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Moenkopi and Chinle Formations of Black Mesa and Adjacent Areas J New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/9 Moenkopi and Chinle Formations of Black Mesa and adjacent areas J. P Akers, M. E. Cooley, and C. A. Repenning, 1958, pp. 88-94 in: Black Mesa Basin (Northeastern Arizona), Anderson, R. Y.; Harshbarger, J. W.; [eds.], New Mexico Geological Society 9th Annual Fall Field Conference Guidebook, 205 p. This is one of many related papers that were included in the 1958 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. Free Downloads NMGS has decided to make peer-reviewed papers from our Fall Field Conference guidebooks available for free download. Non-members will have access to guidebook papers two years after publication. Members have access to all papers. This is in keeping with our mission of promoting interest, research, and cooperation regarding geology in New Mexico. However, guidebook sales represent a significant proportion of our operating budget. Therefore, only research papers are available for download. Road logs, mini-papers, maps, stratigraphic charts, and other selected content are available only in the printed guidebooks. Copyright Information Publications of the New Mexico Geological Society, printed and electronic, are protected by the copyright laws of the United States. No material from the NMGS website, or printed and electronic publications, may be reprinted or redistributed without NMGS permission. Contact us for permission to reprint portions of any of our publications. One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. 88 NEW MEXICO GEOLOGICAL SOCIETY • NINTH FIELD CONFERENCE MOENKOPI AND CHINLE FORMATIONS OF BLACK MESA AND ADJACENT AREAS by J. P. AKERS, M. E. COOLEY, and C. A. REPENNING The varicolored Chinle and Moenkopi formations are limestone near St. Johns accounts for a relief of 20 feet. exposed over large areas in northeastern Arizona, including In this area a medium- to coarse-grained basal sandstone Black Mesa basin, the Defiance uplift and Chinle Valley, of the Holbrook member of the Moenkopi rests unconform- the peripheral part of the Monument Valley upwarp, and ably on 10 to 25 feet of rubble breccia. The rubble is an along Echo Cliffs (fig. 11. The total thickness of these aggregate of limestone blocks and some sandstone which Triassic formations ranges from 1,100 feet in the Four Cor- has been deposited between the blocks and is firmly ce- ners area to more than 1,700 feet near the Little Colorado mented by calcareous materials. River. Where the Moenkopi formation is preserved in the PRE-TRIASSIC UNCONFORMITY southern part of the Defiance uplift area, the pre-Moen- In northeastern Arizona the unconformity at the base kopi unconformity is largely obscured by colluvium and of the Moenkopi formation represents a period of erosion residual material. However, several good exposures show which extended throughout late Permian and part of Early a relief of 1 or 2 feet at the unconformity near Black Creek. Triassic time. The period of erosion was shortest in the Lees In general, the erosion surface is believed to be less flat Ferry area, where the Lower and Middle (?) Triassic Moen- in the Defiance uplift area than it is farther west in the kopi formation lies on the Kaibab limestone of Leonard age. Winslow-Holbrook area, as it is formed by many small A longer period of erosion is indicated in the vicinity of channels filled by sediments of the Holbrook member. Near the Defiance uplift, as the Kaibab limestone is absent and Ganado the Moenkopi is absent, and the Shinarump mem- only the youngest part of the Moenkopi formation is pres- ber of the Chinle formation also is absent locally, so that ent. The Moenkopi formation is absent in the northern the lower red member of the Chinle overlies Permian rocks. part of the Defiance uplift, and the Upper Triassic Chinle MOENKOPI FORMATION formation rests on the DeChelly sandstone. South of the The Moenkopi formation, which includes the oldest Defiance uplift, the Moenkopi formation and Kaibab lime- Triassic strata of northeastern Arizona, is present through- stone extend into the St. Johns area, and in the Zuni Moun- out the area except on the summit of the Kaibab Plateau; tains the Moenkopi rests on the San Andres formation. In it is present also along the southwestern border of the summary, the hiatus represented by this unconformity be- Navajo Indian Reservation, on the central and