Digital Geologic Quadrangle Map Arkansas Geological Survey Geologic Map of the Brownsville Quadrangle Brownsville Quadrangle, Arkansas Bekki White, State Geologist and Director DGM-AR-00106 Cleburne County, Arkansas Richard S. Hutto, Ty C. Johnson, and Garrett A. Hatzell
2016
BROWNSVILLE QUADRANGLE Witts Springs Formation (Lower Pennsylvanian, Morrowan) Correlation of Map Units Ùw - consists predominantly of sandstone, including fossiliferous (PARMA) UNITED STATES ARKANSAS
calcareous sandstone, with minor sandy limestone. Lesser DEPARTMENT OF THE INTERIOR 7.5 MINUTE SERIES (TOPOGRAPHIC) (DRASCO) units of shale and siltstone are also present. Sandstone is typi-
5 92°00' GEOLOGICAL SURVEY 5 589 90
5 5 87 1 990 000 FEET cally thin to thick bedded, and commonly cross bedded. Locally
5 84 (PRIM) 86 2'30" 35°37'30" Holocene and
92°07'30" 5 000m. R 11 W R 10 W 5 82 5'
80 E. 70 A o Qto Quaternary cross beds are overturned. Weathering commonly masks
35°37'30" ^ 4 Pleistocene
^ bedding so that it appears massive, and rounded or blocky.
w ^ o o b Unconformity
o Sandstone is typically fine grained, but locally medium to
o o o S 3
T 12 N o S ^ w
6^ o
5 ^ 4 coarse grained, and friable. Orange to buff on fresh surfaces, 12 ^ ^
^ 4 Ù T 11 N 4 b but weathers gray to brown, or orange. Commonly contains o9 49 b 44 o w shale and quartz pebbles, pebble molds, and trace fossils. Liese- ^ 7 o 39 000m. 4 o 39 w Unconformity Morrowan Pennsylvanian
42 N. o9 42 gang banding, honeycomb weathering, and soft sediment defor-
^ b ^ Qto 3
^ mation are common. Calcareous sandstone and sandy lime-
^ 3 Ù o o w
10 6 o stone typically contain crinoid fragments, but other fossils pres-
ent may include: ammonoids, bryozoans, brachiopods, gastro-
Choctaw^ Creek Fault 8 b o pods, and rugose and tabulate corals. Fossils commonly o o ^
4 o weather out leaving molds. Calcareous units are gray to brown 7 8
8 o on fresh surfaces, but weather brown to dark brown. Shale and
3 o siltstone units are commonly interbedded. Both are dark gray to S o
3 black on fresh surfaces, but weather tan to orange. Up to 380 ^ 47 w w Ozark Plateaus feet (115.8 meters) thick. 3941 3941
b o 7 o 6 8 Springfield Salem w o
12 o 3 o Stratigraphic Column
6 Boston Mountains 3940 o 3940 SystemSeries Formation
4 Ç Brownsville 700 o
o 460 000 b 200 FEET Brownsville quadrangle location within the Ozark Plateaus.
