G. E. LEWIS J. H. IRWIN R. F. WILSON AGE of the GLEN CANYON GROUP (TRIASSIC and JURASSIC) on the COLORADO PLATEAU Abstract

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G. E. LEWIS J. H. IRWIN R. F. WILSON

AGE OF THE GLEN CANYON GROUP (TRIASSIC AND JURASSIC) ON THE COLORADO PLATEAU

Abstract: The paleontologic and stratigraphic evi- rather than Early Jurassic(P) age, and that the dence for age designations of the Glen Canyon lower part of the Navajo sandstone is of Late group has been reappraised. This evidence suggests Triassic(P) rather than Jurassic(r) age. that the Kayenta formation is of Late Triassic(?)

Age designations for the formations of the only does the presence here of Protosuchus sug- Glen Canyon group of the Colorado Plateau gest an age for the Kayenta essentially the as recognized by the U. S. Geological Survey same as that of the Moenave, but its associa- were, in descending order: tion with the tritylodont also suggests a cor- Navajo sandstone—Jurassic and Jurassic(P) relation of the Kayenta and Moenave with the Kayenta formation—Early Jurassic(?) Stormberg series of South Africa. The Storm- Moenave formation—Late Triassic(P) berg series contains Tritylodon longaevus, re- Wingate sandstone—Late Triassic lated to the tritylodont found in the Kayenta, A recent appraisal of paleontologic and strati- associated with the protosuchian species Noto- graphic evidence by a group of geologists1 of champsa istedena and Erythrochampsa longipes, the U. S. Geological Survey at Denver resulted and with species of Semionotus. The Kayenta in the proposal that the Kayenta formation and tritylodont is more closely related to Tritylodon the lower part of the Navajo sandstone be as- and to Bienotherium, a tritylodont described by signed a Late Triassic (?) age. Young (1947) from the Lufeng series (Keuper) The Moenave formation, which as currently of China, than to the known Rhaetic to Early recognized consists of the Dinosaur Canyon Jurassic Oligokyphus, or to the Middle Jurassic sandstone member at the base and the Spring- Stereognathus, the last survivor of the tritylo- dale sandstone member at the top, is now donts. Watson (1942) has made a careful evalu- questionably referred to Late Triassic time. It ation of the upper Stormberg fauna and its has yielded the holostean fish Semionotus probable age; he correlated it with the Keuper (Lepidotus) walcotti, S. fanabensis, and Semio- (Late Triassic, older than the latest Triassic notus cf. S. gigas (Eastman, 1917; Hesse, 1935; Rhaetic). Haughton (1924) has made an ex- Schaeffer and Dunkle, 1950). The crocodilian haustive study of Stormberg stratigraphy and Protosuchus richardsoni (Brown, 1933; 1934;also has studied the Stormberg fauna; he too Colbert and Mook, 1951), the only member of correlated the Stormberg with the Keuper. the suborder Protosuchia known outside of There have been some, however, who believed South Africa, is present in the Dinosaur Canyon the Stormberg is of Rhaetic or of Early Jurassic member 24 miles south of Moenave, Arizona age (Broom, 1904). We believe it is fair to say (Fig. 1). Most authorities accept all these spe- that today most authorities favor a Keuper age. cies as being of Triassic age. A carnivorous dinosaur, "Megalosaurus" Protosuchus richardsoni and a new genus of wetheritti, has been described by Welles (1954) tritylodont reptile are present from 8 to 10 from beds assigned to the lower part of the feet below the top of the Kayenta formation Kayenta. Welles believed the dinosaur to be on Comb Ridge 6 miles east of the type lo- Jurassic because of the relative proportions of cality near Kayenta, Arizona (Fig. 1). Not the limb bones as compared to those of other Megalosaurs. However, Swinton said (1955, p. 1F. W. Cater, Jr., L. C. Craig, J. H. Irvvin, G. E. 134): "... the main elements of the skull, the Lewis, S. W. Lohman, E. D. McKce, F. G. Poole, J. D. scapula, and the pelvic bones are not those of Strobell, Jr., R. F. Wilson, and J. C. Wright typical Megalosaurs ... it is not Megalosaurus."

