THE TAPHONOMY OF MAASTRICHTIAN INOCERAMIDS IN THE BASQUE REGION OF FRANCE AND SPAIN AND THE PATTERN OF THEIR DECLINE AND DISAPPEARANCE

After having been very abundant in the Early Maastrichtian Globotrunca na gansseri zone, Inoceramus remains disappear from five stratigraphic sections in the Basque region of France and Spain in the lower Abatho mphalus mayaroensis zone, approximately 2.5 m.y. before the Cretaceous -Tertiary boundary. Several lines of evidence demonstrate that these s hell fragments are preserved in place and accurately record the patter n of the decline and disappearance of the group. The dominant taphonom ic process seems to have been passive disaggregation of the shell as s hell proteins decayed. The resulting shell fragments were dispersed on ly locally by burrowing organisms. Shell fragments decline in abundanc e over tens of meters of section and there are subtle differences betw een sections which suggests Inoceramus was eliminated by gradual chang es in ecological conditions that affected the basin roughly simultaneo usly but with some geographic variability.