Pg. 79. Yazoo clay marl of Jackson group. Drab or yellowish calcareous clays showing heavy bedding and distinct jointing. Thickness 300 feet. Of marine origin. Most notable fossil ZEUGLODON. Included in Jackson group. Underlies Moody's Branch green marls. [Age is late Eocene.]
[Named from exposures in bluff of Yazoo River at Yazoo City, MS.]

Source: US geologic names lexicon (USGS Bull. 896, p. 2383).

Pg. 186-198. Yazoo clay member of Jackson formation overlies Moodys marl member, which includes, at top, the bed called "ZEUGLODON bed" in Alabama. [Age is late Eocene.]
[See also GNC remark under Wilmarth (ca. 1930).]

Source: US geologic names lexicon (USGS Bull. 896, p. 2383).

Yazoo clay member of Jackson formation. Later work [post-1918] led Cooke to modify the definitions so as to include the ZEUGLODON-bearing bed in Yazoo clay member. (See AAPG Bull., v. 17, no. 11, p. 1387-1388, 1933.) These modified definitions are those now followed by the USGS, which treats the Yazoo and Moodys as members of Jackson formation, instead of as formations of Jackson group. The Yazoo clay is overlain by Vicksburg group. Cooke (1918) described the Yazoo as almost entirely calcareous, very plastic clay of various colors, but in most places blue or green when wet and gray when dry. He gave its thickness at Vicksburg as 600 feet, at Jackson as 200 feet, at Shubata as 70 feet. In western Alabama the lower part of Yazoo clay of Mississippi is represented by Cocoa sand member of Jackson formation, and the name Yazoo is there restricted to the overlying clay beds. The Yazoo and Moodys have not been separately mapped. Age is late Eocene.

Source: US geologic names lexicon (USGS Bull. 896, p. 2383).

Pg. 98-105. Yazoo clay, as used in this report [Grant and La Salle Parishes, central northern Louisiana], includes all materials between Danville Landing beds above and Moodys Branch marl below. Includes Tullus clay member (new) below and Verda member (new). Thickness 275 to 375 feet. Jackson group. [Age is late Eocene.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 4320).

[Chart originally published in Mississippi Geol. Soc. Gdbk. 1, Feb. 1940; revised chart published in AAPG Bull. (submitted Oct. 1940).] Yazoo clay of Jackson group. Massively bedded yellow to green calcareous clay. Interbedded lignitic clay in western Mississippi. Bentonitic zone near base. Thickness 90 to 600 feet. Underlies Forest Hill sand; overlies Moodys marl. Contains Cocoa sand member. [Age is late Eocene.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 4320).

Pg. 12 (table), 18-22. Yazoo clay member of Jackson formation. Conformably overlies Moodys Branch marl member; conformably underlies Forest Hill sand member. Thickness about 500 feet. [Age is late Eocene.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 4320).

Yazoo clay of Jackson group. In Quitman fault zone area, Clarke and Wayne Counties, Mississippi, is divided into two tongues by Cocoa sand member. Estimated thickness 125 feet in southeastern part of area; thickens northwest to 250 feet in Jasper County, Mississippi. Overlies Moodys marl; underlies Red Bluff clay. [Age is late Eocene.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 4320).

Pg. 1838 (fig. 6), 1839. Yazoo clay, in Mississippi and Alabama, divided into (ascending) North Creek clay (new), Cocoa sand, Pachuta clay (new), and Shubuta clay (new) members. [Age is late Eocene.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 4320).

Pg. 97 (fig. 5). Chart shows Yazoo group, consisting of North Creek clay, Cocoa sand, Pachuta marl, and Shubuta clay, as Eocene-Oligocene.

Source: US geologic names lexicon (USGS Bull. 1200, p. 4320).

