, respectively. Palaeosol dating (12 radiocarbon dated samples) and stratigraphical and sedimentological analysis of several dunefields in quarries and boreholes allow the distinction of four periods of palaeosol development since the Allerød. Aeolian sediments commonly rest on fluvial deposits, which were themselves the major source area for aeolian sands. These fluvial deposits have an age of about 14,000 cal yr BP. The first phase of aeolian activity postdates these fluvial sediments and has an upper age of about 12,000–11,700 cal yr BP, probably corresponding to the last cold oscillation of the Lateglacial (Younger Dryas). The second phase ranges from about 11,500 to 9500 cal yr BP, during which period the majority of dunes in the Tierra de Pinares area formed. This is also a major phase of aeolian activity in other areas of the Iberian Peninsula. A third and probably discontinuous phase of aeolian activity took place between 6800 and about 3000 cal yr BP. The age for this phase is supported by the presence of Visigothic burial sites covered by aeolian sands. The presence of charred material and degraded slipfaces clearly indicate stabilisation by vegetation and the final degradation of the aeolian system at the end of the fourth aeolian phase (990–540 cal yr BP). Minor aeolian activity has also occurred subsequently in this area, since aeolian sand movement was even reported in the 20th century. The aeolian phases can be tentatively correlated with aeolian phases in Europe. Aeolian activity tends to occur regionally during specific time-intervals, especially in dunefields with little human disturbance. This argues for a broad climatic forcing in Holocene aeolian accumulation, such has been previously suggested for the little ice age. The precise timing of these phases, however, is not strictly coincident, probably due to the delayed responses of aeolian environments to climatic and subsequent vegetation change.