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Effects of radiation exposure on indicators of thermal maturity
Org. Geochem.Vol. 5, No. 4, pp. 183-186, 1984 Printed in Great Britain
0146-6380/84 $3.00+ 0.00 Pergamon Press Ltd
Effects of radiation exposure on indicators of thermal maturity ROGER SASSEN Exploration and Production Research Center, Getty Oil Company, Houston, TX 77042, U.S.A.
(Received 24 June 1983; accepted 12 September 1983) Abstract--Study of fossil wood samples with varying contents of uranium suggests that radiation exposure over geologic time results in alteration of vitrinite. The alteration is shown by increased reflectance of vitrinite, increased values of Thermal Alteration Index, decreased atomic H/C ratios, and by loss of fluorescence. Each of these parameters is used to estimate the thermal maturity of kerogen. Unless recognized during interpretation of analytical results, radiation damage of vitrinite results in overestimation of thermal maturity.
INTRODUCTION A primary application of thermal maturity studies on kerogen is to assist in identification of effective source rocks for petroleum. Vitrinite reflectance and other indicators of thermal maturity have been used to estimate the time-temperature exposure of organic matter in sediments. Factors other than time and temperature that influence the reflectance and other properties of vitrinite are of interest to petroleum geochemists. Increased reflectance as well as other chemical and physical changes within coals have been observed as a consequence of radiation from decay of uranium and daughter products (Teichmiiller and Teichmiiller, 1958; Jedwab, 1965; Breger, 1974). The present study focuses on uraniferous fossil wood in which alteration of vitrinite has been particularly extensive.
Jurassic or Early Cretaceous (Lee and Brookins, 1978). At the location of the Poison Canyon Mine, deposition of coflinite (USiO4) and other minerals occurred in reducing microenvironments associated with terrestrial organic matter (Tessendorf, 1980). It should be emphasized that changes in the distribution and mineralogy of uranium have occurred over geologic time. Fracturing related to formation of the Zuni uplift in the Late Cretaceous permitted access by mildly oxidizing solutions that redistributed much of the primary coffinite (Rapaport, 1963). A second and more intense phase of redistribution occurred as a consequence of erosional unroofing during the Pleistocene (Tessendorf, 1980). The occurrence of tyuyamunite [Ca(UO2)2(VO4)2.5-8H20] characterized this final phase of mineralization. Where redistribution has taken place, uranium is no longer in equilibrium with daughter products.
GEOLOGY AND MINERALOGY
EXPERIMENTAL PROCEDURE
The Grants mineral belt of northwestern New Mexico consists of a linear trend of uranium deposits along the southern margin of the San Juan Basin. Up to 2000 m of sediments are present in the basin that range in age from Pennsylvanian to Cretaceous. Nearly all ore deposits have been found in fluvial sandstones of Late Jurassic age in which terrestrial organic matter has played a role in accumulation of uranium (Breger, 1974). The present study concerns itself with samples of uraniferous fossil logs from the now-inactive Poison Canyon Mine in McKinley County, part of the Ambrosia Lake ore district. There, uraniferous logs occur in a sandstone ore body of the Brushy Basin member of the Upper Jurassic Morrison Formation. Locally, this unit is known as the Poison Canyon sandstone. Timing of mineralization is not known with certainty, but appears to have taken place in the Late 183
Samples Discrete coalified logs with varying contents of uranium were collected by the author at the Poison Canyon Mine. Care was taken to collect only authentic woody material. The logs had been buried simultaneously during the Late Jurassic, as shown by their clustered distribution along less than 3 m of a single bedding surface of the Poison Canyon sandstone. On this basis, all fossil wood samples have experienced the same time-temperature history since burial.
Analytical approach Vitrinite of fossil wood was isolated from mineral matter by treatment with HCI and HF. Measurements of mean vitrinite reflectance and observations of fluorescence were performed using a Zeiss Model 01K microscope photometer equipped with a IIIRS vertical illuminator. Aliquots of isolates were also
184
R o G ~ S,~SSEN
used for estimates of Thermal Alteration Index (TAI) in transmitted light. In addition, polished sections of mineralized fossil wood were examined in reflected light. Uranium contents of samples were determined by standard fluorimetric techniques. A scanning electron microscope (AMRAY Model 1200) equipped with an energy dispersive X-ray analysis system (Kevex Corp.) was used for investigation of fossil wood and identification of associated minerals. Elemental analysis of fossil wood samples was carried out by Geochem Laboratories, Inc. (Houston, Texas). RESULTS AND DISCUSSION
2.0
~
8 g
~ 10-
>
g
/ D~ Q . o
F 05
:g
0.2 -
Maceral analysis 0.0
There are no great differences in maceral composition between samples. Macerals of the vitrinite group are the major components of each sample. Both telinite (wood tissue) and collinite (amorphous gel) are present within the vitrinite fractions. Trace amounts of fungal spores and exinite were noted in some samples.
