Bird Spring Group Research Articles

Early Permian corals from the Providence Mountains, San Bernardino County, California

Rugose and tabulate corals from the Lower Permian (Wolfcampian) part of the Bird Spring Group in the Providence Mountains, San Bernardino County, southeastern California, comprise eight species in eight genera.Heritschioides mckassonin. sp. is the lowest stratigraphic record for this index genus on the undoubted shelf of western North America.Paraheritschioides applegatein. sp. is the first record for the genus in southern California.Neomultithecopora providensisn. sp. is a second species for the genus in the southern Great Basin. The other five species provide close ties to previously described faunas from the Spring Mountains and the Arrow Canyon Range of southwestern and southeastern Nevada. The combined Wolfcampian coral faunas of these three areas are somewhat closer at the genus and species level to the McCloud Limestone Wolfcampian faunas of northern California than to the Wolfcampian shelf faunas in east-central Nevada. Additional species present in the combined faunas are known originally from the Wolfcampian of central Nevada and Kansas and a genus is not otherwise known south of British Columbia. The faunas suggest a subprovince of the Durhaminid Coral Province for the southern California and southern Nevada area and perhaps imply partial isolation from the more northerly parts of the province by land barriers such as the Antler Highlands.

Early Permian corals from Arrow Canyon, Clark County, Nevada

Rugose and tabulate corals from the Lower Permian (Wolfcampian) part of the Bird Spring Group in Arrow Canyon, Arrow Canyon Range, Clark County, Nevada, comprise eight species in eight genera.Stylastraea rowettin. sp. is the first unequivocal record of this genus west of Texas in North America.Heritschiella girtyi, the only endemic North American waagenophyllid genus and species, is recorded outside Kansas for the first time.Paraheritschioides stevensiformerly was known only from northern California. The other species also occur elsewhere in the Permian of Nevada and nearby. This southeast Nevada shelf area has the first known intermixture of corals from the Durhaminid Coral Province and subprovinces of far western North America and the Cyathaxonid Coral Province of middle and southwestern North America.

Permian corals from the Spring Mountains, Nevada

Rugose and tabulate corals from the Lower Permian (Wolfcampian, Leonardian) Bird Spring Group in the Lee Canyon section of the Spring Mountains, Clark County, Nevada, are referred to eight genera and ten species. New taxa are Fomichevella nevadensis n. sp., F. waltersi n. sp., Mccloudius parvus n. sp., and Paraheritschioides richi n. sp. The fauna is most similar to the shelf fauna in eastern Nevada, but there are significant similarities to corals from the Antler Highland embayments of central Nevada and southern Idaho and to faunas of the same age in northern California and northern British Columbia. The paleogeography is interpreted as shallow water near the east side of the mouth of a south-opening coastal sea, bordered on the east by the continent and on the west by the Antler Highland. Corals migrated south along the western shores of the Antler Highland and mixed with the shelf fauna, perhaps with some corals crossing from Tethys to the coast. The modern eastern Pacific tropical coral faunas, which have several hermatypic coral genera and species derived from the western Pacific in the Pleistocene, may occupy a somewhat similar geography near the mouth of the modern Gulf of California.

The genus Glyptospira (Gastropoda: Trochacea) from the Permian of the southwestern United States

Glyptospira is a small, highly ornamented, turriteliform gastropod found in the Lower Permian of the southwestern United States. Two species, Glyptospira cristulata Chronic and G. arelela Plas, have been previously described from the Kaibab Formation, Arizona, and the Bird Spring Group, Arrow Canyon Range, Nevada, respectively. The genus is most diverse in the Wolfcampian Hueco Formation of West Texas and southern New Mexico and the Colina Limestone of southeastern Arizona. This contribution describes four new species of Glyptospira from the southwestern United States: two bicarinate forms, G. huecoensis and G. turrita, and two tricarinate forms, G. tricostata and G. cingulata.A phylogenetic analysis of all known species of Glyptospira was performed using qualitative characters for which transformation series could be established and two quantitative characters for which transformation series could not be established. The phylogenetic results provided the best available hypothesis of the evolutionary history of the genus.