Ä 6 600 Ä o 3 500 Bloyd 3939 3939 b Introduction 400 This map depicts the bedrock and surficial geology of the b w w Brownsville 7.5-minute quadrangle. In this area, approxi- mately 660 feet (201 meters) of Early Pennsylvanian (Morrowan) 100 300 Morrowan carbonate and clastic rocks are exposed. These rocks formed Pennsylvanian b from sediment deposited in near-shore marine, deltaic and w fluvial environments. The area is situated in the Interior High- 200 3938 lands Region on the southern flank of the Ozark Dome, a struc- Witts Springs 35' tural high centered in southeast Missouri. The dome has 35' eroded to form several broad plateaus, the southernmost of 100
which is the Boston Mountains Plateau, on which this quad- rangle is located. Due to this structure, strata dip an average of
about one degree to the south. Bench and bluff topography is
o 0ft. 0m 3 characteristic of the area, and is due to differential weathering
o o of sandstone and shale units. In 1962, the U.S. Army Corps of
5 6
^ Engineers completed a dam at Heber Springs that flooded the ^ valley of the Little Red River upstream creating Greers Ferry
39 ^ Äo
37 Brownsville Fault Lake. This lake now covers much of the area of this quad- sandstone cross-bedded
^ b
w 3937
^ rangle. sandstone
4 unconformable
^ There are three named structural features delineated on the o
3 o map. The Choctaw Creek Fault in the northwest corner is part surface ^
o 5 of a fault system that can be traced at the surface at least 28.5 ^ 3
miles (45.9 km). It is a normal fault downthrown approximately shale with calcareous
^ w 50 feet (15 meters) to the south. An antithetic fault forms a siltstone sandstone
^ graben south of the main fault. Preferential erosion along this
^ w fault system created the distinctive lineament which shapes the
3 ^ northern part of Greers Ferry Lake. The Brownsville Fault is a
^
o
Ä ^ normal fault downthrown approximately 50 feet (15 meters) to
3936
b ^ the south. The Shiloh Fault is a normal fault downthrown
^ approximately 150 feet (46 meters) to the south. Also, there are
o Ç 6 o several strath terraces deposited by the Little Red River in the 3 mapped area. These terraces were stranded when the river cut
o w down from an elevation at least 260 feet (79 meters) above the
3
o modern channel bed. Samples of terrace material were
(GREERS FERRY) (GREERS
(GREERS FERRY DAM) collected and submitted for age analysis using optically stimu-
7 o
5 o lated luminescence (OSL) methods. o o
o The geology of this area was mapped at the 1:100,000 scale
7 o b b 6 for the Geologic Map of Arkansas circa 1973 by E. E. Glick.
3935 7 7 3935
3 o
o This map is primarily based on data collected by field observa-
o tions made between September 2015 and January 2016. Rep-
o 5
4 o
o
o resentative rock samples were collected at various sites and
o 6
S 5
^ 4 7 thin sections were made to aid in petrographic and provenance
^ 3 o 4
o studies. Site locations were recorded with a portable data
^
o
4 21 6o
o collector. o ^ ^
54 o
o 10S 3 o o 3 4 o 4 o
^ 5 o b 4 25 7 o 82 o 4
5
39
3934 5 Shiloh Fault ^ 34
^ b 3 Description of Map Units
o o b 8 o ^ Old terrace and alluvial deposits (Quarternary) - consists of 5 o Qto unconsolidated clay, silt, sand, and gravel deposited by the 5
b 6 Little Red River. Gravel consists primarily of white to orange, ^ 32'30"
3 rounded sandstone cobbles, and rarely white to gray, sub-
32'30" o ^ o
o 6 rounded chert cobbles. Gravel is typically medium pebble to
9 o 9 5
^ o b Ç
7 5 o o small boulder sized, but ranges beyond these sizes. Matrix is o
o oo ^ o
^
39 o 39 typically sandy clay, locally, cemented by iron-oxide. Thick-
33 7 4 ^ 33
^ o 7 10 o ness unknown.
