Early Phanerozoic outer shelf succession of Baltica beneath the Caledonian nappes: a first evaluation of the sedimentary record from the COSC 2 core hole, Sweden

“斯堪的纳维亚加里东尼德斯的碰撞造山运动”（COSC）钻探项目是国际科学钻探计划（ICDP）和瑞典科学钻探计划（SSDP）的组成部分。COSC的研究重点是早古生代Iapetus洋的闭合和波罗的海与劳伦提亚之间的加拿大大陆-大陆碰撞，导致波罗的海边缘在志留纪中晚期在劳伦提亚下部分俯冲，形成喜马拉雅型造山带。coc -1在Åre地区（2014年钻探了与俯冲相关的下西弗推覆体和下伏的下级Särv推覆体）研究了高变质异位体的侵位，而coc -2将在Järpen东南的Liten湖研究大量的古生代演替（下异位体和上位体）、主要的加里东期构造和芬诺斯坎德盾的前寒武纪基底。建议的DFG项目将重点研究外陆架和前陆盆地背景下的寒武纪-志留纪沉积序列。在中奥陶世至志留纪期间，Iapetus洋的连续闭合、波罗的海与Laurentia的碰撞、大陆边缘的弯曲载荷以及挪威-瑞典变形前沿的逆冲片叠置改变了波罗的斯坎迪亚盆地的构造，并在与造山带平行的前陆盆地中形成了不同的深相关环境。将详细研究目标区域的沉积盖层的相和海平面变化。上奥陶统潜在的地层缺口和石灰岩矿床（Llandovery）可能的岩溶作用可能反映了中奥陶统晚期至上志留统冰窖期的冰川事件和剧烈的气候波动。对沉积在深水环境中的上奥陶统沉积物的研究将包括在Iapetus地区寻找强烈火山活动（k -膨润土）的痕迹，以及在加里东前深层寻找附近的陨石撞击。在其他研究课题上，如地热和地球物理等，与各pi密切合作是该项目的主要重点。详细的岩性研究对于地热模型的取样是很重要的。将钻孔地球物理数据与沉积记录进行校准，可以讨论基于所调查样带中详细反射地震研究的以前的地下解释，以确定COSC-2钻探地点。沉积序列是理解整个COSC靶区地下地震资料的关键。

The ‘Collisional Orogeny in the Scandinavian Caledonides’ (COSC) drilling project represents an integral part of the International Scientific Drilling Program (ICDP) and the Swedish Scientific Drilling Program (SSDP). COSC is focusing on the Early Palaeozoic closure of the Iapetus Ocean and the Scandian continent-continent collision between Baltica and Laurentia resulting in partial subduction of the Baltoscandian margin beneath Laurentia in the mid-late Silurian and the formation of a Himalayan-type orogen. While the emplacement of high-grade metamorphic allochthons was studied during COSC-1 in the Åre area (drilling of the subduction-related Lower Seve Nappe and underlying lower-grade Särv Nappe in 2014), COSC-2 will investigate the substantial Palaeozoic succession (Lower Allochthon and Autochthon), the main Caledonian décollement and the Precambrian basement of the Fennoscandian Shield at Liten Lake southeast of Järpen. The proposed DFG project will focus on the Cambro-Silurian sedimentary succession developed in outer shelf and foreland basin settings in the upper >1200 m of the core. The successive closure of the Iapetus Ocean, the collision between Baltica and Laurentia, flexural loading on the continental margin and stacking of thrust sheets along the Norwegian-Swedish deformation front changed the configuration of the Baltoscandian Basin and created different depth-related environments in a foreland basin parallel to the orogen during Middle Ordovician through Silurian times. The sedimentary cover in the target area will be studied in detail for facies and sea-level changes. Potential stratigraphic gaps in the Upper Ordovician and possible karstification in the limestone deposits (Llandovery) likely reflect glacial events and drastic climate fluctuations during the late Middle Ordovician through Upper Silurian Icehouse Period. The investigation of the Upper Ordovician sediments deposited in deeper water environments will include the search for traces of the intense volcanic activity (K-bentonites) in the closing Iapetus region and of near-by meteorite impacts in the Caledonian fore-deep. Close cooperation with the PIs on other research topics such as geothermics and geophysics are a main focus of the project. A detailed lithological study is important for the sampling related to a geothermal model. Calibration of the borehole geophysical data with the sedimentary record will allow discussing former subsurface interpretations based on detailed reflection seismic studies in the transect investigated for deciding on the COSC-2 drill site. The sediment succession is the key for an understanding of the seismic data in the subsurface across the COSC target area.