BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA

VOL 39, PP. 435-446 JUNE 30. 1928

TERTIARY STRATIGRAPHY OF WEST TENNNESSEE 1

BY JOSEPH K. ROBERTS {Bead before the Society December SO, 1927) CONTENTS Page Introduction...... 435 Stratigraphy...... 436 General characterics...... 436 Midway group...... 436 Clayton formation...... 436 Porters Creek clay...... 437 Wilcox group...... 438 Holly Springs formation...... 438 Grenada formation...... 439 Jackson formation...... 441 Pliocene-Pleistocene deposits...... 442 Correlation of the Eocene of west Tennessee with that of Mississippi and Alabama...... 444 Sediments of the embayment region of Tennessee...... 445 Conclusions...... 446

I ntroduction The Tertiary and younger formations of west Tennessee were studied by R. L. Collins and the writer in the summers of 192# and 1-925, and in 1925 Mr. Collins mapped the deposits and collected plants from the Wilcox group. We were accompanied by E. W. Berry, who gave advice on formation boundaries and collecting fossil plants. The Tennessee Geological Survey had mapped the Tertiary of this part of the Mississippi embayment as Porters Creek and Lagrange and had assigned certain beds of sand, gravel, and loess to the Pleistocene. The stratigraphy as here described is in accord with the correlations established by Berry and Cooke in Mississippi and Alabama. The Tertiary outcrop belt extends from Mississippi across Tennessee into Kentucky, including nearly all the region between the Tennessee 1 Manuscript received by the Secretary of the Society, December 29, 1927. XXIX— B u l l . G e o l . S o c . Am., V o l . 39, 1927 ( 4 3 5 )

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 436 J. K. ROBERTS----TERTIARY STRATIGRAPHY OF WEST, TENNESSEE and the Mississippi rivers. It is about 11 o miles long, about 70 miles wide on the Mississippi line, and about 60 miles wide on the Kentucky line. In the western third of the belt the strata are concealed by sur- ficial deposits of sand and gravel. The Tertiary deposits comprise lower and upper Eocene, middle Eocene (Claiborne) being absent. Part of the surficial sand and gravel are Tertiary. The classifications in Ten­ nessee are as follows: I’liocene-Pleistocene ...... Lafayette formation. • Unconformity Upper Eocene...... Jackson formation. Unconformity ["Wilcox group...... ^Grenada formation. Lower Eocene -j------Unconformity ^ Holly Springs formation, (Midway group...... j Porters Creek clay. ------Unconformity- ) Clayton formation.

