Isaque C. Rodrigues , Anderson J. Maraschin , André W. Borba , Ana M.P. Mizusaki
{"title":"细粒沉积岩的地球化学：圣玛丽亚地层（三叠纪，巴西巴拉那盆地）的源区、古风化作用、古气候和产地的影响","authors":"Isaque C. Rodrigues , Anderson J. Maraschin , André W. Borba , Ana M.P. Mizusaki","doi":"10.1016/j.jsames.2024.105167","DOIUrl":null,"url":null,"abstract":"<div><p>The integration of ICP-OES, XRD, chemical analysis, and scanning electron microscopy was used to investigate the source area, weathering, paleoclimate conditions, and provenance of the siltstones of the Santa Maria Formation (Middle to Upper Triassic, Southern Brazil). This unit is regionally subdivided, from base to top, into the Passo das Tropas Member (Late Anisian–Middle Ladinian) and the Alemoa Member (Middle Ladinian–Carnian). The Chemical Index of Alteration (CIA) was calculated for both members to highlight the weathering processes of primary minerals. The CIA results indicate moderate to extreme weathering of the source rocks for the siltstones. The extreme chemical alteration observed in the Passo das Tropas siltstones (CIA = 76.97–90.83) and in the mid-section of the Alemoa Member (CIA = 87.96–89.63) suggests weathering under more humid conditions, related to an increase in paleorainfall. Paleoclimate was interpreted as semi-arid to arid, with alternating wet and dry seasons. These results align with the geochemical behavior of uranium and thorium. Samples with higher CIA values show higher Th/U ratios, indicating a shift toward a more humid climate. X-ray diffraction analysis of the fine fraction (FF < 2 μm) of the samples identified mixed-layered illite-smectite (I/S) clay minerals with minor amounts of quartz. Regarding provenance, Th/U ratios coupled with Th vs. Sc and La-Th-Sc plots, suggest an upper crustal protolith for the southern Santa Maria siltstones, consisting of uplifted rocks from the crystalline basement of the Sul-Rio-Grandense shield and sedimentary rocks of the Camaquã Basin. The Th/Sc, Sc/Th, Co/Th, and La/Sc ratios, along with the contents of Al₂O₃, SiO₂, TiO₂, Co, V, Ni, and Sc, indicate a more felsic composition for the Passo das Tropas Member. Meanwhile, the source rocks of the Alemoa Member sediments demonstrate a more mafic composition in the mid-section, transitioning to a felsic composition in the uppermost succession.</p></div>","PeriodicalId":1,"journal":{"name":"Accounts of Chemical Research","volume":null,"pages":null},"PeriodicalIF":16.4000,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Geochemistry of fine-grained sedimentary rocks: Implications for source area, paleoweathering, paleoclimate, and provenance of the Santa Maria Formation (Triassic, Paraná Basin, Brazil)\",\"authors\":\"Isaque C. Rodrigues , Anderson J. Maraschin , André W. Borba , Ana M.P. Mizusaki\",\"doi\":\"10.1016/j.jsames.2024.105167\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>The integration of ICP-OES, XRD, chemical analysis, and scanning electron microscopy was used to investigate the source area, weathering, paleoclimate conditions, and provenance of the siltstones of the Santa Maria Formation (Middle to Upper Triassic, Southern Brazil). This unit is regionally subdivided, from base to top, into the Passo das Tropas Member (Late Anisian–Middle Ladinian) and the Alemoa Member (Middle Ladinian–Carnian). The Chemical Index of Alteration (CIA) was calculated for both members to highlight the weathering processes of primary minerals. The CIA results indicate moderate to extreme weathering of the source rocks for the siltstones. The extreme chemical alteration observed in the Passo das Tropas siltstones (CIA = 76.97–90.83) and in the mid-section of the Alemoa Member (CIA = 87.96–89.63) suggests weathering under more humid conditions, related to an increase in paleorainfall. Paleoclimate was interpreted as semi-arid to arid, with alternating wet and dry seasons. These results align with the geochemical behavior of uranium and thorium. Samples with higher CIA values show higher Th/U ratios, indicating a shift toward a more humid climate. X-ray diffraction analysis of the fine fraction (FF < 2 μm) of the samples identified mixed-layered illite-smectite (I/S) clay minerals with minor amounts of quartz. Regarding provenance, Th/U ratios coupled with Th vs. Sc and La-Th-Sc plots, suggest an upper crustal protolith for the southern Santa Maria siltstones, consisting of uplifted rocks from the crystalline basement of the Sul-Rio-Grandense shield and sedimentary rocks of the Camaquã Basin. 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引用次数: 0
