Late Pliocene continental magnetochronology in the Guadix-Baza Basin (Betic Ranges, Spain)

Abstract

The late Pliocene shallow lacustrine sequences in the Guadix-Baza basin (Betic Ranges, southeast Spain) are a suitable setting for mammal chronology because of the abundance of rich, mammal-bearing sites. Stratigraphic superposition of late Ruscinian and Villanyian vertebrate fossils makes the Galera Section very appropriate for magnetostratigraphic dating. Sediments are characterized by a weak but measurable magnetization predominantly carried by magnetite. Other remanence carriers, such as iron sulphides and hematite, may be significant only in some particular lithologies, such as dark palustrine organic silts and red alluvial beds, respectively. Direct correlation of the Galera Section to the geomagnetic polarity time scale provides a reliable dating of the late Ruscinian and Villanyian mammal units. The Ruscinian/Villanyian boundary (MN15/MN16) is found to occur in the lower Gauss chron, and approximately correlates to the 3.3 Ma cooling event observed in stable-isotope and planktonic foraminifera deep sea records. The earliest occurrence of late Villanyian assemblages (MN17) in the lower part of the Matuyama chron allows dating of the early/late Villanyian boundary (MN6/MN17) to approximately 2.4–2.6 Ma. Based on the presence of late Villanyian assemblages underlying the base of the Olduvai chron, a maximum age of 1.95 Ma (top of C2r) is attributed to the Villanyian/Biharian (MN17/MmQ) boundary. A 300 kyr sedimentary gap in the Galera Section is suggested to correlate with a probable early Villanyian hiatus, an hypothesis that agrees with the absence of fossils of this age elsewherein the Baza Formation.