Hernández southern Pyrenees , Spain boundary in differing palaeogeographical settings from the The palynological record across the Cretaceous-Tertiary Geological Society

North American and Pacific spore-pollen records show a major extinction event at the Cretaceous Tertiary (K-T) boundary, and abrupt changes are similarly found in many marine organisms world-wide. In contrast, records from the Old World reveal little evidence of terrestrial vegetational change across the boundary. In order to improve the characterization of changes across the K-T boundary, palynological assemblages from two sections in the southern Pyrenees have been evaluated. The abundance and diversity of trilete fern spores are high in Maastrichtian samples and show a statistically significant decrease during the Danian. The 'fern spike' of low-diversity spores found elsewhere is not recorded in the Pyrenean region. Minor replacements of taxa across the K-T boundary are also noted, as well as an increase in inaperturate gymnosperm pollen in the Danian. Comparing our two examined sections with one another reveals important differences in angiosperm pollen composition. )ramatic floral changes have been documented across the Cretaceous-Tertiary (K-T) boundary in the North American and Pacific records. Here, a major extinction event in the plant record, and a sudden, brief increase in fern abundance (the 'fern spike'), have been correlated with an iridium anomaly related to an extraterrestrial impact at the boundary (Johnson et al. 2000; Vajda et al. 2001, and references therein). However, the palynological record in the Old World has not yet shown any appreciable changes during this critical period, which hinders the detection of the K-T boundary. ,_Jntil now, some of the best-documented continuous sections dated by biostratigraphy and magnetostratigraphy across the K-T boundary in Europe and Africa have failed to show any significant palynological changes (M6on 1990, 1991; M~dus et al. 1988, 1992; Ldpez-Martinez et al. 1999; Mayr et al. 1999). This lack of a clear palynological K-T boundary in the Old World contrasts with the abrupt change observed in the fossil record of many protists (coccoliths, planktonic foraminifera) and metazoans (molluscs, sharks and reptiles). In the Pyrenean Basin, a thick succession of red beds characterizes the Tremp Formation, which dates from Late Cretaceous to Early Tertiary. Within this succession Ashraf & Erben From: BEAUDOIN, A.B. & HEAD, M.J. (eds) 2004. Geological Society, London, Special Publications, 230, "ond ,m 9~04 (1986) recorded an impoverishment of plant species, which they interpreted as representing the palynological K-T boundary. However, biostratigraphic and magnetostratigraphic dating subsequently demonstrated an older age for this interval at around the CampanianMaastrichtian transition (sensu Gradstein et al. 1995; L6pez-Martinez et al. 1999; Ard~vol et al. 2000; L6pez-Martinez et al. 2001). A decrease in plant diversity is recorded in other Old World regions (Stets et al. 1996; Markevitch et al. 2000), but this event can be correlated better with the Campanian-Maastrichtian transition than with the K-T boundary. Therefore, no regional events in the Old World Late Cretaceous palynological succession have yet been demonstrably correlated with this boundary. The apparently smooth transition across the K-T boundary in the palynological record of the Old World may be due to incomplete sampling or to palaeoenvironmental factors. We have therefore studied the palynological record across the boundary in the south central Pyrenees (Spain) by comparing two sections about 50km apart in differing palaeogeographical