摘要
该研究综合运用了 ICP-OES、XRD、化学分析和扫描电子显微镜等方法，对圣玛丽亚地层（中三叠世至上三叠世，巴西南部）粉砂岩的产地、风化、古气候条件和出处进行了研究。该单元从底部到顶部按区域细分为 Passo das Tropas 组（晚安尼西安期-中拉迪南期）和 Alemoa 组（中拉迪南期-卡尼西安期）。计算了这两个岩层的化学蚀变指数（CIA），以突出原生矿物质的风化过程。化学蚀变指数结果表明，粉砂岩的源岩发生了中度到极端的风化。在 Passo das Tropas 粉砂岩（CIA = 76.97-90.83）和 Alemoa 组份中段（CIA = 87.96-89.63）观察到的极端化学蚀变表明，风化是在更加潮湿的条件下进行的，与古降雨量的增加有关。古气候被解释为半干旱至干旱，干湿季节交替。这些结果与铀和钍的地球化学行为一致。CIA值较高的样本显示出较高的Th/U比值，表明气候向更加潮湿的方向转变。对样本细小部分（FF < 2 μm）的 X 射线衍射分析发现了混合层状伊利石-直闪石（I/S）粘土矿物和少量石英。关于产地，Th/U 比值以及 Th vs. Sc 和 La-Th-Sc 图表明，南部圣玛丽亚粉砂岩的原岩为上地壳原岩，由来自南里约-格兰登斯盾状结晶基底的隆起岩石和卡马夸盆地的沉积岩组成。Th/Sc、Sc/Th、Co/Th 和 La/Sc 比率以及 Al₂O₃、Si₂、Ti₂、Co、V、Ni 和 Sc 的含量表明 Passo das Tropas 成员的成分更偏向于长晶岩。与此同时，Alemoa 成员沉积物的源岩在中段显示出更多的黑云母成分，在最上部的演替中过渡到长石成分。
Geochemistry of fine-grained sedimentary rocks: Implications for source area, paleoweathering, paleoclimate, and provenance of the Santa Maria Formation (Triassic, Paraná Basin, Brazil)
The integration of ICP-OES, XRD, chemical analysis, and scanning electron microscopy was used to investigate the source area, weathering, paleoclimate conditions, and provenance of the siltstones of the Santa Maria Formation (Middle to Upper Triassic, Southern Brazil). This unit is regionally subdivided, from base to top, into the Passo das Tropas Member (Late Anisian–Middle Ladinian) and the Alemoa Member (Middle Ladinian–Carnian). The Chemical Index of Alteration (CIA) was calculated for both members to highlight the weathering processes of primary minerals. The CIA results indicate moderate to extreme weathering of the source rocks for the siltstones. The extreme chemical alteration observed in the Passo das Tropas siltstones (CIA = 76.97–90.83) and in the mid-section of the Alemoa Member (CIA = 87.96–89.63) suggests weathering under more humid conditions, related to an increase in paleorainfall. Paleoclimate was interpreted as semi-arid to arid, with alternating wet and dry seasons. These results align with the geochemical behavior of uranium and thorium. Samples with higher CIA values show higher Th/U ratios, indicating a shift toward a more humid climate. X-ray diffraction analysis of the fine fraction (FF < 2 μm) of the samples identified mixed-layered illite-smectite (I/S) clay minerals with minor amounts of quartz. Regarding provenance, Th/U ratios coupled with Th vs. Sc and La-Th-Sc plots, suggest an upper crustal protolith for the southern Santa Maria siltstones, consisting of uplifted rocks from the crystalline basement of the Sul-Rio-Grandense shield and sedimentary rocks of the Camaquã Basin. The Th/Sc, Sc/Th, Co/Th, and La/Sc ratios, along with the contents of Al₂O₃, SiO₂, TiO₂, Co, V, Ni, and Sc, indicate a more felsic composition for the Passo das Tropas Member. Meanwhile, the source rocks of the Alemoa Member sediments demonstrate a more mafic composition in the mid-section, transitioning to a felsic composition in the uppermost succession.
期刊介绍：
Accounts of Chemical Research presents short, concise and critical articles offering easy-to-read overviews of basic research and applications in all areas of chemistry and biochemistry. These short reviews focus on research from the author’s own laboratory and are designed to teach the reader about a research project. In addition, Accounts of Chemical Research publishes commentaries that give an informed opinion on a current research problem. Special Issues online are devoted to a single topic of unusual activity and significance.
Accounts of Chemical Research replaces the traditional article abstract with an article "Conspectus." These entries synopsize the research affording the reader a closer look at the content and significance of an article. Through this provision of a more detailed description of the article contents, the Conspectus enhances the article's discoverability by search engines and the exposure for the research.
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