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山脉碰撞造山运动”（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的重点是早古生代Iapetus海洋的关闭和波罗的海和劳伦提斯之间的Scandian大陆-大陆碰撞，导致Baltoscandian边缘在志留纪中后期部分俯冲到劳伦提斯之下，形成喜马拉雅型造山带。在COSC-1期间，在Brachre地区研究了高级变质外来体的就位（2014年钻探了与俯冲有关的下塞夫推覆体和下伏的低级塞夫推覆体），COSC-2将调查大量古生代序列（下外来体和原地体）、主要的加里东期滑脱和雅尔彭东南部利滕湖芬诺斯堪地盾的前寒武纪基底。拟议的DFG项目将重点关注在岩芯上部>1200 m的外陆架和前陆盆地环境中发育的寒武纪-志留纪沉积序列。连续关闭的Iapetus海洋，碰撞之间的波罗的海和劳伦，大陆边缘的挠曲负荷和堆叠逆冲岩片沿着挪威-瑞典变形前改变了配置的Baltoscandian盆地，并创建不同的深度相关的环境中奥陶纪至志留纪时期平行于造山带的前陆盆地。将详细研究目标区域的沉积物覆盖层的岩相和海平面变化。上奥陶统潜在的地层缺口和石灰岩沉积物（Llandovery）中可能的岩溶作用可能反映了中奥陶世晚期至上志留世冰库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世沉积物的调查将包括寻找关闭Iapetus地区的强烈火山活动（K-Haponites）的痕迹和加里东前渊附近陨石撞击的痕迹。 该项目的一个主要重点是在地热学和地球物理学等其他研究课题上与专业研究人员密切合作。详细的岩性研究对于地热模型相关的取样是重要的。利用沉积记录校准钻孔地球物理数据，将允许根据为确定COSC-2钻井地点而调查的断面中的详细反射地震研究，讨论以前的地下解释。沉积序列是理解COSC目标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.