Phosphoria Research Articles

Evaluation of the molybdenum isotope system as a petroleum tracer: The Phosphoria petroleum system, western U.S.A.

The molybdenum (Mo) isotope composition of organic-rich mudrocks is used to infer paleo-ocean redox conditions but the potential of this isotope system as a petroleum tracer is uncertain. In this study, we measured the Mo isotope compositions of crude oils, asphaltene separates, and organic-rich source mudrocks (Meade Peak Member and Retort Member of the Permian Phosphoria Formation) for the Phosphoria petroleum system, western U.S.A. Crude oils from the Bighorn Basin have Mo concentrations of 0.01–0.39 μg/g that are significantly lower than Mo concentrations of 10–443 μg/g for the organic-rich mudrocks (2.4–16.6 wt% total organic carbon; TOC), suggesting inefficient transfer of Mo from source rock kerogen to oils. Asphaltene Mo concentrations are elevated (1.0–3.2 μg/g), indicating that asphaltene is an important host of Mo in the Phosphoria crude oils. However, statistically insignificant correlation between crude oil and asphaltene Mo concentrations as well as differences between the δ98Mo of some crude oils and their asphaltene separates (Δ98Moasphaltene–crude oil between −0.5‰ and +0.1‰) suggests other important hosts for Mo in the non-asphaltene fraction of the Phosphoria oils. The overall range of δ98Mo for fifteen Phosphoria crude oils and six asphaltene separates is 0.5–1.7‰ and 0.8–1.5‰, respectively. Crude oils unaltered by reservoir processes (biodegradation, water washing, thermochemical sulfate reduction) have δ98Mo of 1.1–1.4‰ whereas crude oils mildly affected by biodegradation and/or water washing span a wider range of δ98Mo (1.0–1.7‰). Five crude oils altered by thermochemical sulfate reduction (TSR), as indicated by higher δ34S, have lower δ98Mo (0.5–0.9‰), suggesting that TSR decreases the δ98Mo of crude oils via redox reactions and/or the introduction of external fluids containing isotopically light Mo into the oil reservoir. Biodegradation may cause variable δ98Mo in crude oils via kinetic isotope effects, microbial processes, or the recapture of isotopically distinctive Mo released from biodegraded oils elsewhere. A statistically significant inverse correlation between δ98Mo and δ34S for non-TSR altered oils may reflect a decrease in the δ98Mo of crude oils with increasing thermal maturity, perhaps associated with de-metalation reactions and/or formation of new organo-metal compounds. The δ98Mo of the unaltered crude oils falls within the range of δ98Mo for the Mo- and TOC-rich source rocks of the Retort and Meade Peake Members (1.0–2.0‰), suggesting the Mo isotope system has potential as an oil – source rock tracer. This application will have the most success in petroleum systems whose source rock(s) exhibit a narrow range of distinctive δ98Mo. Our study shows the Mo isotope system has promise as a petroleum tracer and potentially could be useful for studies on petroleum contamination in the environment.

Possible Involvement of Permian Phosphoria Formation Oil as a Source of REE and Other Metals Associated with Complex U-V Mineralization in the Northern Bighorn Basin?

The origin of V, U, REE and other metals in the Permian Phosphoria Formation have been speculated and studied by numerous scientists. The exceptionally high concentrations of metals have been interpreted to reflect fundamental transitions from anoxic to oxic marine conditions. Much of the oil in the Bighorn Basin, is sourced by the Phosphoria Formation. Two of the top 10 producing oil fields in Wyoming are located approximately 50 km west of two abandoned U-V mining districts in the northern portion of the basin. These fields produce from basin margin anticlinal structures from Mississippian age reservoir rock. Samples collected from abandoned U-V mines and prospects hosted in Mississippian aged paleokarst in Montana and Wyoming have hydrocarbon residue present and contain anomalous high concentrations of many metals that are found in similar concentrations in the Phosphoria Formation. As, Hg, Mo, Pb, Tl, U, V and Zn, often metals of environmental concern occur in high concentrations in Phosphoria Formation samples and had values ranging from 30–1295 ppm As, 0.179–12.8 ppm Hg, 2–791 ppm Mo, <2–146 ppm Pb, 10–490 ppm Tl, 907–86,800 ppm U, 1240–18,900 ppm V, and 7–2230 ppm Zn, in mineralized samples from this study. The REE plus Y composition of Madison Limestone- and limestone breccia hosted-bitumen reflect similar patterns to both mineralized samples from this study and to U.S. Geological Survey rock samples from studies of the Phosphoria Formation. Geochemical, mineralogical and field data were used to investigate past theories for mineralization of these deposits to determine if U present in home wells and Hg content of fish from rivers on the proximal Crow Indian Reservation may have been derived from these deposits or related to their mode of mineralization.