Stkatigraphy GENERAL CHARACTERISTICS The Tertiary formations consist of impure limestone, clay, sand, lig­ nite, greensand, gravel, clay conglomerate, and numerous thin layers of ferruginous clay, sand, and gravel. The structure is monoclinal, with a low dip, which ranges from west to southwest. No folding or faulting was observed. There are several local unconformities, the most extensive of which are at the lower limits of the Clayton, the Wilcox, and the Jackson functions. The Midway is overlapped by the Holly Springs formation, which is in turn overlapped by the Grenada formation. MIDWAY GROUP Clayton formation.—The Clayton formation includes thin lenses of impure and highly weathered limestone and greensand, with limestone at the base. It is a northward extension of the Clayton formation of Mississippi and it is exposed intermittently for nearly 35 miles north of the State line. According to Cooke2, the Clayton is thickest in eastern Alabama and thins toward the west. In Tennessee it is probably not over 60 feet thick. The limestone is best exposed near Trim's Mill, in southeastern Hardeman County, about 4 miles southeast of Middleton and about the same distance north of the Mississippi line. At this place Stephenson measured a section of 7 feet of limestone containing characteristic Midway fossils, overlain by 30 feeet of glauconitic sand 2 Wythe Cooke : Correlation of the Eocene Formations in Mississippi and Alabama. U. S. Geol. Survey Prof. Paper 140 E, 1925, p. 134.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 STRATIGRAPHY-----MIDWAY GROUP 437 and clay showing imperfect impressions of leaves. A very siliceous and weathered phase of the formation occurs just east of Middleton, where it lies unconformably on upper Cretaceous beds. The impure limestone is moderately hard and it contains casts of Turritella and other marine gastropods, somei pelecypods, and considerable greensand. A representa­ tive sample of the 'greensand was found to contain about 70 per cent of calcium carbonate and 4% per cent of glauconite. The siliceous beds near Middleton contain as much as 84 per cent of silica and 0.88 per cent of potash, which may/haye replaced calcareous matter. The particles of greensand are rather uniform in size, being mostly .8 millimeter or more in diameter. They weathered to a rich reddish brown color. Associated with the greensand are small quantities of muscovite and biotite. The beds are dark to medium green when fresh, but become light brown on weathering. The greensand north of the exposures at Middleton is not indurated. Porters Creek clay.—The outcrop of Porters Creek clay, the upper member of the Midway group, extends across the State in a belt having a maximum width of about 8 miles. North of the termination of the Clayton formation the Porters Creek clay lies unconformably on the Upper Cretaceous deposits. This clay is very uniform in its color and texture and in its peculiar fracture. It is a fine, smooth clay, of light dove color when dry and plastic and of dark dove color when wet. Because of its greasy feel it is locally known as “soapstone.” It is not much indurated and it includes no hard ferruginous layers. It contains some muscovite, much of which is altered to chlorite. At a few places it yields foramini- fers, casts of gastropods and pelecypods, crab claws, and fish scales. Its characteristic color, smoothness, hackly fracture, and stratigraphic posi­ tion make it easy recognizable. In Madison County, near the middle of the belt, it is 85 feet thick, and its thickness in some wells is said to reach 125 feet. In the southern half of the belt the clay is cut by numerous sandstone dikes, some of which are hard, though many of them consist of loose sand. Only the larger ones are indurated and the cementing material in these is iron oxide. The grains of sand are uniform in size, ranging from 100 to 200 mesh. Associated with the quartz in these dikes are mus­ covite, limonite, some greensand, angular fragments of Porters Creek clay, and a few foraminifers and gastropods. ' The dikes range in thick­ ness from a fraction of an inch to 22 feet and intersect one another at almost any angle, apparently without systematic orientation. They can be traced for no great distance—50 feet at the most—and appear to cut no beds younger than the Porters Creek clay.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 438 J. K. ROBERTS----TERTIARY STRATIGRAPHY OF WEST TENNESSEE WILCOX GROUP Holly Springs formation.—The Holly Springs and Grenada forma­ tions make up the Wilcox group in Tennessee, where as the basal mem­ ber of that group, the Akerman, is absent. The Holly Springs formation lies unconformably on the Porters Creek clay. The outcrop of the Holly Springs formation is about 20 miles wide along the southern boundary of the State and about 8 miles wide on the Kentucky border. The for­ mation consists of intercalated lenses of sand and clay, a clay conglomer­ ate, and a few thin layers of ferruginous sand and clay. It carries a dis­ tinct flora, and this fact and certain of its lithologic features distinguish it from the Grenada, which formerly was included with it in the La­ grange formation. The clay conglomerate, which is exposed along the eastern border of the belt, lies at or near the base of the Holly Springs formation. It consists of rounded clay pellets, the largest about 10 inches in diameter, which are in a light-colored sandy clay matrix without apparent sorting or systematic orientation. The pellets are light to medium gray and not lignitie. This member is not continuous, but occurs at intervals, sug­ gesting gully fillings, and it seems to be confined to the southern half of the belt. The sands of which the Holly Springs formation principally consist vary greatly in size, but are mostly round, and while some are polished, others are corroded. Associated with the quartz grains are small quanti­ ties of chert, muscovite, biotite, rutile, tourmaline, and iron oxide. The variations in the latter cause the wide range in the color of the beds. In the sand pits at Saulsbury, in Hardeman County, there are 22 vari­ ously “colored layers, each not more than 3 inches thick, ranging in color from gray through green, purple, and red to dark brown. The matrix of the sand contains much clay, but consists mainly of finely divided silica. In addition to the minerals named, there are clay pellets and some con­ cretions of pyrite. At Pine Top, Hardeman County, the sand is fairly well indurated, more so than at any other place, but it disintegrates rapidly when it is removed. At this place it contains a fairly well pre­ served flora. The best sections of the Holly Springs formation in Ten­ nessee are at Lagrange, Saulsbury, and Pine Top, in Hardeman County. The formation contains less clay than sand. The clay is of three types: (1 ) a white plastic clay containing little or no sand and grit and rarely fossiliferous; (2) a dark to black lignitie clay, the lighter-colored, laminated parts of which carry an abundant flora; and (3) a sandy white clay, which is fossiliferous at but few places. The laminated clay