Pg. 96-99. Most continuous section of Yazoo formation in Sabine Parish, central northern Louisiana, extends from bottom of Caney Creek (in SW/4 SE/4 sec. 34, T. 4 N., R. 12 W.) approximately 100 yards south of bridge and thence eastward in ditches along Clare-Toro ward road. At this locality, about 65 feet of Yazoo clay is exposed. Included in this section is a 5.8-foot bed of highly fossiliferous, glauconitic, sandy marl, which is equivalent to basal sediment of Wooleys Bluff clays (member?) of Wellborn formation of Texas, and a 7-foot fossiliferous sand, which is probably equivalent to some part of sands reported overlying Wooleys Bluff clays at Sabine River in Texas. Overlies Moodys Branch marl with contact transitional; underlies Danville Landing beds. Jackson group. [Age is late Eocene.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 4320).

Basal member of Yazoo in MS and AL renamed North Twistwood Creek member to reflect correct name of Creek.

Source: GNU records (USGS DDS-6; Reston GNULEX).

Age of Yazoo Formation changed in this report from late Eocene to: late Eocene and early Oligocene, based on study of planktonic Foraminifera. [This revised age is not widely accepted by other workers in the area.]

Source: GNU records (USGS DDS-6; Reston GNULEX).

The upper Eocene Jackson Group in the study area is divided into ascending Moodys Branch Formation, Yazoo Clay, and Crystal River Formation. Yazoo Clay consists of four members (ascending): North Twistwood Creek Clay, Cocoa Sand, Pachuta Marl, and Shubuta Members. North Twistwood Creek consists 40 to 60 ft of greenish-gray to bluish-gray fossiliferous, calcareous, micaceous, silty clay and marl. The disconformably overlying Cocoa Sand includes about 60 ft of gray fossiliferous, calcareous, massive, fine- to medium-grained sand at its type locality in Choctaw Co., AL, but thins to the east and west and in some areas consists only of a thin sandy marl which is difficult to distinguish from the gradationally overlying Pachuta Marl. Pachuta consists throughout the study area of 6 to 12 ft of greenish-gray indurated, fossiliferous, argillaceous marl and limestone that grades upward into the marine clay of the overlying Shubuta Member. Shubuta, at its type locality in Clarke Co., MS, consists of about 90 ft of grayish-olive-green blocky to massive, fossiliferous, calcareous clay. Shubuta thins eastward into southwestern AL and thickens into south-central AL where it intertongues with the Crystal River Formation. To the east and into the FL panhandle, the lower three members of the Yazoo also grade into the Crystal River Formation. In these areas, the Crystal River is considered to be equivalent to the entire Yazoo Clay interval of MS.

Source: GNU records (USGS DDS-6; Reston GNULEX).

Yazoo Formation is the younger of two formations of the Jackson Group and in eastern MS and southwestern AL has been divided into four members. In eastern Wayne Co., MS, near the AL border, the Yazoo is 175 ft thick. Unit thickens westward to 515 ft in the subsurface of Warren Co. The Cocoa Sand Member pinches out abruptly to the west within Wayne Co. The Pachuta Marl Member extends at least as far west as Rankin Co. in central MS. The North Twistwood Creek Member decreases in thickness from 150 ft in eastern Wayne Co. to 60 ft in the western part of the county and into Rankin Co. The Shubuta Clay Member thickens from 25 ft in eastern Wayne Co. to 295 ft in eastern Rankin Co. The biostratigraphy of the Yazoo is well known and at the Miss-Lite clay pit at Cynthia, MS, is suggestive of an upper NP19/20 zonal assignment for the lower part and a lower NP21 zonal assignment for the upper part of the sequence. However, the exact level of the Eocene/Oligocene boundary in the upper part of the Yazoo of central and western MS is still questioned. Bentonite beds recorded from both outcrops and cores in the upper Eocene Yazoo of western MS provide information on the age of the Eocene/Oligocene boundary. An age of 34.3 Ma was determined on the upper bentonites (335 ft above the base of the Yazoo) at Satartia in Yazoo Co. and (378 ft above the base) at Society Ridge in Hinds Co., an age consistent with that reported from the boundary stratotype in Italy, but younger than the 37 Ma age used by Berggren and others (1985) for their Cenozoic time scale.

Source: GNU records (USGS DDS-6; Reston GNULEX).