Calcareous Nannofossils and Late Pliocene-Early Pleistocene Biostratigraphy Louisiana Continental Shelf

Abstract

The vertical distributions of calcareous nannofossils and pertinent planktonic foraminifers within the late Neogene strata of the Louisiana Continental Shelf were studied and compared with that in other areas including the type section of the Pleistocene in southern Italy. Thirty-two species of nannofossils from twenty genera arc identified and illustrated from sidewall core samples taken from four wells drilled in the Ship Shoal Area, offshore Terrebonne Parish, Louisiana. Though the ranges of nine of these species are considered stratigraphically significant, only the extinction of Discoaster brouweri Tan Sin Hok and the approximate first appearance of Gephyrocapsa caribbeanica Boudreaux and Hay are recognized as useful stratigraphic criteria for delineating the Pliocene-Pleistocene boundary in this area. A new formation, the Terrebonne Shale, is described from the basal Pleistocene section on the Louisiana Continental Shelf. Other results include: 1) delineation of a phylogenetic series extending from Coccolithus doronicoides Black and Barnes in the middle Pliocene section to Emiliania huxleyi (Lohmann) in the Holocene; 2) recognition of the co-occurrence of Ceratolithus cristatus (Kamptner) and Ceratolithus rugosus Bukry and Bramlette in the earliest Pleistocene sediments; 3) extension of the geologic range of Gephyrocapsa protohuxleyi McIntyre and Cricolithus jonesi Cohen back to the early Pleistocene; 4) the first reported fossil record of Homozygosphaera wettsteni (Kamptner) and Calyptrosphaera oblonga Lohmann; and, 5) generic reassignment of Coccolithus productus (Kamptner), n. comb., and Cristallolithus macroporus (Deflandre), n. comb.