SEDIMENTATION AND STRATIGRAPHIC ARCHITECTURE OF A MIDDLE DEVONIAN (LATE GIVETIAN) TRANSGRESSIVE-REGRESSIVE CARBONATE-EVAPORITE CYCLE, CORALVILLE FORMATION, IOWA AREA
B.J. Witzke and B.J. Bunker
Geological Society of America Special Paper 321, 1997, p.
Studies in Honor of J. Granville ("Jess") Johnson: Boulder, Colorado
Paleozoic Sequence Stratigraphy, Biostratigraphy, and Biogeography
Klapper, G., Murphy, M.A., and Talent, J.A., eds.
Depositional facies of Coralville strata in the Iowa area characterize late stages of the Taghanic marine onlap and offlap along the margins of the Transcontinental Arch in the cratonic interior of North America. The Coralville Formation forms a discrete transgressive-regressive (T-R) depositional cycle bounded by subaerial unconformity surfaces in the shoreward areas and submarine discontinuity surfaces in more offshore areas. Distinctive sedimentary and biotic associations are identified in inner and middle shelf settings of the continental interior. (1) During transgression, the inner shelf region was characterized by muddy, relatively quiet-water carbonate sedimentation, with low diversity, probably euryhaline shelly faunas. Regression was marked by the progradation of peritidal and evaporitic sediments, and the loss of shelly faunas across the inner shelf. (2) Current energy was frictionally dissipated across the distal inner shelf and shelf margin during sea-level highstand, and peritidal facies prograded to the shelf margin during regression. (3) The middle shelf region was characterized by subtidal carbonate deposition throughout the Coralville cycle. Relatively diverse normal-marine shelly faunas typify the middle shelf region, but lower diversity faunas may suggest salinity stresses during late stages of sea-level fall. The limited biotope across the inner-shelf formed an effective environmental filter that restricted faunal migrations between eastern and western North America during sea-level highstands. Migrations ceased altogether during sea-level lowstands, as inner shelf areas became emergent.