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 STRATIGRAPHY----WILCOX GROUP 439 generally contains fossil plants, but the massive clay has yielded none. In many of the exposures the contact between the light-colored clay and the lignitic clay is sharp. The fossil plants of the clay, and to a less extent those of the sand, are varied both in number and in variety. Many forms have been described by Berry.3 The collections originally made at Pur- year, Henry County, show the greatest number and variety, including 88 genera and 181 species. Additional collections made at Puryear and at other places have increased this number. The plants occur as imprints and as carbonized remains of leaves and stems and include a few fruits and flowers. Some of the imprints of leaves are the same color as the clay in which they are embedded, but others are rich reddish brown or dark gray to black, and thus stand out in contrast to the lighter-colored clay. The few fossils other than plants that have been found consist of a wing of a termite, described by Collins,4 in a clay lens south of Grand Junction, Hardeman County, and a few elytra of beetles. Berry5 has recently described a new type of caddis case which has heretofore been regarded as an isopod belonging to the genus Lygida. The Holly Springs formation contains a few thin layers of hardened sand and clay, mostly less than five feet thick, cemented by iron oxide. Some of these layers containing fossil plants occur at various horizons in the formation and probably represent old ground-water levels. Many hard layers that lie at the contact between sand and clay may have been in­ durated by the precipation of iron oxide from descending water. At some of these contacts the sand lies above the clay, a relation that suggests the precipitation of iron oxide from artesian water. The Holly Springs formation is probably two to four times as thick as the Porters Creek clay. The diagnostic features of the formation as a whole are ( 1 ) the prevailing coarseness of the sand, (2) the association of chert grains with the sand, (3) the several types of clay, and (4), most notably, the distinctive flora. Grenada formation.—The Grenada formation, which overlies the Holly Springs formation unconformablv, outcrops in a belt that entends north­ ward. across west Tennessee, with width increasing from about 20 miles to the south to about 25 miles along the northern boundary. The forma­ tion is concealed near its western border by surficial deposits and on the whole is not so well exposed as the Holly Springs formation. It consists a E. W. Berry: The lower Eocene floras of southeastern North America. U. S. Geol. Survey Prof. Paper 91, 1916. 4 R. L. Collins: A lower Eocene termite from Tennessee. Am. Jour Sci., vol. 9, 1925, pp. 406-410. 6 E. W. Berry : A new type of caddis case from the lower Eocene of Tennessee. U. S. Nat. Mus. Proc., vol. 71, 1927, pp. 1-4.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 440 ,T. K. ROBERTS----TERTIARY STRATIGRAPHY OF WEST TENNESSEE mainly of beds of sand and clay, but includes some layers of indurated clay. The Grenada formation closely resembles the Holly Springs, but it contains a peculiar flora and it has certain distinctive lithologic fea­ tures so that it can be separated. The sand in the formation is iriterbedded with clay in about the same manner as that in the Holly Springs formation. The grains are generally smaller, ranging between 150 and 200 mesh, a difference probably indi­ cating that the conditions of deposition were more unifrom in upper than in lower Wilcox time. The sand is more uniform in color, with gray tones predominating, and organic matter has played little or no part in coloring it. The quartz is the cleanest found in the Eocene sand of Tennessee, and tourmaline, hornblende, rutile, zircon, muscovite, bio- tite, and chlorite also occur. Hornblende is the principal dark constit­ uent. Limonite occurs mostly in the form of concretions, which are of two types. One type is cylindrical, 2 to 4 inches in length and up to one-fourth of an inch in diameter. Some of the cylinders are hollow. The other type is round and flat and has a limonite shell and a clay cen­ ter. At a few places thin layers of low-grade limonite occur along the contacts of sand and clay. Some of these show two sets of fractures, which resemble woody structure. The sand is at many places bedded. It has yielded no fossil plants. Clay in the Grenada formation occurs as a smooth, white, dove- colored to brown, fine-textured clay and as gritty, light-colored clay. The darker clay contains in places variable amounts of lignitic material and is usually fossiliferous. The fossils consist of imprints of leaves, frag­ ments of stems, and a few fruits and flowers. The best plant localities are north and south of Somerville, in Fayette County. A characteristic feature of the clay is the occurrence in it of numerous small crystals of selenite, which average 2 to 3 millimeters in length. Other minerals found in it are muscovite, biotite, marcasite, and pyrite. It contains a few clay concretions, which are of about the same color and texture as the soft clay in which they occur. The clay is not indurated and when wet is rather plastic. On weathering it breaks down into small rectangular pieces, its. fracture being somewhat like that of the Porters Creek clay, but not so pronounced. The layers of indurated clay which occur throughout the Grenada formation are composed of clay and iron oxide of reddish to yellowish brown color. It was from material of this sort, at a place 3 miles south of Somerville, that Safford collected plants, which he sent to Lesquereux for determination; they combined seven genera and eleven species.6 The 9 J. B. Safford : Geology of Tennessee. Nashville, Tenn., 1860, pp. 4*26-428.