Spontaneous Imbibition Experiments of Enhanced Oil Recovery with Surfactants and Complex Nano‐Fluids

AbstractTwo types of porous media were analyzed with the intention of exploring alternative enhanced oil recovery methods. Core samples were taken from the Tensleep Formation of the Black Mountain Field in Hot Springs County, WY. The lithology is mainly sandstone and dolomite. The measured effective porosity values ranged from 13.0 to 18.0%, and permeabilities from 19 to 68 md. Production from the Tensleep and Phosphoria formations using conventional methods has resulted in a low secondary recovery factor, possibly due to high capillary forces and an oil‐wet formation. Different surfactants were investigated to determine the viability of a possible enhanced oil recovery process using a spontaneous imbibition process in Amott cells. A very high enhanced recovery factor of more than 89% was achieved using a complex nano‐fluid that consists of a mixture of surfactant, solvent, co‐solvent and water. These recovery factors compared with 13% by brine imbibition and up to 21% using commercial surfactants. At the other end of the scale, very high porosity volcanic pumice was also subjected to the same tests. For this rock the porosity values ranged from 65 to 90% and permeabilities were 2.0–2.7 d. Secondary recovery showed values up to 81% on spontaneous imbibition and up to 91% when surfactants were employed. These experimental results indicate that pumice has favorable reservoir characteristics, but, due to its weak brittle nature, it would not be expected that it could withstand the overburden stress at any significant depth. However, it does represent a useful laboratory specimen.

New U–Pb constraints identify the end-Guadalupian and possibly end-Lopingian extinction events conceivably preserved in the passive margin of North America: implication for regional tectonics

AbstractThe discovery and dating of a volcanic ash bed within the upper Phosphoria Formation in SE Idaho, USA, is reported. The ash occurs 11 m below the top of the phosphatic Meade Peak Member and yielded a 206Pb/238U date of 260.57 ± 0.07 / 0.14 / 0.31 Ma, i.e. latest Capitanian, Guadalupian. The stratigraphic position of this ash near the top of the Meade Peak phosphatic Member of Phosphoria Formation indicates plausible completeness of the sedimentation within the Guadalupian–Lopingian and probably at the Permo-Triassic (P-T) transitions. The new radiometric age reveals that the regional biostratigraphy and palaeontology of Phosphoria and Park City formations requires serious reconsideration, particularly in cool water conodonts, bryozoans and brachiopods. The new age proposes that the Guadalupian–Lopingian boundary (GLB) coincides with the Meade Peak – Rex contact and consequently with the end-Guadalupian extinction event. The lack of a major unconformity at the P-T transition suggests that the effects of the Sonoma orogeny were not as extensive as has been assumed.

Effects of thermal maturation and thermochemical sulfate reduction on compound-specific sulfur isotopic compositions of organosulfur compounds in Phosphoria oils from the Bighorn Basin, USA

Compound-specific sulfur isotope analysis was applied to a suite of 18 crude oils generated from the Permian Phosphoria Formation in the Bighorn Basin, western USA. These oils were generated at various levels of thermal maturity and some experienced thermochemical sulfate reduction (TSR). This is the first study to examine the effects of thermal maturation on stable sulfur isotopic compositions of individual organosulfur compounds (OSCs) in crude oil. A general trend of 34S enrichment in all of the studied compounds with increasing thermal maturity was observed, with the δ34S values of alkyl-benzothiophenes (BTs) tending to be enriched in 34S relative to those of the alkyl-dibenzothiophenes (DBTs) in lower-maturity oils. As thermal maturity increases, δ34S values of both BTs and DBTs become progressively heavier, but the difference in the average δ34S value of the BTs and DBTs (Δ34S BT-DBT) decreases. Differences in the isotopic response to thermal stress exhibited by these two compound classes are considered to be the result of relative differences in their thermal stabilities. TSR-altered Bighorn Basin oils have OSCs that are generally enriched in 34S relative to non-TSR-altered oils, with the BTs being enriched in 34S relative to the DBTs, similar to the findings of previous studies. However, several oils that were previously interpreted to have been exposed to minor TSR have Δ34S BT-DBT values that do not support this interpretation. The δ34S values of the BTs and DBTs in some of these oils suggest that they did not experience TSR, but were derived from a more thermally mature source. The heaviest δ34S values observed in the OSCs are enriched in 34S by up to 10‰ relative to that of Permian anhydrite in the Bighorn Basin, suggesting that there may be an alternate or additional source of sulfate in some parts of the basin. These results indicate that the sulfur isotopic composition of OSCs in oil provides a sensitive indicator for the extent of TSR, which cannot be determined from other bulk geochemical parameters. Moreover, when combined with additional geochemical and geologic evidence, the sulfur isotopic composition of OSCs in oils can help to identify the source of sulfate for TSR alteration in petroleum reservoirs.

