AMMONITES NEAR THE CRETACEOUS/PALEOGENE BOUNDARY IN NORTHWESTERN MOROCCO

The Cretaceous/Paleogene boundary section in northwest Morocco is world famous for its vertebrate fossils. However, it also contains abundant ammonites (Baculites anceps). We present a lithostratigraphic and biostratigraphic column based on three sections representing the upper Maastrichtian and lower Paleocene. The sections are mostly composed of phosphatic beds with intermittent limestone layers. Biostratigraphic analysis based on nannofossils permits a delimitation of the boundary. However, it appears that the boundary itself is unconformable. The ammonites occur in two limestone beds approximately 8 and 10 m below the boundary, representing the upper, but not necessarily the uppermost Maastrichtian. The ammonites occur in flood abundance (hundreds to thousands of specimens) and consist mostly of adults, possibly microconchs and macroconchs. The baculites are oriented northwest-southeast, providing information about prevailing current directions. Many of the shells are encrusted with bryozoans. The genus Baculites is one of the most widespread ammonites at the end of the Cretaceous and is purported to have survived the K/Pg boundary for several hundred thousand years. This site thus contributes to our understanding of the world-wide distribution of ammonites at the end of the Maastrichtian.