Geological Society of Hfflerica Bulletin, v. 72, p. 1437-1440, 1 fig., September 1961 1437

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RYCE CANYON / NATIONAL PARK >

IOB° Figure 1. Index map of Colorado Plateau

It would therefore seem that the comparisons which is long ranging and not diagnostic of age of the limb proportions of this dinosaur to the (Baker, 1933), and two species of fresh-water limb proportions of typical Megalosaurs are not gastropods, Valvata gregorii and Lymnaea hopii, applicable for age determinations. Whatever which Yen (1951) assigned to the Late Triassic. the genus may be, it should be closely com- Therefore the evidence, although not conclu- pared to the carnivorous dinosaurs found in the sive, strongly suggests that the Kayenta forma- Lufeng with Bienotherium. tion is of Late Triassic age. Invertebrate remains also have been reported Finally, the age and relations of the over- from the Kayenta formation. They consist of a lying Navajo sandstone should be re-evaluated species of fresh-water pelecypod, Unto sp., in the light of recent field work, and the fauna

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should be reconsidered. Harshbarger, Repen- Wilson, in the Kanab area (Fig. 1), also have ning, and Irwin (1957, p. 28) reported collec- demonstrated that the lower part of the Navajo tions identified by J. B. Reeside, Jr., R. W. sandstone intertongues with the Kayenta for- Brown, R. E. Peck, and I. G. Sohn. These col- mation (Averitt, et al., 1955, p. 2520-2523). lections, from near Shonto, Arizona (Fig. 1), The intertonguing between the Kayenta and include nondiagnostic bivalved Crustacea re- Navajo occurs through an interval of as much ferred to Lioestheria aff. L. ovata (Lea)—for- as 700 feet and extends laterally for at least 100 merly referred to Cyzicus—and to a genus sim- miles. Accordingly the lower part of the ilar to Candona, fragmentary fern leaves and Navajo, which intertongues with the Kayenta, wood, and the very long-ranging plant Equi- should be considered to have the same age as setum. These invertebrates and plant remains the Kayenta. are of no help in age determination, but Ree- Intertonguing between the upper part of the side commented that "the association is much Navajo sandstone and the fossiliferous Carmel like that in the Newark Triassic." The only formation of Middle and Late Jurassic age in other known fossils from the Navajo are two southwestern Utah has been demonstrated genera of carnivorous dinosaurs also from near through recent field work by D. A. Phoenix Shonto: Segisaurus, from the middle part of and J. C. Wright of the U. S. Geological Sur- the Navajo "500 feet above its base," was de- vey. A prominent tongue of the Navajo about scribed by Camp (1936, p. 39, 52) who stated 200 feet thick near Lees Ferry, where it sep- that "it could be placed in either the Triassic arated from the main body of the formation, or the Jurassic." The other was referred by has been mapped by D. A. Phoenix (1961, Brady (1935, p. 210, 215; 1936, p. 150) to written communication) and traced north- Ammosaurus sp., a genus characteristic of the westward about 70 miles along the outcrop to Newark group of Late Triassic age of the Con- the base of the Pink Cliffs near Bryce Canyon necticut Valley; it was collected from "80 to National Park (Fig. 1). 100 feet below the top of the formation" and A still lower part of the Navajo sandstone, only about 0.1 mile from the nearest outcrop named the Temple Cap member by Gregory of the overlying Carmel. In short, the scanty (1950, p. 89), also extends as a tongue into the evidence suggests a Late Triassic age for much Carmel formation. It is about 150 feet thick of the Navajo. where it separates from the rest of the forma- The stratigraphic relations support the pale- tion north of Kanab and it can be traced nearly ontologic evidence. We believe that the Spring- 30 miles to the western part of Zion National dale sandstone member of the Moenave forma- Park (J. C. Wright and F. G. Poole, written tion correlates, at least in part, with the type communication, July 27, 1960). The part of section of the Kayenta formation near Kayenta, the Navajo sandstone that intertongues with Arizona. This correlation seems valid because the Carmel formation, therefore, can be con- the Springdale and type Kayenta are litho- sidered of definite Jurassic age. logically identical, occupy the same strati- The stratigraphic evidence indicates the graphic interval, and appear to have the same following: the Moenave and Kayenta are source and transport direction. Harshbarger, partial rock equivalents, the Kayenta and the Repenning, and Irwin (1957, Pi. 2) showed lower part of the Navajo are partial rock that the Springdale sandstone member grades equivalents, and the upper part of the Navajo into and is indistinguishable from the Kayenta and the lower part of the Carmel are partial formation about 10 miles west of Kayenta. rock equivalents. Equivalent, intertonguing There is a similar gradation in the Lees Ferry parts of any two of these formations must have and Paria areas (Fig. 1). These stratigraphic a similar age, at least in the area of inter- relations indicate that the Moenave and tonguing. Kayenta formations are partial stratigraphic In light of the paleontologic and strati- equivalents. graphic evidence presented here, the Geologic Large-scale intertonguing between the Kay- Names Committee of the U. S. Geological Sur- enta formation and the overlying Navajo sand- vey has approved the following age assignments stone is present in northern Arizona and south- for the formations of the Glen Canyon group, western Utah (Harshbarger, Repenning, and in descending order: Irwin, 1957, p. 18). Averitt, in the Cedar City Navajo sandstone—Late Triassic(P) and area 20 miles north of Zion National Park, and Jurassic

