The Atarque Sandstone is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

. 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, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

dating back to the

late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

Description

The formation consists of very fine to fine buff fossiliferous

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

with a maximum thickness of . The beds are flat, massive and have low-angle

crossbedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The Principle ...

. The formation intertongues with the underlying Rio Salado Tongue of the Mancos Shale and is overlain by either the Carthage Member of the Tres Hermanos Formation or the Moreno Hill Formation. It was deposited during the early to middle

Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...

Age Age or AGE may refer to: Time and its effects * Age, the amount of time someone has been alive or something has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

of the

. The formation is interpreted as a coastal barrier sandstone deposited by a regression of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, or the Western Interior Sea) was a large inland sea (geology), inland sea that existed roughly over the present-day Great Plains of ...

to the northeast.

Fossils

The formation contains fossil

pelecypod Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

s and

plesiosaur The Plesiosauria or plesiosaurs are an Order (biology), order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period (geology), Period, possibly in the Rhaetian st ...

vertebra. It also contains fossils of the

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

''Spathites rioensis'' characteristic of the middle Turonian.

History of investigation

The unit was first defined as the Atarque Member of the

Mesaverde Formation History The Mesaverde Formation was first described by William Henry Holmes, W.H.Holmes in 1877 during the Hayden Survey. Holmes described the formation in the northern San Juan Basin as consisting of three units, which were a "Lower Escarpment ...

by W.S. Pike in 1947. Pike assigned the lowermost of the Mesaverde in the

San Juan Basin The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah a ...

to the unit. S.C. Hook and coinvestigators revised the Cretaceous stratigraphy of the San Juan and Zuni basins in 1983 and assigned both Pike's Atarque Member and beds in the Zuni Basin assigned to the lower Gallup Sandstone to the Tres Hermanos Formation. The Atarque Member was redefined as the lower sandstone beds of the Tres Hermanos Formation. Simultaneously, M.W. McLellan and coinvestigators raised the Atarque to formation rank as the Atarque Sandstone in the Salt Lake coal field of west-central New Mexico.

Footnotes

References

* * * * {{Clear Sandstone formations of the United States Cretaceous formations of New Mexico

Description

Fossils

History of investigation

See also

Footnotes

References