Palaeoenvironmental changes in the Padul Basin (Granada, Spain) over the last 1 Ma based on the biomarker content
The n-alkane components of sediments were measured in 530 samples taken from a 107 m-long core in the Padul Basin (Andalusia, Spain) covering from the Lower Pleistocene (ca. 1 Ma) to the mid-Holocene (ca. 4.5 ka B.P.). We show that the relative percentages of the high molecular weight n-alkanes (C27, C29 and C31) are useful tools to reconstruct the ancient vegetation and palaeoclimatological evolution of this basin. On the basis of these proxies, we distinguished twelve long-term climatic periods linked to alternating dry/humid scenarios: 6 Dry Episodes alternating with 5 Humid Episodes were interpreted in the Pleistocene record, together with a final Episode covering the Holocene. Dry scenarios produced the recession of forests and the development of grasses, whereas the inverse pattern was interpreted during humid phases. The good correlation with the Guadix-Baza Basin record showed that, in most cases, dry periods coexisted with warm conditions, while humid ones were linked to temperate-colder conditions. Only during the last long-term Dry Episode of the Pleistocene, which coincided with the end of the Last Glacial Period, did low temperatures concur. The relative percentages of the high molecular weight n-alkanes also indicate rapid changes in vegetation produced by short-scale arid cycles during the last Glacial Period (< 100 ka B.P.), which are linked to the Heinrich Events and Younger Dryas. This interpretation has been confirmed by previous pollen analysis performed in the Padul Basin. Likewise, a correlation was observed with Marine Isotope Stages (MIS). These results show that vegetation responds to long-term cycles (orbital scale) and millennial-scale global cycles. Therefore, climatic variations in the Padul Basin responded to global climatic changes, although with local climatic effects. Good correspondence was also observed with elemental, isotopic and other molecular organic proxies, thereby amplifying the palaeoclimatological knowledge of the Padul Basin during the Pleistocene, especially in some spans that were previously unclear.