Petro97 field trip

Note: This document was prepared informally and contains jargon and unconventional abbreviations.

GEOL 3164 PETROLOGY FIELD TRIP SPRING 1997
WICHITA MOUNTAINS, OKLAHOMA, WITH STOPS IN ARBUCKLE AND OUACHITA MOUNTAINS IN OKLAHOMA, AND THE CRETACEOUS OF ARKANSAS

This field trip concentrates most of its time to the Wichita Mountains of SW Oklahoma, where compostionally bimodal igneous rocks can be seen, also with stops in the Arbuckles to see carbonate sedimentary rocks as well as Precambrian gneiss, and in the Ouachitas to see clastic sedimentary rocks and a Mississippian tuff. In addition is one stop to see Cretaceous evaporites. Unfortunately the trip was cut short by some truly awful weather that literally flooded out our first night of camping with a thunderstorm that lasted all night long and was followed by freezing temperatures in the morning. Plan any trip of this nature for after April 15, if done in the spring!

The photos shown on the web page are from another field trip taken to some of the same sites (ie. in an earlier year). Click here to see additional photos.

BRIEF INTERPRETIVE GEOLOGIC HISTORY OF THE WICHITA MOUNTAINS AREA:

A pictoral sequence of events is summarized in Fig. 1 (Wichita Mtns area) from bottom to top. A supercontinent is thought to have existed in the late Precambrian. Rifting of that continent to form an ocean basin occurred in the latest Precambrian through middle Cambrian. Part of the rifting system included an aulacogen (a failed rift arm) called the Southern Oklahoma Aulacogen. In that aulacogen the rifting process included intrusion of a series of mafic igneous rocks including the Glen Mountains layered complex (GMLC). Later, intrusions and extrusions of felsic igneous rocks created rocks such as the Carlton Rhyolite, Mt. Scott Granite, and Quanah Granite. Following rifting, this area subsided below sea level, receiving about 4.5 km of sediment, much of which was carbonates (showing that this area was continental shelf during that time). These rocks (upper Cambrian through Mississippian age) are exposed in the Slick Hills, nearby to the north on the edge of the Wichita Mtns., but a more complete section is exposed in the area of the Arbuckle Mtns, where we will stop briefly on the second day of the field trip. In the Pennsylvanian, uplift of this area began along north verging, south dipping thrust faults (related to the closure of the ocean basin and the creation of "Pangea"). [Note that the "frontal faults" shown in top diagram of Fig. 1 are shown as vertical, but this was purely schematic, and the author acknowledges that they dip 30-40^oS, as shown in Fig. 2). The thrusting in the Wichitas area is probably a related deformation event to that of the Ouachitas in Arkansas and eastern Oklahoma, and the deformation of the rocks in the Arbuckle area also is the same. As uplift proceeded, sediments were shed off the rising and eroding upthrust sheets. These Pennsylvanian through Permian sediments collected in the downwarping Anadarko basin to the north of the Wichita Mtns area (downwarped because of the tectonic loading of the crust?), accumulating another 7 km of sediments there. Thus, only 10-15 mi north of the summit of Mt. Scott, rocks equivalent to those exposed on Mt. Scott and the area of the Wichita Mtns are buried under 12 km of sediment. (Contemplate the magnitude of uplift!) Part of this sediment, the Permian Post Oak Conglomerate, occurs unconformably on the rocks in our field trip area.

DAY 1: Drive to Wichita Mountains area

DIRECTIONS: Go about 260 mi to OK City on I-40. Go SW on I-44 (Bailey Turnpike) about 90 mi to exit for Rt 49 (near Ft. Sill). Go W about 7 mi through Medicine Park to Wichita Mtns Wildlife Refuge where we will camp at the Doris campground.

DAY 2: View igneous rocks and features of mafic/ultramafic and of granitic intrusions

We will see in a series of exposures in the Wichita Mountains various igneous intrusive and extrusive features.

STOP 1. Mt. Scott summit.
From campground go few miles east on Rt 49. Take summit road on north side of road to the top.

Discuss local geology in overlooking scenery and the aerial photo (Fig. 3). Also look at the Mt Scott granite, a fairly fine grained hypersolvus granite (one alkali feldspar, exsolved into perthite). An A-type granite (alkalic) with chloritized hb + mt, in places "granophyric". Look for characteristic "ovoid feldspar phenocrysts" (these probably are not really that large).

STOP 2. Metamorphic rocks and Carlton Rhyolite

This is at the base of the Mt Scott summit drive at the Mt Scott picnic grounds. See Fig. 3&4. The picnic area is underlain by Meers "dirty" facies metaquartzite (metagraywacke?). Look for exposures in two broad, shallow excavated pits immediately south of the east picnic area restrooms.

Look for area of contact of Meers quartzite and Carlton Rhyolite near west end of picnic area (see map). Alignment of feldspars in rhyolite taken as bedding orientation. Strike N50-80E, dip 10-15N. Interpreted as rhyolite overlying Meers quartzite.

Go to area where a gulley (see photo and map) crosses Rt 49, just east of the ramp that connects to summit road. Go up the gulley and see otcs of Meers quartzite. Just before culvert where gulley goes under summit road is otc of Mt Scott granite. For about 10 m up section it is "Facies B" of the granite, a finer grained rock; then it becomes regular Mt Scott granite (Facies A). The granite must be in a horizontal sill-like body with the base exposed here because back across the road on the other side of the picnic area is more Mt. Scott granite (see B-B' cross section). A little west (about 1500 ft) the quartzite/rhyolite contact is truncated at the granite contact. The granite is younger than both of the other units.

STOP 2, ALTERNATE. Carlton Rhyloite/Mt. Scott Granite timing relations. Post Oak Cgl.

To get to this stop from Stop 1, turn east on Rt-49 out of summit drive. As approach area of Medicine Park Fish Hatchery (no more than about 3 mi?), just after Medicine Creek, is a small picnic site on the N side of the road. Park there. A small bluff/road cut trends east from there.

Mt Scott granite here is the "Facies B" type (finer grained, thought to be sort of near outer contacts). The granite is cut by a Carlton Group rhyolite dike. Apophyses of the rhyolite into the granite, and feldspar phenocrysts aligned with the margins both prove the younger age of the rhyolite. Since the rhyolite is finer grained than the granite, there must have been some uplift and erosion of the terrane after intrusion of the granite and before intrusion of this rhyolite. Other places (including Stop 2 above) have the granite post dating rhyolite! During the felsic magmatic event there must have been extrusion of volcanics, intrusion of magma into the extruded pile, further uplift, further intrusion of felsic magma as shallow dikes (presumably feeding to the surface) through the coarser intrusions, etc.

At the east end of the cut is Post Oak conglomerate of Permian age with clasts of Mt Scott granite and Carlton Rhyolite. The clasts in the cgl are the geologic proof that the cgl post-dates the two igneous rocks. The contact therefore is a nonconformity. The white bleaching of the rock near the contact is thought to be a result of greater degrees of ground water flow in that zone.

STOP 3. French Lake area. (See Fig. 5)

From stop 2 go back past campgrounds a few more miles to Wildlife Refuge Headquarters (not "Quanah Parker Visitors Center"). Turn south there on Indiahoma Rd to French Lake parking area (a short distance).

West side of the parking area should have otcs of Post Oak cgl (Permian) with rounded clasts of Mt. Scott granite (age relations!!).

East out of parking area is a bridge at a trail head. Across it is otcs of Quanah Granite (hopefully distinguishable from Mt. Scott granite). Go right after bridge and take Elk Trail Loop. Guide book says "to proceed on the Elk Trail Loop, cross the bridge, turn right (southerly) onto the trail system, and then turn left at the first opportunity to arrive on the Elk Trail segment." Then is says "Immediately behind the trail signpost and between the trail segments are inclusions of Mt. Scott Granite and metasediments; there are also aplites--some with pegmatitic margins." TRY TO FOLLOW THESE DIRECTIONS AND LOOK FOR THESE OTCS.

Further up the trail look for pegmatites with feld xls growing off margin into interior. (Quanah is the main rock still here). See spheroidal wx as going up hill. Going down other side of the small ridge, look to see xenoliths of Carlton Rhyolite.

Eventually the trail joins the lakeside trail. Go right (east) around bulge in lake to dam site. Cross dam (or downstream if necessary). Otc on other side @ base of dam has mostly Quanah granite (a little coarser here), which is most resistant to wx, + weathered anorthosite of the L zone of the Glen Mountains Layered Complex (GMLC). There are several granite dikes in the GMLC rx parallel to the contact. This proves the granite intruded the GMLC. In the granite are many xenoliths of metaseds, metarhyolite, and Mt Scott granite (+ some other pancake-shaped ones that might be mafic mixed phase). There are also aplite dikes.

Return via the lakeside trail. About 600 ft from where turnoff for the bridge is is a boulder with a bend in the trail around it. In it are incluions of porphyritic Mt Scott granite with ovoid felds + angular rhyolite xeno on top + metased inclusions.

Stop 4. Ultramafic rocks of Glen Mountains Layered complex (GMLC)

To get there from Stop 3, go back to the Refuge Headquarters and go W on Rt. 49. A few miles (exiting refuge) come to Rt. 54 and go north about 8 mi. to vicinity of Cooperton. Go W on Rt 19 toward Roosevelt. Go 7.6 miles to a road cut.

A field trip guidebook from the South Central GSA meeting, 1976, says there is a road cut here that shows well-developed layering in anorthosites of the GMLC. Also later diabase dikes occur here, as well as aplite dikes related to the granitic intrusive suite. [After a brief look in 1997 field trip, I did not see any obvious layering].

Stop 5. More ultramafic rocks of Glen Mountains Layered complex (GMLC)

Continue a couple more miles on Rt 19 to Roosevelt, where you turn S on US 183 & go about 5 miles to the area of Lake Tom Seed. Look for a turnoff to the right for "Cold Springs...." and "Mountain Park Wildlife Management" (or something like that). Turn right there. The road then bends left and heads for and crosses the railroad tracks; but just before them, turn right on a road that parallels the tracks. Go about 3 mi and then go left over the tracks on another road that crosses. After crossing make your way to the large pile of rocks that were left there when the nearby railroad cut was blasted out. There is a dirt track going right shortly after crossing railroad tracks, but it is quite rough. The second dirt track might be easier to negotiate, but you'll have to double back a little. Park near the pile of rocks. Watch for snakes in such a place!

The rock faces of the railroad cut that is just NE of where we park expose rocks of the mafic/ultrmafic complex. See what is to be seen there, then return to the rock pile. There are a variety of mafic/ultramafic igneous rocks in this pile--a good place to get samples.

Retrace steps back to Doris Campground in the Wichita Mtns Wildlife Refuge.

Day 3: Paleozoic rocks of the southern midcontinent and Ouachita "geosyncline"

We will gradually travel back to ATU and stop at some places to see rocks of the Paleozoic continental shelf and adjacent deep-water facies. We also intend to stop at a locality to see some of the overlying, post-Ouachita-orogeny Cretaceous sediments.

From the Wichita Mtns Wildlife Reserve return to I-44 and go south. At Lawton, go E on Rt 7 (24 mi) to a "T" @ US-81. Go S on Rt-81/7 to Duncan (6 mi), where you again go E on Rt-7. After about 45 mi you come to I-35. Get on I-35 and go one exit south to US 77. Go south on US 77 a few miles to Turner Falls overlook.

Stop 6. Turner Falls overlook.

We will just have a short time to look at the falls from the overlook. From this vantage we can see the tufa buildups at the falls. The river that feeds this falls is fed by springs out of the limestone bedrock and is saturated with CaCO₃. As it is agitated going over the falls, some of the CO₂ comes out of solution, lowering the amount of "carbonic acid" and also lowering the solubility of CaCO₃. Thus calcite precipitates out at the falls and has been building up over the years as tufa deposits.

Stop 7. Paleozoic shelf-facies carbonates of the southern midcontinent.

From Turner Falls, continue south on US 77 to intersection with I-35. Go south to next exit. Get off, cross over, and get back on I-35 going north. Stop at vicinity of milepost 45 to look at road cut. The series of road cuts along I-35 (and some other exposures in this vicinity) are considered to the the best single exposure of the midcontinent Paleozoic section (Cambrian through Mississippian) anywhere in the US. These rocks are by and large shallow marine type, dominated by carbonates. Many of the formations exposed here are petroleum source beds and reservoirs in the deep subsurface in other areas. Here they are at a structurally higher level because of the formation of the Arbuckle anticlinorium. Shelf-facies rocks akin to these occur in northern Arkansas.

Stop 8. Mid-Proterozoic "basement" gneiss in core of Tishomingo anticline

Return north on I-35 to Rt-7. Go E through Sulphur, then another 6 mi to a "T" @ Rt-1 (just past some RR trx). Here Rt-7 turns S; stay on it 7 mi (pass Mill Creek [town]) to where Rt-7 again goes E. Follow Rt-7 through Reagan to Rt-99 (5 mi). Now go S on Rt-99 about 0.6 mi to a county road [SEE REAGAN QUAD]. Go left (S) on the county road; then after 0.5 mi go left (E) on another road. After 0.5 mi it bends S; then another 1.5 mi more it bends E. After another 1 mi you come to an intersection [NOW ON CONNERVILLE SE QUAD] where you go N. A little over a mile up that road and it becomes a dirt road and bends E; then after another mile or so you arrive at Blue River. Take the dirt road going S (See figure 6) through camp sites to where it crosses a tributary creek. Park.

Figure 7 shows a generalized geologic map of the area known as the "Arbuckle Mountains". There are thrust faults with hanging-wall anticlines in this area that have brought up lower Paleozoic rocks, and even Precambrian basement below them, to higher structural levels, and thus these rocks through erosion have been exposed. The Blue River Gneiss exposed here is the oldest rock exposed within hundreds of miles of this area. It predates the intrusive rocks of the Wichitas and also the 1,350 Ma granitic intrusives in the Arbuckles, and also the similar-aged intrusive rocks of the southern Missouri St. Francis Mountains area. And this is the only known outcrop of this gneiss! There are also some "amphibolite" dikes. These were mafic intrusive rocks that through metamorphism have become amphibolites.

Stop 9. Beavers Bend State Park: Paleozoic Ouachita facies rocks

Retrace route to Rt-99 N. Go a short distance to Rt-7 E through Wapanucka to Atoka. At Atoka take Rt-3 E to the town of Broken Bow (82 mi). Go N on US-259 for 7 mi to Beavers Bend State Park. Turn right (E) into the Park and loop through Park to see the outcrops described below.

The descriptions are given by Nielsen, KC (1988) in a field trip guidebook published as the GSA Centennial Field Guide. I describe here what I think we will be able to see based on his description. However, a number of statements are ambiguous as to whether or not we'll be able to find the features. I put in italics sections of Nielsen's description that may be more apparent when we get there and will be used to try and find outcrops of some of the major geologic mapping units of the Ouachitas. By the way, all these units continue into Arkansas.

Stop 9A (Locality 2 of Nielsen): Take US-259A to the park and into it. Continue to the main park area (a few miles from US-259). Come to a stop sign west of the park museum; turn left and drive west. Proceed to a T intersection and turn right and cross a river. Park either by the swimming area to the west (left) ro in the park area to the east (right). Refer to Figure 8 (taken from Nielsen's Fig.4).

To begin the traverse in the oldest units, walk about 800 ft west of US-259A. North of you there will be a small valley cut into Devil's Backbone. This valley has developed at the contact between the Blaylock Sandstone and Missouri Mountain Shale. I assume that outcrops in the Missouri Mtn Shale will be visible near the break in slope apparent on the map where the strike and dip symbol showing the 211 E dip of the rocks occurs. There should be outcrops or "float" of Blaylock Sandstone to the west of the small valley.

The contact between the Arkansas Novaculite and Missouri Mountain Shalel is fairly abrupt, with black siliceous shale overlain by the massively bedded white-to-gray chert. This contact can be seen along the slope north of the swimming area at this locality. Proceeding to the northeast corner of the parking area and just at the foot of the road bed, the first massive chert can be observed. I am not sure if we are supposed to look for the swimming area or if so where on "the slope north of it" the contact is exposed. Perhaps that is in the bank of the river and visible from the river only (?). It may be that we are just supposed to walk back to the parking area, find the northeast corner and see the massive bedded chert. However a conflicting statement occurs in another paragraph it says that the "Lower Division" of the novaculite is thin in this area and covered by the road. If the lower division is covered, then I do not know how we could see the lower contact.

Because of the shallow dip, the novaculite sequence is exposed along the full length of the cliff behind the power station. I take it to mean that we are supposed to walk along the foot of a cliff that is behind a power station and be walking up through the stratigraphic section. Exposures of the Middle Division extend to the east side of the power station. East of the power station, the cliff exposure is mainly the upper division which is usually a thick-bedded novaculite, but here it is said to contain two carbonate units that are apparent because of cavities developed in the weathered surface, each being 10-20 ft thick. Walking to the east, take time to look closely at these units, which reveal very irregular replacement textures. The carbonate occurs as thin laminations, small elongate irregular pods or large nodules. It is not clear, but I think he is saying that the "replacement" is silica replacing carbonate. He says that the lower carbonate has only 20% carbonate, being more silicified than the upper, which has 50% carbonate. He also mentions massive sandstone layers, interbedded chert and shale, and thin conglomeratic layers being associated with these carbonate layers in the Upper Division, but does not make clear if this is somewhere else in the general area or right here at this locality.

At the eastern end of the low ridge, there is a wide area (1400 ft) of nearly horizontal black fissile shale. This shale is the basal Stanley Formation. Examination of the black shales behind the water tank above the power station reveals significant sulfide accumulation and evidence for soft-sediment deformation. I guess we are supposed to go up the the water tank to see the Stanley well, but I wonder if it is going to be readily accessible.

