The Early Pennsylvanian (Bashkirian/Morrowan) Round Valley Limestone of northeastern Utah was deposited on the Wyoming shelf, a slowly subsiding depositional surface located between the Eagle and Oquirrh basins. The 311-foot-thick Round Valley Limestone displays a distinct cyclicity formed by stacked, meter-scale parasequences, comprised of a limited suite of open- to restricted-marine limestones with minor interbeds of siltstone and shale. Open-marine deposits are characterized by mudstone and heterozoan wackestone-packstone microfacies (MF1-4) and comprise the lower portions of parasequences. Rocks of these microfacies were deposited during maximum high-order transgression of the shelf. As sediment filled the limited accommodation, the shelf became restricted, leading to deposition of mollusk-peloid dominated wackestone microfacies (MF6). Grainstones (MF5) microfacies are volumetrically limited in the Round Valley and represent deposition on isolated sand shoals that populated the shallow shelf. The complete Round Valley section at Split Mountain in Dinosaur National Monument is comprised of 5 intermediate-order sequences and 48 higher-order parasquences. Twenty-one of the shallowing-upward cycles are bounded by exposure surfaces as indicated by the occurrence of rhizoliths, glaebules, autobreccia and alveolar structures. Four of these that also indicate a significant drop in sea level (abnormal subaerial exposure surfaces and surfaces with erosional relief) constitute candidate sequence boundaries. The high percentage of cycles capped by exposure surfaces indicates that deposition of the Round Valley took place intermittently and that the Wyoming shelf was exposed during a significant portion of the Bashkirian epoch. Intermittency of deposition is confirmed by comparing the thickness and sequence architecture of the Round Valley Limestone with coeval strata in the eastern Oquirrh basin (Bridal Veil Limestone). The Bridal Veil Limestone is four times thicker and contains 24 cycles not represented on the Wyoming shelf.



College and Department

Physical and Mathematical Sciences; Geological Sciences



Date Submitted


Document Type





Lower Pennsylvanian, Bashkirian, Sequence Stratigraphy, Round Valley Limestone, Carbonates, Carbonate Deposition, Shelf



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Geology Commons