Paradox Member Research Articles

3D numerical modelling of graben interaction and linkage: a case study of the Canyonlands grabens, Utah

AbstractGraben systems in extensional settings tend to be segmented with evidence of segment interaction. To gain a better understanding of the evolution of structures formed during graben growth and interaction, we here study the Grabens area of Canyonlands National Park, Utah, where a wide range of such structures is well exposed. With the aid of 3D numerical models, we attempt to reproduce structures observed in that region and to understand controls on the structural style of graben interaction by varying the spacing between pre‐existing structures. The sensitivity of the system to the thickness of the salt layer is also tested. Four distinct types of structures are observed when the spacing between inherited weak zones is varied: (1) grabens connecting in a relay zone divided by a narrow central horst; (2) graben segments interacting via a secondary stepover graben; (3) grabens propagating alongside each other with limited segment interaction; and (4) an abandoned graben segment in a system of multiple competing grabens. The presence of a basal salt layer (Paradox Member) promotes efficient graben propagation. A comparison between the observed structures and the numerical model results indicates that the detachment salt layer is relatively thin in the study area.

Clay-Mineral Transformation as an Indicator of Depositional and Diagenetic Conditions in Pennsylvanian Black Shales, Paradox Member of the Hermosa Formation, Utah and Colorado

The dominant clay minerals in the Paradox basin black shale facies include a detrital, aluminum-rich illite/smectite and a series of magnesium-rich, interstratified chlorite/smectite minerals. Black shales from the Gothic and Chimney Rock layers of the Paradox Member of the Hermosa Formation were sampled from 13 wells in southwestern Colorado and southeastern Utah. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Inductively-Coupled Plasma (ICP), and Rock-Eval pyrolysis were used to determine the nature of a reaction believed to consume aluminum-rich detrital clays to precipitate magnesium-rich authigenic clays. The potential for magnesium enrichment in the clay assemblage was found to be influenced by the following processes: particle size as a function of distance from detrital source area, paleosalinity as a function of transgressive-regressive stage, and the presence of large amounts of organic matter. The basic reaction that forms chlorite/smectite or corrensite (perfectly ordered chlorite/smectite with 50% smectite layers) from detrital clays is Illite/Smectite (detrital) + Mg(aq)[sup 2+] + (OH)[sup [minus]] [yields] Corrensite + K[sup +] + Al[sup 3+]. Farther from detrital source areas, this recreation proceeds easily. Within this constraint, the remaining variables either aid or inhibit the proposed reaction from taking place. Higher salinity during deposition results in more chlorite layersmore » within the chlorite/smectite structure. Large amounts of organic matter strongly inhibit the reaction from occurring, possibly due to pH effects from the production of organic acids during burial.« less

Evaporite Cycles and Cycle Boundaries in the Upper Part of the Paradox Member, Hermosa Formation of Pennsylvanian Age in the Paradox Basin, Utah and Colorado

The evaporites of the Paradox Member of the Hermosa Formation of Pennsylvanian age in southeastern Utah and southwestern Colorado are direct precipitates from marine brines and have been changed only slightly by subsequent events. Geophysical logs of deep wells indicate that the Paradox Member is composed of at least 30 evaporite cycles. Lithologies that make up the cycles, in order of increasing salinity, are organic carbon-rich carbonate shale (black shale), dolomite, anhydrite, and halite (with or without potash). Studies of core from two wells in the central part of the basin show that some of the cycles in the upper part of the Paradox Member are remarkably symmetrical, indicating regular changes in salinity. Detailed petrologic studies have revealed newly recognized lithologic textures and cycle boundaries in 11 evaporite cycles, indicating very regular cyclicity of subaqueous sedimentation in a basin in which salinity was probably controlled by Gondwana glaciation.

A new explanation for cyclic deposition in marine evaporite basins: Meteoric water input

One of the least discussed processes affecting the deposition of marine evaporites is the role of meteoric water. Sand and fine-grained clastic sediments deposited from river system in a marginal evaporite-basin facies, the oxygen isotope record in the carbonate minerals (mainly dolomites), and the Br/Cl ratios of second-cycle salts, are some of the evidence for influxes of meteoric water. Important meteoric water influxes are not limited to sabkha and salina evaporites, but may also affect deep-water evaporite basins. One can see in the oxygen isotope record of carbonate minerals an imprint of meteoric water, just as the sulfur isotope record reflects the imprint of the marine water. Sedimentological characteristics of evaporite sequences could be interpreted as variations in the amount of precipitation in the evaporite basin catchment area, rather than as a result of changes in sea level. For example, the varved structures may reflect seasonal flooding of the basin by meteoric water; evaporite facies cycles may be the result of longer-term weather variation. For example, the Paradox Member cycles (Pennsylvanian, Utah) could reflect periods of increased precipitation, which are associated with glacial-interglacial cycles.