22 o b S 6 3 o
10
6 ^
62 T 11 N o
5 o Bloyd Formation - undifferentiated (Lower Pennsylvanian, T 11 N
4 o
o
S Ùb T 10 N 6 ^ Morrowan) - consists of interbedded sandstone, siltstone, and 3 ^ o T 10 N shale units. A massive sandstone unit is typically present at the Topographic map of the Brownsville quadrangle showing loca- o9 Qto 50 12 base in the northern part of the quadrangle. Sandstone beds are tions of data collection points in black, thin-section sampling o4 medium to thick, typically flat to lenticular, and locally stylo- points in blue, and OSL sampling points in green. Qto litic. Sandstone is very fine grained to fine grained, less com-
3932 3932 monly, medium-grained and locally micaceous. Typically b o3 orange, but locally tan, red, and/or white on fresh surfaces. Weathers light brown to dark brown. Locally displays rippled b bedding, cross bedding, and soft sediment deformation. Locally b contains shale and quartz pebbles, pebble molds, trace fossils, Joint Frequency o5 ironstone concretions, liesegang banding, boxwork, scour-and- o3 fill structures, shale-partings, and petrified wood casts and molds. Fossils are rare but ammonoids are found locally. Shale 0 6 5 is dark gray and siltstone is tan on fresh surfaces. Both weather o o tan to orange. Rests unconformable upon the Witts Springs o3 3931 Formation. Up to 280 feet (85.3 meters) thick. o5 Ä 3931 b o 3 7 Qto 4 Ç 3 430 000 o o o FEET Symbols 270 90 Qto Contact 3930 b 3930
5
o 3 4 o oo Normal fault - dotted where con-
Qto o 50 4 cealed, bar on downthrown side, o 7 S
Ço 6 arrow indicates dip direction and
5 magnitude of fault plane
5 o
b o 3 o S
9 o7 Strike and dip of beds 180 n = 834 39 b 3929000m. N. 29 o 5 o Rose diagram of strike frequency of joints recorded within the 10 Ä 35°30' Gravel Pit Brownsville quadrangle. INTERIOR - GEOLOGICAL SURVEY, RESTON, VIRGINIA - 1982 35°30' 5 5 5 86 2'30" 5 000m. 5 R 10 W 83 5' 84 (HEBER SPRINGS) A' 90 E. 92°00' 80 R 11 W 1 970 000 FEET (WEST PANGBURN) 92°07'30" Ç Quarry
The topographic base is a Digital Raster Graphic (DRG). The DRG is a Road Classification A A’ Line of cross-section (QUITMAN) 0 14’ References scanned image of a U.S. Geological Survey standard series topographic Secondary highway map published in 1973 and photorevised in 1981. Monocline Glick, E. E., 1973, Partial geologic map of the Batesville quad- Light duty road rangle, Arkansas: Arkansas Geological Survey, Geologic Projection and 10,000-foot grid ticks: Arkansas coordinate system, Worksheet, 1 sheet, 1:100,000 north zone (Lambert conformal conic). Unimproved road 1000-metre Universal Transverse Mercator grid ticks, zone 15, shown Contour Interval 20 Feet QUADRANGLE LOCATION State Route in blue. 1927 North American datum. National Geodetic Vertical Datum of 1929 Approximate mean declination 2016 Acknowledgements: This map was produced for the National Cooperative Geologic Mapping Program (STATEMAP), a matching-funds grant program administered by the U.S. Geo- logical Survey, under Cooperative Agreement Award G15AC00223. Special thanks to the private landowners who graciously allowed access to their properties. Very special thanks to Angela Chandler for serving as principal investigator for this mapping project. This map is dedicated to the memory of Nathan Taylor (1990-2016). He served for 11 years at the Arkansas Geo- logical Survey, and during that time he was integral to publish- North South ing our STATEMAP products, designing and managing our A A' geodatabase, and answering our many technical questions. He 1200 1200 will be missed. 1100 Greers Ferry Lake Greers Ferry Lake 1100 Rocky Branch Creek 1000 Limitations: This map, like all geologic maps, is based on inter- 1000 Greers Ferry Lake Heber Springs pretations which were made from the data available at the time 900 900 it was created. As work continues and new information is Choctaw Creek Brownsville 800 Fault 800 collected, the contacts, structures, and other features depicted 700 Fault Shiloh 700 on this map may be changed. 600 Fault 600 500 For the latest edition of this and other Arkansas Geological 500 Survey maps and publications, please call Publication Sales at 400 400 501-296-1877, or visit the Vardelle Parham Geology Center, 300 300 3815 West Roosevelt Road, Little Rock, Arkansas 72204. This 200 200 map is also available at: 100 100 Sea Level Sea Level http://www.geology.ar.gov/geologic_maps/dgm24k.htm Geologic Cross-Section A-A' Scale: Suggested citation for this map: Hutto, R. S., Johnson, T. C., and Hatzell, G. H., 2016, Geologic Horizontal: 1 Inch = 2000 Feet map of the Brownsville Quadrangle, Cleburne County, Arkansas: Vertical: 1 Inch = 500 Feet (Exaggeration: 4x) Arkansas Geological Survey, Digital Geologic Map, DGM-AR- 00106, 1 sheet, 1:24,000
Map and cross-section digitized by Brian Kehner.