Uranium contents and physical properties All fossil wood samples are characterized by relatively high contents of uranium (Table 1). However, measured uranium contents of samples occur in two groups that correspond to color of fossil wood in hand specimen and to mineralogy. Brown, friable woody material displays a remnant vascular structure and is characterized by total uranium contents in the 2.95-5.40% range. Brown fossil wood appears to mainly contain dispersed coffinite of poor crystallinity. Black fossil wood is harder, denser, and richer in uranium (15.50-19.50%). The occurrence of uranium minerals in black fossil wood is apparent to the unaided eye. Although not all uranium minerals in black fossil wood could be identified, tyuyamunite is the major component. The secondary mineral occurs as greenish-yellow concentrations in voids and fractures of the black logs.
Increased vitrinite reflectance Increased reflectance as a result of radiation damage from uranium decay has been observed as microscopic halos surrounding discrete uranium minerals in coals (Teichm/iller and Teichmiiller, 1958; Jedwab,
I 5.0
I I 10.0 15,0 % Uranium
I 20.0
Fig. 1. Plot of me a n vitrinite reflectance and ura ni um content of fossil wood samples. Higher contents of ura ni um are associated with enhanced reflectances of vitrinite.
1965; Breger, 1974). In these examples, radiation damage has been localized to the immediate vicinity of the source and the bulk of the coal remains unaltered. However, the increased reflectance from radiation effects is much more extensive in the highly mineralized samples from the Poison Canyon Mine. Examination of polished sections of highly mineralized samples reveals large coalescent areas of enhanced reflectance rather than isolated halos. Samples of fossil wood with higher uranium contents display increased vitrinite reflectance. Mean vitrinite reflectance and uranium contents are plotted in Fig. 1. The vitrinite reflectance histograms are shown in Fig. 2. In brown logs with lower uranium contents, mean reflectance ranges from 0.41% to as high as 0.54%. Since all samples have probably been altered to some extent, the lowest mean reflectance (0.41%) provides the best estimate of thermal maturity. The black fossil wood samples with higher uranium contents are characterized by significantly higher mean reflectance values (0.63-0.82%), falsely implying more advanced thermal maturity. Given that the maceral compositions and burial histories of the wood samples are identical, the differences measured in mean vitrinite reflectance are attributed to the effects of radiation damage over geologic time.
Table 1. Summary of geochemical data on uraniferous fossil wood samples from the Poison Canyon Mine Sample No.
Color of hand specimen
Dominant mineral
Mean vitrinite reflectance
Number of measurements
PCM-I PCM-2 PCM-3 PCM-4 PCM-5 PCM-6 PCM-7 PCM-8
Brown Brown Brown Brown Black Black Black Black
Coflinite Coflinite Coflinite Coffinite Tyuyamunite Tyuyamunite Tyuyamunite Tyuyamunite
0.41 + 0.06 0.50 -1-0.16 0.48 4- 0.04 0.54 4- 0.05 0.81 ± 0.16 0.82 :t: 0.12 0.78 _+0.1 i 0.63 4- 0.12
100 100 100 100 100 98 I00 99
TAt
% Uranium
% Organic carbon
Atomic H/C ratio
3.0 3.0 3.0 3.0 4.0 4.0 4.0 4.0
4.70 2.95 5.40 4.70 15.50 19.50 18.50 16.87
27.5 19.4 24.7 23.9 38.8 40.5 27.9 39.5
1.00 0.80 0.78 0.75 0.65 0.59 0.65 0.63
Radiation effects on indicators of thermal maturity
185
25 20
.~M-1 )
)=041
PCM-3
PCM-4
'~o = 0 . 4 8
RO = 0.54
15 10 5
~¢,-
o
I
O0
1.0
0.0
1.0
0.0
1.0
0.0
1.0
o"
20
PCM-5
PCM- 6
PCM-7
PCM - 8
I0
5 0
I
0.0
1.0
I
0,0
1.0
0.0
1.0
0.0
1.0
% Reflectance
Fig. 2. Vitrinite reflectance histograms of uraniferous fossil wood. The exceptionally high concentrations of uranium in samples PCM-5 through -8 (l 5.50-19.50% ) have resulted in extensive alteration of vitrinite.
