ABSTRACT: Timing of Evaporite Dissolution, Prairie Formation, North-Central North Dakota

Wayne Harris

Previous studies indicate that dissolution of the Prairie Formation has occurred along the eastern margin of the Williston basin. Evidence used to document dissolution includes anomalous thinning of the Prairie Formation across relatively short lateral distances; structural and stratigraphic disturbances above the zone of suspected dissolution, but not below it; presence of a breccia immediately above the zone of suspected dissolution; and anomalously thick stratigraphic units at various levels above the zone of suspected dissolution. Many of the questions concerning the evaporite dissolution phenomenon have been addressed; however, many have yet to be answered.

The objective of this study is to determine the areal extent and timing of salt dissolution that occurred along the eastern depositional margin of the Prairie Formation. This will be accomplished by documenting the effects it had on stratal thickness, paleostructures, and modern structures in the study area, which includes all or part of Bottineau, Rollette, Ward, and McHenry Counties of north-central North Dakota.

As a result of this study, spatial and temporal patterns of the effects of evaporite dissolution should be recognized and causal relationships identified. This could provide a means for predicting the structure and stratigraphy outside of the present-day salt dissolution edge of the Prairie Formation.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990