On the late Miocene closure of the Mediterranean–Atlantic gateway through the Guadix basin (southern Spain)

Abstract

The late Miocene Mediterranean–Atlantic connection through southern Spain is generally thought to have closed during the late Tortonian, but accurate constraints on palaeobathymetry, shallowing rates and closure age are still lacking. We present integrated biostratigraphic (planktonic, benthonic foraminifera and mammals) and magnetostratigraphic results from the marine to continental La Lancha section of the Guadix Basin, refining the chronology for the Miocene–Pliocene sedimentary sequences of this basin that occupied a central position in the marine gateway. In addition, we perform palaeobathymetric analyses on the marine sedimentary sequence to reconstruct sea level fluctuations and vertical motions. Deposition of the Lower Marine Unit took place between 8.1 and 7.85 Ma with accumulation rates of ∼ 1 m/kyr. A rapid shallowing from palaeodepths of 500–300 m to a depth of 300–200 m took place at ∼ 8.0 Ma coinciding with a decrease in downslope transport. Surprisingly, no shallowing trend has been observed towards the unconformable contact with the Transitional Unit, which was deposited in a shallow (∼ 90 m) marine environment. The youngest open marine marls are still indicative for a palaeodepth of > 200 m. This leads to the conclusion that fully marine environments in Guadix persisted until at least 7.85 Ma. The palaeomagnetic polarity pattern of the Upper Continental Unit, in combination with the presence of the murid Paraethomys meini in the basal part of this sequence, indicates that the entire continental unit at La Lancha is attributed to the latest Messinian–Zanclean time. This age is in strong contradiction with previous correlations to the late Tortonian. Consequently, we conclude that a major hiatus of at least 2 Myr, comprising most of the Messinian stage, is present in the Guadix basin. Therefore a late Tortonian closure age of the Mediterranean–Atlantic gateway through Guadix has not been confirmed by our results, so that the possibility of a Messinian gateway through southern Spain cannot be completely ruled out.