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Chapter 2 REGIONAL GEOLOGY OF STUDY AREA

REGIONAL STRUCTURE OF STUDY AREA

The study area in Oklahoma County, Oklahoma is on a major continental structural feature, the Nemaha Ridge, shown in Figure 2-1. The ridge runs from north to south from southern Minnesota through Kansas and ends south of the study area in Norman, Oklahoma. Large fault zones bound the ridge, causing basement structures that sometimes result in prolific structural oil and gas production, such as the Oklahoma City oil and gas field. Many significant faults have been intermittently active for hundreds of millions of years and are still active now (Luza and Lawson, 1981). The McClain County fault complex defines the western border of the Nemaha Ridge (Burkett, et al, 1985), where a major depression ­ the Anadarko Basin ­ is a significant sediment trap. Geomorphic features in Oklahoma are significantly affected by the regional structure. The major river systems in the Midwest generally run from west to east due to the tilt of the Great Plains by the Rocky Mountain system. Rivers in the northern two-thirds of Oklahoma are forced to bend south as much as 75 miles before they are able to cut across the Nemaha Ridge. In addition, LANDSAT and photo anomalies, as well as surface and subsurface geology and geophysics, have proven that fracture lineaments, faults and structures define and control the shape and course of Oklahoma rivers (Cannon, 1973, p.21-22, 80; Davis, 1909, p. 343; Ken Johnson, oral communication 1999; Luza, et al, 1982, p. 11, 1987, p. 15-17; Petzel, 1974; Zabawa, 1976). Stewart (1962, p. 62) bluntly stated that in Cleveland County, Oklahoma, "streams, fracture traces and lineaments are affected by subsurface folds and faults."

PROJECT AREA GEOLOGY

Figure 2-1 Structural Provinces of Oklahoma (after Northcutt, R., and Campbell, J., 2004)

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 6 of 80

The project area consists of sediments of lower Permian age, dominated by the undifferentiated sandstones of the Garber Formation and the sands, shales, and mudstones of the Wellington Formation (see Figure 2-2 and Figure 2-3). The area is situated on the eastern side of the Anadarko Basin. The Nemaha Ridge defines much of the eastern edge of the Anadarko Basin, while to the east was subarial terrain (Johnson, 1988). Farther east was the source of the Garber-Wellington streams, the Ozark Mountains. The Lower and Middle Garber-Wellington sequence was probably trangressive. Fluvial channel deposits that trend generally east-west characterized the sequence. These channels were characterized by active downcutting and filling of scour channels with sand. Such deposition in a fairly flat terrain indicates a terrestrial upper delta deposition. The Upper Garber (especially in the western part of the area) appears to have been a terrestrial sequence representing very arid conditions, such as a sabka. These deposits are less confined to thick, well-defined channel sandstones, and correlate more often with wide, uniform sand sheets encompassing large areas. Hennessey shale conformably overlies this Upper Garber section.

Hennessey Shale Sediments

The overlying Hennessey Shale Group is predominantly of marine origin. The lowest portion of the Hennessey contains shales with a few stray sandstones. The percent of sand increases in a southerly direction. South and southwest of the study area the Hennessey Shale Group grades laterally into the Duncan Sandstone (OWRB, 1971, p. 24). Highway excavations have shown that the weathering zone in the Hennessey shales is ten to fifteen feet in depth. These weathered zones are fractured due to the expansion and contraction

Figure 2-2 Generalized Stratigraphic Column ­ Project Area

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 7 of 80

Figure 2-3 Simplified Geologic Map of Project Area (after OGS, 2003)

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 8 of 80

Figure 2-4 Garber Sandstone Outcrop on Sherrywood Road

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 9 of 80

of the shale and the leaching of minerals. Along the truncation of the Hennessey, the unit produces some usable water in a perched water table. These sediments indicate increasingly marine conditions higher in the section and westward into the old Anadarko Basin. Higher in the section, the shales are interspersed with thin gypsum beds (1/2-2 inches thick). Bedded gypsum has been recovered in cores and cuttings from all but the basal twenty feet of the Hennessey in Cleveland, Oklahoma and Canadian counties (Becker, et al, 1997). Hennessey shale is very tight, impermeable shale (Becker, et al, 1997). However, this shale produces water for hundreds of domestic wells, especially in western Oklahoma County and eastern Canadian County. Adequate water for domestic and irrigation use can be acquired from the Hennessey if one drills in a fracture. These fractures can produce 50 gpm in a small bore well. Springs are commonly found at the intersection of two or more fractures in the Hennessey shale.

