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 Globotruncana gansseri zone, Inoceramus remains disappear from five stratigraphic sections in the Basque region of France and Spain in the lower Abathomphalus mayaroensis zone, approximately 2.5 m.y. before the Cretaceous-Tertiary boundary. Several lines of evidence demonstrate that these shell fragments are preserved in place and accurately record the pattern of the decline and disappearance of the group. The dominant taphonomic process seems to have been passive disaggregation of the shell as shell proteins decayed. The resulting shell fragments were dispersed only locally by burrowing organisms. Shell fragments decline in abundance over tens of meters of section and there are subtle differences between sections which suggests Inoceramus was eliminated by gradual changes in ecological conditions that affected the basin roughly simultaneously but with some geographic variability.