Timing of Onset of Volcanic Centers in the Campanian of Western North America as Determined by Distal Ashfalls

• 作者: Janet L. Bertog
• 来源期刊: 地质学期刊(英文)
• 学科: 地球科学
• 关键词: PIERRE Shale Niobrara Formation VOLCANISM FOREARC CAMPANIAN
• 年，卷（期）: 2013,（2）
• 页码范围: 121-133
• 页数: 13页
• 分类号: P5

摘要

Strata of the Late Cretaceous Niobrara Formation and Pierre Shale Group include bentonites that provide a distal record of volcanic activity taking place to the west. Detailed stratigraphic analysis combined with mineralogy and geochemistry of the bentonites indicates the following timing of events: 1) Eustatic sea level fall as a result of the end of the Niobrara Cycle;2) Tectonic deformation of the Western Interior Seaway coincident with tectonism on the Absoroka Thrust in Wyoming and Late Canyon Range Thrust in Utah;3) Backarc volcanism in Montana associated with the Little Elkhorn Mountain volcanic complex;4) Forearc volcanism in the Cascades area indicates subduction of a hot oceanic crust where plagioclase in the oceanic crust is being incorporated into the melt;5) Cessation of tectonic activity results in a return of sedimentation patterns to north-south trending belts with the Boyer Bay and Burning Brule members of the Sharon Springs Formation deposited to the east and the Mitten Black Shale Formation deposited in the basin.