Plio-Pleistocene continental paleoclimate record from the Zújar section, Guadix-Baza Basin (SE Spain)

Abstract:

The intramontane Guadix-Baza Basin (SE Spain) preserves an extensive record of Neogene continental sedimentation during an interval of important global climatic and ecologic changes, including the onset Northern Hemisphere glaciation and the evolution of grassland biomes on several continents. Several localities within this basin represent mammal biostratigraphic reference sections for the Plio-Pleistocene of Western Europe, and have been the focus of much previous bio-, magneto-, and cyclostratigraphic work. Here we report new stratigraphic and geochemical results from one of these reference sections near the village of Zújar in the central part of the Guadix-Baza Basin. We interpret Plio-Pleistocene climatic history from lacustrine and pedogenic sediments at Zújar, based on new paleomagnetic results coupled with stable carbon and oxygen isotopic (δ¹³C and δ¹⁸O) analyses of carbonate and bulk organic matter, thin-section petrography, cathodoluminescence and scanning electron microscopy, and semi-quantitative X-ray diffraction.

Paleoclimatic variability in the Zújar section is reflected in the highly variable composition of carbonate-rich beds, which fluctuate between nearly pure micritic calcite and dolomite but commonly display mixed carbonate phases. The δ¹⁸O values of these carbonates are also highly variable (-8.2 to +1.9‰ VPDB) and are strongly correlated with dolomite content (r² = 0.79). The δ¹³C values are less variable (-8.8‰ to -4.2‰ VPDB) and are similar between calcite- and dolomite-rich samples. We interpret periods of wet climate and lake-level highstand from calcite-dominated beds with variable δ¹³C values and low (-7 to -8‰ VPDB), invariant δ¹⁸O values that likely represent equilibrium calcite precipitation from minimally evolved lake source waters. Several mixed-carbonate beds display covariant δ¹³C and δ¹⁸O, representing evaporative enrichment of lake waters during more arid periods. We interpret maximum aridity and lake-level lowstand in the Zújar section from dolomite-rich palustrine beds with evidence of subaerial exposure (root traces, microkarst). The δ¹⁸O values of these beds are up to 6‰ higher than that expected for dolomite in equilibrium with mean δ¹⁸O for the calcite-dominated beds, and likely represent waters heavily influenced by evaporation.