Open-File Report 2007-1360

U.S. Department of the Interior

U.S. Geological Survey

Characterization of Petroleum Residue in the

Entrada Sandstone, Colorado National Monument
Characterization of Petroleum Residue in the 

Entrada Sandstone, Colorado National Monument 

By Paul G. Lillis and J. David King 

Open-File Report 2007-1360 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

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Suggested citation: 

Lillis, P.G., and King, J.D., 2007, Characterization of petroleum residue in the Entrada 

Sandstone, Colorado National Monument: U.S. Geological Survey Open-File Report 2007-1360, 

18 p. 

2
Characterization of Petroleum Residue in the 

Entrada Sandstone, Colorado National Monument 

By Paul G. Lillis and J. David King 

Introduction 

As part of the U.S. Geological Survey’s (USGS) petroleum resource assessment of the 

Uinta-Piceance Province, Colorado and Utah, in 2000 (USGS Uinta-Piceance Assessment Team, 

2003), some 170 oils, oil stains, and oil seeps were geochemically characterized and divided into 

genetic types (Lillis and others, 2003). Recognized oil types include Minturn, Phosphoria, 

Grassy Trail Creek, Mancos, Mesaverde, and Green River. Subsequent to that study, the 

existence and general locality of petroleum residue in the Middle Jurassic Entrada Sandstone in 

Colorado National Monument (CNM) was brought to the attention of the authors (Scott and 

others, 2001). Because the analysis of such non-commercial petroleum deposits commonly 

yields valuable regional resource-trend information, we collected and characterized the reported 

CNM petroleum residue and compared the results with identified oil types in the Uinta-Piceance 

Province. 

Three samples of Entrada Sandstone with petroleum residue (table 1) were collected near 

Little Park Road along the south edge of the CNM in sec.20, T.12S., R.101W. (fig. 1). The 

approximate extent of the petroleum staining was determined by field testing with solvent, and 

the stains appear to be restricted to the upper part of the “board beds” unit (informal name, Scott 

and others, 2001) of the Entrada Sandstone between the two fault traces of the Glade Park fault 

(figs. 2, 3). 

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Figure 1. Map of the Colorado National Monument showing the petroleum residue sample 

area (modified from the National Park Service). 

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Figure 2. Dark petroleum residue is observed in the pore space of the upper part of the 

“board beds” unit (informal name, Scott and others, 2001) of the Entrada Sandstone. 

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Figure 3. Photograph of outcrop at head of No Thoroughfare Canyon, looking west, showing sampled area in the “board beds” unit of the Entrada Sandstone between south and north 

fault traces of the Glade Park Fault (in red). 

Table 1. Bulk geochemical data of petroleum residue in the Jurassic Entrada Formation, 

Colorado National Monument. 

[EOM, extractable organic matter (ppm, weight/weight); S/A, saturated hydrocarbons/aromatic hydrocarbons ratio; S wt%, sulfur 

weight percent; δ13Cs, stable carbon isotopes, C15+ saturated hydrocarbons, per mil, PDB; δ13Ca, stable carbon isotopes, C15+

aromatic hydrocarbons, per mil, PDB; CV, canonical variable (Sofer, 1984) equal to -2.53 δ13Cs + 2.22 δ13Ca – 11.65; δ13Cb, 

stable carbon isotopes, C15+ whole extract, per mil, PDB; ---, no data] 

Sample No. Sample Name EOM S/A S wt % δ13Cs δ13Ca CV δ13Cb 

 

04039-001 04PL0915-001 3791 3.0 1.46 -27.92 -27.46 -1.97 -27.89 

04039-002 04PL0915-002 2831 3.9 1.64 -27.57 -27.47 -2.88 --- 

04039-003 04PL0915-003 5802 --- --- --- --- --- --- 

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Methods 

Petroleum residue was extracted from the rock samples using a Soxhlet extraction 

apparatus with chloroform as a solvent. The extracts were separated into asphaltene and maltene 

fractions by precipitation in excess volumes of iso-octane followed by centrifugation and 

filtration (asphaltenes are the precipitate). Saturated hydrocarbon, aromatic hydrocarbon, and 

polar hydrocarbon fractions were separated from the maltene fraction by column 

chromatography with alumina-silica columns and successive elution with iso-octane, benzene, 

and benzene-methanol azeotrope, respectively. The stable carbon isotope values (δ13C) of the 

