突尼斯东南部全新世sebkhas沉积物的石英颗粒微质地:对沉积过程和沉积环境的影响

IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of African Earth Sciences Pub Date : 2024-07-03 DOI:10.1016/j.jafrearsci.2024.105329
Mariem Ben Ameur , Hamdi Omar , Sameh Masmoudi , Chokri Yaich
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引用次数: 0

摘要

对从突尼斯东南部 Sebkha 沉积物中提取的碎屑石英颗粒进行了扫描电子显微镜分析,以确定沉积物的来源并评估盐碱环境对石英颗粒的影响。从 Sebkha el Melah 和 Sebkha Mhabeul 采集的岩心沉积物分别涵盖了公元前 5000 年和 2000 年。两个岩心中最上层的第三单元根据其石英颗粒的机械微观结构呈现出两种截然不同的面貌。风化层沉积物的特征是石英颗粒具有圆形轮廓、上翻板块和新月形冲击痕迹。与此相反,流积面沉积物的石英颗粒则具有近方形轮廓、V 形冲击裂纹和锥形断裂。对sebkhas石英颗粒的观察表明,石英颗粒经过多次搬运和加工,表明石英颗粒经过长距离搬运,沉积速度很快。大部分石英颗粒似乎来自周围的地形,反映了该地区动态的地质历史。本研究深入探讨了石英颗粒表面的微纹理变化与sebkhas地区特定历史气候条件之间的联系。通过研究岩心沿线的地球化学变化,盐浓度较高的岩面与较温暖的时期相对应,这些岩面显示出广泛的风化石英颗粒。通过微观纹理,如定向蚀坑、吻合溶解网络和溶蚀裂隙,可以明显看出这种严重的化学蚀变。深度溶解严重影响了石英晶格,导致石英颗粒分解,形成 "菜花状 "或 "海绵状",抹去了之前的微纹理。相反,在温度较低的时期,石英溶解的程度较轻,因此保留了微纹理。砂粒表面对迁移过程和物理化学环境的变化都非常敏感。在突尼斯东南部sebkhas的高盐度和封闭环境中,由于物理化学条件的剧烈波动,强大的沉积后过程可能会抹去和掩盖之前环境中砂粒上记录的原始微观纹理。
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Quartz grain microtextures of Holocene sebkhas sediments in southeast Tunisia: Implications for sedimentary processes and depositional environments

Detrital quartz grains extracted from sebkha sediments in southeastern Tunisia underwent scanning electron microscopy analysis to identify sediment sources and assess the influence of the saline environment on the grains. Core sediments collected from Sebkha el Melah and Sebkha Mhabeul cover the last 5000 and 2000 BP, respectively. The uppermost Unit III, present in both cores, exhibits two distinct facies based on the mechanical microtextures of its quartz grains. The aeolian facies sediments are characterized by quartz grains with rounded outlines, upturned plates, and crescentic percussion marks. In contrast, the fluvial facies sediments are associated with quartz grains featuring subangular outlines, v-shaped percussion cracks, conchoidal fractures. Observations on the quartz grains of the sebkhas suggest multiple transportation and processing events, indicating long-distance transport and rapid deposition rates. The majority of quartz grains appear to originate from the surrounding terrain, reflecting the dynamic geological history of the region. This study delves into the connection between microtexture variations on quartz grain surfaces and specific historical climatic conditions in the sebkhas. By examining geochemical variations along the cores, facies with elevated salt concentrations corresponding to warmer periods reveal extensively weathered quartz grains. This substantial chemical alteration is evident through microtextures such as oriented etch pits, anastomosed dissolution networks and solution crevasses. The profound dissolution has significantly impacted the quartz lattice, resulting in the decomposition of the grains and the formation of "cauliflower" or "spongy" shapes, erasing prior microtextures. Conversely, during less warm periods, quartz dissolution was less severe, thereby preserving microtextures.

Sand grain surfaces are notably sensitive to both transport processes and variations in the physicochemical environment. In the hypersaline and confined environments of sebkhas in southeastern Tunisia, potent post-sedimentary processes can obliterate and obscure the original microtextures recorded on grains from previous environments due to highly fluctuating physicochemical conditions.

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来源期刊
Journal of African Earth Sciences
Journal of African Earth Sciences 地学-地球科学综合
CiteScore
4.70
自引率
4.30%
发文量
240
审稿时长
12 months
期刊介绍: The Journal of African Earth Sciences sees itself as the prime geological journal for all aspects of the Earth Sciences about the African plate. Papers dealing with peripheral areas are welcome if they demonstrate a tight link with Africa. The Journal publishes high quality, peer-reviewed scientific papers. It is devoted primarily to research papers but short communications relating to new developments of broad interest, reviews and book reviews will also be considered. Papers must have international appeal and should present work of more regional than local significance and dealing with well identified and justified scientific questions. Specialised technical papers, analytical or exploration reports must be avoided. Papers on applied geology should preferably be linked to such core disciplines and must be addressed to a more general geoscientific audience.
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