摘要
陆相红层是记录古气候、古环境、类比研究行星古环境与地质演化的重要载体。白斑作为红层中局部褪色的还原区,形态上多为灰白或灰绿色球状、椭球状。在生物地球化学上,白斑可能记录早期地下深部生物圈活动,同时其矿物—光谱特征为地外行星的生命探测可提供潜在指标。其成因长期存在争议,涉及流体渗透、有机质降解及微生物作用等多种机制。但目前对于其形成机制还存在一定的争议,需要进一步精细化的定量分析研究。文章结合扫描电镜X射线光电子能谱仪和扫描电镜,对白斑与周围陆相红层的元素、矿物进行对比分析,结果显示:白斑区Fe^(2+)/Fe^(3+)比值较红层略高(约为1.00),呈轻微还原环境,说明Fe^(3+)部分被还原并迁移流失;同时Al的质量分数升高,与硅铝酸盐蚀变及粘土化过程相符。扫描电镜结果揭示白斑内部普遍发育碳酸盐充填、绿泥石化及含Cr—Fe—Ti重矿物蚀变等特征,反映出酸性还原流体沿孔隙和裂隙渗透的过程。综合分析认为,白斑的形成是孔隙流体与重矿物耦合作用的结果,微生物在其中可能起催化还原与漂白作用。文章从矿物学与价态角度揭示了陆相红层白斑的形成机制,为理解陆地沉积环境下的氧化还原过程及地下微生物活动提供了新的证据。
Continental red beds serve as crucial archives for paleoclimatic and paleoenvironmental data,facilitating analog studies of ancient environments and planetary geological evolution.Within these deposits,white spots are localized bleached reduction zones that typically appear as grayish-white to gray-green spheroidal,ellipsoidal,or banded structures.In biogeochemistry they preserve signatures of the early deep subsurface biosphere.In addition,their mineralogical and spectral characteristics have potential as indicators in the search for extraterrestrial life.Their genesis has long been debated,involving complex interactions among pore-fluid infiltration,organic matter degradation,and microbial processes.Despite this,the formation mechanism remains a subject of debate,necessitating further quantitative analysis and research.This study employed scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),to conduct a comparative analysis of the elemental and mineralogical compositions of the white patches and surrounding continental red-layer deposits.The XPS results indicate a slightly elevated Fe^(2+)/Fe^(3+)ratio(~1.00)within the white spots,implying mildly reducing conditions and partial reduction-mobilization of Fe^(3+).Concurrent enrichment of Al is consistent with feldspar alteration and clay mineralization processes.SEM observations reveal widespread carbonate cementation,chloritization,and alteration of Cr-Fe-Ti-bearing heavy minerals within pore spaces and fractures,reflecting the penetration of acidic reducing fluids.These findings suggest that the formation of white spots resulted from coupled interactions between pore fluids and detrital heavy minerals,with microorganisms likely serving as catalytic agents in local reductive bleaching.The study provides mineralogical and redox evidence for understanding reduction-oxidation dynamics and potential subsurface microbial activity in continental sedimentary environments.
作者
符贵瑜
况城
徐能钊
陈可妮
谭婉琪
于明杰
FU Guiyu;KUANG Cheng;XU Nengzhao;CHEN Keni;TAN Wanqi;YU Mingjie(School of Geography,South China Normal University,Guangzhou 510631,China)
出处
《华南地理学报》
2025年第3期101-116,共16页
South China Geographical Journal
基金
国家自然科学基金青年科学基金项目(42102075)
大学生创新训练计划项目(S202510574242)。
关键词
陆相红层
白斑
微生物
矿物转化
丹霞山
Continental red beds
white spots
microorganisms
mineral transformation
Danxiashan