Evaporite Mineral Cycles, Paradox Basin, Utah and Colorado: ABSTRACT

The evaporites of the Paradox Member of the Hermosa Formation of Pennsylvanian age in southeast Utah and southwest Colorado are direct precipitates from marine brines and have been changed only slightly by subsequent events. Geophysical logs of deep wells indicate that the Paradox Member is composed of 29 evaporite cycles. Lithologies that make up the cycles, in order of increasing salinity, are: black calcareous shale, dolomite, anhydrite, and halite (with or without potash). Studies of cores from two wells in the central part of the basin show that some of the cycles in the upper part of the Paradox Member are remarkably symmetrical above and below the black shale, indicating regular changes in salinity. Lithic texture, crystal morphology, and bromine distribution are s ggestive of primary sedimentation with only minor early diagenesis related to burial dehydration. End_of_Article - Last_Page 1698------------

Valley anticlines of the Needles District, Canyonlands National Park, Utah

Valley anticlines of two types exist in the Needles District of Canyonlands National Park: (1) large, upright anticlines following major drainages, and (2) small, generally asymmetrical anticlines confined to rocks along the floors of smaller tributary valleys. The first type includes the Meander anticline along the Colorado River and anticlines following four deep tributary valleys east of the river. The Meander anticline is about 35 km long and follows the sinuosities of the Colorado River. The tributary anticlines also follow valley sinuosities. Severity of folding decreases upward from the valley floors, but arching is still evident at the level of canyon rims, as much as 600 m above the valley floors. These large valley anticlines appear to be due to upward flow of evaporites of the Paradox Member of the Hermosa Formation (Pennsylvanian). The differential stress driving this flow is a result of the unloading generated by canyon erosion. Much smaller anticlines occur in the Salt Creek, Butler Wash, and Chesler Canyon drainages 4 to 17 km east of the Meander anticline. These small anticlines are confined to 25 m of thin-bedded rocks straddling the base of the Cutler Formation (Permian) and have been found only where these thin-bedded rocks occur on valley floors. Most have straight limbs and sharp hinges, and all appear to die out downward and laterally so that the rocks of the valley walls and rocks at depth beneath the valley floors are unfolded. The folded rocks show no evidence of plastic behavior of any kind. Although some of the folding could be due purely to elastic rebound following valley erosion, fold amplitudes are best explained by excess horizontal compressive stress. A close correspondence between structure and landforms generally is interpreted as being due to structural control of landform development through differential erosion. In contrast, fluvial valleys predate folding and have determined the locations and mechanics of formation of anticlines in the Needles District and in a few other localities in the world.

Geochemistry and hydrodynamics of the Paradox Basin region, Utah, Colorado and New Mexico

The Paradox Basin region is approximately bounded by the south flank of the Uinta Basin to the north, the Uncompahgre uplift and San Juan Mountains to the east, the Four Corners structural platform to the southeast, the north rim of the Black Mesa Basin and the Grand Canyon to the south and southwest, and the Wasatch Plateau and Hurricane fault system to the west. Some of these geologic features are areas of ground-water recharge or discharge whereas others such as the Four Corners platform do not directly influence fluid movement. The aquifer systems studied were: (1) Mississippian rocks; (2) Pinkerton Trail Limestone of Wengerd and Strickland, 1954; (3) Paradox Member of the Hermosa Formation; (4) Honaker Trail Formation of Wengerd and Matheny, 1958; (5) Permian rocks. Recharge in the Paradox Basin occurs on the west flank of the San Juan Mountains and along the west side of the Uncompahgre uplift. The direction of ground-water movement in each analyzed unit is principally southwest-ward toward the topographically low outcrop areas along the Colorado River in Arizona. However, at any point in the basin, flow may be in some other direction owing to the influence of intrabasin recharge areas or local obstructions to flow, such as faults or dikes. A series of potentiometric surface maps was prepared for the five systems studied. Material used in construction of the maps included outcrop altitudes of springs and streams, drill-stem tests, water-well records, and an electric analog model of the entire basin. Many structurally and topographically high areas within the basin are above the regional potentiometric surface; recharge in these areas will drain rapidly off the high areas and adjust to the regional water level. With a few exceptions, most wells in formations above the Pennsylvanian contain fresh (< 1,000 mg/l T.D.S. 2 2 Milligrams per liter Total Dissolved Solids. ) to moderately saline (< 10,000 mg/l T.D.S.) water. In only a few cases are true brines (> 35,000 mg/l T.D.S.) reported. Most water samples from strata below the Permian are brines of the sodium chloride type but with large amounts of calcium sulfate or calcium chloride type water commonly occurring. Because evaporite facies occur in the Paradox Member, this unit has brines with as much as 400,000 mg/l dissolved solids content. Previous analysis of the San Juan Basin has indicated the presence of an osmotic membrane system. The highly permeable Jurassic formations were postulated to be the outflow side of the membrane. It is also possible that the Upper Paleozoic units with known brines and with an otherwise inexplicably high potentiometric surface in the Four Corners area of New Mexico could be the outflow receptors of the San Juan membrane system.

