Big Bend National Park - Geology

Geology

The oldest recorded tectonic activity in the park is related to the Paleozoic Marathon orogeny, although it is possible that Proterozoic events (over 550 mya) have some deep control. The Marathon orogeny (part of the Ouachita-Marathon-Sonora orogenic belt) is part of thrusting of rocks from the South American Plate over the North American Plate. This can be best seen in the Persimmon Gap area of the park. This orogenic event is linked to the lack of Triassic- and Jurassic-age rocks in the park.

Between the Triassic and the Cretaceous the South American Plate rifted from the North American Plate, resulting in the deposition of the Glen Rose Limestone, Del Carmen Limestone, Sue Peaks Formation, Santa Elena Limestone, Del Rio Clay, Buda Limestone and Boquillas formations (preserved in the Sierra del Carmen–Santiago Mountains, Nine Point Mesa, Mariscal Mountain and Mesa de Anguila areas). Also during this time, the Chihuahua trough formed as the Gulf of Mexico opened, which resulted in east-west striking normal faulting. As a result of this depositional time, there are dinosaur, forest and other fossils preserved in the park.

Following the ending of rifting in the Late Cretaceous to the early Tertiary, the Big Bend area was subjected to the Laramide orogeny. This period of (now east-west) compression caused the northeast-facing Mesa de Anguila (an uplifted monocline on the southwest margin of the park), the southwest-facing Sierra del Carmen–Santiago Mountains (an uplifted and thrust-faulted monocline that forms the boundary of the park on the east) and the Tornillo Basin. During the middle Tertiary most of the volcanic rocks, including the Chisos group, the Pine Canyon caldera complex and the Burro Mesa Formation, formed.

The most recent tectonic activity in the park is Basin and Range faulting from the late Tertiary to Quaternary. This period of east-west extension has resulted in Estufa and Dehalo bolsons in the Chisos Mountains, as well as the Terlingua and Sierra del Carmen, Chalk Draw and Burro Mesa faults. The Rio Grande has entered the Big Bend area roughly 2 mya, and since then extensive erosion and down cutting has occurred.