Abstract

Ammonites and inoceramid bivalves were stratigraphically collected from lower and upper Maastrichtian units in continuous exposure along the seacoast near Zumaya, Spain. Three ammonite teilzones can be recognized: (1) a lower zone correlative with parts of the Globotruncana ganserri planktonic foram zone and characterized by numerous inoceramids among three different species as well as Pachydiscus neubergicus, a noded Baculites, Polyptychoceras sipho, and Hauericeras renbda; (2) a middle zone that has no inoceramids but that has Pachydiscus fresvillensis and P. neubergicus and is correlative with the lower parts of the Abathomphalus mayaroensis Zone (planktonic foram); and (3) an upper zone that has P. colligatus and is correlative with the upper parts of the A. mayaroensis Zone. These three teilzones may be the basis for a Tethyan, facies-wide ammonite zonation of the Maastrichtian. The four main components of the fossil record at the Zumaya section show differing range characteristics with respect to the Cretaceous/Tertiary (K/T) boundary exposed in this section. The inoceramids disappear at the top of the lower Maastrichtian, except for the small enigmatic form Tenuipteria, which has a restricted range in the uppermost levels of the Cretaceous. Ammonites range upward to levels approximately 10 m below the boundary. Most larger planktonic forams and many nannofossil species disappear within several centimetres of the boundary. Echinoid fossils range up to, and possibly across, the K/T boundary. The Zumaya section is thus characterized by apparently nonsynchronous or graded extinctions of most of its fossil content.

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