The Chainons Bearnais is a salt-detached fold belt in the northern Pyrenees that formerly occupied the axis of the Cretaceous Pyrenean rift. Geological map revision and cross-section construction from surface geology and industrial well and seismic reflection data emphasize the role of salt diapirism in the folding of the belt during the Cretaceous extension and the subsequent Pyrenean orogeny. Pre-rift Triassic evaporites played a fundamental role during rifting, allowing the sedimentary basin lying above to detach and slide down the hyper-extended margins onto a central exhumed mantle tract. Since the Early Cretaceous (and locally probably since the Jurassic) a system of low-amplitude salt walls evolved in shallow marine environments punctuated by episodic emersion. During the main stage of crustal extension, in late Aptian to early Cenomanian times, carbonate shelves rapidly drowned giving rise to deeper marine sedimentation. This was a period of major rise of salt walls, progressively detached from their substratum. These salt walls enclosed minibasins that accumulated thick flysch deposits arranged in growth stratal patterns. Depocenter migration and foundering of previous diapiric highs controlled further flysch deposition during the Late Cretaceous, while moderate extension probably persisted until the onset of the Pyrenean compression. During the late Santonian to Paleogene Pyrenean orogeny, the sedimentary lid of the Chainons Bearnais basin climbed back along the Triassic detachment onto the colliding continental margins, leading to salt wall squeezing and further rising. Based on the Cretaceous timing and style of growth folding, we suggest that salt wall squeezing was not solely related to the Pyrenean compression, but shortening affected the diapiric ridges during the syn-rift sliding by gravity and crowding in the basin center, as the rifted margins were pulled apart from beneath. This makes the Chainons Bearnais belt a unique field analog for contractional salt-tectonic systems in distal continental margins.

中文翻译：

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比利牛斯裂谷（Chaînons Béarnais，法国）盐结构的演化：从超伸展到构造反转

Chainons Bearnais 是位于比利牛斯山脉北部的一条盐分分离褶皱带，以前占据白垩纪比利牛斯裂谷的轴线。地表地质、工业井和地震反射数据的地质图修订和横截面构建强调了盐底辟在白垩纪伸展和随后的比利牛斯造山运动期间带折叠中的作用。裂谷前的三叠纪蒸发岩在裂谷过程中发挥了重要作用，使位于上方的沉积盆地分离并沿超延展边缘滑落到中央挖出的地幔束上。自早白垩世（局部可能自侏罗纪以来）以来，一个低振幅盐壁系统在浅海环境中演化，间断出现偶发性渗出。在地壳伸展的主要阶段，在 Aptian 晚期到 Cenomanian 早期，碳酸盐岩架迅速淹没，导致更深的海洋沉积。这是盐墙主要上升的时期，逐渐脱离其底层。这些盐墙封闭了小盆地，这些小盆地积累了以生长地层模式排列的厚复理石沉积物。沉积中心迁移和先前底辟高点的沉没控制了晚白垩世期间进一步的复理石沉积，而适度的伸展可能持续到比利牛斯压缩开始。在桑托阶晚期至古近纪比利牛斯造山运动期间，Chainons Bearnais 盆地的沉积盖沿三叠纪拆离向后爬回到碰撞大陆边缘，导致盐壁挤压并进一步上升。根据白垩纪生长褶皱的时间和方式，我们认为盐壁挤压不仅与比利牛斯挤压有关，而且在重力作用下同裂谷滑动和盆地中心拥挤期间，由于裂谷边缘被从下方拉开，缩短影响了底辟脊。这使得 Chainons Bearnais 带成为远端大陆边缘收缩盐构造系统的独特场模拟。