Complex sentence: The Ouachita Mountains were extensively eroded between the Permian and the Jurassic, and much of the Ouachita system was subsequently buried beneath Mesozoic and Cenozoic sediments to the southeast and southwest.
Split into simpler sentences: The Ouachita Mountains were extensively eroded between the Permian and the Jurassic. Much of the Ouachita system was buried beneath Mesozoic and Cenozoic sediments to the southeast and southwest.