Magnetostratigraphy and biostratigraphy of Cretaceous-Tertiary continental deposits, Ager Basin, Province of Lerida, Spain
Abstract At Fontllonga (Northeast Spain, Province of Lerida) a nearly continuous outcrop covers the stratigraphic interval from the Maastrichtian to the Thanetian in continental deposits. Magnetostratigraphy of the section was determined from 72 samples. The magnetic polarity sequence was satisfactorily correlated with chrons 32R to 26R (top of Lower Maastrichtian to Lower Thanetian). Chron 29R, in which the K/T boundary occurs, is unambiguously recognizable considering the biostratigraphic data (charophyte, ostracod, palynomorph). The K/T boundary occurs in the uppermost part of the Microchara cristata subzone, which includes Late Cretaceous and Early Palaeocene species. This subzone is interpreted as an interval of crisis, following the Late Maastrichtian extinctions and preceeding the Palaeocene radiation. No Ir-rich horizon has been yet found in this section. The stratigraphic position of the last dinosaur remains, found in the chron 31N interval, leaves open the question of a causal link between the extinction of Cretaceous reptiles and the K/T event.