Basinal mudrocks and associated facies assigned to the Wolfcamp and lower Leonard lithostratigraphic units in the Midland Basin are prolific producers of oil and gas. Four facies are recognized in core on the basis of macroscopic examination, XRD analysis, and ED-XRF elemental chemistry: (1) siliceous mudrock, (2) calcareous mudrock, (3) muddy bioclast–lithoclast floatstone, and (4) skeletal wackestone/packstone. Mudrocks are largely hemipelagic deposits of fine-grained sediment delivered by suspension settling.

Explore the landscapes, rocks, and resources of Texas and 1.7 billion years of Earth history in Texas Through Time by noted geoscientist Thomas E. Ewing. Visit the ancient rocks of the Llano and Van Horn areas, the legacy of now-eroded Himalaya-type ranges that initially rose more than 1 billion years ago. Marvel at the giant West Texas Basin, so prolific in oil and gas, and the enigmatic Marathon and Ouachita Mountains. Watch North America separate from the supercontinent Pangea and create the enclosed, salt-rich Gulf of Mexico in its wake.