Lake Waco Formation

The Lake Waco Formation is a geologic formation within the Eagle Ford Group deposited during the Middle Cenomanian to the Early Turonian of the Late Cretaceous in central Texas.[1] The formation was named for outcrops near Lake Waco, south of the city of Waco, Texas by W. S. Adkins and F. E. Lozo in 1951.[2] The Lake Waco Formation is primarily composed of shale, with minor amounts of limestone and volcanic ash beds (bentonites). It is subdivided into three members: Bluebonnet Member, Cloice Member, and the Bouldin Member.[2] The Bluebonnet Member is 10 to 20 ft (3 to 6 m) thick, and is made up of broken pieces (prisms) of inoceramid clams and planktonic foraminifera.[3] The Cloice Member is 35 ft (11 m) thick at its type section on the Cloice Branch of the South Bosque River, whereas the Bouldin Member was named for outcrops on Bouldin Creek south of downtown Austin, where it is roughly 9 ft (3 m) thick. They are both made up of shales rich in organic matter with thin limestones and volcanic ash beds.[2]

Lake Waco Formation Stratigraphic range: Mid Cenomanian-Early Turonian ~96–93.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓ [1]
Type	Geological formation
Unit of	Eagle Ford Group
Sub-units	Bluebonnet Member, Cloice Member, Bouldin Member
Underlies	South Bosque Formation
Overlies	Pepper Shale
Lithology
Primary	Shale
Other	Marl, limestone, volcanic ash beds
Location
Region	East Texas
Country	United States
Type section
Named for	Lake Waco near Waco, Texas[2]
Named by	Adkins and Lozo[2]

Plesiosaur remains, shark's teeth, ammonites, and inoceramid clams are among the fossils that have been recovered from its strata.[3][4]

See also

• Plesiosaur stratigraphic distribution

References

1. Denne, R. A., Breyer, J. A., Callender, A. D., Hinote, R. E., Kariminia, M., Kosanke, T. H., Kita, Z., Lees, J. A., Rowe, H., Spaw, J. M., and Tur, N. (2016). Biostratigraphic and geochemical constraints on the stratigraphy and depositional environments of the Eagle Ford and Woodbine Groups of Texas: in Breyer, J. A. (ed.), The Eagle Ford Shale: A renaissance in U.S. oil production, AAPG Memoir 110, p. 1-86.
2. Adkins, W. S., and F. E. Lozo, 1951, Stratigraphy of the Woodbine and Eagle Ford, Waco area, Texas, in F. E. Lozo, ed., The Woodbine and adjacent strata of the Waco area of central Texas, a symposium for the 1951 field trip sponsored by the East Texas Geological Society: Southern Methodist University Press, Fondren Science Series 2, Dallas, Texas, p. 101–163.
3. Silver, B. A. (1963) The Bluebonnet Member, Lake Waco Formation (Upper Cretaceous), Central Texas-A lagoonal deposit: Baylor Geologic Studies Bulletin 4, Waco, Texas, 46 p.
4. Thurmond, John T. (1968). "A New Polycotylid Plesiosaur from the Lake Waco Formation (Cenomanian) of Texas". Journal of Paleontology. jstor.org. 42 (5): 1289–1296. JSTOR 1302265.