Allamore Formation (TXpCAa;0)

State	Texas
Name	Allamore Formation
Geologic age	preCambrian-Proterozoic [Grenville]
Original map label	pCa
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.
Primary rock type	limestone
Secondary rock type	conglomerate
Other rock types	phyllite; tuff; lava flow; volcanic rock (aphanitic)
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
Map references	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
Unit 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.
Geographic coverage	Culberson - Hudspeth