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Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 258, part 4
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Leptotriticites and the Howe Limestone Member Assemblage

All the fusulinids from the two exposures of the Howe Limestone Member are medium-sized fusiform species of Leptotriticites (Plates 1 and 2), a genus originally defined as a subgenus of Triticites by Skinner and Wilde (1965) in their study of fusulinids from the Big Hatchet Mountains of southwestern New Mexico. That subgenus was later elevated to genus status by Loeblich and Tappan (1987). Skinner and Wilde (1965) distinguished Leptotriticites by its distinctly thin and poorly developed two-layered schwagerinid test wall, a small proloculus, intense septal fluting, a narrow tunnel, and often massive chomata. Within Leptotriticites, they included all 10 midcontinent species assigned to Dunbarinella by Thompson (1954). They also recognized L. victorioensis (Dunbar and Skinner, 1937), a species originally described from the Wolfcampian Hueco Group of west Texas, and they described the new species L. hatchetensis Skinner and Wilde, 1965, and L. gracilitatus Skinner and Wilde, 1965, from the early Wolfcampian (Nealian) of the Big Hatchet Mountains, New Mexico.

For many years, Leptotriticites was considered characteristic of the interval previously considered to be "early Wolfcampian" (= Admire and lower part of Council Grove Groups = "Bursumian"), but with the upward shift of the Carboniferous (Pennsylvanian)-Permian boundary, that interval is now assigned to the latest Pennsylvanian (latest Virgilian or Gzhelian). As more fusulinid data were generated, Leptotriticites is now known to range from the late Virgilian (Wabaunsee Group of Kansas) to the late Wolfcampian (Lenoxian Substage of New Mexico and California) (fig. 3). Nevertheless, in the midcontinent and adjacent Permian basin region, Leptotriticites is most common in latest Virgilian to earliest Wolfcampian strata.

Figure 3--Ranges of the fusulinid genus Leptotriticites from important stratigraphic sections in the United States midcontinent (Kansas), Southwest (Glass Mountains, west Texas, and Big Hatchet Mountains, southwestern New Mexico), and Far West (Bird Spring Platform, southeastern California). Until recently, the range of Leptotriticites was generally considered to be only from the latest Virgilian ("Bursumian") to earliest Wolfcampian (early Nealian), as shown by Thompson (1954) (i.e., Admire to middle Council Grove Groups) in the northern United States midcontinent. However, Sanderson and Verville (2000) and Sanderson et al. (2001) reported older species of Leptotriticites from the Wabaunsee Group (late Virgilian) of Kansas, and Wilde (2006) and Stevens and Stone (2007) described species of Leptotriticites ranging up into the late Wolfcampian (Lenoxian) of New Mexico and California, respectively.

Comparison of fusulinids in Carboniferous and early Permian in Kansas West Texas, New Mexico, and California.

Wahlman and King (2002) cited Leptotriticites aff. L. glenensis, L. hughesensis, and L. aff. L. gracilitatus from the latest Pennsylvanian ("Bursumian") in the Robledo Mountains of south-central New Mexico.

Wilde (2006), in an expanded study of Big Hatchet Mountains fusulinids, described several new species of Leptotriticites, as well as the midcontinent species L. americana and L. fivensis from the so-called "Newellian" part of the section. "Newellian" is an unsubstantiated local term that he used for strata that are more or less equivalent to the "Bursumian" interval of Ross and Ross (1998), the PW-1 zone of Wilde (1990), and the Admire and lower part of the Council Grove Groups of the midcontinent. In the overlying Wolfcampian part of the Big Hatchet Mountains, in association with the inflated fusulinids Pseudoschwagerina and Paraschwagerina, Wilde also recognized L. hatchetensis, L. gracilitatus, and L. victorioensis, and described the new species L. aculeatus, L. globuloparvus, L. varius, L. pseudokoschmanni, L. cylindricus, and L. minoris. Some of those species ranged high into the late Wolfcampian (Lenoxian) section, extending the range of the genus much higher than is known in the midcontinent region.

Stevens and Stone (2007) recently recognized several species of Leptotriticites from the Bird Spring Group of southeastern California. From the latest Pennsylvanian Fusulinid Zone 2, they recognized L. aff. L. americanus, L. glenensis, L. aff. L. hatchetensis, L. cf. L. hughesensis, L. cf. L. varius, L. wetherensis, and L. cf. L. koschmanni. In their early Wolfcampian (Nealian) Fusulinid Zone 3, where Pseudoschwagerina and Paraschwagerina appear, they recognized L. aff. L. gracilitatus, L. aff. L. hatchetensis, L. cf. L. hughesensis, L. cf. L. koschmanni, and described the new species L. californicus and L. panamintensis. In their late Wolfcampian (Lenoxian) Fusulinid Zone 4, they described L. californicus n. sp. and L. warmspringensis n. sp., confirming Wilde's (2006) extension of the range of the genus into the late Wolfcampian (Lenoxian) in the southwestern United States.

