The Permian and Cretaceous Aquifer Systems of Far West Texas Matthew M. Uliana, Ph.D., P.G. Geology Program and Aquatic Resources (Dept. of Biology)

Talk Outline Introduction Paleozoic depositional setting Aquifers in Paleozoic rocks –Marathon, Capitan, Rustler, Bone Springs Cretaceous depositional setting Aquifers in Cretaceous rocks –Edwards-Trinity (Plateau) aquifer Regional flow systems –Structural controls on groundwater flow

Aquifers of West Texas Edwards-Trinity (Plateau) Bone Springs-Victorio Peak Rustler Capitan Marathon

Paleozoic Depositional Settings Permian –Area was on the edge of a major super-continent called Pangea –Basin surrounded by a large reef system Aquifers include –Marathon –Capitan –Rustler –Bone Springs- Victorio Peak Aquifers

Marathon Aquifer Located in Brewster County north of Big Bend –Ordovician to Pennsylvanian age (~500 – 300 million years ago) –Located in the Marathon Uplift Water found in fractures and cavities in subsurface Not particularly productive

Capitan Aquifer Occurs in the Capitan Reef Complex –Ancient reef which formed around the margins of the Delaware Basin in the Permian Period (~250 million years ago) algae, sponges, and tiny colonial animals called bryozoans –Excellent exposure of the reef in Guadalupe Mountains National Park El Capitan

Delaware Basin A B

Flow under Apache Mts. Flow through the Apache Mts. Area is not in the reef complex rocks –Flow is in the basin sediments –Probably controlled by fractures

Rustler Aquifer Permian; also associated with the Delaware Basin –Evaporites (gypsum and anhydrite) –Formed when the basin closed and dried up Great Salt Lake

Rustler Water Quality Well yields are generally low –Controlled by fractures –Quite variable Usually high in sulfates –Rarely good enough for regular human consumption

Bone Springs-Victorio Peak Located in the Dell City area Limestone deposited between the reef and the continent –Controlled by fractures Recharge comes from New Mexico –Primarily from the Sacramento River

Cretaceous Depositional Settings Much of North America was covered by shallow tropical sea for millions of years Lots of limestone deposited throughout Texas –Most of the Cretaceous aquifers in Texas are in limestone

Edwards-Trinity Plateau Cretaceous limestones Only westernmost part is in the Trans-Pecos Hydraulically-connected to the Cenozoic Pecos Alluvial Aquifer

Regional Flow Systems Connections between different aquifers –Some can cover dozens to hundreds of miles –Controlled by several factors

Structural Controls The tectonic events of the past billion years created structural grains in the regional bedrock Creates patterns of fractures that control groundwater flow paths Examples include… –Permian carbonates in Apache Mts. –Otero Mesa in New Mexico/ Hudspeth County

Conclusions Paleozoic aquifers in far west Texas are considered minor aquifers Aquifer properties… –Location, flow paths, permeability, water quality … are generally controlled by the depositional setting and the regional structural trends