Increased thermal alteration index Increasing time--temperature exposure results in gradual change in color and translucency of organic matter in transmitted light (Staplin, 1969). TAI is based on the progressive shift in color of organic matter from yellow to brown and finally to black at advanced levels of thermal maturity. As noted above, the mean vitrinite reflectance of 0.41~o probably provides the truest estimate of thermal maturity for Poison Canyon Mine samples. This value implies that the color of uraniferous organic matter in transmitted light should be yellow, corresponding to a TAI in the 2-2.5 range (Hrroux et al., 1979). However, samples are characterized by higher TAI values than would be predicted (Table 1). Indeed, the highly mineralized black fossil wood displays a black color in transmitted light that is nor-
mally associated with a TAI of 4, suggesting incorrectly that the fossil wood has experienced advanced levels of thermal maturity.
Radiochemical dehydrogenation The research summarized by Breger (1974) shows that increased reflectance of uraniferous logs is accompanied by loss of hydrogen. This progressive dehydrogenation mimics the effects of increasing thermal maturity. Radiochemical dehydrogenation has evidently also occurred in samples from the Poison Canyon Mine. Atomic H/C ratios vary widely and were measured in the 0.59-1.00 range. As shown in Fig. 3, increasing reflectance of vitrinite is related to decreasing atomic H/C ratio. Although vitrinite reflectance continues to increase, radiation appears to be less effective as an agent of hydrogen loss at higher doses.
LOSS of fluorescence The brown fossil wood with lower uranium contents shows some weak yellow and dark brown fluorescence of organic matter. However, no fluorescence could be detected in the organic matter of black fossil wood with higher uranium contents. Once again, the data imply wide differences in thermal maturity that are unlikely to exist.
08
8 -~ 0 7
,~ 0 6
g
0.5
,<
CONCLUSIONS
04
10
09
08 Atomic H / C
0?
06
rotio
Fig. 3. Plot of mean vitrinite reflectance and atomic H/C ratios of fossil wood samples. Although reflectance continues to increase, radiation appears to be less effective as an agent of hydrogen loss at higher doses. O.G. 51~--B
This study contributes evidence that radiation exposure over geologic time results in alteration of vitrinite. The radiation-induced alteration of vitrinite evolves along pathways that resemble the effects of increasing thermal maturity.
186
Roolm SASSEN
Acknowledgements--The writer wishes to express his debt of gratitude to the late Dr Irving A. Breger, a debt that encompasses twenty years of association. This paper represents the last research that we discussed together. In addition, the organic petrographic work carried out by Dr Pieter van Gijzel of Getty Oil Company is appreciated. The writer also wishes to thank the Getty Oil Company for permission to publish this paper.
REFERENCES
Breger I. A. (1974) The role of organic matter in the accumulation of uranium: The organic geochemistry of the coal-uranium association. In Formation of Uranium Ore Deposits, pp. 99-124. International Atomic Energy Agency, Vienna. H6roux Y., Changnon A. and Bertrand R. (1979) Compilation and correlation of major thermal maturation indicators. Bull. Am. Assoc. Pet. Geol. 63, 2128-2144. Jedwab J. (1965) Les d6gats radiatifs dan le charbon uranif~re du Schaentzel. Geol. Runsch. 55, 445-453.
Lee M. J. and Brookins D. G. (1978) Rubidium-strontium minimum ages of sedimentation, uranium mineralization, and provenance, Morrison Formation (Upper Jurassic), Grants mineral belt, New Mexico. Bull. Am. Assoc. Pet. Geol. 62, 1673-1683. Rapaport I. (1963) Uranium deposits of the Poison Canyon ore trend, Grants district. In Geology and Technology of the Grants Region (Edited by Kelley V. C.), pp. 122-135. New Mexico Bureau of Mines and Mineral Resources Mem. 15. Staplin F. L. (1969) Sedimentary organic matter, organic metamorphism, and oil and gas occurrence. Bull. Can. Petrol. Geol. 17, 47--66. Teichmiiller M. and Teichmfiller R. (1958) Inkohlungsuntersuchungen und ihre natzanwendung. Geol. En Mijnb. 20, 41-66. Tessendorf T. N. (1980) Redistributed ore bodies of Poison Canyon Sec. 18 and 19. T.13N., R.9W., McKinley County. In Geology and Mineral Technology of the Grants Uranium Region (Edited by Rautman C. A.), pp. 226-229. New Mexico Bureau of Mines and Mineral Resources Mem. 38.