The midcontinent species of Leptotriticites, which were described by Thompson (1954) as Dunbarinella, are, in ascending stratigraphic order: L. eoextenta (Waldrip Shale Member of Texas, and Americus Limestone Member of Kansas), L. extenta (Waldrip Shale Member of Texas), L. fivenesis (Five Point Limestone Member), L. americana (Americus Limestone Member), L. hughesensis (Hughes Creek Shale Member), L. glenensis (Glenrock Limestone Member), L. wetherensis (Camp Creek Shale and Stockwether Limestone Members of the Pueblo Formation, Texas), and the three large species L. koschmanni (Skinner, 1931), L. tumida (Skinner, 1931), and L. obesa (Beede, 1916) from the Neva Limestone Member of the Grenola Limestone (middle part of Council Grove Group). Those last three Neva Limestone Member species are the largest and stratigraphically highest species of the genus in the midcontinent and are the only previously described midcontinent species of Leptotriticites from above the new Carboniferous (Pennsylvanian)-Permian boundary horizon.

It is noteworthy that in studies on the fusulinids of Wolfcampian stratotype and underlying Late Pennsylvanian Gaptank Formation in the Glass Mountains of west Texas (Bostwick, 1962; Ross, 1963, 1965), the only Leptotriticites reported was L. koschmanni from the lower part of the Neal Ranch Formation (early Wolfcampian, Nealian), which suggests correlation to the Neva Limestone Member in the midcontinent.

Significantly, additional midcontinent species of Leptotriticites have been described and/or illustrated (but not formally described) from the late Virgilian Wabaunsee Group, which underlies the Admire Group. Douglass (1962) described L. brownvillensis (Douglass, 1962) from the Brownville Member of the Wood Siding Formation of Kansas, which is the uppermost unit of the Wabaunsee Group, and immediately underlies the Admire Group and the previously recognized systemic boundary. More recently, Sanderson and Verville (2000) illustrated, but did not formally describe and name, three species of Leptotriticites (L. "taylori", L. "elkensis" and L. n. sp.) from four horizons in the middle and upper parts of the Wabaunsee Group (below the Brownville limestone) in southeastern Kansas. Sanderson et al. (2001) showed the stratigraphic occurrences of those Waubaunsee species on a range chart of Virgilian fusulinids in Kansas.

The Leptotriticites from the midcontinent Howe Limestone Member belong to the closely related group of medium-sized species that includes L. americana, L. hughesensis, L. glenensis, and L. wetherensis. Thompson (1954) observed that this group of species was a series of closely related Leptotriticites that became progressively larger upward through the Admire and lower part of the Council Grove Groups. L. americana (Americus Limestone Member) is the smallest species in the series and is characterized by an elongate fusiform test with a straight axis and sharp poles, and relatively small chomata and slight axial fillings. L. hughesensis (Hughes Creek Shale Member) has a slightly larger test size, larger chomata, and more axial fillings. L. glenensis (Glenrock Limestone Member) is larger and more inflated than L. hughesensis, and has more massive chomata. L. wetherensis, from correlative strata in north-central Texas, has a fusiform to slightly inflated fusiform test shape, small chomata, and essentially no axial fillings. The species L. americana is probably ancestral to L. wetherensis as both are characterized by small chomata and little to no axial fillings. L. hughesensis was probably ancestral to L. glenensis, as both of those species are characterized by larger chomata and distinct axial fillings.

The Howe Limestone Member Leptotriticites assemblage described here includes L. hughesensis, L. wetherensis, L. glenensis, and L. aff. L. gracilitatus (fig. 1, Plates 1 and 2). The species L. hughesensis and L. glenensis were previously known from the lower part of the Council Grove Group just beneath the recently designated Carboniferous (Pennsylvanian)-Permian boundary. Leptotriticites hughesensis was described from the Hughes Creek Shale Member in the Foraker Limestone, where it was associated with large Triticites, such as T. ventricosus and T. meeki, and Schwagerina longissimoidea. L. glenensis was described from the Glenrock Limestone Member, immediately beneath the new systemic boundary, where it is associated with Schwagerina campa and Triticites rockensis. L. wetherensis was described by Thompson (1954) from the Camp Creek Shale and Stockwether Limestone Members of the Pueblo Formation in north-central Texas, where it is associated with Triticites ventricosus and T. creekensis, and Schwagerina campensis. According to Darwin Boardman (March 2010, personal communication), conodonts from the Stockwether Limestone Member suggest that it is slightly younger than the Red Eagle Limestone of Kansas, and that the systemic boundary is probably within the underlying Camp Creek Shale Member. Leptotriticites gracilitatus is a species described from the earliest Wolfcampian (Nealian) of New Mexico (Skinner and Wilde, 1965; Wilde, 2006), but L. aff. gracilitatus was also tentatively recognized in latest Pennsylvanian strata ("Bursumian") in the Robledo Mountains of New Mexico (Wahlman and King, 2002).

