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Filling in Gaps in the Sedimentary Record: An Integrated Study of Discontinuity Surfaces in Devonian Epeiric Carbonates, Iowa

Christopher Bowie
California State University, Fresno
Department of Earth and Environmental Sciences
Fresno, California, USA
[email protected]

Discontinuity surfaces develop in carbonate successions due to rapid environmental changes resulting in a hiatus in sediment accumulation or erosion of previously deposited material. Each discontinuity surface therefore, represents a gap in the sedimentary record. Although pieces of the sedimentary record are lost to an unconformity, the diagenetic record is continuous and contains information about the environment and climate leading up to and after a depositional break. By studying discontinuity surfaces, it is possible to explain the cause of these breaks in sedimentation and fill in these gaps in the sedimentary record.

The Middle-Late Devonian Cedar Valley Group was deposited in the Iowa Basin during three third-order transgressive-regressive cycles that flooded the Laurentian craton, depositing shallow subtidal and peritidal carbonates across Iowa and adjacent states. The irregular parasequence stacking patterns and missing depositional cycles in these cratonic ramp carbonates are thought to be the result of a stressed carbonate factory due to poor circulation in the shallow epeiric sea. This hypothesis remains speculative and is in need of further study to constrain the environmental factors that contributed to suppression of the Middle-Late Devonian carbonate factory in the Iowa Basin. An integrated microfacies analysis and magnetic susceptibility study of discontinuity surfaces in the Little Cedar and Coralville formations will be conducted in order to determine the environmental cause of each depositional hiatus and to resolve the high-frequency sea level history of the Iowa Basin.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects