1 Three-day field trip to see Tertiary, Cretaceous and Paleozoic Rocks in the Big Bend area of Texas
2 Geologic Sketch Map of the Field Trip Area Tx. Mexico Main part of the Trans Pecos Volcanic Field Study Butte x Marathon Uplift, Paleozoic rocks Cretaceous Rocks Big Bend portion of the Trans Pecos Volcanic Field
3 General Geology This area is underlain by flat-lying, Cretaceous sedimentary rocks of marine origin Overlying the Cretaceous rocks in places are Tertiary age volcanic rocks. These have been partly eroded away but they are well exposed. They are part of the Trans-Pecos Magmatic Province (Price, et.al., 1986). There are associated Tertiary age intrusions.
4 General Geology (continued) Underlying the Cretaceous sedimentary rocks is an unconformity and beneath that are Paleozoic sedimentary rocks. These are marine in origin and they are highly folded. They are exposed in the area of Marathon, where the Cretaceous rocks have been eroded away.
5 E Sketch Map of General Geology W Tertiary Volcanics Cretaceous Marathon region Paleozoic Cretaceous
6 A- portion of the field trip In this portion of the trip we see mainly volcanic rocks of the TPVF. The first stop is along highway 17, the following stops along highway 118, except for the last stop along highway 90 west of Alpine.
7 Stop # 1 Star Mountain Formation This unit consists of a series of widespread, lava-like flows of silicic composition Note the banding illustrated by the arrow
8 Star Mountain Rhyolite
9 Stop # 2 Class picture of the Historical Geology class - Spring, 2001 This photo was taken on the side of Mount Locke.
10 Class picture
11 Stop # 2 Base of the Barrel Springs Formation This is the bottom of a lava flow like unit Side of Mount Locke Arrow at the basal contact
12 Barrel Springs Formation
13 Stop # 2 Breccia zone near the top of a lava like unit in the Barrel Springs Formation Side of Mount Locke
14 Breccia zone in the Barrel Springs Fm.
15 Stop # 3 Behind Fort Davis the volcanic rocks of the Sleeping Lion Formation are exposed These rocks show well defined jointing
16 Fort Davis
17 Stop # 4 Rocks of the Frazier Canyon Formation At this site basalt lies on top of volcanic ash Note the lobe of intrusive igneous rock on the right emplaced into these volcanics
18 Frazier Canyon Formation
19 Stop # 5 Volcanic rocks of the Paisano Volcano On the left is rhyolite, on the right the gray rock is part of an intrusive dike
20 Volcanic rocks of the Paisano Volcano
21 Stop # 5 Part of a rhyolite lava flow This flow makes up a part of the Paisano volcano This is right along highway 90 west of Alpine, Tx.
22 Part of the Paisano Volcano
23 Stop # 6 Wind turbines near Dr. Bob Martin s place in the Davis Mountains Here the energy of wind is converted into electricity
24 Wind Turbines
25 B - portion of the field trip Here we head south of Alpine and first view Tertiary volcanics, moving south we see Cretaceous limestones and Tertiary intrusions, arriving in the Big Bend National Park we see more volcanic rocks, and finally, we wind up at a high angle fault where Cretaceous limestones are visible in the uplifted block. Rt. Follows highway 118 and the Maxwell Drive in the park.
26 Stop # 1 Good view of two tertiary age lava flows in contact with each other South of Alpine, Tx. Main part of the TPVF
27 Contact between lava flows
28 Stop # 2 Tertiary age lava rock Close-up of the rock types seen in the previous slide
29 Lava Rock
30 Stop # 3 Contact between tertiary age lava flows Main part of the TPVF Notice fow the two flows weather differently
31 Contact between lava flows
32 Stop # 4 Santiago Peak This is a resistant mass of intrusive igneous rock that stands up well to erosion View is roughly 34 miles N of Study Butte
33 Santiago Peak - Intrusive Mass
34 Stop # 5 Cretaceous limestones exposed along a roadcut about 25 miles N of Study Butte The sediments that make up these rocks were deposited in a shallow sea Note the well defined layering
35 Cretaceous Limestone
36 Stop # 6 Willow Mountain Tertiary age intrustion roughly four miles N. of Study Butte Shows good columnar jointing
37 Willow Mt Intrusion
38 Stop# 7 Igneous dike exposed by erosion Notice how the resistant igneous rock stands up as a wall-like feature Geologic age - Tertiary Located in the Big Bend portion of the Trans-Pecos Volcanic Field
40 Stop # 8 View of Burro Mesa Very top is the Burro Mesa Rhyolite Rocks are Tertiary in age Again from the Big Bend (BB) portion of the Trans-Pecos Volcanic Field (TPVF)
41 B u r r Burro Mesa M e s a
42 Stop # 9 Contact between the overlying Burro Mesa Rhyolite and the underlying Wasp Spring Flow Breccia Tertiary-age igneous rocks Burro Spring Pour-Off BB portion of the TPVF
44 Stop # 10 Tuff layers above lava flows Tuff Canyon Tertiary age volcanics In the BB portion of the TPVF Please note steep cliffs are here be careful if accompanied with small children
45 Tuff Lava
46 Stop # 11 Cerro Castelon Erosional remnant of Tertiary age igneous rocks Resistant Burro Mesa Rhyolite is on top BB portion of the TPVF
47 Cerro Castelan
48 Stop # 12 Looking into Santa Elana Canyon This is a mass of Cretaceous rocks, mainly limestones, that have been up-lifted along a fault. The Rio Grande River then cut down into it and carved the canyon View is from the down-thrown side of the fault
49 Santa Elena Canyon
50 Stop # 13 Santa Elena Canyon again, this time from a distance
51 Santa Elena Canyon
52 C - portion of the field trip Here we visit the Marathon region where Paleozoic age, marine sedimentary rocks have been folded and highly deformed. The bedding is sometimes near vertical. Outcrops are viewed along highway 385 south of Marathon and 90 east of Marathon.
