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Pennsylvanian Rocks and Fusulinids

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Faunal Summary and Stratigraphic Correlation

Pennsylvanian Fusulinid Faunal Zones


Fusulinid foraminifers occur throughout most of the Pennsylvanian system in central United States and have proved to be among the best index fossils for regional and interregional correlations of Pennsylvanian rocks. Land barriers between relatively narrow seaways seem to have dominated the paleogeography of the western midcontinent and Rocky Mountains areas during Pennsylvanian time. Many fusulinid species are restricted in their geographic distribution, perhaps due largely to land barriers and to marine tracts unsuited to them. Generic groups and their biologic stages of development have been found most useful for correlation of time-stratigraphic units over wide areas. Pennsylvanian rocks in most of North America can be referred to 5 major faunal zones based on the predominance of fusulinid genera, as indicated in following paragraphs. All 5 faunal zones are not represented completely in any single stratigraphic section, and it can not be demonstrated that the boundaries of all adjacent zones coincide.

Zone of Millerella

The lowermost recognized Pennsylvanian fusulinid zone is designated as the Zone of Millerella. Species of Millerella Thompson occur throughout most of the marine Pennsylvanian section of America, but because the genus predominates in rocks of Morrowan age, almost to exclusion of other fusulinids, this part of the Pennsylvanian is conveniently defined as the Zone of Millerella. More highly developed fusulinids with which Millerella is commonly associated in post-Morrowan Pennsylvanian rocks distinguish these strata from the Zone of Millerella. Rocks referred to the Zone of Millerella are widespread in the midcontinent region; they include the Kearny formation of Kansas, the type Morrowan of Arkansas, the Wapanucka limestones and shales of Oklahoma, the lower part of the Dornick Hills formation of southern Oklahoma, the lower part of the Marble Falls limestone (type area) of central Texas, the Belden formation of Utah and Colorado, and at least the middle part of the "Amsden formation" of south-central Wyoming.

Zone of Profusulinella

The genus Profusulinella Rauser-Cernoussova has a short stratigraphic range in America. In New Mexico the most primitive species occurs in the basal part of the Green Canyon group (Derryan) and the youngest form occurs in the upper part of the Green Canyon group. In other regions of America the genus seems to be as restricted stratigraphically as in New Mexico; Therefore, lower and middle Derryan and equivalent parts of the Pennsylvanian are referred to the Zone of Profusulinella. [Note: Many American paleontologists prefer to use the term Fusiella Lee for the fusulinids here referred to Profusulinella.] This index genus occurs in the lower part of the Big Saline group of Texas and the lower part of the Atoka formation of Oklahoma. In New Mexico, Texas, and Oklahoma, Profusulinella is associated with Millerella, Pseudostaffella, and Eoschubertella.

Zone of Fusulinella

Species of Fusulinella Möller are widespread in North America, appearing first in rocks of middle Derryan age (lower Mud Springs group) and ranging into the Desmoinesian. Stratigraphic and biologic studies indicate that Fusulinella was derived from Profusulinella. Species of Millerella, "Nankinella," Pseudostaffella, and Eoschubertella are associated with Fusulinella in the upper Derryan, and Fusulina is associated with it in much of its range in the Desmoinesian. Typical forms of Fusulinella predominate in the faunas of the upper Derryan and more highly developed forms of the genus predominate in the fusulinid faunas of rocks here considered to be early Desmoinesian. The early Desmoinesian Fusulinella forms occur in the lower part of the type Desmoinesian of Iowa, upper part of the "Pottsville series" of eastern Ohio (Mercer limestones), lower part of the Elephant Butte formation of southern New Mexico, Sandia formation of northern New Mexico, Hell's Canyon formation of Utah and Colorado, and lower part of the McCoy formation of northcentral Colorado. At some of these localities, Fusulinella is associated with primitive forms of Fusulina, Many of the lowermost Desmoinesian fusulinids are so nearly intermediate in development that they are arbitrarily assigned to Fusulina or to Fusulinella. Most of them seem more closely related to the genotype of Fusulinella than to that of Fusulina, however, and accordingly they are referred by me to Fusulinella, Therefore, the upper Derryan and lowermost Desmoinesian rocks of central United States are referred to the Zone of Fusulinella.

Zone of Fusulina

Species of Fusulina Fischer-de- Waldheim are abundant throughout most of the Desmoinesian of North America. Their lower limits are shortly above the base of the Desmoinesian and they have not been found in uppermost Desmoinesian rocks. Therefore, most of the Desmoinesian is referred to the Zone of Fusulina. Few large areas in America contain Pennsylvanian rocks that are not at least partly of Desmoinesian age.

Fusulina is believed to have been derived from Fusulinella and they overlap stratigraphically. In fact, forms occur near the top of the Desmoinesian (Thompson, 1945) that seem to be intermediate in nature between Fusulinella and Fusulina. Millerella, Pseudostaffella, Eoschubertella, "Nankinella," and Wedekindellina are associated with Fusulina in the Desmoinesian. However, Wedekindellina has not been found in lowermost or uppermost Desmoinesian rocks.

Zone of Triticites

Triticites Girty occurs abundantly and widely in North America from near the base of the Missourian to above the base of the Permian Wolfcampian. Missourian and Virgilian rocks contain fusulinid faunas dominated by Triticites and are referred to as the Zone of Triticites. Faunas of Millerella, "Nankinella," Schubertella, Waeringella, and Dunbarinella make up only minor parts of the fusulinid faunas of the upper Pennsylvanian.

