Vegetation cycles in a disturbed sequence around the Cobb-Mountain subchron in Catalonia (Spain)

A 52-m-long lacustrine sequence was recovered from the basin of Bobila-Ordis, near Banyoles (N-E Spain). The presence of Early Biharian rodent teeth (Early Pleistocene) and of a c. 9-ka-long palaeomagnetic reversal (Cobb-Mountain subchron) suggests an age centred on 1.2 Ma, making this sequence one of the very few well-dated terrestrial sequences of that age in Europe. The first 22.5 m (with an interglacial character) are very homogenous owing to sedimentation affected by underwater springs. In the middle part of the sequence, palynological analyses, supported by sediment visual description, ostracod and mollusc assemblages, allow the reconstruction of one glacial-interglacial cycle, with vegetation succession. A second incomplete climatic cycle is recorded in the top part, within a shallower lake. These brief interruptions in the two climatic cycles are possibly linked to lake bank collapse caused by Hippopotamus amphibius or faulting linked to karst. The succession is likely to correlate to MIS 36-33. The Bobila-Ordis lacustrine series (including two other nested lakes) covers altogether some sections of four glacial and four interglacial periods, not all contiguous.