Biomarkers reveal the terrigenous organic matter enrichment in the late Oligocene−early Miocene marine shales in the Ying-Qiong Basin, South China Sea
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Abstract: The increase of total organic carbon content of the late Oligocene−early Miocene terrigenously-dominated marine shales in the shallower depth intervals was reported in the Ying-Qiong Basin, South China Sea. The organic enriched lower Sanya Formation shales (early Miocene) have biomarker characteristics of tropical/subtropical plants, with abundant high molecular weight n-alkanes, angiosperm-derived oleanane, rearranged oleananes I, II, II, tricyclic/tetracyclic terpanes including des-A-oleanane, X, *, Y, Z, Z1 and bicadinanes W, T, T1, R. The biomarker characteristics are suggestive of larger influx of the dominant tropical/subtropical angiosperms in flora under a warming and more humid climate during depositions of the lower Sanya Formation (early Miocene) than the older Lingshui Formation (late Oligocene). The tropical/subtropical angiosperm input was thought as the prime control of terrigenous organic matter enrichment relative to the redox condition, and the coeval sea level changes and seafloor spreading in the South China Sea. Enrichment of the terrigenous organic matter in the early Miocene shales is likely in association with the coeval peak East Asian summer monsoon intensity in the South China Sea.
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Key words:
- total organic carbon /
- higher plant-derived biomarkers /
- tropical/subtropical plants /
- East Asian monsoonal climate
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Figure 1. Map of global palaeogeographical features at 29−20 Ma (a), present map of the regional geographical features and Asian monsoonal features relevant to the Ying-Qiong Basin (b), and map of the Ying-Qiong Basin south of Hainan Island in the South China Sea, showing the well locations from which samples were obtained, and the structural divisions of the Ying-Qiong Basin (c). In a, the red empty rectangle represents the location of the Ying-Qiong Basin; this map is adapted from Golonka et al. (2006). In b, the light red colored arrow and the light white arrow indicate the general directions of the East Asian summer monsoon and the East Asian winter monsoon, respectively; the red dotted line in a represents the location and boundary of the Ying-Qiong Basin. In c, ① and ② indicates the two large faults in the Ying-Qiong Basin.
Figure 2. Scatter plots of S1+S2 versus TOC (a), and Tmax versus HI of shales (b) in the Ying-Qiong Basin. Scatter plots of S1+S2 versus TOC of shales in Well L2-1 (c), Well S36-1 (d), Well S24-1 (e), Well B20-1 (f), Well B19-2 (g), Well Y7-4 (h). Tmax indicates temperature of maximum generation; S1+S2 indicates free hydrocarbons+pyrolyzed hydrocarbons; HI is the hydrogen index, equals S2/TOC×100.
Figure 5. Representative partial m/z 191, 412, 369, and 217 mass chromatograms of the aliphatic fractions from the representative lower Sanya Formation shale sample (3 380 m) in Well B19-2 (a) and the Sanya Formation shale sample (3 588−3 590 m) (b), showing distributions of tricyclic/tetracyclic compounds, rearranged oleananes I, II and III, 18α(H)-oleanane, 3β-methyl-24-nor-18β(H)-oleanane, 19α(H)-taraxastane and 3β-methyl-24-nor-18β(H)-taraxastane, bicadinanes W, T, T1, R, diasteranes and regular steranes. d1=13β(H),17α(H)-C27 diasterane 20S; d2=13β(H),17α(H)-C27 diasterane 20R; d3=13α(H),17β(H)-C27 diasterane 20S; d4=13α(H),17β(H)-C27 diasterane 20R; d5=24-methyl-13β(H),17α(H)-C28 diasterane 20S; d6=24-methyl-13β(H),17α(H)-C28 diasterane 20R; d7=24-ethyl-13β(H),17α(H)-C29 diasterane 20R. 10=24-ethyl-5α(H),14α(H),17α(H)-C29 sterane 20S; 11=24-ethyl-5α(H), 14β(H), 17β(H)-C29 sterane 20R; 12=24-ethyl-5α(H),14β(H),17β(H)-C29 sterane 20S.
Figure 7. Depth plots showing variations with depth of total organic carbon (TOC) in shales from seven wells in the Ying-Qiong Basin. a−g are vertical TOC variations in Well H29-1 (a), Well Y7-4 (b), Well L2-1 (c), Well S36-1 (d), Well S24-1 (e), Well B20-1 (f), Well B19-2 (g), respectively. The lower left subfigure shows the locations of these wells.
