Vallesian

The Vallesium is a regional level in the terrestrial Neogene. It corresponds to the zone MN 9 and 10 of the European land mammal chronology ( ELMMZ = " European Land Mammal Mega - Zones" ). The Vallesium is underlain by Astaracium and overlaid by Turolium.

History and type locality

The stage was proposed by Miquel Crusafont i PAIRO (1950) and named after the Vallès - Penedès Basin, Catalonia, where the type locality is located.

Definition

The lower limit is defined by the onset of large mammal species Hippotherium, Decennatherium and Machairodus. In the small mammal animals represents the first appearance of the genus Cricetulodon the base Represents the end of the stage ( and the beginning of Turolium ) is marked by the first appearance of the species Hyaenictis almerai, Adcrocuta eximia, Microstonyx major, Tragoportax gaufryi. For small mammals, these are the species and genera Rotundomys, Pliopetaurista, Schreuderia and Progonomys cathalai. The Vallesium is currently correlated with a large part of the Lower and Middle Tortonian, the lower chronostratigraphic stage of the Upper Miocene. Geochronological corresponds approximately to the period of 2.4 million years (from 11.1 before to 8.7 million years ago ).

Subdivision

The stage is divided into two biozones MN 9 and MN 10. Occasionally, the stage is divided into a lower and an upper Vallesium, the lower the biozone Vallesium MN 9 and the upper Vallesium the biozone 10 corresponds.

Vallesium crisis

As Vallesium crisis (English: Vallesian Crisis ) an abrupt change of flora and fauna is referred to around 9.6 million years, which is occupied among other mammals. The changes in species composition was first detected in the Vallès - Penedès Basin and was the result of a significant change in climate in Europe and in the northern and eastern Africa. From the Spanish Mediterranean region starting disappeared in Western and Central Europe, the subtropical evergreen forests as a result of gradual cooling; in its place was followed by deciduous trees and in some southern regions steppes. This had the effect, among other things, that most until then living in Europe genera of anthropoids - including Dryopithecus, Ankarapithecus and Graecopithecus - extinct. As a cause of climate change is considered a change of ocean currents, which in turn is associated with the unfolding of the Himalayas and the Tibetan highlands.