Middle Miocene planktonic microfossils and lower bathyal foraminifera from offshore southern California

Abstract

Lower bathyal sediments representing portions of the Luisian and Mohnian stages of Kleinpell (1938) occur on a submarine ridge near Tanner Bank, offshore southern California. The presence of abundant and well-preserved calcareous nannofossils, diatoms, silicoflagellates, radiolarians and foraminifera allows accurate correlations with the onshore type sections of these stages. In terms of the calcareous nannofossil zones, the age range is from the Sphenolithus heteromorphus Zone to the Discoaster kugleri Zone. Although abundant benthic foraminifera indicative of the Luisian and Mohnian are present, they are accompanied by species more characteristic of the Pliocene Repettian Stage of Natland (1952) and the Pliocene-Miocene “Delmontian” Stage of Kleinpell (1938). Many of these latter species live today at lower bathyal depths (below 2,000 m), others occur in lower bathyal sediments as old as Oligocene, but are absent in the onshore type sections of the Luisian and Mohnian stages in coastal California. We ascribe their absence in onshore sequences to deposition at middle bathyal depths. The known chronostratigraphic ranges of several species are extended and five new species and two new subspecies of benthic foraminifera are described.The following new taxa are described: Bolivina pelita n. sp., Cassidulinella inflata n. sp., Globocassidulina undulata n. sp., Cibicidoides mckannai miocenicus n. subsp., C. mckannai sigmosuturalis n. subsp., Pullenia fragilis n. sp., Parafissurina inornata n. sp.