Foraminiferal assemblages of the Bric della Muda laminites (Nizza Monferrato, Piedmont): Proxies of cyclic palaeoenvironmental changes in the early Messinian of Northwestern Italy |
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Authors: | Donata Violanti Lorenzo Mariano Gallo |
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Affiliation: | a Dipartimento di Scienze della Terra, Università di Torino and CNR, Istituto di Geoscienze e Georisorse, Sezione di Torino (afferent), via Valperga Caluso 35, 10125 Torino, Italia b Museo Regionale di Scienze Naturali, via Giolitti 36, 10123 Torino, Italia c CNR-IDPA (Istituto per la Dinamica dei Processi Ambientali), via Mangiagalli 34, 20133 Milano, Italia |
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Abstract: | Foraminiferal assemblages in laminites cropping out at the Bric (i.e. Hill) della Muda (Nizza Monferrato, Piedmont, Northwestern Italy) document deep marine conditions during the early Messinian, spanning a time-interval approximating, or slightly wider than the stratigraphic range of Globorotalia nicolae (6.82-6.72 Ma). Fluctuations in abundance of planktonic warm-water oligotrophic taxa and cold-water eutrophic species show a cyclical pattern, very comparable to variations measured in cyclically-bedded formations of the pre-evaporitic Messinian in the Mediterranean area. A subtropical climate with cyclic warmer and cooler episodes, characterized by surface water stratification and vertical mixing in the water column, respectively, is also documented. A depositional depth close to or larger than 1000 m is inferred on the basis of planktonic assemblages yielding also the deep planktonic Hastigerinella digitata and of very high P/(P + B) ratios. Anoxic or strongly dysoxic bottom conditions are indicated by the absence or rareness of benthic foraminifers, which are represented by taxa tolerant of low-oxygen or high organic content (Bolivina pseudoplicata, Chilostomella oolina, Globobulimina affinis). A slight decrease in P/(P + B) ratios, and the presence of rare shallow-water forms in the uppermost layers suggest a mild dysoxia and a probable shallowing, when compared with coeval events in Northern Apennines and Southern Greece sections. |
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Keywords: | Foraminifers Early Messinian Palaeoenvironment Piedmont Northwestern Italy |
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