Uncompahgre Front and Salt Anticline Region of Paradox Basin, Colorado and Utah

Growth of the salt anticlines of the Paradox basin, Colorado and Utah, began in Middle Pennsylvanian time shortly after deposition of the salt of the Paradox Member of the Hermosa Formation. Several of the salt structures developed adjacent to structurally high areas in pre-salt rocks that apparently were in existence prior to and during salt deposition. The northeast margin of the salt basin was bordered by the front of the ancestral Uncompahgre uplift, and arkosic debris derived from the crystalline core of the uplift was shed into the margin of the basin. A pulse of uplift on the ancestral Uncompahgre range, marked by the spread of arkosic debris into the basin, resulted in termination of conditions requisite for evaporite deposition. Initial gentle folding of the salt structures probably occurred at this time. During the remainder of Middle and Late Pennsylvanian time the basin continued to sink while receiving a cover of dominantly marine sediments, and the major salt structures in the basin increased their amplitudes by an amount that generally matched the thickness of beds deposited on their flanks. Arkosic debris derived from the Uncompahgre was shed several miles into the basin. Strong uplift on the ancestral Uncompahgre range, which occurred near the end of Pennsylvanian time, resulted in withdrawal of the seas and in the spread of arkosic debris across the basin. Thick sections of continental sediments were deposited adjacent to and between the salt structures in the deep-trough part of the basin, and by the end of Permian time the salt structures had amplitudes ranging from about 5,000 to 9,000 feet. By the end of Permian time, most of the salt may have been transferred from beneath the flanks of the salt structures into their cores, and the growth of the salt structures slowed considerably or ceased. Renewed pulses of uplift in the Uncompahgre, occurring from latest Permian through Middle Triassic time, were marked by corresponding renewed active growth o the salt structures. Uplift of the Uncompahgre largely ceased by Late Triassic time and the crystalline core of the uplift near the Uncompahgre front was buried by a veneer of Upper Triassic and younger sediments. The salt structures grew slowly during Late Triassic and Early and Middle Jurassic time, and probably most were buried in Late Jurassic time.

Revised Lower Paradox Member (Pennsylvanian) Cross Section in Four Corners Region: GEOLOGICAL NOTES

Revised Lower Paradox Member (Pennsylvanian) Cross Section in Four Corners Region: GEOLOGICAL NOTES

Structural Development of Salt Anticlines of Eastern Utah and Western Colorado: ABSTRACT

The salt anticlines of eastern Utah and western Colorado formed in the deepest part of Paradox basin, a basin developed during Pennsylvanian time and filled by great thicknesses of upper Paleozoic sediments, including a thick sequence of evaporites belonging to the Paradox member of the Hermosa formation. The salt anticlines originated either as tectonic folds or as folds over basement faults soon after the evaporites were deposited, probably in Middle Pennsylvanian time. These structures were parallel to and probably formed concomitantly with the rise of the ancestral Uncompahgre highland, the front of which paralleled rather closely that of the southwest front of the present-day Uncompahgre Plateau. Rapidly accumulating arkosic sediments of the Permian Cutler formation, derived from this highland, probably buried parts of the salt anticlines; elsewhere along the anticlines the salt rose isostatically as rapidly as the sediments were deposited. In places the Cutler was later intruded by the cores of the buried salt anticlines. Parts of the cores were exposed at the surface at least until the Morrison formation was deposited in Late Jurassic, so that the formations pinch out along the flanks of the salt cores. Variations in thicknesses--chiefly thinning--of the Morrison and later Mesozoic formations over the crests of the salt cores indicate that salt flowage was still active after the salt cores were buried. The salt anticlines attained their present form--except for modifications imposed by later collapse of the crestal parts of the anticlines--during the early Tertiary when the rocks of the region were folded, and the salt anticlines were accentuated. End_of_Article - Last_Page 413------------

