Nature and age of Middle to Upper Quaternary basin deposits in the Zafarraya Polje (Southern Spain)

Abstract

The Zafarraya Polje is an endorheic tectonic basin located in the external zone of the Betic Cordillera. While geophysical information is available on recent tectonics and the general structure of the basin, the nature and age of basin deposits is poorly known. To elucidate the processes and the timing of sedimentary infill and geomorphogenesis within the polje (about 20 km2), a series of vibracorings were conducted down to 15 m below surface (b.s.). Sediments were sampled and analysed for magnetic susceptibility (Bartington MS field spectrometer), geochemical composition (portable XRF, Thermo Scientific; CN-elemental analysis, Elementar) and grain size distribution (conventional wet sieving and pipette method). Physical dating included age estimates by Optically Stimulated Luminescence (OSL) on samples taken from liner cores and AMS radiocarbon datings on humic acids. In addition, electrical resistivity measurements were carried out at the coring locations. In the eastern part of the polje, the uppermost basin fill consists of fluvial brown sand, silty loam and loamy clay with gravel layers accumulated by the Arroyo de la Madre, an ephemeral river draining the basin. At 7.5 m b.s., a palaeosol testifies a period of reduced sediment accumulation and geomorphodynamic stability. Near the ponor of Arroyo de la Madre in the western part of the polje, reddish brown clayey loam and clay occur near the surface of alluvial fans and pediments. These sediments represent reworked residual loams of carbonate weathering subsequently eroded from the hill sides. Shortly above the boundary between brown and red sediment layers, a palaeosol again documents a period of reduced geomorphodynamics. The uppermost basin fill thus provides detailed insight into the landscape evolution during the Middle to Upper Quaternary.

Resources

• Kehl 2012 QI abstract Zafarraya.pdf

Bibliography

Kehl, M. (2012): Nature and age of Middle to Upper Quaternary basin deposits in the Zafarraya Polje (Southern Spain). – In: Quaternary International, p: 238-239, DOI: 10.1016/j.quaint.2012.08.543