Wolfcampian brachiopods from the Bird Spring Group, Wamp Spring area, Las Vegas Range, Clark County, Nevada

The Wamp Spring section of the Bird Spring Group consists of approximately 1,600 feet of carbonate rocks subdivided into a basal platy limestone member, lower cliff-forming member, and upper cliff-forming member.Triticites, Schwagerina, andSchubertella kingiin the platy limestone member indicate an early Wolfcampian age.Schwagerina, Schubertella kingi, and a distinctive assemblage of brachiopods, similar to the West Texas fauna, includingKozlowskia kingi, Elliottellaaff.E. multicostata, Leurosina sinesulca, Gypospirifercf.G. infraplicus, andCompositacf.C. apheles, indicate that the upper cliff-forming member is late Wolfcampian. The lower cliff-forming member is tentatively assigned to the middle Wolfcampian. The Wamp Spring sequence correlates temporally with the BSe “formation” of the Bird Spring Group.In addition to the previously mentioned taxa, the fossil-rich upper cliff-forming limestone member includes the new speciesPontisia boodi, Crurithyris wampensis, andCalliprotonia(?) n. sp. A, as well asHustedia culcitula, Crenispirifer(?) sp.,Cenorhynchia(?) sp.,Kutorginella(?) sp., marginiferids, lyssacine hexactinellid sponges, pleurotomarid and bellerophontid gastropods, cidaroid echinoids, rugose corals, cylindrical cryptostome bryozoans, and nuculids.

Biostratigraphy and Paleoecology of Desmoinesian (Pennsylvanian) Brachiopods, Bird Spring Group, Arrow Canyon, Clark County, Nevada: ABSTRACT

The Bird Spring group is abundantly fossiliferous, appears free from hiatus, and is being considered for several Pennsylvanian stratotypes. Thus, its brachiopods are of widespread interest. Twenty-nine species and 18 genera occur in the Desmoinesian at Arrow Canyon. Twenty-one species are shared with both the Rocky Mountain and Midwest areas, and seven occur in Ohio. Orthotichia morganiana (Derby), previously recorded in the Itaituba Series, reinforces an association with faunas of the Amazon basin, as also indicated by an Atokan Brasilioproductus at Arrow Canyon. Microfacies 0 through 5 define 13 complete cycles from relatively deep to shallow-water deposition in the Bird Spring Desmoinesian. Only Orbiculoidea sp., Buxtonia sp., and Composita ovata, all adapted to soft substrates, occur in microfacies 0. Twelve species from microfacies 1, calcisiltite with as much as 30% calcarenite, lived in somewhat shallower water. There, productids dominate and are accompanied by Composita spp. and two alate spiriferids. Microfacies 2, calcisiltite with 30-50% calcarenite in a microcrystalline matrix from just below wave base, contains 24 brachiopod species. Spiriferids dominate productids, and the genera Rhipidomella, Orthotichia, Derbyia, Mesolobus, and Hustedia are restricted to this microfacies. Microfacies 3, grain-supported calcarenite in calcisiltite from just above wave base, yielded only Composita ovata,more » Neospirifer dunbari, and Punctospirifer kentuckensis. However, brachniopod bioclasts reportedly peak in microfacies 3. Microfacies 4 and 5, from shallower environments, lack brachiopods.« less

Biostratigraphy and Paleoenvironment of Morrowan (Zone 2) Brachiopoda, Bird Spring Group, Arrow Canyon, Clark County, Nevada: ABSTRACT

