| Summary: | Abstract The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project focuses on mountain building processes in a major mid-Paleozoic orogen in western Scandinavia and its comparison with modern analogues. The transport and emplacement of subduction-related highgrade continent-ocean transition (COT) complexes onto the Baltoscandian platform and their influence on the underlying allochthons and basement is being studied in a section provided by two fully cored 2.5 km deep drill holes. These operational data sets concern the second drill site, COSC-2 (boreholes ICDP 5054-2-A and 5054-2-B), drilled from mid April to early August 2020. COSC-2 is located approximately 20 km eastsoutheast of COSC-1, close to the southern shore of Lake Liten between Järpen and Mörsil in Jämtland, Sweden. COSC-2 drilling started at a tectonostratigraphic level slightly below that at COSC-1’s total depth. It has sampled the Lower Allochthon, the main Caledonian décollement and the underlying basement of the Fennoscandian Shield, including its Neoproterozoic and possibly older sedimentary cover. COSC-2 A reached 2276 m driller's depth with nearly 100 % core recovery between 100 m and total depth. COSC-2 B, with a driller’s depth of 116 m, covers the uppermost part of the section that was not cored in COSC-2 A. The operational data sets include the drill core documentation from the drilling information system (mDIS), full round core scans, MSCL data sets, a preliminary core description and the geophysical downhole logging data that were acquired during and subsequent to the drilling operations. All downhole logs and core depth were subject to depth correction to a common depth master (cf. operational report for detailed information). The COSC-2 drill core is archived at the Core Repository for Scientific Drilling at the Federal Institute for Geosciences and Natural Resources (BGR), Wilhelmstr. 25–30, 13593 Berlin (Spandau), Germany.
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