Evolution of the Miocene carbonate shelf of Monferrato (North-western Italy)

A multidisciplinary study including sequence stratigraphy, biostratigraphy, paleoecology and paleoclimatology was performed on Lower Miocene carbonate sedimentary rocks, the “Pietra da Cantoni Group” within which two depositional sequences bound by discontinuity surfaces were recognized. Sequence 1 consists of bioturbated inner-middle shelf packstones and wackestones (lower Burdigalian), resting unconformably on the silty slope facies sediments of the Marne di Antognola Fm. In this sequence the benthic foraminiferal assemblages, dominated by epifaunal and epiphytic taxa, indicate a well-oxygenated substratum within the photic zone. Climatic indices, among the planktonic foraminifera, suggest cool-temperate climate conditions. These sediments likely record the Burdigalian transgression at the beginning of the TB2 supercycle, as defined by Haq et al. (1987). Sequence 2 includes two superimposed units. The lower unit (upper Burdigalian) consists of rhodalgal rudstones and packstones of shelf environment with a mobile substrate and well-oxygenated water, rich in benthic foraminifera and Corallinaceae, deposited in warm-temperate conditions. A drowning unconformity surface bounds this unit from the second and reflects a relative sea-level rise that could be correlated with the maximum flooding surface within the cycle TB2.2. The upper unit (upper Burdigalian-lower Langhian) consists of foraminifera and glaucony-rich packstones ranging from inner shelf environment, characterized by epiphytic foraminifera and Miogypsinids, to outer shelf environment suggested by the increase of planktonic and benthic deep-water taxa and rhodoliths, deposited in warm-temperate conditions. This succession grades upward to upper Langhian-lower Serravallian planktonic foraminifer-rich marls of the Mincengo Fm. . Deposition of the carbonate sediments of the Sequence 2 is linked to the combined effect of: (1) tectonic reorganization of the basin; (2) sea level oscillations; (3) upwelling of nutrient-rich waters; (4) increase of trophic resources connected to increasing erosion of uplifted alpine relieves, favoring the development of “temper