Uppermost Lower Cambrian-Middle Cambrian stratigraphy and sedimentary petrography of the Almbacken drill-core, Scania, southern Sweden

Abstract: The uppermost Lower Cambrian and Middle Cambrian of the Almbacken drill-core, drilled 1949 in Södra Sandby, are described and correlated with other sections in Scania (the Gislövshammar-2 core and the Forsemölla, Gislövshammar and Brantevik sections). The core consists of Middle Cambrian bituminous alum shales with stinkstone lenses and three beds of fossiliferous limestone, the Andrarum, Exsulans, and "Fragment" limestones. The lower part of the core, containing the Middle-Lower Cambrian boundary, consists of calcareous and siliciclastic shallow marine deposits. The alum shale has a fairly high calcium carbonate content (CaC03) and a low total organic content (TOC) compared to the alum shales in other areas in Scandinavia. The low TOC in the alum shales of the Almbacken core is due to a high content of terrigenous material and heating through Permo-Carboniferous igneous activity (resulting in migration of lighter hydrocarbons) in the Södra Sandby area. The thickness of the Middle Cambrian in Södra Sandby is c. 34.6 m, which is the maximum thickness recorded in Scania. The Middle Cambrian is thinning out towards the southeast and on Bornholm it measures only c. 3 m. The higher content of terrigenous material reported in the "Fragment" and Exsulans limestones in localities located southeast of Södra Sandby, compared to Almbacken, may indicate deposition in shallower water during the Middle Cambrian.