50. PALEOBIOGEOGRAPHIC EVOLUTION OF SHALLOW-WATER ORGANISMS FROM THE APTIAN TO THE EOCENE IN THE WESTERN PACIFIC1

Shallow-water organisms recovered from drilling four guyots in the western Pacific (from the southern Marshall Islands to the Japanese Seamounts) allow the recognition of changes in bioprovinces through time. The Tethyan low-latitude bioprovince characterizes the early Aptian worldwide. In the late Albian, however, shallow-water floral and f aunal assemblages from the drilled guyots, although predominantly composed of cosmopolitan forms, yielded few elements with an areal distribution more restricted to either the Caribbean-central American region or the Mediterranean, suggesting that two bioprovinces had already differentiated at low latitude at that time. During the late Campanian-Maastrichtian, the guyots' area was under the influence of the Caribbean bioprovince, but foraminifer assemblages also include some Mediterranean elements, suggesting that colonization occurred both westward and eastward. In the latest Paleocene-early middle Eocene, the direction of colonization reversed, with prevalent migration from the Mediterranean toward the Pacific.