A.J. van der Meulen

A new chronology for the middle to late Miocene continental record in Spain

Abstract The first detailed chronology for the middle to late Miocene continental record in Spain is presented, based on high-resolution magnetostratigraphic data of mammal-bearing sections which were studied in several basins (Calatayud-Daroca, Teruel, Valles-Penedes, Duero and Jucar-Cabriel). Our results indicate that these sections compose an almost complete magnetostratigraphic succession from the lower Aragonian (MN4) to the middle Turolian (MN12). Seven successive Mammal Neogene (MN) zone boundaries are directly dated in these sections, which often contain faunas of two successive zones in superposition. The three oldest boundaries are dated in the Aragonian type area (Calatayud-Daroca Basin). The MN4/MN5 boundary (Vargas section) occurs in chron C5Cr(o) with a corresponding age of 17.26 ± 0.01 Ma, the MN5/MN6 boundary (Aragon section) in chron C5ACn(0.8), with an age of 13.75 ± 0.03 Ma, and the MN6/MN7–8 boundary (Aragon section) in the interval C5Ar.1n–C5Ar.3r with an age of 12.75 ± 0.25 Ma. The MN7–8/MN9 (Aragonian/Vallesian) boundary, occurring in chron C5r.1n at 11.1 Ma, and the MN9/MN10 boundary, in chron C4Ar.3r at 9.7 ± 0.1 Ma, are recorded in the Valles-Penedes Basin (Vallesian type area) and are supported by the results from the Duero Basin (Torremormojon section). In the Turolian type area (Teruel Basin), the MN10/MN11 (Vallesian/Turolian) boundary (La Gloria section) occurs in chron C4An(y) at 8.7 ± 0.1 Ma. Taking into account the pre-existing data from the Jucar-Cabriel Basin, the MN11/MN12 boundary (Cabriel Valley section) is recalibrated to C4n.1n, at an age of 7.5 ± 0.1 Ma.

Magnetostratigraphic dating of the middle Miocene climate change in the continental deposits of the Aragonian type area in the Calatayud-Teruel basin (Central Spain)

The exceptionally dense mammalian faunal record of the Aragonian type area in Central Spain shows that an important climate change towards a cooler and more humid climate is recorded during the Neogene Mammal Zone MN 5 [1]. The magnetostratigraphic results from mammal-bearing middle Miocene continental sections in the Aragonian type area indicate that the onset of this climate change, at the MN 4/MN 5 boundary, occurs in the reversed chron C5ACr and has an age of 14.1 Ma, according to the geomagnetic polarity timescale (GPTS) of Cande and Kent [2]. This age is consistent with the age estimate of 14.1-14.05 Ma for the main increase in 6 ~SO in the marine record [3]. These independent observations of time-equivalent cooling in both continental and marine records confirm and accurately date a global cooling event in the middle Miocene. The age of 14.1 Ma for the MN 4/MN 5 boundary is significantly younger than previously recorded in continental timescales [4,5]. This results in a longer duration, by approximately 3 Myr, of the MN 4 zone, which is consistent with the many important faunal changes occurring in MN 4. Furthermore, the MN 5/MN 6 boundary occurs in chron C5ACn (13.8-13.9 Ma) and the MN 6/MN 7-8 boundary in the interval C5Ar.ln-C5Ar.3r (12.7-13.0 Ma).

Updated Aragonian biostratigraphy: Small Mammal distribution and its implications for the Miocene European Chronology

This paper contains formal definitions of the Early to Middle Aragonian (late Early–Middle Miocene) smallmammal biozones from the Aragonian type area in North Central Spain. The stratigraphical schemes of two of the best studied areas for the Lower and Middle Miocene, the Aragonian type area in Spain and the Upper Freshwater Molasse from the North Alpine Foreland Basin in Switzerland, have been compared. This comparison allows the analysis of the order of shared mammal events in the two countries, and the quantification of the resulting asynchronies based on their temporal correlations. The order of the events is very similar in Spain and Switzerland. In order to estimate the diachrony, two age-model options are used for the Swiss record. Our preferred option yields no discrepancies with SW European paleomagnetic and radiometric calibrations of the Ramblian and Early Aragonian bioevents. All Swiss first taxa occurrences precede those in the Aragonian type area by 0.74Myr on average. The asynchronies (1-2Myr) of the species arriving in the late Middle to early Late Aragonian may be higher than in the Early Aragonian (0-1Myr). The implications for the biochronological mammal Neogene system are discussed. Evidence is given confirming the unfeasibility of a formal European biozonation, since it is realised, that 1) most indicator species and many genera of rodents yielding the most detailed zonations have limited geographical ranges hampering recognition of the mammal Neogene zones; and 2) first and last taxon occurrences are diachronical. Therefore, the mammal Neogene system based on a sequence of time-ordered reference localities is preferred to the one based on selected bioevents “developed in widespread geographic areas”.