Magnetostratigraphy of the Baoji loess-paleosol section in the north-central China Loess Plateau

Abstract

The Baoji Section is judged to be the most complete, accessible Quaternary loess-paleosol section in the north-central China Loess Plateau; it is located 5 km north of the city of Baoji. It contains 37 paleosols and was recently named the type-pedostratigraphic section. The pedostratigraphic units (geosols) of the Baoji Section can be correlated throughout the Loess Plateau by a combination of magnetostratigraphy, and character, position and association of pedostratigraphic units. Magnetic properties were determined from 483 samples taken from 159 m of loess that overlies the Red Clay formation. All major reversals that occurred in the last 2.5 Ma were recorded. The Brunhes/Matuyama boundary occurs at a depth of 58.5 m within loess unit L 8, the Jaramillo Subchron between 72.0 m in loess unit L 10 and 76.4 m in paleosol S 11, the Olduvai Subchron between 125.5 m in loess unit L 25 and 131.5 m in loess unit L 27, and the Gauss/Matuyama boundary at 157.8 m within loess unit L 33, just above the contact with the Red Clay formation. This is the only known site where all major magnetic reversals are clearly defined in distinct field identifiable loess-soil units in one section. The magnetostratigraphy of the Baoji Section is thus recommended as the type section for the Loess Plateau.