Abstract The composition of organic matter in early Miocene sediment cores obtained from International Ocean Discovery Program Expedition 359 (IODP Exp. 359) was analysed using tetramethylammonium hydroxide (TMAH) thermochemolysis, a method used to determine concentrations of lignin phenols, fatty acids, sterols and hopanoids. These early Miocene sediment cores contain thick sequences (∼100 m) of interbedded light (organic-poor) and dark (organic-rich) sedimentary layers. A total of 49 samples from cores between 704.4 mbsf to 803.95 mbsf (∼20–23 Ma) at Site U1466 (518 m water depth) was selected with particular emphasis placed on the dark layers, although the light layers were also sampled. While organic compounds were below detection limits in the lighter (white) coloured sedimentary layers, the dark layers, with concentrations of organic carbon up to 20%, contained varying concentrations of all analysed compounds. Although sterols were present, hopanoids were more abundant in the dark layers. The contribution of prokaryotic organisms, estimated from the ratio ([hopanols and hopanoic acids]/[sterols + hopanols and hopanoic acids]), indicates that it was prokaryotic organisms rather than eukaryotic organisms that contributed the majority (∼90%) of the organic matter in the dark layers. In conjunction with this record, more negative δ15N values in the darker layers suggest that the prokaryotic organisms were nitrogen-fixing microorganisms (presumably cyanobacteria). The long-to-short fatty acid ratios, together with sterol distributions and the concentration of lignin phenols, suggest the input of terrestrial plant material occurred during a high total organic carbon (TOC) interval (∼770–810 mbsf), which coincides with more negative carbon isotope ratios. Additionally, the long-to-short fatty acid ratio in this interval was significantly higher in the dark layers than the light layers, suggesting that terrestrial environments suitable for vegetation growth expanded during the interval represented by the dark layers. Furthermore, the ratio of cinnamyl lignin phenols to vanillyl lignin phenols (C/V) is relatively high during these intervals. From these biomarker tracers, we speculate that the terrestrial vegetation was dominated by herbaceous plants adapted to frequent sea-level changes.

中文翻译：

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原核生物和陆生植物对马尔代夫环礁间腐烂的贡献：来自有机生物标志物的证据

摘要 使用四甲基氢氧化铵 (TMAH) 热化学分解法分析了从国际海洋发现计划远征 359 (IODP Exp. 359) 获得的早中新世沉积岩芯中有机质的组成，该方法用于确定木质素酚、脂肪酸、甾醇和藿香甙。这些早中新世沉积岩心包含浅色（有机质贫乏）和深色（有机质丰富）沉积层的厚层序（~100 m）。总共从 704.4 mbsf 到 803.95 mbsf（~20-23 Ma）的 U1466 站点（518 m 水深）的岩心中选择了 49 个样本，特别强调了暗层，尽管也对亮层进行了采样。虽然有机化合物在较浅（白色）颜色的沉积层中低于检测限，但在深色层、有机碳浓度高达 20%，包含不同浓度的所有分析化合物。尽管存在甾醇，但在暗层中更丰富的hopanoids。原核生物的贡献，根据比率（[hopanols 和hopanoic酸]/[sterols + hopanols 和hopanoic酸]）估计，表明是原核生物而不是真核生物贡献了大部分（~90%）的有机暗层中的物质。结合这一记录，较暗层中更多的负 δ15N 值表明原核生物是固氮微生物（可能是蓝藻）。长短脂肪酸比例，以及甾醇分布和木质素酚的浓度，表明陆生植物材料的输入发生在高总有机碳 (TOC) 区间 (~770–810 mbsf) 期间，这与更负的碳同位素比率一致。此外，该区间长短脂肪酸比在暗层显着高于亮层，表明适合植被生长的陆地环境在以暗层为代表的区间扩大。此外，在这些时间间隔内，肉桂基木质素酚与香草基木质素酚的比率 (C/V) 相对较高。根据这些生物标志物示踪剂，我们推测陆地植被以适应频繁海平面变化的草本植物为主。该区间长短脂肪酸比在暗层显着高于亮层，表明适合植被生长的陆地环境在以暗层为代表的区间扩大。此外，在这些时间间隔内，肉桂基木质素酚与香草基木质素酚的比率 (C/V) 相对较高。从这些生物标志物示踪剂中，我们推测陆地植被以适应频繁海平面变化的草本植物为主。该区间长短脂肪酸比在暗层显着高于亮层，表明适合植被生长的陆地环境在以暗层为代表的区间扩大。此外，在这些时间间隔内，肉桂基木质素酚与香草基木质素酚的比率 (C/V) 相对较高。从这些生物标志物示踪剂中，我们推测陆地植被以适应频繁海平面变化的草本植物为主。在这些时间间隔内，肉桂基木质素酚与香草基木质素酚的比率 (C/V) 相对较高。根据这些生物标志物示踪剂，我们推测陆地植被以适应频繁海平面变化的草本植物为主。在这些时间间隔内，肉桂基木质素酚与香草基木质素酚的比率 (C/V) 相对较高。从这些生物标志物示踪剂中，我们推测陆地植被以适应频繁海平面变化的草本植物为主。