Print this pageMigration of Cretaceous Depocenters in Response to Dynamic Subsidence above the Farallon Plate
Backstripped and decompacted cross-sections through Upper Cretaceous strata across southern Wyoming and central Utah and Colorado demonstrate that depocenters migrated eastward at rates corresponding to model-predicted rates of migration of the nearly flat slab of the Farallon plate. Maximum rates of subsidence occur when the crest of the flat slab passes beneath a given location. This subsidence pattern is consistent with a dynamic topographic low created by the weight of the sinking Farallon plate.
From 99 Ma to 91 Ma (Cenomanian and most of Turonian) there is little evidence of dynamic subsidence in the Central Rocky Mountains sedimentary basins. At this time, only the inclined leading edge of the Farallon plate had reached the region and this had little impact on subsidence. From 91 Ma to 84 Ma (latest Turonian, Coniacian and Santonian) the dynamic component of subsidence had become dominant, creating regional subsidence across a 500-km wide basin including the Greater Green River basin to the north and the Uinta-Piceance basins to the south. The cross sections document continued eastward migration of depocenters, reaching the Denver-Julesburg basin in the Middle Campanian (80 - 75 Ma), essentially coincident with the arrival of the flat slab portion of the underlying plate.
Total subsidence and the creation of accommodation space also include a narrow western foreland basin within about 160 km of the Sevier fold and thrust-belt. This basin did of course also move eastward over time but a much shorter distance than the dynamic subsidence basin. Also, there is subsidence related to the sediment loading across this entire basin. Finally, global sea levels were about 250 meters higher in the late Cretaceous than they are today, because of much younger seafloor crust in the Pacific-Panthalassan ocean. These four factors combined to create extensive flooding and marine sediment accumulation along the West Coast of North America in the late Cretaceous and also account for similar marine sediment wedges along continental margins overlying subducted oceanic plates elsewhere in the world at the same time (e.g. Western South America, northern and southern margins of the Tethys Ocean in south/central Asia and Middle East/North Africa).
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009