Multivariate statistics and geochemical approaches for understanding source-sink relationship - a case study from close-basin lakes in Southeast Amazon

Abstract

Multivariate statistical approaches were applied on geochemical data of lake sediments and the catchment basin materials (Al-enriched crusts and soils) from four upland lakes (namely LB1, LB2, LB3, and LB4) in the Serra da Bocaína, Southeast Amazon, to recognize the geochemical signatures of lake sediments and their link with source rocks. This is also compared with Fe-enriched crusts and soils, which collected from Serra Sul de Carajás. The major and trace elements were analyzed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and X-ray Fluorescence (XRF), and Inductively Coupled Plasma Mass Spectrometry (ICP-MS), respectively. The data closure effect was reduced by centred log ratio (clr) transformation. The upper continental crust (UCC) normalized patterns show that sediments are mainly enriched with Ti, Fe, P, Se, V and Cr, similar to catchment basin crusts and soils. The distribution of elements varied between lakes, which is mainly influenced by the morphology and lithology of the basin. The chemical index of alternation (CIA) values were very high (>90) for both lake sediments and catchment materials, which indicates intense source area weathering. Index of lateritization (IOL) shows that the catchment crusts are strongly lateralized and it identifies samples between extremely weathered and reworked samples that do not meet the criteria for strict in situ formation. The principal components analysis (PCA) and Spearman correlation matrices based on clr-transformed data revealed four geochemical groups in sediments. The major detritic geochemical association of sediments (Group 1: Al–Ti-Ga-Cr-V-Ti-Nb-Sc, which indicative of mafic/metavolcanic rock; and Group 2: Zr-Hf-HREEs, which refers to the heavy mineral fractions that remain stable during lateritization) had a close relationship with catchment lateritic crust, except a few alterations, which possibly influenced by weathering and transport processes. REE pattern normalized to chondrite and the geochemical ratios show the analogies between the lake sediments and the catchment lateritic crusts. The linear discriminant analysis (LD) and PCA distinguished Al-rich laterites from Fe-rich laterites and indicates that the former (which likely derived from mafic/metavolcanic rocks) is the main source of lake sediments.