Utah: A geologist’s wonderland
Chetan Patel (USA)
Often referred to as the Red Rock Country, the state of Utah boasts some of the most breathtaking landscapes formed from years of erosional artistry. Dominating this impressive landscape is the Colorado Plateau that spans the four states of Colorado, New Mexico, Arizona and Utah. Adjacent to the Colorado Plateau, separated by the Wasatch Fault Zone, is the Basin and Range Province, another expanse of geological wonder formed during the Laramide Orogeny. These spectacular landscapes, dominated by the eponymous red rock, offers geologists a great opportunity to study both modern and ancient processes in great detail. With favourable weather and easily accessible outcrops, Utah serves up an exciting geological journey.
Within Utah, resides what is commonly referred to as the mecca of sequence stratigraphy, the Book Cliffs. These offer a wonderland of stratigraphic sequences to the travelling geologist. In fact, hosting a wide variety of easily-accessible outcrops, Utah has become a premier location for the study of sequence stratigraphy, specifically in the oil and gas industry. The well-exposed outcrops offer a detailed look into facies relationships providing the perfect outcrop analogues to subsurface exploration. The name “Book Cliffs” was coined by the early settlers of the region to which the alternating layers of shale and sandstone resembled the pages of a book on its side.
The Book Cliffs lay within the Colorado Plateau, with the escarpment spanning over 250km and across the two states of Colorado and Utah. The well-preserved cliffs record a large series of prograding clastic sedimentary wedges, deposited along the western margin of the Western Interior Seaway during the Cretaceous period. The cliffs were uplifted during the Sevier Orogeny and have undergone little deformation with a gentle structural dip. Several of these prograding wedges can be traversed and logged in great detail, revealing insights into the complex stratal architectures and the controls on such sequences.
Travelling through the towns of Helper and Green River, across the cliffs, provides a unique journey into the prograding wedges. Shallow marine depositional systems dominate in the Book Cliffs with the base succession being a thick layer of marine shale, known as the Mancos Shale. Within this are ‘tongues’ of interfingering prograding shallow marine sandstone formations, such as the Panther Tongue. These different sandstone bodies represent different parasequences and marked bounding surfaces. By correlating the different successions observed, stratal stacking patterns and geometries can be established, providing a significant understanding about subsurface hydrocarbon reservoirs.
Utah also offers the greatest concentration of national parks in the US, with the Arches National Park serving as a great break from the geology. Carved out of the Entrada sandstone, erosional processes have carved impressive arches only a short hike away from the park centre.
References
Map of Colorado taken from http://folk.uib.no/nglhe/coloradoPlateau.html.
Gary J., Hampson, John A. Howell, and Stephen S. Flint, (1999), A Sedimentological and sequence Stratigraphic Re-Interpretation of the Upper Cretaceous Prairie Canyon Member (“Mancos B”) and Associated strata, Book Cliffs Area, Utah, U.S.A, Journal of Sedimentary Research, Section B: stratigraphy and Global Studies, Vol. 69, No. 2, Pages 414-433.
http://www.sepmstrata.org – Sequence Stratigraphy resource.