C15+ saturated and aromatic hydrocarbon fractions of the extracts were determined using a Carlo 

Erba elemental analyzer (EA) interfaced to a Micromass Optima continuous-flow isotope ratio 

mass spectrometer (IRMS). Sample aliquots were introduced into the EA furnace heated to about 

1,020°C, and flash combusted in a quartz combustion tube filled with oxygen. The evolved CO2

passed through chromium oxide (to complete oxidation), copper granules (reducing agent), and 

anhydrone (to remove water) before being swept into the IRMS with a helium carrier gas. The 

results are expressed in the delta (δ) notation that represents the deviation of the 13C/12C ratio in 

parts per thousand (per mil, or ‰) relative to the Peedee belemnite (PDB) standard. The sulfur 

content of the extracts was determined by combustion using a Carlo Erba 1110 elemental 

analyzer. 

The maltene fractions of the extracts were analyzed by gas chromatography and gas 

chromatography/mass spectrometry. Gas chromatography of the extract was performed on a 

Hewlett Packard 6890 gas chromatograph with a DB-1 (bonded phase 100 percent 

dimethylpolysiloxane, 0.25-μm thickness) capillary column (60 m long by 0.32-mm inner 

diameter), splitless injection, flame ionization detector (FID), and programmed heating 

7
8

(40 ̊C to 330 ̊C at 4.5 ̊C/minute, held at 330 ̊C for 15 min). Biological marker (biomarker) 

distributions of the extracts were determined on a Hewlett-Packard 6890 gas chromatograph 

interfaced with a JEOL GCmate magnetic sector mass spectrometer using selected ion 

monitoring (SIM) at mass-to-charge (m/z) ratios of 191.1800, 217.1956, 231.1174, and 

253.1956. The gas chromatography analysis used a DB-1701 (bonded phase 14 percent 

cyanopropylphenyl, 86 percent dimethylpolysiloxane copolymer, 0.25-μm thickness) capillary 

column (60 m long by 0.31-mm inner diameter), splitless injection, and an oven temperature 

program of 50 to 150 ̊C at 50 ̊C/min, 150 to 300 ̊C at 3 ̊C/min, and a final hold time of 9 min at 

300 ̊C. 

Results 

The results of the bulk geochemical analyses are listed in table 1. All three Entrada 

samples contain high concentrations of petroleum residue (extractable organic matter > 2500 

ppm). Figure 4 shows saturated hydrocarbon δ13C vs. aromatic hydrocarbon δ13C isotope ratios 

for the CNM samples in comparison with other crude oils, oil seeps, and petroleum stains 

throughout the Uinta-Piceance Province. Gas chromatograms of the extracts (fig.5) show large 

unresolved “humps” and resolved biomarker peaks (between 40 and 70 min), but are missing the 

regular series of normal alkane peaks that are observed in most petroleum. 

Molecular biomarker parameters are listed in table 2. Figures 6 and 7 are the mass 

chromatograms for m/z 191.1800 and 217.1956, representing polycyclic terpanes and steranes, 

respectively. Figures 8 and 9 are a comparison of the terpane and sterane distributions, 

respectively, between the least altered CNM sample (04039-001) and typical production crude 

oils representing Phosphoria and Mancos oil types. 
Figure 4. Stable carbon isotope analyses of petroleum residue extracts from the Entrada 

Sandstone in Colorado National Monument (CNM), as well as production crude oils, oil stains, 

and oil seeps from within the Uinta-Piceance Province (Lillis and others, 2003). Solid line 

distinguishes waxy from nonwaxy oils (Sofer, 1984). Dashed line (canonical variable (CV) equal 

to -1.3) separates Cretaceous from Paleozoic oils (Lillis and others, 2003). Numbers refer to 

sample numbering system. 