northern comes progressively greater eastward across northeastern parts of the Defiance uplift, in the Carrizo Mountains, and Arizona and northwestern New Mexico. in parts of Monument Valley. It is of Early and Middle (?) The lower boundary of the Triassic is not very con- Triassic age. spicuous in northeastern Arizona. No angular discordance The Moenkopi formation ranges in thickness from has been observed in the unconformity; however, local ir- about 500 feet at Lees Ferry to an irregular wedge-edge regularities of relief, caused by small channels, occur in on the Defiance uplift and in other areas adjacent to the the Lees Ferry area. Also, the development of karst topo- San Juan basin (fig. 2). It ranges in thickness from 300 graphy in the underlying limestone near St. Johns and in to 350 feet in the Cameron-Leupp-Hopi Buttes area, from the Zuni Mountains causes a marked relief at the boundary. 0 to 200 feet on the Defiance uplift, and from 150 to 250 Channels as deep as 15 feet have been cut into the feet in the area adjacent to the Petrified Forest National underlying Kaibab limestone in the Lees Ferry area. They Monument. are filled with reworked angular chert and limestone frag- In the Little Colorado River valley the Moenkopi for- ments, ranging from a quarter of an inch to 8 inches in dia- mation has been subdivided into three members (McKee, meter, and numerous partly rounded sandstone boulders 1954): the basal Wupatki member, the medial Moqui up to 3 feet in diameter. Southward from Lees Ferry along member, and the upper Holbrook member. The Wupatki Echo Cliffs the lower boundary of the Triassic is marked by member, exposed along Echo Cliffs and southeast of the a thin zone of greenish-yellow shaly mudstone. Lenses con- Little Colorado River in the Cameron-Leupp area, comprises taining limestone pebbles and fragments of angular chert a lower slope unit of lenticular very thin- and thin-bedded up to 2 inches in diameter occur locally in shallow depres- layers of reddish-brown siltstone, sandy siltstone, and silty sions at the base of the Moenkopi formation along Echo very Fine-grained sandstone. This unit is 475 feet thick Cliffs and in most of the lower part of the valley of the near Lees Ferry and 95 feet thick in the type area near Little Colorado River. Near Winslow the pre-Moenkopi Wupatki Pueblo; it thins to the southeast, is less than 5 unconformity is nearly flat, the local relief being only 1 to feet thick in the Winslow-Holbrook area, and is not rec- 3 feet. The erosion surface parallels the bedding of the ognizable southeast of Holbrook. Ripple marks and a few Kaibab limestone, with no noticeable angularity. To the salt casts are characteristic of the silty sandstone beds. east, as the Kaibab limestone thins eastward toward the The upper unit of the Wupatki member, informally called Defiance uplift, the contact appears to be depositional. the "lower massive" sandstone by McKee (1954), is a However, in the vicinity of Holbrook, pre-Moenkopi ero- poor- to fair-sorted silty very fine- to fine-grained sand. sion may have removed a considerable part of the Kaibab It is siltier in the upper part and grades upward into the limestone, as the unconformity is cut partly on the Coco- Moqui member. The sandstone ranges from 20 to 40 feet nino sandstone. To the southeast, near St. Johns, the Kai- in thickness and is lenticularly bedded. It is commonly bab limestone is more than 250 feet thick. crossbedded with low-angle small- to medium-scale cross- Development of a karst topography on the Kaibab beds of the trough type. The base is sharp and has a relief of 1 or 2 feet, but in places small, narrow channels Publication authorized by the Director, U. S. Geological are exposed. Survey. NEW MEXICO GEOLOGICAL SOCIETY <> NINTH FIELD CONFERENCE 89 UTAH ;COLORADO member was deposited directly on Permian rocks. Monument 1Tour Corners In the type area at Holbrook the member consists of Owl Valley Carrixo Rock Mts. pale-red thin- to thick-bedded channel deposits of sand- stone and some lenticular thin-bedded siltstone. The sand- RoundeRock stone is poorly sorted, is very fine to medium grained, and contains considerable silt. The sandstone beds are lenticu- 7 lar and wedge shaped and have small- to medium-scale 0. ■Sonsela low- to medium-angle trough-type crossbedding. Lenses U — Buttes of limestone and mudstone pellet conglomerate which grade laterally into sandstone are common in the member.
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