STEPWISE FAUNAL CHANGE DURING EVOLUTIONARY TURNOVER - A CASE-STUDY FROM THE NEOGENE OF CURACAO, NETHERLANDS-ANTILLES

Assemblages of reef corals through the Middle Miocene to Late Pliocene Seroe Domi Formation, in Curacao are described and statistically anal yzed to document patterns of change in these associations during a Lat e Pliocene Caribbean-wide episode of accelerated faunal turnover The d ata are based on large field collections made systematically at 73 loc alities within a sequence of bedded siliciclastics and coralgal limest ones near Sint Michielsberg. Geologic age dates are newly determined f or the sequence using high-resolution chronostratigraphic methods incl uding paleomagnetics and strontium-isotope analyses, and the localitie s are subdivided into five Locality-groups-Middle Miocene flatiron, La te Miocene salina-base, Mio-Pliocene salina-top, Early to Late Pliocen e ridges, and Late Pliocene sea-cliff Using a consistent set of morpho logic characters, a total of 99 species are identified in the collecti ons, and their occurrences are compared with first and last species oc currences reported elsewhere in the Caribbean. Frequencies of Stylopho ra, Acropora, and extant species are compared among the five locality- groups using non-parametric statistical tests. Occurrence matrices (99 species x 35 localities) are assembled for the collections using both relative abundance codes and presence-absence data, and average linka ge cluster analysis and detrended correspondence analysis are performe d to further examine the nature of the differences in the fauna among locality-groups. Interpretations of the results suggest that assemblag es in the three older Locality-groups (flatiron, salina-base, salina-t op) are composed of >75% pre-turnover species, whereas assemblages in. the youngest group (sea-cliff) are composed of 63% post-turnover spec ies. The ridges localities (44% post-turnover species) represent a tra nsitional step between the two extremes and contain assemblages in whi ch dominant members of the old and new faunas co-occurred Age estimate s for the transition. correspond generally with those reported for a s imilarly prolonged faunal transition in the Limon Group of Costa Rica. The flatiron Localities differ distinctively in faunal composition fr om the other four locality-groups, which overlap in composition. Wide variation is observed within each locality-group This variation. is un related to stratigraphy and can be only partially attributed to enviro nmental and taphonomic factors. Instead, it appears to be caused by th e irregular, patchy local distributions often characteristic of reef b uilders and, together with the overlap among locality-groups, suggests that faunal change was not coordinated and that species were independ ently distributed through the sequence.