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Lineament Block Tectonics

COMMENTARY
Lineament block tectonics characterize the structural motif or architectonic pattern in continental lithosphere. Lineament blocks are important for shallow gas exploration because:
1. paleotectonism controls deposition and erosion of reservoir rocks, source beds, and seals;
2. post-depositional deformation concentrates small structures in lineament zones between relatively underformed large blocks;
3. fractures along lineament zones influence the movement of gas, oil, and water.

The idea that continental lithosphere is a mosaic of basement blocks outlined by lineament zones is not new. An early interpretation in the Williston Basin was made by Gilbert Thomas (1974); later work throughout the Northern Great Plains was done by the US Geological Survey (Anna, 1986; Brown and Brown, 1987). Over the past twenty years the number of “true believers”, as represented by participants in the conferences on basement tectonics, has grown. Canadians have always seemed more receptive to the ideas, perhaps because the Canadian Shield is an important part of geologic education in Canada.

Landsat images are a primary tool for my interpretations of lineament blocks. J.C. Harkson, during his time with the South Dakota Geological Survey, once suggested that the linear features mapped on images were buffalo trails. It’s a creative thought, but the most complete interpretations incorporate lineament zone expressions from a variety of data layers (Ideas: Figure 3):
1. linear features are visible on satellite images, high altitude air photos, topographic maps, and digital elevation models;
2. basement blocks and the bounding lineament zones have expression on aeromagnetic and gravity maps;
3. patterns in thickness and lithofacies are documented on subsurface stratigraphic maps;
4. geologic structures concentrated in corridors along the lineament zones are shown on structure contour maps and seismic sections;
5. fluid movements influence gas and oil accumulations, ground water composition variations, and surface geochemical anomalies.

CHRONOLOGY
The following list gives an overview of the topical bibliography on Lineament Block Tectonics found in the Publications portion of this website. Complete citations for these GeoShurr papers are in the topical bibliography.

Satellite images, geophysical maps, and stratigraphic data are used to map lineament blocks throughout the Northern Great Plains:
••South Dakota (1981 and 1994)
••North Dakota (1995 and 1996)
••Montana (1989 and 1995)

The structural significance of lineament zones:
••South Dakota and Wyoming (1982 and 1988)
••North Dakota and Montana (1996 and 2000)

Fluid movements along lineament zones take place at a variety of scales:
••Large block boundaries (1989)
••Specific structural features (1990 and 2000)
••Fractured reservoirs (1993 and 2001)

FEEDBACK STARTER QUESTIONS
1. What is the relative importance of horizontal and vertical displacements along block-bounding lineament zones?
2. How does the variation in strength properties, i.e. the “mechanical stratigraphy” influence the vertical assemblage of geologic structures within a lineament zone?
3. Are there examples of geomorphic changes, such as stream gradients, across specific linear features?
4. Why is gas trapped within some lineament zones, but leaks off others? Hydrodynamics? Fracture porosity and permeability?

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