Gondolellid conodonts and depositional setting of the Phosphoria Formation

The Phosphoria Formation and related rocks were deposited over an 8.9 m.y. interval beginning approximately 274.0Ma and ending approximately 265.1Ma. The Meade Peak Phosphatic Shale Member was deposited in southeastern Idaho and adjacent Wyoming over 5.4 m.y. from approximately 273.2 to 268.6 Ma. The Retort Phosphatic Shale Member was deposited in southwestern Montana and west-central Wyoming over 1.3 m.y. from approximately 267.4 to 266.1Ma. The base of the Roadian Stage of the Middle Permian occurs within the lower phosphate zone of the Meade Peak. The base of the Wordian Stage occurs within the upper phosphate zone of the Meade Peak. The presence of a cool-water brachiopod fauna, cool-water conodont faunas, and the absence of fusulinids throughout the Phosphoria basin indicate the presence of pervasive cool, upwelling waters. Acritarchs are intimately associated with phosphorites and phosphatic shales and may have been the primary organic producer to help drive phosphate production. The gondolellid conodont fauna of the Phosphoria Formation links a geographic cline of Jinogondolella nankingensis from the Delaware basin, West Texas, to the Sverdrup basin, Canadian Arctic, and shows distinct differentiation in species distribution, as do other conodont groups, within the Phosphoria basin. Ten species and two subspecies of gondolellid conodonts are recognized from the Phosphoria Formation and related rocks that belong to Mesogondolella and Jinogondolella.

Bryozoa of the uppermost Gerster Limestone (late Wordian, Permian), Medicine Range, northeastern Nevada, U.S.A.

Abundant bryozoans occur in the uppermost Gerster Limestone (Permian) in a saddle directly west of the main Medicine Range section of the Gerster Limestone of northeastern Nevada. The stratigraphic position of this shaly limestone is confirmed by the conodont Merrilina praedivergens (late Wordian), which occurs elsewhere in the uppermost Gerster Limestone. Three new genera and five new species of bryozoans have been discovered in this shaly limestone. Subsequent analyses identified the new genera as Autospinifera n. gen., Utgaardostylus n. gen., and Wyseotrypa n. gen. The new species are Autospinifera rossae n. sp., Utgaardostylus stylata n. sp., Wyseotrypa parallela n. sp., Dyscritella triangulara n. sp., and Dyscritellina laminata n. sp. Other species of bryozoans present were previously described from the Russian Far East, Murdock Mountain Formation of the Leach Mountains of northeastern Nevada, Phosphoria Formation of eastern Idaho, and Gerster Limestone of the Medicine Range section of Nevada. This bryozoan fauna represents a late middle-Permian boreal fauna.

Effects of smectite on the oil-expulsion efficiency of the Kreyenhagen Shale, San Joaquin Basin, California, based on hydrous-pyrolysis experiments

The amount of oil that maturing source rocks expel is expressed as their expulsion efficiency, which is usually stated in milligrams of expelled oil per gram of original total organic carbon (). Oil-expulsion efficiency can be determined by heating thermally immature source rocks in the presence of liquid water (i.e., hydrous pyrolysis) at temperatures between 350°C and 365°C for 72 hr. This pyrolysis method generates oil that is compositionally similar to natural crude oil and expels it by processes operative in the subsurface. Consequently, hydrous pyrolysis provides a means to determine oil-expulsion efficiencies and the rock properties that influence them. Smectite in source rocks has previously been considered to promote oil generation and expulsion and is the focus of this hydrous-pyrolysis study involving a representative sample of smectite-rich source rock from the Eocene Kreyenhagen Shale in the San Joaquin Basin of California. Smectite is the major clay mineral (31 wt. %) in this thermally immature sample, which contains 9.4 wt. % total organic carbon (TOC) comprised of type II kerogen. Compared to other immature source rocks that lack smectite as their major clay mineral, the expulsion efficiency of the Kreyenhagen Shale was significantly lower. The expulsion efficiency of the Kreyenhagen whole rock was reduced 88% compared to that of its isolated kerogen. This significant reduction is attributed to bitumen impregnating the smectite interlayers in addition to the rock matrix. Within the interlayers, much of the bitumen is converted to pyrobitumen through crosslinking instead of oil through thermal cracking. As a result, smectite does not promote oil generation but inhibits it. Bitumen impregnation of the rock matrix and smectite interlayers results in the rock pore system changing from water wet to bitumen wet. This change prevents potassium ion () transfer and dissolution and precipitation reactions needed for the conversion of smectite to illite. As a result, illitization only reaches 35% to 40% at 310°C for 72 hr and remains unchanged to 365°C for 72 hr. Bitumen generation before or during early illitization in these experiments emphasizes the importance of knowing when and to what degree illitization occurs in natural maturation of a smectite-rich source rock to determine its expulsion efficiency. Complete illitization prior to bitumen generation is common for Paleozoic source rocks (e.g., Woodford Shale and Retort Phosphatic Shale Member of the Phosphoria Formation), and expulsion efficiencies can be determined on immature samples by hydrous pyrolysis. Conversely, smectite is more common in Cenozoic source rocks like the Kreyenhagen Shale, and expulsion efficiencies determined by hydrous pyrolysis need to be made on samples that reflect the level of illitization at or near bitumen generation in the subsurface.

