Harald S. Poelchau1, John H. Doveton1, Daniel F. Merriam1
(1) Kansas Geological Survey, University of Kansas, Lawrence, KS
ABSTRACT: Estimating Maximum Burial and Erosion for Basin Modeling in Western Kansas
Kansas, although situated in the continental Stable Interior, has had a varied tectonic history. The stratigraphic column displays several major unconformities. In order to understand the basin history and model the thermal evolution of the area, we need to reconstruct the amount of burial and erosion involved. Important are the late Cretaceous event that exposed the present surface and the late Paleozoic event that removed a considerable amount of Permo-Pennsylvanian sediments.
K. Magara's method of extrapolating sonic-log transit-time values is used in this area for the first time to estimate maximum burial. Among the abundance of wells in Kansas there are a few that were logged with the sonic tool in the shallow Cretaceous formations. Selecting only the transit time values from shales (as identified from the gamma-ray log), a semi-log plot for the most compacted shales in each formation can be extrapolated to normal surface values (ca. 200 µs/ft). The difference in depth above the present surface is an indication of how much additional burial the area has experienced in the past.
Based on estimates from a number of wells across western Kansas, a trend surface of maximum burial (and erosion) has been mapped to help with reconstruction of burial history for basin modeling. The estimation, however, is complicated by the tectonic history of the area as well as by the laterally changing composition of the stratigraphic units. A particularly interesting problem is presented by the marly nature of many shales, influenced by their position on the eastern shelf of the Cretaceous Interior Seaway, and the change in their compaction behavior. A further challenge is the problem of unraveling the compaction history of the Paleozoic shales that have undergone several events of burial and erosion.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado