Steroidal hydrocarbons of the Kishenehn Formation, northwest Montana

Org. Geochem. Vol. I I, No. 4, pp. 233-244, 1987 Printed in Great Britain. All rights reserved

0146-6380/87 $3.00 + 0.00 Copyright I~'~1987 Pergamon Journals Ltd

Steroidal hydrocarbons of the Kishenehn Formation, northwest Montana JOSEPH A. CURIALE Unocal, Inc., P.O. Box 76, Brca, CA 92621, U.S.A. (Received ! 1 August 1986; accepted 2 February 1987)

Abstract--The Oligocene Kishenehn Formation of northwest Montana and southeast British Columbia consists of fluvial and lacustrine sediments (marlstones, lignites and oil shales) deposited in an elongate, intermontane half-graben. The petroleum source rock potential and steroidal hydrocarbon distribution of selected shales of the Kishenehn Formation were examined. Several steroidal hydrocarbon series were documented, including 4-desmethylsteranes, 4-methylsteranes, sterenes, diasterenes, spirosterenes, C-ring monoaromatic steroids and B-ring monoaromatic anthrasteroids. Non-steroid hydrocarbons present include hopenes, ~-hopanes, moretanes, perylene, botryococcane, a series of alkylcyclohexanes, and a fused-ring aromatic tentatively identified as a tetrahydrochrysene. Source rock analysis indicates that the Kishenehn Formation possesses excellent petroleum source potential. Conventional thermal maturity parameters (vitrinite reflectance and Rock-Eval T ~ values), as well as maturity parameters derived from molecular parameters (n-alkane, steroid and hopanoid distributions) suggest that much of the Kishenehn Formation is currently undergoing organic diagenesis. Typical molecular indicators of thermal immaturity include the occurrence of high relative amounts of: (a) 5~(H) desmethylsteranes; (b) 14a(H) B-ring monoaromatic anthrasteroids; and (c) 4/I(CH3) methylsteranes. A near-shore freshwater lacustrine depositional environment is indicated, with some input of terrigenous organic matter (high-CPI C23-C31 n-alkanes and relatively high ethylcholestane content), while the presence of 4-methyisteroids and botryococcane indicate significant contributions from dinoflagellates and Botryococcus braunii. The occurrence in the Kishenehn Formation of a diverse selection of 4-methyl and 4-desmethyl aliphatic and aromatic steroids provides a unique opportunity to monitor co-variance of molecular maturity indicators in sediments deposited under relatively constant depositional conditions. Key words: biomarkers, Kishenehn, Montana, lacustrine, 4-methylsteranes,anthrasteroids, spirosterenes

INTRODUCTION

The Kishenehn Basin is a fault-bounded intermontane Tertiary basin located in northwest Montana and southeastern British Columbia (Fig. 1). The basin is structurally configured as a northwestsoutheast trending half-graben. Slippage along the east-bounding listric normal fault was contemporaneous with deposition, and has resulted in a uniformly northeastern dip (Constenius, 1981). The basin is filled with fluvial and lacustrine sediments and sapropelic coals of the Oligocene Kishenehn Formation, and contains numerous oil shale beds within the Kishenehn's Coal Creek member (Russell, 1964; Jones, 1969; McMechan and Price, 1980; McMechan, 1981; Constenius, 1981, 1982; Constenius and Dyni, 1983). The samples discussed in this paper are from the Tunnel Creek section of the Kishenehn Formation, located along the west bank of the Middle Fork of the Fiathead River (Fig. 1; Constenius and Dyni, 1983). The purpose of this research is to assess the source rock potential and thermal maturity of the Kishenehn Formation, and to examine the occurrence of steroidal biomarker hydrocarbon suites in O.O. I 1~4--A

selected samples. Nine outcrop samples from the Tunnel Creek section were chosen for source rock analysis; of these, three were examined in detail for molecular distributions. EXPERIMENTAL

Samples were analyzed for total organic (TOC) and Rock-Eval pyrolytic yields. Selected samples were also examined for vitrinite reflectance (VR). Standard techniques were used for all TOC and Rock-Eval determinations; analyses were made by DGSI (Houston). VR determinations were made on whole rock (plug) preparations. Rock extraction and compound class preparation techniques generally followed those in Curiale et al. (1985). The aromatic hydrocarbon fraction and the branched and cyclic aliphatic hydrocarbon fraction (following removal of n-paraffins by zeolite sieving, as described by O'Conner et ol., 1962), were each analyzed by gas chromatography-mass spectrometry (GCMS), using a Finnigan Triple Stage Quadrupole 4500 Series Mass Spectrometer. A 25 m DB-5 gas chromatographic column was used, with splitless injection. Oven temperature was held at 50°C for 233

JOSEPH A. CURIALE

234

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::::::

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U.S.A.

FLATHEAD ,~ FAULT

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N.W. MO~iNA .~..~._ AReA TUNNEL CREEK SECTION 0

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Fig. 1. Location map of Kishenehn Basin, adapted from Constenius and Dyni (1983). Basin sediments are of Tertiary age, and dip uniformly to the northeast. Study samples were obtained from outcrops at the Tunnel Creek section, on the west bank of the Middle Fork of the Flathead River.

2min, ramped to 150°C at 20°C/min, then to 300°C at 3°C/min, and held there for 10min. The first quadrupole was scanned from 70 to 600 amu every 1.322 sec; about 4000 full scans were obtained. Further details can be found in Curiale et al. (1985). The sampleschosen for detailed GCMS analyses are typical of the nine samples analyzed for source potential. The biomarker distributions of these three samples are similar to one another, and most of the results presented here are for a single sample (Table 1, Sample 3). Compound identifications were made by comparison with authentic standards, by mass spectral interpretation, or by comparison with literature data (Brassell et al., 1981, 1984; Hussler and Albrecht, 1983; McKirdy et aL, 1986; Palmer, 1984; Peakman et al., 1984; Wolff et al., 1986; Aizenshtat, 1973; Johns et aL, 1966; Mackenzie, 1984; Moldowan and Seifert, 1980; Rubinstein and Strausz, 1979; Rullkotter and Welte, 1983; Simoneit, 1986; Spyckerelle e t al., 1977; ten Haven et al., 1985 Robinson et al., 1984a, b; Mattern e t a / . , 1970).

RESU LTS

Source rock analysis

Total organic carbon and Rock-Evai data for nine Tunnel Creek section samples are given in Table 1. Hydrogen index (HI) values indicate consistently excellent source potential for the Kishenehn at this location. The Hydrogen Index-Oxygen Index plot in Fig. 2 further indicates that the organic matter in these samples includes Type I kerogen, and is thermally immature (Tissot and Welte, 1984). Vitrinite reflectance values in the Tunnel Creek section range from 0.39 to 0.43% Ro. Thermal immaturity is further indicated by the low Tm,~ and Production Index (PI) values (Table 1), and by the strong odd-carbon number n-alkane predominance in the C22-C32 range (Fig. 3). The prominent occurrence of these odd-carbon number n-alkanes also suggests the input of land plant organic matter to the Kishenehn lake system. This implies a near-shore location. In summary, the Tunnel Creek section of the Kishenehn

i;~

,

Kishenehn steroids

235

1000 ~

800

II

6oo

E x

_z z

o T

400-

%

mg/g

200

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O X Y G E N INDEX ( r a g / g )

Fig. 2. Hydrogen index vs oxygen index data for nine outcrop samples from the Tunnel Creek section of the Kishenehn Formation. Type I kerogen designation is based upon these data. Insets show variation of total organic carbon (TOC) and $2 Rock-Eva] pyrolytic yields for the samples. More upsection samples are plotted at higher "ordinate" values in the insets. Note consistency of hydrogen and oxygen indices despite wide variability in TOC and $2 values. Data listed in Table 1.

27

Formation contains excellent, immature, oil source rocks.

SteroMal hydrocarbons

"27" CARBON NUMBER I "pr" PItlSTANE

Several different suites of steroidal hydrocarbons are present in the Tunnel Creek samples. The occurrence o f most o f these is related exclusively to the immature character of the Kishenehn Formation at this location (e.g. sterenes, diasterenes, monoaromatic anthrasteroids). However, other steroidal hydrocarbon suites are strongly indicative "of initial organic matter composition (e.g. 4-methylsteranes). This section will cite the occurrence of these faciesindicative hydrocarbons in Kisbenehn sediments, while a later section will comment on the composition of the steroidal hydrocarbons with regard to both thermal maturity and source input. Emphasis will be on those steroidal hydrocarbons which are indicative of the diagenetic phase of organic matter alteration. This phase will be defined for our purposes as those chemical and biochemical changes in hydrocarbon

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Fig. 3. Gas chromatosram of aliphatic hydrocarbons of a typical Kishenelm Formation Tunnel Creek sample. Run conditions as noted in text. Note high odd-carbon n-a]kane predominance, low pristane/phytane ratio, and low nheptadecane/pristane ratio.

236

JOSEPH A. CURIALE 100.0

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5a, 14a, 17a, 20R -- STERANE$ e~ 5,8, 14a, 47~, 20R -- STERANES R

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Fig. 4. Top: m/z 217 mass chromatogram of aliphatic hydrocarbons, showing distribution of 4-desmethylsteranes in a typical sample. Note presence of 5fl-steranes. Bottom: m/z 231 mass chromatogram of aliphatic hydrocarbons, showing the distribution of 4-methylsteranes. Note difference in carbon number distribution between compound classes (top and bottom). composition occurring prior to significant thermal generation (from kerogen and polar compounds) and expulsion of hydrocarbons. The 4-desmethylsteranes in all samples are dominated by 14~(H), 17(~H), 20R-cholestanes and their 24-methyl and 24-ethyl analogs (Fig. 4, top). Ratios of 5~,(H)/5~(I-I) are consistently about 4:1. A series of 5a(H)-4-methylsteranes is also present in all samples (Fig. 4, bottom), ranging in carbon number from C28 through C30 (Mattern et al., 1970; Wolff et al., 1986). Note that the 4~/4a ratio appears to decrease slightly with increasing carbon number. This ratio has been proposed as a maturation parameter (for a single carbon number): 4//(CH3) isomers generally decrease relative to 4~(CH3), with increasing thermal maturity (Wolff et al., 1986). Note that the carbon number distributions (C27, C28, C29 vs C28, C29, C30) for the 4-de~a©thyisteranes and the 4-m©thylsteranes are significantly different (Fig. 4).

Homologous series of 20S and 20R rearranged sterenes (diaster-13(17)-enes) and spirosterenes (Peakman et al., 1984; Brasseil et al., 1984) are also present in relatively high concentration in all samples (Fig. 5). In addition, minor quantities of 4-methyl spirosterenes (ten Haven et al., 1985) have been tentatively identified in a few samples (Fig. 5, bottom, m / z 220). These compounds are accompanied by a relatively strong series of ring-B monoaromatic anthrasteroids in most samples (Fig. 6), as monitored by the m / z 211 mass chromatogram (Hussler and Albrecht, 1983). Note that the 14B(H)/14c(H) ratio in these aromatics appears to increase systematically with increasing carbon number for these compounds. Other hydrocarbons

Several other compounds and compound families are present in the Kishenehn in varying quantities. Pentacyclic triterpanes occur as the 17/~(H), 21/~(H)

237

Kishcnehn steroids 100.0

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ION INTENSITYPRESERVEDj (MAP)

m/z 234 E:201 oJ20S

S : C2 Hs

m/z R=H

Fig. 5. Top: m/z 257 mass chromatogram of aliphatic hydrocarbons, showing distribution of diaster13(I 7)-enes. Bottom: Original ion intensity MAP (INCOS) of m/z 206, 220 and 234, indicating distribution of spirosterenes. Note minor quantities of 4-methyl spirosterenes in the m/z 220 pattern.

series, the 17fl(H), 21~(H) series (moretanes) and the 17u(H), 21fl(H) series (Fig. 7). Note the high relative concentration of ~-hopanes, the virtual absence of 18~,(H)-trisnorhopane and the extremely low 22S/22R-homohopane ratios. In addition, minor amounts of C30 and C31 hop-17(21)-enes (showing 22S/22R ratios of approximately 1.0) were found in some samples. Two C19 tricyclic terpanes are also present, and were tentatively assigned a fichtelite carbon skeleton (Palmer, 1984). A series of alkylcyclohexanes (C12-C30, having a slight odd carbon number preference) occurs in most samples. Several acyclic isoprenoids have also been identified, including pristane, phytane and botryococcane (Moidowan and Seifert, 1980; McKirdy et al., 1986).

Certain distinctive aromatic compounds, not discussed previously, are also present in all samples. In addition to perylene (Aizenshtat, 1973; Wakeham et a/., 1979), a fused ring aromatic tentatively identified as 3,3,7-trimethyl-l,2,3,4-tetrahydrochrysene is present in several samples, and may be a ~ff-amyrin derivative (Spyckerelle et a/., 1977). C-ring monoaromatic steroid hydrocarbons (Seifert et al., 1983) also occur in all samples; the C28 and C29 members of this steroid class are in highest relative concentration (as was also the case with the other 4-desmethylsteroids). DISC~ION General

The aliphatic hydrocarbon Reconstructed Ion

238

JOSEPH A. CUP.tALE II

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i

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.

m/z 394

i

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Fig. 6. Series of mass chromatograms of the aromatic hydrocarbons, depicting the occurrence of ring B monoaromatic anthrasteroids. The uppermost ehromatogram, m/z 211, gives the distribution of the major fragment from this series; the three other ehromatograms are parent scans. Chromatogram (RIC) for the steroidal biomarker region of a typical Kishenehn rock sample is shown in Fig. 8. 4-Desmethyl and 4-methyl stcranes predominate, with a desmethyl/methyl ratio of approxi-

100.0j

mately 2:1. Note in the RIC that the regular sterenes, diasterencs and spirosterenes are in very low abundance, relative to the saturated alicyelics. Although the carbon number distribution of regu-

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i

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i

Fig. 7. m/z 191 mass chromatogram of the aliphatic hydrocarbons in a typical Tunnel Creek section sample. Note high relative concentrations of the ##-hopanes, and low 22S/22R-homobopane ratio.

Kishenehn steroids

239

S,T S,T M I~ 4-METHYLSTERANES(M) ~I PENTACYCLICTRITERPANES(T) (HOPANES/MORETANES) m Sa, 14(~, 17,,, 20R-STERANES(S) L~ DIASTERENES(D)

M

D M, NI NI

T

I

I

i

280°C

290°C

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T

T

Fig. 8. Reconstructed ion chromatogram of a typical aliphatic hydrocarbon GCMS experiment on a Kishenehn Formation extract. Steranes, methylsteranes and pentacyclic triterpanes dominate the chromatogram. lar steranes has been used as a depositional environment indicator (Meinschein and Huang, 1981; Philp, 1985, and references therein), the analogous distributions in the diagenetic precursors of the steranes

have generally not been considered. The carbon number distribution o f the 4-methylsteranes is also rarely investigated. Figure 9 is a ternary plot of carbon number distributions for six steroidal homol-

Cn+ 4

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STEROIDCARBON \NUMBER DISTRIBUTION \ n = 27 for all except

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Fig. 9. Ternary diagram showing the distribution of five steroid (n = 27) and one methylsteroid (n = 28) series in Sample 3 (Table 1). The linear trend through the five desmethylsteroid series seems to suggest that relative differenms in the C29 component govern this distribution.

240

JOSEPH A . CURIALE

ogies: diasterenes (20R + 20S); B-ring monoaromatic anthrasteroids (14n(H)+ 14fl(H)); desmethyl steranes (5~(H) + 5fl(H)); spirosterenes (20R + 20S); regular sterenes (sum of two isomers tentatively identified as delta-4 and delta-5); and 4-methylsteranes (4a(CH3) + 4~(CH3)). In each case, distribution calculations were made based on major ion fragments, and assume little variation in the relative intensity of the principle fragment ions in the mass spectra of each compound type for members of the same series but different carbon number. The variability within the five 4-desmethylsteroid series shown in Fig. 9 is greater than that expected solely from analytical imprecision. The linear extent (Fig. 9, dashed line) of this variability tends to nearly bisect the C27-C28 axis of the ternary diagram, indicating that much of the variance is due to relative changes in the C29 component. Note however that the final diagenetic product of the 14~(H), 17ct(H) configuration of these series, namely the 4-desmethylsteranes, is not an end-member of this linear trend. In general, although no genetic similarity among these various 4-desmethyl series is evident from Fig. 9, certain comparisons are noteworthy. For example, both diasterenes and spirosterenes are clay-catalyzed backbone rearrangement products of sterene diagenesis (Kirk and Shaw, 1975), yet differences in carbon number distribution are present for both of these series. Further, the carbon number distributions of diasterenes and B-ring monoaromatic anthrasteroids are very similar, despite different diagenetic origins (Brassell et al., 1984). It is clear that carbon number distribution changes in 4-desmethylsteroidal hydrocarbons attributable to organic diagenesis cannot be directly inferred from Figure 9, and that the accuracy of preservation of the number of carbon atoms during diagenesis remains indeterminate (Meinschein and Huang, 1981). Of further interest in Fig. 9 is the distinct difference of the carbon number distributions between the 4-methyl and the 4-desmethyl series. Such a difference may suggest distinctive organic matter sources for each compound class, as discussed below. Thermal maturity

Conventional maturity parameters, including the

Tm,~, VR and carbon number n-aikane preference data discussed earlier, indicate that the shales of the

Tunnel Creek section of the Kishenehn Formation are thermally immature. Vitrinite reflectance values fall in the narrow range of 0.39-0.42% Ro, while Tmax values are 432-444°C (Table 1). Furthermore, atomic H/C ratios in the kerogens are 1.58-1.67 (note that these values also indirectly support the previous Type I kerogen determination; see also Fig. 2). Biological marker data further indicate that the Tunnel Creek section of the Kishenehn is thermally immature. For example, the presence of regular sterenes, diasterenes, spirosterenes, B-ring monoaromatic anthrasteroids, hopenes,/~/~-hopanes, 5~(H)-steranes, low 20S/20R-sterane ratios and low 22S/22R-homohopane ratios all suggest that these sediments are still actively undergoing organic diagenesis (Philp, 1985; Brassel et aL, 1984; and references therein). The occurrence of hopenes and pp-hopanes also supports this conclusion (Mackenzie, 1984). Several of these compounds completely convert to their saturated or fully aromatized counterparts with increasing thermal input, while others isomerize to more thermally stable configurations (Mackenzie, 1984; Brassell et aL, 1984; Hustler and Albrecht, 1983; Peakman et al., 1984). The utility of 4-methyisterane distributions as a thermal maturity parameter has recently been documented for immature Toarcian shales of the Paris Basin (Wolff et al., 1986). The occurrence of these compounds in all Kishenehn samples analyzed to date suggests their use as a maturation parameter in the Kishenehn Basin (Fig. 4). Wolff et al. (1986) noted the disappearance of the 4#(CH3) isomer (relative to the 4a(CH3) isomer) with increasing thermal maturity for the Paris Basin samples, the m / z 231 mass chromatogram in Fig. 4 indicates that the 4fl/4a ratio for the Tunnel Creek Kishenehn shales is still approximately one (i.e. immature). The occurrence of unsaturated steroidal hydrocarbons in these samples may provide a rare opportunity to measure molecular distribution changes as a function of very small changes in thermal maturity. For instance, anthrasteroids are commonly encountered in immature sediments (Hussler and Albrecht, 1983; Simoneit, 1986). It has been suggested, using stability arguments, that during organic diagenesis the 14fl(H)/14a(H) ratio of anthrasteroids (Fig. 6) might increase with increasing thermal maturity (Hussler and Albrecht, 1983). Early applications of

Table I. Source rock parameters, Tunnel Creek section Sample

TOC (%)

SI (rag/g)

S2 (mg/g)

$3 (mg/g)

T~, CC)

HI (rag/g)

OI (rag/g)

PI

1 2 3 4 5 6 7 9 l0

5.37 3.68 12,92 5.03 6.17 7.06 10.04 7.90 5,18

1.34 0.52 1.57 0.75 1.02 1.35 3.91 1.64 2.19

45.60 28.16 124,86 45.52 55.57 65.88 91.59 73,50 45.72

2.27 1.48 3,57 1,65 2.52 3,06 2.64 2.61 2.02

438 435 444 439 441 443 438 441 435

849 765 966 904 901 933 912 930 882

42 40 28 33 41 43 26 33 39

0.03 0,02 0.01 0.02 0.02 0.02 0.04 0.02 0.05

Kishenehn steroids this idea have been proposed by Brassell et al. (1984; see also Rullkotter and Welte, 1983), and are currently being pursued for a regionally extensive sample set from the Kishenehn Basin. The conversion from a 20R-diaster-13(17)-erie to a 20R + 20S isomeric mixture represents another potential tool for monitoring short term diagenetic changes (Brassell et al., 1984). The m / z 257 mass chromatogram in Fig. 5 indicates that, for this sample, isomerization at C-20 is almost complete. Brassell et al. (1984) also proposed, and indeed found in DSDP Leg 71 Falkland Plateau sediments, an analogous isomerization trend for the spirosterenes at C-20. Data for a typical Kisbenehn sample at the Tunnel Creek section (Fig. 5, bottom) indicate that, as with the diasterenes, isomerization of the spirosterenes is also essentially complete. Finally, the occurrence of 4-methyl spirosterenes (ten Haven et aL, 1985) in the Kishenehn Formation may be useful as a maturity parameter in an analagous sense, for samples possessing higher relative concentrations than those present in this sample (Fig. 5, bottom). The 20S/20R ratios in the spirosterenes of the Kishenehn Formation vary systematically with carbon number (Fig. 5, bottom), in a similar fashion to that observed by Brasseil et al. (1984) for Angolan Basin black shales. The occurrence of several suites of diagenetic steroidal hydrocarbons in the Kishenehn Formation provides an opportunity for comparison of maturity indices based on molecular carbon number. Figure 10 shows the distribution of maturity ratios vs carbon number, for four such suites in a single Kishenehn sample. Increasing thermal maturity is shown in an upward direction on the vertical axis. In three classes (anthrasteroids, spirosterenes

241

and diasterenes), the change is monotonic, while no systematic change is present in the other two classes (steranes and methylsteranes). For the anthrasteroids and spirosterenes, the higher carbon number components appear "more mature", yet the reverse is true for the diasterenes. This is of particular interest because both the spirosterenes and diasterenes are essentially isomerized. Also of interest is that the absolute variation (from the mean) is less than 6% in all cases except the diasterenes (10%). Interpretation of the trends in Fig. 10 may be influenced by experimental conditions. Stereospecific standards were unavailable for several of these compounds. Consequently, some of the data in Fig. 10 were derived directly from the relevant mass chromatograms (without mass spectrometric fragment intensity corrections) perhaps resulting in artificial ratio differences (S. Brassell, personal communication). If we assume that such instrumental response variations do not completely overprint real differences in maturity parameters, then two conclusions may be derived from Fig. 10. Firstly, it is clear that comparisons of diagenetic steroidal hydrocarbon maturity parameters should be confined to a single carbon number. This approach has the benefit of "normalizing" any potential mass spectrometric response variations. Secondly, further changes in the relevant maturity parameters, defined for a specific carbon number, arc to be expected for certain st~'oidal hydrocarbons (e.g. desmethyisteranes) in these Kisbenehn samples, as maturation levels increase. In any event, the pre~nce of such a large number of potential molecular maturation indicators in the Kishcnehn Formation suggests that a regional study of the molecular geochemistry of this unit might

t.0

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0

0,6

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I

..

l!

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~

i l

ANTHRASIEROIDS

+ 20R - SPIROSTERENES

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20S I .................

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0

5a

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D E S l d ~ B

TOTAL VARIATION I

Cn

I

Cn+ 4 CARBON NUMBI:R

I

Cn+2

Fig. 10. Changes in five steroidal biological marker hydrocarbon ratios with differing carbon number (calculated without instrumental response corrections--see text). An increasing ratio on the ordinate corresponds to presumed increasing thermal maturity. Total variation in each ratio is shown on the left. Absolute variation from the mean is less than or equal to 10% in all cases.

242

JOSEPHA. CUglALE

successfully be used to aid in the reconstruction of basinal development. Ongoing research seeks to determine the regional variation in thermal maturity in the Kishenehn, and to assess the sensitivity of each of these molecular maturation parameters in this particular basin. Origin o f organic matter

Information from biological marker distributions can be used to refine our understanding of source rock depositional environment. Concerning the Oligocene Kishenehn Formation, we can say that, at the very least, steroid, hopanoid and other molecular data presented above support the freshwater lacustrine environment previously proposed for this basin (Russell, 1964; Constenius and Dyni, 1983). When interpreted in detail however, these molecular data are also capable of defining specific depositional conditions, and excluding others, as well as assessing potential molecular contributions from specific organisms. The strong odd-carbon n-paraflin predominance (Fig. 3) indicates that land plant organic matter has made a contribution to these sediments (Albrecht and Ourisson, 1971). Such a conclusion is also supported using the biological marker data presented thus far. Although the classic terrigeneous indicators, such as oleanane and most tricyclic terpanes (Ekweozor et al., 1979; Noble, 1986), are only present in very low concentrations, relatively high concentrations of 24-ethylcholestane (Figs 4 and 9), and minor amounts of fichtelite and perylene, have been observed. These latter compounds are generally considered land plant source indicators (Mackenzie, 1984; Aizenshtat, 1973; however, see Wakeham et al., 1979, concerning alternative sources for perylene), implying near-shore conditions for the Tunnel Creek section of the Kishenehn Formation (Constenius, 1981). The dominance of elastic input in the Kishenehn Basin during Oligocene time is reflected in the occurrence of many of the unsaturated alicyclic components discussed above. Several of these unsaturated steroidal hydrocarbons initially form and isomerize rapidly in the presence of (Lewis-) acid catalytic conditions provided by the surface of smectite-family clays (Rubinstein et al., 1975; Kirk and Shaw, 1975; Brasseli et al., 1984). Thus, although several Kishenehn samples are calcareous, the steroid distributions still strongly reflect the catalytic effects of predominantly elastic input to these lacustrine sediments. Again, a near-shore environment is indicated for the Tunnel Creek section. In addition to such gross environmental inferences, the existence of certain organisms in the water column during Kishenehn time can be inferred, based upon the occurrence of their geochemical molecular remnants in the rock. The occurrence of 4-methylsteranes in the Kishenehn strongly supports a dinoflagellate input to the sediment, insomueh as the relationship between 4-methylsteranes in sediments

and 4-methylsterols in living dinoflagellates within the overlying water column is now fairly well established (Robinson et al., 1984b; Wolff et al., 1986; however, see Bird et al., 1971). Further, the dinoflagallates responsible for these methylsteranes are probably freshwater species, insomuch as freshwater flora and fauna are common in the Coal Creek member of the Kishenehn Formation (Russell, 1964; Constenius, 1981). The occurrence of 4-methylsteroids in fossil organic matter of nonmarine origin has been noted (Moldowan et al., 1985), and several nonmarine dinoflagellate species have been identified (Withers, 1983; Sarjeant, 1974). However, detailed analyses of steroid composition in nonmarine species is rare (Cranwell et al., 1985). Although the identification of dinoflagellates specifically in nonmarine shales is not known to this author, they have been identified in various swamp, lacustrine and lignite deposits, some of Oligocene age (Traverse, 1955; Sarjeant, 1974). It must be noted however, that methyisteranes are not clearly dominant over desmethylsteranes within most of the Kishenehn samples (e.g. Fig. 8). This is in contrast to the clear dominance of 4-methylsterols over desmethylsterois in most (marine) dinoflagellates (Kokk¢ et al., 1981), and suggests that dinoflagellates are not solely responsible for the steroid input to the Kishenehn sediments. That this is the case is indicated by the C29 bias of the desmethylsteroids (Fig. 9), suggestive of terrigenous (land plant) input. Botryococcane, also found in minor quantities in the Coal Creek member oil shales of the Kishenehn Formation, is another marker for a particular organism. However, this compound is considerably more species-specific than the methylsteranes: the occurrence of botryococcane in crude oils is directly attributable to original input of a freshwater/brackish water alga, Botryococcus braanii (Moldowan and Seifert, 1980; McKirdy et al., 1986). The occurrence of botryococcane in these sediments further supports the conclusions that the dinoflagellates responsible for the 4-methylsteroid input are nonmarine species. The presence of a homologous series of alkylcyclohexanes in the Kishenchr~ Formation may also eventually provide useful environmental information. These compounds appear at present in a wide variety of environments; potential precursors include fatty acids present in certain bacteria (Rubinstein and Strausz, 1979, and references therein). Beyond this possibility, their origin is unclear, although assignment to a land plant origin must be considered suspect, in view of the occurrence of alkylcyclohexanes in the Precambrian Nonesuch Formation (Johns et al., 1966). CONCLUSIONS

The contribution of both land plant (e.g. waxes) and freshwater/brackish water (e.g. dinoflagellates;

Kishenehn steroids B. braunii) organic matter to the Coal Creek member shales is consistent with a near-shore lacustrine environment of deposition for the Kishenehn Formarion at Tunnel Creek. The occurrence of a wide variety of 4-desmethyl and 4-methyl alipharic and aromatic steroids, pentacyclic triterpanes and triterpenes, botryococcane and perylene, provides a unique natural laboratory for the study o f short-term changes in thermal maturation parameters in a welldefined environmental setting. In addition, particular organism-biomarker generic correlations are possible, allowing further refinement o f current ideas on the deposirional environment for these sediments. Molecular geochemistry provides an opportunity to understand the Kishenehn Formation from a regional perspective. Our current understanding of the relationship between marker compounds and source organisms, and recently discovered empiricallyderived molecular maturity parameters generally confined to the zone of diagenesis, make a basinal model derived from molecular data a possibility. Conceivably, the deposirional environment o f these rocks is deducible solely from the remnant molecular distributions contained therein. Studies currently underway seek to provide such an understanding for the Kishenehn from a regional perspective. Aclmowledfements--I thank the National Park Service (Glacier National Park) and the Forest Service (Flathead National Forest) for permission to collect on their lands. I especially wish to thank S. W. Sperry, who taught me a great deal about the geology of northwest Montana, and whose help was invaluable during the field work phase of this project. Thanks are also extended to S. R. Latter for a thorough review of an early draft. M. Jacob and D. Cardin assisted in sample preparation and GCMS analyses, respectively. Finally, I thank Unocal management, particularly J. R. Fox, for the opportunity to conduct this research, and permission to publish. REFERENCES Aizenshtat Z. (1973) Perylene and its geochemical significance. Geochim. Cosmochim. Acta 37, 559-567. Albrecht P. and Ourisson G. (1971) Biogenic substances in sediments and fossils. Angewandte Chem. (International F,~) 10, 2O9-225. Bird C. W., Lynch J. M., Pirt F. J., Reid W. W., Brooks C. J. W. and Middleditch B. S. (1971) Steroids and glunlene in Methylococcus capsulatus grown on methane. Nature 230, 473. Brassell S. C., Gowar A. P. and Eglinton G. (1981) Computerised gas chromatography-mass spectrometry in analyses of sediments from the Deep Sea Drilling Project. In Advances in Organic Geochemistry 1979. (Edited by Douglas A. G. and Maxwell J. R.), pp. 421-426. Pergamon Press, Oxford. Brassell S. C., McEvoy J., Hoffmann C. F., Lamb N. A., Peakman T. M. and Maxwell J. R. (1984) Isomerisation, rearrangement and aromatisation of steroids in distinguishing early stages of diagenesis. Org. Geochem. 6, 11-23.

Constenius K. N. (1981) Stratigraphy, sedimentation and tectonic history of the Kishenehn basin, northwestern Montana. M. S. thesis, University of Wyoming, 125 pp. Constenius K. (1982) Relationship between the Kishenehn Basin, and the Flathead listric normal fault system and

243

Lewis Thrust salient. In Geologic Studies of the Cordilleran Thrust Belt (Edited by Powers R. B.), Vol. II, pp. 817-830. Rocky Mountain Association of Geologists, Denver. Constenius K. N. and Dyni 3. R. (1983) Lacustrine oil shales and stratigraphy of part of the Kishenehn Basin, Northwestern Montana. Miner. Energy Resour., Col. School Mines 26, !-16. Cranwell P. A., Robinson N. and Eglinton G. (1985) Esterified lipids of the freshwater dinoflagellate Peridinium iomniekii. Lipids 20, 645-651. Curiale J. A., Cameron D. and Davis D. V. (1985) Biological marker distribution and significance in oils and rocks of the Monterey Formation, California. Geochim. Cosmo. chim. Acta 49, 271-288. Ekweozor C. M., Okogun J. l., Ekong D. E. U. and Maxwell J. R. (1979) Preliminary organic geochemical studies of samples from the Niger delta, Nigeria: I. Analyses of crude oils for triterpanes. Chem. Geol. 21, 11-28.

Hussler G. and Albrecht P. (1983) C27--C29 monoaromatic anthrasteroid hydrocarbons in Cretaceous black shales. Nature 304, 262-263. Johns R. B., Belsky T., McCarthy E. D., Burlingame A. L., Haug P., Sehnoes H. K., Richter W. J. and Calvin M. (1966) The organic geochemistry of ancient sediments If. Geochim. Cosmochim. Acta 30, 1191-1222. Jones P. B. 0969) The Tertiary Kishenehn Formation, British Columbia. Bull. Can. Pet. Geol. 17, 234-246. Kirk D. N. and Shaw P. M. (1975) Backbone rearrangement of steroidal 5-cries. J. Chem. Soc. Perkin 1 2284-2294. Kokke W. C. M. C., Fenical W., Bohlin L. and Djerassi C. (1981) Sterol synthesis by cultured zooxanthellac: implications concerning sterol metabolism in the hostsymbiont association in Caribbean gorgonians. Comp. Biochem. Physiol. !!68, 281-287. Mackenzie A. S. (1984) Applications of biological markers in petroleum geochemistry. In Advances in Petroleum Geochemistry (Edited by Brooks J. and WeRe D.), pp. 115-214. Academic Press, London. Mattern G., Albrecht R. and Ourisson G. (1970) 4-Methylsterols and sterols in Messel Shale (Eocene). Commun. 1570-1571. McKirdy D. M., Cox R. E., Volkman J. K. and Howell V. J. (1986) Botryococcane in a new class of Australian non-marine crude oils. Nature 320, 57-59. McMechan R. D. (1981) Stratigraphy, sedimentology, structure and tectonic implications of the Oligocene Kishenehn Formation, Fiathead Valley Graben, southeastern British Columbia. Ph.D. Dissertation, Queen's University, Canada, 327 pp. McMecban R. D. and Price R. A. (1980) Reappraisal of a reported unconformity in the Paleogene (Oligocene) Kishenehn Formation: Implications for Cenozoic tectonics in the Fiathead Valley Graben, southeastern British Columbia. Bull. Can. Pet. Geol. 28, 37-45. Meinschein W. G. and Huang W.-Y. (1981) Stenols, stanols, steranes and the origins of natural gas and petroleum. In Origin and Chemistry of Petroleum, Proceedings of the Third Annual Karcher Symposium (Edited by Atkinson G. and Zuckerman J. J.), pp. 33-56. Pergamon Press, Oxford. Moldowan J. M. and Seifert W. K. (1980) First discovery of Botrycoccane in petroleum. J. Chem. Soc. Chem. Commun. 912-914. Moldowan J. M., Seifert W. K. and Gallegos E. J. (1985) The relationship between petroleum composition and the environment of deposition of petroleum source rocks. AAPG Bull. 69, 1255-1268. Noble R. A. (1986) A geochemical study of bicyclic alkanes and diterpenoids hydrocarbons in crude oils, sediments and coals. Unpublished Ph.D. dissertation, The University of Western Australia, 365 pp.

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O'Conner J. G., Burow F. H. and Norris M. S. (1962) Determination of normal paraffins in C20 to C32 paraffin waxes by molecular sieve adsorption. Anal. Chem. 34, 82-85. Palmer S. E. (1984) Hydrocarbon source potential of organic facies of the lacustrine Elko Formation (Eocene/Ofigocene), northeast Nevada. In Hydrocarbon Source Rocks of the Greater Rocky Mountain Region (Edited by Woodward J., Meissner F. F. and Clayton J. L.), pp. 491-511. Rocky Mountain Association of Geologists. Peakman T. M., Lamb N. A. and Maxwell J. R. (1984) Naturally occurring spiro steroid hydrocarbons. Tetrahedron Lett. 26, 349-352. Philp R. P. (1985) Biological markers in fossil fuel production. Mass Spectrom. Rev. 4, 1-54. Robinson N., Eglinton G., Bras,~ll S. C. and Cranwell P. A. (1984a) DinoflageUate origin for sedimentary 4a-methylsteroids and 5~(H)-stanols. Nature 308, 439-442. Robinson N., Cranwell P. A., Finlay B. J. and Eglinton G. (1984b) Lipids of aquatic organisms as potential contributors to lacustrine sediments. Org. Geochem. 6, 143-152. Rubinstein I. and Strausz O. P. (1979) Geochemistry of the thiourea adduct fraction from an Alberta petroleum. Geochim. Cosmochim. Acta 43, 1387-1392. Rubinstein I., Siesking O. and Albrecht P. (1975) Rearranged sterenes in a shale: Occurrence and simulated formation. J. Chem. Soc. Perkin 1 1833-1836. Rullkotter J. and Welte D. H. (1983) Maturation of organic matter in areas of high heat flow: A study of sediments from DSDP Leg 63, offshore California and Leg 64, Gulf of California. In Advances in Organic Geochemistry 1981 (Edited by Bjorey M. et aLL pp. 438--448. Wiley, Chichester. Russell L. S. (1964) Kishenehn Formation. Bull. Can. Pet. Geol. 12, 536-543.

Sarjeant W. A. S. (1974) Fossil and Living Dinoflagellates, 182 pp. Academic Press, London. Seifert W. K., Carlson R. M. K. and Moldowan J. M. (1983) Geomimetic synthesis, structure assignment and geochemical correlation application of monoaromatized petroleum steroids. In Advances in Organic Geochemistry 1981 (Edited by Bjorzy M. et aLL pp. 710-724. Wiley, Chichester. Simoneit B. R. T. (1986) Biomarker geochemistry of black shales from Cretaceous oceans--An overview. Mar. Geol. 70, 9--41. Spyckerelle C., Greiner A. Ch., Albrecht P. and Ourisson G. (1977) Hydrocarbures aromatiques d'ofigine geologique. III. Un tetrahydrochrysene, derive de triterpenes, dans des sediments recents et anciens: 3,3,7-trimethyl-l,2,3,4tetrahydrochrysene. J. Chem. Res. (M) 3746-3775. ten Haven H. L., de Lceuw J. W. and Schenck P. A. (1985) Organic geochemical studies of a Messinian evaporitic basin, northern Apennines (Italy) I: Hydrocarbon biological markers for a hypersaline environment. Geochim. Cosmochim. Acta 49, 2181-2191. Tissot B. P. and Welte D. H. (1984) Petroleum Formation and Occurrence, 699 pp. Springer, Berlin. Traverse A. (1955) Pollen analysis of the Brandon lignite of Vermont. In Rept Bureau Mines, U.S. Dept Interior No. 5151, 107 pp. Wakeham S. G., Schaffner C., Giger W., Boon J. J. and Leeuw J. W. (1979) Perylene in sediments from the Namibian Shelf. Geochim. Cosmochim. Acta 43, 1141-1144. Withers N. (1983) DinoflageUate sterols. In Marine Natural Products (Edited by Schener E.), pp. 87-130. Academic Press, New York. Wolff G. A., Lamb N. A. and Maxwell J. R. (1986) The origin and fate of 4-methyl steroid hydrocarbons. I. Diagenesis of 4-methyl steranes. Geochim. Cosmochim. Acta 50, 335-342.