Permeability controls in the Santana Tuff, Trans-Pecos Texas

Conference · Mon Feb 01 00:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:6137895

Smyth, R C; Sharp, Jr, J M ^[1]

---

1. Univ. of Texas, Austin, TX (United States). Dept. of Geological Sciences

The Santana Tuff is a poorly to densely welded rhyolitic ash-flow tuff that erupted from the Sierra Rica caldera complex in Chihuahua, Mexico, 27.8 m.y. ago. The portion of the Santana Tuff examined in this study crops out over a 125-km[sup 2] area in the Big Bend Ranch State Natural Area in Trans-Pecos Texas. A review of recent literature has revealed the need to incorporate realistic values for permeability due to fracture spacing into groundwater models. Permeability/porosity relationship for fracture skins and unaltered tuff are significant to problems of solute transport. Permeability measurements of tuff samples vary over four orders of magnitude. The most densely welded samples have the lowest permeability. The least densely welded ones have the highest permeability. However, effective permeabilities of the differentially welded layers are quite different if fractures are considered. The spacing of cooling fractures in poorly to densely welded layers of the Santana Tuff also varies considerably. Degree of welding of the different Santana Tuff units has been quantified by length-to-width ratios (flattening) of pumice fragments. Lognormally distributed fracture spacing measurements correlate directly with the degree of welding. Rose diagrams and stereonets indicate that fracture orientations are not always random, as might be inferred from a cooling origin, but may have preferred orientation patterns.

• OSTI ID: 6137895
• Report Number(s): CONF-9303212-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 25:1; Conference: 27. annual Geological Society of America (GSA) South-Central Section meeting, Fort Worth, TX (United States), 15-16 Mar 1993; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GEOLOGIC FORMATIONS
HYDROLOGY
PERMEABILITY
TEXAS
TUFF
FLOW MODELS
GEOLOGIC FRACTURES
GEOLOGIC HISTORY
GROUND WATER
RHYOLITES
DEVELOPED COUNTRIES
GEOLOGIC STRUCTURES
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
MATHEMATICAL MODELS
NORTH AMERICA
OXYGEN COMPOUNDS
ROCKS
USA
VOLCANIC ROCKS
WATER
580000* - Geosciences