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ETAYO-SERNA, FERNANDO, National University of Colombia, SantafE de Bogota, Colombia

ABSTRACT: Ammonitina Speciation and Eustacy

It is herein proposed that major global sea level changes, as observed in the Colombian Cretaceous epicontinental deposits, can be linked to the concurrence of ammonitina of the following characters: (1) Mid-latitude, common, short lived, and (2) Low-latitude, rare, endemic types.

Recent model simulations of the circulation in the Tethyan Ocean show similar patterns to those of modern mid-latitude oceans. This pattern, a gyro-like flow, is affected by the location of the continents and changes in sea level.

It is suggested that during times of sea-level rise the gyro-like oceanic currents could reach the epicontinental domains and mixing of mid- and low-latitude "pseudo-larvae" could occur. Conversely, during times of sea level fall, the area affected by these occurrents would be limited to the central oceanic realm and "pseudo-larval" mixture would not occur. This could result in endemic (isolated) faunas and an increased speciation rate.

The above is exemplified by: (1) Early Late Valanginian sea level rise (SLR) results in the concurrence of mid-latitude species (MLS) Saynoceras verrucosus and low-latitude species (LLS) Santafecites santafecinus. (2) Early Barremian SLR results in the concurrence of MLS Parasaynoceras horridum and LLS Buergliceras buergli.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.