Neogene Silicoflagellates of the Eastern Equatorial Pacific, Deep Sea Drilling Project Hole 503A

Abstract

Neogene silicoflagellates are especially abundant and well preserved in Deep Sea Drilling Project (DSDP) Miocene Cores 30 to 54 of DSDP Hole 503A; Pliocene assemblages in Cores 12 to 30 are less abundant and contain increased numbers of solution-thinned specimens. The Asperoid/Fibuloid ratio of Dictyocha reversed six times during the late Miocene, making questionable the placement of the D. brevispina to the D. fibula Zone boundary. Transitional forms in the late Miocene D. neonautica lineage are identified. An associated population of Mesocena diodon nodosa may have evolved from the D. neonautica transitional group. Several recently described guide species for the Pliocene first occur in Pliocene Cores 12 to 30, including D. angulata, D. delicata var. bisecta, D. ornata africana, and D. perlaevis flexatella. The first D. stapedia stapedia, marking the base of the D. stapedia Zone, occurs in the middle of the Pliocene, helping to establish the age of the zone base. Relative paleotemperature values for silicoflagellates are typically high; brief maximum coolings occur only in the upper Miocene interval between Cores 31 to 37, in and near the upper D. neonautica Subzone. Six new silicoflagellate taxa are described, including D. arbutusensis Bukry, n. sp., D. perfecta Bukry, n. sp., D. transenna Bukry, n. sp., Distephanus cruxcarolae Bukry, n. subsp., D. speculum bispicatus Bukry, n. subsp., and D. speculum tenuis Bukry, n. subsp.