COMPARISON OF TWO EOCENE FORALGAL REEFS IN THE SOUTH PACIFIC OCEAN: THE BURTON GUYOT LIMESTONE (UNIT IIA) AT IODP SITE U1376 AND THE UITOÉ LIMESTONE OF NEW CALEDONIA (Invited Presentation)

Reefs during the early to middle Paleogene are poorly documented. Paleogene reefs are generally classified as foralgal reefs where the framework is built by the interaction of red algae, encrusting foraminifera, and larger foraminifera. Paleogene sections containing reefs are under studying understudied and an overall sedimentologic and paleoecologic model is lacking. In order to build a collective understanding of the foralgal reef system, two middle Eocene foralgal reef limestones from the South Pacific region are compared: i) the Burton Guyot Limestone (Unit IIa) from IODP site U1376 on Burton Guyot and ii) the Uitoé Limestone of New Caledonia Although the two limestones are in the same region, they formed in different tectonic settings, the Burton Guyot Limestone forming on an isolated seamount and the Uitoé Limestone forming as a syntectonic unit on a convergent margin.

The Burton Guyot Limestone at IOPD site U1376 is 16 m thick unit of boundstones, packstones, and grainstones. By comparison, the 34 m thick Uitoé Limestone is predominantly grainstone with minor boundstone and packstone. Uitoé Limestone has a more diverse benthic foraminifera fauna than IODP site U1376 likely due to the relative isolation of Burton Guyot during the middle Eocene. Both the Burton Guyot Limestone at IODP site U1376 and the Uitoé Limestone in New Caledonia contain alternating biofacies of frondose and crustose red algae in succession. These alternating pairs of biofacies interpreted here in as parasequences with the frondose red algal biofacies associated with the initial increase in accommodation space and the crustose biofacies with the later phase of each parasequence. In both sections, planktonic foraminifera are associated with the frondose biofacies and the larger benthic foraminifera are associated with the crustose red algal biofacies. The later association of crustose red algae and larger foraminifera is considered as a typical the foralgal boundstone structure.

Despite being from different tectonic settings, both reefs responded equally to relative sea-level chanhe in similar ways. It is anticipated that the Paleogene reefs which are currently being studied will preserve the same parasequence succession.