TAXONOMY OF ALBIAN GAVELINELLIDAE (FORAMINIFERA) FROM THE LOWER SAXONY BASIN, GERMANY

Abstract

Abstract: The family Gavelinellidae was one of the most widespread and abundant groups of benthic foraminifers in the Cretaceous. This group evolved in the Early Cretaceous and became dominant in the Aptian and Albian together with some other families of Rotaliina. The reasons for this evident evolutionary success are unclear, and even the taxonomy and palaeoecology of the group are still a matter of debate. This paper goes ‘back to basics’ and begins by adjusting the terminology, description and evaluation of gavelinellid species identified during high‐resolution studies of the Albian Kirchrode borehole in the Lower Saxony Basin. This is the type area of Reuss' classical (1863) monograph on foraminifera from north German Hils and Gault. In order to avoid terminological misunderstandings, a new definition of test orientation applied to gavelinellids is used. The ventral side is described here as the side that bears the aperture or its extension along the margin, and the dorsal side is the opposite side of the test. The interpretative relationship of the test to the substrate is, therefore, avoided. Albian gavelinellids from the Kirchrode II borehole are represented by two genera, Berthelina and Lingulogavelinella, and six species. The morphology of most gavelinellids, including all documented taxa, is indistinct, which is the main reason for their confusing taxonomy. Species often show strongly overlapping characters, and variability within the species may be comparable or even higher than the variability between different taxa. Morphological details are usually the only features enabling the identification of species. The detailed description and photographic documentation of identified gavelinellid taxa presented herein is based on investigations of over 14 000 individuals augmented by comparative studies of various archival collections. Several diagnostic characters of gavelinellid tests, useful for taxonomic identification, are discussed and compared.