Continuing the traverse toward the east, across the low area, the next sequence of rocks is the lowest of five major tuff sequences within the Stanley Formation. Two of the units are exposed here. Walking up the western flank of Rattlesnake Bluff, you first cross through the Beavers Bend Tuff and then, at the top of the hill, the Hatton Tuff. ...There is an interval between the tuffs with quartzose and feldspathic turbidites.

The Arkansas Novaculite and units below it are considered to have accumulated slowly in a deep Oceanic basin off the south margin of the Paleozoic continent. The Stanley Formation is considered to have been deposited more rapidly as a sudden deepening of the basin occurred because of downward flexure of the lithosphere as oceanic lithosphere to the south began to be subducted beneath an approaching continent. Volcanism from a continental magmatic arc that was above that subduction zone to the south is considered to be the source of the Hatton Tuff and the other related tuffs.

Stop 9B (Locality 4 of Nielsen): Get back on US-259A and continue on to the Dam. Cross the dam and stop at the Scenic Overlook on the east side of the road north of the dam. Look east across the lake and see at the soreline a sequence of tight overturned folds in the Blaylock Sandstone. I know this is Petrology, but we can't pass up an opportunity to see such nice structures! Besides, it is important to point out that after the deposition of much of the Paleozoic sequence, a compressional event occured with folding and thrusting of the basinal facies rocks. This is considered to have occurred from continent-continent collision in the late Paleozoic to form Pangea.

Stop 10. Cretaceous sediments (post Ouachita) exposed in Highland Gypsum Quarry

From the last stop in Beavers Bend State Park, continue on US-259A, which finishes the loop back at US-259. Return south to Broken Bow and take US-70 east into Arkansas. At DeQueen, US-71 joins US 70. Continue east on this joint highway. About 8 miles out of town they diverge agin. Follow US-71 south 5 miles to SH-24 at Lockesburg. Go east 7 miles on SH-24; then take SH-26 NE through Center Point and on to Highland. At Highland look for the entrance to the Highland Gypsum Quarry on the left.

At the Highland quarry, the DeQueen Formation (L.K., Trinity Group) is exposed. This stop is discussed in detail in an article by J.D. McFarland of the Arkansas Geological Commission. Note here the contrast in the nature of these rocks with those just a little farther north in the Ouachitas. The rocks here are much less lithified than the Ouachita rocks, and also these lie horizontally. Drilling for water wells in this area would, at a fairly shallow depth, intersect hard Paleozoic rocks beneath these in the subsurface. There is an angular unconformity between these. This unconformity provides relative dating evidence that the Ouachita orogeny occurred sometime postdating the early Pennsylvanian, and predating at least the Cretaceous.

The DeQueen Formation consists of limestones, gypsum, mudstones, and minor sands. This mixture of carbonate/evaporite plus terrigenous siliciclastic sediments is interpreted to have been deposited in a broad, shallow lagoon just off the Cretaceous coast. This lagoon was protected by a reef called the Glenrose Reef. This reef is interpreted from rocks of similar age that occur now in the subsurface farther south. The mudstones, siltstones, and sandstones have brackish water fossils in them. Toward the top, some of the rocks have calcite pseudomorphs after halite. The gypsum beds in the DeQueen Formation are discontinuous when looked at over large areas. The layers have an overall lenticular geometry. These observations suggest that the gypsum was deposited in depressions of limited areal extent on tidal mud flats. The calcite pseudomorphs after halite indicate that there were time periods of supratidal (above sea level) exposure with drying out of saline waters. Both the halite pseudomorphs and the gypsum probably indicate supratidal brine pools. Note: some zones near the middle of the highwall contain celestite nodules.

REFERENCES FOR FURTHER STUDY

DONOVAN, R.N., RAGLAND, D.A., AND SCHAEFER, D. (1988) Turner Falls Park; Pleistoscene tufa and travertine....: Geol. Soc. Amer. Centennial Field Guide--South-Central Section, p. 153-158.

FAY, R.O. (1988) I-35 Roadcuts; Geology of Paleozoic strata in the Arbuckle Mountains of southern Oklahoma: Geol. Soc. Amer. Centennial Field Guide--South-Central Section, p. 183-188.

GUILBERT, C.N., AND DONOVAN, R.N. (1982) Geology of the eastern Wichita Mountains, sou

HAM W.E. (1978) Regional Geology of the Arbuckle Mountains, Oklahoma: Oklahoma Geological Survey Special Publication.

NIELSEN, K.C. (1988) Beavers Bend State Park, Broken Bow Uplift, Oklahoma: Geol. Soc.

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