Comprehensive study of the Morrowan brachiopod faunas of the Bird Spring Group at Arrow Canyon, Clark County, Nevada, is important because the section has been suggested as a stratotype for the base and top of the Pennsylvanian Subsystem and for the Atoka Series. Twenty-three species of brachiopods belonging to 17 genera occur in zone 20 at Arrow Canyon. Many of these also occur in described Morrowan faunas in Wyoming, Colorado, Utah, and New Mexico; but similarities with the Mid-Continent and Appalachian assemblages are less. However, no striking regional differences are evident, and it appears that the North American Morrowan fauna is more or less homogeneous. In contrast to the exotic South American and Arctic elements known from Atokan, Missourian, and Virgilian rocks at Arrow Canyon, no foreign taxa have been noted in zone 20. Microfacies and faunal associations indicate four distinct brachiopod-bearing environments: (1) relatively deep water below turbulence with few brachiopods on a soft substrate; (2) somewhat shallower, more turbulent water with many species, of which only a few are represented by large populations, living on a more firm substrate; (3) environments just below the zone of turbulence in which many species of brachiopods are represented by substantial populations on a calcarenitic substrate; and (4) crinoidal bars in the zone of turbulence with a few species represented by relatively few individuals. End_of_Article - Last_Page 313------------

Late Atokan Brachiopod Biostratigraphy, Bird Spring Group, Arrow Canyon, Clark County, Nevada: ABSTRACT

Pennsylvanian rocks at Arrow Canyon have been proposed as a stratotype for the base and top of the Pennsylvanian System and for the Series. Fusulinaceans and conodonts document an essentially continuous biostratigraphic succession, and detailed petrographic descriptions have been published. Systematic descriptions and local ranges for the extensive and biostratigraphically significant brachiopod fauna are, as yet, unpublished. This report on brachiopods from the Zone of Fusulinella is part of an ongoing investigation of the Arrow Canyon invertebrate fauna being conducted at the University of Illinois. Materials under study include about 1,000 weathered-free specimens, and silicified material etched from about 500 pounds of matrix. Twenty-eight taxa have been iden ified, most notably a new species of Brasilioproductus Mendes, a genus previously known only from the Amazon basin. Ranges of Spiriferellina ceres, Antiquatonia hermosana, Neochonetes dominus, Cleiothyridina milleri, and Rhipidomella elyensis are here extended into the late Atokan. Composita trinuclea, characteristically Mississippian, also occurs. Biostratigraphic correlation with both the southern Rocky Mountain region and Ohio is strong. Midcontinental correlations are less firm, probably because Atokan rocks in that area are poorly fossiliferous. End_of_Article - Last_Page 489------------

Missourian and Virgilian Brachiopod Biostratigraphy, Bird Spring Group at Arrow Canyon, Clark County, Nevada: ABSTRACT

The Arrow Canyon section of the Bird Spring Group has been proposed as a stratotype section for the base of the Pennsylvanian and of the Permian because of its apparently uninterrupted deposition across those boundaries, extensive invertebrate fauna, nearly total exposure, and readiness of access. Both fusulinid zonation and detailed petrographic studies have already been End_Page 594------------------------------ completed. The Missourian and Virgilian sequence includes about 132 m of carbonate rocks divided into 46 units for collection and description. Eighteen of these units yielded a silicified brachiopod assemblage totaling 21 strophomenids and 17 taxa of other orders. Fossil abundance is greatest in the lower part of the Missourian and from the topmost Missourian through the middle Virgilian. Correlation with the middle Virgilian of North Texas and, perhaps, the lower Missourian of the southwest is especially strong. Notable range extensions include: (1) Paeckelmanella? n. sp., an otherwise Arctic Permian taxon, in the Virgilian; (2) Mesolobus euampygus in the Early Missourian, an extension of generic range from the Desmoinesian; (3) Paucispinifer n. sp., a Permian genus occurring in the issourian; and (4) Neospirifer latus lateralis, a Missourian species occurring in the Virgilian. In addition, Calliprotonia n. sp. is reported the second occurrence of this genus in the North American Virgilian. End_of_Article - Last_Page 595------------

Distribution of Stigmaria wedingtonensis (Lycopsida) in the Chesterian (Upper Mississippian) of North America

Stigmaria wedingtonensis occurs in Nevada, Arkansas, Illinois, Kentucky and Indiana. It is found throughout the Chesterian Series (Upper Mississippian) and has a longer stratigraphic range than that of S. stellata, a similar European form. In the Indian Springs Formation of the Bird Spring Group in Arrow Canyon, Clark Co., Nevada, Stigmaria was found in situ extending down into the underlying marine limestone of the Battleship Wash Formation. It represents a

