Chambers Tuff mapped as one of seven formations of Vieja Group in the Sierra Vieja area, Presidio Co, west TX in the Permian basin. Vieja Group is shown on the Correlation of Map Units as consisting of (ascending): Gill Breccia, Colmena Tuff, Buckshot Ignimbrite, Chambers Tuff, Bracks Rhyolite, Capote Mountain Tuff, and Mitchell Mesa Welded Tuff. Chambers is fine-grained, crystal-vitric tuff, moderate to well bedded, pale red, grayish pink, grayish green, pale purple, and grayish orange pink; a persistent layer of coarse sandstone in southern part of the area, with some conglomerate 130 ft above base. Thickness 105-750 ft. Contains Oligocene vertebrate fossils. [Author states that correlation of volcanic rocks from area to area on Marfa sheet is uncertain--little attempt is made to correlate between areas. The rocks are described by area.] Of Oligocene age. Geologic map.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Pg. 14. Chambers Tuff of Vieja Group. Sample from tuffaceous sediment (locality unknown) yielded a K-Ar age of 40.9 +/-2.8 Ma (alkali feldspar). Data from R.K. DeFord, 1958 (Texas Jour. Sci., v. 10, p. 1-37), and J.A. Wilson and others, 1968 (Amer. Jour. Sci., v. 266, p. 590-604); age recalculated using decay constants of Steiger and Jager, 1977 (Earth Planet. Sci. Letters, v. 36, p. 359-362).
[Age considered Eocene (from Geologic Names Committee, USGS, 1983 ed. geol. time scale, with additions from N.J. Snelling, 1985, The Geol. Soc. Mem., no. 10).]

Source: Publication.