The late Middle Jurassic (Callovian) Entrada Sandstone has been divided into two general facies associations consisting primarily of eolian sandstones in eastern Utah and "muddy" redbeds in central Utah. Sedimentary structures within the redbed portion are explained by the interfingering of inland sabkha, alluvial, and eolian depositional systems. A complete succession from the most basinward facies to the most terrestrial facies in the Entrada Sandstone consists of inland sabkha facies overlain by either alluvial or eolian facies. Where both alluvial and eolian facies interfinger, alluvial facies overlain by eolian facies is considered a normal succession. Sequence boundaries, often identified by more basinward facies overlying more landward facies, are observed in the Entrada Sandstone and are extrapolated for the first time across much of Utah, including both the eolian-dominated and redbed-dominated areas. Using these sequence boundaries as well as recent tephrochronologic studies, three time correlative surfaces have been identified in the Entrada. Based on the facies interpretations at each surface, five paleogeographic reconstructions and five isopach maps have been created, illustrating two major intervals of erg expansion and the location of the Jurassic retroarc foreland basin's potential forebulge. Eolian (erg-margin) sandstones pinch-out into muddy redbeds creating combination traps, as evidenced by dead oil (tar) and bleached eolian sandstone bodies within the Entrada. The Entrada Sandstone is a world-class analog for similar systems, such as the Gulf of Mexico's Norphlet Sandstone, where eolian facies grade into muddy redbed facies.
College and Department
Physical and Mathematical Sciences; Geological Sciences
BYU ScholarsArchive Citation
Jennings, George R. III, "Facies Analysis, Sequence Stratigraphy and Paleogeography of the Middle Jurassic (Callovian) Entrada Sandstone: Traps, Tectonics, and Analog" (2014). All Theses and Dissertations. 4083.
Entrada Sandstone, late Middle Jurassic, Callovian, facies analysis, paleogeographic reconstruction, isopach map, hydrocarbon trap, stratigraphic trap, eolian, alluvial, sabkha, redbed, erg-margin, Norphlet Formation, sequence stratigraphy, Utah, terrestrial sequence stratigraphy