Evaluation of the rhenium–osmium geochronometer in the Phosphoria petroleum system, Bighorn Basin of Wyoming and Montana, USA

Rhenium–osmium (Re–Os) geochronometry is applied to crude oils derived from the Permian Phosphoria Formation of the Bighorn Basin in Wyoming and Montana to determine whether the radiogenic age reflects the timing of petroleum generation, timing of migration, age of the source rock, or the timing of thermochemical sulfate reduction (TSR). The oils selected for this study are interpreted to be derived from the Meade Peak Phosphatic Shale and Retort Phosphatic Shale Members of the Phosphoria Formation based on oil–oil and oil–source rock correlations utilizing bulk properties, elemental composition, δ13C and δ34S values, and biomarker distributions. The δ34S values of the oils range from −6.2‰ to +5.7‰, with oils heavier than −2‰ interpreted to be indicative of TSR. The Re and Os isotope data of the Phosphoria oils plot in two general trends: (1) the main trend (n=15 oils) yielding a Triassic age (239±43Ma) with an initial 187Os/188Os value of 0.85±0.42 and a mean square weighted deviation (MSWD) of 1596, and (2) the Torchlight trend (n=4 oils) yielding a Miocene age (9.24±0.39Ma) with an initial 187Os/188Os value of 1.88±0.01 and a MSWD of 0.05. The scatter (high MSWD) in the main-trend regression is due, in part, to TSR in reservoirs along the eastern margin of the basin. Excluding oils that have experienced TSR, the regression is significantly improved, yielding an age of 211±21Ma with a MSWD of 148. This revised age is consistent with some studies that have proposed Late Triassic as the beginning of Phosphoria oil generation and migration, and does not seem to reflect the source rock age (Permian) or the timing of re-migration (Late Cretaceous to Eocene) associated with the Laramide orogeny. The low precision of the revised regression (±21Ma) is not unexpected for this oil family given the long duration of generation from a large geographic area of mature Phosphoria source rock, and the possible range in the initial 187Os/188Os values of the Meade Peak and Retort source units. Effects of re-migration may have contributed to the scatter, but thermal cracking and biodegradation likely have had minimal or no effect on the main-trend regression. The four Phosphoria-sourced oils from Torchlight and Lamb fields yield a precise Miocene age Re–Os isochron that may reflect the end of TSR in the reservoir due to cooling below a threshold temperature in the last 10m.y. from uplift and erosion of overlying rocks.The mechanism for the formation of a Re–Os isotopic relationship in a family of crude oils may involve multiple steps in the petroleum generation process. Bitumen generation from the source rock kerogen may provide a reset of the isotopic chronometer, and incremental expulsion of oil over the duration of the oil window may provide some of the variation seen in 187Re/188Os values from an oil family.

Remediation scenarios for selenium contamination, Blackfoot watershed, southeast Idaho, USA

Extensive phosphate mining in the Blackfoot watershed of Idaho (USA) has substantially increased the selenium (Se) concentration in the river during both snowmelt and baseflow when groundwater discharge dominates. Phosphate mines create a linkage between Se-laden shale that occurs in the Phosphoria Formation and the underlying regional Wells Formation aquifer. Using a reconnaissance-level transport model, mines in the watershed were prioritized for remediation and for comparing the results of simulations of remediation scenarios with a baseline of no remediation, for which Se concentration in the river will exceed the aquatic standard along an extensive length. An accurate simulation of recharge distribution around the watershed and simulated flux to the river is essential. Remediation of mines north of the river will substantially decrease the size of the Se plume, although significant Se will continue to discharge to the river. Similarly, remediation of three mines south of the river would decrease the Se discharge to the river but allow substantial amounts to remain stored in the groundwater north and far south of the river. A lack of calibration data is not a reason to forgo remediation, but rather ongoing data collection can be used to fine-tune plans as they are implemented.

