Parachute Creek Member Research Articles

An organic geochemical investigation of organic matter sources and carbon cycling within Eocene Lake Uinta, Parachute Creek Member, Green River Formation, Uinta Basin

An organic geochemical investigation of organic matter sources and carbon cycling within Eocene Lake Uinta, Parachute Creek Member, Green River Formation, Uinta Basin

Foliage and Fruits of Early Poplars (Salicaceae: Populus) from the Eocene of Utah, Colorado, and Wyoming

A new species of poplar is recognized based on abundant specimens from the early Middle Eocene Parachute Creek Member of the Green River Formation in eastern Utah and western Colorado and compared with two other contemporary species. A rare twig bearing both leaves and fruits serves as a Rosetta stone, linking the vegetative and reproductive structures that formerly were only known from dispersed organs. Fruit and foliage characters distinguish Populus tidwellii sp. n. from Populus cinnamomoides (Lesquereux) MacGinitie (typified on specimens from Green River Station, WY), to which the isolated leaves had formerly been attributed. In addition, new data from fruits and foliage confirm that there were two distinct sympatric species of Populus in the Parachute Creek flora (P. tidwellii and Populus wilmattae). These species, together with Pseudosalix and Salix, provide our earliest record of diverse Salicaceae. An interesting feature of P. tidwellii is that the inflorescence is terminal in contrast to extant species of Populus, in which the catkins are axillary and borne on wood of the previous season. In addition, the infructescence shows lateral branching near its base, distinguishing it from the simple racemes of extant species of the genus.

Partial resolution of sources of n-alkanes in the saline portion of the Parachute Creek Member, Green River Formation (Piceance Creek Basin, Colorado)

Systematic variations in the 13C contents of individual extractable n-alkanes (C 16–C 29) can be modelled quantitatively and interpreted as indicating contributions from at least five distinct sources. These appear to be cyanobacterial ( C 16– C 18, δ 13 C = − 37 0 00 vs PDB ), phytoplanktonic C 16–C 23, δ = −32 0 00 ), chemoautotrophic bacterial ( C 20– C 29, δ = −38 0 00 ), phytoplanktonic or heterotrophic bacterial ( C 20– C 29, δ = −30‰ ), and vascular plants ( C 23– C 29, δ = −29‰ ). Hydrous pyrolysis of related kerogens yields large quantities of additional n-alkanes with different and much more uniform δ values. The latter materials are apparently derived from the thermolysis of aliphatic biopolymers whose presence in the Green River Oil Shale has been recognized visually.

Compound specific isotopic variability in Uinta Basin native bitumens: paleoenvironmental implications

We have analyzed the solvent extracts from three different types of native bitumens from the Uinta Basin in northeastern Utah by a variety of analytical techniques, including GC-IRMS, to evaluate variations in the paleodepositional environment during two periods of Lake Uinta deposition. The gilsonite and tabbyite bitumens are associated with Parachute Creek Member sediments deposited during a major expansion of ancient Lake Uinta. Compound specific isotopic analyses of ß-carotane and phytane ( δ 13 C = −32.6 to −32.1% 0 ) from these bitumens reflect input from primary photosynthetic producers such as cyanobacteria. Sterane δ 13C values (−34.5 to −29.2% 0) refflect contributions from lacustrine algae, while extremely depleted δ 13C values for methylhopanes (−58.1 to −61.5% 0) suggest input from methanotrophic bacteria. Variations in the δ 13C values of the αβ-hopanes (−51.4 to 37.7% 0) imply additional input from other bacterial sources. The wurtzilite bitumen was generated from the Saline Facies of the Green River Formation deposited during a later regression of Lake Uinta. Compound specific isotopic analyses of phytane ( δ 13 C = −30.1% 0 ) and steranes δ 13 C = −29.6 to −26.7% 0 ) from this bitumen indicate continued input from primary producers and eukaryotes. The higher relative concentrations of gammacerane ( δ 13 C = −26.9% 0 ) indicate increasing input from aerobic protozoa. We observed a slight enrichment in δ 13C in the wurtzilite extract (and several biomarkers) and suggest that this is a result of sulfate-reducing bacteria outcompeting methanogens, thereby, eliminating the influence of methanotrophs in this later saline stage of deposition.

