Palaeoclimatic interpretation based on Middle Miocene planktonic Foraminifera: the Silesia Basin (Paratethys) and Monferrato (Tethys) records

Abstract

A comparative study of the distribution and palaeoclimatic interpretation of temperature-related taxa of Middle Miocene planktonic foraminifera from the Paratethys Silesia Basin (southern Poland) and Tethys Monferrato area (northwestern Italy) is presented. The time span considered (Badenian–Langhian/Serravallian) is the last period of significant connection between the Paratethys and Mediterranean Tethys, even though the depositional conditions, water circulation and connection with the oceanic realm were not always favourable to the life and preservation of significant planktonic foraminiferal taxa. The Silesia Basin, located in the western segment of the Karpathian Foredeep, is filled by an autochthonous, non-folded cover of Miocene deposits. Four stratigraphic sections were studied in this area, characterised by Carpathian sandy deposits of the Kłodnica Formation, Lower Badenian unbedded marly clays, marls and strongly bedded Lithothamnium marls (Skawina Formation), Middle Badenian anhydrite and laminated clay shales (Krzyźanowice Formation), Upper Badenian unbedded marly clays, followed by fine-grained sands, sandy limestone layers, and bioclastic levels rich in molluscs and calcareous algae (Gliwice Formation). The Monferrato area corresponds to the northwestern termination of the Apennines thrust belt and consists of an Eocene–Miocene mainly terrigenous succession, resting unconformably on Upper Cretaceous and Eocene Ligurian flysch. Three stratigraphic sections are studied in the eastern area, characterised by Late Oligocene to Early Burdigalian deepwater terrigenous sediments (Marne di Antognola Formation), followed unconformably by Early to Middle Miocene carbonate sediments, originating in a foramol platform depositional environment (Pietra da Cantoni Group), and by grey–whitish glauconitic marls of the Marne di Mincengo Formation (Late Langhian–Serravallian). Twenty-three species of Tethys and Paratethys planktonic foraminifera were grouped in cold ( Globigerina bulloides, Globigerina quinqueloba, Globigerina praebulloides gr., Globorotaloides spp., Catapsydrax spp.), cold–temperate ( Zeaglobigerina woodi, Z. brazieri Globorotalia scitula gr., Globorotalia bykovae), warm ( Globigerinoides spp., orbuliniforms, including Praeorbulina spp. and Orbulina spp., Globigerina ciperoensis, Dentoglobigerina altispira gr., Velapertina indigena, Globorotalia praemenardii), and warm–temperate indices ( Paragloborotalia siakensis gr., Dentoglobigerina baroemoenensis gr., Globoquadrina praedehiscens and G. dehiscens, Tenuitellinata angustiumbilicata, Globigerinella obesa, Globigerina venezuelana). Their relative abundance was used to reconstruct palaeoclimatic curves. Comparison of the palaeoclimatic curves makes it possible to recognise a climatic change from warmer conditions in the Langhian towards relatively colder conditions in the Serravallian. The fall in warm-related taxa was much more pronounced in the Silesia Basin than in the Monferrato area. This palaeoclimatic evidence may be interpreted as the beginning of a series of oscillations pointing to a period of cooling, corresponding to one of the major global changes in the palaeoclimatic/palaeoceanographic history of the Cenozoic, i.e. the ‘Mid-Miocene event’, Mi3 [Miller et al. (1991) Paleoceanography 6, 33–52].