Helms Shale, Rancheria Formation, Las Cruces Limestone, Percha Shale, and Canutillo Formations, undivided (TXMDh;0)

State	Texas
Name	Helms Shale, Rancheria Formation, Las Cruces Limestone, Percha Shale, and Canutillo Formations, undivided
Geologic age	Late Mississippian; Chesteran; and Devonian
Lithologic constituents	Major Sedimentary > Clastic > Mudstone > Shale (Bed) Sedimentary > Carbonate > Limestone (Bed) Incidental Sedimentary > Chemical > Chert (Bed) Sedimentary > Clastic > Sandstone
Comments	(from Van Horn-El Paso Sheet, Geol. Atlas of Texas, 1968). Limestone, shale, and chert. Franklin Mtns: five units not separately mapped, Mississippian--(1) Helms Shale, gray and green shale, ss., impure fossiliferous ls., 150 ft thick; (2) Rancheria Fm. ls., argillaceous, bituminous, cherty, black; weathers rusty brown, 250 ft thick; (3) Las Cruces Limestone {named for town of Las Cruces, Dona Ana Co., NM, Orogrande Basin}-- ls., aphanitic, evenly bedded, black; weathers gray; sparsely fossilif.; 60 ft thick; Devonian rocks, (4) Percha Shale, black shale, 40 ft thick; (5) Canutillo Fm. fossiliferous limestone, in part cherty, lt. brn. and lt. gray; some sandstone, black, weathers brown; thickness 135 ft. Hueco Mtns: Mississippian rocks, upper part--shale, sandy shale, and nodules of fossilif. ls. grading down to brn-weathering flaggy sandy ls.; lower part--gray, thin- to medium-bedded limestone, upperhalf cherty; 500+ ft thick. Devonian rocks, upper part--blue shale; lower part--mostly bedded chert, white, gray, brownish yellow and brn.; some interbedded ls., thickness 150 +ft. Sierra Diablo: Mississippian rocks--mostly black, purplish, dk.gray shale; lenses and beds of fossilif. earthy ls.; sm. phosphatic and pyritic nodules in shale; max. exposed thickness 135 ft (Barnett Shale of P.B. King). Devonian rocks--mostly bedded chert, yellowish brown, brown, white, gray, black, and green; thin interbeds of black and brown siliceous shale in upper part, dolomitic ls. in lower part; thickness 125+-ft.
References	Bureau of Economic Geology, 1968, Van Horn-El Paso Sheet, Geologic Atlas of Texas: Bureau of Economic Geology, The University of Texas at Austin, scale 1:250,000. Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000.
NGMDB product	NGMDB product page for 68390
Counties	El Paso - Hudspeth

State

Texas

Name

Helms Shale, Rancheria Formation, Las Cruces Limestone, Percha Shale, and Canutillo Formations, undivided

Geologic age

Late Mississippian; Chesteran; and Devonian

Lithologic constituents

Major

Sedimentary > Clastic > Mudstone > Shale (Bed)

Sedimentary > Carbonate > Limestone (Bed)

Incidental

Sedimentary > Chemical > Chert (Bed)

Sedimentary > Clastic > Sandstone

Comments

(from Van Horn-El Paso Sheet, Geol. Atlas of Texas, 1968). Limestone, shale, and chert. Franklin Mtns: five units not separately mapped, Mississippian--(1) Helms Shale, gray and green shale, ss., impure fossiliferous ls., 150 ft thick; (2) Rancheria Fm. ls., argillaceous, bituminous, cherty, black; weathers rusty brown, 250 ft thick; (3) Las Cruces Limestone {named for town of Las Cruces, Dona Ana Co., NM, Orogrande Basin}-- ls., aphanitic, evenly bedded, black; weathers gray; sparsely fossilif.; 60 ft thick; Devonian rocks, (4) Percha Shale, black shale, 40 ft thick; (5) Canutillo Fm. fossiliferous limestone, in part cherty, lt. brn. and lt. gray; some sandstone, black, weathers brown; thickness 135 ft. Hueco Mtns: Mississippian rocks, upper part--shale, sandy shale, and nodules of fossilif. ls. grading down to brn-weathering flaggy sandy ls.; lower part--gray, thin- to medium-bedded limestone, upperhalf cherty; 500+ ft thick. Devonian rocks, upper part--blue shale; lower part--mostly bedded chert, white, gray, brownish yellow and brn.; some interbedded ls., thickness 150 +ft. Sierra Diablo: Mississippian rocks--mostly black, purplish, dk.gray shale; lenses and beds of fossilif. earthy ls.; sm. phosphatic and pyritic nodules in shale; max. exposed thickness 135 ft (Barnett Shale of P.B. King). Devonian rocks--mostly bedded chert, yellowish brown, brown, white, gray, black, and green; thin interbeds of black and brown siliceous shale in upper part, dolomitic ls. in lower part; thickness 125+-ft.

References

Bureau of Economic Geology, 1968, Van Horn-El Paso Sheet, Geologic Atlas of Texas: Bureau of Economic Geology, The University of Texas at Austin, scale 1:250,000.

Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000.

NGMDB product

NGMDB product page for 68390

Counties

El Paso - Hudspeth