Stratigraphy of the Parachute Creek Member of the Green River Formation, Sunnyside Tar Sands Area, Carbon County, Utah: ABSTRACT

Stratigraphy of the Parachute Creek Member of the Green River Formation, Sunnyside Tar Sands Area, Carbon County, Utah: ABSTRACT

Lacustrine Hummocky Cross-Stratification in Green River Formation, Southern Uinta Basin, Utah: ABSTRACT

Hummocky cross-stratification (HCS) is a common sedimentary structure in marine strata but has only been reported in a few lake deposits. However, recent field investigations in the southern Uinta basin show that HCS occurs within several different depositional environments and lithologies in the lacustrine Green River Formation (Eocene). HCS is well developed within the open-lacustrine informal S2 marker unit of the Parachute Creek Member, where it exhibits many of the characteristics common in marine HCS: numerous low-angle, second-order truncations; antiforms (hummocks); association with planar laminations and ripples; gently curved parallel to nearly parallel laminations; fanning of laminations into swales; and scattered dip directions of truncation surfaces and laminae. Hummock spacing ranges from 20 cm to approximately 2.75 m. Hummocks produced by laminae that thicken toward the hummock crest indicate that at least some of the HCS was produced by bed forms molded by the flow, and not by a random scour-and-drape mechanism. Common laminae downlap at set boundaries, and asymmetric hummocks indicate that at least some of the hummocks were subject to minor migration during growth.

Review of the stratigraphic distribution and diagenetic history of abelsonite

Abelsonite is a crystalline nickel (II) porphyrin, derived from one of the chlorophylls, found only in the Parachute Creek Member of the Green River Formation, an Eocene lacustrine deposit in the Uinta Basin, Utah. Since its original observation in 1969, numerous samples of abelsonite have been collected and their stratigraphic position within the formation plotted. It was observed that abelsonite occurs in six distinct narrow stratigraphic zones, which can be described with respect to the distribution of organic matter. The zones of abelsonite occurrence were designated M9, M7, M2, L6, L0, and K1 based on Green River Formation stratigraphic nomenclature. Abelsonite displays a secondary mode of occurrence, occurring in vugs, fractures, and along bedding lamina, strongly implying migration or movement. The origin of abelsonite can probably be attributed to the unique geochemical conditions of Lake Uinta, chlorophyll diagenesis, and the transport of an aqueous solution of a relatively insoluble precursor into sediments of favorable lithologic characteristics.

Penstemon Debilis (Scrophulariaceae): A New Species from Colorado Endemic to Oil Shale

Penstemon debilis, collected near Parachute on Mount Callahan in western Colorado, is described and illustrated. The species is endemic to the Parachute Creek Member of the Green River Formation. Oil shale endemism is discussed and the species is compared morphologically to similar species in sectionsGlabri, Coerulei, andPenstemon.

Trace element distribution and oil yield data from the parachute creek member of the green river formation, colorado

The determination of trace element concentrations in oil shale before mining and retorting is required for proper solid-waste management planning. Using routine Fischer assay oil yield data collected during resource characterization as indicators of potential trace element concentrations could lead to a standard method of identifying strata containing high trace element levels. In order to determine a correlation between trace element concentrations and oil yield, shale samples were selected from four statigraphic zones of the Parachute Creek Member of the Green River Formation for analysis. All samples were analyzed for total elemental concentrations, mineralogy, and Fischer assay oil yield. The results of these analyses demonstrated that the Mahogany zone shales contain significantly greater trace element concentrations (antimony, arsenic, cadmium, chromium, copper, lead, lithium, mercury, molybdenum, nickel, selenium, silver, and vanadium) than the other three shale zones. These high trace element concentrations have been identified within well-defined interbedded tuff deposits in the Mahogany zone. In addition, all trace elements evaluated, except boron, show either increasing or decreasing concentrations as oil yield increases within all oil shale zones. With an increased number of analyses of existing oil shale cores, oil yield data will be correlated to specific stratigraphic units containing high trace element concentrations.

