Pleistocene paleoenvironmental evolution at continental middle latitude inferred from carbon and oxygen stable isotope analysis of ostracodes from the Guadix-Baza Basin (Granada, SE Spain)

摘要

A representative paleoenvironmental reconstruction of continental middle latitude from ca. 2 my to the upper part of Middle Pleistocene (279 +/- 77 ky) was obtained from the carbon and oxygen stable isotopes analyzed in ostracode shells (Cyprideis torosa) recovered in the Guadix-Baza Basin (SE Spain), an intramontaneous closed depression filled by alluvial and lacustrine sediments. This study was performed along a 356-m-thick composite section, dated previously by paleornagnetism and the amino acid racemization method. delta C-13 and delta O-18 profiles reflected changes in temperature, the evaporation/infill ratio in the water bodies and the amount of rain. delta C-13 is also affected by changes in plant biomass: periods with high delta C-13 and delta O-18 values are associated with warm and dry regimes, and with less vegetation, which, in some cases, coincide with the development of displacive gypsum crystals, whereas low delta C-13 and delta O-18 values correlate with cold and humid episodes, which cause more vegetation biomass and, therefore, increasing the input of isotopically light carbon. Intermediate delta O-18 values are linked to temperate dry or humid episodes when they coincide with high or low delta C-13 values, respectively. 86 paleoclimatic events were distinguished in the Pleistocene record from the delta C-13 and delta O-18 profiles. From both the statistical analysis of the geochemical data and the geological observations, four Cold and Humid Long Periods (low delta O-18) and four Warm and Dry Long Periods (high delta O-18) were defined. This differs with respect to the palcoclimatological behavior established for the Northern Hemisphere where during cold periods (glacial), no water was available while permafrost conditions persisted, whereas in warm episodes (interglacial), higher precipitation rates occurred. Good correspondences between the Guadix-Baza Basin paleoclimatic record and a marine oxygen-isotope sequence, two continental cores and other long Mediterranean paleoenvironmental records (pollen sequences from Israel) were found, which suggested that climate changes in the Guadix-Baza Basin were in tune with global climatic changes. 0 2006 Elsevier B.V All rights reserved.