Palaeoenvironmental dynamics of an Early Miocene palaeolake in eastern Iberia: vegetation, climate, and hydrology

Abstract

The Rubielos de Mora lacustrine basin in eastern Spain is a key site for understanding Early Miocene ecosystems due to its exceptional fossil record, which preserves diverse taxa from multiple biological groups. Previous studies have interpreted the basin's vegetation and hydrology as reflecting varying degrees of xeric conditions, with some even proposing sub-desertic environments and steppe-like landscapes. These interpretations contrast with broader European trends, where forested environments predominated during the Early Miocene. Owing to these distinctive vegetation reconstructions, the basin has become central to discussions on southwestern European landscapes during the early Neogene. Here, we revisit the Rubielos de Mora Basin using a multiproxy approach that integrates palynological, diatom, and geochemical data from two well-studied surface sections from the eastern and western sectors of the basin to reassess its palaeoenvironmental evolution and situate it within the broader context of Cenozoic vegetation dynamics in Europe. Our results from both sectors converge on a consistent picture of regional vegetation dominated by diverse semi-open forests or woodlands during the Burdigalian. These habitats were mostly composed of thermophilous evergreen taxa adapted to relatively xeric conditions, possibly co-existing with mesic, deciduous elements. The flora of Rubielos de Mora reveals a largely forested ecosystem with increasing signs of xericity prior to the Miocene Climate Optimum. From a hydrological perspective, the Rubielos paleolake underwent alternating humid and dry phases, which affected lake productivity and water chemistry. Geochemical and palynological indicators suggest that these climatic fluctuations led to oxic–anoxic sediment cycles. Palaeoclimatic reconstructions indicate warm conditions during the Burdigalian, with mean annual temperatures of at least 16.8–18.5 °C and coldest-month means above 10 °C, suggesting a frost-free climate with pronounced seasonality.