Foraminiferal paleoecology of a submarine swell -the Lower Badenian (Middle Miocene) of the Mailberg Formation at the Buchberg in the Eastern Alpine Foredeep: initial report

• Main Author: Oleg Mandic
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Planktonic foraminifera
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1069.7165; http://verlag.nhm-wien.ac.at/pdfs/105A_161174_Mandic.pdf

Abstract The present paper investigates the depositional setting of the Middle Miocene Mailberg Formation based on benthic and planktonic foraminifera. The studied section is situated in an abandoned quarry at the Buchberg W. Mailberg in Lower Austria. The succession comprises an interbedding of coralline algal limestone with marly intercalations. The sedimentation took place on a submarine paleo-swell that was isolated from any significant siliciclastic influence. Its numerical age ranges between 15.034 and 14.888 Ma and falls into the Lower Badenian. Cibicidoides-and Cibicidoides-Elphidium assemblages indicate fully marine, shallow water, high oxic conditions with oxygen levels ranging from 3.0-6.0 mL/L. Similarity/Dissimilarity Term Analyses, non-metric Multi-Dimensional Scaling and Agglomerative Hierarchical Clustering revealed an assemblage aberrance within a thin marly interlayer. This is defined by an abundance peak of Melonis pompilioides and by a minimum level of taxonomic richness and heterogeneity. The abrupt decrease of plankton abundance to 1.6% within the thin marly layer coincides with a short-term eutrophication event. Despite the predominance of oxic indicators in a subsequent recovery phase, the sudden euthrophication apparently resulted not only in a decrease of limestone production but also in the abundance peak of suboxic pioneers inhabiting the bottom sediments before the return of oxic conditions. The plankton abundances ranging between 24.3 and 28.4% indicate upper to middle shelf conditions in an open sea. Based on the macrofauna, the depositional depth for carbonates was maximally 30 m. The foraminiferal assemblages from marls, however, indicate greater depths of about 50 m. Hence, the presence of short-termed, orbitally forced sea level fluctuations is assumed for the section, producing periodical water mass eutrophication and a shut-down of the carbonate factory. The distribution of thermophilic taxa among the plankton indicates a minor sea water cooling in the topmost part of the ...