作者: Timothy David John England
DOI:
关键词: Forearc 、 Sedimentary rock 、 Cretaceous 、 Fold and thrust belt 、 Terrane 、 Geomorphology 、 Crust 、 Paleogene 、 Paleontology 、 Structural basin 、 Geology
摘要: Georgia Basin is an elongate forearc basin that initially developed in the Late Cretaceous (Turonian - Maastrichtian). Its origin ascribed to subduction- related lithospheric downwarping of Wrangellian crust trapped within arc-trench gap during active convergence on Pacific margin North America. The sedimentary record this period development siliciclastic Nanaimo Group. group composed distinct, alternating, dominantly coarse grained and fine formations, deposited times high low rates sediment delivery basin, respectively. main control grain size believed be local tectonic activity. Restored thicknesses exceed 5 km. Study western part eastern Vancouver Island adjacent islands reveals a broad spectrum facies associations, including alluvial, fluvial, paralic, neritic mid-bathyal marine deposits. A series regional maps are presented for successive stages basin. Based new paleontological data detailed stratigraphic structural studies, revisions proposed lithostratigraphic nomenclature -- Vitrinite reflectance show much Group mature oil gas generation. reflectance/depth gradients range from 0.17 0.21 log %R₀/km. Thermal history modeling shows prevailing geothermal burial were (heat flux < 58 mW/m²). Tectonic subsistence was up 2.7 km 22 m.y., occurring at essentially constant between 100 200 m/m.y.. lies beneath Strait and/or Cenozoic remained buried until mid- late Eocene after which it tectonically shortened uplifted. southwestern now preserved as southwest-verging, linked thrust system involving its basement, termed Cowichan fold belt. interpreted leading imbricate fan. geometry belt plan profile perspectives illustrates thick-skinned style. Thrusting most likely in-sequence, creating estimated minimum 20-30% shortening basement/cover interface. Both fault-propagation fault-bend folding evident, former being more common. Kinematic indicators no evidence significant transpressional or transtensional displacement fields. sole fault rise northwest southeast deep lateral oblique ramps merge with extension San Juan Fault. This explains rapid westward thickening wedge thrusted basement. In east, locally have permitted overthrust Terrane. Investigation how westward-progressing terrane accretion accommodated region dominated by large slab rigid, semicontinental crust.