--> Abstract: Delta{18}O and Delta{13}C Composition of Middle Cretaceous Platform Interior Dolostones: Implications for Diachronous Erosion of the Florida Escarpment, Eastern Gulf of Mexico, by R. P. Freeman-Lynde and J-W. Moon; #90987 (1993).

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FREEMAN-LYNDE, RAYMOND P., Department of Geology, University of Georgia, Athens, GA; JAI-WOON MOON, Department of Geology, University of Georgia, Athens, GA. (Now at: Korea Ocean Research & Development Institute, Ansan, Seoul)

ABSTRACT: Delta{18}O and Delta{13}C Composition of Middle Cretaceous Platform Interior Dolostones: Implications for Diachronous Erosion of the Florida Escarpment, Eastern Gulf of Mexico

The mean stable oxygen and carbon isotopic composition determined for fifty 10-40 mg microsamples of Middle Cretaceous (Aptian-Cenomanian) peritidal and lagoonal dolostone dredged from the Florida Escarpment at Florida Canyon (24 degrees 30'N) and at 25 degrees N and 27 degrees N is (approx.) +3 o/oo delta{18}O PDB, +3 o/oo delta{13}C PDB. However, mean isotopic composition varies by geographic position and depth. The heaviest delta{13}C and lightest delta{18}O composition occurs in dolostone dredged from Florida Canyon at depths greater than 2800 meters. The delta{18}C composition of samples taken from depths shallower than 2800 meters at all three locations is isotopically lighter than that of deeper samples.

The delta{18}O composition of the Florida Escarpment dolostones is heavier than that of coeval dolostones recovered at ODP Site 627 (north flank of Little Bahama Bank), while the delta{13}C composition is lighter. We feel that the ODP Site 627 dolostones preserve the original isotopic composition of dolomite deposited on the Florida-Bahama Platform during the Middle Cretaceous, and that the isotopic composition of the Florida Escarpment dolostone has been altered by its exposure to deep-marine water (following erosion of the escarpment). The deep samples from Florida Canyon have an isotopic composition closest to that of the Site 627 samples, suggesting that they have been altered least. The shallower samples have a greater difference, reflecting greater alteration.

We attribute these different degrees of alteration to different lengths of time of exposure to deep-marine water as a result of the diachronous erosion of the Florida Escarpment, with Florida Canyon and the deeper portions of the escarpment experiencing the latest erosion.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.