Magnetobiochronology of Lower Miocene (Ramblian) continental sediments from the Tudela Formation (western Ebro basin, Spain)

Abstract

The calibration of European Lower Miocene continental stages is poorly constrained due to the lack of robust magnetostratigraphic data from continental sediments of this age. In this paper, we present the first magnetostratigraphic results from the mammal fossil-bearing continental sediments of the Lower–Middle Miocene Tudela Formation (western Ebro basin, Spain). The study is based on 331 paleomagnetic sites distributed along a 790-m-thick composite section. The resulting magnetostratigraphy provides an independent correlation to the geomagnetic polarity time scale and allows accurate dating of previously known and new Ramblian (upper Lower Miocene) fossil localities of the Tudela Formation. The new age constraints derived for the Tudela Formation fossil localities provide, together with a revaluation of other Iberian faunas, the first magnetochronology for the Ramblian continental stage. The lower boundary of the Ramblian is placed at the lower part of chron C6r (ca. 20.4 Ma), and the boundary between the lower and upper Ramblian is located at the middle of chron C6n (ca. 19.6 Ma). The upper boundary of the Ramblian, and hence the base of the Aragonian, is placed at the upper middle part of chron C5Cr (16.8–17 Ma). Our results also provide the first magnetostratigraphically dated MN3 faunas in Spain, which, together with a revaluation of other Iberian and European faunas, provide a revised calibration of European mammal zone MN3. The lower boundary of zone MN3 is placed at the boundary between chrons C6r and C6n (ca. 20.1 Ma), and its upper boundary is located at the upper middle part of chron C5Cr (16.8–17 Ma).