Contributions to Geology 24.2

Paleontology and deposition of the Phosphoria Formation

BRUCE R. WARDLAW U.S. Geological Survey, Washington, D.C. 20560
JAMES W. COLLINSON Ohio State University, Columbus, Ohio 43210

Pages
107-142

Keywords
Phosphoria, Cordilleran, carbonate, biostratigraphy, fossils, Meade Peak, conodont

Abstract
The Phosphoria Formation and related rocks were deposited in an interior sag basin developed in the Cordilleran miogeocline of western North America. Deposition can be characterized as a fringing bank complex on a carbonate ramp. Conodont-brachiopod biostratigraphy provides a sufficient relative time framework for correlation of the many units. These age correlations and the distribution of fossils, plus the biofacies of conodonts and brachiopods in particular, indicate that phosphate deposition was a cool-water, deeper ramp facies that transgressed over the carbonate bank twice, representing the Meade Peak and Retort Phosphatic Shale Members of the Phosphoria Formation. Conodont data that substantiate the above are presented, and a new genus and species, Sweetina triticum, is described.

Depositional environments and phosphatization of the Meade Peak Phosphatic Shale Tongue of the Phosphoria Formation, Leach Mountains, Nevada

STEVEN G. MARTINDALE Texaco USA, Western Exploration Division 10 Universal City Plaza Universal City, California 91608-1097

Pages
143-156

Keywords
Meade Peak, Phosphoria, Nevada, Leach Mountains, Permian, phosphatization, fossils

Abstract
The Meade Peak Phosphatic Shale Tongue of the Phosphoria Formation (Lower Permian) is well exposed in a trench in the Leach Mountains, northeastern Nevada. The 27.8 m thick Meade Peak section is composed of: calcareous, phosphatic siltstone and sandstone; phosphatic, calcareous sandstone; peloidal and oolitic, calcareous, phosphatic packstone; richly fossiliferous, phosphatic, lime mudstone and wackestone; calcareous sandstone; and calcareous, phosphatic mudstone. Phosphatic intraclasts and rip-up clasts are present throughout. Fossils are most abundant in the phosphatic, calcareous mudstone and wackestone, and include crowded and mixed, whole and fragmental gastropods, pelecypods, brachiopods, scaphopods, ostracodes, sponge spicules, ammonoids, and fecal pellets. The fauna lived in water that was nearly normal marine, probably slightly hypersaline.

The presence of abundant rip-up clasts and intraclasts, the occurrence of concentrated ooids, the presence of crowded and mixed shallow-water fauna, and the stratigraphic position between rocks interpreted as deposited in shallow subtidal to supratidal environments, suggest the Meade Peak Phosphatic Shale Tongue was deposited in intertidal to shallow subtidal environments.

Phosphatization at, and or directly beneath, the sediment-water interface is implied by rip-up clasts and intraclasts that are more phosphatic than their enclosing rocks, and by a distinctively dark lamina of fluorapatite-cemented sandstone at the very top of a bed within a unit that is otherwise calcareous sandstone.

Phosphatization directly from the water column is implied by concentric laminae in ooids composed of fluorapatite that show no indication of secondary mineral replacement.

Preliminary report on the geology and phosphate resources of the Freeman Ridge area, southeastern Idaho

R. DAVID HOVLAND and STEVEN W. MOORE Bureau of Land Management, Division of Mineral Resources, Idaho State Office, Boise, Idaho 83706

Pages
157-168

Keywords
Meade Peak, Phosphoria, Freeman Ridge, Idaho, phosphate, ore

Abstract
The Meade Peak Phosphatic Shale Member of the Permian Phosphoria Formation contains significant phosphate resources within unleased Federal lands in the Freeman Ridge area, southeastern Idaho. Within this area, the Meade Peak crops out for 7 km, strikes north, and dips easterly along the eastern limb of the Snowdrift anticline.

The Meade Peak thins southward from 61 m to 50 m as measured at three localities. The upper phosphate zone thins to the south, resulting in a loss of about 2.5 m of high- and medium-grade rock. The lower phosphate zone maintains consistent thickness; however, the relative proportions of high-, medium-, and low-grade rock vary from north to south. Most of the thinning of the Meade Peak is within the middle waste zone. In addition, the overlying Franson Tongue of the Permian Park City Formation thins and abruptly terminates to the south within the area.

Chemical analyses of samples of the Meade Peak at three localities indicate that phosphate rock in the Freeman Ridge area meets the chemical criteria required for efficient and economic ore processing. CaO/P2O5 is less than 1.5 for samples from locality CP-75. Fe2O3 + Al203 average values are less than 5 weight percent for combined high-, medium-, and low-grade rock. A maximum MgO content of 0.6 weight percent is also well within acceptable economic processing limits. Potential byproducts of phosphate production are suggested by maximum concentrations of chromium (2,874 ppm), vanadium (4,706 ppm), and uranium (212 ppm) from individual trench samples.

Continuing detailed geologic mapping and geochemical analyses will provide further refinement of the phosphate resource potential of the Freeman Ridge area.