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 STRATIGRAPHY---- JACKS05T FORMATION 441 leaf imprints obtained from these layers show excellent detail. No layer exceeds 3 feet in thickness and none extends far. It has also been reported in many artesian wells at Memphis. Ocher and low-grade limonite are associated with the clay in the southern part of the State. The Grenada formation is between 100 and 150 feet thick. Its struc­ tural features are like those of the Holly Springs formation. The in­ durated layers lie in such manner at some places as to suggest structure, but slumping is so widespread 'that their attitude should not be inter­ preted as significant. JACKSON FORMATION The upper Eocene is represented by sediments of Jackson age and is bounded above and below by unconformities. The Jackson formation crops out in the Chickasaw Bluffs along the Mississippi and its outcrop zone extends across Tennessee. The formation consists of sand, clay, a few thin layers of lignite, and beds of indurated sand differing greatly from those of the Wilcox. The sand is finer and is more uniorm in size than any other Eocene sand except that of the dikes which cut the Porters Creek clay. There is much admixture of silica and clay and some grains of chert, muscovite, pyrite, marcasite, and small fragments of lignite. The beds look green but contain no greensand. Lamination is well developed, with nearly horizontal bedding planes. The. sand has yielded no fossils except -a few lignitized logs. It contains many small seams of clay, some of them less than an inch thick. The clay in the formation contains thin seams of lignite, three of which are between 12 and 18 inches thick.. A large part of the clay is dark brown to black, but some of it ranges from gray to dove color. The darker colors are due to the presence of lignitic matter. The clay is smooth, containing relatively little grit. It contains a small amount of muscovite. On weathering it breaks down into large, irregular masses. The lignitic clay has yielded a fairly well preserved flora of carbonized leaves, fragments of stems, and a few fruits. The leaves curl up and peel off on drying, leaving a faint imprint of the same color as the' clay. About nineteen species have been described by Berry,7 and recent col­ lections have probably increased this number. The lignitic layers are best developed at Richardsons Landing, in Tipton County, where there are three layers of lignite, about 20 feet apart, underlain by sand and overlain by clay. The lignite grades up­ ward into lignitic clay, which grades into dove-colored clay. The lig­ 7 E. W. Berry: The middle and upper Eocene floras of southeastern North America. U. S. Geol. Survey Prof. Paper 92, 1924.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 442 ,T. K. ROBERTS----TERTIARY STRATIGRAPHY OF WEST TENNESSEE nite is dark brown to black and gives a reddish brown streak. On weathering it breaks into rectangular blocks. Marcasite, both in the form of small concretions and in a finely divided state, is more or less evenly disseminated through it. In the northern part of the State, along the Chickasaw Bluffs, east of Reelfoot Lake, there is a 5-foot lens of indurated sand which is practi­ cally a sandstone. The sand grains are very small and of uniform size and are held together by a matrix of silica with less than 2 per cent of lime. The silica content is about 75 per cent. The Jackson formation is 70 to 120 feet thick, but this is only a part of its original thickness, and therefore it does not represent all of the Jackson time. The formation in Tennessee is probably of the same age as the lower (marine) Jackson of Crowleys Ridge, Arkansas. East of Chickasaw Bluffs, where the deposits would be expected to outcrop, they are concealed by sand and gravel, so thick that the deepest gullies show no Jackson deposits. PLIOCENE-PLEISTOCESE DEPOSITS Throughout west Tennessee a thick mantle of sand and gravel covers much of the Eocene, Cretaceous, and older deposits, most of it consisting of weathered and reworked Eocene and Cretaceous material. Qlenn8 has called these deposits the Lafayette formation. They correspond to the upper part of the Lafayette of McGee.9 The gravel consists of fragments of quartz, chert, sandstone, quartzite, and some clay pellets. It includes a few reworked Paleozoic fossils, such as fragments of corals, crinoid stems, spirifers, bryozoans, and gastropods. The gravels are generally unconsolidated and are mixed with sand. Along the bluffs of the Mis­ sissippi, south of Memphis especially, masses of consolidated gravel a foot or more in diameter and of about the shape of a tree stump have been dislodged from the beds. The gravel consists of well rounded and flat­ tened pebbles from 1 to 2 inches in diameter. The sand is of about the same compensation as the gravel, except that its iron content seems to be higher. In texture it ranges from very coarse to medium, but most of it is coarse. Its grains are well rounded and are coated with iron oxide. Its prevailing color is reddish brown, though many light-gray streaks run at random through the beds. The beds contain alternating brown and gray layers. The gray layers are 8 L. C. Glenn : Underground waters of Tennessee and Kentucky west of Tennessee Elver and of an adjacent area in Illinois. U. S. Geol. Survey Water Supply and Irriga­ tion Paper 164, 1906, pp. 40-43. 9 W J McGee : The Lafayette formation. Twelfth Ann. Rept. U. S. Geol. Survey, Pt. I, 1891, p. 497.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 STRATIGRAPHY---- PLIOCENE-PLEISTOCEiTE DEPOSITS 443 composed of sand having a closer texture than th.e brown, a texture due to a higher content of clay in the matrix. The ifon content of the sand probably averages less than 2 per cent. Besides forming an opaque envelope around the grains, it is distributed through the matrix. At some places the beds of sand and gravel attain , a thickness of* 30 feet. The beds of gravel are thickest-near; streams. One of the thickest occurs along Chickasaw Bluffs east of Reelfoot Lake. Their proximity to streams suggest their terrace origin. The sand and gravel beds may be recognized by (1 ) their prevailing red color, (2) their coarse sand, (3) their great weathering, (4) their uneven contact with the underlying deposits, (o) their widespread occur­ rence, (6) their flattened gravels, and (7) their content of reworked Paleozoic fossils.

