Subsidence And Its Mechanism Of The Late Cretaceous Western Interior Basin In Utah-colorado

The traditional view is that the genesis of the Western Interior Basin in North America during the Late Cretaceous is mainly the flexural subsidence of the lithosphere in response to thrust loading and sediment loading.However,research at the beginning of this century discovered that the subsidence of the Western Interior Basin in North America is also related to the dynamic subsidence caused by the subduction of the Farallon plate.In the late Campanian or Maastrichtian age,the shallow subduction of the Farallon plate led to the development of Laramide orogeny and other faults,and the termination of the Western Interior Seaway.The basins formed by Laramide orogen were closely related to basement-cored uplifts.In order to better understand and study the subsidence mechanism of the Western Interior Basins in North America,we select the range of basin from northern Utah to southern Colorado as the object.After systematically analyze the history and mechanism of the basin subsidence in the Late Cretaceous,it is found that Sevier thrusting,Laramide orogeny and dynamic topography jointly controlled the formation of the Western Interior Basin in North America during the Late Cretaceous in the study area.Based on well data,we established a section across northeast Utah and southeast Colorado.According to the current stratum thickness,we use techniques such as decompaction,paleo-water depth correction,and Airy backstripping to calculate the subsidence of sediment of each well,obtaining the tectonic subsidence curves of each wells,analyzing the one-dimensional subsidence characteristics,and then combine the subsidence data of each well to establish a two-dimensional tectonic profile and conduct two-dimensional subsidence analysis.The late Cretaceous strata in the study area can be divided into four megasequence,each of which represents a large-scale transgression-regression cycle.The tectonic subsidence curve of the basin shows different characteristics due to different tectonic factors or intensity of tectonic activity.The tectonic evolution of the Sevier thrust belt has affected the subsidence changes of the basin.Two rapid subsidence in the basin can be related to the Pavant duplex and the Paxton thrust system activity.According to the characteristics of the tectonic subsidence curves,we believe that the active time of Pavant duplex is 93.6-87.3 Ma;the active time of Paxton thrust is 85.6-80.2 Ma.The restored two-dimensional tectonic subsidence profile shows that the basin strata absolutely record the components of dynamic subsidence,which shows that the subsidence centers were dissimilar in different transgression-regression cycles and migrated eastward,and the average subsidence per million years are completely dissimilar.This indicates that the mantle flow that causes the dynamic subsidence is changing at any time.After85 Ma,the subsidence history of the eastern Uinta basin and the Piceance basin showed a shortperiod fast-slow cycle.This short-term cycle may have to do with the basement uplifts,representing that the onset of Laramide orogeny in the study area can be traced back to the Santonian age.