Ecology and paleoecology of triserial planktic foraminifera

Abstract

Guembelitrinidae are a group of small-sized planktic foraminifera that ranges from the Middle Cretaceous to the Present. In this paper we discuss the morphology and stratigraphic distribution of triserial planktic foraminifera and establish the ecology of the living ones to draw parallels with fossil counterparts. In surface water plankton pump samples (0–5 m) from the North Indian Ocean the modern representative Gallitellia vivans (Cushman) has its highest relative frequencies south of India, where upwelling waters cause highly variable conditions on the outer shelf. Oxygen isotope analysis on specimens from a ☐core taken in the Banda Sea (Indonesia) indicates that G. vivans belongs to the planktic community and that, in open marine circumstances, it lives inbetween the surface dwellers Globigerinoides trilobus (Reuss) and Globigerina bulloides d'Orbigny and the deep dwelling Globorotalia menardii (d'Orbigny). Similar habitats can be deduced for fossil Guembelitrinidae. The triserials can live in environments with variable, or extreme conditions as exemplified by Guembelitria cretacea Cushman, which is one of the few Cretaceous planktic foraminiferal species that survived the Cretaceous/Tertiary boundary event. For the most part, open ocean sediments contain few specimens, but triserials may be common to abundant in assemblages from sediments that represent unstable marine conditions (e.g., El Kef, Tunisia). Presumed gaps in the stratigraphic range of triserial planktics appear to be a sampling artifact, caused by their patchy geographic distribution and their small size. Only very rare specimens are present in the > 63 μm fraction. We found Guembelitria cretacea to be present in the 45–63 μm fraction of Coniacian, Santonian and Campanian sediments of a section near El Kef, Tunisia. An extensive search of the small-sized fractions (63–125 μm) of samples from various localities and ages showed that the range of Gallitellia vivans can be extended into the late Pliocene. As a part of this stratigraphic study, a new species, Guembelitria turrita Kroon and Nederbragt, is described from Upper Campanian/Lower Maastrichtian sediments.