0146-6380/84 $3.00+ 0.00 Pergamon Press Ltd
Effects of radiation exposure on indicators of thermal maturity ROGER SASSEN Exploration and Production Research Center, Getty Oil Company, Houston, TX 77042, U.S.A.
(Received 24 June 1983; accepted 12 September 1983) Abstract--Study of fossil wood samples with varying contents of uranium suggests that radiation exposure over geologic time results in alteration of vitrinite. The alteration is shown by increased reflectance of vitrinite, increased values of Thermal Alteration Index, decreased atomic H/C ratios, and by loss of fluorescence. Each of these parameters is used to estimate the thermal maturity of kerogen. Unless recognized during interpretation of analytical results, radiation damage of vitrinite results in overestimation of thermal maturity.
INTRODUCTION A primary application of thermal maturity studies on kerogen is to assist in identification of effective source rocks for petroleum. Vitrinite reflectance and other indicators of thermal maturity have been used to estimate the time-temperature exposure of organic matter in sediments. Factors other than time and temperature that influence the reflectance and other properties of vitrinite are of interest to petroleum geochemists. Increased reflectance as well as other chemical and physical changes within coals have been observed as a consequence of radiation from decay of uranium and daughter products (Teichmiiller and Teichmiiller, 1958; Jedwab, 1965; Breger, 1974). The present study focuses on uraniferous fossil wood in which alteration of vitrinite has been particularly extensive.
Jurassic or Early Cretaceous (Lee and Brookins, 1978). At the location of the Poison Canyon Mine, deposition of coflinite (USiO4) and other minerals occurred in reducing microenvironments associated with terrestrial organic matter (Tessendorf, 1980). It should be emphasized that changes in the distribution and mineralogy of uranium have occurred over geologic time. Fracturing related to formation of the Zuni uplift in the Late Cretaceous permitted access by mildly oxidizing solutions that redistributed much of the primary coffinite (Rapaport, 1963). A second and more intense phase of redistribution occurred as a consequence of erosional unroofing during the Pleistocene (Tessendorf, 1980). The occurrence of tyuyamunite [Ca(UO2)2(VO4)2.5-8H20] characterized this final phase of mineralization. Where redistribution has taken place, uranium is no longer in equilibrium with daughter products.
GEOLOGY AND MINERALOGY
EXPERIMENTAL PROCEDURE
The Grants mineral belt of northwestern New Mexico consists of a linear trend of uranium deposits along the southern margin of the San Juan Basin. Up to 2000 m of sediments are present in the basin that range in age from Pennsylvanian to Cretaceous. Nearly all ore deposits have been found in fluvial sandstones of Late Jurassic age in which terrestrial organic matter has played a role in accumulation of uranium (Breger, 1974). The present study concerns itself with samples of uraniferous fossil logs from the now-inactive Poison Canyon Mine in McKinley County, part of the Ambrosia Lake ore district. There, uraniferous logs occur in a sandstone ore body of the Brushy Basin member of the Upper Jurassic Morrison Formation. Locally, this unit is known as the Poison Canyon sandstone. Timing of mineralization is not known with certainty, but appears to have taken place in the Late 183
Samples Discrete coalified logs with varying contents of uranium were collected by the author at the Poison Canyon Mine. Care was taken to collect only authentic woody material. The logs had been buried simultaneously during the Late Jurassic, as shown by their clustered distribution along less than 3 m of a single bedding surface of the Poison Canyon sandstone. On this basis, all fossil wood samples have experienced the same time-temperature history since burial.
Analytical approach Vitrinite of fossil wood was isolated from mineral matter by treatment with HCI and HF. Measurements of mean vitrinite reflectance and observations of fluorescence were performed using a Zeiss Model 01K microscope photometer equipped with a IIIRS vertical illuminator. Aliquots of isolates were also
184
R o G ~ S,~SSEN
used for estimates of Thermal Alteration Index (TAI) in transmitted light. In addition, polished sections of mineralized fossil wood were examined in reflected light. Uranium contents of samples were determined by standard fluorimetric techniques. A scanning electron microscope (AMRAY Model 1200) equipped with an energy dispersive X-ray analysis system (Kevex Corp.) was used for investigation of fossil wood and identification of associated minerals. Elemental analysis of fossil wood samples was carried out by Geochem Laboratories, Inc. (Houston, Texas). RESULTS AND DISCUSSION
2.0
~
8 g
~ 10-
>
g
/ D~ Q . o
F 05
:g
0.2 -
Maceral analysis 0.0
There are no great differences in maceral composition between samples. Macerals of the vitrinite group are the major components of each sample. Both telinite (wood tissue) and collinite (amorphous gel) are present within the vitrinite fractions. Trace amounts of fungal spores and exinite were noted in some samples.