Evaluating Re–Os systematics in organic-rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments

Successful application of the 187Re–187Os geochronometer has enabled the determination of accurate and precise depositional ages for organic-rich sedimentary rocks (ORS) as well as establishing timing constraints of petroleum generation. However, we do not fully understand the systematics and transfer behaviour of Re and Os between ORS and petroleum products (e.g., bitumen and oil). To more fully understand the behaviour of Re–Os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks: the Permian Phosphoria Formation (TOC=17.4%; Type II-S kerogen) and the Jurassic Staffin Formation (TOC=2.5%; Type III kerogen). The laboratory-based hydrous pyrolysis experiments were carried out for 72h at 250, 300, 325 and 350°C. These experiments provided us with whole rock, extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of Re–Os isotopic and elemental abundance.The data from these experiments demonstrate that the majority (>95%) of Re and Os are housed within extracted rock and that thermal maturation does not result in significant transfer of Re or Os from the extracted rock into organic phases. Based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of Re and Os than sulphides.Across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187Re/188Os ratios show small variations (3.3% and 4.7%, for Staffin, respectively and 6.3% and 4.9% for Phosphoria, respectively). Similarly, the 187Os/188Os ratios show only minor variations for the Staffin and Phosphoria whole rock and extracted rock samples (0.6% and 1.4% and 1.3% and 2.2%). These isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the Re–Os systematics in ORS as supported by various studies on natural systems.The elemental abundance data reveal limited transfer of Re and Os into the bitumen from a Type III kerogen in comparison to Type II-S kerogen (0.02% vs. 3.7%), suggesting that these metals are very tightly bound in Type III kerogen structure. The 187Os/188Os data from the pyrolysis generated Phosphoria bitumens display minor variation (4%) across the experimental temperatures, with values similar to that of the source rock. This indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation. These data further support the premise that the Os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks.Oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of Re or Os (∼120 and ∼3ppt, respectively), in contrast to natural oils (2–50ppb and 34–288ppt for Re and Os, respectively), which may suggest that kinetic parameters are fundamental to the transfer of Re and Os from source rocks to oils. From this we hypothesise that, at the temperatures employed in hydrous pyrolysis, Re and Os are assimilated into the extracted rock as a result of cross-linking reactions.

Evaluation of Aquifer Diversion After Large Polymer-Gel Water-Shutoff Treatments

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 132978, ’Quantitative Evaluation of Aquifer Diversion to Surrounding Wells After Multiple Large Polymer Gel Water Shutoff Treatments,’ by Ben Turner, SPE, Tiorco, and Jude Nwaozo, SPE, and Brad Funston, SPE, Marathon Oil Company, originally prepared for the 2010 SPE Production and Operations Conference and Exhibition, Tunis, Tunisia, 8-10 June. The paper has not been peer reviewed. From April through August of 2009, seven producing wells in the Spring Creek field in the Big Horn basin of Wyoming were treated with chromium-acetate-crosslinked polyacrylamide in an attempt to reduce water production, lower fluid levels, and achieve greater drawdown, resulting in improved oil production. The wells were chosen because of their high productivity, high water cut, suboptimal operation because of pump limitations, and in some cases, marginal economics. Introduction The Spring Creek field is on the west flank of the Big Horn basin in Park County, Wyoming. Structurally, Spring Creek forms an asymmetrical anticline. The main oil reservoirs in Spring Creek are the Tensleep sandstone (Pennsylvanian) and the Phosphoria formation (Permian). Both the Phosphoria and the Tensleep are connected to prolific aquifers that supply reservoir energy, but also supply a high rate of water. In most wells in the field, both formations are produced and commingled, but in many wells, the Tensleep is so productive that the well is limited in lifting capacity and the Phosporia has not been perforated. The well spacing in the field averages approximately 5 acres. Strategy The operator has an extensive history of shutting off water production by use of chromium-crosslinked polyacrylamide gels. By using chromium acetate as a delayed crosslinker for partially hydrolyzed polyacrylamide, a large volume (as much as 11,500 bbl in this case) can be injected and then allowed to cure for a week. When the gel cures, it reduces the permeability of the fracture and is able to withstand a high differential pressure such as that seen in the near-wellbore region of a producing well. The gel is bullheaded through tubing, with a packer set above the productive formations. Because of the large permeability difference between the fractures and the formation matrix, the gel will penetrate the fractures and significantly reduce the permeability, reducing the water production and fluid level, thus allowing the well to be pumped off and oil production to be increased. This technique has been used quite successfully in several hundred applications throughout the USA.

