DELTA-O-18 VALUES OF COEXISTING BRACHIOPODS AND FISH - TEMPERATURE DIFFERENCES AND ESTIMATES OF PALEO-WATER DEPTHS

To estimate vertical thermal gradients and paleo-water depths to marin e platforms we present a new method based on the difference between de lta(18)O values of contemporaneous brachiopod carbonate and fish phosp hate. Present-day marine fauna of well-known ecology from the surface to the sea floor record isotopic temperatures that agree with measured temperatures. We predict distributions of isotopic data that result f rom sampling strategy, basin morphology, and fauna ecology and discuss limitations. Application of the method to the Jurassic Paris-London b asin gives vertical thermal variations of up to 14 degrees C associate d with depths varying from a few meters to 170 +/- 30 m. The estimated depths are minimum values and are greater than those estimated from s edimentological criteria for this ancient epicontinental sea.