The Field Experience, Saturday-Sunday 18-19 October

Participants will be divided into three groups and the field conference will proceed in half-day sections with each group beginning at a different site. Everyone will make all the same stops over the day and a half. Buses will depart promptly from the Ardmore Convention Center/Holiday Inn parking lot at 8:00 am Saturday and return by 5:00 pm. Departure for the field Sunday will likewise be at 8:00 am, returning at 1:00 pm. The following half-day routes with stops are planned:

ARBUCKLE ANTICLINE

OHMEGCO

Development of shale-oil and gas resources over the past 15 years has demonstrated that shales are much more diverse in composition and physical properties than previously realized. This field trip location will provide a hands-on opportunity to walk a previously unexamined and complete section of the Woodford Shale while armed with a synthetic spectral gamma ray log of the outcrop. Comparisons will be made between the gamma-ray response and the different lithologies of the shale while moving up and transitioning between the depositional successions. The lower, middle, and upper informal members of the Woodford will be highlighted. Lithofacies and sequence stratigraphic correlations of the outcrop to the subsurface and to another complete Woodford outcrop section located a few miles away (Henry House Creek) will be discussed. A complete section of the Woodford can be measured at this locality as both the lower unconformable Hunton and overlying Sycamore can be identified. NOTE: Alternate activities based on physical abilities. Measured outcrop is very steep with loose talus. Recommend boots with lugs, walking stick helpful. Correlative units are weathered but easier to observe in same outcrop farther west.

TURNER FALLS OVERLOOK

From the Turner Falls Overlook the East Timbered Hills are visible. Cambrian igneous rocks are exposed here, but due to time constraints and accessibility these will not be observed during the field conference. These rocks consist primarily of extrusive units and felsic intrusions belonging to the Carlton Rhyolite Group and are overlain unconformably by clastic and carbonate sedimentary strata of Upper Cambrian to Orovician Timbered Hills and Arbuckle Groups. Diabase intrusions penetrate the rhyolite succession and represent the youngest phase of Cambrian igneous activity related to the development of the Southern Oklahoma Aulacogen in the Arbuckle region.

Honey Creek and Turner Falls are part of the active karst environment in the Arbuckle Mountains. The source of Honey Creek is a spring 7 miles to the southwest of Turner Falls. Active and inactive travertine and tufa deposits are records of five distinct stages of Pleistocene climate change. Turner Falls is actually building outward as a result of deposition of travertine at this time.

The Cool Creek Formation of the Arbuckle Group is exposed at the overlook. Sedimentary structures of peritidal carbonates and a diversity of morphologic growth forms of algal stromatolites can be observed.

CEDAR VILLAGE (affectionately known as the Fried Pies outcrop)

Standing in a vertical position, the Chimney Hill Group, the Henryhouse and Haragan of the Hunton Group can all be found bordered by the older Sylvan Shale and the younger Woodford Shale. Several unconformities exist between members and formations of the Chimney Hill and Hunton Groups. The contact between the Sylvan and the Chimney Hill Group is abrupt. There appears to be some channeling of the basal Keel Formation into the underlying Sylvan Shale. Previous to Stanley's 2001 work others had not mentioned an erosional surface at the top of the Sylvan. The Bois d'Arc and Frisco Formations are absent at this site; otherwise this location would represent the entire Hunton Group. The excellent exposure of the Sylvan-Hunton contact on the south and the Hunton-Woodford contact on the north make this a most interesting site, spanning about 70 million years. The contacts are sharp and well defined. Still further northward you may see the contact between the Woodford and the Sycamore Limestone. Pyrite clusters and shards of selenite can be found in the Sylvan Shale. The Keel Formation contains silicified ooliths and green flecks of glauconite which help identify it in the sub-surface. The limestone units may contain fossil brachiopods, bryozoans, and crinoid flotation bulbs.

