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Geologic units in Polk county, Arkansas

Jackfork Sandstone (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early [Morrowan]) at surface, covers 47 % of this area

Jackfork Sandstone

Lithology: sandstone; shale

Arkansas Novaculite (Phanerozoic | Paleozoic | Devonian-Late Carboniferous Mississippian-Early) at surface, covers 23 % of this area

Arkansas Novaculite - Includes upper division (Mississippian), middle division (Mississippian and Devonian), and lower division (Devonian)

Lithology: novaculite; shale

Pole Creek Shale (Upper Ordovician) and Bigfork Chert (Upper and Middle Ordovician) (Phanerozoic | Paleozoic | Ordovician-Middle Ordovician-Late) at surface, covers 14 % of this area

Polk Creek Shale (Upper Ordovician) and Bigfork Chert (Upper and Middle Ordovician)

Lithology: chert; shale; limestone

Missouri Mountain Shale and Baylock Sandstone (Phanerozoic | Paleozoic | Silurian) at surface, covers 12 % of this area

Missouri Mountain Shale and Baylock Sandstone - The Baylock Sandstone is present only in the Cross, Cossatot, and Trap Mountains. Missouri Mountain Shale is mapped with Polk Creek Shale and Bigfork Chert in the area between Paron, Saline County, and Little Rock

Womble Shale (Middle Ordovician) (Phanerozoic | Paleozoic | Ordovician-Middle) at surface, covers 2 % of this area

Womble Shale (Middle Ordovician)

Lithology: shale; limestone; sandstone

Stanley Shale (Phanerozoic | Paleozoic | Carboniferous Mississippian-Early) at surface, covers 2 % of this area

Stanley Shale - Includes Chickasaw Creek Chert equivalent of Harlton (1938) near top and Hatton Tuff Lentil and Hot Springs Sandstone Member near base

Stanley Group or Stanley Shale (Phanerozoic | Paleozoic | Carboniferous Mississippian) at surface, covers 1 % of this area

ARDMORE-SHERMAN- "Stanley Shale"- Shale, dark-gray, siliceous,with some gray to buff fine-grained sandstones; thickness,10,000 feet Occurs in the OUACHITA MNTS McALESTER TEXARKANA- "Stanley Group"- Shale, olive-green to gray, illitic, chloritic, with many5- to 30-foot-thick beds of poorly sorted, micaceous, quartzose sandstones and some thin siliceous cherty beds and black shales; several tuff beds occur in basal 1,000 feet and are indicated by red line in Stanley exposures as designated on map; many asphaltite, lead, and quartz veins occur along fault zones; mostly Chesterian age; thickness, 7,500 to 14,000 feet or more. Occurs in the OUACHITA MTNS SOUTH OF TI VALLEY FAULT

Lithology: shale; sandstone; chert; tuff

Jackfork Group or Jackfork Sandstone (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early) at surface, covers 0.3 % of this area

ARDMORE-SHERMAN- "Jackfork Sandstone"- Sandstone, gray, white, and tan, coarse-grained, cherty, with gray shale and some boulders up to 7 feet in diameter; thickness 1,150 to 5,000 feet Occurs in the OUACHITA MNTS McALESTER TEXARKANA- "Jackfork Group"- Sandstone, tan to gray, fine- to coarse-grained, quartzose, with some mica, poorly to well-indurated, quartzitic has some gray shale and several maroon shales; black, white-speckled "Chickasaw Creek Chert" is at base; thickness, 1,500 to 6,000 feet or more. Occurs in the OUACHITA MTNS SOUTH OF TI VALLEY FAULT

Lithology: sandstone; shale; chert

Johns Valley Shale (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early [Morrowan]) at surface, covers 0.3 % of this area

Johns Valley Shale

Lithology: shale; sandstone; limestone

Atoka Formation - Lower part (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Middle [Atokan]) at surface, covers 0.1 % of this area

Atoka Formation - Lower part

Lithology: sandstone; shale

Lynn Mountain Formation (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early) at surface, covers < 0.1 % of this area

McALESTER TEXARKANA- Shale, gray to tan, with many fine- to coarse-grained, quartzose, micaceous sandstone with many bottom markings; top eroded; thickness, 3,000 to 7,000 feet or more; unconformable upon Goddard, Delaware Creek, Woodford, and older beds that are exposed north and west of Ti Valley Fault. Occurs in the OUACHITA MTNS