Upper Wolfcampian (?) mollusca from the Arrow Canyon Range, Clark County, Nevada

An abundant and diverse silicified fauna comprised mostly of gastropods, but including pelecypods, scaphopods, chitons, small orthoconic nautiloids, sponges, ostracodes, a trilobite species, and foraminifers, occurs in association with the alga Mizzia in a structurally isolated portion of the upper Bird Spring Group (BSe Unit). At least three gastropod species, Amaurotoma zappa, Glyptospira arelela, and Anomphalus jaggerius, are new. The assemblage resembles, in some respects, that described by Chronic (1952) from the Kaibab Formation (Leonardian-Guadalupian) of Arizona as well as undescribed assemblages from the Loray Formation (upper Leonardian) of eastern Nevada and the Bird Spring Group (middle Wolfcampian ?) of the Providence Mountains in southwestern Nevada. The fauna is tentatively assigned an uppermost Wolfcampian age on the basis of Schwagerina cf. S. crassitectoria Dunbar & Skinner, which occurs several hundred feet above the mollusk-bearing bed, as well as on the occurrence of Mizzia cf. M. yabei (Karpinski), previously reported from Middle to Late Permian rocks. Color markings are preserved on some of the gastropods, a chiton and a nautiloid.

Facies and bed thickness distributions of limestones

Bed thicknesses in terrigenous clastics have long been observed to follow a lognormal distribution but data on carbonate rocks are rare. Studies of facies intervals, determined by detailed thin-section analysis, and bed thicknesses, described in field notes, for the Bird Spring Group and Callville Formation (Pennsylvanian and Permian) of southern Nevada have revealed that limestones also follow a lognormal trend. This is true for the separately investigated limestone facies (F 1 : micrite; F 2 : sparsely fossiliferous micrite; F 3 : packed biomicrite or pelmicrite; F 4 : biopelsparite) and for the data resulting when all these facies are combined. The universality of a lognormal distribution for populations of facies and bed thicknesses in limestones precludes the use of Markov chain analysis in which lithologic identifications are made at equal intervals along a vertical section.

Markov Chain Analysis of Carbonate Rocks: Applications, Limitations, and Implications as Exemplified by the Pennsylvanian System in Southern Nevada

Markov chain analysis may be used as a technique for evaluating the presence of determinism (“memory”) in a sequence of physical events. Application to the vertical facies changes found in the Pennsylvanian carbonate sequences of southern Nevada shows that (1) the interval examined in the Arrow Canyon Range (1846 ft, miogeosynclinal, Bird Spring Group) has a chi-square value of 167.41, indicating “memory” present; (2) the Callville Formation at Frenchman Mountain (1055 ft, shelf) yields a chi-square of 26.40, also indicating the presence of “memory”; and (3) the Callville at Azure Ridge (779 ft, shelf) yields a chi-square of 15.02, indicating no “memory.” All of these values were obtained with recognition of four facies with multistory relationships. Investigation of potential sources of error shows that consistency from studied section to studied section in choice of number of facies, evaluation of facies changes, and whether multistory or unit facies are recognized is essential if results are to be compared. The presence of covered intervals, while detrimental, does not obscure results where less than 20 percent of the total number of facies units are labeled covered.

