New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/15 The Lincoln fold system Campbell Craddock, 1964, pp. 122-133 in: Ruidoso Country (New Mexico), Ash, S. R.; Davis, L. R.; [eds.], New Mexico Geological Society 15th Annual Fall Field Conference Guidebook, 195 p. This is one of many related papers that were included in the 1964 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 • FIFTEENTH FIELD CONFERENCE THE LINCOLN FOLD SYSTEM Campbell Craddock University of Minnesota Minneapolis, Minnesota INTRODUCTION well exposed, but the San Andres Limestone is flat lying over most of the region and only locally buckled into In the walls of the valley of the Rio Bonito at Lin- sharp narrow folds. Previous investigations have dealt coln, New Mexico, the Yeso formation contains large with these folds incidentally or have been confined to a folds that provide a startling contrast with the low dips few anticlines or localities. During this study a number of the formation prevalent in the surrounding region, and of unmapped folds have been discovered. This paper in the overlying San Andres Limestone. Field work re- summarizes the distribution and probable origin of all vealed that these Permian formations show similar these folds, designated here the Lincoln fold system. An crumpling over an area of at least 3,500 square miles index map (fig. 2) shows the location of areas portrayed (fig. 1). The incompetent Yeso is generally folded where on the more detailed tectonic maps (figs. 3-7). GEOLOGIC 81 TECTONIC MAP OF M PARTS OF LINCOLN, CHAVES, a S S OTERO COUNTIES, NEW MEXICO Major intrusiyes, Geologic contact early Tertiary ( f-----f Major fault Post- San Andres, M Synclinal oxis I mainly Mesozoic .."."1.--• Anticlinal axis Son Andres tmn. S Permian) / Gentle regional • Carrizozo strike 9 dip Yeso fmn (Permian) 0 5 10 15 20 Miles Roswell CROSS — SECTION THROUGH BORDER HILLS EAST OF SUNSET NW SE S M Floodplain of Rio Hondo 0 100 Feet 200 300 Figure I. — Regional geologic and tectonic map. This article is an enlargement of a paper published in the Report of the International Geological Congress, 21st Ses- sion, Report, part 18, p. 34-14, Copenhagen, 1960. 122 NEW MEXICO GEOLOGICAL SOCIETY • FIFTEENTH FIELD CONFERENCE STRATIGRAPHY N Over most or all of the map area the Yeso Formation separated from the basement by less than a few hun- ENCINOSO is 5 MILES dred feet of lower Permian red beds and locally some TUCSON Pennsylvanian strata (Dunn, 1954) . One of the Picacho MT CA p i AN wells, six miles southwest of Sunset, penetrated about AR AEIECA-- M 0 300 feet of pre-Yeso elastic rocks above the basement; Tq / N farther north the Yeso lies directly on the Precambrian NOGAL (Lloyd, 1949). CA PITAN The Yeso is the oldest formation exposed in the map FORT area and generally consists of 1,200 to 1,800 feet of silt- L I N COL STANTO stone, limestone, shale, mudstone, and evaporites (Pray, 1954). The lower Yeso does not crop out here, but GLENCOE where it is exposed to the southwest along the Sacra- HOND T INNIE mento escarpment red beds and evaporites are the pre- i P IC ACHO dominant rocks. An incomplete section measured in the RUI DOS 0 GREEN Bonito valley just east of Lincoln canyon (fig. 8) in- TREE cluded 480 feet of Yeso, 65 percent siltstone and mud- stone, 25 percent limestone, and 10 percent gypsum. The limestones form 14 to 35 foot units interbedded in the Figure 2. Index map showing location of detailed siltstone and their resistance to weathering causes the tectonic maps. magnificient fold exposures at this locality. Above the uppermost limestone and below the base of the San An- dres is a unit of red siltstone and gypsum of widely vary- The deformed region includes parts of Lincoln, Cha- ing thickness. Seven sections measured through this in- ves, and Otero Counties and lies between the Great terval ranged from 30 to 224 feet in thickness, and had Plains to the east and the Cordilleran mountain system, a mean thickness of 100 feet. Single beds of gypsum expressed to the west in a series of north-south fault- as much as 40 feet thick occur in some of these sections, block ranges. Over most of the map area the surface but evaporites are absent in others. formations are Permian strata that dip almost 1° to the The San Andres Limestone consists of the Glorieta east or east-southeast. West of Lincoln these beds form Sandstone Member and an overlying limestone member. a broad arch and descend westward with dips of 5 to 15° The Glorieta, equivalent to the Hondo Sandstone Mem- into a structural basin of middle Tertiary age with an ber of Lang (1937, p. 850), was measured east of state igneous complex underlying its mountainous axis. South road 368 miles south of Arabela. At this locality it is and southeast of Sierra Blanca is the Sacramento-Guad- 131 feet thick, and includes 60 feet of limestone and 71 alupe Range, a gently eastward and northeastward dip- feet of sandstone and siltstone. The upper unit is a 38- ping homocline separated from the desert basins to the foot bed of massive, cross-bedded, fine-grained, yellow to west by major normal faults. Southeast of the map area buff sandstone which makes a distinctive key bed is the important petroleum province, the Permian basin throughout the area. The overlying limestone member of west Texas and New Mexico. Throughout most of consists of rather uniform 3 to 24 inch beds of finely the west half of the map area lower Permian formations crystalline, medium to dark gray limestone and dolo- rest on a Precambrian basement, which indicates the mitic limestone; beds of gypsum as much as 16 feet existence of a south-trending rib of land in late Penn- thick occur locally. The total thickness of the San An- sylvanian and early Permian time. Lower Paleozoic for- dres is about 1,000 feet. mations occur east, south, and west of this buried land- No evidence of an unconformity between the Yeso mass. and San Andres could be found in the field. At first The writer learned of the Lincoln folds in 1954 and glance the exposures near Lincoln ( fig. 9) seem to ex- has worked on them intermittently since then. Prelimi- hibit such evidence but the contact was observed closely nary reconnaissance on aerial photographs was followed at 37 localities over the area and the two formations by field study during the summers of 1957-59. Thanks were found to be parallel and conformable in all cases. are due Professor John Eliot Allen of Portland State Post-San Andres formations are preserved in the College, Dr. Robert H. Weber of the New Mexico Bu- east near Roswell and in the west in the Sierra Blanca reau of Mines and Mineral Resources, and Mr. Walter basin. These formations include the Chalk Bluff Forma- A. Mourant of the U.S. Geological Survey for providing tion of Permian age 500 feet of siltstone, gypsum, unpublished information from their work in various parts sandstone, and limestone; the Dockum Group of Trias- of the area and for help and encouragement during the sic age — 375 feet of variegated shale and coarse elas- field work. The writer expresses his gratitude to Harvey tics; the Dakota Sandstone of upper Cretaceous age Meyer, Howard Stensrud, Neil Muncaster, John Ander- 135 feet, the Mancos Shale, of upper Cretaceous age — son, and Jack OBrien for assistance in the field. Mr. minimum, 390 feet, and the Mesaverde Formation of Mark D. Wilson has been both generous and helpful upper Cretaceous age — minimum, 630 feet; Cub Moun- in sharing his broad experience in the regional geology tain Formation of Bodine, 1956 2,200 feet of conglom- of the area. This work was made possible by grants from erate, sandstone, siltstone, and variegated shales; and the Graduate School of the University of Minnesota.