Selenium and other trace element in phosphorites: A comparison between those of the Bayovar-Sechura and other provenances

Data of trace element composition of phosphorites are scarce and incomplete. Phosphorites of different origins can vary substantially in trace element contents. In this paper 20 trace element concentrations of 35 sample phosphorites are reported. The geographical provenance is: Bayovar-Sechura (Peru), Khouribga, Youssoufia and Boucraa (Morocco), Gafsa (Tunisia), Florida (USA), Idaho and Phosphoria Formation (USA), North Carolina (USA), Algeria, Israel, Senegal, Syria and Togo. Aqua regia extracts were used to estimate the “pseudototal” values, following standard procedures (ISO 11466, 2002) and measured by ICP-AES and ICP-MS. The ratio of medians of trace elements from Sechura versus other provenances, decreases in the following sequence: Co(9) > Mo (3.5) > Mn (2.75) > As (1.65) > Sn (1.21) > Sr (1.16) > Cr, Cu, Ni, Pb (1.02) > Tl (0.86) > Se (0.67) > U (0.53) > Cd, Th (0.5) > V (0.44) > Sb (0.38) > Zn (0.29) > Ag (0.25) > B (0.24). Using multivariate methods we have seen that there are three main clusters: a first group with Phosphoria Formation, Idaho, Youssoufia and Senegal samples; a second group with Sechura phosphorites, enriched in Co and Mo and the third consisting of the remaining samples. The highest trace element enrichment factors in decreasing order are: Cd, 386 (Idaho, USA) > Ag, 78.5 (Idaho, USA) > Se, 73.3 (Youssoufia, Morocco) > U, 46.5 (Israel) > Mo, 43 (Sechura II, Peru) > Cr, 41 (Tobene, Senegal) > B, 11.6 (Khouribga KIIC, Morocco) > Sr, 10.4 (Israel) > Zn, 10.2 (Idaho, USA). Mo enrichment is peculiar to Phosphorites of Sechura. The Permian phosphorites from Idaho and Phosphoria Formation, accumulate Cd, Ag, Se, Zn Sb, V, As, Tl and Cu. The depleted trace element assemblages of Sechura phosphorites are different from the other provenance phosphorites. Selenium and B normality is the main difference between Sechura phosphorites versus the other provenance. The whole of the normal, enriched and depleted trace element in phosphorites, both individually and in assemblages, can be a useful tool such as a discriminating fingerprint in the research of the origin of the phosphorites.

Kinetics of selenium release in mine waste from the Meade Peak Phosphatic Shale, Phosphoria Formation, Wooley Valley, Idaho, USA

Phosphorite from the Meade Peak Phosphatic Shale member of the Permian Phosphoria Formation has been mined in southeastern Idaho since 1906. Dumps of waste rock from mining operations contain high concentrations of Se which readily leach into nearby streams and wetlands. While the most common mineralogical residence of Se in the phosphatic shale is elemental Se, Se(0), Se is also an integral component of sulfide phases (pyrite, sphalerite and vaesite–pyrite ss) in the waste rock. It may also be present as adsorbed selenate and/or selenite, and FeSe 2 and organo-selenides. Se release from the waste rock has been observed in field and laboratory experiments. Release rates calculated from waste rock dump and column leachate solutions describe the net, overall Se release from all of the possible sources of Se listed above. In field studies, Se concentration in seepage water (pH 7.4–7.8) from the Wooley Valley Unit 4 dump ranges from 3600 µg/L in May to 10 µg/L by Sept. Surface water flow, Q, from the seep also declines over the summer, from 2 L/s in May to 0.03 L/s in Sept. Se flux ([Se] ⁎ Q) reaches a steady-state of < 150 mg/day in 1–4 months, depending upon the volume of Q. Se release (mg/L) follows a first order reaction with a rate constant, k , = 1.35 – 6.35e−3 h − 1 (11.8–55.6 yr − 1 ). Laboratory experiments were performed with the waste shale in packed bed reactors; residence time varied from 0.09 to 400 h and outlet pH ∼ 7.5. Here, Se concentration increased with increasing residence time and release was modeled with a first order reaction with k = 2.19e−3 h − 1 (19.2 yr − 1 ). Rate constants reported here fall within an order of magnitude of reported rate constants for oxidation of Se(0) formed by bacterial precipitation. This similarity among rate constants from both field and laboratory studies combined with the direct observation of Se(0) in waste shales of the Phosphoria Formation suggests that oxidation of Se(0) may control steady-state Se concentration in water draining the Wooley Valley waste dump.

