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A hydrogeological conceptual model for the groundwater dynamics in the ferricretes of Capão Xavier, Iron Quadrangle, Southeastern Brazil
Catena ( IF 6.2 ) Pub Date : 2021-08-19 , DOI: 10.1016/j.catena.2021.105663
Jordania Cristina dos Santos Dias 1 , Luis de Almeida Prado Bacellar 2
Affiliation  

In the Iron Quadrangle (IQ), southeastern Brazil, ferricretes usually overlie the banded iron formations (BIFs) of the Cauê Formation, rocks that not only host the most important iron ore deposits of this region but are also its major groundwater source. Little is known about the water dynamics in ferricretes and therefore how they influence the recharge of the subjacent aquifer (Cauê aquifer). The objective of this research was to identify ferricrete typologies and investigate their water dynamics in the Capão Xavier region, northwest of IQ. Field work consisted of macroscopic description of ferricretes, infiltration tests and multitemporal electrical resistivity surveys. Two ferricrete typologies were distinguished: structured ferricretes, which are older and occur on top of plateaus, and detrital ferricretes of colluvial-alluvial origin, which were deposited downslope and in topographic lows. The structured ferricretes preserve the medium- to high-angle foliation inherited from the underlying BIFs, whereas the detrital ferricretes constitute thick packs subparallel to the topographic surface and are intercalated with argillaceous layers in areas of karstic depressions. The structured ferricretes are more porous (20.8% to 24.4%) than the detrital ferricretes (14.4% to 17.6%), hence they have higher mean basic infiltration rates (8.3x10-6 m/s) than detrital ferricretes (2.8x10-6 m/s). Despite these low mean basic infiltration rates, infiltration advances thanks to the karstic-fissural porosity (fractures and joints widened by karstification), and superficial cavities that are connected to caves in the interface between the ferricrete and the subjacent, less resistant, transition horizon. Karstification is controlled by the subvertical foliation in the structured ferricretes and subparallel layering in the detrital ferricretes. Some factors that favor infiltration and deep percolation of water are superficial rugosity in structured ferricretes, and karstic depressions in both typologies. The recharge of the Cauê aquifer is diachronic, firstly taking place via the karstic-fissural system and later via the ferricrete matrix.



中文翻译:

巴西东南部铁四边形 Capão Xavier 铁质混凝土中地下水动态的水文地质概念模型

在巴西东南部的铁四边形 (IQ),铁质混凝土通常覆盖在 Cauê 组的带状铁层 (BIF) 上,这些岩石不仅拥有该地区最重要的铁矿床,而且还是其主要的地下水源。人们对铁质混凝土中的水动力学知之甚少,因此对它们如何影响下层含水层(Cauê 含水层)的补给知之甚少。这项研究的目的是在 IQ 西北部的 Capão Xavier 地区识别铁质混凝土类型并调查它们的水动力学。现场工作包括对铁质混凝土的宏观描述、渗透测试和多时相电阻率调查。区分了两种铁质混凝土类型:结构性铁质混凝土,它们更老并出现在高原顶部,以及冲积冲积成因的碎屑铁质混凝土,沉积在下坡和地形低点。结构化铁质混凝土保留了从下层 BIF 继承的中到大角度叶理,而碎屑铁质混凝土构成了与地形表面平行的厚堆积物,并在岩溶洼地中夹杂着泥质层。结构化铁质混凝土比碎屑铁质混凝土(14.4% 至 17.6%)的孔隙率更高(20.8% 至 24.4%),因此它们具有更高的平均基本渗透率(8.3x10-6 m/s) 比碎屑铁质混凝土 (2.8x10 -6 m/s)。尽管平均基本入渗率较低,但由于岩溶-裂隙孔隙度(岩溶作用扩大的裂缝和节理)以及与铁质混凝土和下方阻力较小的过渡层之间界面中的洞穴连接的表层空洞,渗透仍在推进。岩溶作用受结构铁质混凝土中的近垂直叶理和碎屑铁质中的次平行分层控制。有利于水渗透和深层渗透的一些因素是结构化铁质混凝土的表面凹凸不平,以及两种类型的岩溶洼地。Cauê 含水层的补给是历时性的,首先通过岩溶-裂隙系统进行,然后通过铁质基质进行。

更新日期:2021-08-19
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