Pictured Cliffs Sandstone Research Articles

Geologic controls on transgressive-regressive cycles in the upper Pictured Cliffs Sandstone and coal geometry in the lower Fruitland Formation, northern San Juan Basin, New Mexico and Colorado

Three upper Pictured Cliffs Sandstone tongues in the northern part of the San Juan Basin record high-frequency transgressive episodes during the Late Cretaceous and are inferred to have been caused by eustatic sea level rise coincident with differential subsidence. Outcrop and subsurface studies show that each tongue is an amalgamated barrier strand-plain unit up to 100 ft (30 m) thick. Successive upper Pictured Cliffs tongues display an imbricate relation and are offset basinward, reflecting net shoreline progradation northeastward. Upper Pictured Cliffs barrier strand-plain sandstones underlie and bound thickest Fruitland coal seams on the seaward side. Controls on Fruitland coal-seam thickness and continuity are a function of local facies distribution in a coastal-plain setting, shoreline positions related to transgressive-regressive cycles, and basin subsidence. During periods of relative sea level rise, the Pictured Cliffs shoreline was temporarily stabilized, allowing thick, coastal-plain peats to accumulate. Although some coal seams in the lower Fruitland tongue override abandoned Pictured Cliffs shoreline deposits, many pinch out against them. Differences in the degree of continuity of these coal seams relative to coeval shoreline sandstones are attributed to either differential subsidence in the northern part of the basin, multiple episodes of sea level rise, local variations in accommodation and progradation, stabilization of the shoreline by aggrading peat deposits, or a combination of these factors. Fruitland coalbed methane resources and productivity are partly controlled by coal-seam thickness; other important factors include thermal maturity, fracturing, and overpressuring. The dominant production trend occurs in the northern part of the basin and is oriented northwestward, coinciding with the greatest Fruitland net coal thickness. Similar relationships between trends of thick coal seams of coeval origin with stacked shoreface sandstones exist in other Western Interior basins in the United States and serve as models for coalbed methane exploration in other basins of the world.

Compositional Variability, Origins, and Migration of Pictured Cliffs Sandstone Gases, San Juan Basin, New Mexico: ABSTRACT

Compositional Variability, Origins, and Migration of Pictured Cliffs Sandstone Gases, San Juan Basin, New Mexico: ABSTRACT

Peat accumulation in coastal-plain mires: a model for coals of the Fruitland Formation (Upper Cretaceous) of southern Colorado, USA

In the northwestern part of the San Juan basin, Colorado, thick high-volatile B bituminous coal deposits in the Upper Cretaceous Fruitland Formation are associated with nearshore marine sandstones of the Pictured Cliffs Sandstone. Detailed work along the outcrop and examination of drill cores, revealed two coal-bearing zones in the lower 60 m of the Fruitland Formation. Each zone is up to 13 m thick and consists of interbedded bright and dull coal (average ash values of 17 and 34% on a moisture-free basis, respectively), thin fine-grained clastic partings and abundant altered volcanic ash partings. Isopachs of the interval between the top of the Pictured Cliffs Sandstone and a marker bed (Huerfanito Bentonite Bed) in the underlying Lewis Shale show linear zones where the interval abruptly thickens. These zones, which trend northwest to southeast, represent areas where the shoreline paused during an overall migration to the northeast. Isopach maps of coal in the lower part of the Fruitland Formation and subsurface correlation of shoreface sandstones with coal zones show that the thickest accumulation of coal is 20–25 km landward of these coeval shorelines. The Fruitland coals may be compared to the high-ash peats of the Dismal Swamp in the southeastern U.S.A., which form in pocosin mires about 20 km inland from the Atlantic coast. Clastic deposirion, resulting from coastal processes, precludes the formation of peat in low-lying mires adjacent to the shoreline. The high ash yield, numerous partings and the relationship with the coeval shoreline suggest that the coals in the lower part of the Fruitland Formation accumulated in mires that were transitional from low-lying to raised.