Figure 8. Variation n-alkane parameters with depth of the late Oligocene−early Miocene shales from Well B19-2. TAR=terrestrial/aquatic ratio=(nC27+nC29+nC31)/(nC15+nC17+nC19); ACL=average chain length of long-chain n-alkanes=(25×nC25+27×nC27+29×nC29+31×nC31+33×nC33)/( nC25+nC27+nC29+nC31+nC33). Paq=(nC23+nC25)/(nC23+nC25+nC29+nC31).
Figure 9. Relationships of oleanane/C30 αβ hopane versus taraxastane/C30 αβ hopane (a), taraxastane/C30 αβ hopane versus (W+T+T1+R)/C30 αβ hopane (b), oleanane/C30 αβ hopane versus (W+T+T1+R)/C30 αβ hopane (c) and (Des-A-oleanane+*+X+Y+Z+Z1+III+II+I+taraxastane+W+T+T1+R)/C30 αβ hopane (d). Des-A-oleanane, *, X, Y, Z, Z1 are angiosperm-sourced tricyclic/tetracyclic biomarkers in the Sanya Formaton shales. Compounds W, T, T1 and R are bicadinanes. The red points are the parameter values of the Sanya Formation samples, and the light blue dotted lines are the correlation lines between two parameters.
Figure 11. Terrigenous organic matter accumulation model of the marine shales under the strong monsoonal climate during deposition of the lower Sanya Formation (early Miocene, 23.0−18.3 Ma). This model was adapted from Clift et al. (2014). Plant taxa in flora and their ecological adaptations were from Ding et al. (2021). The scale is not respected.
Table 1. Summary of data ranges, average values and sample numbers of the measured total organic carbons, vitrinite reflectance and pyrolysis data of the shale samples in the Ying-Qiong Basin
Formation TOC/% Ro/% Tmax/°C S1 rock/(mg·g−1) S2 rock/(mg·g−1) S1+S2 rock/(mg·g−1) HI TOC/(mg·g−1) Upper Meishan 0.32−0.78 0.42−0.63 412−427 0.01−0.56 0.16−3.21 0.17−3.37 55−428 0.44 (20) 0.52 (6) 422 (22) 0.09 (22) 1.01 (22) 1.10 (22) 177 (22) Lower Meishan 0.07−0.33 0.35−0.65 406−432 0−0.29 0.02−4.17 0.02−4.33 8−479 0.33 (50) 0.53 (11) 416 (39) 0.04 (49) 0.37 (49) 0.40 (49) 81 (49) Upper Sanya 0.08−1.09 0.37−0.67 412−435 0−0.32 0.04−3.37 0.04−3.60 10−396 0.46 (77) 0.58 (22) 425 (76) 0.07 (77) 1.33 (77) 1.42 (77) 180 (62) Lower Sanya 0.18−2.9 0.39−0.95 403−447 0−0.65 0.07−6.41 0.07−7.01 18−434 0.72 (81) 0.62 (27) 430 (74) 0.15 (75) 1.41 (75) 1.55 (75) 132 (37) Upper Lingshui 0.14−2.40 0.61−0.74 407−450 0.01−0.67 0.02−5.10 0.06−5.77 11−226 0.67 (38) 0.66 (8) 427 (32) 0.15 (38) 0.94 (38) 1.10 (38) 97 (38) Middle Lingshui 0.11−1.37 0.63−0.86 420−441 0−1.13 0.02−2.64 0.03−2.89 10−313 0.51 (72) 0.72 (16) 428 (33) 0.16 (62) 0.68 (62) 0.84 (62) 102 (62) Lower Lingshui 0.16−2.02 0.72−0.88 425−445 0.01−0.41 0.09−2.42 0.10−2.67 9−310 0.51 (45) 0.77 (10) 432 (29) 0.12 (41) 0.77 (41) 0.89 (41) 138 (41) Upper Yacheng 0.28−0.78 0.84−1.05 422−453 0−0.12 0.21−0.69 0.25−0.81 58−100 0.46 (19) 0.95 (7) 439 (8) 0.07 (8) 0.39 (8) 0.46 (8) 74 (8) Note: In a−b, a and b are minimum and maximum values, respectively; in c ( d ), c is the average value, and d is the sample numbers. All the original data of the shale samples from these seven wells are shown in Supplementary Table S1. Table 2. Biomarker parameters of the shale samples from Well H29-1, Well B19-2 and Well S29-2 in the Ying-Qiong Basin
Well name Depth/m Formation Lithology Sample type TAR ACL Paq (nC31/(nC27+
nC29+nC31)CPI Pr/Ph Pr/nC17 Ph/nC18 C19 TT/(C19 TT+C23 TT) des-A-oleanane/C30 $\alpha \beta $ hopane */C30 $\alpha \beta $ hopane X/C30 $\alpha \beta $ hopane Y/C30 $\alpha \beta $ hopane Z/C30 $\alpha \beta $ hopane H29-1 3 038−3 040 lower Meishan shale cuttings 0.76 28.01 0.65 0.26 1.14 2.33 2.25 0.72 0.18 0.11 0.00 0.02 0.00 0.02 H29-1 3 088−3 094 lower Meishan shale cuttings 0.69 27.85 0.66 0.24 1.22 2.28 2.37 0.73 0.21 0.11 0.01 0.03 0.01 0.02 H29-1 3 528 Sanya shale cuttings 0.93 27.78 0.65 0.24 1.00 2.69 1.48 0.48 0.30 0.09 0.02 0.06 0.03 0.01 H29-1 3 562 Sanya shale cuttings 1.57 28.53 0.53 0.39 1.06 2.40 1.38 0.54 0.22 0.15 0.02 0.04 0.02 0.03 H29-1 3 578 Sanya shale cuttings 1.25 28.19 0.56 0.32 1.03 2.17 1.38 0.52 0.20 0.10 0.01 0.04 0.01 0.02 H29-1 3 580−3 582 Sanya shale cuttings 1.12 28.14 0.58 0.28 1.10 2.48 1.43 0.53 0.16 0.05 0.02 0.01 0.02 0.01 H29-1 3 586 Sanya shale cuttings 0.92 28.23 0.57 0.29 1.02 2.38 1.09 0.45 0.42 0.09 0.05 0.06 0.02 0.02 H29-1 3 588−3 590 Sanya shale cuttings 1.24 28.20 0.58 0.29 1.08 2.44 1.44 0.48 0.19 0.09 0.02 0.02 0.02 0.01 H29-1 3 593 Sanya fine sandstone sidewall core 6.01 28.60 0.41 0.31 1.06 1.64 0.54 0.24 0.22 0.17 0.05 0.10 0.04 0.03 H29-1 3 595 Sanya fine sandstone sidewall core 6.86 29.08 0.32 0.37 1.07 2.18 0.72 0.26 0.26 0.10 0.02 0.04 0.02 0.03 B19-2 2 350 lower Meishan shale cuttings 1.02 27.50 0.61 0.18 0.86 1.69 3.69 1.33 0.32 0.05 0.01 0.03 0.00 0.02 B19-2 2 748 upper Sanya shale cuttings 2.16 28.74 0.44 0.33 0.93 2.92 4.05 1.11 0.34 0.06 0.01 0.02 0.00 0.02 B19-2 2 880 lower Sanya shale cuttings 5.71 28.87 0.37 0.34 0.94 4.64 6.98 1.22 0.57 0.06 0.00 0.01 0.00 0.02 B19-2 3 100 lower Sanya shale cuttings 8.15 28.69 0.35 0.30 0.97 4.79 7.36 1.31 0.60 0.10 0.01 0.01 0.01 0.02 B19-2 3 238 lower Sanya shale cuttings 4.52 28.30 0.47 0.27 1.09 4.04 6.59 1.22 0.62 0.14 0.01 0.01 0.01 0.02 B19-2 3 300 lower Sanya shale cuttings 4.14 28.34 0.50 0.28 