Austin Chalk stratigraphic column in Texas

The Buda Limestone is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

in the

High Plains High Plains refers to one of two distinct land regions: *High Plains (United States), land region of the western Great Plains * High Plains (Australia), land region adjacent to the Great Dividing Range See also * Altiplano (disambiguation) The ...

and

Trans-Pecos The Trans-Pecos, as originally defined in 1887 by the Texas geologist Robert T. Hill, is the portion of Texas that lies west of the Pecos River. The term is considered synonymous with Far West Texas, a subdivision of West Texas. The Trans-Pe ...

regions of

West Texas West Texas is a loosely defined region in the U.S. state of Texas, generally encompassing the arid and semiarid lands west of a line drawn between the cities of Wichita Falls, Abilene, and Del Rio. No consensus exists on the boundary betwe ...

and in southern

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

, whose strata date back to the

Late 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'', ...

Pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the Order (biology), order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cre ...

remains are among the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s that have been recovered from the formation.Barrett, P.M., Butler, R.J., Edwards, N.P., & Milner, A.R. Pterosaur distribution in time and space: an atlas. p61-107. in Flugsaurier: Pterosaur papers in honour of Peter Wellnhofer. 2008. Hone, D.W.E., and Buffetaut, E. (eds). Zitteliana B, 28. 264p

/ref>

Description

The Buda Limestone is a dense white to yellow sparry

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

with numerous

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scra ...

veins that weathers to yellowish or pinkish due to its iron content. In far western Texas, the formation overlies the

Del Rio Formation The Del Rio Formation is a geologic formation in Texas. It preserves fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, ...

and is in turn overlain by the

Eagle Ford Group The Eagle Ford Group (also called the Eagle Ford Shale) is a 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 predominantly compos ...

. The total thickness is about . In trans-Pecos Texas, the formation rests on the

Grayson Formation The Grayson Formation is a geologic formation in Texas. It preserves fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, ...

and is overlain by the

Boquillas Formation The Boquillas Formation is a geologic formation deposited during the Late Cretaceous in modern-day West Texas. It is typically composed of alternating marls and limestones with thin volcanic ash beds (bentonites). It was named for outcrops near ...

. In the

Big Bend National Park Big Bend National Park is an American national park located in West Texas, bordering Mexico. The park has national significance as the largest protected area of Chihuahuan Desert topography and ecology in the United States, and was named after ...

area, the formation is divided into three informal members. The lowest is of hard microgranular grayish-white limestone that breaks with a conchoidal fracture. The middle member is about of an

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay mineral ...

or marly nodular grayish-white limestone. The upper member is up to of limestone similar to the lower member.

Fossils

Foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

are poorly preserved, but may include ''

Globigerina ''Globigerina'' () is a genus of planktonic Foraminifera, in the order of Rotaliida.Gl ...

''. Gastropods, a few ''

Gryphaea ''Gryphaea'', one of the genera known as devil's toenails, is a genus of extinct oysters, marine bivalve mollusks in the family Gryphaeidae. These fossils range from the Triassic period to the middle Paleogene period, but are mostly rest ...

'' oysters, and the

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...

'' Alectryonia carinata'' has also been found in the formation. Abundant bivalve fossils are found in the formation east of Big Bend National Park. Exposures in

Hays County, Texas Hays County is located on the Edwards Plateau in the U.S. state of Texas. Hays County is part of the Austin-Round Rock metropolitan area. As of the 2020 census, its official population had reached 241,067. The county seat is San Marcos. ...

have yielded fossil remains of ''

Pterodactyloidea Pterodactyloidea (derived from the Greek words ''πτερόν'' (''pterón'', for usual ''ptéryx'') "wing", and ''δάκτυλος'' (''dáktylos'') "finger" meaning "winged finger", "wing-finger" or "finger-wing") is one of the two traditional ...

'', ''

Ornithocheiroidea Ornithocheiroidea (or ornithocheiroids) is a group of pterosaurs within the extinct suborder Pterodactyloidea. They were typically large pterosaurs that lived from the Early to Late Cretaceous periods (Valanginian to Maastrichtian stages), with fo ...

'' and ''

Ornithocheiridae Ornithocheiridae (or ornithocheirids, meaning "bird hands") is a group of pterosaurs within the suborder Pterodactyloidea. These pterosaurs were among the last to possess teeth. Members that belong to this group lived from the Early to Late Cr ...

''.

Economic resources

The Buda Limestone is an important

petroleum reservoir A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presenc ...

that has been exploited for decades via conventional vertical drilling. It is now being exploited using techniques such as

horizontal Horizontal may refer to: *Horizontal plane, in astronomy, geography, geometry and other sciences and contexts *Horizontal coordinate system, in astronomy *Horizontalism, in monetary circuit theory *Horizontalism, in sociology *Horizontal market, ...

and underbalanced drilling. While the vertical wells relied on the porosity of the formation (up to 6%), the horizontal wells exploit a system of natural vertical fractures in the formation.

History of investigation

The formation was originally named the Shoal Creek Limestone, but this name was preempted, and the formation was renamed the Buda Limestone by T.W. Vaughan in 1900. By 1935, the formation had been included in the Washita Group.

References

Limestone formations of the United States Cretaceous formations of New Mexico Cretaceous geology of Texas {{paleo-site-stub