53 Stop # C1 Marathon Limestone This unit is Cambrian or Ordovician in age This is a shallow water marine deposit
54 Marathon Limestone
55 Stop # C2 Here is the Caballos Novaculite in a roadcut This is a very distinctive silica rich rock It is probably Silurian in age
56 Caballos Novaculite
57 Stop # C3 Flat-irons of Caballos Novaculite in the distance South of Marathon
58 Caballos Novaculite
59 Stop # C4 Probable Tesnus or Haymond Formations These are very interesting beds! They are alternating beds of sandstone and shale - turbidite deposits, probably laid down on the deep sea floor. Also, these beds stand almost in a vertical position now due to deformation!
60 Probable Tesnus or Haymond Formations
61 Stop # C4 Probable Tesnus or Haymond Formations Probably Devonian to Pennsylvanian in age
62 Probable Tesnus or Haymond Formations
63 Stop # C5 Syncline in highly deformed Paleozoic rocks
64 Syncline in deformed Paleozoic rocks
65 Stop # C6 Dimple Limestone Note high angle of the beds Age is Pennsylvanian
66 Dimple Limestone
67 On the way home!
68 On the way home. On the way home we see lots and lots of Cretaceous limestones. Here are some from west of Sanderson
69 Cretaceous limestones
70 Remember Safety first and always on field trips These slides and other information give an idea of the geology at various locations but the best way to get to know it is to really visit these sites in person - geologic observations in the field form the raw data on which the geosciences are based. References follow.
71 References 1. Henry, C.D., Kunk, M.J., and McIntosh, W.C. 1994, 40Ar/39Ar chronology and volcanology of silic volcanism in the Davis Mountains, Trans-Pecos Texas. GSA Bull. v. 106, pg Henry,C.D.and others,1988, Widespread, lavalike silic volcanic rocks of Trans-Pecos, Texas. Geology, vol.16, pg McBride, E., 1988, Geology of the Marathon Uplift, West Texas. GSA Centennial Field Guide - South Central Section. 4.Parker, D.F., Tsuchiya, L.C. and McKnight,C.l.,1991, The Davis Mountains Volcanic Field. Guidebook of the SW Association of Student Geological Societies. (continued).
72 References 5.Parker, D.F., 1983, Origin of the trachyte-quartz trachyte-peralkalic rhyolite suite of the Oligocene Paisano Volcano, Trans-Pecos Texas. GSA Bull. vol. 94, pg Parker,D., 1988, Davis Mountains Volcanic Field, west Texas. GSA Centennial, SC Section. 7.Price,J.G, Henry, C.D., Parker, D.F. and Barker, D.S., 1986, Igneous Geology of Trans-Pecos Texas. Field Trip Guide and Research Articles. Texas Bureau of Economic Geology, Guidebook Spearing, D., 1991, Roadside Geology of Texas. Mountain Press. 9.Maxwell, R.A., et.al., 1967, Geology of the Big Bend National Park, Texas. Bureau of Economic Geology, Texas. (cont.)
73 References 10.Barker,D.S., 2000,Down to Earth at Tuff Canyon, Big Bend National Park, Texas. Texas Bureau of Economic Geology. 11.Geologic Atlas of Texas, Ft. Stockton Sheet. Texas Bureau of Economic Geology. Anderson, J.E., Geologic Atlas of Texas, Emory Peak-Presidio Sheet. Texas Bureaui of Economic Geology.Brown, J.B., et.al.,2001.
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