Conodont biostratigraphy of the Permian Meade Peak Phosphatic Shale Member, Phosphoria Formation, southeastern Idaho

FRED H. BEHNKEN ARCO Exploration and Technology, Richardson, Texas 75080
BRUCE R. WARDLAW U.S. Geological Survey, Washington, D.C. 20560
LARRY N. STOUT Oklahoma Geological Survey, Norman, Oklahoma 73019

Pages
169-190

Keywords
conodont, Meade Peak, Phosphoria, Idaho, Neogondolella idahoensis, N. serrata

Abstract
Abundant conodont faunas of the Meade Peak Phosphatic Shale Member, Phosphoria Formation, and portions of the underlying and overlying units can be used to define three zones. These are the: (1) Neostreptognathodus sulcoplicatus Zone in the upper part of the Grandeur Member of the Park City Formation and lower part of the Meade Peak; (2) Neogondolella gracilis-N. serrata Zone, restricted to the Meade Peak in southeastern Idaho; and (3) Neogondolella phosphoriensis Zone in the uppermost part of the Meade Peak and lower part of the Rex Chert Member of the Phosphoria Formation.

The faunal change from Neogondolella idahoensis to N. serrata occurs in the lower part of the Meade Peak, and marks the Neostreptognathodus sulcoplicatus to N. gracilis-N. serrata zonal boundary. This faunal change is widespread, occurs in the lower part of the Road Canyon Formation in the West Texas regional standard section, and is a significant chronostratigraphic datum. The zonal transition of N. gracilis-N. serrata to N. phosphoriensis is correlated with the currently accepted Leonardian-Guadalupian boundary.

Bryozoans from the Phosphoria Formation (Permian), southeastern Idaho

ERNEST H. GILMOUR Department of Geology, Eastern Washington University, Cheney, Washington 99004
ROBERT C. WALKER Meridian Minerals Co., 411 108th Avenue NE, Suite 500, Bellevue, Washington 98004

Pages
191-210

Keywords
bryozoans, Phosphoria, Idaho, Rex Chert, Murdock Mountain, Gerster

Abstract
Bryozoans are present throughout five measured sections of a limestone tongue within the Rex Chert Member of the Phosphoria Formation in the South Sage Creek area of southeastern Idaho. Dyscritellina grandicora n. sp. and eight previously described species are present in this limestone. Seven of the species are conspecific with bryozoans described from the Soviet Union. These bryozoans commonly occur with brachiopods and crinoids, and occasionally with gastropods and pelecypods. Two species each of Dyscritella, Dyscritellina, and Pseudobatostomella are present. Species of Neoeridotrypella, Stenopora, and Morozoviella also occur. Abundant small fragments of fenestrates were found throughout the five sections but were too fragmental to be identified. Cystoporate fragments are rarely present. During compaction of the sediments, bryozoans were usually crushed between the brachiopod and pelecypod shells and their endozones were destroyed.

The bryozoans in the limestone tongue of the Rex Chert Member have faunal affinities with bryozoans from the upper limestone tongues in the Murdock Mountain Formation and the basal part of the Gerster Limestone. These bryozoans occur in the Thamnosia depressa Zone and the Kuvelousia leptosa Zone defined by Wardlaw and Collinson (1979). Based on the bryozoans of this study, and the brachiopods and conodonts zoned by Wardlaw and Collinson, the age of the limestone tongue of the Rex Chert Member is Ufimian (Wordian).

Stellahexaformis and Morozoviella, two new genera of Bryozoa from the Gerster Formation, northeastern Nevada

ERNEST H. GILMOUR Department of Geology, Eastern Washington University, Cheney, Washington 99004
EDWARD M. SNYDER Division of Science and Mathematics, Shepherd College, Shepherdstown, West Virginia 25443

Pages
211-218

Keywords
bryozoans, Gerster, Nevada, Permian, Stellahexaformis, Morozoviella, Trepostomida

Abstract
Two new genera of bryozoans and their type species, Stellahexaformis gersterensis n. gen., n. sp. and Morozoviella curriensis n. gen., n. sp., occur in the Gerster Formation (Guadalupian; Permian) of northeastern Nevada. S. gersterensis belongs to the order Trepostomida, suborder Amplexoporina and M. curriensis belongs to the order Cryptostomida, suborder Timanodictyina. S. gersterensis occurs in the upper 95 m of the Medicine Range section and M. curriensis occurs throughout the formation. The two new genera promise to be useful in future biostratigraphical studies of the Permian in the western U.S.

