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Lost Branch Formation

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Memorial Shale (revised)

The name Memorial Shale is revived and revised herein to apply to the largely terrestrial formation that underlies the Lost Branch Formation. The name Memorial was originally applied to shale extending upward from the top of the Eleventh Street limestone to the "base of the Seminole Formation" in the Tulsa area by Dott (1941). It is revised herein to extend farther upward to include the Dawson coal bed and its seat earth and their lateral equivalents, which underlie the Lost Branch Formation along the entire outcrop belt. The type section is that originally selected by Dott (1941), with the higher beds added from nearby (outcrop 26 in fig. 8). This upward extension of the Memorial Shale is a reasonable consequence of the more recent discoveries (explained previously) that the Dawson coal, the overlying marine strata (Lost Branch Formation), and the underlying sandy beds ("lower Seminole sandstone") are Desmoinesian in age, equivalent to the upper part of the type Holdenville Shale and therefore not part of the Seminole Formation. Thus the former upper contact of the Memorial Shale at the base of the "lower Seminole sandstone," which was believed to be the Desmoinesian-Missourian unconformity, loses its stratigraphic significance. This loss of significance and the general observation that most sandstones by their depositional nature are notoriously lenticular within more widespread shale-dominated horizons of terrestrial to deltaic strata render basal sandstone contacts far less desirable as formation boundaries than the widespread regressive exposure surfaces upon which marine transgression took place. Such an exposure surface now forms the revised upper boundary of the Memorial Shale at the base of the Lost Branch Formation.

The informal name Jenks sandstone has been used by Bennison (1984) for the sandstones that lie below the Dawson coal horizon and that previously were incorrectly considered the "lower Seminole sandstone." Because this zone of sandstones is sufficiently persistent through Tulsa County and southward to warrant a name, the term Jenks sandstone is herein regarded as a useful but informal subdivision of the Memorial Shale where the sandstone facies is present.

Because the Memorial Shale, as redefined, extends from the top of the Eleventh Street limestone, which is equivalent to only the Norfleet Limestone Member (the lower member of the Lenapah Limestone), up to the base of the Lost Branch Formation, the revised Memorial Shale is equivalent to the medial Perry Farm Shale Member and the upper Idenbro Limestone Member of the Lenapah Limestone and to the strata lying above the Idenbro and below the Lost Branch (figs. 4 and 8). Furthermore, because a marine horizon recognized below the Jenks sandstone at several places in the Tulsa region is the probable southern equivalent of the Idenbro Limestone Member (Bennison, 1984), the revised type Memorial Shale (outcrop 26 in fig. 8) can be subdivided into three informal members (lower, middle, and upper) with known northern equivalents.

The lower member is a 60-ft (18-m) thick sequence of silty shale with thin-bedded sandstone above the middle at the Memorial Shale type section along East Eleventh Street in Tulsa [units 7, 8, and 9 of Dott (1941, p. 1,595)]. It includes all but the top of the originally defined Memorial Shale and is equivalent to the Perry Farm Shale Member of the Lenapah Limestone.

The middle member is 0.2 ft (0.06 m) of brown crinoidal limestone at the Memorial Shale type section [unit 10 of Dott (1941)] and includes the sandy, fossiliferous limestones reported by Bennison (1984, p. 117) along 71st Street west of the Arkansas River (along center of north line of NW sec. 12, T. 18 N., R. 12 E.) and noted elsewhere in the Tulsa region [e.g., by Oakes (1952, measured sections 33, 39, and 75)]. On the basis of its stratigraphic position, this marine horizon is considered the southward equivalent of the Idenbro Limestone Member of the Lenapah Limestone, which can be traced readily in both outcrops and cores (fig. 8) from its type area in southern Kansas southward to the vicinity of Talala (outcrop 24) and Ramona (core ORC) in northern Rogers and southern Washington counties.

The upper member of the revised Memorial Shale includes the upper several feet of silty shale of the original Memorial Shale type section [unit 11 of Dott (1941)] and the entire "lower sandy zone" (="lower Seminole sandstone") and the lower part of the "middle shaly zone" of the Seminole Formation of Oakes (1952), which consists of the Dawson coal, its underclay, and the underlying sandy shale. This member includes the informal Jenks sandstone of Bennison (1984) as a local facies in the Tulsa region and southward. Northward, where the Idenbro Member is thick, the upper Memorial Shale consists of only the Dawson coal and its underclay (fig. 8). Both the section below the Lost Branch Formation stratotype near Mound Valley in Labette County, Kansas (outcrop 19 in fig. 8), and the section on Wolf Creek west of Delaware in Nowata County, Oklahoma (outcrop 22), serve as reference sections for this member. Although these beds had been referred to as the Dawson coal horizon in Missouri, the name Dawson has been preoccupied by a Cretaceous-Paleocene formation in Colorado since 1912 (Keroher, 1966, p. 1,052); therefore, although the name Dawson can be retained informally for the coal bed, it cannot be applied formally to a new member. I believe that a new formal name is unnecessary, as the informal term "upper Memorial Shale" suffices for these strata.

