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Unravelling calcrete environmental controls in volcanic islands, Gran Canaria Island, Spain
Palaeogeography, Palaeoclimatology, Palaeoecology ( IF 3 ) Pub Date : 2020-09-01 , DOI: 10.1016/j.palaeo.2020.109797
Ana María Alonso-Zarza , Álvaro Rodríguez-Berriguete , Andrea Martín-Pérez , Rebeca Martín-García , Inmaculada Menéndez , José Mangas

Abstract Volcanic islands are unique contexts to analyze the controls on calcrete development in settings with varied relief, climate and vegetation, and lacking carbonate host rocks. This paper discusses the formation of Quaternary calcrete profiles in Gran Canaria volcanic Island, under direct influence of the SAL (Saharian Air Layer). Calcrete profiles are multi-storey and composed of prismatic, massive, laminar, pisolithic, ooid-bearing, sandy mudstones with rhizoliths and brecciated horizons. Host rocks include basalts, siliceous mudstones, volcanic sands and gravels and bioclastic-rich sands. Carbonate is mostly calcite but some dolomite occurs in massive horizons. The main microfabrics include laminated micrite, fine crystalline dolomite, desiccated micrite, micrite-clay groundmass, oriented Mg-rich clays, peloids, spherulites and coated grains. δ13C varies from −3.26 to −9.18‰ VPDB and δ18O from +0.86 to −3.24‰ VPDB. The 87Sr/86Sr ratios are between 0.707504 and 0.708860, indicating that calcium was mostly supplied from the CaCO3-rich aeolian dust coming from the Sahara Desert. Calcrete profiles are mostly pedogenic with roots and microorganisms enabling carbonate precipitation within the soils. The correlation trend of δ13C and δ18O points to a climate control on precipitation, with the heavier isotope values in the horizons containing dolomite. Sedimentation rates interplayed with calcrete formation processes and erosion to outline the profiles/horizons. Amalgamated laminar horizons formed when the rate of calcrete formation was higher than sedimentation and erosion, whereas areas or periods with relatively higher sedimentation allowed the separation of calcrete horizons. The direction of the winds supplying aeolian dust, and the varied relief, vegetation and climate favored better development of calcretes in the relatively arid and lowland areas of the eastern side of the island. Our study shows that calcretes contain the record of the paleoenvironmental controls that operated in volcanic islands with no previous carbonate substrates.

中文翻译:

解开西班牙大加那利岛火山岛的钙质环境控制

摘要 火山岛是分析在具有不同地形、气候和植被且缺乏碳酸盐主岩的环境中对钙质发育的控制的独特背景。本文讨论了在 SAL(撒哈拉空气层)的直接影响下,大加那利火山岛第四纪钙质剖面的形成。钙质混凝土剖面是多层的,由棱柱状、块状、层状、松质、含卵形、含根石和角砾岩层的砂质泥岩组成。主岩包括玄武岩、硅质泥岩、火山砂和砾石以及富含生物碎屑的砂。碳酸盐主要是方解石,但也有一些白云岩出现在巨大的地层中。主要的微结构包括层状泥晶、细晶白云石、干燥泥晶、泥晶-粘土基质、定向富镁粘土、球状体、球晶和涂层晶粒。δ13​​C 从 -3.26 到 -9.18‰ VPDB 和 δ18O 从 +0.86 到 -3.24‰ VPDB 变化。87Sr/86Sr 比值介于 0.707504 和 0.708860 之间,表明钙主要由来自撒哈拉沙漠的富含 CaCO3 的风尘提供。钙质剖面大多是土壤的,根和微生物使土壤中的碳酸盐沉淀成为可能。δ13​​C和δ18O的相关趋势表明气候对降水有控制作用,层位中同位素值较重,含白云石。沉积速率与钙质混凝土形成过程和侵蚀相互作用,勾勒出轮廓/地平线。当钙质形成速率高于沉积和侵蚀速率时,形成混合层状层位,而相对较高沉积的地区或时期允许钙质层分离。供给风成尘的风向,以及多样的地形、植被和气候,有利于岛东相对干旱和低地地区的钙凝土更好地发育。我们的研究表明,钙质混凝土包含在以前没有碳酸盐基质的火山岛上运行的古环境控制记录。
更新日期:2020-09-01
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