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Kayenta formation—Late Triassic(P) the lower part of the Navajo sandstone to the Moenave formation—Late Triassic(P) Triassic without query, except that: (1) the Wingate sandstone—Late Triassic formations are unfossiliferous in most areas; We would have suggested reassignment of (2) there are still some differences of opinion the Kayenta and Moenave formations and also regarding the age of some of the fossils.

References Cited Avcritt, Paul, Detterman, J. S., Harshbarger, J. W., Repenning, C. A., and Wilson, R. F., 1955, Re- visions in correlation and nomenclature of Triassic and Jurassic formations in southwestern Utah and northern Arizona: Am. Assoc. Petroleum Geologists Bull., v. 39, p. 2515-2524 Baker, A. A., 1933, Geology and oil possibilities of the Moab district, Grand and San Juan counties, Utah: U. S. Geol. Survey Bull. 841, 95 p. Brady, L. F., 1935, Preliminary note on the occurrence of a primitive theropod in the Navajo: Am. Jour. Sci., 5th ser., v. 30, p. 210-215 1936, A note concerning the fragmentary remains of a small theropod recovered from Navajo sandstone in northern Arizona: Am. Jour. Sci., 5th ser., v. 31, p. 150 Broom, Robert, 1904, On a new crocodilian genus (Notochampsa) from the upper Stormberg beds of South Africa: Geol. Mag., v. 1, p. 582-584 Brown, Barnum, 1933, An ancestral crocodile: Am. Mus. Novitates 638, 4 p. 1934, A change of name: Science, n.s., v. 79, p. 80 Camp, C. L., 1936, A new type of small bipedal dinosaur from the Navajo sandstone of Arizona: Univ. Calif. Dept. Geol. Sci. Bull., v. 24, no. 2, p. 39-55 Colbert, E. H., and Mook, C. C., 1951, The ancestral crocodilian Protosuchus: Am. Mus. Nat. History Bull., v. 97, art. 3, p. 149-182 Eastman, C. R., 1917, Fossil fishes in the collection of the United States National Museum: U. S. Natl. Mus. Proc., v. 52, p. 235-304 Gregory, H. E., 1950, Geology and geography of the Zion Park region, Utah and Arizona: U. S. Geol. Survey Prof. Paper 220, 200 p. Harshbarger, J. W., Repenning, C. A., and Irwin, J. H., 1957, Stratigraphy of the uppermost Triassic and the Jurassic rocks of the Navajo Country: U. S. Geol. Survey Prof. Paper 291, 74 p. Haughton, S. H., 1924, The fauna and stratigraphy of the Stormberg series: South African Mus. Annals, v. 12, p. 323-497 Hesse, C. J., 1935, Semionotus cf. gigas, from the Triassic of Zion Park, Utah: Am. Jour. Sci., 5th ser., v. 29, p. 526-531 Schaeffer, Bobb, and Dunkle, D. H., 1950, A semionotid fish from the Chinle formation, with considera- tion of its relations: Am. Mus. Novitates, no. 1457, 29 p. Swinton, W. E., 1955, Megalosaurus, the Oxford dinosaur: Adv. Sci., v. 12, p. 130-134 Watson, D. M. S., 1942, On Permian and Triassic tetrapods: Geol. Mag., v. 79, p. 81-116 Welles, S. P., 1954, New Jurassic dinosaur from the Kayenta formation: Geol. Soc. America Bull., v. 65, p. 591-598 Yen T.-C., 1951, Some fresh-water gastropods from northern Arizona: Am. Jour. Sci., v. 249, p. 671-675 Young, C. C., 1947, Mammal-like reptiles from Lufeng, Yunnan, China: Zool. Soc. London Proc., v. 117, p. 537-597

U. S. GEOLOGICAL SURVEY, DENVER, COLO. MANUSCRIPT RECEIVED BY THE SECRETARY OF THE SOCIETY, MARCH 20, 1961 PUBLICATION AUTHORIZED BY THE DIRECTOR, U. S. GEOLOGICAL SURVEY

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