A long lacustrine record from the Piànico-Sèllere Basin (Middle-Late Pleistocene, Northern Italy)

Abstract

Abstract The stratigraphical succession of the Pianico-Sellere Basin (Northern Italy) represents an exceptionally well preserved sedimentary assemblage which formed in a closed lake basin during the Middle–Upper Pleistocene. These deposits are grouped into the hereby proposed “Pianico Formation”. This includes four lacustrine, fine-grained, laminated lithostratigraphical units containing a 10.5 m thick interval of well preserved varved carbonates. The lacustrine units are coeval, and laterally heteropic to lake-marginal, talus cone/fan delta debris flow deposits accumulated within the lake. The stratigraphical study and sedimentary facies analysis throughout the lacustrine succession, combined with a preliminary pollen and microstratigraphical investigation, provide evidence of a complex environmental and climatic evolution which occurred during the lacustrine deposition. The Pianico Formation shows multiple changes in sedimentary processes which indicate a transition from a peri/proglacial to a temperate lacustrine environment. Within forested phases a complex evolution is evident. Main changes in vegetational patterns from conifer to broad-leaved, warm temperate forests correspond to changes in sediment composition from distal sand silt turbidites to a regular continuous succession of endogenic calcite-rich annual varves. An increased rate of erosional processes on the surrounding slopes is also indicated by debris flow deposits. Stratigraphically, their frequency within the fine-grained basinal sediments increases upwards which would indicate increasing subaerial erosion processes at the end of the sedimentation of the Pianico Formation. These data highlight the sensitivity of the Pianico-Sellere Basin sedimentation in recording minor climatic fluctuations and related environmental changes which occurred before the Last Glacial Maximum probably during oxygen isotope stage 5, 7 or 9.