THERMAL EXCURSIONS IN THE OCEAN AT THE CRETACEOUS-TERTIARY BOUNDARY (NORTHERN MOROCCO) - DELTA-O-18 RECORD OF PHOSPHATIC FISH DEBRIS

High precision oxygen isotope analyses were made of phosphate extracte d from 17 samples of nektonic and benthic fish debris sampled across t he stratigraphic Cretaceous-Tertiary boundary in northern Morocco. A r efinement of the silver phosphate method was used to isolate phosphate from biogenic materials. Measured delta(18)O values of 18.6-20.5 part s per thousand are interpreted as reflecting high-resolution thermal v ariations that affected the ocean water column of the western Tethys. The warm (27 degrees C) water masses that characterized Maastrichtian times underwent rapid cooling and stabilized at an average temperature of 19 degrees C during the Dano-Montian and Thanetian. This period of constant and cool temperature was followed by a relatively rapid but more gradual warming to about 25 degrees C achieved in the Middle Ypre sian. Significant small shifts in delta(18)O Values between nektonic a nd benthic fauna recorded only during the stages of rapid warming or c ooling may correspond to averaged thermal differences within the water column that developed in response to global climatic changes. The ind icated temperature distribution could have been caused by thermal chan ges in the atmosphere rather than some signal carried by deep ocean cu rrents. The oxygen isotope data coupled with previous measurements of REE and epsilon(Nd(T)) on the same samples support the suggestion that paleo-Pacific westward currents progressed as far as the northwestern part of the African platform at the end of the Cretaceous period.