Regional Stratigraphic and Depositional Study of Rock Units in Upper Garden Gulch and Parachute Creek Members of Green River Formation, Piceance Creek Basin, Colorado: ABSTRACT

The Eocene Green River Formation in the Piceance Creek basin, Colorado, is well known for its thick sequence of rich oil shale and associated saline minerals. In the subsurface, rocks of economic interest extend from the upper part of the Garden Gulch Member to the top of the Parachute Creek Member. These rocks are lacustrine deposits that represent open-and near-shore sedimentation in ancient Lake Uinta. The depocenter of the lake formed in the northern part of the basin where rates of subsidence exceeded rates of sedimentation. The Garden Gulch and Parachute Creek Members can be divided into a series of laterally gradational rock units that can be traced from the eastern part of the Piceance Creek basin westward into the south-central part of the Uinta basin, Utah. Alon the margins of the Piceance Creek basin, the lower and middle units consist of fissile argillaceous shale of low organic content, silty claystone, and siltstone. Toward the depositional center of the basin, these rocks grade into a thick sequence of carbonate-rich, kerogenous shale and lean marlstone that is interbedded with a saline facies composed of nahcolite, dawsonite, and halite. The gradational boundary between these facies represents the contact between the Garden Gulch and Parachute Creek Members. In the subsurface, the contact can be recognized by a change from a low to high resistivity log response which reflects the transition from clay-rich to carbonate-rich rock. The regional thickness distribution pattern of individual units suggest that, during the middle Eocene, Lake Ui ta gradually expanded from a shallow, relatively fresh, semirestricted body of water to a saline, alkaline lake that occupied a closed basin. A pronounced thickening of the lowermost units along the southern margin of the basin is attributed to streams that prograded northward into the basin from the southern and southwestern margin of the lake. The middle and upper units, however, thin toward the basin edge, suggesting the lake gradually expanded to the south. During the late Eocene, open-lacustrine sedimentation shifted from the Piceance Creek basin westward into the Uinta basin, Utah, due to a large influx of siliciclastic sediment (Uinta Formation). Structural analysis of individual units indicates that present day intrabasinal tectonic features were not in existence during Parachute Creek time. End_of_Article - Last_Page 535------------

Nonlinear Creep Behavior of Oil Shale: ABSTRACT

Oil shale resources in the United States are important as an energy source. Knowledge of the mechanical properties, including the creep behavior, is essential to any form of development. The creep behavior of oil shale samples taken from the Parachute Creek Member of the Green River Formation has been studied. A pneumatic-driven testing machine with long-term displacement monitors was used. The set of duplicate test specimens required for creep testing were cut from the same horizon of oil shale using a diamond-impregnated-wire saw to avoid surface damage. Duplicate samples were tested at various stress levels of the ultimate compressive strength. Samples with different organic contents were taken at different depths of the core. A nonlinear rheological model was develope and a multi-parametric statistical analysis was performed. It was concluded that the organic content and the stress levels were important parameters. The creep phenomenon can be represented by a nonlinear strain-time equation upon which a nonlinear pseudo 3-D creep model can be built, relating the strains to the stresses. End_of_Article - Last_Page 962------------

