Big Bend Geology -- Louis Jacobs -- Lone Star Dinosarus -- 1995

1. Texas: three areas of dinosaurs.

• panhandle: oldest
• north-central: DFW, Ft Worth, Grapevine, particularly, between oldest (panhandle) and youngest (Big Bend)
• Big Bend, southwest corner of the state: youngest dinosaurs in the state; two counties: Brewster and Presidio of most interest

Trivia (page 127)

• during the late Triassic Period: dinosaurs were not major players in Texas
• no dinosaurs of Jurassic age are known from Texas --- very, very interesting -- Jurassic -- as in Jurassic Park when dinosaurs flourished
• the Cretaceous Period is rich in dinosaurs from the middle portion and from the end

Big Bend:

• Wann Langston, Jr; UT
• student at UT: Tom Lehman, now a professor at Texas Tech University (1995)
• explained how Big Bend fit into bigger picture of dinosaurs
• Glen Rose Sea: stretched over the southern half of Texas; stretching all the way from Glen Rose to Big Bend
• Glen Rose, Texas, is about 80 miles southwest of Grapevine, TX
• dinosaurs were on the northeast short of the Glen Rose sea
• on the south side, the water seemed to extend forever, certainly all the way to what would ultimately become the Sierra Madre Occidental mountains in Mexico
• Big Bend is the region where the platform of the shallow sea dove into the deeper ocean; today, the border between Texas and Mexico
• Rose Glen Formation
• from east Texas to the Rio Grande
• all underwater
• Big Bend remained inundated but the terrestrial Paluxy Formation containing the bones of dinosaurs was being deposited in north-central Texas (DFW)
• time marching toward the end of the Cretaceous Period, the western shore of the ocean advanced from the Sierra Madre Occidental toward Big Bend
• eventually the waters withdrew; Big Bend emerged from the depths: the Aguja Formation is the record of dinosaurs wandering back into Texas -- they came in from the north
• they had left since the Woodbine Formation because of dearth of dry land and a prevalence of ocean
• Big Bend became high and dry but most of Texas remained submerged until well into the age of mammals (Cenozoic Era)
• at this time, the continent of North America was divided in half by the Western Interior Seaway
• the western land mass: a huge finger of land, a peninsula, projecting southward from eastern extremity of Asia -- this explains the dinosaur fossils in Asia
• Big Bend was the southern part of that peninsula -- wow -- a direct shot to Asia -- so when the author says dinosaurs were coming back to Texas from the north, they were coming from Asia
• during the final stage of the Cretaceous, the Western Interior Seaway began to recede northward (the Arctic) and southward (the Gulf of Mexico).

Formations of interest

Two formations of interest

The Aguja Formation is the older of the two major dinosaur-bearing rock units in Big Bend.

The Javelina, is the younger; overlies the Aguja.

Aguja: between 84 and 74 million years ago (asteroid, 66 million years ago).

At that time, the Western Interior Seaway was complete.

The rock unit resulting from the deposition of river sands and muds in channels and on the floodplains is caled the Javelina Formation (74 to 66 million years ago). So that's the geologic setting.

Mountains were also starting to be uplifted in western US at this time.