Geology of Pennsylvanian Gas in Four Corners Region

Pennsylvanian accumulations of gas and casing-head gas in the Four Corners region (junction of Utah, Colorado, New Mexico, and Arizona) occur in carbonates of Desmoinesian age in four lithologic zones of the Paradox member of the Hermosa formation. These zones, from oldest to youngest, have been named Barker Creek, Akah, Desert Creek, and Ismay. They are shelf counterparts of basinal evaporitic sequences. Reservoir beds are calcirudite, calcarenite, and sparsely to moderately fossiliferous carbonate, which is nearly in place, and was deposited in biostromal and biohermal complexes. Dolomitization and other diagenetic changes have affected these units. Vuggy and intercrystalline porosity is predominant; fracturing is important in some places. In only a few instances can the type of trap, with fair assurance, be defined from present subsurface control. Structurally, all of the gas fields are on surface or subsurface highs of varying relief and areal extent. Sedimentary compaction has contributed to this relief in some places, and late Pennsylvanian-Permian warping has occurred. Most of the present structural relief of these structures is due to folding during the Laramide orogeny. Stratigraphic variations, from porous reservoir beds to non-porous units, contribute to most accumulations, and are the controlling factor in some. Eleven gas and five casing-head gas fields have been found, but these are still largely undeveloped with respect to gas. The cumulative gas production to July 1, 1959, in the Aneth Complex was 9,682,004 MCF. To September 1, 1959, the cumulative production from sour zones was 179,825,593 MCF at the Barker Creek field, representing slightly more than half of the calculated original recoverable reserves of 315 billion cubic feet of gas at Barker Creek. These Pennsylvanian gas accumulations seem to be essentially in situ occurrences. The source beds are believed to be present in each zone; migration was predominantly local, not exceeding a few miles; and entrapment occurred in laterally adjacent areas of bioclastics and sparsely to moderately fossiliferous carbonates. After initial entrapment, some later re-migration probably occurred in places.

Pennsylvanian Gas in Four Corners Region: ABSTRACT

Pennsylvanian accumulations of gas and casing-head gas in the Four Corners region (junction of Utah, Colorado, New Mexico, and Arizona) occur in carbonates of Desmoinesian age (Middle Pennsylvanian) in four lithologic zones of the Paradox member of the Hermosa formation. These zones, from oldest to youngest, have been named Barker Creek, Akah, Desert Creek, and Ismay. They are shelf counterparts of basinal evaporitic sequences. Reservoir beds are calcirudite, calcarenite, and sparsely to moderately fossiliferous carbonate, which is nearly in place and was deposited in biostromal and biohermal complexes. Dolomitization and other diagenetic changes have affected these units. Vuggy and intercrystalline porosity are predominant; fracturing is important in some places. Only in a few instances can the type of trap, with fair assurance, be defined from present subsurface control. Structurally, all of the gas fields are found on surface or subsurface highs of varying relief and areal extent. Sedimentary compaction has contributed to this relief in some places, and late Pennsylvanian-Permian warping has occurred. Most of the present structural relief of these structures is due to folding during the Laramide orogeny. Stratigraphic variations, from porous reservoir beds to nonporous units, are a contributing factor in most accumulations, and the major controlling factor in some. Eleven gas and five casing-head gas fields have been found to date, but these are still largely undeveloped. The cumulative gas production to July 1, 1959, in the Aneth Complex was 9,682,004 MCF. To September 1, 1959, the cumulative production from four zones was 179,825,593 MCF at the Barker Creek field which represents slightly over one-half of the calculated original recoverable reserves of 315 billion cubic feet. Gas from the Barker Creek field, and from the Aneth Complex, is transmitted to Kirtland, New Mexico, and from there to Topock, Arizona. Buyers at Topock distribute to customers in California and southern Nevada. These Pennsylvanian gas accumulations are believed to be essentially in situ occurrences. Migration was predominantly local, not exceeding a few miles; and entrapment occurred in laterally adjacent areas of bioclastics and sparsely to moderately fossiliferous carbonates. After initial entrapment, some later re-migration is believed to have occurred. End_of_Article - Last_Page 960------------

Lithologic Zone Boundaries in Pennsylvanian Paradox Member, Paradox Basin: GEOLOGICAL NOTES

Lithologic Zone Boundaries in Pennsylvanian Paradox Member, Paradox Basin: GEOLOGICAL NOTES

