Allamore Formation

Allamore Formation
State Texas
Name Allamore Formation
Geologic age preCambrian (Proterozoic); Grenville Series
Lithologic constituents
Major
Sedimentary > Carbonate > Limestone (Bed)interbedded cherty limestone, limestone-pebble conglomerate
Minor
Igneous > Volcanic > Mafic-volcanicAllamore Fm. includes numerous shallow intrusions of igneous rock, pyroclastic rock, and lava flows
Igneous > Hypabyssalformation contains pyroclastic rock and lava flows (percentage unknown)
Incidental
Sedimentary > Chemical > Chert (Bed)interbedded cherty limestone, limestone-pebble conglomerate
Comments spelled Allamore (on the Geologic Map of Texas, 1992) and Allamoore (Geologic Atlas of Texas, 1968, Van Horn-El Paso Sheet, 1:250,000 scale). Type area in Van Horn region. Name derived from Allamoore, TX, 11 mi west of Van Horn (railroad station spelled the village name Allamore). Allamoore is characteristically thin-bedded, blue, gray, or brown limestone, with nearly all beds seamed at regular intervals by thin chert bands. Differential weathering of chert and ls. gives outcrops a ribbed appearance. Parts of ls. are dark gray or black. Analyzed speciments indicate color is due to organic matter, which suggests existence of life during deposition. Few indications of fossils; but, certain features in ls. may be algal origin. Associated with the ls. are great masses of volcanic rocks, including diabasic flows and various pyroclastic rocks, such as breccias and well-bedded tuffs. Volcanics are interbedded in thin to thick members, indicating that limestone deposition and volcanic activity alternated rapidly. Many shallow instrusions of igneous rock. Exposed only in strongly folded belt north of overthrust mass of Carrizo Mountain schist; rocks very disturbed here, and thickness uncertain. Over wide areas, however, beds stand nearly verical; thickness here perhaps thousands of feet. Overlies Carrizo Mountain schist; underlies Hazel sandstone.
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
Counties Culberson - Hudspeth