陆相湖盆高盐度对伽马蜡烷生成的抑制机制

doi:10.13745/j.esf.sf.2025.5.2

摘要/Abstract

摘要：

伽马蜡烷传统上被认为是一种与水体分层密切相关的C₃₀三萜类生物标志物,并将这种分层性与盐度紧密关联。但高盐度水环境沉积物中伽马蜡烷缺失的机制仍不明确。本研究以德国南部中新世诺德林根(Nördlinger Ries)湖相页岩为对象,通过矿物学、有机地球化学(总有机碳、总硫、生物标志化合物、干酪根元素和热解分析)等多指标综合研究,揭示了伽马蜡烷的保存与水化学环境控制的微生物活动间的关联。结果表明: 湖盆水体古盐度演化经历了中盐度→超咸水→中盐度→淡水的变化,但伽马蜡烷丰度在相对低、高盐度下与盐度分别呈现出正、负向协同演化关系。淡水-正常海、弱氧化-弱还原条件下(盐度<40‰,剖面中、上部),伽马蜡烷丰度与水体分层性、盐度呈正相关关系。中盐度-超咸水、强还原条件下(盐度>40‰,剖面中、下部),因水化学环境改变(盐度、缺氧度增大)引发的食物链断裂(伽马变形菌门等原核生物减少),导致纤毛虫活性受抑制,进而降低伽马蜡烷生成和反硝化作用强度。同时,伽马变形菌衰亡削弱了硫酸盐还原菌的增殖,抑制有机质硫化过程,表现为有机硫含量与热解T_max值的协同变化。研究证实,伽马蜡烷的保存不仅依赖水体分层,更受控于微生物群落的生态响应,为高盐湖盆中伽马蜡烷地质意义的复杂性与局限性提供了新解释。

关键词: 伽马蜡烷, 水体分层, 超咸水, 硫酸盐型湖盆, 陆相盆地

Abstract:

Gammacerane, a C₃₀ triterpenoid biomarker traditionally interpreted as an indicator of water column stratification and salinity, remains enigmatic due to its frequent absence in high-salinity sedimentary environments—a contradiction to conventional models. This multidisciplinary study of Miocene lacustrine shales from the Nördlinger Ries (southern Germany) integrates mineralogy with organic geochemical proxies—including total organic carbon (TOC), total sulfur (TS), biomarkers, kerogen elemental composition, and pyrolysis parameters—to elucidate how water chemistry controls gammacerane preservation through microbial ecology. Our data reveal that the paleolake evolved sequentially through mesosaline, hypersaline, mesosaline, and freshwater phases. Gammacerane abundance shows contrasting correlations with salinity: (1) a positive correlation at lower salinities (e.g., <40‰) in suboxic to weakly reducing conditions, and (2) a negative correlation in hypersaline, intensely anoxic settings. In the latter, extreme salinity and anoxia triggered a collapse of the microbial food web (reflected in diminished prokaryotic biomass). This suppressed the metabolic activity of ciliates (the primary producers of gammacerane), which in turn reduced both gammacerane biosynthesis and denitrification efficiency. The decline of Gammaproteobacteria further limited the proliferation of sulfate-reducing bacteria, as evidenced by coupled shifts in organic sulfur and pyrolysis T_max, thereby curtailing organosulfur compound formation. This study demonstrates that gammacerane preservation is controlled not simply by stratification but rather by ecological feedbacks within the microbial community. It provides a revised framework for interpreting gammacerane records in hypersaline lacustrine systems.

Key words: gammacerane, column stratification, hyper-saline, sulfate-type lake, lacustrine basin

中图分类号:

赵子斌, 王晓梅, 侯读杰, 侯卫国, 张坤, 刘诗局. 陆相湖盆高盐度对伽马蜡烷生成的抑制机制[J]. 地学前缘, 2026, 33(2): 493-502.

ZHAO Zibin, WANG Xiaomei, HOU Dujie, HOU Weiguo, ZHANG Kun, LIU Shiju, Ralf LITTKE. Inhibition mechanism of gammacerane production by high salinity in lacustrine basin[J]. Earth Science Frontiers, 2026, 33(2): 493-502.

图/表 10

图1 研究区地理位置和地层柱状图

Fig.1 Geographical location and stratigraphic column chart of the study area

图2 Nördlinger Ries盆地中新统页岩α-/总MTTC与Pr/Ph交汇图

Fig.2 Crossplot of α-/total MTTC vs. Pr/Ph for Miocene shales in the Nördlinger Ries Basin

图3 Nördlinger Ries盆地中新统页岩氧化还原性(a)、盐度(b)、碱度(c[18,29-30])和伽马蜡烷指数(d)剖面

Fig.3 Redox (a), salinity (b), alkalinity (c[18,29-30]) and gammacerane index (d) profiles of Miocene shales in the Nördlinger Ries Basin

图4 Nördlinger Ries盆地中新统页岩α-/总MTTC与Pr/Ph交汇图

Fig.4 Crossplot of α-/total MTTC vs. Pr/Ph for Miocene shales in the Nördlinger Ries Basin

图5 Nördlinger Ries盆地中新统页岩有机质来源随盐度变化剖面

Fig.5 Variations in organic matter sources vs. salinity of Miocene shale in the Nördlinger Ries Basin

图6 Nördlinger Ries盆地中新统页岩有机质来源变化剖面

Fig.6 Variations in organic matter sources of Miocene shale in the Nördlinger Ries Basin

图7 Nördlinger Ries盆地中新统页岩C27-29规则甾烷/17α-藿烷与伽马蜡烷/(伽马蜡烷+C30 αβ藿烷)交汇图

Fig.7 Crossplot of C27-29 regullar steranes/17 α-hopanes vs. gammacerane/(gammacerane+C30 αβ hopane) of Miocene shale in the Nördlinger Ries Basin

图8 Nördlinger Ries盆地中新统页岩干酪根裂解噻吩及其同系物/甲苯与有机硫/有机碳原子比交汇图

Fig.8 Crossplot of pyrolytic thiophenes/toluene vs. atomic organic sulfur/organic carbon of kerogen in the Nördlinger Ries Basin

图9 Nördlinger Ries盆地中新统页岩有机硫和Tmax剖面

Fig.9 Variations in organic sulfur content and Tmax of Miocene shale in the Nördlinger Ries Basin

图10 Nördlinger Ries盆地中新统页岩干酪跟裂解噻吩及其同系物/甲苯与伽马蜡烷/(伽马蜡烷+C30 αβ藿烷)交汇图

Fig.10 Crossplot of pyrolytic thiophenes/toluene vs. gammacerane/(gammacerane+C30 αβ hopane) of Miocene shale in the Nördlinger Ries Basin

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