Southward, the Memorial Shale is defined at the top by the base of the Lost Branch Formation, which is at or just below the base of the Nuyaka Creek black shale bed or the underlying Homer School limestone bed. It is not known whether the marine sandy horizon near the top of the Memorial Shale at the Bearden section (outcrop 32) in Okfuskee County is equivalent to the Idenbro Limestone Member or is a younger marine horizon in the Jenks interval, which might be expected in this more basinal region. Southward, in Seminole County, the top of the Memorial Shale consists of green to red shale and pebbly sandstone, noted by Dott and Bennison (1981, pp. 16-17) below the Homer School limestone bed. The base of the Memorial Shale is defined as far south as the underlying Eleventh Street limestone is definitely recognized (currently, southern Tulsa County). The lower Memorial Shale is poorly known southward except for two exposures south of Okemah in Okfuskee County, where gray shale with a sparse Neognathodus-dominated conodont fauna overlies a dark-red limestone that may be equivalent to the Eleventh Street limestone at the High Spring locality of Bennison (1984). Farther southward, gray shale with a similar but more abundant fauna lies 70 ft (21 m) below the Lost Branch Formation, exposed in the ravine southeast of Bearden (see appendix, outcrop 32 for details), suggesting that it is the southward equivalent of the Eleventh Street limestone.

Northward, where the Lenapah Limestone is thick in its type area in Nowata and Labette counties along the Oklahoma-Kansas border, all members of the Memorial Shale can be delineated, but the lower and middle members are the Perry Farm Shale Member and the Idenbro Limestone Member, respectively, which are included as the upper two members of the Lenapah Limestone because the Perry Farm Shale Member is only 1 ft (0.3 m) thick and the entire Lenapah Limestone forms a more natural lithic grouping (figs. 4 and 8). In this area only the upper member would be readily classified in the Memorial Shale. Northward beyond the northern limit of definite Idenbro limestone (currently at Elk Creek, in Linn County, Kansas; outcrop 12 in fig. 8) or its probably equivalent coal at Trading Post just to the north (outcrop 11), the Memorial Shale extends as a coherent lithic unit from the top of the Norfleet Limestone Member to the base of the Lost Branch Formation throughout Missouri and parts of Iowa. It is mainly a gray to reddish blocky mudstone and gray shale with thin local sandstones in this region. If the Idenbro horizon can be identified in this sequence in Missouri, then the Perry Farm Shale Member can be delineated, although lithically it is more appropriately included in the Memorial Shale throughout the entire region from east-central Kansas to Missouri. Where the Norfleet Limestone Member is missing, the term Nowata-Memorial Shale is appropriate for strata from the top of the Altamont Limestone to the base of the Lost Branch Formation (figs. 4 and 8).

The extension of members from one formation (Memorial Shale) laterally into another (Lenapah Limestone) is consistent with the 1983 North American Stratigraphic Code, Article 24d. Deciding which formation name to use for these members at a particular locality in Kansas depends on either traditional usage or the relative prominence of limestone (Idenbro, Lenapah) or shale (Perry Farm, Memorial) and probably is best left to the user's judgment.

The name "Mound Valley formation" had been used tentatively in a redefined sense for strata now included within the Memorial Shale in Kansas, Missouri, and Iowa [e.g., by Swade (1985) and Greenberg (1986)]. Recent recorrelation of overlying lower Missourian strata has revived the original designation of Mound Valley (Adams, 1896; Haworth, 1898) as a valid name for a Missourian limestone in Labette and adjacent counties in Kansas that had been lithically miscorrelated with the Swope Limestone for many years.

