Twenty-five monoterpanes from six types of essential oils and hydrogenated turpentine oil have been identified and their stable carbon isotope composition determined. Monoterpanes in essential oils sourced from terrestrial higher plants display a δ 13 C value in the range of −34‰-26‰, and mostly between −29‰ and −27‰. The δ 13 C value of any single monoterpane is very consistent in different essential oils. Acyclic monoterpanes show closer isotope composition between −28.6‰ and −26.2‰, with an average value of −27.7‰. In contrast, the isotope composition of cyclic monoterpanes is more scattered with an average value of −28.6‰. Isotopic fractionation with 13 C enrichment has been observed during both artificial and geological hydrogenation of monoterpenoids to monoterpanes, and this is more obvious for the acyclic monoterpenoids. In addition to higher plants, acyclic monoterpane 2,6-dimethylheptane in crude oil can also be originated from other organic inputs. monoterpenoids, stable carbon isotope, essential oil, crude oil Citation:Zhang D J, Wang P R, Mao Z C, et al. Stable carbon isotope composition of monoterpanes in essential oils and crude oils.
Devonian strata in the Guizhong region, Guangxi, China consist mainly of marine deposition carbonates (limestones and dolomites) as well as restricted clastic rocks. The strata thickness is measured as 2041m and classified into 14 formations. An integrated field geological, petrographic, sedimentological, palaeobiological, and geochemical study of these strata reveals that the depositional paleoenvironments were carbonate tidal flat, restricted platform, open platform, shelf, platform margin slop, and algal herm. The total organic carbon (TOC) of sedimentary organic matter ranges between 0.07% and 1.96% with average of 0.21%. The organic matter types are Type І and Type II 1 . The vitrinite reflectance (R 0 ) of kerogen ranges between 0.99% and 2.03%, indicating the maturated and highly maturated stages. The analytical results of the representative samples collected from shelf and subtidal facies show that the differences of organic matter type and biological diagnostic compounds are related to the types of source rocks deposited in different paleoenvironments. Guangxi, Devonian system, depositional environment, sedimentary organic matter, biomarker compounds
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