Spiroplectinata, key benthic foraminifer genus for palaeoceanographic reconstruction of the Albian Lower Saxony Basin

This paper is focused on Albian Spiroplectinata, a morphologically unique, benthic, agglutinated foraminifer genus, and its application for reconstruc ting changes in the water masses within the Lower Saxony Basin. A new inter pretation of microhabitat preferences and feeding habit for Spiroplectinata is proposed and discussed. Their functional morphology, composition of the ir tests, and their relationships with adherent foraminifera suggest that a t least adult individuals of Spiroplectinata were epibenthic and were eithe r suspension or deposit feeders. The suspension-feeding mode is favoured be cause this genus is associated with adherent suspension-feeding foraminifer a and it does not correlate with other epibenthic deposit feeders. Spirople ctinata constructed an elongated uniserial terminal part, which probably fa cilitated an erect position to spread a reticulopodium well above the sedim ent/water interface. The distribution of this foraminifer can, therefore, b e used here as a sensitive indicator for the existence of bottom currents. Four (or five) periods of intensified bottom water circulation around the E arly/Middle Albian boundary (S-1), Middle (S-2), late Middle to earliest La te Albian (S-3, probably represents two intervals) and early Late Albian (S -4) are reconstructed and well marked by maxima of Spiroplectinata annecten s, S. complanata, and Spiroplectinata sp. A. S. annectens is known from strata in the Western Tethys (i.e. in the Late A ptian and Early Albian) that are older than those in the 'Boreal' realm. It s first appearance in the Lower Saxony Basin occurs in the late Early Albia n, followed by the first maximum just above the Early/Middle Albian boundar y, and probably represents the main immigration event into the Lower Saxony Basin. This supports the idea that the deep water in the late Early to ear ly Late Albian 'Boreal' epicontinental sea during 'the Spiroplectinata inte rvals' came from the Tethys and not from the polar regions. If one interpre ts the plankton/benthos foraminifera ratio as reflecting sea-level changes, it implies that sea-level rises may have been responsible for opening and/ or deepening of 'Boreal'/Tethyan gateways that activated extensive exchange of water masses. This late Early Albian and early Late Albian 'invasion' o f Tethyan water can be correlated with a general global warming, and shifti ng of climate zones. (C) 2001 Elsevier Science B.V. All rights reserved.