Molecular organic geochemical records of the ANT28-D5-06 sediment core in the Weddell Sea of West Antarctica and their petroleum geology significance

The chromatography - mass spectrometry of soluble extracts from organic sediment source ANT28-D5-06 in the Weddell Sea of West Antarctica allows investigations on molecular biomarkers (n-alkanes, isoprenoid, serroid terpane), organic carbon and isotope, forming environment, organic maturity, hydrocarbon-generation potential and hydrocarbon migration of this core sediment. The results show that, n-alkanes show a unimodal distribution, with peak carbons of nC
₁₆
, nC
₁₇
and nC
₁₈
, and weak high-carbon peak group; the organic matter type is sapropel, with (ΣC
₂₁
*/ΣC
₂₂
⁺
) and (C
₂₁
+C
₂₂
)/(C
₂₈
+C
₂₉
) ratios greater than 1.0, indicative of the derivation of organic matter chiefly from a marine environment; the organic sediment is abundant with tricyclic terpanes and pentacyclic triterpane, with a high content of gammacerane and a distribution dominance of C
₂₉
sterol and C
₂₇
sterol, further suggesting the organic matter is dominated by input of lower organisms; isotopes of organic carbon (δ
¹³
C) lie between -25.30
⁰
/
₀₀
and -25.91
⁰
/
₀₀
, implying a characteristic of marine aquatic organisms; Pr/Ph ratios range from 0.41 to 0.97, indicating a strong reducing environment; organic carbon in 2cm-11cm of the site ANT28-D5-06 is greater than 1.5; C
₂₉
ααα20S/C
₂₉
ααα(20S+20R) ratios are mostly between 0.32 and 0.48; C
₂₉
αββ/C
₂₉
(ααα+αββ) ratios lie in a range of 0.31-0.54; C
₃₂
22S/C
₃₂
(22S+22R) ratios range from 0.56 to 0.62; Ts/(Tm+Ts) ratios lie between 0.33 and 0.51; all these indices for discrimination of mature oil illustrate that, the organic sediment ANT28-D5-06 has an overall high maturity, close to high-quality organic sediment source, possessing favorable hydrocarbon-generation conditions, and some organic sediment source horizons have reached hydrocarbon-generation peak, which indicate a great prospecting potential for the Weddell basin.