Characteristics of Some Oil Shale, East-Central Uinta Basin, Utah: ABSTRACT

Oil-yield, lithologic, and mineral-distribution data were determined for cores taken from a 152-m drill hole in the upper part of the Parachute Creek Member of the Eocene Green River Formation. The drill hole, in Sec. 3, T12S, R24E, started just below the contact between the Uinta Formation and the underlying Green River Formation, and ended 10 m below the Mahogany oil shale bed (the richest oil shale bed in the interval examined) in the lower part of the Mahogany zone. Most of the interval studied is composed of kerogen- and carbonate-rich, very fine-grained sediments. Several thin (less than 1 m) oil shale beds which yield as much as 25 gal of oil per ton (104.3 l per metric ton) are above the Mahogany zone, but are probably not of economic interest. The studied sequence contains several tuff beds; the maximum thickness of these beds is about 0.6 m, but the average thickness rarely exceeds 0.2 m. Two oil-saturated tuff beds occur approximately 20 m above the Mahogany oil-shale bed. Although these two tuffs are exposed in nearby surface outcrops, they do not contain oil in these outcrops. The Mahogany zone is approximately 21 m thick at the drill site; the lowermost few feet were not penetrated. The Mahogany zone is covered by 132.6 m of overburden. Fischer assays indicate that 12.9 m of oil shale within the Mahogany zone could yield at least 25 gal of oil per ton (104.3 l per metric tone) from beds at least 3 m thick. Although analcime is a common accessory mineral in the upper 50 m of the core hole, it was not identified in the Mahogany zone. Illite and mixed-layer clay minerals occur together above the Mahogany zone. The mixed-layer clays decrease in quantity as the Mahogany zone is approached, and no mixed-layer clays are detected in the Mahogany zone. Illite was detected in all samples examined from the Mahogany zone. Examination of X-ray diffraction patterns obtained from bulk rock samples from cores did not reveal the presence of any potentially valuable accessory minerals in the stratigraphic interval studied. End_of_Article - Last_Page 944------------

Fluorine: its mineralogical residence in the oil shale of the Mahogany Zone of the Green River Formation, Piceance Creek Basin, Colorado, U.S.A.

The Eocene oil shales of northwestern Colorado comprise one of the major resources of hydrocarbon fuels in the U.S.A. Oil shales of the Mahogany Zone (Parachute Creek Member, Green River Formation) contain up to 2100 mg/kg fluorine. The content of fluorine changes rapidly within short stratigraphic intervals, and, although not organically bound, correlates positively with the organic content of the rock. Studies of the mineralogical residence of fluorine in oil shale were made possible by combining the methods of low-temperature ashing, high-speed centrifugation in a liquid with a density gradient, X-ray diffraction, X-ray fluorescence, nuclear inelastic scattering, and electron microscopy. A major portion of the fluorine in the Mahogany Zone appears to be associated with the ubiquitous micaceous clay minerals, especially illite. Other fluorine-bearing minerals, such as fluorite (CaF 2), cryolite (Na 3AlF 6), and fluorapatite [Ca 5(PO 4) 3F] were not detected in the eleven samples studied. However, this does not exclude the possible presence of discrete crystals or crystal aggregates of these minerals in other portions of the Mahogany Zone.

Definition of Depositional Facies of Parachute Creek Member of Green River Formation, Colorado--Evidence from Sulfur Isotopes and Whole-Rock Mineralogic Data: ABSTRACT

The Parachute Creek Member of the Green River Formation in the southern Piceance Creek basin displays four major lacustrine and marginal-lacustrine facies: deltaic-interdeltaic mudflat, carbonate mudflat, proximal open lacustrine, and distal open lacustrine. These facies are strongly gradational across the basin and their definition is not clearly evident from study of the physical characteristics of each facies. Additional evidence from whole-rock mineralogy (defined by X-ray diffraction) and sulfur isotopes, however, help to clarify each facies. The deltaic-interdeltaic mudflat facies contains channel-form cross-stratified sandstone intercalated with pyritic mudrock and marlstone. Detrital quartz, K-feldspar, Na-plagioclase, and rock fragments characterize the sandstone. The mudrock and marlstone contain both calcite and dolomite plus detrital silicate minerals; ^dgr34S values of pyrite from this facies range from 2 to 26 per mill and average 12 per mill. The carbonate mudflat facies is dominated by dolomitic algal stromatolite, oolite, pisolite, and interclastic carbonate rock, and interbedded green to gray pyritic marlstone. The marlstone contains both calcite and dolomite and considerable authigenic analcime; ^dgr34S values range from 5 to 40 per mill and average 16 per mill. End_Page 824------------------------------ Proximal open-lacustrine deposition produced well-stratified marlstone and lean oil shale, and rare algal stromatolite. Detrital silicate minerals become less abundant and are volumetrically replaced by dolomite, Fe-dolomite, excess-Ca ankerite, analcime, and rare dawsonite. The ^dgr34S values of pyrite from this facies range from 22 to 54 per mill and average about 30 per mill. The distal open-lacustrine facies is represented by richer grades of oil shale (greater than 15 gal/ton) and saline minerals (nahcolite and halite). The oil shale contains abundant Ca-Fe-Mg-carbonate phases, authigenic quartz, K-feldspar, Na-plagioclase, and dawsonite. Analcime is rare. The ^dgr34S values of pyrite and marcasite range from 18 to 66 per mill and average 35 per mill. Overall, the Parachute Creek Member shows that detrital silicate minerals and calcite are concentrated in the marginal-lacustrine facies but authigenic silicate minerals, complex Mg-Ca-Fe-carbonate minerals, and saline minerals are concentrated in the open-lacustrine facies. Sulfur-isotope data show that iron sulfide minerals become progressively enriched in 34S toward the open-lacustrine environment of deposition. End_of_Article - Last_Page 825------------

