Definition and global correlation of the Santonian Campanian boundary
Review of biostratigraphical evidence from different regions shows that criteria used by workers on various marine fossil groups to define the Santonian-Campanian boundary differ considerably in relative age and position. Probably the most widely recognizable of these criteria is the extinction of the distinctive crinoid Marsupites testudinarius (North America, Europe, Asia, north Africa, Australia), which, coincides exactly with two separate definitions of the boundary - appearances of the ammonite Placenticeras bidorsatum and the belemnite Gonioteuthis granulataquadrata - and may also coincide with a third - entry of the planktic foraminiferan Globotruncana elevata. A comparison of evidence from upper Santonian and lower Campanian successions in widely separated regions allows us to place a series of important biostratigraphical markers in correct order. Defining the boundary at the extinction of M. testudinarius corresponds to a 87Sr/86Sr of 0.707479, and a small positive excursion in δ13C. The base of magnetochron 33R, generally considered to coincide with, or fall just above the base of the Campanian, is shown to lie within the upper Santonian Uintacrinus socialis Zone.