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Regional Geophysical Investigations of the Moab-Needles Area, Utah

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Regional Geophysical Investigations of the Moab-Needles Area, Utah Regional Geophysical Investigations of the Moab-Needles Area, Utah GEOLOGICAL SURVEY PROFESSIONAL PAPER 516-C Prepared partly on behalf of the U.S. Atomic Energy Commission REGIONAL GEOPHYSICAL INVESTIGATIONS MOAB-NEEDLES AREA, UTAH Aerial view of Upheaval Dome, San Juan County, Utah. Regional Geophysical Investigations of the Moab-Needles Area, Utah By H. R. JOESTING, ]. E. CASE, and DONALD PLOUFF GEOPHYSICAL FIELD INVESTIGATIONS GEOLOGICAL SURVEY PROFESSIONAL PAPER 516-C Prepared partly on behalf of the U.S. Atomic Energy Commission Gravity and magnetic surveys of parts of Canyonlands National Park UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966 GEOPHYSICAL FIELD INVESTIGATIONS REGIONAL GEOPHYSICAL INVESTIGATIONS OF THE MOAB-NEEDLES AREA, UTAH By H. R. JoESTING,1 J. E. CAsE, and DoNALD PLOUFF ABSTRACT southern part of the area is interpreted to be the result of com­ paratively dense basement and thinning of eva.porites at the Aeromagnetic and gravity surveys were made of about 1,450 north nose of the Monument uplift. Regional lo\vs near Mean­ square miles in the Moab-Needles area of Utah, in the north­ der anticline along the Colorado River may be associated with central parot of ·the Colorado Plateau. The area is within the less dense or deeper basement and thicker evaporites. Paradox evaporite basin, a subsurface feature of Pennsylvanian Another major buried trough and its flanking structural highs, age. These surveys were made to gain broad-scale information in the Mississippian and older rocks, trends northeast along the on the depth, composition, and configura,tion af the Precambrian Colorado River. These structures are indicated by gravity and basement, and on major salt ran'ticlines that may have influenced magnetic data and are partly corroborated by data from deep the occurrence of uranium, oil, and potassium-bearing evaporites. drilling. Minor rejuvenation of these features during Cenozoic Exposed sedimentary rocks range in age from Pennsylvani,an time may have affected the course of the Colorado River. to Recent. Oam'brian, Devonian, and Mississippian rocks have been found in deep wells. No igneous rocks have been reported, INTRODUCTION and no Precambrian ·rock•s have been penetrated by the drill. According to geophysical evidence, the P·recambrian rocks This report describes the results of aeromagnetic and differ in magnetization and density, reflecting differences in regional gravity surveys in southeastern Utah in the composition. The sedimentary rocks are almost nonmagnetic, area between Moab and The Needles, near the junction but their densities vary widely. In the northern third of the area, which lies within the of the Green and Colorado Rivers (fig. 1). It is one of deeper pavt of the Paradox evaporite basin, magnetie gradients a series of regional geophysical studies of the Colorado are lO'W, thus indicating almost uniform magnetization of the Plateau, made to gain additional broad-seale informa­ basement. This magnetization does, however, increase grad­ tion on the depth and configuration of the buried Pre­ ually tOIWard the northeast. In the southern third of the area, cambrian basement, and on regional structures that may which includes the north end of the Monument uplift, the mag­ netic field is diverse, an indication of compositional diversity have influenced the occurrence of uranium, potassium­ of the basement. In the central part, evidently a transition zone bearing salts, and oil ( J oesting and Byerly, 1958 ; between basin and uplift, are three prominent magnetic highs, Byerly and Joesting, 1959; Case and others, 1963). associated with large stocklike masses in the basement that are The area discussed here includes The Knoll, Moab, Up­ surrounded by rocks having about the same magnetization as heaval Dome, Hatch Point, The Needles, and Harts those in the northern part. Cpheaval Dome, a remarkable structural dome probably formed by an intrusive salt plug, is Point 15-minute quadrangles in parts of Grand, San near the crest of one of the magnetic highs, but the high is at J nan, V\r ayne, Garfield, and Emery Counties (fig. 1). least four times as wide as the dome. No surface structural The Canyonlands National Park lies partly within the features are associated with the other magnetic highs. area. The gravity anomalies are associated with density contrasts The Moab-Needles area is a land of broad high mesas within both the Precambrian and the sedimentary rocks, par­ ticularly between the evaporites and the sandstone, shale, ·and and of deep precipitous canyons cut into multicolored limestone. Prominent lows occur over the large salt anticlines sandstone and shale by the Colorado and Green Rivers of Moab and Salt Valleys in the northern pavt of the area. p.art and their tributaries. lTpheaval