Barrier-Strandplain Deposits of the Pictured Cliffs Sandstone and Coal Occurrence in the Fruitland Formation, Northern San Juan Basin, Colorado and New Mexico: ABSTRACT

Barrier-Strandplain Deposits of the Pictured Cliffs Sandstone and Coal Occurrence in the Fruitland Formation, Northern San Juan Basin, Colorado and New Mexico: ABSTRACT

Characterization of coal-derived hydrocarbons and source-rock potential of coal beds, San Juan Basin, New Mexico and Colorado, U.S.A.

Coal beds are considered to be a major source of nonassociated gas in the Rocky Mountain basins of the United States. In the San Juan basin of northwestern New Mexico and southwestern Colorado, significant quantities of natural gas are being produced from coal beds of the Upper Cretaceous Fruitland Formation and from adjacent sandstone reservoirs. Analysis of gas samples from the various gas-producing intervals provided a means of determining their origin and of evaluating coal beds as source rocks. The rank of coal beds in the Fruitland Formation in the central part of the San Juan basin, where major gas production occurs, increases to the northeast and ranges from high-volatile B bituminous coal to medium-volatile bituminous coal ( R m values range from 0.70 to 1.45%). On the basis of chemical, isotopic and coal-rank data, the gases are interpreted to be thermogenic. Gases from the coal beds show little isotopic variation ( δ 13C 1 values range −43.6 to −40.5 ppt), are chemically dry (C 1/C 1–5 values are > 0.99), and contain significant amounts of CO 2 (as much as 6%). These gases are interpreted to have resulted from devolatilization of the humic-type bituminous coal that is composed mainly of vitrinite. The primary products of this process are CH 4, CO 2 and H 2O. The coal-generated, methane-rich gas is usually contained in the coal beds of the Fruitland Formation, and has not been expelled and has not migrated into the adjacent sandstone reservoirs. In addition, the coal-bed reservoirs produce a distinctive bicarbonate-type connate water and have higher reservoir pressures than adjacent sandstones. The combination of these factors indicates that coal beds are a closed reservoir system created by the gases, waters, and associated pressures in the micropore coal structure. In contrast, gases produced from overlying sandstones in the Fruitland Formation and underlying Pictured Cliffs Sandstone have a wider range of isotopic values ( δ 13C 1 values range from −43.5 to −38.5 ppt), are chemically wetter (C 1/C 1–5 values range from 0.85 to 0.95), and contain less CO 2 (< 2%). These gases are interpreted to have been derived from type III kerogen dispersed in marine shales of the underlying Lewis Shale and nonmarine shales of the Fruitland Formation. In the underlying Upper Cretaceous Dakota Sandstone and Tocito Sandstone Lentil of the Mancos Shale, another gas type is produced. This gas is associated with oil at intermediate stages of thermal maturity and is isotopically lighter and chemically wetter at the intermediate stage of thermal maturity as compared with gases derived from dispersed type III kerogen and coal; this gas type is interpreted to have been generated from type II kerogen. Organic matter contained in coal beds and carbonaceous shales of the Fruitland Formation has hydrogen indexes from Rock-Eval pyrolysis between 100 and 350, and atomic H:C ratios between 0.8 and 1.2. Oxygen indexes and atomic O:C values are less than 24 and 0.3, respectively. Extractable hydrocarbon yields are as high as 7,000 ppm. These values indicate that the coal beds and carbonaceous shales have good potential for the generation of liquid hydrocarbons. Voids in the coal filled with a fluorescent material that is probably bitumen is evidence that liquid hydrocarbon generation has taken place. Preliminary oil-source rock correlations based on gas chromatography and stable carbon isotope ratios of C 15+ hydrocarbons indicate that the coals and (or) carbonaceous shales in the Fruitland Formation may be the source of minor amounts of condensate produced from the coal beds at relatively low levelsof thermal maturity ( R m =0.7).

