Magnetostratigraphy and paleontology of Aït Kandoula basin (High Atlas, Morocco) and the African-European late Miocene terrestrial fauna exchanges

Abstract

A magnetostratigraphic study has been carried out on a middle Miocene to upper Pliocene lacustrine sedimentary deposit in the central part of the Aït Kandoula basin, which contains micromammal faunas and is situated in the southern High Atlas (Morocco). In total, 113 samples were subjected to paleomagnetic analysis: 60 out of the 113 studied samples representing 52 different stratigraphic levels yielded a paleomagnetic direction and at least the polarity could be recognized in 42 specimens. Eleven specimens were submitted to AF demagnetization. The mean direction for normal-polarity samples was D = 349.4, I = 50.7 (N = 36, α 95 = 4.5, k = 27) and for reversed polarity samples D = 191.2, I = −53.4 (N = 16, α 95 = 12.32, k = 9). These results yielded a polarity sequence which we interpret as spanning from Chron C5n.2n to the beginning of Chron C3n.4n. This interpretation relies on biostratigraphic data previously proposed for a part of the continental fauna found in the basin. This result is in agreement with the 40Ar/ 39Ar dating previously carried out on a volcanic ash layer, which provided an age of 5.9 ± 0.5 Ma [1] and which is shown here to be reversely magnetized. This layer is correlated here with the reverse polarity zone corresponding to Chron C3r. Biostratigraphic studies on the same section have shown that the micromammal levels extend here only from middle Vallesian to upper Turolian (upper Miocene). Four localities have yielded western European species of micromammals, indicating trans-Mediterranean terrestrial faunal exchanges between these two continents during the late Miocene. The European murid rodent Occitanomys is recorded for the first time in North Africa in level 8 of the Afoud section, an age younger than 5.32 Ma being assigned to this level by the present study. Level 1 of the same section yields the lagomorph Prolagus cf. michauxi, with an age of 6.1 Ma. The magnetostratigraphic data suggest therefore that the beginning of terrestrial faunal exchanges between North Africa and Western Europe took place in subchron C3An.1n, at about 6.1 Ma, some 0.4 Myr before the beginning of the Messinian salinity crisis.