Early Cretaceous Shallow-Water Benthic Foraminifers and Fecal Pellets from Leg 143 Compared with Coeval Faunas from the Pacific Basin, Central America, and the Tethys

Abstract

Early Cretaceous shallow-water benthic foraminifers and fecal pellets were recovered from Allison and Resolution guyots in the western Mid-Pacific Mountains (MPM) during Ocean Drilling Program Leg 143. These faunas are used to date the carbonate platform owing to the near absence of other microfossils. Four sites contained the Early Cretaceous assemblages: Site 865 on Allison Guyot, and Sites 866, 867, and 868, which were drilled as part of a transect across the perimeter of Resolution Guyot. Of these sites, Site 866, located about 1.5 km inward from the perimeter mound on Resolution Guyot, provided the most complete record of carbonate sedimentation because drilling penetrated about 1600 m of Hauteri vian to late Albian shallow-water carbonate rocks capped by a thin veneer of Maastrichtian to Pliocene pelagic sediments before encountering basalt. The Hau-terivian age of the basal limestone pre-dates the clastic limestone of Barremian age from Deep Sea Drilling Project Site 463 in the MPM and thus represents the oldest shallow-water carbonate rocks yet recovered from the Pacific Basin. Forty-four species of benthic foraminifers, including the new species Nezzazata isabellae and Vercorsella wintered, and three species of fecal pellets are grouped into five biostratigraphically significant assemblages: Assemblage I = late Albian, Assemblage II = middle(?) to late Albian(?). Assemblage III = late Aptian(?) to early Albian(?), Assemblage IV = Barremian to early Aptian, and Assemblage V = Hauterivian. This biostratigraphic succession served as the standard for dating and comparing the Aptian(?)-to-Albian sequence at Site 865 and the Albian sediments at Sites 867/868, as well as the Aptian-to-Albian shallow-water sequences drilled during Leg 144. Although sparse, the Hauterivian to Aptian assemblages represent a mixture of species known from the northern and southern margins of the Tethys. Further, the stratigraphic succession of the Pacific species is the same as that in Tethyan sequences. Late Aptian to Albian assemblages are distinguished by an influx of species from Mexico and Venezuela associated with a Tethyan fauna. Based on the benthic faunas, three major paleoenvironments corresponding to the development of the platform are recognized at Site 866: (1) sandy, normal-marine conditions in the Hauterivian, (2) restricted lagoonal conditions with stromatolites during the Barremian to early Aptian, and (3) muddy facies with sponges and normal-marine lagoonal conditions during the late Aptian and Albian.