Middle Pennsylvanian Rocks of Eastern Great Basin

The Atokan and Desmoinesian Series in the eastern Great Basin consist mostly of nine major carbonate rock types ranging from carbonate mudstone through micritic allochemical limestone to grainstone. On the east, in the region of the Oquirrh Formation, orthoquartzites are important, and in some local sections they constitute nearly half the sedimentary sequence. Stratigraphic and petrographic data were combined to define lithofacies which were linked in a paleogeographic pattern and model of sedimentation. Areas demarked by the main lithofacies correspond closely to distribution of lithostratigraphic units recognized in the region: (1) the upper Ely Group, particularly the Hogan Formation, comprises a basin assemblage deposited mostly in relatively deep water; (2) the Bird Spring Group and Callville Limestone represent a transition between a shallow shelf on the east and southeast, and the basin in east-central Nevada and west-central Utah; (3) the Oquirrh Formation is a transitional slope assemblage between the basin and Weber shelf on the east. During the Atokan, the basin was not large, and the central Great Basin region was dominated by shifting conditions resulting from sea level changes superimposed on differentially subsiding areas. Conditions were more regular in the basin during the Desmoinesian Epoch, when the basinal environment expanded southward and eastward. However, in the area of the Oquirrh Formation, periodic subsidence coupled with rapid sea level fluctuations resulted in alternation of orthoquartzite and quiet water calcareous sedimen s. Orthoquartzites in the Oquirrh Formation are polygenetic, but most are considered to have been built westward by shore progradation following pulses of subsidence. Transport down a paleoslope by density currents following subsidence probably was another important means of deposition. Maximum thickening of Middle Pennsylvanian rocks was not in the basin, but in the region encompassed by the Oquirrh Formation as a result of greater subsidence. Determination of the original thickness of the Desmoinesian Series in the central Great Basin is made difficult by probable erosion of all or part of the Desmoinesian record at several key localities. Coupled with this is the difficulty in evaluating amounts of compaction in the predominantly fine-grained sediments of the basin. The Middle Pennsylvanian part of the Bird Spring Group does not show significant thickening. Previous attempts to correlate areas of maximum thickening with environmental centers of deposition have resulted in difficulties in environmental interpretation. Post-Paleozoic structural deformation was not evaluated in this study, although the effects probably were great.

Pennsylvanian-Permian Miogeosyncline to Nearshore Shelf Carbonate Facies Transition, Clark County, Nevada: ABSTRACT

Pennsylvanian and Lower Permian carbonates of Clark County, Nevada, were studied at Arrow Canyon (AC), Frenchman Mountain (FM), and Azure Ridge (AR). Distinct facies changes are observed from the AC section (2,193 ft, Bird Spring Group, restricted, miogeosynclinal) where limestones are 65.5% micrite to FM section (1,055 ft, Callville Formation, outer shelf) where limestones are 57.2% pelsparites, biosparites, or oosparites to AR (779 ft, Callville Formation, inner shelf) where limestones are 50.9% pelsparites, biosparites, and oosparites. The marked change in facies provides evidence for support of a dual terminology, Bird Spring Group for the basin facies and Callville Limestone for the shelf. The Bird Spring-Callville interval is subdivisible into a lower eastward thinning member (1,634 ft, AC; 634 ft, FM; 322 ft, AR) characterized by abrupt vertical fluctuations in facies (AC 14.3, FM 8.0, AR 15.2 fluctuations per 100 ft) causing the steplike outcrop appearance characteristic of the interval. Gray to buff weathering and lack of quartz silt distinguish the lower member from the arenaceous buff to brown upper member. The latter contains several quartz sandstone units (zero AC, 41.7% FM, 51.1% AR) in which the size of the fine ( End_of_Article - Last_Page 350------------

Statistical Analysis of Calcisiltites from Bird Spring Group, Mountain Springs, Nevada: ABSTRACT

Seventeen petrographic variables observed in duplicate thin sections for each of 62 calcarenites and calcisiltites collected from the Monte Cristo Limestone and the Bird Spring Group are the basis for this study. The samples are assigned to 6 microfacies, of which 31 and 17 belong to microfacies 0 and 1, respectively. R-mode cluster analysis grouped the variables into 7 clusters; 5 are composed of various organic and inorganic grains and associated alteration products, 1 is composed of acid insolubles, and 1 of sparite and micrite. Interclass and intraclass variation was tested by means of the Mahalanobis D2 and associated F statistics. The null hypothesis was accepted for all diagonal elements and rejected for all nondiagonal elements. Initial clustering of ra - and transformed-data sets by means of Q-mode factor analysis--first using 17 primary variables, and then using 2 derived variables--indicated that the 2-variable case provided the best separation between microfacies 0 and 1. Null hypotheses concerning group dispersion and the equality of sample centroids were rejected for both the raw and transformed 2-variable case; consequently, an appropriate form of the T2 statistic was employed to test for a significant difference between these two microfacies. Associated F values indicate a statistically significant difference between these microfacies for both raw- and transformed-data sets. Computed discriminant functions are approximately 98 and 79% efficient for the raw and transformed cases, respectively. The upper Monte Cristo Li estone was deposited under relatively stable environmental conditions that produced massive, low-energy micrites with very few biogenic grains. After an interval of erosion, the alternate quartzose sandstones and biomicrites of the lower Bird Spring Group were deposited under relatively unstable conditions. Environmental stability increased during the deposition of the upper Bird Spring Group, which consists of an almost unbroken sequence of micrites and biomicrites. End_of_Article - Last_Page 556------------