1.10 4.37 5.33 1.01 0.65 0.14 0.01 0.02 0.01 0.02 B19-2 3 380 lower Sanya shale cuttings 2.87 28.19 0.52 0.26 1.10 3.67 3.49 0.74 0.57 0.07 0.01 0.01 0.00 0.01 B19-2 3 460 upper Lingshui shale cuttings 3.84 28.21 0.50 0.26 1.13 3.97 4.61 0.91 0.57 0.17 0.02 0.04 0.01 0.03 B19-2 3 878 middle Lingshui shale cuttings 1.89 27.74 0.62 0.21 1.25 4.54 1.94 0.33 0.38 0.10 0.05 0.06 0.02 0.02 B19-2 3 980 middle Lingshui shale cuttings 2.14 27.89 0.61 0.22 1.12 2.53 1.07 0.24 0.21 0.01 0.01 0.01 0.01 0.01 B19-2 4 020 middle Lingshui shale cuttings 2.44 27.88 0.60 0.23 1.19 3.49 3.27 0.66 0.40 0.13 0.03 0.03 0.01 0.01 B19-2 4 092 middle Lingshui shale cuttings 1.11 27.40 0.71 0.18 1.22 3.34 0.95 0.21 0.29 0.03 0.01 0.01 0.01 0.01 B19-2 4 182 middle Lingshui shale cuttings 1.25 27.40 0.71 0.19 1.32 2.35 1.61 0.34 0.14 0.01 0.00 0.00 0.00 0.01 B19-2 4 220 middle Lingshui shale cuttings 1.74 27.25 0.71 0.17 1.05 1.07 1.11 0.30 0.19 0.02 0.01 0.01 0.01 0.01 B19-2 4 330 middle Lingshui shale cuttings 1.77 26.91 0.76 0.07 1.71 1.47 2.70 0.63 0.10 0.01 0.03 0.03 0.05 0.03 B19-2 4 394 middle Lingshui shale cuttings 1.41 27.65 0.60 0.20 1.11 1.23 1.08 0.56 0.11 0.03 0.01 0.02 0.00 0.01 B19-2 4 510 lower Lingshui shale cuttings 0.71 26.93 0.74 0.06 1.13 1.26 1.25 0.64 0.13 0.01 0.01 0.01 0.00 0.01 B19-2 4 718 lower Lingshui shale cuttings 0.59 26.87 0.78 0.08 1.09 0.99 1.45 0.79 0.13 0.09 0.07 0.06 0.01 0.06 B19-2 4 810 lower Lingshui shale cuttings 0.72 26.86 0.76 0.07 1.67 1.85 2.06 0.96 0.19 0.02 0.00 0.00 0.01 0.01 S29-2 2 215 upper Meishan shale cuttings 2.25 28.94 0.42 0.36 1.28 2.00 2.63 0.96 0.11 0.04 nd nd nd nd S29-2 2 535−3 555 lower Meishan shale cuttings 2.25 28.75 0.50 0.36 1.23 2.01 2.54 1.00 0.18 0.07 nd nd nd nd S29-2 2 658−2 662 upper Sanya shale cuttings 1.26 28.55 0.56 0.35 1.32 2.16 2.59 0.92 0.20 0.02 nd nd nd nd S29-2 2 934−2 936 upper Sanya shale cuttings 3.06 28.90 0.41 0.35 1.41 3.29 3.68 0.94 0.25 0.08 nd nd nd nd S29-2 3 286−3 288 lower Sanya shale cuttings 3.75 28.48 0.45 0.29 1.20 3.69 3.78 0.80 0.70 0.11 nd nd nd nd S29-2 3 336−3 338 lower Sanya shale cuttings 5.34 28.54 0.42 0.29 1.22 3.66 4.20 0.79 1.00 0.10 nd nd nd nd S29-2 3 832−3 834 upper Lingshui shale cuttings 1.17 27.82 0.62 0.23 1.12 4.44 1.90 0.37 0.47 0.16 nd nd nd nd S29-2 3 942−3 944 upper Lingshui shale cuttings 1.25 27.60 0.66 0.20 1.07 4.31 1.38 0.25 0.38 0.11 nd nd nd nd S29-2 4 020−4 022 middle Lingshui shale cuttings 1.80 27.83 0.60 0.23 1.11 3.97 1.30 0.29 0.36 0.16 nd nd nd nd S29-2 4 050 middle Lingshui shale cuttings 3.21 27.61 0.65 0.21 1.11 1.98 1.65 0.34 0.20 0.02 nd nd nd nd S29-2 4 158 middle Lingshui shale cuttings 3.34 27.81 0.60 0.23 1.14 1.83 1.43 0.30 0.17 0.01 nd nd nd nd Well name Z1/
