Origin and geochemical implication of relatively high abundance of 17α (H)-diahopane in Yabulai basin, northwest China

Distribution and Geochemical Significance of Rearranged Hopanes in Jurassic Source Rocks and Related Oils in the Center of the Sichuan Basin, China

“…In the Songliao Basin, China, a positive correlation was found between the gammacerane index and the abundance of diahopanes in crude oils . Similarly, Jin et al suggested that the relatively high abundance of 17α­(H)-diahopanes in extracts from the Yabulai Basin, northwest China, is the result of a brackish water depositional environment . In the present study area, the abundances of 17α­(H)-diahopanes and early-eluting rearranged hopanes in the Jurassic source rocks generally increase with the increase of Ga/C 30 H values (Figure ).…”

“…As shown in Figure , the relative abundance of the different rearranged hopanes fluctuates frequently and markedly in both P103 and G17 profiles. The C 30 D/C 30 H ratio (>1.3) in a source rock sample collected at a depth of 2472 m in well G17 is several times higher than that of a sample from a depth of 2472.5 m. A similar phenomenon was also observed in the Yabulai Basin, northwest China …”

“…10 Similarly, Jin et al suggested that the relatively high abundance of 17α(H)diahopanes in extracts from the Yabulai Basin, northwest China, is the result of a brackish water depositional environment. 27 In the present study area, the abundances of 17α(H)-diahopanes and early-eluting rearranged hopanes in the Jurassic source rocks generally increase with the increase of Ga/C 30 H values (Figure 8). Based on the study of major elements and trace elements, the Jurassic source rocks were evidenced to be deposited in a shallow lake, with fluctuating depth, in fresh to saline water conditions.…”

“…Clay-mediated acidic catalysis may be another key factor affecting the generation of rearranged hopanes in the study area. Confusingly, the abundances of rearranged hopanes in source rocks from many other basins are much lower than in those of the Sichuan Basin, even in basins with similar depositional environments and maturation levels. − Perhaps a bloom of aquatic life, or some other biological group, in the early Jurassic in the study area had some influence on the enrichment of diahopanes . Although the mechanism causing such a high abundance of rearranged hopanes remains unclear, the study of the geochemical characteristics of rearranged hopanes may have significant implications for oil-source correlation in the study area.…”

Origin and Geochemical Implications of Hopanoids in Saline Lacustrine Crude Oils from Huanghekou East Sag and Laizhouwan Northeastern Sag, Bohai Bay Basin

“…Hopanoids < C 30 are mainly formed from diplopterol and diploptene without a long side chain at C-22, which can be found in almost all hopanoid-producing bacteria . Because of the comprehensive impact of the origin, depositional environment, and diagenetic effects, the hopanoids occur in many novel types with various structures, such as hopenes, , isohopanes, , rearranged hopanes, − aromatized hopanes, , sulfur-containing hopanes, − and nitrogen-containing hopanes. , Intriguingly, most hopanoid precursors were found in aerobic bacteria, although their biosynthesis does not require oxygen. However, some hopanoids were also found in anaerobic bacteria, such as planctomycetes, Petrosia sp .…”