Markov Chain Analysis of Carbonate Rocks: Applications, Limitations, and Implications as Exemplified by Pennsylvanian Carbonates in Southern Nevada: ABSTRACT

Markov chain analysis is a simple, powerful, mathematical tool for testing the presence, absence, and length of in a sequence of events. Use of this method on the Pennsylvanian carbonates of southern Nevada revealed the presence of a (X2 = 32.55 with 15 df) in the thick basinal interval of the Bird Spring Group of the Arrow Canyon Mountains and a relative lack of memory (X2 = 20.5 with 15 df) in the thinner, age-equivalent, shelf deposits of the Callville Limestone on Frenchman Mountain. Covered intervals have little effect in situations End_Page 857------------------------------ where the number of intervals is less than 20% of the total number of identified units. Best results are obtained if coincident layers of identical lithology are treated as a unit facies rather than as multistory facies. The effect of varied identification of lithologies is critical. For example, grouping clay and shale gives markedly different results from cases in which they are distinguished. It can be concluded that (1) Markov tests support current beliefs in that they indicate relative lack of memory in shelf sediments indicating many breaks in sedimentation, and (2) consistent evaluation of facies is critical, as different labels for the same lithology cause large-scale variation in numerical results. End_of_Article - Last_Page 858------------

Petrography of a Carbonate Transgressive-Regressive Sequence: The Bird Spring Group (Pennsylvanian), Arrow Canyon Range, Clark County, Nevada

A stratigraphic interval of 1846 feet belonging to the Lower and Middle Bird Spring Group and ranging from Lower Morrowan to Lower Missourian has been investigated petrographically in order to unravel the cyclic sedimentation of this miogeosynclinal limestone sequence. More than 2095 samples collected at an average interval of 10 inches were divided into eleven microfacies, given here in order of decreasing relative depth of deposition or increasing energy level: an almost pure calcisiltite (microfacies 0), a calcisiltite with scattered sand-size organic debris (microfacies 1), a calcisiltite with abundant scattered sand-size organic debris (microfacies 2), a grain-supported biocalcarenite with calcisiltite matrix (microfacies 3), a grain-supported biocalcarenite with clear calcite cement (microfacies 4), and a grain-supported oolitic biocalcarenite with clear calcite cement (microfacies 5). Microfacies designated as 0a, 1a, 2a, 3a and 4a are the detrital quartz-rich equivalents of microfacies 0 to 4 and include rocks with more than 10 percent of detrital quartz. The following microscopic parameters were measured: frequency and clasticity of crinoid fragments, oolites, pellets (fecal, lithic and algal coated) and detrital quartz; frequency of debris of brachiopods and bryozoans, ostracodes, calcispheres, arenaceous benthonic foraminifers and pyrite. These data, together with symbols representing many other minor components were plotted alongside the columnar section as variation curves showing the stratigraphic behavior of the parameters. A combination of these measurements with the above textural classification of the microfacies led to the drafting of a relative bathymetric curve (expressing in this environment also the energy level) which represents the final interpretation of the oscillations in energy level and related water depth during deposition. A total of 78 complete cycles were recognized. They are variants of 3 fundamental ideal cycles (or statistically most frequent successions of microfacies) established on the basis of the average values of all the measured parameters. Two of these ideal cycles characterize the Morrowan which consists of 46 cycles with features expressing a gradual transgression. A massive inflow of fine detrital quartz coincides with the deepest phase of the transgression. The third type of ideal cycle is typical of the Atokan-DesMoinesian-Missourian interval which consists of 32 cycles with features indicating a gradual regression. Therefore the investigated sequence is a complete major geological cycle of transgression and regression.