Overlying strata

Hepler unit

The name Hepler was applied originally by Jewett (1940) to a sandstone and generally has been used in that way since [e.g., by Searight and Howe (1961) and Zeller (1968)]. Nevertheless, current workers [e.g., Bennison et al. (1984, p. 25)] and I have been informally using it for the entire sequence that directly overlies the Lost Branch Formation, even though sandstone may be subordinate in most sections and absent locally. Just southwest of the stratotype of the Lost Branch Formation (at location 3 in fig. 5a and outcrop 19 in fig. 8), this sequence consists of, in ascending order, units 8, 9, 10, and 11 in fig. 6. Unit 8 is a 2-ft (0.6-m) thick blocky mudstone overlying with abrupt contact the capping calcareous sandstone bed (Glenpool limestone bed) of the Lost Branch Formation. Unit 9 is 0.3 ft (0.09 m) of coal capped by a distinctive bed of silicified log casts; this unit has been referred to informally as the "Hepler" coal. Unit 10 is a dark-gray to black coaly shale [1 ft (0.3 m) thick] that contains megaspores but no conodonts. At the top is unit 11, 0.7 ft (0.2 m) of friable shaly sandstone that is in the position traditionally recognized as the Hepler sandstone in Kansas and Missouri (fig. 8).

The underclay-coal-coaly shale sequence (units 8-10) has also been found at several localities from just southwest of Parsons (west line of NW SW NW sec. 26, T. 31 S., R. 19 E.) through the Mound Valley area to the KGGF radio tower section north of Angola in Labette County, Kansas (outcrop 20, fig. 8). This sequence is found again at Wolf Creek (outcrop 22), west of Delaware in Nowata County, Oklahoma, where the coal is referred to as "Tulsa" coal. This coal was positionally correlated southward into the Tulsa region by A. P. Bennison, where it was called "Seminole" coal by Wilson (1979, 1984). The palynomorph flora recovered from this coal at several localities, from Parsons to South Duck Creek (outcrop 28) south of Tulsa, is considered of Missourian age by R. A. Peppers.

At the top of the sequence, the Hepler sandstone (unit 11) ranges locally at the KGGF tower section (outcrop 20) from 1 ft (0.3 m) thick (center west half of SE SE sec. 19, T. 33 S., R. 18 E.) to 15 ft (4.6 m) thick only 0.2 mi (0.3 km) away (southeast comer of sec. 19, T. 33 S., R. 18 E.). Although it seems to be absent at Parsons, the sandstone appears again northward at scattered localities from South Mound (outcrop 17), where it overlies a black coaly shale containing only megaspores, to Uniontown (outcrop 15), where it overlies the northernmost known exposure of "Hepler" coal. The "Tulsa sandstone" of Bennison (1984, pp. 119-120) lies below the "Tulsa" coal horizon (considered equivalent to the "Hepler" coal, unit 9); thus it would be below the Hepler but would also belong to this terrestrial unit because it lies above the Glenpool limestone bed in the type area for both the Glenpool limestone and the Tulsa sandstone (Bennison, 1984, p. 118).

The sequence of units 8-11 (fig. 6) at location 3 in fig. 5 a near the stratotype for the Lost Branch Formation near Mound Valley is sufficiently well exposed to be designated as an important reference section for the redefinition of the Hepler sandstone as a more useful stratigraphic unit, either at member or formation rank. However, there are several problems with the definition and past application of the name Hepler that need to be resolved before considering its formal application to the terrestrial sequence above the Lost Branch Formation.

The name Hepler originally was applied by Jewett (1940) to a sandstone with a supposed disconformable base and generally has been considered since then to apply only to sandstone in both Kansas (Jewett et al., 1965; Zeller, 1968) and Missouri (Searight and Howe, 1961). In fact, at the type section of the overlying South Mound shale designated by Jewett et al. (1965, p. 6) in the southern part of sec. 2, T. 33 S., R. 18 E., less than 1 mi (1.6 km) east of the Lost Branch Formation stratotype, Jewett et al. specifically excluded the coal and underclay with silicified wood (units 8 and 9 at Lost Branch) from the Hepler sandstone. They included these units instead in the type section of the South Mound shale, presumably because the overlying sandstone, currently regarded as Hepler at Lost Branch, apparently is absent. What Jewett et al. (1965) called Hepler sandstone at the South Mound type section is sandy limestone and calcareous sandstone with brachiopods, that is, unit 7 (fig. 6) at Lost Branch, which I include in the Lost Branch Formation as an upward continuation of the underlying marine shale (unit 6) with no disconformity between them. This older correlation by Jewett et al. (1965) would have the effect of eliminating the Hepler sandstone in the Mound Valley area because the sandstone (unit 11 in fig. 6) appearing above the coal at Lost Branch would be included in the South Mound shale. Consequently, I propose redefining the base of the South Mound shale as the base of the fossiliferous marine shaly limestone and shale sequence (units 12 and 13 in fig. 6). This horizon is shown at the top of the coal at the type section of the South Mound shale, but it is at the top of the overlying sandstone near the type section of the Lost Branch Formation (outcrop 19 in fig. 8). This redefinition keeps all the terrestrial deposits in the same unit, designated as the Hepler unit in figs. 4 and 8.

