Paleoclimate instabilities during late Oligocene - Early Miocene in SW Europe from new geochemical climofunctions based on soils with pedogenic carbonate

In this study, two new climofunctions based on major elements are proposed from the study of 28 modern alluvial soils with pedogenic carbonate from NE Spain. The first climofunction relates a base ratio (CaO, K2O) to the mean annual temperature (MAT), and the second one the clayeness ratio (Al2O3/SiO2) to the mean annual precipitation (MAP). In both climofunctions, the use of the parent material ratio as normalizer gave the best results, taking into account the natural variability of alluvial deposits. Application of these climofunctions to 86 paleosols from Oligo-Miocene alluvial successions in southern France and central Spain was performed, and combined with morphological functions previously proposed, with the aim to build detailed paleoclimatic data for this key period of climate history. This work provides a high frequency record (range of 10s to 100 s kyr) of paleoclimate fluctuations, with estimated MAP from both methods very comparable (mean ~ 550 mm/yr). Estimated MAT and MARP (mean annual range of precipitations) mainly exhibit the same trends: 1) high values followed by a rapid decrease during the early Aquitanian (from 18.8 to 13.5 °C; from 80 to 20 mm), 2) a warming trend towards the middle Aquitanian (up to 16.6 °C, 90 mm), 3) a cooling (down to 13.4 °C, 40 mm) during the late Aquitanian – early Burdigalian. Comparisons with paleoclimate data from paleontological remains indicate similar MAT and two times lower MAP estimated from paleosols. However, consistency between estimated MAP from this study to previous paleopedological investigations in NE Spain suggests a regional climate pattern (southern France and central Spain) precursor of the Mediterranean conditions that developed during middle Neogene whereas humid conditions prevailed in the western coastal basins of Europe. Periods of large amplitude fluctuations in MARP and MAT are interpreted as reflecting the interrelation between the lower Miocene climate instability (Mi1, Mi1a events) and continental climate.