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C o r r e l a t io n o p t h e E o c e n e o f W e st T e n n e s s e e w it h t h a t o f M is s is s ip p i a n d A l a b a m a

Tennessee terms, 1925 Mississippi (C ooke, 1925) Alabama (Cooke, 1925) 444

Jackson formation; equivalent to Lower Jackson for­ Yazoo clay member Jackson for- Ocala limestone TENNESSEE east WEST OF STRATIGRAPHY of ROBERTS------TERTIARY K. J. Jackson of Crowleys Ridge, Arkansas mation Tombigbee River Moodys marl member a Yegua formation O¡3 Gosport sand tc fHC Absent forma-J Koskiuska sand member Lisbon formation £o '3 L Winona sand member O Tallahatta formation Tallahatta formation Grenada Over­ Grenada formation formation lapped Hatchitigbee formation area a 2 Absent Bashi formation bJD X O Holly Springs formation % Holly Springs formation Tuscahoma formation Over­ Akermann Over­ Absent, overlapped south of border lapped formation lapped Nanafalia formation area area Tippah sandstone Unexplored a Porters member area Naheola formation g Porters Creek clay Sbßh & Clay Sucarnochee Overlapped £ clay area § Clayton formation Clayton formation Clayton formation TENNESSEE SEDIMENTS 445

Sediments of the E m baym ent Kegion of T ennessee

Period Subperiod Formation Character Recent Alluvium Gravel, sand, and mud of fluviatile origin Gray and yellowish brown Quaternary Pleistocene Loess loess with some concre­ tions and a sparse fauna “Lafayette” for­ Gravel and sand, with few Plio-pleistocene mation reworked Paleozoic fos­ sils in the gravel Sand, clay, lignite, and Upper Eocene Jackson forma­ indurated layers of the tion clay and sand. Fairly abundant floras Sand, clay, thin beds of Grenada lignite and indurated forma­ clay. Well preserved tion and abundant floras Tertiary Sand, clay, thin beds of indurated sand and clay Lower Eocene Holly and a clay conglomerate Springs with abundant floras in forma­ the clay and to less ex­ tion tent in indurated beds | | Wilcox group Porters Gray clay with a sparse Creek marine fauna, green- clay sand, and sandstone dikes Clayton Thin lenses of limestone forma­ with some greensand Midway Midway group tion and a marine fauna Owl Creek tongue Ripley forma­ McNairy sand member tion Coon Creek tongue Selma formation Chalk and sand Cretaceous Upper Cretace­ ous Eutaw forma­ Coffee sand member tion Tombigbee sand member Tuscaloosa for­ Gravel, sand, and clay mation gravel to the north

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/39/2/435/3414780/BUL39_2-0435.pdf by guest on 01 October 2021 446 J. K. EOBEETS—-TERTIARY STBATIGBAPHY OF WEST TENNESSEE

Conclusions Of the Tertiary deposits in western Tennessee the Clayton formation and the Porters Creek clay are of the marine origin, a fact shown by their fossils. Sediments of Wilcox age appear to have been formed as the water was withdrawing from the-emhayJB

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