Austin Chalk stratigraphic column in Texas

The Trinity Group is a

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic iden ...

(sequence of

rock strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

) in the

Lower Cretaceous Lower may refer to: *Lower (surname) *Lower Township, New Jersey *Lower Receiver (firearms) *Lower Wick Lower Wick is a small hamlet located in the county of Gloucestershire, England. It is situated about five miles south west of Dursley, eight ...

lithostratigraphy Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneo ...

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the Osage ...

Mississippi Mississippi () is a state in the Southeastern region of the United States, bordered to the north by Tennessee; to the east by Alabama; to the south by the Gulf of Mexico; to the southwest by Louisiana; and to the northwest by Arkansas. Miss ...

Louisiana Louisiana , group=pronunciation (French: ''La Louisiane'') is a state in the Deep South and South Central regions of the United States. It is the 20th-smallest by area and the 25th most populous of the 50 U.S. states. Louisiana is borde ...

and

Oklahoma Oklahoma (; Choctaw language, Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by Texas on the south and west, Kansas on the nor ...

. It is named for the Trinity River of Texas. A

stratigraphic column A stratigraphic column is a representation used in geology and its subfield of stratigraphy to describe the vertical location of rock units in a particular area. A typical stratigraphic column shows a sequence of sedimentary rocks, with the oldest ...

at the

Mount Bonnell Mount Bonnell , also known as Covert Park, is a prominent point alongside the Lake Austin portion of the Colorado River in Austin, Texas. It has been a popular tourist destination since the 1850s. The mount provides a vista for viewing the city of ...

Fault location starts with the

Trinity Group overlain by the

Edwards Group The Edwards Group is a geologic group in Texas. It preserves fossils dating back to the Cretaceous period. A stratigraphic column at the Mount Bonnell Fault location starts with the Lower Cretaceous Trinity Group overlain by the Edwards Group ...

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

formations follow, starting with the

Del Rio Clay The Del Rio Clay is a geologic formation in Texas. It preserves fossils dating back to the Cretaceous period. A stratigraphic column at the Mount Bonnell location starts with the Lower Cretaceous Trinity Group overlain by the Edwards Group and ...

Buda Limestone The Buda Limestone is a geological formation in the High Plains and Trans-Pecos regions of West Texas and in southern New Mexico, whose strata date back to the Late Cretaceous. Pterosaur remains are among the fossils that have been recovered from ...

, and then the

Eagle Ford Group The Eagle Ford Group (also called the Eagle Ford Shale) is a Sedimentary rock, sedimentary rock formation deposited during the Cenomanian and Turonian ages of the Late Cretaceous over much of the modern-day state of Texas. The Eagle Ford is pr ...

. Formations within the Trinity Group include the

Hammett Formation The Hammett Shale is a geologic formation in Texas. It preserves fossils dating back to the Cretaceous period. A stratigraphic column at the Mount Bonnell Fault location starts with the Lower Cretaceous Trinity Group overlain by the Edwards Gr ...

, Cow Creek Formation,

Hensel Formation The Hensel Formation or Hensel Sand is a Mesozoic geologic formation in Texas. Fossil ornithopod tracks have been reported from the formation.Weishampel, et al. (2004). "Dinosaur distribution." Pp. 517-607. A stratigraphic column at the Mount Bon ...

, and Lower and Upper

Glen Rose Formation The Glen Rose Formation is a shallow marine to shoreline geological formation from the lower Cretaceous period exposed over a large area from South Central to North Central Texas. The formation is most widely known for the dinosaur footprints ...

. The Hammett and the lower portion of the Upper Glen Rose act as confining units (or

aquitard An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...

) for the Middle Trinity

Aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials (gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characterist ...

. The Upper Glen Rose contains the Upper Trinity Aquifer, which appears to have intra-aquifer

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

flow with the

Edwards Aquifer The Edwards Aquifer is one of the most prolific artesian aquifers in the world. Located on the eastern edge of the Edwards Plateau in the U.S. state of Texas, it is the source of drinking water for two million people, and is the primary water su ...

as water levels are at the same elevation.

Vertebrate fauna

Crocodylomorphs

Dinosaurs

Pterosaurs

References

{{coord missing, Texas Cretaceous Arkansas Lower Cretaceous Series of North America Aptian Stage Geologic groups of Texas Natural history of Texas Geologic groups of Arkansas Geologic groups of Mississippi Geologic groups of Louisiana Geologic groups of Oklahoma