Palaeoenvironmental changes in the Pliocene Intra-Apenninic Basin, near Bologna (Northern Italy)

Abstract

Combined palaeoecologic and sedimentologic studies reveal remarkable palaeoenvironmental changes in the Pliocene Intra-Apenninic Basin (PIB) of the Bologna Apennines (Northern Italy). At the northern margin of PIB, the stratigraphic succession is approximately 1000 m thick, and displays an overall coarsening-upward trend, including a lower mudstone-dominated succession (Argille Azzurre Formation) of Zanclean age, overlain by a sandstone-rich unit (M. Adone Formation), assigned to the Zanclean-Piacenzian. The vertical succession of biofacies within the Argille Azzurre Fm. indicates an obvious shallowing-upward tendency, from slope/outer-shelf (150–300 m water depths) to inner-shelf (30–50 m) environments. A vertical cyclic pattern of facies, with alternating sandy siltstones and sandstone bodies, characterizes M. Adone Formation. Each elementary cycle, about 30–50 m thick, includes a couple of siltstone-dominated inner-shelf and prodelta deposits, passing upwards into progradational delta front, tabular sand bodies. These high-rank cycles, spanning an interval of time in the order of magnitude of 40 ky, are separated by flooding surfaces, clearly recognizable on the basis of palaeoecologic analysis, and reflect an aggradational stacking pattern of parasequences superposed to the general shallowing-upward trend.