The original type section of the Hepler sandstone in the center of sec. 14, T. 27 S., R. 22 E., Bourbon County, along K-7, 2 mi (3.2 km) north of Hepler, is currently poorly exposed, but Jewett (1940) placed its base 16 ft (4.9 m) above the Lenapah Limestone. Two miles (3.2 km) to the northwest, in a stream cut on Prong Creek along K-39 (outcrop 16 in fig. 8), what appears from regional dip to be the same sandstone horizon lies with gradational contact upon 11 ft (3.4 m) of sandy shale containing two thin, fossiliferous shaly limestones (see appendix, outcrop 16 for detail). This sequence rests upon limestone that is now known to be the Norfleet Limestone Member, the lower member of the Lenapah Limestone, and the sandstone appears to be overlain by Idenbro limestone float [since confirmed by the Prong Creek core (KPC)]. This places the type Hepler sandstone within the Perry Farm Shale Member of the Lenapah Limestone. Furthermore, a similar sequence (appendix, outcrop 14) exposed just east of Uniontown, 9 mi (14.5 km) to the north, displays 6 ft (2 m) of sandstone called Hepler sandstone by Jewett (1945, stratigraphic section 51; see the appendix for details) 6 ft (2 m) above the Norfleet Member and just below the Idenbro Member in place and therefore unquestionably within the Perry Farm Shale Member of the Lenapah Limestone. The Nuyaka Creek black shale bed of the Lost Branch Formation is exposed less than 1 mi (1.6 km) northwest of this Lenapah"Hepler" section (outcrop 14) at Uniontown. The Prong Creek core (KPC in fig. 8) shows that the Lost Branch Formation also lies within the 50-ft (15-m) covered interval above the type Hepler equivalent at Prong Creek (outcrop 16); this means that the higher sandstone that crops out above this covered interval 0.5 mi (0.8 km) westward along K-39 (in the southeast comer of sec. 4 and the northwest comer of sec. 10, T. 27 S., R. 22 E.) lies in the position traditionally accorded the name Hepler. This upper sandstone horizon was found by Sutton (1985, who termed it Hepler-C) to be the only one of the three she identified in outcrops as having been called Hepler that was thick enough in the subsurface to be identified as a distinct sandstone horizon on well logs in eastern Kansas.

It seems that almost any sandstone exposed between the lower Lenapah and Hertha Limestones in Kansas was identified by earlier workers as Hepler sandstone and assumed to represent the same stratigraphic horizon, presumably eroding in places into underlying beds because of the supposed unconformity at its base. I currently recognize three different stratigraphic horizons of sandstone that were or might have been identified in the field as Hepler (fig. 8): (1) within the Lenapah Limestone [Hepler-A of Sutton (1985)], (2) between the Lenapah Limestone and the Lost Branch Formation [Hepler-B of Sutton (1985) but only at Uniontown (outcrop 14), where Jewett (1945) considered it higher in the Pleasanton Group], and (3) above the Lost Branch Formation [Hepler-C of Sutton (1985)]. The two lower horizons of Hepler sandstone (A and B) are of Desmoinesian age; they do not seem to be developed outside of Bourbon County and probably Linn County, Kansas (and locally northward in Missouri, for horizon B), and are not thick or widespread enough to be detected in the subsurface. Consequently, even though its original type locality would no longer be called Hepler, it seems reasonable to retain the name Hepler for the well-developed sandy horizon called Hepler-C by Sutton (1985) because this horizon is the position traditionally regarded as Hepler by the Kansas and Missouri geological surveys (fig. 8) and because it is the position of apparently all the sandstones identified as the Hepler sandstone in Missouri. However, because of problems that usually arise with formally naming just a lenticular sandstone facies, I propose that the name Hepler be applied to the entire terrestrial unit above the Lost Branch Formation at either member or formation rank with revised boundaries and redefined lithic content and carefully selected reference sections (Heckel, unpublished).

