Paleogene postcompressional intermontane basin evolution along the frontal Cordilleran fold-and-thrust belt of southwestern Montana
Paleogene postcompressional intermontane basin evolution along the frontal Cordilleran fold-and-thrust belt of southwestern Montana
复制标题
蒙大拿州西南部前科迪勒拉褶皱逆冲带古近纪后挤压山间盆地演化
DOI：
10.1130/b30766.1
复制
发表时间：
2013
影响因子：
4.9
通讯作者：
R. Schwartz
中科院分区：
文献类型：
--
作者：
T. Schwartz;R. Schwartz
古近系雷诺瓦组是美国蒙大拿州西南部科迪勒兰褶皱冲断带海伦娜凸起及其附近最早的挤压后沉积记录。盆地边缘相的古水流和成分数据表明，古扩散远离与现代山区一致的高起伏（≥2 km）高地。古高地内烃源岩均包含太古宙变质岩；元古代、古生代和中生代沉积；中生代深成岩和中生代火山岩在现代隆升中暴露。来自干河砾岩和砂岩的古水流和成分数据证明了一个盆地间排水系统的存在，该系统将三叉盆地、加勒廷盆地西部和汤森盆地与源头连接起来，向西和向西南延伸，靠近今天的蒙大拿-爱达荷州边界。总体而言，古近系山区和盆地的分布与现代地理极为相似，古近系水系与现代密苏里河源头水系极为相似。雷诺瓦组记录了科迪勒拉造山带早期的衰败阶段，包括蒙大拿西南部一个复杂的山间盆地网络的演化。晚白垩世至始新世早期的高能河流系统沿着构造和地层薄弱带将深而大的古山谷雕刻成造山带。在此期间，至少有5公里厚的覆盖层被移除。切口与早新生代区域隆升和亚热带气候条件在时间上相关。雷诺瓦组随后的沉积与隆升停止、地壳伸展开始和气候变冷在时间上是相关的。然而，伸展在盆地早期发育中并没有发挥主要作用。
The Paleogene Renova Formation is the earliest record of postcompressional sedimentation within and adjacent to the Helena Salient of the Cordilleran fold-and-thrust belt in southwestern Montana. Paleocurrent and compositional data from basin-margin facies document radiating paleodispersal away from high-relief (≥2 km) highlands coincident with modern mountainous areas. Source rocks within the paleohighlands included the same Archean metamorphic; Proterozoic, Paleozoic, and Mesozoic sedimentary; and Mesozoic plutonic and vo l canic rocks as exposed in modern uplifts. Paleocurrent and compositional data from trunk fluvial conglomerates and sandstones document the existence of an interbasinal drainage system that connected the Three Forks, western Gallatin, and Townsend Basins with headwaters farther to the west and southwest near the present-day Montana-Idaho border. Overall, the distribution of Paleogene mountainous areas and basins closely resembled modern geography, and the Paleogene drainage network was strikingly similar to the modern Missouri River headwater system. The Renova Formation records the early stages of decay of the Cordilleran orogenic belt, including the evolution of a complex intermontane basin network in southwestern Montana. High-energy Late Cretaceous to early Eocene fluvial systems carved deep, large-scale paleovalleys into the orogenic wedge along zones of structural and stratigraphic weakness. At least a 5 km thickness of overburden was removed during this time. Incision was temporally correlative with early Cenozoic regional uplift and subtropical climatic conditions. Subsequent deposition of the Renova Formation was temporally correlative with the cessation of uplift, the initiation of crustal extension, and climatic cooling. However, extension is not interpreted to have played a major role in earliest basin development.