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

The stratigraphical succession of the Pianico-Sellere Basin (Northern Italy ) represents an exceptionally well preserved sedimentary assemblage which f ormed in a closed lake basin during the Middle-Upper Pleistocene. These dep osits are grouped into the hereby proposed "Pianico Formation". This includ es four lacustrine, fine-grained, laminated lithostratigraphical units cont aining a 10.5 m thick interval of well preserved varved carbonates. The lac ustrine units are coeval, and laterally heteropic to lake-marginal, talus c one/fan delta debris now deposits accumulated within the lake. The stratigr aphical study and sedimentary facies analysis throughout the lacustrine suc cession, combined with a preliminary pollen and microstratigraphical invest igation, provide evidence of a complex environmental and climatic evolution which occurred during the lacustrine deposition. The Pianico Formation sho ws multiple changes in sedimentary processes which indicate a transition fr om a peri/proglacial to a temperate lacustrine environment. Within forested phases a complex evolution is evident. Main changes in vegetational patter ns from conifer to broad-leaved, warm temperate forests correspond to chang es in sediment composition from distal sand silt turbidites to a regular co ntinuous succession of endogenic calcite-rich annual varves. An increased r ate of erosional processes on the surrounding slopes is also indicated by d ebris flow deposits. Stratigraphically, their frequency within the fine-gra ined basinal sediments increases upwards which would indicate increasing su baerial erosion processes at the end of the sedimentation of the Pianico Fo rmation. These data highlight the sensitivity of the Pianico-Sellere Basin sedimentation in recording minor climatic fluctuations and related environm ental changes which occurred before the Last Glacial Maximum probably durin g oxygen isotope stage 5, 7 or 9. (C) 2000 Elsevier Science Ltd and INQUA. All rights reserved.