A preliminary biogeochemistry-based quantification of primary productivity of end-Permian deep-water basin in Dongpan Section, Guangxi, South China

In this paper, the mean primary productivity of the Talung Formation in the deep-water basin (50–500 m depth) of Dongpan, Guangxi, South China, was calculated, roughly ranging from 0.1 to 0.6 g C·m−2·day−1 on the basis of the content of the trace element Cu. Results showed that the primary productivity obtained was comparable with the previously-reported data for the black shale of the Phosphoria Formation, a Permian phosphate deposit in the northwest United States, and also similar to that of the modern deposit in the Cariaco basin, Venezuela. It was observed that the primary productivity increased with the enhanced abundance of algae and photosynthetic bacteria, and with the decrease in both the radiolarian individuals and the body size of brachiopods during the faunal mass extinction. This ecological coupling indicates that the changes of primary productivity are closely related to the propagation and the decline of producers (algae and bacteria), and that consumers (radiolarians and brachiopods) probably have little influence on the changes of primary productivity.

Sedimentary C org:P ratios, paleocean ventilation, and Phanerozoic atmospheric pO 2

The C org:P ratios of organic-rich facies (TOC > 1%) exhibit considerable variation through the Phanerozoic, from < 10:1 in the Permian Phosphoria Formation to > 1000:1 in some Devonian black shales. Relative to the composition of phytoplankton (C:P ∼ 106:1), which provide the bulk of organic C and P to organic-rich marine sediments, the range of Phanerozoic sedimentary C org:P ratios largely reflects the influence of benthic redox conditions on diagenetic pathways of C and P remobilization. Enhanced preservation of organic C at lower redox potentials combined with enhanced sedimentary retention of remineralized organic P at higher redox potentials results in a strong relationship between benthic redox conditions and sedimentary C org:P ratios. The strong secular coherence of the Phanerozoic C org:P record (i.e., limited variation within narrow time slices) suggests that these ratios are controlled primarily by factors influencing benthic redox conditions on a global scale, such as atmospheric pO 2. Inversion and scaling of the Phanerozoic C org:P record yields a new atmospheric pO 2 model that has strong similarities to existing models based on elemental and isotopic mass balances, yet differs in some potentially significant respects. In particular, the new model suggests that atmospheric pO 2 was markedly lower during the Early to Middle Paleozoic than previously inferred. During most of the Devonian, atmospheric O 2 levels may have been sufficiently low (< 13%) as to prevent the sustained combustion of plant material. This feature of the model may account for an anomalous gap in the fossil charcoal record during the Devonian. The redox-dependent burial of P in the ocean results in positive and negative feedback mechanisms that tend to stabilize atmospheric oxygen concentrations on geologic timescales. Temporal variations in the burial of P relative to C suggest that the strength of these feedback mechanisms varied over the Phanerozoic.

Rare-earth elements in the Permian Phosphoria Formation: Paleo proxies of ocean geochemistry

Abstract The geochemistry of deposition of the Meade Peak Member of the Phosphoria Formation (MPM) in southeast Idaho, USA, a world-class sedimentary phosphate deposit of Permian age that extends over 300,000 km2, is ascertained from its rare earth element (REE) composition. Ratios of REE:Al2O3 suggest two sources—seawater and terrigenous debris. The seawater-derived marine fraction identifies bottom water in the Phosphoria Sea as O2-depleted, denitrifying (suboxic) most of the time, and seldom sulfate-reducing (anoxic). This interpretation is supported by earlier research that showed progressively greater ratios in the marine sediment fraction of Cr:Ni>V:Ni⪢Mo:Ni, relative to their ratios in seawater; for which marine Cr, V, and Mo can have a dominantly O2–depleted bottom-water source and Ni a photic-zone, largely algal, source. The water chemistry was maintained by a balance between bacterial oxidation of organic matter settling through the water column, determined largely by primary productivity in the photic zone, and the flux of oxidants into the bottom water via advection of seawater from the open ocean. Samples strongly enriched in carbonate fluorapatite, the dominant REE host mineral, have variable Er/Sm, Tm/Sm, and Yb/Sm ratios. Their distribution may represent greater advection of seawater between the Phosphoria Sea and open ocean during deposition of two ore zones than a center waste and greater upwelling of nutrient-enriched water into the photic zone. However, the mean rate of deposition of marine Ni, a trace nutrient of algae, and PO43−, a limiting nutrient, indicate that primary productivity was probably high throughout the depositional history. An alternative interpretation of the variable enrichments of Er, Tm, and Yb, relative to Sm, is that they may reflect temporally variable carbonate alkalinity of open-ocean seawater in Permian time. A more strongly negative Ce anomaly for all phosphatic units than the Ce anomaly of modern pelletal phosphate is further indicative of an elevated O2 concentration in the Permo-Carboniferous open ocean, as proposed by others, in contrast to the depletion of O2 in the bottom water of the Phosphoria Sea itself. The oceanographic conditions under which the deposit accumulated were likely similar to conditions under which many sedimentary phosphate deposits have accumulated and to conditions under which many black shales that are commonly phosphate poor have accumulated. A shortcoming of several earlier studies of these deposits has resulted from a failure to examine the marine fraction of elements separate from the terrigenous fraction.