C30 $\alpha \beta $
hopaneTs/
(Ts+Tm)C31 $\alpha \beta $
hopane 20S/
(20S+20R)oleanane/
C30 $\alpha \beta $
hopane19$\alpha $(H)-
taraxastane/
C30 $\alpha \beta $ hopaneI/
C30 $\alpha \beta $
hopaneII/
C30 $\alpha \beta $
hopaneIII/
C30 $\alpha \beta $
hopane(III+II+ I)/
C30 $\alpha \beta $ hopaneW/
C30 $\alpha \beta $ hopaneT/
C30 $\alpha \beta $ hopaneT1/
C30 $\alpha \beta $
opaneR/
C30 $\alpha \beta $
opane(W+T+T1+R)/
C30 $\alpha \beta $ hopane(des-A-oleanane+
*+X+Y+Z+Z1+I+
II+III+W+T+T1+R)/
C30 $\alpha \beta $ hopaneC27/C29 $\alpha \alpha \alpha $ 20R steranes C29/C27 $\alpha \alpha \alpha $ 20R steranes C29 20S/(20S+20R) steranes H29-1 0.06 0.49 0.57 0.70 0.11 0.26 0.20 0.25 0.11 0.02 0.15 0.04 0.04 0.25 0.68 0.72 1.39 0.35 H29-1 0.06 0.49 0.59 0.86 0.13 0.31 0.15 0.24 0.10 0.02 0.21 0.05 0.06 0.33 0.80 0.68 1.48 0.39 H29-1 0.06 0.63 0.54 0.77 0.15 0.20 0.18 0.43 0.13 0.16 0.70 0.16 0.15 1.16 1.71 1.03 0.97 0.49 H29-1 0.08 0.57 0.54 1.59 0.20 0.37 0.40 0.75 0.25 0.50 1.98 0.42 0.36 3.26 4.04 0.96 1.04 0.45 H29-1 0.06 0.60 0.55 1.03 0.15 0.34 0.28 0.54 0.21 0.29 1.27 0.30 0.25 2.11 2.71 0.89 1.13 0.44 H29-1 0.04 0.60 0.55 0.55 0.10 0.13 0.25 0.37 0.05 0.15 0.76 0.16 0.18 1.25 1.56 0.49 2.03 0.50 H29-1 0.05 0.64 0.57 1.12 0.16 0.29 0.29 0.60 0.22 0.24 1.09 0.26 0.21 1.80 2.47 1.13 0.88 0.48 H29-1 0.05 0.55 0.54 1.05 0.17 0.22 0.34 0.59 0.10 0.22 1.14 0.28 0.27 1.91 2.39 0.63 1.59 0.42 H29-1 0.11 0.49 0.60 3.05 0.43 0.36 0.71 1.53 0.29 0.58 3.27 0.75 0.63 5.23 6.44 0.50 1.99 0.51 H29-1 0.08 0.53 0.57 2.43 0.34 0.44 0.73 1.36 0.23 0.40 2.72 0.66 0.50 4.29 5.15 0.66 1.53 0.49 B19-2 0.02 0.30 0.50 0.36 0.08 0.26 0.15 0.26 0.06 0.01 0.01 0.01 0.08 0.11 0.65 0.79 1.27 0.12 B19-2 0.05 0.45 0.59 0.41 0.11 0.56 0.56 0.57 0.18 0.01 0.20 0.05 0.04 0.31 0.82 0.70 1.43 0.34 B19-2 0.03 0.35 0.58 0.45 0.12 0.37 0.21 0.28 0.07 0.01 0.08 0.02 0.04 0.15 0.45 0.42 2.38 0.29 B19-2 0.05 0.38 0.60 0.44 0.10 0.59 0.44 0.42 0.14 0.03 0.26 0.07 0.06 0.41 0.84 0.48 2.08 0.35 B19-2 0.07 0.35 0.60 0.45 0.13 0.52 0.45 0.43 0.16 0.07 0.43 0.09 0.06 0.65 1.19 0.47 2.13 0.38 B19-2 0.07 0.42 0.60 0.43 0.14 0.37 0.44 0.51 0.15 0.18 1.11 0.25 0.23 1.78 2.32 0.45 2.22 0.39 B19-2 0.04 0.36 0.58 0.36 0.07 0.11 0.16 0.24 0.05 0.06 0.27 0.06 0.08 0.47 0.73 0.81 1.23 0.38 B19-2 0.09 0.46 0.59 0.45 0.13 0.36 0.36 0.43 0.13 0.21 0.91 0.21 0.18 1.50 2.09 0.67 