Petrographic Classification and Method of Description of Carbonate Rocks of the Bird Spring Group in Southern Nevada

ABSTRACT A descriptive petrographic classification of carbonate rocks from the Bird Spring Group in southern Nevada was devised by combining satisfactory facets of existing classifications. Coupled with the classification is a means for representation of data from thin sections.

Petrographic Analysis of Bird Spring Group (Carboniferous-Permian) Near Lee Canyon, Clark County, Nevada

The thick section of the Bird Spring Group near Lee Canyon, Clark County, Nevada, consists of more than 7,000 feet of predominantly carbonate strata which are subdivided as follows: Chesterian (125±feet), Morrowan (775±feet), Atokan (510±feet), Desmoinesian (520±feet), Missourian (145±feet), Virgilian (525±feet), Wolfcampian (3,075±feet), and Leonardian (1,525±feet). The upper limits of the group could not be determined because of truncation by faulting. A petrographic study was made on the Bird Spring Group near Lee Canyon, and, for descriptive purposes, a classification of carbonate rocks was modified from several existing classifications. That classification is used in this paper. Quartzose sandstone and siltstone, biocalcarenite, biocalcirudite, and biocalcarenitic limestone, with minor fine-grained limestone and calcareous shale constitute the Chesterian rocks and represent reworking in an advancing sea. The body of information now available on Great Basin late Paleozoic stratigraphy indicates major source areas on the northwest, northeast, and east. The relative contribution of each of those regions to the lower several scores of feet in the Bird Spring is not known. Morrowan beds indicate a gradual change to unstable shelf conditions which later altered to stable shelf conditions. Biocalcarenite grades upward through biocalcarenitic and skeletal calcarenitic limestone into silty fine-grained limestone and calcareous shale. Gradation is then back to skeletal calcarenitic and biocalcarenitic limestone and calcarenite. Fish remains are common in these and in the overlying Atokan and Desmoinesian strata. Open shelf conditions prevailed in Atokan and Desmoinesian time when coral and algal biolithites formed. Komia contributed abundantly to this interval and Chaetetes is present in the Atokan portion. Associated with these bioconstructed limestones in a cyclical fashion are biocalcarenite, biocalcarenitic, and skeletal calcarenitic limestone, pelletal limestone, and siltstone. Missourian, Virgilian, and lower Wolfcampian rocks record a change, inaugurated in late Desmoinesian, to unstable shelf conditions and greater influx of terrigenous matter. Impure skeletal-bearing, fine-grained, and skeletal calcarenitic limestone are most abundant in the l wer part of the interval; fossil content increases upward and the uppermost beds are crinoidal biocalcirudites. In late Wolfcampian time, rather abrupt change was to mostly deeper quieter waters. Anaerobic conditions prevailed in the early late Wolfcampian, but restriction later diminished. Convolute laminae and slump structures in mudstone and fine-grained limestone attest to periods of contemporaneous deformation. Intermittently, the waters shallowed and the sea bottom was heavily populated with gastropod-hydrozoan-crinoid-foraminifer-bryozoan-algal communities. Gradually the sedimentary framework reverted to that of an open shelf dominated by biostromal and coral development. At the time the uppermost Bird Spring was deposited, physico-chemical and biochemical precipitation were impor ant, and so oolite calcarenite and algal-pelletal limestone were deposited. The Permian climate in the region was probably arid to semi-arid. It is suggested that the Bird Spring section near Lee Canyon be elevated to group status and appropriate subdivision be made. Indian Springs Formation qualifies for the Chester-lower Morrow portion. The End_Page 1657------------------------------ remainder of the Pennsylvanian and lower Wolfcamp beds constitute another logical subdivision. The upper Wolfcamp sequence may deserve formational rank as well as the uppermost Wolfcamp-Leonard interval. Great thickness of the Bird Spring near Lee Canyon is due primarily to the Wolfcamp sequence, a situation which merits attention when distinguishing between platform and miogeosyncline.