Comparative mineralogy of nearshore and offshore lacustrine lithofacies, Parachute Creek Member of the Green River Formation, Piceance Creek Basin, Colorado, and eastern Uinta Basin, Utah

A comparative study of the relative distribution of analcime, quartz, K-feldspar, Na-plagioclase, calcite, dolomite, and ankerite shows variable partitioning of these minerals between the marginal-lacustrine and open-lacustrine lithofacies of the Parachute Creek Member of the Green River Formation in the southern and western Piceance Creek Basin, Colorado, and the eastern Uinta Basin, Utah. The variations correlate with changes in the depositional environments of ancient Lake Uinta. Four individual, but gradational, environments of deposition are recognized in the Parachute Creek Member: (1) deltaic lacustrine; (2) carbonate flat; (3) proximal open lacustrine; and (4) distal open lacustrine. Rocks from these depositional facies range from sandstone and algal limestone in the first two marginal-lacustrine environments to oil shale, tuff, and saline-mineral beds in the latter two open-lacustrine environments. Detrital quartz, K-feldspar, and Na-plagioclase are most abundant in channel-form sandstone beds in the deltaic-lacustrine facies. In the open-lacustrine facies where oil shale is dominant, these silicates are still abundant but are authigenic or diagenetic in origin. Analcime is found in fine-grained rocks in all environments but is least abundant in oil shale of the distal open-lacustrine environment where saline minerals such as nahcolite and halite are present. Calcite, dolomite, and ankerite show the most complex facies distribution. Calcite is apparently most abundant in the finegrained calcareous rocks intercalated with sandstone and algal limestone in the marginal-lacustrine facies, and it is least abundant in the distal oil shale. Dolomite is abundant throughout the Parachute Creek Member but is most abundant in the distal oil shale. Ankerite is also most abundant in the distal oil shale but is rare in marginal-lacustrine rocks. The overall zonation of the carbonate suggests that the more chemically complex types are found in the more basinward environments. Thus, the pattern for the carbonate distribution is a reflection of local biogeochemical and geochemical conditions and not the result of transportation of carbonate phases from a fringing mud-flat (playa fringe) environment.

Depositional Lithofacies of Parachute Creek Member of Green River Formation, Douglas Creek Arch, Colorado: ABSTRACT

Depositional Lithofacies of Parachute Creek Member of Green River Formation, Douglas Creek Arch, Colorado: ABSTRACT

The permittivity and electrical conductivity of oil shale

An investigation was made of the electrical conductivity and the real part of the complex permittivity of oil shale. Results are reported of a study on oil shale under ambient conditions prior to, and after, retorting to temperatures of 800/sup 0/K. The rocks chosen for investigation came from the Anvil Point's Mine, Colorado; these oil shale specimens are from the Parachute Creek member of the Green River formation, Piceance Creek Basin. Data presented indicate that the unretorted sample is a better conductor by as much as an order of magnitude at 10 kHz. Results of the permittivity and conductivity studies indicate that these variables are directly related to the oil content of the shale and may be used to monitor the retorting of oil shale in situ. (MCG)

