The Basque coastal sections of the K/T boundary – A key to understanding “mass extinction” in the fossil record

 lnvestigations at the K/T boundary section al Zumaya, northern Spain, underline importance of this in (1) establishing a Maastrichtian ammonite zonation and (2) understanding "mass extinctions" fossil record. "Mass extinction" can be restricted to two groups oceanic surface plankton. Ammonites inoceramids exhibit gradual decline through late Cretaceous, as probably also do Temperate belemnites bulk involved vertebrates. Most these disappear long time before boundary. Compared with available environmental factors, course diversity perfectly parallels global sea level changes. Times high extinction rates (e.g. era system boundaries) coincide times maximum regressions, while subsequent evolutionary radiations match new rise. There is no need for any cosmic catastrophy explain most invertebrate vertebrate groups. Coeval short-time plankton itself, following depositional changes were observed: minor (positive well negative) temperature, clay sedimentation, enrichment iridium noble metals, occurrence sanidium spheres shocked quartz, carbon strontium isotopes. Ali events used support Alvarez hypothesis impact But they are much easier explained by increasing explosive volvanicity which, on other hand, might correlate time-equivalent magnetic reversals.