Dome, a symmetrieal of the anomaly along Moa'b Valley is evidently related to a struetural dome into whieh a remarkably deep circular basement fault that may have controlled the position of the salt anticline. A prominent gravity gradient in the central erater has been eroded (see frontispiece), is in the west­ part of the rarea evidently marks a major lithologic and struc­ ern part of the area. The Needles fault zone, with to­ tural change in the basement: from lower density in the deeper pography characterized by tall slender sandstone spires basin to the north to higher density in the buried uplift to the south. Part of the gradient is also related to thinning of evap­ and valleys ·with interior drainage, lies in the south­ orites to the south. The deep~seated basement structural fea­ "·estern part of the area just east of Cataract Canyon ture is also indicated by magnetic data. A gravity high in the of the Colorado River and south of Meander salt anti­ 1 Deceased, May 1965. cline. Broad and elongate valleys have formed along 01 C2 GEOPHYSICAL FIELD INVE1STIGATIONS 38°30' WAYNE Monticello 0 SAN JUAN DOLORES Blanding i 0 I 37°30'~----~~--------4-~~--------------~--------------~~----------------~--~I I, '~V1l' ::J J/ I \%.~ <, Cortez /,../' 0 I ~~ I 0 Bluff } / ~ ~ ~,, I ~/ I ~b. MONTEZU A ( ~/ . / Mexican Hat e.,. I /I //~ 1 ,_ 0 10 201 30 40 MILES / J J ! ~~-#Pu~ I L ~I I / 3ro0,_l _______ i_L _____ _:_~~-L---- UTA_!!__ --~OLOR~DO -~----- ARIZONA ------OF pp.RP.D~-----,.. NEW MEXICO --------------- EXPLANATION Jllllllllll ...__\ll La Sal Mountains Lisbon Valley area Uravan area Sa.lt Valley-Cisco Axis of salt anticline Igneous intrusions in area (Byerly and Joesting, 1959) (Joesting and Byerly, 1958) area or monoclinal uplift the La Sal Mountains (Case and others, 1963) (Joesting and Case, 1962) FIGURE 1.-Location of the Moab-Needles area (stippled) relative to major structures in the Paradox basin, Utah and Colorado. REGIONAL G'EIOPHYIS!lCA:L INVEISTIGATIONS, MOAB-NEED-LES AR'EA, UTAH C3 the breached crests of Moab Valley and Salt Valley the Geological Survey in the salt anticline region were salt anticlines in the northeastern part of the area. summarized by J oesting and Case ( 1960). More de­ Airborne magnetic surveys were made over the area tailed reports ·were prepared on areas adjoining the during 1954, and additional surveys were flown over Moab-Needles area: the Lisbon Valley area (Byerly Upheaval Dome in 1955. The airborne surveys were and J oesting, 1959) ; the La Sal Mountains area (Case directed by J. L. Meuschke and R. W. Bromery; com­ and others, 1963) to the east; and the Salt Valley­ pilation of aeromagnetic data was directed initially Cisco area ( ,J oesting and Case, 1962) to the north (fig. by James Aubrey and later by Paul Yeager. 1). A brief preliminary report on geophysical investi­ The gravity field party was initially under the direc­ gations in the vicinity of lTpheaval Dome was prepared tion of Richard Warrick; most of the fieldwork, how­ by J oesting and Plouff ( 1958). A gravity map and ever, was directed by Donald Plouff, assisted at various brief discussion of the Moab-Needles area also was re­ times by Winthrop Means, Jerome Marks, Marvin Bo­ leased ( J oesting and others, 1962). hannon, and Huntley Ingalls. A line of gravity sta­ This investigation has been supported jointly by the tions was later established down the Green River by U.S. Atomic Energy Commission and the U.S. Geologi­ P. E. Byerly, and a line down the Colorado River to cal Survey. Cataract Canyon by J. E. Case. Ground magnetometer GEOLOGIC SETTING and gravity meter traverses and transit traverses for The ~{oab-Needles area is in the north-central part vertical control were run in Upheaval Canyon and from of the Colorado Plateau, in the Canyon Lands section the rim to the bottom of Upheaval Dome by Joesting of Fenneman (1931). The area is within the Paradox and Plouff and later by J oesting and Case. basin, which is characterized by thick Pennsylvanian Geologic information to aid in the interpretation of evapori,tes that locally form the cores of salt anticlines the geophysical data was obtained mainly from publica­ (fig. 1). Structure of sedimentary rocks at the surface, tions of Baker ( 1933, 1946), Dane ( 1935), and Mc­ hmvever, gives no hint of the buried Pennsylvanian Knight (1940), from oil-company drill logs and from basin; the exposed rocks dip gently northward and oil scout reports. Information was also obtained from northeastward from the Monument uplift, in the south­ photogeologic maps of parts of the area by Bates (1955a, ern part of the area, toward the Uinta Basin, which lies b, c), Bergquist ( 1955), Hemphill ( 1955), and Sable farther north. A deep-seated fault or other vertical (1955a, b, c, and1956); and from unpublished maps of displacement within the Paradox basin, trending west­ parts of the Upheaval Dome and The Needles quad­ northwest across the area, divides the basin into a shal­ rangles by F. A.
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