首页|n-C-27 Predominance and C-13 enrichment by bicarbonate assimilation of race A of Botryococcus braunii in Chinese Maoming oilshales

n-C-27 Predominance and C-13 enrichment by bicarbonate assimilation of race A of Botryococcus braunii in Chinese Maoming oilshales

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  • NSTL
  • Elsevier
In Maoming oilshales, the presence of races B and L of Botryococcus braunii (B. braunii) was confirmed by the detection of botryococcanes and C-40 lycopanes and their derivatives. However, there were no specific biomarkers for race A of B. braunii. The contribution of race A of B. braunii has been implied by the distribution of nonspecific n-alkanes with an odd carbon-number preference and a predominance of n-C-27. However, confirmation of its contribution to oilshales has been lacking until now. We found that n-C-27 is a dominant n-alkane in most Maoming samples which exhibits a positive delta C-13 excursion (approximately 2-3 parts per thousand) compared to other homologues. In addition, the extremely heavy delta C-13 values of botryococcanes (-6.0 parts per thousand to -8.5 parts per thousand) are rationalized to reflect bicarbonate assimilation in race B of B. braunii. The positive excursion of the delta C-13 values of n-C-27 extracted from the same samples could be attributed to bicarbonate assimilation by race A in a similar manner. Bicarbonate assimilation by race A would also explain the isotopic enrichment of n-C-14 similar to n-C-33 alkanes in the range of -20.1 parts per thousand to -26.1 parts per thousand. They are close to the values of some higher plant sources (C-4 plant) and largely different than that of the reported algal n-alkanes (<-30.6%.). The bicarbonate consumption mechanism utilized by both races A and B of B. braunii in Maoming oilshales was triggered by the sharp decrease in pCO(2) during the Late Eocene period, recorded globally at the Eocene-Oligocene transition. The presence of race A of B. braunii in most of Maoming sediments indicates that it was wide spread and populated in Maoming Basin over a long period of time, serving as the main biological source material of oilshales on a large scale.

N-alkanesN-C-27Botryococcus brauniiRaces A and BIsotopic enrichmentBicarbonate assimilationMaoming BasinCARBON CONCENTRATING MECHANISMSMACROCYCLIC-ALKANESDELTA-C-13 ANALYSESOLIGOCENE CLIMATETIBETAN PLATEAUSACRED-LAKEN-ALKANESHYDROCARBONSBASINLIPIDS

Sheng, Guoying、Peng, Ping'an、Hsu, Chang Samuel、Liao, Jing、Feng, Qiao、Lu, Hong

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Chinese Acad Sci

Petro Bio Oil Consulting

Shandong Univ Sci & Technol

2022

10.1016/j.chemgeo.2022.120905

Chemical geology

Chemical geology

EISCI
ISSN：0009-2541
年,卷(期)：2022.602
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