1.49 0.44 B19-2 0.05 0.37 0.56 0.25 0.07 0.16 0.17 0.32 0.08 1.00 3.89 0.79 0.78 6.45 6.88 0.99 1.01 0.46 B19-2 0.01 0.29 0.54 0.12 0.02 0.13 0.07 0.07 0.03 0.21 0.81 0.17 0.20 1.38 1.48 0.81 1.23 0.41 B19-2 0.06 0.37 0.60 0.28 0.11 0.21 0.25 0.35 0.09 0.59 2.25 0.48 0.34 3.66 4.11 0.96 1.04 0.44 B19-2 0.01 0.45 0.54 0.21 0.05 0.09 0.09 0.11 0.03 0.09 0.38 0.09 0.11 0.67 0.81 1.08 0.93 0.33 B19-2 0.01 0.30 0.56 0.06 0.04 0.08 0.08 0.06 0.02 0.16 0.51 0.10 0.12 0.89 0.96 0.84 1.19 0.38 B19-2 0.01 0.38 0.55 0.10 0.03 0.08 0.06 0.12 0.02 0.08 0.28 0.07 0.07 0.50 0.62 0.73 1.37 0.39 B19-2 0.03 0.42 0.52 0.08 0.03 0.05 0.07 0.05 0.07 0.11 0.39 0.08 0.07 0.65 0.84 0.86 1.16 0.40 B19-2 0.01 0.42 0.53 0.07 0.04 0.04 0.02 0.03 0.02 0.02 0.06 0.02 0.01 0.11 0.21 0.85 1.18 0.40 B19-2 0.01 0.44 0.52 0.09 0.03 0.03 0.03 0.04 0.01 0.02 0.10 0.04 0.02 0.18 0.28 0.75 1.33 0.56 B19-2 0.08 0.23 0.44 0.08 0.08 0.02 0.02 0.03 0.03 0.01 0.05 0.02 0.02 0.11 0.59 0.82 1.22 0.37 B19-2 0.01 0.38 0.57 0.09 0.04 0.03 0.02 0.02 0.01 0.02 0.08 0.02 0.02 0.14 0.23 0.83 1.20 0.38 S29-2 nd 0.37 0.47 0.10 nd nd nd nd nd 0.01 0.08 0.02 0.03 0.09 nd 0.85 1.17 0.16 S29-2 nd 0.37 0.55 0.59 nd nd nd nd nd 0.08 0.31 0.05 0.08 0.39 nd 0.80 1.26 0.16 S29-2 nd 0.29 0.57 0.49 nd nd nd nd nd 0.05 0.29 0.08 0.09 0.34 nd 0.88 1.13 0.21 S29-2 nd 0.54 0.57 0.62 nd nd nd nd nd 0.05 0.12 0.02 0.02 0.17 nd 0.53 1.87 0.35 S29-2 nd 0.42 0.61 0.58 nd nd nd nd nd 0.10 0.55 0.19 0.10 0.65 nd 0.36 2.79 0.45 S29-2 nd 0.42 0.60 0.54 nd nd nd nd nd 0.09 0.31 0.09 0.08 0.40 nd 0.33 2.99 0.45 S29-2 nd 0.44 0.56 0.39 nd nd nd nd nd 0.71 2.50 0.40 0.41 3.21 nd 0.49 2.05 0.42 S29-2 nd 0.46 0.56 0.38 nd nd nd nd nd 0.89 2.30 0.31 0.31 3.19 nd 0.66 1.53 0.42 S29-2 nd 0.59 0.58 0.35 nd nd nd nd nd 0.29 0.90 0.18 0.15 1.19 nd 0.62 1.61 0.42 S29-2 nd 0.49 0.55 0.10 nd nd nd nd nd 0.18 0.81 0.12 0.10 0.99 nd 0.55 1.81 0.43 S29-2 nd 0.48 0.55 0.08 nd nd nd nd nd 0.10 0.35 0.08 0.07 0.45 nd 0.55 1.83 0.41 Note: TAR=terrestrial/aquatic ratio=(nC27+nC29+nC31)/(nC15+nC17+nC19); ACL=(25×nC25+27×nC27+29×nC29+31×nC31+33×nC33)/(nC25+nC27+nC29+nC31+nC33); Paq=(nC23+nC25)/(nC23+nC25+nC29+nC31); CPI22-32=Carbon preference index, = 2×(nC23+nC25+nC27+nC29+nC31)/(nC22+nC24+nC26+nC28+nC30+nC32); Pr/Ph=pristane/phytane; C19 TT=C19 tricyclic terpane; C23TT=C23 tricyclic terpane; Compounds *, X, Y, Z, Z1 are tricyclic/tetracyclic terpanes; I, II, III are arranged oleananes; W=cis-cis-trans-bicadinane, T=trans-trans-trans-bicadinane. -
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