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Figure 5. Gas chromatograms of petroleum residue extracts from the Entrada 

Sandstone in Colorado National Monument (CNM). Significant biodegradation is indicated 

by the lack of a series of regularly spaced n-hydrocarbon peaks and by the presence of a large 

unresolved “hump”. Sample 04039-001 has the best resolved biomarker peaks (retention time 

range 40-70 min). 

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Table 2. Selected biomarker ratios of petroleum residue in the Jurassic Entrada Formation, Colorado National M

representative crude oils from the Uinta-Piceance Province. Sample 89047-039 is Mancos oil type, and 00024-001 is Ph(Lillis and others, 2003). 

[GAC31, Gammacerane / C31 22R Hopane; OLH, Oleanane / Hopane; BISH, Bisnorhopane / Hopane; 35C34, C35 22S Hopane / C34 22S Hopane; NORH, C29 Norhopane / Hopane; 

Hopane; C26TET, (C26 S+R Tricyclic Terpanes) / C24 Tetracyclic Terpane; 19_23, C19 Tricyclic Terpane / C23 Tricyclic Terpane; 24_23, C24 Tricyclic Terpane / C23 Tricyclic Terp

Terpane / C25 Tricyclic Terpane by Peak Area; 27ST, C27 ααα 20R Sterane / C27 + C28 + C29 ααα 20R Steranes; 28ST, C28 ααα 20R Sterane / C27 + C28 + C29 ααα 20R Steranes; 

C27 + C28 + C29 ααα 20R Steranes; S1S6, C27 βα 20S Diasterane / C27 ααα 20R Sterane; 29SR, C29 ααα 20S Sterane) / (C29 ααα 20S + 20R Sterane); 29BB, C29 αββ 20R Steran

ααα 20R Sterane) ] 

Sample No. GAC31 OLH BISH 35C34 NORH TRIH 26TET 19_23 24_23 26_25 27ST 28ST 2

04039-001 0.53 0.10 0.03 1.13 1.93 0.22 0.94 0.03 0.88 0.77 0.28 0.23 

04039-002 2.01 0.60 0.34 1.89 1.66 1.55 2.83 0.02 0.93 0.96 0.38 0.20 

04039-003 1.58 0.59 0.30 1.82 1.90 2.05 3.27 0.03 0.85 0.79 0.29 0.19 

89047-039 0.3 0.1 0.07 0.64 0.43 0.15 0.07 0.47 0.8 0.03 0.27 0.35 

00024-001 0.64 0.01 0.03 1.32 0.9 1.19 1.61 0.08 0.46 0.9 0.29 0.21 

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Figure 6. Terpane mass chromatograms of petroleum residue extracts from the Entrada 

Sandstone in Colorado National Monument (CNM). Sample 04039-001 has the best 

resolved pentacyclic terpane peaks. 

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Figure 7. Sterane mass chromatograms of petroleum residue extracts from the Entrada 

Sandstone in Colorado National Monument (CNM).

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Figure 8. Terpane mass chromatograms of petroleum residue extract (Sample 04039-001) 

from the Entrada Sandstone in Colorado National Monument (CNM) and two 

representative crude oils from the Uinta-Piceance Province. 

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Figure 9. Sterane mass chromatograms of petroleum residue extract (Sample 04039-001) 

from the Entrada Sandstone in Colorado National Monument (CNM), and two 

representative crude oils from the Uinta-Piceance Province. 

15
16

Discussion 

Phosphoria, Mancos, and Mesaverde oil types (Lillis and others, 2003) are the 

most likely candidates to have migrated into the Entrada Sandstone in the CNM. Gas 

chromatograms of the CNM extracts show that normal alkanes, acyclic isoprenoids, and 

light aromatic hydrocarbons are missing, indicating significant secondary alteration of the 

petroleum due to biodegradation and water washing (fig.5). Consequently, these 

chromatograms cannot be used for petroleum correlation. The high sulfur content (1.5-

1.6 wt percent, table 1) is due to biodegradation, and the sulfur content of the original oil 

was probably less than 0.7 wt percent. Phosphoria oils in this area range from 0.5 to 1.4 

weight percent sulfur, whereas Mancos and Mesaverde oils have less than 0.5 weight 

percent sulfur. The isotopic (δ13C) composition of the CNM stains is distinct from most 

oils in the area (Lillis and others; 2003), but the canonical variable (Sofer, 1984) values 

(< -1.3) are similar to Phosphoria oils (fig. 4). These data indicate that the stains in this 

study may be genetically related to the Phosphoria oil type, with the shift to heavier δ13C 

values caused by biodegradation. 