Artificial Intelligence Used to Evaluate 23 Single-Well Surfactant-Soak Treatments

Summary Following a series of laboratory imbibition-cell experiments, field tests were conducted to determine the effectiveness of surfactant-soak treatments as a single-well enhanced-oil-recovery (EOR) technique. The tests were conducted in the dolomite interval of the Phosphoria formation. Artificial intelligence was applied to analyze the mixed test results. The analysis suggested that the gamma ray log can be used to predict results and that a minimum amount of surfactant is required to improve production.

Life Cycle of the Phosphoria Formation--From Deposition to the Post-Mining Environment.: J. R. HEIN, EDITOR. Pp. 635. Amsterdam, Elsevier. 2004. ISBN 0-444-51132-6. Price: $250.

The Permian Phosphoria Formation and associated rocks are a major source of phosphate and are important petroleum source and reservoir rocks in the western United States. This volume contains 22 papers that summarize the state of understanding of the Phosphoria Formation that, due to its importance as a primary source of economic phosphate, focus on the Meade Peak member. The Phosphoria Formation, however, is not only comprised of the phosphate and organic matter-rich Meade Peak member, but also includes the spiculitic Rex Chert, the organic matter- and phosphate-rich Retort, and the silty and spiculitic Tosi Chert members. These rock units are interbedded with rocks of the carbonate-dominated Park City Formation. Sedimentary phosphate is an important source of phosphorus and is usually interpreted to result from oceanic up-welling-driven marine productivity. Most ancient deposits are found in epicontinental settings, and may or may not be associated with significant organic-rich and siliceous sediments. The Phosphoria Formation was deposited in an epicontinental embayment on a paleoshelf that was almost flat; the angle of the paleoshelf ranged from 0.04° to 0.22°. The very low angle of the paleoshelf and the epicontinental setting have important implications for models of ancient phosphate deposit formation. The Phosphoria Formation spans a temporal transition between two radically different global climate regimes. Low CO …

Sedimentary environments of the Middle Permian phosphorite–chert complex from the northeastern Yangtze platform, China; the Gufeng Formation: a continental shelf radiolarian chert

Radiolarian chert deposited on a continental shelf occurs in the Middle Permian Gufeng Formation on the northeastern Yangtze platform, China. The sedimentary environments of radiolarian cherts from accretionary complexes have been well studied; however, there are few studies about radiolarian chert deposited on continental shelves. Therefore we have completed a sedimentological and geochemical study of the Gufeng Formation. The Gufeng Formation is subdivided into the Phosphate Nodule-bearing Mudstone Member (PNMM) and the Siliceous Rock Member (SRM) in ascending order. The basal PNMM consists of glauconite-bearing mudstone, which indicates deposition under aerobic shallow-marine conditions, whereas the upper PNMM is composed of mudstone including abundant phosphate nodules, suggesting deposition near the outer shelf in suboxic conditions. The SRM consists mainly of alternating beds of black chert, mudstone, and siliceous mudstone, with minor tuffaceous mudstone and porous chert beds. The black chert contains abundant radiolarians, sponge spicules, and organic matter. Framboidal pyrite occurs in the black chert. Porous chert in the SRM includes abundant rhombohedral cavities, which are dolomite moulds surrounded by quartz, suggesting dolomitization before silicification during early diagenesis. The Gufeng Chert is characterized by high Si, Mo, Ni, Cu, and Zn contents, and extremely low Mn content. The Gufeng Chert has high normal paraffin concentrations with petroleum-like markers. These geochemical features suggest that the Gufeng Chert was deposited under sulfate-reducing conditions; and is not hydrothermal, but rather biogenic in origin. The sedimentological and geochemical data suggest that the Gufeng Formation was deposited mainly on the outer shelf in suboxic–anoxic conditions caused by organic matter produced during upwelling. The upwelling probably led to high radiolarian productivity. Abundant silica and organic matter were deposited in the Gufeng basin. Compared with chert from other sites, the Gufeng Chert shows many similarities with chert from platformal basins, but not with chert from accretionary complexes. Especially, with respect to age, rock type, stratigraphy, and geochemical features, the chert of the Gufeng Formation is similar to that of the Phosphoria Formation in the western U.S.A., which is a world-class phosphorite giant. These similarities suggest that upwelling occurred around the eastern margins of Panthalassa and the Paleotethys concurrently during the Middle Permian. In general, shelf-type radiolarian chert, represented by the Gufeng Chert, usually shows some of the following features: dark color, lack of rhythmical bedding, association with phosphorite, platformal limestone, felsic tuff, abundant organic matter, and sulfides. Shelf-type radiolarian chert is deposited in a poorly aerated restricted basin, or in an oxygen-minimum zone.