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The AAPG/Datapages Combined Publications Database

Abilene Geological Society

Abstract


AAPG Southwest Section Meeting, Transactions and Abstracts., 1999
Pages 73-73

Prospecting with Wrench Faulting in West Texas

G. Pat Bolden

Abstract

In West Texas there are four basic directions of wrench fault movements listed in order of movement: 1. Conjugate Riedel (R'), right lateral & 54° T, 2. Riedel (R), left lateral 90° T, 3. Primary Shear (P), left lateral and a combination of R & R' 320° T, 4. Fold fault(F) right lateral & 355° T. These four directions are mostly straight lineaments, however some are curvilinear. Many of the curvilinears are transiatory faults and rotate large blocks. This changes the directions of the straight lineaments. The straight lineaments should be worked first on High Altitude Photos from EROS Data Center, Sioux Falls, SD, at a scale of 1"= 1250' (Code 66 - 36 inch in color) that will reveal the lineaments in all of the directions of wrench faulting. These can be seen on the photo because of the water in the fracture watering vegetation and also the leakage of hydrocarbons into the fractures change the soil chemistry and vegetation.

The P Shear is left lateral and the south side of the fault moves southeast whereby the R' is right lateral and the south side of this fault moves southwest thus causing a collision of the rocks south of the perpendicular intersection of faults causing a structure to be developed here. This can be seen at Jaybird Field in Garza Co. and Anton Irish Field in Hale and Lubbock Counties, Texas. The biggest of them all would be the Central Basin Platform.

Look for curvilinears that almost make a circle and you are looking at a flower structure or a pop-up-block. These can be between two Primary Shears or two Conjugate Riedel Shears and 700' to 2 miles in diameter.

Along P Shears there are scissor faults that may be found by botryoidal features on the structure. Botryoidal features are caused by oil or gas leaks that change the surface to look like honeycombs on the surface. Brown-Bassett and JM Gas Fields are good examples of scissor faults and a field on each side. These fields also have younger beds on top of the structure.

A photo should never be marked on with a grease pencil (Staedtler Omnichron 108-2 Germany). Always put a clear acetate overlay on the photo and tape only at the top of the photo. Index the acetate overlay with black grease pencil and mark all the culture that is not easy to see, i.e. fence comers, section corners. Do not mark roads that are easy to see, however mark the highway number or name of the lane.

Make all interpretations in red, marking all the straight lineaments first. Even though you see the curvilinears, don't mark them because it prevents your seeing the straight ones. Note directions each fault moves and note collision of rock movement.

Curvilinears are sometimes almost circular and are normally between either P or R'. It makes no difference which way it turns to be a pop-up-block or flower structure.

Go over photo with hand held magnifying glass to look for botryoidal or honeycomb indications.


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