NORTHERN ARBUCKLES

BORAL AGGREGATES DAVIS QUARRY

Deformed Viola Limestone is quarried for aggregate at this location. Quarrying operations provide an opportunity to examine one of the many folds of the northern Arbuckle Mountains near the Washita Valley Fault, in this case an asymmetrical syncline. Associated faults have been mapped in the area and fractures are numerous. Some fractures are calcite filled with solid hydrocarbon residue also present in the fractures. Hydrocarbons of unknown composition seep from fractures in the quarry walls. The surface syncline is riding on a thrust fault dipping southwest. The south-west Davis Field was discovered below the thrust complex and produces from the basal Oil Creek Sandstone in an anticlinal trap. Active wells are present on the west side of quarrying operations that produce from the subthrusted anticline.

HUNTON ANTICLE QUARRY (access is obtained by a walk of about 1/8th of a mile on an old washed-out road with high weeds, with a moderate uphill grade)

Whole-fossil wackestones and carbonate mudstones of the lower Devonian Bois d'Arc and Haragan Formations are exposed within a broad, symmetric anticline along the east and south sides of the quarry walls. The abandoned quarry operations provide a unique opportunity to observe a faulted anticline in three dimensions. This small-scale fold in proximity to the Reagan Fault provides an analog to the overall structural style of the Arbuckle Mountains. Outside and north of the main quarry, good exposures of the Woodford Shale (upper Devonian – lower Mississippian) can be observed, consisting of laminated, black, phosphatic shale, interbedded with thin, light gray chert beds. Multiple studies have been performed on the Woodford Shale at this location due to its importance as a source rock and unconventional reservoir.

EASTERN ARBUCKLES

MILL CREEK GRANITE QUARRY

The rock being quarried is the Troy Granite, which is cut by numerous diabase dikes. The quarry produces crushed stone that is used mainly as railroad ballast. This quarry is the best exposure of diabase dikes in Oklahoma and probably in the central interior of the United States. The diabase dikes are part of a swarm that is widespread throughout the core of the eastern Arbuckle Mountains. They intrude the 1400 to 1365 Ma granitoids of the eastern Arbuckles. The dikes strike predominantly N 60° W parallel to the rifted margin of the Southern Oklahoma Aulacogen. Most the diabases are related to Cambrian opening of that structure. In addition an unknown but probably small number of low-Th diabase dikes were emplaced near the edge of the host granitoids. These, along with a suite of silicic northwest-trending microgranite porphyry dikes, record a Mesoproterozoic structural grain that may have influenced Paleozoic structure.

U.S. SILICA OIL CREEK SAND QUARRY

The basal sand of the Oil Creek Formation is 350 feet of stacked beds of pure quartzose sand. Uniformity of the grain size inhibits the ability to see sedimentary structures. One interpretation is that this sand is the product of storm-influenced sedimentation in an inner-shelf setting. Each storm deposit consists of a sand bed 1-10 inches thick derived from wave action and erosion inshore, capped by a clay layer several millimeters thick deposited after the storm. Textural and compositional evidence suggest that the sand grains have passed through an eolian cycle, and that the sand was probably transported to its present location from the north. The sand is unconsolidated with high porosity and high permeability. In spite of its age, the sand has remained friable because the deposit was not subjected to diagenetic cementation. A sample placed in water soon disaggregates into loose sand grains and a milky clay fraction held in suspension. The sand is 99.9% pure silica sand with clay impurities that are removed by scrubbing/flotation. Iron is the chief impurity in the sand, and the sands mined by hydraulic methods at this quarry have only about 0.010% iron (as Fe2O3,) making them suitable for such applications as optical glass, lenses, and other uses where a very pure sand is required. It has been estimated by Tom Olsen that in the Cumberland Field (5S-7E) to the southeast in Bryan County the Basal Oil Creek has produced in excess of 1 million barrels of oil per well.

AMOS CONLEY ROAD (proposed; due to a recent change of ownership of this property it is unknown if this exposure will be accessible at the time of the field conference)

The road cut exposes the Timbered Hills Group, of Cambrian Age. The Reagan overlaps the underlying Troy Granite on the nonconformity surface. The Honey Creek Limestone can also be seen in this road cut. The Reagan Sandstone and the Honey Creek exhibit thickening and thinning as a response to the underlying topography of the granite surface present at the time of deposition. The Fort Sill Formation shows abrupt gradation of limestone into dolomite in the vicinity of the buried hills. The inference is that both thinness and dolomitization here are related to deposition in extremely shallow water around the shores of granite islands.

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