Cedar Hills Field, San Juan County, New Mexico: a Multi-Well Coal Degasification Project, San Juan Basin, New Mexico--a Case Study: ABSTRACT

Amoco Production Company is operating a multi-well coal degasification site, Cedar Hills field, in San Juan County, New Mexico. Data presented here have been made available by Amoco at public hearings before the New Mexico Oil and Gas Commission. The Cedar Hills field produces from the lowermost coal bed in the Cretaceous, Fruitland Formation, stratigraphically positioned above the Pictured Cliffs Sandstone. The coal bed reservoir is 18-20 ft (5-6 m) thick at a depth of 2,800 ft (853 m). The first well in this field was the Amoco 1 Cahn, completed in 1977 with an initial production of 200-300 MCFGD and 200-300 BWPD. These rates increased to 1.5 MMCFGD and 80 BWPD by January 1984. This well's production history exhibits a negative decline (incline) curve. Gas analyses, water analyses, and reservoir pressure data strongly indicate that the 1 Cahn well is producing from the Fruitland coal bed rather than the Fruitland sandstones or underlying Pictured Cliffs Sandstone. End_of_Article - Last_Page 858------------

Stratigraphy and Palynology of the Upper Lewis Shale, Picture Cliffs Sandstone, and the Lower Fruitland Formation (Upper Cretaceous) near Durango, Colorado

The stratigraphy and palynology of Upper Cretaceous units (upper Lewis Shale, Pictured Cliffs Sandstone, and lower Fruitland Formation) were investigated near Durango, Colorado, on the northern rim of the San Juan basin. This investigation: (1) confirms an interdeltaic depositional setting for these formations in the study area, (2) provides new biostratigraphic data for the Upper Cretaceous rocks on the northern rim of the San Juan basin, and (3) indicates a mostly freshwater origin for the Carbonero coal bed at the base of the Fruitland Formation. The upper Lewis Shale was deposited in lower offshore to upper offshore marine environments. The Pictured Cliffs Sandstone records a major regression on the western margin of the Late Cretaceous sea. The northeastward regression was not one steady event but a series of superimposed transgressive pulses. The depositional environments identified in the Pictured Cliffs Sandstone are upper offshore, shoreface, foreshore, and backshore. The lower part of the Fruitland Formation represents a coastal swamp deposit which developed just landward of the Pictured Cliffs Sandstones. The Carbonero coal bed lies at the base of the Fruitland Formation. At one location, a small tidal channel developed and inundated the local swamp environment. Ten Late Cretaceous palynomorph guide fossils were identified in the Lewis Shale, Pictured Cliffs Sandstone, and Fruitland Formation. The palynomorphs of the Lewis Shale and Pictured Cliffs Sandstone are a marine assemblage. The Fruitland Formation contains a terrestrial assemblage of pollen and spores. Trudopollis meekeri, Kuylisporites scutatus, and cf. Myrtaceoipollenites are a late Campanian Stage palynomorph assemblage in the Fruitland Formation. These findings refute the recent interpretation of a late Maestrichtian age for the Fruitland Formation. The palynological results obtained in this research can be used for correlation and mapping of interbasin and intrabasin sedimentary facies.

Relation of Natural Gas Composition to Thermal Maturity and Source Rock Type in San Juan Basin, Northwestern New Mexico and Southwestern Colorado

San Juan basin is a roughly circular, asymmetric structural depression located in northwestern New Mexico and southwestern Colorado. Ultimate recoverable reserves of predominantly nonassociated gas (23 tcf, 0.65 × 1012 m3) are present in the structurally low part of the central basin. The major producing intervals are low-permeability sandstone reservoirs in the Upper Cretaceous Dakota Sandstone, Mesaverde Group, and Pictured Cliffs Sandstone. Lesser amounts of oil and/or gas are produced from Pennsylvanian, Jurassic, and Cretaceous rocks along the southern and western flanks of the basin. The gases display a trend of becoming isotopically heavier (^dgr13C1 values range from -48.7 to -31.4^pmil and chemically drier (C1/C1-5 values range from 0.75 to 0.99) with increasing depth. These changes are assumed to be the result of thermal cracking processes, and the gases are interpreted to have been generated during the mature and post-mature stages of hydrocarbon generation. However, there is considerable scatter in the data which is interpreted to result from a difference in source rock type. Gases generated from nonmarine (humic) source rocks are isotopically heavier and chemically drier than those generated from marine (sapropelic) source rocks at equivalent levels of maturity. The gases also become isotopically heavier and chemically drier to the northeast, following the trend of increasing maturity of all units in that direction. The increase in maturity is attributed to a combination of greater burial depth and a higher geothermal gradient resulting from batholiths to the north in the San Juan Mountains area. Maximum burial and heat flow occurred during the Oligocene, which probably coincided with peak hydrocarbon generation. Lack of oil in the central basin is believed to be the result of two factors. First, gas in reservoirs such as the Dakota Sandstone may have resulted from thermal cracking of oil generated from marine source rocks during late mature (wet gas-condensate) and post-mature (dry gas) stages of hydrocarbon generation. Second, gas in reservoirs such as Mesaverde Group and Pictured Cliffs Sandstone is nonassociated and probably was generated from nonmarine (coaly) organic matter during the mature and post-mature stages. Minor amounts of condensate, instead of oil, may have been generated from nonmarine source rocks during the mature stage.

