DIGITAL GEOLOGIC QUADRANGLE MAP LESLIE QUADRANGLE, ARKANSAS Arkansas Geological Survey DGM-AR-00485 Bekki White, State Geologist and Director GEOLOGIC MAP OF THE LESLIE QUADRANGLE, SEARCY AND VAN BUREN COUNTIES, ARKANSAS Geology by Richard S. Hutto, Erin E. Smart and Daniel S. Rains Digital compilation by Erin E. Smart 2009 A' 11 Hale Formation (Lower Pennsylvanian, Morrowan) – Batesville Sandstone (Upper Mississippian, Chesterian) – a Correlation of Map Units consists of two members: the Prairie Grove and the Cane Hill. thin- to medium- and locally cross-bedded sandstone. Grains Only the Cane Hill Member is present on this quadrangle. are very fine to medium, moderately well-sorted, subangular Rocks equivalent to the Prairie Grove Member are mapped and carbonate-cemented. Fresh surfaces are dark-gray to with the Witts Springs Formation. dark-brown and weather reddish-brown or tan to buff. Rarely 10 Holocene and Quaternary Cane Hill Member – typically a fissile silty to clay shale fossiliferous, but locally contains external molds where fossils 11 Pleistocene that contains ironstone nodules and discontinuous, thin- have weathered out. Conformable with the underlying Unconformity bedded, limonitic siltstone that weathers to form boxworks. Moorefield Shale. Ranges from approximately 60-80 feet (18- Fresh exposures are dark–gray to black, and weather tan to 24 meters) in thickness. light-orangey-brown. Units of very thin- to thin-, ripple- Hindsville Limestone Member (Upper Mississippian, bedded, very fine- to fine-grained, micaceous silty sandstone Chesterian) – a discontinuous thin- to medium-bedded, finely Unconformity with shale partings are present throughout the Cane Hill. On to coarsely crystalline limestone. Light- to dark-gray on fresh 6 the east side of the quadrangle, these sandstone units are surfaces, but weathers gray to brown. Usually has a Morrowan Pennsylvanian increasingly dominant. Near the base is an especially petroliferous odor when freshly broken. Locally fossiliferous 5 competent sandstone unit that is typically light- to dark-gray and oolitic. Typically interbedded with very thin- to thin- 5 Unconformity on fresh surfaces, and weathers tan or dark-gray to dark- bedded shale, siltstone or sandy siltstone. Only present in brown. It ranges from approximately 40-80 feet (6-24 meters) Trace Creek near Sulphur Springs Cemetery where it is less in thickness, and erodes to form a thick, flaggy colluvium that than 10 feet (3 meters) thick. Not considered mappable at this is commonly collected for building stone. At the lower contact, scale as a separate unit, therefore mapped with the Batesville. Unconformity a discontinuous, orangey-brown, limonitic shale-pebble Conformable with the underlying Moorefield. 9 conglomerate is present that is approximately 12-36 inches (30-91 centimeters) thick. Unconformable with the “Imo 8 shale” below. Ranges from approximately 200-340 feet (61- 4 104 meters) in thickness. Moorefield Shale (Upper Mississippian, Meramecian) – a 12 silty shale with interbedded very thin- to thin-bedded 7 Chesterian siltstone. Shaly zones are usually dark-gray to black on fresh Mississippian surfaces, but weather medium-gray to yellowish-brown. Pitkin Formation (Upper Mississippian, Chesterian) – Siltstone is dark-gray to dark-brown on fresh surfaces, but informally divided into two members, the Pitkin Limestone and weathers light-gray to buff. Unconformable with the Boone the “Imo shale”. Lower contact of the “Imo” placed at the top Limestone below. Reaches a maximum exposure of Mm of the final limestone bed in the Pitkin, and upper contact approximately 50 feet (15 meters). Meramecian placed below the base of a competent, very thin- to thin-, ripple-bedded, silty sandstone that is the first recognizable unit in the Cane Hill Member (Smith, et al., 2007). Imo shale (Upper Mississippian, Chesterian) – consists of several shale units with intervening sandstone units. The lowest unit is a light-gray, calcareous or dark-gray, non- References Introduction calcareous, fissile shale with interbedded, discontinuous sandstone and limestone. This limestone commonly takes the This map graphically summarizes the bedrock geology of form of small, yellowish, platy concretions encrusted with Braden, Angela K., and Ausbrooks, Scott M., 2003, Geologic the Leslie 7.5-minute quadrangle. In this area over 980 feet fossils, especially Chonetes, or light-gray, lenticular, septarian map of the Snowball quadrangle, Searcy County, (299 meters) of Lower Mississippian to Lower Pennsylvanian concretions. Locally, loosely accreted, cigar-sized crinoid Arkansas: Arkansas Geological Commission, Digital 10 carbonate and clastic sedimentary rocks are exposed. The stems weather out. Above this shale is a persistent, fine- to