US EPA

4968905 

Journal Article 

Biomarker evidence for Botryococcus and a methane cycle in the Eocene Huadian oil shale, NE China 

Volkman, JK; Zhang, Z; Xie, X; Qin, J; Borjigin, T 

2015 

1 

Organic Geochemistry
ISSN: 0146-6380 

Elsevier 

78 

Elsevier 

121-134 

English 

10.1016/j.orggeochem.2014.11.002 

WOS:000346389700012 

https://linkinghub.elsevier.com/retrieve/pii/S0146638014002745
Exit
 

The saturated and unsaturated hydrocarbons of two samples (HD-19 and HD-21) from the same section of the Middle Eocene lacustrine Huadian oil shale in NE China were identified and shown to be mainly from algal and bacterial sources. Comparison of the two samples provided an opportunity to explore the contribution from telalginite to the hydrocarbon profiles. Cells identified from microscopy as Botryococcus in the telalginite of HD-21 were confirmed as belonging to the L race of B. braunii from the presence of monoaromatic lycopane derivatives and small amounts of several lycopadienes. Lycopane was abundant and was probably derived from biohydrogenation of lycopadienes and related lipids on the basis of delta C-13 values. Hopane distributions showed a dominance of those with the biological 17 beta, 21 beta-stereochemistry, as expected for an immature shale, with low amounts of 17 beta, 21 alpha-hopanes (moretanes) and 17 alpha,21 beta-hopanes. Two hopenes were also abundant and assigned as C-29 and C-30 neohop-13(18)-enes, which occurred together with the C-29 and C-30 hop-17(21)-enes. These had depleted carbon isotope values (-43.7% to -50.8%), indicative of production by methane oxidizing bacteria (methanotrophs). The high proportion of hopanoids with carbon numbers < C-32 indicates extensive post-depositional diagenetic alteration of bacteriohopanepolyols as well as a direct input of C-30 hopanoids. The data clearly indicate that there was active utilization of methane in this lacustrine depositional setting, but isoprenoid hydrocarbon biomarkers for methanogens, such as pentamethylicosane (PMI) and squalane, were in surprisingly low abundance. It is possible that these bacterial contributions were present as polar lipids. The origins of an unusual C-38 isoprenoid alkane assigned as bipristane are uncertain, but may be from methanogens. Steranes and sterenes were relatively minor components, but abundant diasterenes and 4-methyldiasterenes were present, reflecting significant conversion of the original lipid composition by way of clay-catalysed diagenesis. The biomarker data suggest that the bottom waters in the original depositional environment had low O-2 content, but the sediments were probably neither sulfidic nor strongly reducing. The high content of organic matter in the shale likely reflects both high (but fluctuating) productivity due to eutrophic conditions in the overlying water and good preservation in the sediments. (C) 2014 Elsevier Ltd. All rights reserved. 

Huadian oil shale; Eocene; Biomarkers; Neohopenes; Diasterenes; Botryococcus; Diagenesis; Methane oxidation; Carbon isotopes; Lycopane