611 research outputs found
Precambrian Well Data in Nebraska, Including Rock Type and Surface Configuration
This bulletin presents, in tabular form, information relating to the Precambrian surface and includes a configuration map of this surface in Nebraska. The data from all of the 1460 deep tests reaching the Precambrian as of January 1, 1966 are listed. It is anticipated that further studies utilizing this data will be made due to the important influence of the Precambrian surface on later sedimentation and structure and the possibility of minerals of economic importance being present in Precambrian rocks. Specific information for each well and samples, except as noted in the tabulation, are on file and available for study in the offices of the Nebraska Geological Survey. Separate copies of the included configuration map and blue-line copies of this map at a scale of 1:500,000 are available. Blue-line copies of the detailed configuration of the Precambrian surface for an eleven county area in southwestern .Nebraska and a thirteen county area in southeastern Nebraska are available at a scale of 1:250,000.
Map of Precambrian surface attached below ( 9 MB jpg
Lithostratigraphy and Correlation of the Mississippian System in Nebraska
The purpose of this study is to describe and correlate rocks of Mississippian age within the state of Nebraska. Shales, generally classified as Chattanooga and commonly referred to as Devonian or Mississippian in the northern Mid-Continent, have been included in this study, although these shales are more generally believed to be Devonian and not Mississippian by most stratigraphers and paleontologists at the present time. Since rocks of Mississippian age are present only in the subsurface of Nebraska, the basic information for this report is derived from the microscopic study of cuttings and cores from test wells drilled within the state
Island arcs, accretionary terranes and Midcontinent structure New understandings of the geologic architecture of the U.S. Midcontinent
A data base collected over the last 100 years, containing both surface and subsurface information, has allowed us to begin to understand the physical framework of Nebraska. We have learned that even in the stable Midcontinent region of North America, there has been an active geologic history. This framework has been deciphered by our programs of surface geologic mapping and by the study of rock samples from both water wells and those deeper test wells for oil and gas. Determining the major structural features across the state (figure 1) has allowed us to better understand both the occurrences of its natural resources and natural hazards.
It has been a more difficult problem to explain the process by which this physical framework was established. The last 500 million years of our geologic history is recorded in sedimentary rock layers of sandstone, limestone and shale. These units record an active history of deposition, uplift and erosion. However, it is the older, crystalline igneous and metamorphic rocks of Precambrian age that control the zones of structural weakness across the state. Only by understanding the history of these much older basement rocks - their composition and their method of formation - can we explain the current architecture of our state and possibly anticipate where future activity might occur
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