The Vallesian mammal succession in the Vallès-Penedès basin (northeast Spain): Paleomagnetic calibration and correlation with global events

Abstract

The integrated lithostratigraphic, biostratigraphic and magnetostratigraphic study of new and classical alluvial fan sequences in the Vallès-Penedès Basin (northeast Spain, Western Mediterranean) enabled a considerable refinement of the Vallesian mammalian succession in this basin and its correlation with the Magnetic Polarity Time Scale. Up to 12 new sections were logged and sampled in a search of mammal remains and a paleomagnetic analysis was carried out. The correlation among these sections was based on the small mammal content and the succession of magnetozones, enabling the establishment of four main composite sections (Les Fonts, Montagut, Terrassa and Viladecavalls). As a result, the Vallesian in the Vallès-Penedès Basin appears punctuated by four main mammalian events, which coincide with the appearance of the genera Hipparion, Cricetulodon, Progonomys and Rotundomys. The Hipparion event did not coincide with any further change in the associations of small and large mammals. The dispersal of the cricetid Cricetulodon, in its turn, involved the first set of extinctions in the Vallesian, affecting the rodent and carnivore and artiodactyl associations. The main break during the Vallesian coincided with the dispersal of the murids of the genus Progonomys and implied a sudden drop in the diversity of the rodent and artiodactyl species of warm wet-forested affinities. This phase is characterized by the association of the murid Progonomys and the cricetid Cricetulodon and includes the last record of hominoids in the basin. The replacement of Cricetulodon by the sigmodont cricetid Rotundomys was associated with the entry of some typical early Turolian species. According to the correlation established, it is concluded that the FAD of Hipparion in the Vallès-Penedès Basin is dated at 11.1 Ma, at the base of Chron C5r.1n. This data is congruent with other datings in Northern Africa and Eastern Europe, suggesting the isochrony of this event in the Mediterranean regions. The Cricetulodon FAD is dated to 10.4 Ma, in Chron C5n. The Progonomys dispersal, coincident with the late Vallesian Crisis, is dated at 9.7 Ma, in Chron C4Ar.3r. The Rotundomys FAD is dated at 9.2–9.3 Ma, in the upper part of Chron C4Ar.1n. The Vallesian mammal bioevents affected the peri-Mediterranean zones, including Northern Africa, and other regions in Northern and Western Eurasia. These paleofaunistic changes were caused by temperature descent from subtropical to warm-temperate conditions as well as by changes in the aridity balance and seasonality. This climatic evolution was the result of the interplay of diverse global events (cooling of the high latitude regions, growing of the Antarctica ice sheet, and enhancement of the thermohaline oceanic circulation) and of large-scale tectonic and paleogeographic processes (surface uplift of the Himalayas, the Tibetan Plateau and other tectonic reliefs, closing of gateways between the Mediterranean marine regions and the World Ocean). The magnetobiochronology resulting from the study of the Western Vallès sequences suggests a close chronological correlation between some of these global and regional processes and the Vallesian bioevents recorded.