Karyn A. Alme

Date of Award


Document Type


Degree Name

Master of Science (MS)


Geological Engineering


The western Cold Turkey Creek structural anomaly is a subsurface structure in Bowman County, North Dakota, near the southern margin of the Williston Basin. The stucture was identified by oil explorationists as a possible impact crater, but its origin remained uncertain. The purpose of this study is to attempt to ascertain if sufficient evidence exists to determine that the anomaly is of impact origin.

The study area was confined to a nine township area surrounding the anomalous stucture in Bowman County, North Dakota. One hundred six oil exploration wells were identified in the area, and well logs were examined and interpreted for each. The resulting data were used to generate an isopach map for each of twenty-nine lithologic units identified, and an additional five structure contour maps were generated on the tops of conformable units. Units were correlated and two cross-sections through the structure were generated. One core from a well which penetrated the structure was available for study; it was examined and described. Previously published seismic data were also evaluated and interpreted.

Examination of the isopach maps reveals that significant variations in the thickness of multiple lithologic units occur both within the structural anomaly and in the surrounding study area. Results of this study indicate that all of the lithologic units present within the study area are continuous across the structural anomaly, except one which is discontinuous throughout the study area and doesn't occur in the structure. Examination of the core revealed nothing suggestive of shock due to explosive impact cratering; only normal sediments were seen. Seismic data and structure contour maps indicate that the shape of the structure is neither circular nor bowl-shaped. Cross sections clearly demonstrate that the anomalous structure developed intermittently from at least the Ordovician until possibly as late as Early Jurassic.

The western Cold Turkey Creek structural anomaly is interpreted to be a complex structure with a long history of development, exhibiting rapid thickness variations over small areas that are suggestive of multiple episodes of up and down motion within the structure. The shape of the structure is inconsistent with that of impact craters, and there is a lack of secondary evidence, such as shatter cones or planar deformation features, to suggest impact as a causal factor. Stratigraphic units appear continuous across the structure and do not show the effects of deformation by hypervelocity impact. The subtle variations in shape, size, and location of the structure suggest that it has developed over a long period of time and therefore, is not the result of an instantaneous event.