Jurassic onset of foreland basin deposition in northwestern Montana, USA: Implications for along-strike synchroneity of Cordilleran orogenic activity
Jurassic onset of foreland basin deposition in northwestern Montana, USA: Implications for along-strike synchroneity of Cordilleran orogenic activity
复制标题
美国蒙大拿州西北部前陆盆地沉积的侏罗纪起始：对科迪勒拉造山活动沿走向同步性的影响
作者：
F. Fuentes;P. DeCelles;G. Gehrels
地层学、物源和沉降分析表明，中晚侏罗世前陆盆地系统活跃于美国蒙大拿州西北部。碎屑锆石U-Pb年龄和砂岩碎屑模式指示物源来自西侧的增生杂岩体和变形的微地斜岩。开始下沉。170 Ma左右，为前陆盆地系统特征的S形模式。埃利斯群和莫里森组的薄侏罗系沉积物堆积在后隆沉积带中。区域性不整合和/或古土壤带将莫里森与Kootenai组早白垩世前渊沉积分开。这里提出的模型是一致的区域变形事件登记在内陆地区，并挑战以前的解释强烈的穿时开始从蒙大拿州西北部到加拿大南部的科迪勒纳前陆盆地沉积。
Stratigraphic, provenance, and subsidence analyses suggest that by the Middle to Late Jurassic a foreland basin system was active in northwestern Montana (United States). U-Pb ages of detrital zircons and detrital modes of sandstones indicate provenance from accreted terranes and deformed miogeoclinal rocks to the west. Subsidence commenced ca. 170 Ma and followed a sigmoidal pattern characteristic of foreland basin systems. Thin Jurassic deposits of the Ellis Group and Morrison Formation accumulated in a backbulge depozone. A regional unconformity and/or paleosol zone separates the Morrison from Early Cretaceous foredeep deposits of the Kootenai Formation. The model presented here is consistent with regional deformation events registered in hinterland regions, and challenges previous interpretations of a strongly diachronous onset of Cordilleran foreland basin deposition from northwestern Montana to southern Canada.