How Oil Wells Are Completed in the Paradox Basin

Abstract This paper covers the common completion practices for oil wells in the Paradox Basin fields near the Four Corners. The nature of the producing formations is described and the pertinent drilling problems are discussed. Since the pay consists of carbonate rocks, stimulation by acidizing is the principal ingredient of completions. These methods of acidizing which have been tailored to the reservoir characteristics are described. Introduction As in any other geologic province, the Paradox Basin requires its own combination of the myriad of drilling and completion techniques if optimum productivity is to be obtained at minimum cost. With the boom in development activity since the oil pipelines from this basin were constructed the process of making an oil well has undergone considerable refinement so that today better wells are being completed for less money. This treatise describes how this is done. To facilitate an understanding of the problems peculiar to this area and the reasons for the methods used to cope with them, a complete but generalized description of the reservoirs is presented. Pertinent Drilling Information The proved commercial productive horizons in the Paradox Basin are, for all practical purposes, the porous carbonates of the Pennsylvanian Hermosa formation and those of the Paradox member. In the area of greatest exploration and development, this formation is generally between 5,000 and 6,000 ft deep. Drilling times in the Aneth and Ratherford fields are approximately 25 days, and generally somewhat more in wildcats and outlying fields. Most operators drill 9-in. hole and set 7-in. production casing or drill 7 ⅞-in. hole and set 5 ½-in. production casing. Reservoir pressure of the productive zone is less than hydrostatic, and mud weights of 9.2–10.4 lb/gal have been found to be satisfactory after setting surface casing. The mud weight depends on the weight that is necessary to control the water flow from the De Chelly, which lies some 2,000 ft below the surface. For development wells it is frequent practice to emulsify some oil into the mud before reaching the objective zone which improves drilling characteristics, reduces mud costs, and probably reduces contamination of the pay section.

Developments in Colorado and Western Nebraska in 1958

Total development activity for the two-state area was down slightly from last year. Exploratory tests totaled 838, a decrease of 156 from last year, while development drilling increased to 735 wells or 49 more than 1957. Eight counties in the Denver basin accounted for 66.5% of all the exploratory tests drilled in the two states. Colorado showed an increase in total drilling of 6.5% over 1957 much of which was due to field development and exploration on the Western Slope. Nebraska activity decreased nearly 18% due to a sharp reduction in exploratory drilling both in the Denver basin and on the west flank of the Cambridge arch. Success ratios for exploratory tests increased about 1½% for both states, but again Colorado's Western Slope with its ratio of more than 19% was responsible for this gain. There were 34 oil pools and 30 gas pools discovered in Colorado. Most of the gas pools were in the Piceance basin. Nebraska had 45 pools discovered, all of which were oil producers. None of the 1958 discoveries in either state is likely to achieve major field status. The exploratory activity trend in the Denver basin has become well established as northward and eastward into Nebraska. Deeper drilling on the Western Slope of Colorado was evident with many tests in the southwestern corner going into the Paradox member of the Hermosa formation. Extreme eastern Colorado's Las Animas arch had very heavy leasing activity following early year successes in the Pennsylvanian of northwestern Kansas. An active lease play also followed the announcement of a 12-well exploratory program in the northern part of the Raton basin.

Pennsylvanian Stratigraphy and Productive Zones, Paradox Salt Basin

The Paradox Salt basin is an elongate northwest-southeast Pennsylvanian depositional basin extending from central Utah through the Four Corners area. The Pennsylvanian system is comprised of the Molas formation, a basal dark red shale unit deposited on the karst topography eroded into Mississippian carbonates, and the Hermosa formation. The Hermosa formation, wherever evaporites and carbonates deposited in a restricted environment are present, is divisible into three members: upper Hermosa, Paradox, and lower Hermosa. The Paradox member is an evaporite megacyclothem composed of discrete sedimentary sequences which are complete or partial cyclothems. The member is gradational and interfingers with open marine sediments of the upper and lower members above and below. Latera ly, at the south, southwest, and west, the relationships with the undifferentiated Hermosa formation are similar, but toward the northeast the Paradox member grades into and interfingers with coarse clastics derived from the Uncompahgre uplift. Since 1954 eleven Pennsylvanian discoveries and several important field extensions have resulted in substantial oil and gas reserves, with at least one field, Aneth, of major importance. All accumulations found to date, with the exception of Mexican Hat, are associated with the evaporite cyclothems of the Paradox member or its normal marine lateral equivalents. Two important productive objectives, the Desert Creek and Bluff zones, are widespread in the Four Corners area. Accumulations in reservoirs having similar stratigraphic position to these zones have been found but, except for the Barker Creek gas field, appear to be of less importance. Rapid lateral and vertical variations in the porosity and permeability of potential and proved reservoir beds make facies studies a necessary too of exploration and production in evaluating structures and field development. Daily production is limited to a small fraction of the potential due to lack of outlets.