Transcript Slide 1
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 Bone Springs-Victorio Peak Rustler Capitan Edwards-Trinity (Plateau) 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 SpringsVictorio 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 B A 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