Uranium contents and physical properties All fossil wood samples are characterized by relatively high contents of uranium (Table 1). However, measured uranium contents of samples occur in two groups that correspond to color of fossil wood in hand specimen and to mineralogy. Brown, friable woody material displays a remnant vascular structure and is characterized by total uranium contents in the 2.95-5.40% range. Brown fossil wood appears to mainly contain dispersed coffinite of poor crystallinity. Black fossil wood is harder, denser, and richer in uranium (15.50-19.50%). The occurrence of uranium minerals in black fossil wood is apparent to the unaided eye. Although not all uranium minerals in black fossil wood could be identified, tyuyamunite is the major component. The secondary mineral occurs as greenish-yellow concentrations in voids and fractures of the black logs.
Increased vitrinite reflectance Increased reflectance as a result of radiation damage from uranium decay has been observed as microscopic halos surrounding discrete uranium minerals in coals (Teichm/iller and Teichmiiller, 1958; Jedwab,
I 5.0
I I 10.0 15,0 % Uranium
I 20.0
Fig. 1. Plot of me a n vitrinite reflectance and ura ni um content of fossil wood samples. Higher contents of ura ni um are associated with enhanced reflectances of vitrinite.
1965; Breger, 1974). In these examples, radiation damage has been localized to the immediate vicinity of the source and the bulk of the coal remains unaltered. However, the increased reflectance from radiation effects is much more extensive in the highly mineralized samples from the Poison Canyon Mine. Examination of polished sections of highly mineralized samples reveals large coalescent areas of enhanced reflectance rather than isolated halos. Samples of fossil wood with higher uranium contents display increased vitrinite reflectance. Mean vitrinite reflectance and uranium contents are plotted in Fig. 1. The vitrinite reflectance histograms are shown in Fig. 2. In brown logs with lower uranium contents, mean reflectance ranges from 0.41% to as high as 0.54%. Since all samples have probably been altered to some extent, the lowest mean reflectance (0.41%) provides the best estimate of thermal maturity. The black fossil wood samples with higher uranium contents are characterized by significantly higher mean reflectance values (0.63-0.82%), falsely implying more advanced thermal maturity. Given that the maceral compositions and burial histories of the wood samples are identical, the differences measured in mean vitrinite reflectance are attributed to the effects of radiation damage over geologic time.
Table 1. Summary of geochemical data on uraniferous fossil wood samples from the Poison Canyon Mine Sample No.
Color of hand specimen
Dominant mineral
Mean vitrinite reflectance
Number of measurements
PCM-I PCM-2 PCM-3 PCM-4 PCM-5 PCM-6 PCM-7 PCM-8
Brown Brown Brown Brown Black Black Black Black
Coflinite Coflinite Coflinite Coffinite Tyuyamunite Tyuyamunite Tyuyamunite Tyuyamunite
0.41 + 0.06 0.50 -1-0.16 0.48 4- 0.04 0.54 4- 0.05 0.81 ± 0.16 0.82 :t: 0.12 0.78 _+0.1 i 0.63 4- 0.12
100 100 100 100 100 98 I00 99
TAt
% Uranium
% Organic carbon
Atomic H/C ratio
3.0 3.0 3.0 3.0 4.0 4.0 4.0 4.0
4.70 2.95 5.40 4.70 15.50 19.50 18.50 16.87
27.5 19.4 24.7 23.9 38.8 40.5 27.9 39.5
1.00 0.80 0.78 0.75 0.65 0.59 0.65 0.63
Radiation effects on indicators of thermal maturity
185
25 20
.~M-1 )
)=041
PCM-3
PCM-4
'~o = 0 . 4 8
RO = 0.54
15 10 5
~¢,-
o
I
O0
1.0
0.0
1.0
0.0
1.0
0.0
1.0
o"
20
PCM-5
PCM- 6
PCM-7
PCM - 8
I0
5 0
I
0.0
1.0
I
0,0
1.0
0.0
1.0
0.0
1.0
% Reflectance
Fig. 2. Vitrinite reflectance histograms of uraniferous fossil wood. The exceptionally high concentrations of uranium in samples PCM-5 through -8 (l 5.50-19.50% ) have resulted in extensive alteration of vitrinite.
