Trinity Group (geologic group)

The Trinity Group is a group (sequence of rock strata) in the Lower Cretaceous lithostratigraphy of Texas, Arkansas, Mississippi, Louisiana and Oklahoma.^[2][3][4] It is named for the Trinity River of Texas.

Trinity Group
Stratigraphic range: late Aptian-early Albian, 115–106 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Type	Group
Sub-units	Paluxy Formation Glen Rose Formation Twin Mountains Formation
Underlies	Fredericksburg sands, Goodland Formation
Overlies	Cotton Valley Formation
Location
Region	Texas, Arkansas
Country	United States
Type section
Named for	Trinity Rivers, Texas
Named by	Robert Thomas Hill[1]

Trinity Group stratigraphic column in Texas

A stratigraphic column at the Mount Bonnell Fault location starts with the Lower Cretaceous Trinity Group overlain by the Edwards Group. Upper Cretaceous formations follow, starting with the Del Rio Clay, Buda Limestone, and then the Eagle Ford Group. Formations within the Trinity Group include the Hammett Formation, Cow Creek Formation, Hensel Formation, and Lower and Upper Glen Rose Formation. The Hammett and the lower portion of the Upper Glen Rose act as confining units (or aquitard) for the Middle Trinity Aquifer. The Upper Glen Rose contains the Upper Trinity Aquifer, which appears to have intra-aquifer groundwater flow with the Edwards Aquifer as water levels are at the same elevation.^[5]

Vertebrate fauna

Crocodylomorphs

Crocodylomorphs reported from the Trinity Group
Genus	Species	Location	Stratigraphic position	Material	Notes
Pachycheilosuchus[6]	P. trinquei		Glen Rose Formation		A neosuchian related to Eusuchia. Had procoelous vertebrae.
Paluxysuchus[7]	P. newmani		Twin Mountains Formation		A neosuchian related to Eusuchia

Dinosaurs

Dinosaurs reported from the Trinity Group
Genus	Species	Location	Stratigraphic position	Material	Notes
Acrocanthosaurus	A. atokensis[8]		Twin Mountains Formation		A carcharodontosaurid
Arkansaurus[9]	A. fridayi				An ornithomimosaur
Astrophocaudia[10]	A. slaughteri		Paluxy Formation		A member of Somphospondyli
Cedarosaurus[10]	C. weiskopfae		Paluxy Formation		A brachiosaurid
Paluxysaurus[11]	P. jonesi		Twin Mountains Formation		Junior synonym of Sauroposeidon proteles
Sauroposeidon[10][11]	S. proteles		Twin Mountains Formation		A member of Somphospondyli
Tenontosaurus	T. dossi[12]		Twin Mountains Formation		An iguanodont
Convolosaurus[13]	C. marri[14]		Twin Mountains Formation		A basal ornithopod

Pterosaurs

Pterosaurs reported from the Trinity Group
Genus	Species	Location	Stratigraphic position	Material	Notes
Radiodactylus[15]	R. langstoni		Glen Rose Formation		An azhdarchoid pterosaur