Permian conodont biostratigraphy of the Ishbel Group, southwestern Alberta and southeastern British Columbia

C. M. HENDERSON and A. McGUGAN Department of Geology and Ceophysics, University of Calgary, Calgary, Alberta, Canada T2N IN4

Pages
219-236

Keywords
Phosphoria, Canada, Ishbel, Permian, conodont, Telford

Abstract
The stratigraphy and geological relationships of the Canadian Phosphoria equivalent, the Ishbel Group, are discussed in light of new conodont data. The Permian Ishbel Group, in the Telford thrust plate near Fernie, southeastern British Columbia, includes in ascending order, the Johnston Canyon (phosphatic shale and siltstone), Telford (sandy carbonates), Ross Creek (phosphatic siltstones and carbonates), and Ranger Canyon (diagenetic chert complex) formations. The sequence can be subdivided into five conodont zones including: (1) Idiognathodus ellisoni (Asselian to early Sakmarian); (2) Streptognathodus elongatus (late Sakmarian); (3) Neogondolella bisselli-Sweetognathus whitei (early Artinskian); (4) Neostreptognathodus pequopensis-N. exsculptus (early Artinskian); and (5) Neostreptognathodus ruzhencevi-N. pnevi (early Artinskian). These zones are represented in the Johnston Canyon to Ross Creek formations. To date, conodonts have not been recovered from the Ranger Canyon Formation, which has been dated as late Artinskian to Wordian on the basis of other faunas. Near Banff, Alberta, the sequence is represented by the Johnston Canyon Formation and the unconformably overlying Ranger Canyon Formation. However, conodont data suggest that the Johnston Canyon at this locality is correlative with the entire Johnston Canyon to Ross Creek sequence near Fernie. North of Banff, near the Red Deer River, the Johnston Canyon Formation is conformably overlain by a thin unnamed sequence of sandy carbonate which, in turn, is overlain unconformably by the Ranger Canyon Formation. Conodont data indicate that these sandy carbonates are at least correlative with the Ross Creek Formation near Fernie. This study, which represents the first systematic documentation of Permian conodonts in the eastern Cordillera of western Canada, demonstrates the considerable value conodonts have for refining the biostratigraphy of Permian strata.

Stratigraphy, environment of deposition, and age of a phosphatic unit and adjacent rocks in the Wells Formation, southeastern Idaho, with evidence for a revised Pennsylvanian-Permian stratigraphic boundary

HANS PETER OBERLINDACHER Bureau of Land Management, Idaho State Office, Boise, Idaho 83706
EVE D. ROBERTS-TOBEY 2967 Silverland Drive, San Jose, California 95135

Pages
237-242

Keywords
Wells Formation, Idaho, Pennsylvanian, Permian, fusulinids, fossil, phosphate

Abstract
In southeastern Idaho, a 1.0- to 1.5-m thick peloidal phosphorite and phosphatic mudstone and siltstone unit is located approximately 33 m below the top of the lower member of the Wells Formation. A thinly laminated, foraminiferal, ostracodal wackestone, algal boundstone, and pelletal wackestone underlies the phosphatic unit and exhibits characteristics of a low-energy, intertidal depositional environment with restricted circulation. The interbedded peloidal phosphorite, laminated phosphatic mudstone, and sparsely bioclastic siltstone probably formed in an intertidal zone. Length-slow chalcedony, dolomitization, phosphatic intraclasts, hematite, and abraded fossil debris near the top of the phosphate horizon are interpreted as a shallow-water depositional environment with a fluctuating energy level, reworking of older sediments, periodic restricted circulation, and an increase in salinity and evaporation. The overlying dolomitic siltstones, and silty, finely crystalline dolomites containing phosphatic lithoclasts, and length-slow chalcedony probably formed in an upper intertidal to supratidal environment with restricted circulation, increased salinity, and evaporation, which either predated or postdated a period of non-deposition. The presence of Lower Permian and silicified and probably reworked Middle Pennsylvanian fusulinids suggest a depositional hiatus which began in the Desmoinesian and lasted until early Wolfcampain time. Fossil and petrographic evidence suggests that the top of the phosphate horizon represents both an unconformity and a revised Pennsylvanian-Permian boundary.

Epilogue for the Permian in the western Cordillera-a retrospective view from the Triassic

RACHEL K. PAULL and RICHARD A. PAULL Department of Geological and Geophysical Sciences, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin 53201

Pages
243-252

Keywords
Permian, Cordillera, Triasic, miogeocline, extinction, unconformity

Abstract
Permian history in the Cordilleran miogeocline ended with an erosional interval. Previous studies of this event focused on the amount of missing time, severity of faunal extinction, regional stratigraphic truncation, or type and amount of erosional evidence at the unconformity surface in local areas. It is generally accepted that a significant time gap (1 to 6 Ma) and an important extinction event for marine invertebrates occurred at the Paleozoic-Mesozoic boundary, but little physical evidence exists to document this hiatus in the western Cordillera.

An alternative way to examine the scene at the close of the Permian is to establish the rate of the earliest Triassic (Griesbachian) transgression over the Permian surface. This approach provides retrospective insights about the regional Paleozoic-Mesozoic unconformity. Conodont biostratigraphic analysis indicates that this transgression was geologically instantaneous over the 270,000 square kilometers (105,000 mi2) depositional area of the lowermost Triassic Dinwoody Formation. The calculated rate of transgression is orders of magnitude greater than those suggested for eustatic sea level changes associated with continental glaciation or related to ridge spreading. A reported increase in the absolute rate of movement of the North American plate supports a global sea level change and the resulting Early Triassic transgression. The rapidity of this flood, paucity of reworked Permian material at the base of the Triassic sequence, and nearly conformable relations of Permian and Triassic rocks throughtout the region suggest the eroded Permian surface was a featureless plain of very low relief.