Garber-Wellington Aquifer Sediments

The Garber-Wellington is composed of interbedded sandstones, shales and traces of carbonates. There are major sandstone channel fill deposits with associated levee and splay deposits off the main channels. These channels are associated with inter-channel shales. Freshwater carbonates formed most likely as caliche in the arid environment of the Lower Permian (McBride, 1978, p.105). These caliche beds were reworked in pebble conglomerates in the base of the fluvial sediments (Figure 2-4). The sands are fairly uniform and very fine. Productive water sandstones have a measured porosity range from 25-35% and transmissivity from 5,000-8,000 gallons per day per foot (gpd/ft). In examining deep (exceeding 600 feet) GarberWellington wells, in non-depleted areas one can expect to get 1.2-1.7 gallons per foot of aquifer exposed in the well bore. There are few impurities in this terrestrial clastic system. There are a few rare hematite deposits where iron appears to have concentrated along weathering zones, and even rarer dolomite deposits, which could have been caliche, deposited in the same environment.

Figure 2-5 A Well Log Example

Well Logs

In order to gather data concerning the subsurface geology of the aquifer, geoscientists use geophysical instruments to examine the aquifer sediments and water. Figure 2-5 is an example of a well log. To the left of the log center is the gamma ray log curve. The gamma ray log defines rock quality and composition. A positive gamma ray response (toward the right of the log) indicates shale sediments. As the gamma ray curve moves left of the log, it indicates cleaner sandstones.

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The right side of the log contains the resistivity curves. These curves define water quality (Jones and Buford, 1951, Turcan, 1966, Schultz, 1992, Roberts, 2001). As the curves move toward the left of the log (lower values), the water contains more dissolved ions, especially sulfate, sodium, and chloride. As the curve moves right, zones with high resistivity readings signify higher quality water. Unfortunately, neither of these logs can specifically define amounts of alkalinity, hardness or toxic metals. Geoscientists use geophysical well logs for a variety of purposes, but the major application is to generate cross-sections ­ a visual slice through the earth ­ in order to determine the depth and orientation of each sand or shale in the project area. This is done by lining up well logs in a sequential manner and correlating one sequence of rock on one well log with the same sequence of rock on the next well log.

Cross Sections

Figure 2-7 is a "dip" cross-section, reflecting the regional orientation of the rock units in this area. The Permian units are tilted down to the west at a rate of about 40 feet per mile, although as the cross-section reveals, the rate can vary widely and even occasionally reverse itself. The changes in the regional dip rate are associated with deeper structural features associated with the presence of the Nemaha Ridge. The westernmost well logs show the Hennessey Shale units at the top of the well log (colored in orange), while the well logs at the east side of the project area show the Garber sandstone (yellow) at the surface. The sand units inside the Garber sandstone are extremely difficult to correlate, even over short distances of a mile or less. The well logs show ample evidence of scour and redeposition. The well logs also show few correlatable shale layers in the unit. The older Wellington formation (purple) does have correlatable shale units and were differentiated into four separate units. The Wellington "C" unit has a close association with the sandstone units that produce high arsenic water in this area, based on zone-specific water samples taken in municipal water wells.

Depositional Environment

Previous work in the Garber and Wellington units note the fact that they are surprisingly free of fossils and coal normally associated with a deltaic environment, yet the geophysical log response (Figure 2-7) suggests a fluvial deposition. The morphology of the mapped units (Figure 2-8) suggests also a deltaic pattern. Several authors (Schlottman-Norvell, 1995) have suggested a depositional environment similar to a sabka - a wide area of coastal flats bordering the sea. This would fit the geomorphic model shown in the inset of Figure 2-9 ­ a very arid environment with minimal biological activity, with depositional activity occurring only at intervals associated with large flood events. A typical example of a sabka environment would be the Sinai Peninsula region in the Middle East, as shown in the aerial photo in Figure 2-9.

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 11 of 80

Figure 2-6 Cross-Section Location Map (After ACOG, 2004)

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 12 of 80

Figure 2-7 Cross-Section A-A' (after ACOG, 2004)

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 13 of 80

Figure 2-8 Sand & Shale Distribution Wellington `C' Interval (after ACOG, 2004)

Association of Central Oklahoma Governments Garber-Wellington Association Assistance ID C6-400000-44 Grant Number: 604(b) FY: 2004 Task: 300 Page 14 of 80

Figure 2-9 Sabka Model for the Wellington Unit (Walker, 1984)

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Microsoft Word - Saltwater Contamination Mapping in Oklahoma County.doc
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