99646 doi 10.1344/105.000001670 articleid 16965728v10n3p209 eng Astibia, H. Universidad del País Vasco. Departamento de Estratigrafía y Paleontología Increasing size and abundance of microbialites (oncoids) in connection with the K/T boundary in non-marine environments in the South Central Pyrenees A layer rich in giant microbialites, developed within continental deposits of the Tremp Formation (South-Central Pyrenees) in the aftermath of the end-Cretaceous mass extinctions, is here reported for the first time. Its stratigraphic location just above the Latest Maastrichtian Reptile Sandstone unit, and a characteristic 13C anomaly, are clear proofs linking this so-called “z” layer to the K/T boundary. The great abundance of microbialites, their outsized dimensions (oncoids with coating thickness up to 1.2m; average >50mm), and the great lateral continuity of the “z” layer in the study zone, support the hypothesis that these giant microbialites may represent disaster forms linked to the latest Mesozoic crisis. To our knowledge, this is the first time a record of this type is reported in continental realms. Other large continental oncoids and stromatolite constructions (e.g., in the Late Palaeogene deposits of the Pyrenees, Ebro basin, and Mallorca island) differ from those of the “z” layer in occurring in carbonate rocks and in having less lateral continuity, but they could also have been favoured by palaeoenvironmental crises, such as the global Eocene hyperthermals, Early Eocene Climatic Optimum, Middle Eocene Climatic Optimum, and the climatic cooling of the Eocene-Oligocene transition. It is thus possible that some layers of microbialites may record biotic crises in continental series, as they do in the marine record. Tots els drets reservats http://www.europeana.eu/rights/rr-f/ Anglès Article de fons K/T boundary Oncoids Non-marine environments South Pyrenean basin info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion López-Martínez, N. Universidad Complutense de Madrid. Departamento de Paleontología Elorza, J. Universidad del País Vasco. Departamento de Mineralogía y Petrología Vicens, E. Universitat Autònoma de Barcelona. Departament de Geologia Vol. 10, Núm. 3 (Setembre 2012), p. 209-226 Geologica acta 1696-5728 18 3771834 http://ddd.uab.cat/pub/geoact/geoact_a2012m9v10n3/geoact_a2012m9v10n3p209.pdf 0209 226 Setembre 3 10 geoact_a2012m9v10n3 2012 ARTPUB UAB GEOACT artpubuab oai:ddd.uab.cat:99646 driver