A Miocene (23–12.5 Ma) continental paleotemperature record from the northern Mediterranean region (Digne-Valensole Basin, SE France)

During the Middle Miocene the Earth’s climate shifted from a warm phase, the Miocene Climatic Optimum (MCO, 16.9–14.7 Ma), to a colder phase associated with the formation of major and permanent Antarctic ice sheets. This climatic shift, the Middle Miocene Climatic Transition (MMCT, 14.7–13.8 Ma), had significant impact on the composition and structure of major biomes (e.g. Jimenez-Moreno & Suc, 2007) and impacted worldwide ocean circulation (Holbourn et al., 2014) as well as terrestrial temperature and precipitation patterns (e.g. Methner et al., 2020). While the MCO and the subsequent MMCT are well described in marine records, quantitative continental paleoclimate records are still lacking when it comes to constraining the magnitude and rate of terrestrial environmental change. Collectively, δ¹⁸O, δ¹³C and Δ₄₇ data from soil carbonates provide information about past environmental and climatic conditions, such as (seasonality of) precipitation, soil temperature as well as vegetation patterns. The formation of soil carbonates is mainly controlled by the interplay of environmental factors such as soil water composition, soil temperature, and soil CO₂. We compare the stable (δ¹⁸O, δ¹³C) and clumped (Δ₄₇) isotopic composition of pedogenic carbonate nodules of the Digne-Valensole Basin (SE France) with time equivalent counterparts from central Europe (Northern Alpine Molasse Basin, Switzerland) and present a ca. 23 – 12.5 Ma biostratigraphically-controlled clumped isotope paleotemperature record from the SW-foreland of the European Alps. Alluvial fan deposition and soil formation in the Digne-Valensole Basin occurred near sea level as documented by the intercalation of marine and continental facies (Cojan et al., 2013). Our Δ₄₇ results from the Digne-Valensole Basin indicate relatively warm and stable carbonate formation temperatures (ca. 32°C) for the Early Miocene (23–19.5 Ma) followed by enhanced temperature fluctuations attaining maximum values at the onset of the MCO. The Digne-Valensole temperature pattern correlates with age-equivalent Δ₄₇ temperatures from the Northern Alpine Foreland Basin. In both records, significant climatic changes can be observed at the onset of the MCO and the MMCT, which are documented by major rapid shifts in paleotemperatures (ca. 15°C within 300 ka). However, the proximity to the Mediterranean Basin is clearly visible in the Digne-Valensole records as expressed in rather high δ¹⁸O values of meteoric water that average ca. −3.5 ‰. Combining our data with the Northern Alpine foreland records results in a coherent climate pattern for the Alpine foreland during the Middle Miocene.

 

Cojan et al. (2013) https://doi.org/10.2113/gssgfbull.184.6.583

Holbourn et al. (2014) https://doi.org/10.1130/G34890.1

Jimenez-Moreno & Suc (2007) https://doi.org/10.1016/j.palaeo.2007.03.040

Methner et al. (2020) https://doi.org/10.1038/s41598-020-64743-5