<sup>2</sup>H/<sup>1</sup>H ratio of hopanes, tricyclic and tetracyclic terpanes in oils and source rocks from the Potiguar Basin, Brazil

We report the hydrogen isotope ratio2H/1H (expressed as2H values) of 8 selected hopanes, tricyclic and tetracyclic terpanes from oils and source rocks in the Potiguar Basin, and of associated formation water. Hopanes ranged in2H value from −79‰ to −142‰, whereas tri- and tetracyclic terpanes (TTTs) ranged from −137‰ to −225‰. Formation water2H values ranged from −23‰ to −32‰. The most significant pattern in the data is the systematic2H enrichment of hopanes relative to TTTs, by an average of 45‰ in oils and 78‰ in source rock extracts. The hopanes appear close to hydrogen isotopic equilibrium with coeval formation water, whereas TTTs are significantly more2H depleted. Given the similarities in structure between the two compound classes, it is unlikely that hopanes would be exchanged completely while the others would not. More likely, both classes have undergone a limited extent of exchange, but with the hopanes being biosynthesized with2H values closer to equilibrium. Our data suggest that at least some primary environmental and/or biotic information can be retained in the2H values of biomarkers in oils and extracts, and is not completely obscured by hydrogen exchange.

我们报道了来自波蒂瓜尔盆地的石油和烃源岩中8种选定的藿烷、三环萜烷和四环萜烷以及相关地层水的氢同位素比值²H/¹H（以²H值表示）。藿烷的²H值范围为−79‰至−142‰，而三环和四环萜烷（TTTs）的范围为−137‰至−225‰。地层水的²H值范围为−23‰至−32‰。数据中最显著的模式是藿烷相对于TTTs有系统性的²H富集，在石油中平均富集45‰，在烃源岩提取物中平均富集78‰。藿烷似乎与同时代的地层水接近氢同位素平衡，而TTTs则明显更贫²H。鉴于这两类化合物在结构上的相似性，藿烷完全发生交换而其他化合物不发生交换是不太可能的。更有可能的是，两类化合物都经历了有限程度的交换，但藿烷在生物合成时的²H值更接近平衡。我们的数据表明，至少一些原始环境和/或生物信息可以保留在石油和提取物中生物标志物的²H值中，并且不会完全被氢交换所掩盖。