Differentiation of Delta-Front and Barrier Lithofacies of the Upper Cretaceous Pictured Cliffs Sandstone, Southwest San Juan Basin, New Mexico

The Upper Cretaceous Pictured Cliffs Sandstone represents a regressive littoral marine unit deposited during the final retreat of the Cretaceous epeiric sea in the southwestern San Juan Basin, New Mexico. Differences in rock type, internal and penecontemporaneous deformation structures, textural sequences, mineral composition, and trace fossil content permit recognition of laterally contemporaneous delta-front and barrier lithofacies in the Pictured Cliffs Sandstone. The delta-front lithofacies consists of distal bar, distributary mouth bar, and distributary channel deposits. The barrier lithofacies consists of shoreface, beach, washover channel, tidal inlet, tidal channel, and ebb-tidal delta deposits; these lithofacies are coarsening-upward sequences of shale, siltstone, and sandstone, locally scoured in the upper part by fining-upward channel deposits. The delta-front lithofacies contain abundant penecontemporaneous deformation structures in the form of ball-and-pillow, diapiric, and slump structures as well as convolute bedding and microfaults. In contrast, the laterally equivalent shoreface deposits of the barrier lithofacies lack these deformation structures. The channel deposits of the delta-front lithofacies contain large-scale convolute lamination and a few burrows, in contrast to the channel deposits of the barrier lithofacies, which contain common herring­bone crossbeds separated by reactivation surfaces, bidirectional but ebb dominated festoon crossbeds, and more abundant burrows. Quartz content of the barrier lithofacies varies from 43 to 74 percent, whereas in the delta­ front lithofacies it varies from 29 to 60 percent. The difference in quartz content between these lithofacies suggests some cleaning-up process in the deposition of the barrier lithofacies, particularly in the preserved beach deposit. The delta-front and barrier lithofacies were probably deposited along mesotidal shorelines. The recognition of laterally contemporaneous delta-front and barrier lithofacies of the Pictured Cliffs Sandstone allows delineation of potentially economic coal-producing deposits in the delta-plain lithofacies flanked by back­ barrier lithofacies in the overlying prograded Fruitland Formation.

Stratigraphy and Paleontology of Bisti Badlands, San Juan County, New Mexico: ABSTRACT