Geologic Map, DGM-AR-00800, 1 sheet. U mapped area lies on the northern edge of the Boston medium-grained, thin- to massive- and locally cross-bedded 10 Mountains Plateau, the highest in a series of south-dipping Glick, E.E., 1973, Preliminary Geologic map of the Leslie sandstone. Fresh surfaces are buff to tan and locally mottled quadrangle, Searcy County, Arkansas: Arkansas D 19 plateau surfaces composed of progressively younger rocks in or banded with dark-red iron blebs. Weathers dark-orangey- Geological Commission, Geologic Worksheet, 1 sheet. the Ozark Plateaus Region. brown to gray and blocky. Commonly exhibits pronounced The major structure in this area is the Leslie Fault which stylolites, liesegang banding, and honeycomb weathering. Hutto, Richard S. and Smart, Erin E., 2008, Geologic map of runs the width of this map and beyond. It is a normal fault Locally, a sandy fossiliferous limestone caps the unit. Unit the Canaan quadrangle, Searcy County, Arkansas: downdropped to the south that offsets the rocks from thickness ranges from approximately 15-40 feet (5-12 meters). Arkansas Geological Survey, Digital Geologic Map, DGM- Leslie Fault approximately 240-400 feet (73-122 meters) from west to east. AR-00128, 1 sheet. 18 Above this sandstone is a fossil–bearing, dark-gray to black, A minor fault splays off of this fault to the southeast. The fissile shale. Fossils are abundant and include bivalves Hutto, Richard S. and Smart, Erin E., 2008 Geologic map of 9 15 major drainage in this area is the Middle Fork of the Little Red 12 (commonly nuculoids), cephalopods (commonly conical the Oxley quadrangle, Searcy County, Arkansas: 7 River which flows southeast to Greers Ferry Lake. 18 nautiloids), solitary corals (commonly rugose), crinoids, Arkansas Geological Survey, Digital Geologic Map, DGM- The geology of this area was mapped in 1973 by Glick for brachiopods, gastropods, trilobites and plant material. AR-00666, 1 sheet. the 1:500,000 scale Geologic Map of Arkansas. The current Typically contains lenticular, orange to dark-red fossiliferous mapping builds on the previous work, but uses a revised Smart, Erin E., and Hutto, Richard S., 2008, Geologic map of 30 4 limestone tempestites, rounded, non-fossiliferous ironstone the Harriet quadrangle, Searcy County, Arkansas: stratigraphy and adds certain structural details. The contacts concretions, and secondary, fibrous calcite partings. and structural features on the map were derived from field Arkansas Geological Survey, Digital Geologic Map, DGM- 3 Additional discontinuous, thin-bedded sandstone and AR-00374, 1 sheet. 12 observations made from July 2008 through April 2009. Site limestone beds are interbedded within this upper shale unit. locations were generated with the aid of a global positioning The limestone beds are dark-gray on fresh surfaces, and Smith, Daniel K., and Hutto, Richard S., 2007, Geologic map 5 satellite receiver. Bedrock dipping at less than 2° was weather dark-red. They are fine- to coarse-grained, oolitic and of the Witts Springs quadrangle, Searcy County, 17 considered horizontal. Arkansas: Arkansas Geological Commission, Digital 20 4 fossiliferous. Conformable with the underlying Pitkin. Ranges from approximately 100-160 feet (30-49 meters) in thickness. Geologic Map, DGM-AR-00927, 1 sheet. 5 4 U Pitkin Limestone (Upper Mississippian, Chesterian) – a Zachry, D. L., and Haley, B. R., 1975, Stratigraphic U thin- to very thick-, massive-bedded, fine- to coarse-grained, relationships between the Bloyd and Atoka Formations D 15 25 D Description of Map Units locally oolitic bioclastic limestone. Contains abundant fossils (Pennsylvanian) of northern Arkansas in Contributions to including crinoid fragments, the bryozoan Archimedes, corals, the geology of the Arkansas Ozarks: Arkansas Geological 14 7 nautiloids, brachiopods, gastropods, and trilobites. Fresh Commission, Miscellaneous Publication 12, p. 96-106. 25 5 5 Alluvium and terrace deposits (Quaternary) – composed of surfaces are light- to dark-gray, and usually weather light- to 10 unconsolidated clay, silt, sand and gravel deposited by major medium-gray. Grades to a tan color near the upper contact 15 due to an increase in silt content. Commonly has a 13 streams, including deposits on one or more terrace levels. 18 petroliferous odor when freshly broken. About half way up the 3 section, there is a black shale interval that typically forms a bench. Conformable with the underlying Fayetteville Shale. 6 4 Landslide deposits (Quaternary) – typically derived from 10 Ranges from approximately 160-240 feet (49-73 meters) in Morrowan units, especially breakdown of thin-bedded, flaggy 18 thickness. Stratigraphic Column sandstone in the Cane Hill Member and undercutting of massive-bedded,