Evolution of the Cordilleran foreland basin system in northwestern Montana, U.S.A.
Evolution of the Cordilleran foreland basin system in northwestern Montana, U.S.A.
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美国蒙大拿州西北部科迪勒拉前陆盆地系统的演化
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发表时间：
2011
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影响因子：
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通讯作者：
G. Gehrels
中科院分区：
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作者：
F. Fuentes;P. DeCelles;K. Constenius;G. Gehrels
新的岩石地层学和年代地层学，地质年代学和沉积岩石学数据阐明了从中侏罗世到始新世在蒙大拿州西北部的北美科迪勒拉前陆盆地系统和相邻的冲断带的发展历史。前陆盆地系统中最古老的沉积物由相对较薄的区域性板状沉积物组成，这些沉积物为海相埃利斯群和河流-河口莫里森组，它们在巴若期至基默里纪时期积累。碎屑锆石U-Pb年龄和砂岩模式岩相学数据表明，170 Ma，内陆地区的微斜地岩层发生变形和剥蚀。斯威夫特组和莫里森组的砂岩含有来自山间带的碎屑锆石。侏罗纪沉积物可能聚集在早期前陆盆地的远，后隆起沉积带，如构造沉降和板状几何学的缓慢速度所建议的。一个区域不整合面将侏罗纪地层与晚巴列姆世（？）前渊沉积这种不整合可能是前隆迁移、动力沉降减少和海平面升降的综合作用的结果。巴雷姆阶晚期（？）早期Albian Kootenai组是第一个不断向西增厚的单元，正如在前渊沉积带中所预期的那样。此时的沉降曲线开始表现出前渊的上凸模式特征。到了阿尔比期，褶皱冲断带向东扩展，并将带超群的元古宙岩石纳入其中，这一点可从砂岩成分、黑叶组中的碎屑锆石年龄以及冲断带中涉及带超群岩石的冲断岩席中的横切关系中看出。一个主要的海洋洪水和黑色页岩沉积（玛丽亚河页岩）之间发生的森诺曼阶和中Santonian，其次是由上Santonian-mid-Campanian电报溪，Virgelle和两个医学地层代表的海退序列。物源数据不解决的时间在Cenomanian-early Campanian时间的个人推力位移。上坎帕尼亚熊爪组代表了前陆盆地最后一次主要的海洋淹没。到最晚的坎帕尼亚时期，刘易斯逆冲断层系统的一个主要滑动事件已经开始，正如近端前渊沉积带中的杨柳溪组和圣玛丽玛丽组所记录的那样。古新世-早始新世Fort Union组和Wasatch组记录了科迪勒拉褶皱冲断带和前陆盆地系统演化的最后阶段，它们保存在远前陆区。沿着褶皱冲断带的区域性伸展断裂作用始于始新世中期。这里提出的结果，使以前的地质工作在加拿大和更好地了解部分在美国的科迪勒纳前陆盆地之间的联系。
New lithostratigraphic and chronostratigraphic, geochronologic, and sedimentary petrologic data illuminate the history of development of the North American Cordilleran foreland basin system and adjacent thrust belt from Middle Jurassic through Eocene time in northwestern Montana. The oldest deposits in the foreland basin system consist of relatively thin, regionally tabular deposits of the marine Ellis Group and fluvial-estuarine Morrison Formation, which accumulated during Bajocian to Kimmeridgian time. U-Pb ages of detrital zircons and sandstone modal petrographic data indicate that by ca. 170 Ma, miogeoclinal strata were being deformed and eroded in hinterland regions. Sandstones of the Swift and Morrison Formations contain detrital zircons derived from the Intermontane belt. The Jurassic deposits probably accumulated in the distal, back-bulge depozone of an early foreland basin, as suggested by the slow rates of tectonic subsidence and tabular geometry. A regional unconformity separates the Jurassic strata from late Barremian(?) foredeep deposits. This unconformity possibly resulted as a combined effect of forebulge migration, decreased dynamic subsidence, and eustatic sea-level fall. The late Barremian(?)-early Albian Kootenai Formation is the first unit that consistently thickens westward, as would be expected in a foredeep depozone. The subsidence curve at this time begins to show the convex-upward pattern characteristic of foredeeps. By Albian time, the fold-and-thrust belt had propagated to the east and incorporated Proterozoic rocks of the Belt Supergroup, as indicated by sandstone compositions, detrital zircon ages in the Blackleaf Formation, and by crosscutting relationships in thrust sheets involving Belt Supergroup rocks in the thrust belt. A major episode of marine inundation and black shale deposition (Marias River Shale) occurred between the Cenomanian and mid-Santonian, and was followed by a regressive succession represented by the Upper Santonian–mid-Campanian Telegraph Creek, Virgelle, and Two Medicine Formations. Provenance data do not resolve the timing of individual thrust displacements during Cenomanian–early Campanian time. The Upper Campanian Bearpaw Formation represents the last major marine inundation in the foreland basin. By latest Campanian time, a major episode of slip on the Lewis thrust system had commenced, as recorded in the foreland by the Willow Creek and St. Mary River Formations in the proximal foredeep depozone. The final stage in the evolution of the Cordilleran fold-and-thrust belt and foreland basin system is recorded by the Paleocene–early Eocene Fort Union and Wasatch Formations, which were preserved in the distal foreland region. Regional extensional faulting along the fold-and-thrust belt began during the middle Eocene. The results presented here enable the establishment of links between previous geological work in Canada and the better known parts of the Cordilleran foreland basin in the United States.