Concentration and mineralogical residence of elements in rich oil shales of the Green River Formation, Piceance Creek basin, Colorado, and the Uinta Basin, Utah — A preliminary report

Ten samples from drillcore of two rich oil-shale beds from the Parachute Creek Member of the Eocene Green River Formation, Piceance Creek basin, Colorado, and Uinta Basin, Utah, were analyzed for 37 major, minor, and trace elements. For 23 of these elements, principal mineralogical residence is established or suggested and such studies may provide data which are useful for predicting the kinds and amounts of elements and compounds that might be released into the environment by oil-shale mining operations.

Primary and Secondary Sedimentary Structures in Fine-grained Lacustrine Rocks of Green River Formation (Eocene), Piceance Creek Basin, Colorado: ABSTRACT

A study of 285 polished slabs (59.0% oil shale, 23.0% carbonate, and 18.0% fine-grained clastic rock) collected from four measured sections along the southern and eastern edge of the Piceance basin reveals important sedimentologic information on the distribution of primary and secondary sedimentary structures. The slabs were studied under low-power binocular magnification, and individual stratification characteristics were noted. A total of 528 primary structures and 334 secondary structures were observed in the slabs. Eleven descriptive classes of primary structures are important: (1) even parallel stratification; (2) discontinuous even parallel stratification; (3) wavy parallel and nonparallel stratification; (4) discontinuous wavy parallel and nonparallel stratification; (5) discontinuous curved parallel stratification; (6) curved nonparallel stratification; (7) structureless; (8) mottled; (9) brecciated; (10) algal stratification; and (11) graded stratification. Of these classes, the oil shale is dominated by classes 1, 2, 3, and 4, and the carbonate and fine-grained clastic rocks by classes 6, 7, 8, and 10. Classes 5 and 9 are rarely represented. Apparently there is a correlation between the organic content and the stratification type of the oil shale. As oil shale increases in organic content, classes 2 and 4 become more abundant and classes 1 and 3 are less so. In the oil shale of the Parachute Creek Member of the two easternmost measured sections, class 1 decreases, whereas classes 2 and 4 increase upward through the sections. The older classes remain approximately the same. These vertical changes correlate with indications of desiccation in the depositional environment in the upper parts of the Parachute Creek Member. Six classes of secondary sedimentary structures are common: (1) loop structure; (2) fault displacement; (3) crystal-growth displacement; (4) bioturbation; (5) contortion; and (6) total disruption. Most of these classes are restricted to oil shale, and loop, fault and crystal-growth types are most abundant. The frequency End_Page 912------------------------------ of occurrence of the secondary structures, like the primary structures, varies with lithology. Crystal-growth disruption (sulfides and carbonate clots) in the oil shale increases with increasing organic content. In a vertical sequence of oil shale in the Parachute Creek Member, crystal-growth disruption of laminae increases upward through the section, and loop and fault structures decrease. Contortion of laminae is almost exclusive to the oil shale, and bioturbation is restricted to claystone and very limy claystone. End_of_Article - Last_Page 913------------

Green River shale-oil yields: correlation with elemental analysis

Abstract A rapid and practical test for oil-shale richness is of considerable technical importance. Although the Fischer-Schrader method has gained universal acceptance for determination of shale richness, there is need to relate results from this determination to fundamental parameters of the shale. One much-used relation is with elemental analysis, and numerous equations have been derived to correlate shale richness with organic carbon content. These relations have been reviewed, and from a number of intensively analysed samples selected from a coring in the Parachute Creek member of the Green River Formation equations relating oil yield by Fischer-Schrader determination to organic carbon content have been developed † oil ( wt %) = 0·8317(% C org ) − 0·2509 and oil (gal/ton) = 2·216(% C org ) − 0·7714 Additionally, more detailed knowledge of the uniformity of organic material throughout the Green River Formation was obtained. It was found that the fraction of kerogen which on pyrolysis yields liquid products is constant stratigraphically throughout the formation, even though the oil composition is not.