New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/12 Triassic and Jurassic rocks of the Albuquerque area Clay T. Smith, 1961, pp. 121-128 in: Albuquerque Country, Northrop, S. A.; [ed.], New Mexico Geological Society 12th Annual Fall Field Conference Guidebook, 199 p. This is one of many related papers that were included in the 1961 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. 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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. NEW MEXICO GEOLOGICAL SOCIETY TWELFTH FIELD CONFERENCE 121 TRIASSIC AND JURASSIC ROCKS OF THE ALBUQUERQUE AREA CLAY T. SMITH New Mexico Institute of Mining and Technology The Albuquerque area may be defined as the Albu- the upper part, although this is not the case in exposures querque-Belen basin of the Rio Grande depression ( Kelley, in parts of the Lucero Mesa area (Kelley and Wood, 1946). 1952) and the adjacent associated platforms, uplifts, chan- Maroon, reddish purple, and brown colors are prominently nels, and constrictions (see Fig. 1). The present con- developed and often serve as identifying features for this figuration is chiefly the result of Tertiary and Quaternary rock sequence. Locally the sandstones and conglomerates diastrophism and bears little relation to the distribution of may be buff to nearly white in color and stand out sharply Triassic and Jurassic rocks except as it controls the out- against the bright-red mudstone slopes. Bentonitic clays crops of these beds. are abundant in the mudstone units and the alternate Many of the units so well known in the classical sec- shrinking and swelling of the soil in the semi-arid south- tions of the Colorado Plateau region are either missing or western climate results in characteristic "crazed" exposures. have merged with other members until all become un- In the upper part of the lower sendy facies, petrified wood recognizable. The areas in which outcrops occur are widely and chert pebbles are locally abundant. scattered, commonly confined to the mountain blocks, or to The Chinle formation was named by Gregory (1917) isolated structural basins and complexly faulted zones from exposures in Chinle Valley, Arizona; Gregorys ori- along the margins of the Rio Grande depression. ginal description of the formation did not include the TRIASSIC ROCKS Shinarump conglomerate, which he considered a separate Traditionally, the Triassic system has been subdivided formation. McKee and others (1959) included the Shina- into tripartite units usually labeled lower, middle, and up- rump as a lower member of the Chinle formation and in- per. As additional information has been collected it is dicated that it extends little if any distance east of the obvious that such a separation is not everywhere appli- New Mexico-Arizona stateline. Other local members of cable. McKee and others (1959) utilized three intervals, the Chinle formation have been described in Arizona, such A, B, C, in ascending order, in their treatment of the Trias- as the Petrified Forest member, Owl Rock member, and sic rocks of the United States, although recognizing that in- Sonsela sandstone member, but these cannot be extended terval B has a very restricted distribution. The intervals A, very far to the east or north (Stewart, 1957). Wood and B, and C of their paper are correlative with the German Northrop (1946) subdivided the Chinle formation in the tripartite division of the Triassic, as well as with accepted Nacimiento uplift into four units, in ascending order: Agua groupings of the Alpine European stages. Zarca sandstone, Salitral shale, Poleo sandstone, and the The classic Colorado Plateau section consisting of the upper Chinle beds. These units are not readily recognizable Moenkopi, Shinarump, and Chinle formations is assigned to away from the type localities northwest of the Jemez intervals A and C by McKee and others (1959) and has Mountains and were not individually delineated on the been enlarged through inclusion of the Wingate forma- Nacimiento uplift map. Along the north flank of the Zuni tion of the Glen Canyon group in the C interval by Harsh- Mountains, Smith (1954) mapped a lower member, a mid- barger, Repenning, and Irwin (1957). The Dockum group dle sandstone member, and an upper member of the Chinle of eastern New Mexico, West Texas, Oklahoma, and south- formation; these beds had originally been erroneously western Colorado is apparently confined to the C interval described by Darton (1928) as Moenkopi, Shinarump, and and has not been as extensively subdivided as has the Chinle formations. The lower and middle members in the Colorado Plateau section. Zuni Mountains suggest correlation with t4 lower Petri- In the Albuquerque area only rocks of the C interval fied Forest and the Sonsela sandstone members of the Ari- are present, corresponding to the German Keuper or the zona section while the upper member contains limestone combined Karnian, Norian, and Rhaetian stages of the layers and lenses similar to the Owl Rock member. In the European marine sequence. The Albuquerque area lay on Lucero Mesa area Kelley and Wood (1946) divided the a shelf between a western basin containing more than Chinle formation into two units: a lower red shale member 2,000 feet of Chinle sediments in the Zuni Mountains-St. and the overlying Correo sandstone member; they also Johns area, and an eastern basin containing more than recognized a thick unit between the Chinle formation and 2,000 feet of Dockum sediments in and near Lea County, the underlying Paleozoic limestones which they referred to New Mexico, and Yoakum County, Texas. Correlation be- the Shinarump conglomerate; however, it seems likely that tween Chinle-type sediments west and north of Albuquer- these beds are merely the lower sandy facies of the Chinle que, and Dockum-type sediments east and south of Albu- formation and may correlate much more closely with the querque has been difficult because of the intervening Santa Rosa sandstone member of the Dockum group to the present-day Rio Grande structural trough. The southerly east, or with the Agua Zarca, Salitral, and Poleo members depositional margin of the Triassic rocks induced facies farther north. The Correo sandstone member has a very changes that are rapid and unpredictable owing to local local distribution and is not recognized away from Mesa variations in tectonic activity. Local names have been in- Gigante in the northern part of the Lucero Mesa area. troduced in several areas, including some originating in West of the Albuquerque area, the Chinle formation is the Albuquerque area, and the relationships between such a thick mass of red mudstone, siltstone, and sandstone with local units are not always clear (see Table 1). marly beds and intercalated conglomerate lenses. A sandy The Triassic sediments of the Albuquerque area are facies occupies the lower one-third to one-half of the forma- predominantly fine-grained sandstone, siltstone, and mud- tion while mudstone and shale are predominant in the up- stone with intercalated lenticular conglomerate and coarse- per portion. The lower sandy facies averages 300 to 500 grained sandstone beds. 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