Increased thermal alteration index Increasing time--temperature exposure results in gradual change in color and translucency of organic matter in transmitted light (Staplin, 1969). TAI is based on the progressive shift in color of organic matter from yellow to brown and finally to black at advanced levels of thermal maturity. As noted above, the mean vitrinite reflectance of 0.41~o probably provides the truest estimate of thermal maturity for Poison Canyon Mine samples. This value implies that the color of uraniferous organic matter in transmitted light should be yellow, corresponding to a TAI in the 2-2.5 range (Hrroux et al., 1979). However, samples are characterized by higher TAI values than would be predicted (Table 1). Indeed, the highly mineralized black fossil wood displays a black color in transmitted light that is nor-
mally associated with a TAI of 4, suggesting incorrectly that the fossil wood has experienced advanced levels of thermal maturity.
Radiochemical dehydrogenation The research summarized by Breger (1974) shows that increased reflectance of uraniferous logs is accompanied by loss of hydrogen. This progressive dehydrogenation mimics the effects of increasing thermal maturity. Radiochemical dehydrogenation has evidently also occurred in samples from the Poison Canyon Mine. Atomic H/C ratios vary widely and were measured in the 0.59-1.00 range. As shown in Fig. 3, increasing reflectance of vitrinite is related to decreasing atomic H/C ratio. Although vitrinite reflectance continues to increase, radiation appears to be less effective as an agent of hydrogen loss at higher doses.
LOSS of fluorescence The brown fossil wood with lower uranium contents shows some weak yellow and dark brown fluorescence of organic matter. However, no fluorescence could be detected in the organic matter of black fossil wood with higher uranium contents. Once again, the data imply wide differences in thermal maturity that are unlikely to exist.
08
8 -~ 0 7
,~ 0 6
g
0.5
,<
CONCLUSIONS
04
10
09
08 Atomic H / C
0?
06
rotio
Fig. 3. Plot of mean vitrinite reflectance and atomic H/C ratios of fossil wood samples. Although reflectance continues to increase, radiation appears to be less effective as an agent of hydrogen loss at higher doses. O.G. 51~--B
This study contributes evidence that radiation exposure over geologic time results in alteration of vitrinite. The radiation-induced alteration of vitrinite evolves along pathways that resemble the effects of increasing thermal maturity.
186
Roolm SASSEN
Acknowledgements--The writer wishes to express his debt of gratitude to the late Dr Irving A. Breger, a debt that encompasses twenty years of association. This paper represents the last research that we discussed together. In addition, the organic petrographic work carried out by Dr Pieter van Gijzel of Getty Oil Company is appreciated. The writer also wishes to thank the Getty Oil Company for permission to publish this paper.
REFERENCES
Breger I. A. (1974) The role of organic matter in the accumulation of uranium: The organic geochemistry of the coal-uranium association. In Formation of Uranium Ore Deposits, pp. 99-124. International Atomic Energy Agency, Vienna. H6roux Y., Changnon A. and Bertrand R. (1979) Compilation and correlation of major thermal maturation indicators. Bull. Am. Assoc. Pet. Geol. 63, 2128-2144. Jedwab J. (1965) Les d6gats radiatifs dan le charbon uranif~re du Schaentzel. Geol. Runsch. 55, 445-453.
Lee M. J. and Brookins D. G. (1978) Rubidium-strontium minimum ages of sedimentation, uranium mineralization, and provenance, Morrison Formation (Upper Jurassic), Grants mineral belt, New Mexico. Bull. Am. Assoc. Pet. Geol. 62, 1673-1683. Rapaport I. (1963) Uranium deposits of the Poison Canyon ore trend, Grants district. In Geology and Technology of the Grants Region (Edited by Kelley V. C.), pp. 122-135. New Mexico Bureau of Mines and Mineral Resources Mem. 15. Staplin F. L. (1969) Sedimentary organic matter, organic metamorphism, and oil and gas occurrence. Bull. Can. Petrol. Geol. 17, 47--66. Teichmiiller M. and Teichmfiller R. (1958) Inkohlungsuntersuchungen und ihre natzanwendung. Geol. En Mijnb. 20, 41-66. Tessendorf T. N. (1980) Redistributed ore bodies of Poison Canyon Sec. 18 and 19. T.13N., R.9W., McKinley County. In Geology and Mineral Technology of the Grants Uranium Region (Edited by Rautman C. A.), pp. 226-229. New Mexico Bureau of Mines and Mineral Resources Mem. 38.