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Carbonate Megaturbidites: Examples from Gulf of Mexico and French Pyrenees

Larry J. Doyle, Robert Bourrouilh

Because carbonates seem to accumulate relatively slowly on tectonically stable margins, they are not usually considered candidates for the formation of large-scale turbidites. However, two carbonate megaturbidites--one from the Gulf of Mexico and one from the French Pyrenees--show that carbonates can accumulate at substantial rates and in tectonically active settings, and thus, commonly form turbidite sequences.

Although the Gulf of Mexico is considered a siliciclastic province, samples from Deep Sea Drilling Project Site 615, Leg 96, located in the southeastern gulf, revealed a massive carbonate turbidite more than 25 m thick. This unit occupies the interval between 488.2 and 513.7 m below the sea floor and can be traced seismically across the entire throat of the gulf. Carbonate constituents indicate that the unit was derived either from the carbonate outer margin of west Florida or from the Yucatan Peninsula. Apparently, part of these two areas periodically fails, injecting large carbonate masses that eventually become intercalated in the clastic sequence on the gulf floor. We documented sedimentation rates on the west Florida slope that range from tens to hundreds of centimeters/1,000 yea s.

The Cretaceous carbonate megaturbidite in the western French Pyrenees is more than 30 m thick in its most proximal exposure, and more than 10 m thick 90 km away. It was deposited in a tectonically active trough that accumulated several kilometers of carbonate flysch between the Iberian and European plates.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.