Austin Chalk stratigraphic column in Texas

The Buda Limestone is a geological formation 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 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 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

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Description

The Buda Limestone is a dense white to yellow sparry limestone with numerous

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

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 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 (geology), 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 nam ...

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

Fossils

Foraminifera are poorly preserved, but may include '' Globigerina''. Gastropods, a few '' Gryphaea'' 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, bival ...

'' 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 have yielded fossil remains of '' Pterodactyloidea'', '' Ornithocheiroidea'' and '' Ornithocheiridae''.

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 presence ...

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 Underbalanced drilling, or UBD, is a procedure used to drill oil and gas wells where the pressure in the wellbore is kept lower than the static pressure of the formation being drilled. As the well is being drilled, formation fluid flows into the w ...

. 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 The Washita Group is a geologic group in Texas. It preserves fossils dating back to the Cretaceous period. See also * List of fossiliferous stratigraphic units in Texas * Paleontology in Texas Paleontology in Texas refers to paleontological re ...

References

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