Belden Formation

The Belden formation is highly fossiliferous and contains abundant algae, brachiopods, corals, bryozoans, crinoid fragments, and foraminifers. Trilobites and pelecypods are less common. Fusulinid foraminifers are exceedingly abundant in many of the shales and limestones throughout most of the formation in the White River uplift and Uinta Mountains. In fact, some thin limestones are composed largely of fusulinids. All fusulinids so far discovered in the Belden formation are referable to the genus Millerella, which was originally described from the upper part of the Marble Falls limestone of Texas. Congeneric species are known to occur stratigraphically from near the base of the Morrowan series to near the top of the Pennsylvanian system. It is probable that further study will demonstrate the occurrence of Millerella in rocks older than the Morrowan.

Where species of Millerella have been found in rocks younger than Morrowan, they are closely associated with more highly developed fusulinids, such as Pseudostaffella, Eoschubertella, Profusulinella, Fusulinella, Fusulina, Wedekindellina, and Triticites. However, in the lower part of the Derryan in the southern Rocky Mountains region and in Texas, species of Millerella dominate the fusulinid faunas, and species of Pseudostaffella, Eoschubertella, and Profusulinella occur sparsely. It is evident that the mere presence of Millerella can not be considered diagnostic.

The fusulinid fauna of the Belden formation, part of which is described below, contains: Millerella advena Thompson, M. inflecta, n. sp., M. circuli, n. sp., M. d. M. pressa Thompson, M. aff. M. marblensis Thompson, and M. sp. A. Numerous undescribed forms of Millerella are also known from the Belden formation. However, the above fauna will suffice to demonstrate the general nature of the Belden fusulinids.

Millerella has not been studied sufficiently to determine the nature of biological development within the genus. It is not possible in all cases to determine the stratigraphic position from any one species of the genus. Species from the Belden formation are closely similar to forms from the Kearny formation of Kansas, the Bloyd shale of the type Morrowan of Arkansas, and the Wapanucka limestone of Oklahoma. It is believed that the Belden is closely similar in age to these rock units. The Belden probably is closely similar in age to the Morrowan limestone of extreme western Texas.

Hell's Canyon Formation

Many of the calcareous shales and limestones of the Hell's Canyon formation are highly fossiliferous and contain abundant brachiopods, algae, crinoid fragments, corals, and foraminifers. Fusulinids dominate the foraminiferal faunas and include species of Millerella, Pseudostaffella, Eoschubertella, and Fusulinella. The following species, discussed and illustrated below, include some of the fusulinids from the Hell's Canyon formation of the Uinta Mountains: Pseudostaffella cf. P. keytei var. maccoyensis Thompson, Fusulinella iowensis var. leyi, n. var., F. lounsberyi, n. sp., F. uintaensis, n. sp., and F. haywardi, n. sp.

The species of Fusulinella in the Hell's Canyon formation are highly developed forms of the genus. They have well-defined diaphanotheca, and in most of them the septa are highly fluted in the extreme polar regions. In some forms the septal fluting extends across the central part of the shell and they may be more closely related to the genotype of Fusulina than to Fusulinella. Species from the Hell's Canyon formation are closely similar to undescribed species from the basal part of the Desmoinesian of New Mexico and Oklahoma. The form from the lower part of the Hell's Canyon formation, F. iowensis var. leyi, is similar biologically to F. iowensis Thompson from the basal Desmoinesian of Iowa and F. iowensis var. stouti Thompson from the Mercer limestone of Ohio. It is therefore believed that the Hell's Canyon formation should be referred to the upper part of the Zone of Fusulinella.

The species of Fusulinella from the lower part of the Hell's Canyon formation at Juniper Mountain are believed to be younger than the fusulinids from the lower part of the Pennsylvanian (Reclamation group) exposed at Hartville, Wyo. The fusulinid from the latter locality, F. velmae, is a primitive species of Fusulinella. In fact, that form seemingly is transitional in nature between Profusulinella and Fusulinella.

Youghall Formation

The Youghall formation is highly fossiliferous and contains abundant brachiopods, corals, algae, crinoidal remains, and fusulinid foraminifers. Some strata of the formation are composed largely of fusulinid tests and others of brachiopod shells. The following fusulinid fauna is described from the Youghall formation: Wedekindellina matura, n. sp., W. henbesti (Skinner), Fusulina prima, n. sp., F. pristina, n. sp., F. rockymontana Roth and Skinner, F. curta, n. sp., F. spp., Forms A, B, C, and D. Fusulina predominates in the fusulinid fauna of this formation and it is referred to the Zone of Fusulina. However, Wedekindellina is abundant in some strata.

Wedekindellina and Fusulina occur in many limestones in the middle and upper parts of the Youghall formation at Sheep Mountain Canyon. The lower fusulinid faunas of the formation at Juniper Mountain are composed of primitive species of Fusulina. Some of the upper limestones at Juniper Mountain Canyon contain Wedekindellina and Fusulina. Wedekindellina and Fusulina occur throughout much of the type section. It is concluded that the Youghall corresponds in age to a part of the Cherokee of the type section of the Desmoinesian series in Iowa and to a part of the Cherokee of Kansas.

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Kansas Geological Survey, Geology
Placed on web Sept. 10, 2017; originally published Oct. 15, 1945.
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