Abstract Highly oil prone source rocks containing sapropelic Type I and mixed Types I and III kerogen are found in 233 m of the 500 m deep, fully cored ENRECA-3 well drilled on Bach Long Vi Island, located at the junction between the Beibuwan and the Song Hong basins offshore northern Vietnam. The cored succession is made up entirely by Oligocene, deep lacustrine deposits. The origin of the organic matter (OM) in 62 samples is evaluated on the basis of gas chromatography-mass spectrometry (GC-MS and GC-MS/MS). OM in 55 samples is sourced primarily from lacustrine organisms and contains abundant 4-methylsteranes, tetracyclic polyprenoids (TPP) and lycopane, and no markers for marine organic matter. The proportion of triterpanes derived from angiosperms is low in most saturated fractions and only traces of gymnosperm diterpanes are detected. In contrast, all aromatic fractions have a high proportion of compounds having an origin from both gymnosperms and angiosperms. Very high concentrations of hopanoids in both fractions suggest significant bacterial alteration of the original OM. Most samples have a high concentration of rare C31 diaromatic 8,14-secohopanes with a fluorene moiety. Low pristane/phytane (Pr/Ph) ratios indicate that anoxic/suboxic bottom water conditions existed during OM accumulation. The presence of β-carotane, gammacerane and traces of arylisoprenoids could indicate a stratified water column. OM in a few samples with lower than average hydrogen index (HI) is mainly of terrestrial origin with a higher proportion of C29 steranes, diterpanes and oleanoids and lower concentrations of both saturated and aromatic hopanes. Higher Pr/Ph, a higher C34 isohopane ratio (IHR34) and a lower homohopane index (HHI) indicate that this low-HI OM was originally deposited under more oxic conditions and subsequently transported to deeper water. Low sterane and hopane isomerization ratios show that no samples have reached the oil-window. Some novel maturity parameters for immature lacustrine samples are proposed.

中文翻译：

---

越南北部近海北部湾-松洪盆地交界处渐新世湖相烃源岩的生物标志物

摘要 在位于北部湾与北部湾交界处的 Bach Long Vi 岛钻探的 500 m 深、全取芯的 ENRECA-3 井中，在 233 m 处发现了含有腐泥型 I 型和混合型 I 型和 III 型干酪根的高含油烃源岩。越南北部近海的宋洪盆地。岩心系列完全由渐新世深湖沉积物组成。基于气相色谱-质谱联用（GC-MS 和 GC-MS/MS）评估了 62 个样品中有机物 (OM) 的来源。55 个样品中的 OM 主要来自湖泊生物，含有丰富的 4-甲基甾烷、四环聚异戊二烯 (TPP) 和番茄红素，并且没有海洋有机物质的标记物。来自被子植物的三萜在大多数饱和部分中的比例很低，并且仅检测到裸子植物二萜的痕迹。相比之下，所有芳香族馏分都含有大量来自裸子植物和被子植物的化合物。两个部分中非常高浓度的藿烷表明原始 OM 发生了显着的细菌改变。大多数样品都含有高浓度的稀有 C31 双芳族 8,14-环庚烷和芴部分。低原始烷/植烷 (Pr/Ph) 比率表明在 OM 积累过程中存在缺氧/亚氧底水条件。β-胡萝卜素、γcerane 和痕量芳基异戊二烯的存在可能表明存在分层水柱。少数氢指数 (HI) 低于平均氢指数 (HI) 的样品中的 OM 主要来自陆地，具有较高比例的 C29 甾烷、二萜和齐墩果，以及较低浓度的饱和和芳香族藿烷。更高的 Pr/Ph, 较高的 C34 异戊烷比率 (IHR34) 和较低的同花烷指数 (HHI) 表明这种低 HI OM 最初是在更多有氧条件下沉积的，随后被输送到更深的水中。低甾烷和藿烷异构化比率表明没有样品达到油窗。提出了一些新的未成熟湖泊样品的成熟度参数。