Study of 29 stratigraphic sections of the Upper Cretaceous Cliff House Sandstone, Lewis Shale, Pictured Cliffs Sandstone, Fruitland Formation, and Kirtland Shale in the Bisti Badlands of northwestern New Mexico suggest deposition in deltaic environments. Cliff House Sandstone littoral, Lewis Shale prodelta and delta-front, Pictured Cliffs strand-plain, levee, and distributary-channel, Fruitland Formation paludal, estuarine, and delta-plain, and Kirtland Shale flood-plain facies document the transgression and regression of the last epeiric seaway for the San Juan basin. Littoral and strand-plain paralic facies, respectively, delineate transgressive and regressive sequences, whereas prodelta and delta-front facies reflect deposition in offshore open-marine waters. Late Campanian fossils represented by marine mollusks, sharks and dinoflagellates, pelagic foraminiferids, benthic ostracods, littoral and shallow-neritic Ophiomorpha burrows, and terrestrial palynomorphs illustrate that marine conditions prevailed but were contaminated by terrestrial biotas. Deposition of delta-front sandstones 1 km or more from shore is substantiated by the hypopycnal inflow formula. Terrestrial environments, represented by levee, distributary-channel, paludal, delta-plain, and flood-plain facies, exhibit the deposits of vertically accreted shale, laterally accreted channel sandstones, and coal. Overbanking of distributary channels formed natural levees on the periphery of interdistributary marshes, thereby preserving a coal to shale to sandstone vertical sequence. Local transgression due to channel abandonment and delta-lobe subsidence deposited estuarine shale and upward-coarsening, crevasse-splay sandstones. Delta-plain to flood-plain facies shows the transition from thick commercial coals and shale, to shale and channel sandstones, to shale which contain local coal, bentonite, and channel sandstones. The transition represents, respectively, poorly drained swam s, well-drained delta-top tracts, and riverine with lacustrine regions. Aquatic bivalves and gastropods plus fish, turtle, crocodile, and dinosaur bones occur as lag deposits to channel sandstones. Locally, articulated dinosaur, turtle, and crocodile bones are present in the vertically accreted shale. Nine hundred million metric tons of coal from four coal seams of the lower Fruitland Formation represent a major energy resource for New Mexico. Western Coal Co., Albuquerque, intends to strip mine 80 million metric tons of coal found within the study area. End_of_Article - Last_Page 562------------

Mollusca from Upper Cretaceous Fruitland and Kirtland Formations, Western San Juan Basin, New Mexico: Review: ABSTRACT

Renewed interest in the development of substantial coal reserves in the San Juan basin has given new impetus to the determination of the potential impact of expanded mining on paleontologic resources and to a reconsideration of depositional environments of Fruitland coals. Reanalysis of molluscan localities from the Fruitland and Kirtland Formations on lands of the Navajo Nation, in preparation for more extensive field studies, indicates that, of the 24 localities collected by C. M. Bauer in 1915, 12 are type localities for 17 species, representing a large percentage of the total fauna known from these formations. Differentiation of brackish and nonmarine environments on the basis of biostratigraphic distribution of species divides the Fruitland Formation into upper and lower units. Near the western margin of the San Juan basin, predominantly brackish environments are present near the base of the Fruitland, underlain by the littoral-marine Pictured Cliffs Sandstone, and extend up to 35.6 m in total thickness. Exclusively nonmarine sediments are present bove this horizon to the top of the Fruitland and throughout the Kirtland Formation. Nonmarine molluscan diversity seems to increase markedly at approximately 35.6 m. Below this horizon, only 7 taxa indicate freshwater environments. At 35.6 m, 8 taxa are introduced, and of these 7 occur only at this level. Above 35.6 m, only 2 taxa are introduced: Physa reesidei at about 61 m and Unio baueri at 123.5 m (Kirtland Formation). The only terrestrial mollusk reported is Planorbis chacoensis from near the base of the Fruitland Formation. End_of_Article - Last_Page 560------------

Pictured Cliffs Sandstone--Upper Cretaceous Distributary-Channel, Delta-Front, and Beach-Bar Deposits, Southwestern San Juan Basin, New Mexico: ABSTRACT

The Upper Cretaceous Pictured Cliffs Sandstone in the Bisti-Burnham area in southwestern San Juan basin, New Mexico, contains distributary-channel, delta-front, and beach-bar deposits. The distributary-channel deposit is a basally erosional, festooned, convoluted, and rippled sandstone. The delta-front deposits include distributary-mouth-bar sandstone, distal-bar sandstone, siltstone, shale, and intervening contorted sandstone. The distributary-mouth-bar sandstone is subparallel laminated, rippled, and festooned. The distal-bar sandstone is subparallel laminated and rippled. The intermediate contorted sandstone contains fold and ball-and-pillow structures. The distributary-channel and delta-front sandstones are very fine to fine grained, quartz poor (39%), and sparsely bu rowed by Ophiomorpha. The beach-bar deposits include shoreface-beach sandstone, siltstone, and shale, and tidal-channel and washover sandstones. Lower-shoreface deposits include parallel-laminated, rippled sandstone and bioturbated shale and siltstone. Middle-shoreface sandstone consists of a subparallel-laminated, rippled, and locally burrowed lower part, and a planar-cross-bedded and commonly burrowed upper part. Upper-shoreface-beach deposits consist of planar-cross-bedded, sparsely burrowed sandstone and lenticular, festooned, rippled, burrowed sandstone grading upward into subparallel-laminated, festooned, burrowed sandstone. The shoreface-beach deposits are dissected by bidirectionally End_Page 451------------------------------ festooned and planar-cross-bedded tidal-channel sandstone and festooned, burrowed washover sandstone. The beach-bar sandstones are very fine to medium grained, quartz rich (54%), and commonly burrowed by Ophiomorpha. Differentiation of Pictured Cliffs Sandstone depositional environments led to recognition of deltaic and back-barrier coal deposits of the overlying Fruitland Formation. End_of_Article - Last_Page 452------------