The biomarkers in the CNM extracts have been altered by biodegradation and 

water washing to varying degrees, making interpretations more difficult. Sample 04039-

001 is the least biodegraded, as indicated by having (1) the best resolved biomarker peaks 

in the extract gas chromatogram (fig. 5), and (2) more identifiable pentacyclic terpanes in 

the terpane mass chromatogram (fig. 6). 

Sample 04039-001 contains low tricyclic terpane concentrations (for example, C23

tricyclic terpane / hopane ratio = 0.22) and possibly a small oleanane peak, similar to the 

Mancos oil type in the area (fig. 8). However, this sample contains high 

norhopane/hopane and C35/C34 hopane values that are similar to the Phosphoria oil type. 
17

The sterane composition most closely resembles the Phosphoria oil type, based on the 

relatively low C27 diasterane content, and high C29 14α(H),17α(H) and C29

14β(H),17β(H) sterane content (fig. 9). 

Conclusions 

The Entrada Sandstone in the Colorado National Monument (CNM) locally 

contains high concentrations of petroleum residue. These petroleum stains have been 

extremely altered by biodegradation and water washing; consequently, geochemical 

analyses are difficult to interpret. The least degraded sample most closely resembles the 

Phosphoria oil type, but some of the data correlate with the Mancos oil type. It is possible 

that the CNM residue is a mixture of both types, similar to oil in the Upper Jurassic 

Morrison Formation in Rangely field (Lillis and others, 2003). 

Acknowledgments 

We gratefully acknowledge Lisa Claussen, Dave Price, and Bruce Noble of the 

National Park Service for logistical support and access in the Colorado National 

Monument. David Allin and Bill Hood, Grand Junction, Colorado, provided insights and 

advice on the local geology and petroleum staining localities. Nicholas Battaglia and 

Augusta Warden aided in performing oil analyses at the USGS Central Energy Resources 

Organic Geochemistry Laboratory in Denver, Colorado. We also greatly appreciate 

thorough and constructive reviews by Joseph Hatch and Michael Pribil (USGS, Denver). 

Figure 1 was modified from a map produced by the National Park Service that was 

downloaded from the website http://www.nps.gov/hfc/carto/index.htm. 
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References Cited 

Lillis, P.G., Warden, A., and King, J.D., 2003, Petroleum Systems of the Uinta and 

Piceance Basins— Geochemical Characteristics of Oil Types, in Petroleum Systems 

and Geologic Assessment of Oil and Gas in the Uinta-Piceance Province, Utah and 

Colorado: U.S. Geological Survey Digital Data Series DDS-69-B, Chapter 3, 25 p., 

7 figures, 1 table [CD-ROM]. 

Scott, R.B., Harding, A.E., Hood, W.C., Cole, R.D., Livaccari, R.F., Johnson, J.B., 

Shroba, R.R., and Dickerson, R.P., 2001, Geologic Map of Colorado National 

Monument and Adjacent Areas, Mesa County, Colorado: U.S. Geological Survey 

Geologic Investigations Series I-2740, 40 p., 1 map. 

Sofer, Z., 1984, Stable carbon isotope compositions of crude oils: application to source 

depositional environments and petroleum alteration: American Association of 

Petroleum Geologists Bulletin, v. 68, p. 31-49. 

USGS Uinta-Piceance Assessment Team, 2003, Petroleum Systems and Geologic 

Assessment of Oil and Gas in the Uinta-Piceance Province, Utah and Colorado: 

U.S. Geological Survey Digital Data Series DDS-69-B.