New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/18 Permian stratigraphy of the Defiance Plateau, Arizona H. Wesley Peirce, 1967, pp. 57-62 in: Defiance, Zuni, Mt. Taylor Region (Arizona and New Mexico), Trauger, F. D.; [ed.], New Mexico Geological Society 18th Annual Fall Field Conference Guidebook, 228 p. This is one of many related papers that were included in the 1967 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. 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WESLEY PEIRCE Arizona Bureau of Mines University of Arizona INTRODUCTION (1917), is a composite unit; that is, it is compounded from smaller units that are differentiated on the basis of (1) In recent years some rather sweeping nomenclatural nature and distribution of primary sedimentary structures, changes have been proposed for certain Permian sedimen- (2) color, (3) grain size aspects, (4) composition, (5) cemen- tary rocks in parts of both New Mexico and Arizona tation characteristics, and (6) topographic expression. (Baars-1962). A response to those proposals applicable to Using these general criteria, it is possible to subdivide the Defiance Plateau was published and it was concluded the DeChelly Sandstone into five units. (Table 1). Each that Baars treatment of the Permian stratigraphy of the is not equally developed at all localities; indeed, all five Defiance Plateau is fundamentally unsound (Peirce-1964). are not developed at any single locality, with the possible I welcome this opportunity to review and update the sub- exception of Bonito Canyon. Only after the DeChelly ject and to present proposals developed by combining Sandstone is subdivided into its integral parts is it pos- unpublished data with the contributions published by sible to constructively speculate not only as to its relation- previous workers. ships to Permian stratigraphy away from the Defiance Plateau, but as to its local internal relationships as well. GENERAL STATEMENT The names or handles applied herein are neither sacred As has been emphasized often, the Defiance Plateau is nor important except as they might aid in depicting re- an island of Permian strata in a sea of Mesozoic sedimen- lationships and point a finger at phenomena that deserve tary rocks. Not only is the Defiance region isolated from the consideration of those interested in this general other regions of Permian exposures (Mogollon Rim 100 problem. miles to the southwest and the Zuni Mountains 30 miles The relationships between the five described units are to the southeast), but the exposures on the Defiance shown in Figure 1. At the outset, two principal observa- Plateau, limited as they are to deep canyons, also suffer tions should be made: (1) the interval between the Per- from lateral discontinuity. mian Supai or Supai-Yeso "red beds" and the Triassic On the Defiance Plateau, approximately 1200 feet of Shinarump or Moenkopi strata thins from approximately outcropping Permian strata overlie Precambrian meta- 800 feet at the type area of Canyon DeChelly to less than morphic, igneous, and sedimentary rocks (Lance-1958). 200 feet in the subsurface at the south end of the Defiance The lower portion consists of "red beds" that have been Plateau, most of the thinning having taken place on the variously equated with the Cutler, Supai, Abo, and Yeso Plateau itself; and (2) each unit has a pinch out somewhere formations. However, it is the upper portion, a sequence within the Plateau which emphasizes the composite nature dominated by cliff-forming sandstones, that has attracted of the sequence and suggests the need to evaluate the local most of the attention given to Permian strata of the Defi- relationships before attempting regional correlations. ance Plateau and with which this paper is primarily con- The subdivisions of the DeChelly Sandstone outlined cerned. These sandstones have been subdivided in various in Table 1 are manifestations of shifting environments of ways and such terms as Upper Cutler, Lower and Upper deposition—environments that are naturally grouped to- DeChelly, DeChelly, San Andres, Glorieta, and Coconino gether in space and time but which transgress and regress have been applied to them. in response to external factors. Lateral relationships are a problem, but in such a setting arc probably near gradational DISCUSSION for the most part. White House Member DE CHELLY SANDSTONE In the type area of Canyon DeChelly, underlying the On the Defiance Plateau, lying gradationally above the Triassic Shinarump Member of the Chinle Formation, it red detrital rocks of the Permian Supai Formation and un- is the White House Member (about 570 feet thick) that conformably below Triassic formations, are conspicuous forms the impressive sheer canyon walls. Approximately cliff-making sandstones ranging in thickness from over 800 95% of its thickness consists of 25 cross-stratified eolian feet at Canyon DeChelly to less than 250 feet at the units having an average thickness of 21 feet. The remain- southern end of the Defiance Plateau (Fig. 1). This sand- ing 5% consists of 11 horizontally stratified, water-depos- stone interval, called the DeChelly Sandstone by Gregory ited, truncating units having an average thickness of 3 feet. 58 NEW MEXICO GEOLOGICAL SOCIETY—EIGHTEENTH FIELD CONFERENCE TABLE 1. SUBDIVISIONS OF THE DE CHELLY SANDSTONE OF THE DEFIANCE PLATEAU DE CHELLY SANDSTONE (Peirce, 1962; 1964) REMARKS Ft. Defiance Member Sandstone and siltstone, interbedded; dark- Moenkopi of Darton (1925); "Red (0 - 105) reddish-brown to pale reddish-brown; small beds" of Baker and Reeside (1929), to medium scale cross-stratification and horizontal stratification, McKee (1934), and Balk (1954); aqueous ripple marks; forms a ledgy slope. San Andres equivalent of Baars (1962). Black Creek Member Sandstone; grayish-orange to moderate orange- Upper DeChelly of Read Wanek (0 - 225) pink; interbedded medium-scale cross-strati- (1961); Glorieta or Coconino of fied and horizontally stratified sandstones; an orthoquartzite of mixed Read (1951); Glorieta of Baars environmental type; forms a cliff. (1962); "Coconino-like" sand- stone of McKee (1934) at Bonito Canyon. White House Member Sandstone; pale reddish-brown to moderate Principal unit in type area of (0 - 570) reddish-orange; large-scale cross-strati- Canyon DeChelly. Upper Member fication, flat truncation surfaces frequently overlain by thin, water- of McKee in type area (1934); worked sandy siltstones; a subarkose of eolian origin; forms a cliff. Lumped with Hunters Point Mem- ber to form undivided DeChelly Sandstone of Baars (1962). Oak Springs Member Sandstone and Sandstone, silty; micaceous, Middle Member of McKee (1934) at (0 - 128) pale reddish-brown; horizontally stratified; Canyon DeChelly; Transition of water deposited; forms a slope. Read (1951) on east flank; Yeso (restricted) of Baars (1962), Tongue of Supai of Read Wanek (1961). Hunters Point Member Sandstone; pale reddish-brown to moderate Lower Member of McKee (1934) and (0 - 238) orange-pink; small to medium scale cross- Read (1951). Upper Cutler of stratification and horizontal stratification, channeling, aqueous Balk (1954); lumped with White ripple marks; a subarkose of aqueous origin; forms a cliff or slope. House Member to form undivided DeChelly Sandstone of Baars (1962) The water-deposited dark siltstones and silty sand- Black Creek Member stones represent local environments due, most probably, In the sections on the east flank (excluding Buell Park) to locally effluent water table conditions. the White House Member is but a lower part of the Sand grains in the cross-stratified