A Study of Rock-Solution Interaction and Its Effect on Archie's Law

The electrical conductivity (?) of cylindrical cores of 25.4-mm diameter and length Pictured Cliffs sandstone (permeability range, 7 × 10-4 × 10-1 millidarcy (md); porosity range, 3.8-4.9 percent) was measured at a frequency of 1 kHz under ambient conditions after saturation in tap water. Kinetics of rock-water interaction and the effect of Soxhlet extraction on the ? of the rock were also investigated. Formation factors (F) and the ? display time-dependent behavior up to 4500 h. Smooth asymmetrical conductivity maxima occur for all samples at times which increase with increasing porosity. The observed timedependence of F in Archie's Law (F = ?-1, ? = porosity, n = a parameter) is influenced by the kinetics of ion transport between the Pictured Cliffs sandstone and the aqueous pore fluid. Soxhlet extraction lowers F, but does not significantly change its time dependence.

Environment of Deposition of Late Cretaceous Fruitland Formation Coal Deposits of San Juan Basin, New Mexico and Colorado: ABSTRACT

The Fruitland Formation in the San Juan basin contains large resources of subbituminous and bituminous coal. The thickest beds are in the lowermost part of the formation and in many places lie directly on the underlying Pictured Cliffs Sandstone. The coal beds were deposited in a coastal-swamp environment. This environment shifted northeast together with the Pictured Cliffs shoreline as the Late Cretaceous sea withdrew from the San Juan basin. The coal swamps trended northwest, parallel with the shoreline. The thickness of vegetal matter buildup in these coastal swamps is related closely to the manner in which the Pictured Cliffs shoreline retreated from the basin area. The retreat of the sea was primarily the result of sediment infilling along the edge of a subsiding dep sitional basin. When sediment influx was great, the shoreline regressed rapidly, swamps soon were filled and covered, and the resultant coal beds were thin. When sediment influx was moderate, the shoreline remained geographically stable, shoreline sandstone deposits built up vertically, swamp deposits of vegetal matter also built up vertically, and the resultant coal beds were thick. When sediment influx was small, the shoreline transgressed continental deposits, swamps were filled and covered by marine sandstone, and resultant coal beds were thin. Another paleoenvironmental factor affecting swamp configuration was streams passing through the coastal swamp area to the sea. This process tended to limit the length of swamps. In addition, variations in the paleotopography of the coastal swa p area due to the presence of bars and dunes limited the areas which the swamps occupied. End_of_Article - Last_Page 214------------

A Recent Rockslide near Durango, in La Plata County, Colorado

Contrary to the somewhat sensational accounts in the public press, the rockslide on Carbon Mountain does not exhibit any unusual features. The slide involves the lower 100-125 feet of the Fruitland formation, of Upper Cretaceous age, which consists largely of shale and lies immediately above the Pictured Cliffs sandstone. The mass involved is about 1,800 feet long, 600 feet wide, and 100 feet deep and has moved about 700 feet obliquely down the back slope of a hogback of Pictured Cliffs sandstone, which dips about 21° SE. The slope along the direction of the major movement has a gradient of only 40 per cent. The mass moved slowly, the maximum recorded rate being about 30-45 feet a day.