Lipid biomarkers for the reconstruction of deep-time environmental conditions

Lipids can survive long geological intervals within sediments and provide a unique tool that allows the reconstruction of past organismic diversity and environmental conditions. The lipids discussed in this review include all substances produced by organisms that are insoluble in water but extractable by organic solvents. Lipid biomarkers refer to both functionalized biolipids as well as their hydrocarbon derivatives in geological materials that contain diverse information about biotic sources and environmental conditions. In spite of diagenetic and catagenetic alteration, lipid biomarkers commonly preserve the hydrocarbon structure of their biotic counterparts and have been found in rocks up to 1.6 billion years in age. These features have promoted the use of lipid biomarkers in many fields, including petroleum geology, paleoclimatology, oceanography, meteorology, geobiology and environmental science. Here, we (i) review the use of lipid biomarker records for the reconstruction of environmental conditions in deep time, including climatic conditions (temperature), sedimentary environments (redox, salinity and chemical composition) as well as catastrophic terrestrial events (soil erosion and wildfire), and (ii) generate new insights into environmental perturbations during the Permian Triassic transition based on investigation of lipid biomarkers. We further propose that the ratio of dibenzothiophene to phenanthrene (DBT/P) in marine carbonates may be a robust proxy for seawater sulfate concentrations in deep time. Our compiled DBT/P records show substantial variations in seawater sulfate levels through Earth history that are consistent with the results of other proxies. We discuss the future outlook for application of lipid biomarker records to deep-time environmental research.

脂质能够在沉积物中历经漫长的地质时期而留存，为重建过去的生物多样性和环境条件提供了一种独特的工具。本文所讨论的脂质包括生物产生的所有不溶于水但可被有机溶剂提取的物质。脂质生物标志物既指官能化的生物脂质，也指地质材料中它们的烃类衍生物，这些物质包含有关生物来源和环境条件的多种信息。尽管经历了成岩作用和后生作用的改变，脂质生物标志物通常保留其生物对应物的烃类结构，并且在年龄达16亿年的岩石中被发现。这些特性促进了脂质生物标志物在许多领域的应用，包括石油地质学、古气候学、海洋学、气象学、地球生物学和环境科学。在此，我们（i）综述了脂质生物标志物记录在重建远古环境条件方面的应用，包括气候条件（温度）、沉积环境（氧化还原、盐度和化学成分）以及灾难性的陆地事件（土壤侵蚀和野火），并且（ii）基于对脂质生物标志物的研究，对二叠纪 - 三叠纪过渡期间的环境扰动有了新的认识。我们进一步提出，海相碳酸盐中苯并噻吩与菲的比率（DBT/P）可能是远古时期海水硫酸盐浓度的一个可靠指标。我们汇编的DBT/P记录显示，地球历史上海水硫酸盐水平存在显著变化，这与其他指标的结果一致。我们讨论了脂质生物标志物记录在远古环境研究中应用的未来前景。