黔北早寒武世缺氧事件:生物标志化合物及有机碳同位素特征
Early Cambrian oceanic anoxic event in northern Guizhou: biomarkers and organic carbon isotope

陈兰 ¹ 钟宏 ¹ 胡瑞忠 ¹ 肖加飞 ¹ 邹艳荣 ²

文摘	本文首次报道了黔北早寒武世黑色岩系的生物标志化合物,并结合有机碳同位素组成特征,探讨该时期所发生的重大地质事件.所有样品均检出了丰富的正构烷烃、类异戊二烯烃、萜类化合物以及甾类化合物.在GC谱图上,正构烷烃显示明显的单峰型分布特征,碳数分布范围为nC14-nC31,主峰碳为nC18、nC19或nC20,nC17/nC31为1.15～50.17,显示轻烃组分占绝对优势,OEP值为0.84～1.11,CPI值为0.92～1.16,接近平衡值1.0,无明显的奇偶碳数优势分布.Pr/Ph值为0.24～0.79,具有明显的植烷优势.萜烷化合物以C30藿烷占优势,其相对丰度三环萜烷＞五环三萜烷＞四环萜烷,并且检出少量的γ-蜡烷.规则甾烷C27-C28-C29呈"V"字型分布,∑(C27+C28)＞∑C29,其比值为1.25～1.99,∑C27/∑C29为0.78～1.22,重排甾烷C27/规则甾烷C27值为0.21～0.47.4-甲基甾烷普遍存在,但丰度相对较低.在地层剖面上,有机碳含量(TOC(%))从0.05～7.91%,平均为2.52%;有机碳同位素组成(δ13Corg)从-29.49‰～-34.41‰(PDB),发生负偏移,偏移量达到4.3‰,代表该期海平面处于上升阶段,底层水处于严重缺氧状态,底栖生物缺乏.本文根据生物标志化合物特征参数,结合有机碳同位素组成变化,详细分析了黔北早寒武世这套黑色岩系的有机质来源、成熟度、沉积环境以及古海洋意义,将为我国南方早寒武纪古地理重建、地质事件记录提供可靠依据.
其他语种文摘	This paper first provides biomarkers of Early Cambrian black rock series in the Zunyi area, Northern Guizhou. Integrated with organic carbon isotope compositions, the significant geological events are discussed in detail. Abundant biomarkers, including n-alkanes, isoprenoid, steranes and terpanes from the Late Sinian-Early Cambrian black rock series, have been detected by GC and GC-MS. The n-alkanes are composed of nC_(14)-nC_(31) with nC_(18), nC_(19) and/or nC_(20) as the main peaks, and characteristic of single peak distribution. The nC_(17)/n_(C31) ratios of 1.15 to 50.17 show the predominance of light hydrocarbons in the n-alkanes, OEP values vary from 0.94 to 1.11, and CPI from 0.93 to 1.13, close to equilibrium value of 1.0, indicating no obvious odd-even carbon number predominance. Pr/Ph values range between 0.24 and 0.47, and they fluctuate in the vertical section. In the m/z191 GC-MS, C_(30) hopane is the most abundant in the terpanes. According to the relative abundance, tricyclic terpanes are characterized by highest abundances, pentacyclotriterpanes by the second, and then tetracyclic terpanes. Minor gammacerane is presented. In the m/z217 GC-MS, the regular steranes C_(27)-C_(28)-C_(29) distributed with "V" shape, and ∑(C_(27) + C_(28)) > ∑C_(29) with varying ratios between 1.25 and 1.99, whereas steranes ∑C_(27)/∑C_(29) from 0.78 to 1.22 and rearranged steranes C_(27)/regular steranes C_(27) from 0.21 to 0.47. 4-methyl steranes have been detected, but their abundance are relatively lower. The sedimentary organic matter of anomalously organic-carbon-rich laminated shales across the Zunyi area is characterized by high organic-carbon contents, ranging between 0.05 and 7.91%. The carbon isotope curve displays δ(13)C values of the kerogen (δ~(13)C_(org)) fluctuating from -29.49 to -34.41‰ PDB with a negative excursion close to 4.3‰, which may have been associated with seal level rise, anoxic water in the bottom and scarcity of benthic fauna. On the basis of geochemical parameters of biomarkers and organic carbon isotope compositions of the black rock series in the Zunyi area, this paper discussed the maturity of rocks, quality and origin of organic matter, depositional environments and palaeoceanography. This study will provide reliable evidence for the paleogeographic reconstruction and geological events record in Early Canibrican of southern China.
来源	岩石学报 ,2006,22(9):2413-2423 【核心库】
关键词	早寒武世 ; 黑色岩系 ; 生物标志化合物 ; 有机碳同位素 ; 缺氧事件 ; 黔北
地址	1. 中国科学院地球化学研究所, 矿床地球化学国家重点实验室, 贵阳, 550002 2. 中国科学院广州地球化学研究所, 有机地球化学国家重点实验室, 广州, 510640
语种	中文
文献类型	研究性论文
ISSN	1000-0569
学科	地质学
基金	中国科学院“百人计划”项目
文献收藏号	CSCD:2631753