ABSTRACT The Krkonoše Piedmont Basin, an early post-Variscan basin (c. 310–280 Ma) located in the NE Bohemian Massif (Czech Republic, central Europe), contains up to 300-m-thick non-marine Lower Permian (Asselian) deposits of the Vrchlabí Formation that crop out in its western part. The Early Permian Krkonoše Piedmont Basin exhibits striking similarities—in terms of tectonostratigraphic evolution, depositional patterns, and volcanism—to other early post-Variscan, near-equatorial intermontane basins. This work focuses on sedimentological analysis of the Vrchlabí Formation using outcrop data, combined with borehole and newly acquired field gamma spectrometry data. The formation consists predominantly of fluvial deposits in the southern part of the basin that pass laterally into deltaic and lacustrine deposits of the Rudník Member, located in the central part of the basin. Fluvial deposits are formed by sandstone and conglomeratic bodies, decimeters to several meters thick, interpreted as single-story and multi-story channel fills as well as various macroforms (e.g., bars) deposited by a low-sinuosity fluvial system. Channel fills intercalate with floodplain deposits centimeters to few meters thick. Vertically, the studied fluvial succession is divided into five intervals based on i) variable preservation ratio between channel fill and floodplain deposits and ii) external and internal geometries of sandstone and conglomerate channel bodies. In order to explain the observed vertical changes in fluvial style and to determine the main controlling factors, the interaction of the fluvial system with the contemporaneous lake was investigated by interpreting base-level changes of the fluvial system and their correlation with lake level changes. In the central part of the basin the transition from fluvio-deltaic to lacustrine deposits is represented by alternating beige to gray sandstones centimeters to few meters thick and by dark gray mudstones up to several meters thick that pass northwards into shales. At the outcrop scale, the new sedimentological data in combination with newly acquired gamma-ray logs enabled tracing the lateral extent of individual fluvial bodies. The integration of the new data with older borehole data leads to a substantially better understanding of lateral and vertical relationship between the fluvio-deltaic and the lacustrine facies at the basin scale. Tectonic subsidence played a substantial role during the initial deposition of the Vrchlabí Formation. However, the external geometries, the internal architecture of fluvial channel bodies, and the variable degree of floodplain preservation throughout the entire Vrchlabí Formation cannot be explained by tectonics only, but requires the consideration of climatic controls. The Early Permian fluvial system is interpreted to reflect seasonal discharge variability with dry and wet periods under long-term subhumid climatic conditions that shifted towards more arid conditions during the latest depositional stage of the Vrchlabí Formation.

中文翻译：

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早期二叠纪沉积系统河流演替中气候和构造印记的评估（Asselian VrchlabÍ 组，Krkonoše Piedmont Basin，捷克共和国）

摘要 Krkonoše Piedmont 盆地是一个早期的后 Variscan 盆地（约 310-280 Ma），位于 NE Bohemian Massif（捷克共和国，中欧），包含高达 300 米厚的非海相下二叠纪（Asselian） Vrchlabí 组的沉积物出现在其西部。早二叠世克尔科诺谢山前盆地在构造地层演化、沉积模式和火山作用方面与其他早期的后华力西、近赤道山间盆地有着惊人的相似之处。这项工作的重点是利用露头数据结合钻孔和新获得的现场伽马能谱数据对 Vrchlabí 组进行沉积学分析。该地层主要由盆地南部的河流沉积物组成，横向进入鲁德尼克段的三角洲和湖泊沉积物，位于盆地中部。河流沉积物由砂岩和砾岩体形成，厚度为分米到几米，被解释为单层和多层河道填充物以及由低弯曲度河流系统沉积的各种宏观形态（例如，条形）。河道填充物夹有几厘米至几米厚的泛滥平原沉积物。在垂直方向上，研究的河流序列根据 i) 河道填充物和泛滥平原沉积物之间的可变保存率和 ii) 砂岩和砾岩河道体的外部和内部几何形状分为五个区间。为了解释观测到的河流样式的垂直变化并确定主要控制因素，通过解释河流系统的基准面变化及其与湖泊水位变化的相关性，研究了河流系统与同期湖泊的相互作用。在盆地的中部，从河流三角洲向湖相沉积的过渡表现为米色和灰色砂岩交替出现，厚度为厘米至几米，深灰色泥岩厚度达几米，向北进入页岩。在露头尺度上，新的沉积学数据与新获得的伽马射线测井相结合，可以追踪单个河流体的横向范围。新数据与旧钻孔数据的整合有助于更好地理解盆地尺度上河流三角洲和湖泊相之间的横向和纵向关系。构造沉降在 Vrchlabí 组的初始沉积过程中发挥了重要作用。然而，整个Vrchlabí组的外部几何形状、河道体内部结构以及泛滥平原保存程度的变化不能仅用构造来解释，而需要考虑气候控制。早二叠世河流系统被解释为反映在 Vrchlabí 组的最新沉积阶段向更干旱条件转变的长期亚湿润气候条件下干湿期的季节性流量变化。整个 Vrchlabí 组的洪泛区保存程度不一，不能仅用构造来解释，而需要考虑气候控制。早二叠世河流系统被解释为反映在 Vrchlabí 组的最新沉积阶段向更干旱条件转变的长期亚湿润气候条件下干湿期的季节性流量变化。整个 Vrchlabí 组的洪泛区保存程度不一，不能仅用构造来解释，而需要考虑气候控制。早二叠世河流系统被解释为反映在 Vrchlabí 组的最新沉积阶段向更干旱条件转变的长期亚湿润气候条件下干湿期的季节性流量变化。