Lithology: shale; sandstone

Blaylock Sandstone (Phanerozoic | Paleozoic | Silurian) at surface, covers < 0.1 % of this area

McALESTER TEXARKANA- Sandstone, greenish-gray, fine grained, well indurated, alternating with dark-gray to brown phyllites and shales in lower 100 feet; occurs only in Broken Bow Uplift and adjacent area; thickness, 670 to 804 feet, with maximum thickness in Arkansas 1,500 feet. Occurs in POTATO HILLS, BROKEN BOW UPLIFT or ADJACENT SMALLER UPLIFTS IN SOUTHEASTERN PART OF OUACHITA MOUNTAINS

Lithology: sandstone; shale; phyllite

Arkansas Novaculite (Phanerozoic | Paleozoic | Silurian Devonian(?) Carboniferous Mississippian-Early ) at surface, covers < 0.1 % of this area

McALESTER TEXARKANA- Chert, fine- to very fine-grained, gray, green, tan, black, white, and pink, with interbedded black to gray shale in 1-to 18-inch beds; some interbedded conglomerates and in places a basal conglomerate; upper part has been determined to be Mississippian in age and lower part to be Early Silurian, on basis of examination of palynomorphs from Potato Hills; thickness, 600 feet or more. Occurs in the OUACHITA MTNS SOUTH OF TI VALLEY FAULT.

Alluvium (Phanerozoic | Cenozoic | Quaternary | Holocene) at surface, covers < 0.1 % of this area

WOODWARD- Lenticular and interfingering deposits of gravel, sand, silt, and clay. Generally light-tan to gray. Thickness along major streams ranges up to 100 feet and probably averages 40 feet; along minor streams the thickness ranges up to 45 feet and probably averages 20 feet. ENID- Sand, silt, clay, and locally gravel. Maximum thickness ranges from 30 to 80 feet (9 to 24 m) along major streams and from 0 to 60 feet (0 to 18 m) along minor streams. TULSA- Gravel, sand, silt, and clay. TULSA- Gravel, sand, silt, and clay. OKLAHOMA CITY- Sand, silt, clay, and lenticular beds of gravel. Thickness ranges from about 30 to 100 feet and probably averages about 50 feet along major streams. Along minor streams, thickness ranges from a few feet to about 50 feet and probably averages about 25 feet. LAWTON- Sand, clay, and gravel as much as 50 feet (15 m) thick; Shown only along major streams and tributaries . ARDMORE-SHERMAN- Gravel, sand, silt, and clay, including low terraces; thickness, about 25 to 100 feet. McALESTER TEXARKANA- Gravel, sand, silt, and clay, including low terraces about 30 feet above channels; thickness, about 50 feet along Little River and 110 feet along Red River

Lithology: alluvium

Missouri Mountain Shale (Phanerozoic | Paleozoic | Silurian) at surface, covers < 0.1 % of this area

McALESTER TEXARKANA- Shale, greenish-gray to maroon to black; grades into phyllite in Broken Bow Uplift; contains some thin sandstones and gray conglomerates; a fossiliferous limestone occurs in Southeast quarter section 29, Township 4 South, Range 23 East; mapped as SmOp in Potato Hills, where it is included with Polk Creek Shale; thickness, 60 to 110 feet or less. Occurs in POTATO HILLS, BROKEN BOW UPLIFT or ADJACENT SMALLER UPLIFTS IN SOUTHEASTERN PART OF OUACHITA MOUNTAINS

Johns Valley Formation or Johns Valley Shale (Phanerozoic | Paleozoic | Carboniferous Pennsylvanian-Early) at surface, covers < 0.1 % of this area

ARDMORE-SHERMAN- "Johns Valley Formation"- Shale, dark-gray, with boulder conglomerate; thickness, 425 to 900 feet. Occurs in the OUACHITA MNTS McALESTER TEXARKANA- "Johns Valley Shale"- Shale, dark-gray, with some stringers of Wapanucka-like limestone in northwestern part of area; contains exotic boulders of southern Arbuckle Mountain facies, ranging from Fort Sill to Goddard and as large as 369 feet in diameter; some Wapanucka nodules are not exotic but were formed in place; thickness, 300 to 1,000 feet. Occurs in the OUACHITA MTNS SOUTH OF TI VALLEY FAULT.