The early Pleistocene deposits of southeastern Louisiana consist of basal regressive sandstone overlain by a thick marine transgressive shale unit to which various informal names have been applied. This early Pleistocene shale has an areal extent of more than 20,000 sq mi and ranges in thickness from 100 ft in updip areas to several thousand feet in the continental shelf. This study was based on sidewall cores from 4 wells drilled more than 60 mi offshore from the coastline in the southern part of the Ship Shoal area, Terrebonne Parish, Louisiana. Samples also were examined from piston cores taken in the Atlantic and Pacific Oceans and the distribution of pertinent calcareous nannofossils in these samples was compared with distributions in the Louisiana sections.

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Thirty-two species of calcareous nannofossils from 20 genera have been identified from the late Pliocene and early Pleistocene strata of the Louisiana continental shelf. Of these 32 species, 2 are restricted sufficiently to be useful as stratigraphic criteria. The significant occurrences are, the extinction of Discoaster brouweri Tan Sin Hok and the first appearance of Gephyrocapsa caribbeanica Boudreaux and Hay and these 2 species may be used to define the base of the early Pleistocene marine shale in the north-central Gulf Coast. 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 cris atus (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, and (4) the first reported fossil record of Homozygosphaera wettsteini (Kamptner) and Calyptrosphaera oblonga Lohmann.

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