South Mound shale

Above the Hepler sandstone (as traditionally recognized) lies the South Mound shale (fig. 4), for which the type section was designated by Jewett et al. (1965) in sec. 2, T. 33 S., R. 18 E., less than 1 mi (1.6 km) northeast of Lost Branch on the south side of Mound Valley, Kansas. Both units have been grouped as the component members of the Seminole Formation in Kansas (fig. 3). Because the description of the South Mound type section by Jewett et al. (1965, p. 6) raises the problems that were elaborated earlier, I now regard the South Mound shale at the Lost Branch Formation type section (outcrop 19 in fig. 8) to comprise just units 12 and 13 in fig. 6 (Heckel, unpublished). There the South Mound shale contains a distinctly marine horizon in its lower part, consisting of a thin argillaceous limestone (unit 12) at the base with abundant invertebrates extending up into the overlying shale (unit 13), which forms the bulk of the unit. The South Mound shale is overlain by a limestone (unit 14) that appears to correlate with perhaps the upper part of the Checkerboard Limestone of Oklahoma.

In Kansas the South Mound shale is well exposed mainly in the Mound Valley region of Labette County and just east of South Mound in Neosho County, Kansas, where it is 12 ft (3.7 m) thick at a well-exposed road cut (outcrop 18 in fig. 8). This exposure was apparently misinterpreted by Jewett et al. (1965) when they chose a type section (see appendix). I propose that this exposure near South Mound (outcrop 18) be designated the principal reference section of the South Mound shale. The South Mound contains a coal at the top at Tacket Mound between Parsons and Mound Valley. The South Mound appears to grade northward, with an increasing amount of sandstone, into the top of the Hepler unit, as seen in the partly exposed section along the tributary to West Bachelor Creek 3 mi (4.8 km) north of South Mound and in the well-exposed stream bank 3.3 mi (5.4 km) east of Kimball in northeastern Neosho County (Heckel, unpublished).

In Oklahoma the South Mound shale is recognizable only in the northernmost core (OSC), 3 mi (4.8 km) south of the Kansas border, where it is a 19.1-ft (5.8-m) thick, sparsely fossiliferous shale with argillaceous limestone at the base, resting with a thin [0.2 ft (0.06 m)] intervening sandstone directly upon weathered shale of the Lost Branch Formation. Another 9 mi (14.5 km) to the south, in core OLC and in all other cores southward toward Tulsa, the entire sequence between the Checkerboard Limestone and the Tulsa coal is dominantly sandstone that has been classified as Seminole Formation (fig. 8). Whether the South Mound grades laterally into this sandstone or thins and grades laterally into the lower part of the shaly Checkerboard Limestone of the more southern cores remains an open question (fig. 4). The apparent truncation of the Hepler unit (including the "Tulsa-Hepler" coal) and of the Glenpool limestone bed in the top of the Lost Branch by the South Mound shale in the South Coffeyville core (OSC), as illustrated in fig. 8, suggests that the marine South Mound shale here fills an erosional channel cut during deposition of the Hepler unit elsewhere; but the channel was not filled until after the minor South Mound marine transgression, except for the thin [0.2 ft (0.06 m)] sandy bed at the base classified as Hepler (see appendix). Its marine character suggests that the South Mound is more related depositionally to the marine Checkerboard Limestone than to the terrestrial Seminole Formation.

The Exline limestone of Missouri and Iowa is correlated with the basal part of the lower Tacket shale sequence above the Checkerboard Limestone (fig. 4), based on Pavlicek's (1986) and my conodont data. If the limestone identified as Checkerboard in the section above the Lost Branch Formation stratotype (unit 14 in fig. 6) is at the same horizon as the type Checkerboard Limestone in the area south of Tulsa, then the Hepler unit and the South Mound unit together constitute the Seminole Formation as the term is currently used by the Oklahoma Geological Survey in the Tulsa area (revised to exclude the Lost Branch and upper Memorial strata) and could be used as currently recognized in Kansas. However, if the limestone called Checkerboard near Lost Branch (outcrop 19 in fig. 8) is largely stratigraphically higher than type Checkerboard, a possibility suggested by Pavlicek (1986) and discussed further in the commentary on the Wolf Creek section (outcrop 22) in the appendix, then the type Checkerboard Limestone may be equivalent mainly to the thin limestone at the base of the South Mound shale, and the Seminole Formation would be equivalent to the Hepler unit alone.

More work is being done on the rocks overlying the Lost Branch Formation, but further subdivision has not yet been formalized. In the meantime, the more general designation "lower Pleasanton," similar to that used in Iowa (fig. 4) for the Lost Branch-Exline interval, is available to include both the Hepler unit and the South Mound shale.

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Kansas Geological Survey, Geology
Placed on web Nov. 2, 2010; originally published 1991.
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