Fusulinid Assemblages across the Midcontinent Carboniferous (Pennsylvanian)-Permian Boundary

Fusulinid faunas appear to be quite transitional across the recently designated conodont-based Carboniferous (Pennsylvanian)-Permian boundary in the North American midcontinent (fig. 2). The Howe Limestone Member samples contain species of Leptotriticites that range upward from the lower part of the Council Grove Group (L. hughesensis and L. glenensis) beneath the systemic boundary, and earliest Wolfcampian (early Nealian) species (L. wetherensis and L. aff. L. gracilitatus) described from north-central Texas and New Mexico, respectively. The extension of the species ranges of L. glenensis and L. hughesensis across the systemic boundary is not surprising considering that the Glenrock and Howe Limestone Members are the transgressive and regressive phases, respectively, of the same Red Eagle 4th order depositional sequence, and the correlation of the early Nealian species matches the Howe Limestone Member position very well.

As previously noted, the maximum flooding horizon for the Admire-Council Grove-Chase Group interval is in the basal Bennett shale, where the basal Permian conodont assemblage occurs (fig. 2). According to geochemical studies on paleosols through that stratigraphic interval, a regional paleoenvironmental change occurred during the deposition of the Roca Shale, which overlies the Howe Limestone Member. Geochemical composition data from the Roca Shale stacked paleosols indicate the onset of more arid paleoclimatic conditions (Miller et al., 1996; Sawin et al., 2006). The overlying lower Grenola 4th order depositional sequence is composed of very shallow-water, marginal-marine facies that lack fusulinids. Then, in the next higher upper Grenola 4th order depositional sequence, the first definitive Wolfcampian inflated schwagerinid Paraschwagerina kansasensis appears in the Neva Limestone Member (fig. 2). Paraschwagerina kansasensis is associated with Leptotriticites koschmanni, L. tumida, and L. obesa, the largest and the stratigraphically highest species of that genus in the midcontinent, and with Schwagerina longissimoidea, a primitive species that ranges up from the Hughes Creek Shale Member across the new systemic boundary. Therefore, whereas the Neva Limestone Member assemblage contains the first early Permian inflated schwagerinid, it also contains several taxa that show a greater affinity to earlier faunas.

The next higher Beattie Limestone 4th order depositional sequence consists of two 5th order sequences (Boardman et al., 2009). The lower Beattie 5th order sequence is composed of the Cottonwood Limestone and Florena Shale Members, and their fusulinid assemblage consists of the lowest occurrence of Schwagerina jewetti, the first more typical Wolfcampian species of that genus, S. emaciata, a species that ranges across the new systemic boundary, and the highest reported occurrence of the genus Triticites in the midcontinent (Thompson, 1954) (fig. 2). In the overlying upper Beattie 5th order depositional sequence, Schwagerina vervillei appears, which is morphologically similar to species of Schwagerina that co-occur with early species of Pseudoschwagerina in the early Nealian of the American Southwest (e.g., S. andresensis and S. pugunculus) (fig. 2).

In the midcontinent, the first Pseudoschwagerina (i.e., P. texana) does not appear until stratigraphically much higher, in the Florence Limestone Member of the Barneston Limestone (middle part of Chase Group) (fig. 2). In the American Southwest, Pseudoschwagerina texana is a large species that is preceded stratigraphically by several smaller and more primitive species (e.g., P. beedei, P. morsei). In fact, according to conodont data cited by Boardman et al. (2009, fig. 3), the Florence Limestone is the basal unit of the global Artinskian Stage, and therefore the entire Asselian-Sakmarian interval in midcontinent North America lacks Pseudoschwagerina. That delayed appearance of Pseudoschwagerina in the midcontinent is almost certainly due to the lack of suitable offshore paleoenvironmental conditions during the period of relatively low sea-level highstands represented by the upper part of the Council Grove and lower part of the Chase Groups.

It is noteworthy that the early Wolfcampian fusulinid assemblage of the middle part of the Council Grove Group in the northern midcontinent (i.e., Paraschwagerina kansasensis, Schwagerina jewetti, S.vervillei, S. emaciata, Leptotriticites koschmanni, L. tumida, and L. obesa) is apparently not present in the southern midcontinent outcrop section of north-central Texas. In Texas, there are about 100 ft (30.5 m) of strata that lack fusulinids between occurrences of L. wetherensis in the Camp Creek Shale and Stockwether Limestone Members of the Pueblo Formation, and Pseudoschwagerina texana and Schwagerina complexa in the Gouldbusk Limestone Member of the Moran Formation (Thompson, 1954, fig. 3). The thinner stratigraphic section and the lack of fusulinids in north-central Texas suggest that deposition of the earliest Wolfcampian (Nealian) was either nonmarine and abbreviated, or perhaps the Nealian marine section was removed by erosion during the so-called mid-Wolfcampian sea-level lowstand, a widespread erosional event that is strongly expressed in the adjacent Permian basin of west Texas. This question warrants further investigation.


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