Geochemical constrains for unravelling the condition of sedimentation, provenance, paleoclimate variation, and metallogenic implication of the cretaceous deposits of Mayo Oulo Basin (North Cameroon, Africa)

IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
J. Ngo Elogan Ntem , V. Ngounfack Tiokeng , R. Toyama , Y. Berinyuy Konglim , J.F. Takou , N. Togoum , T. Ngnotue , M.S. Tchouatcha
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引用次数: 0

Abstract

The sediments from the Mayo Oulo intracontinental Basin, along the N–S cross section between the Gadavou and Lombel localities in central part of the basin, were investigated through major and trace elements geochemistry associated with palynological analysis to determine their condition of sedimentation, paleoclimate evolution and metallogenic implication along the Cretaceous sequence from the N–S cross section of the central part of this basin. From bottom to top of this sequence there are various types of facies with various concentrations of carbonate. Based on their major oxides compositions, the sediments were classified as Shales associated with Fe-shales, Fe-sands, Wacke and Litharenite. The CIX (Chemical Index of Alteration, 62.65 to 98.14) and PIX (Plagioclase Index of Alteration, 65.00 to 99.13) sediments underwent a various chemical weathering; little chemical weathering in the middle to the upper part of the sequence and moderate to high chemical weathering in the lower part. The discriminant function-based multidimensional tectonic diagrams indicate mainly and respectively arc-collisional and Island arc-active continental margin settings which are consistent with the Precambrian geological history of the study area. The SiO2 vs. Al2O3+K2O + Na2O, C-values, associated with trace elements plots such as Sr/Ba, and Rb/Sr, and palynological content (continental or terrestrial species exclusively, dominated by Gymnosperm pollens such as. Inaperturopollenites sp., Araucariacites sp. and Classopollis sp, associated with spores such as Cicatricosisporites sp) indicate mainly arid to semi-arid climate with periodic humid to semi-humid conditions. The Sr/Ba values ranging from 0.084 to 6.408 suggest a fluctuating and sometimes high salinity (Hypersaline milieu). The rare earth elements data show high LREE/HREE ratios (2.86–13.31); high negative and positive Eu anomaly (Eu/Eu∗ = 0.33 to 1.38) and no Ce anomaly (Ce/Ce∗ = 0.94 to 1.02); these features, together with mixed major and trace element ratios and plots such as, Al2O3/TiO2 ratios (14.31–54.26); Th/Co ratios (0.30–14.58); Ce vs La/Yb, Zr vs TiO2 and La/Sc vs Th/Co plots, indicate that the sediments are derived mainly from felsic to intermediate or mafic rock composition. Ni/Co (1.86–3.59) and U/Th (0.03–0.76) ratios are consistent with oxic conditions from bottom to top of the sequence. The Al/Si ratio shows positive correlation with CIA, Th, Zr, Hf, Na, K and negative correlation with Ca and Mg. The positive correlation with K, Hf, Na, Zr, and Th from detrital origin and negative correlation with Ca and Mg from chemical origin could suggest the geochemical composition control of grain size. According to the ternary Al–Fe–Mn diagram metallogenic classification, the studied samples are essentially terrigenous and partially weakly metalliferous, close to those from the Babouri –Figuil and Mamfe Basins (Cameroon) and contrary to those from the Sob area (Polar Urals). No marine or transitional fossil species are recorded. The presence of numerous tetrads to dyads indicate a lacustrine or swampy environment surrounded by vegetation.

揭示马约乌洛盆地(非洲喀麦隆北部)白垩纪沉积物的沉积条件、产地、古气候变化和成矿影响的地球化学制约因素
通过主要元素和痕量元素地球化学以及古生物学分析,研究了马约乌洛大陆内盆地中部加达乌和隆贝尔两地之间沿 N-S 断面的沉积物,以确定该盆地中部 N-S 断面白垩纪层序的沉积条件、古气候演变和成矿影响。该层序自下而上分布着各种类型的碳酸盐岩面。根据其主要氧化物成分,沉积物被划分为与铁页岩相关的页岩、铁砂、片麻岩和闪长岩。CIX(化学蚀变指数,62.65 至 98.14)和 PIX(斜长石蚀变指数,65.00 至 99.13)沉积物经历了不同程度的化学风化;序列中上部的化学风化程度较轻,下部的化学风化程度中等至较重。基于判别函数的多维构造图分别显示了主要的弧碰撞型和岛弧活动型大陆边缘环境,这与研究区域的前寒武纪地质历史相一致。SiO2 vs. Al2O3+K2O + Na2O、C 值、相关微量元素图(如 Sr/Ba、Rb/Sr)和古植物学含量(大陆或陆地物种,以裸子植物花粉为主,如 Inaperturopollenites sp.Inaperturopollenites sp.、Araucariacites sp.和 Classopollis sp.,并伴有 Cicatricosisporites sp 等孢子)表明,这里主要是干旱至半干旱气候,并伴有周期性的潮湿至半潮湿条件。Sr/Ba 值从 0.084 到 6.408 不等,表明盐度时高时低(高盐环境)。稀土元素数据显示 LREE/HREE 比值较高(2.86-13.31);Eu 负异常和 Eu 正异常较高(Eu/Eu∗=0.33-1.38),而 Ce 无异常(Ce/Ce∗=0.94-1.02);这些特征以及混合的主要元素和微量元素比值和图谱,如 Al2O3/TiO2 比值(14.31-54.26);Th/TiO2 比值(14.31-54.26);Ce/Ce∗=0.94-1.02。31-54.26);Th/Co 比(0.30-14.58);Ce vs La/Yb、Zr vs TiO2 和 La/Sc vs Th/Co 图等,表明沉积物主要来自长英岩到中黑或黑云母岩石成分。Ni/Co(1.86-3.59)和U/Th(0.03-0.76)比值从序列底部到顶部都与氧化条件一致。Al/Si比率与CIA、Th、Zr、Hf、Na、K呈正相关,与Ca和Mg呈负相关。与K、Hf、Na、Zr和Th呈正相关的是碎屑源,与Ca和Mg呈负相关的是化学源,这说明地球化学成分对晶粒大小有控制作用。根据铝-铁-锰三元图金属成因分类法,所研究的样本基本上属于陆相化石,部分属于弱金属化,与巴布里-菲吉尔盆地和马姆费盆地(喀麦隆)的样本接近,而与索布地区(极地乌拉尔)的样本相反。没有海洋化石或过渡化石物种的记录。大量四分化石和二分化石的出现表明这里是一个被植被环绕的湖泊或沼泽环境。
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来源期刊
Solid Earth Sciences
Solid Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
3.60
自引率
5.00%
发文量
20
审稿时长
103 days
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