Micromorphology and petrography of Late Weichselian glaciolacustrine varves in southeastern Sweden

The purpose of this investigation is to describe and interpret the sedimentology and petrography of Late Weichselian varves in southeastern Sweden in order to determine their nature and origin. It is focused on the microscopic evidence for glaciolacustrine varve sedimentation in the Baltic Ice Lake and the possibilities of making a detailed facies classification of the sediments in an area with an established varve chronology. The material examined was cores taken from five representative localities in an area below the highest shoreline of the Baltic Ice Lake in the provinces of Skåne and Blekinge, i.e., below an altitude of 55–65 m. The investigations included chemical analyses, XRD, microscopy (polarized) and SEM-EDX investigations of the summer and winter layers of the varves. The results of the chemical, clay mineralogy (XRD) and microscopic examinations of the bedrock and mineral fragments indicate that the material in the different facies of the varved clay is mainly produced by moderate alteration and erosion from the local bedrock of predominantly granitoid rocks and of residual kaoline deposits. It is possible to distinguish microscopic evidence of four varve types differing in texture depending on the water depth and how close to the ice the different facies were deposited, i.e., if they were deposited proximally, distally or extramarginally in relation to the ice margin. It is also possible to relate these differences to changes in the palaeoclimate during the deglaciation of the area in the Bölling and Older Dryas chronozones.