Trace element and OH content of quartz grains in the Amazon river: Potential application in provenance analysis

Author(s)

Stalder, R. ; Jaeger, D. ; Ando, S. ; Garzanti, E. ; Chiessi, C. M. ; Sawakuchi, A. O. ; Ludwig, T. ; Strasser, M.

• Document type: Journal article
• Source: SEDIMENTARY GEOLOGY; v. 480, p. 9-pg., 2025-03-05.

Abstract

Quartz grains in sediment carried by the Amazon River and five of its major tributaries were analyzed by FTIRspectroscopy and secondary ion mass spectrometry to evaluate their potential for provenance analysis. Additionally, heavy mineral analysis was performed in the same samples to support sediment discrimination and provenance interpretation. Average defect water contents in quartz grains carried by branches with headwaters draining the Andes are higher (Solimoes River 8.8 wt ppm, Madeira River 7.2 wt ppm) than in branches exclusively draining cratonic areas (Xingu River 6.5 wt ppm, Tapajo<acute accent>s River 4.6 wt ppm, Negro River 4.7 wt ppm); values in one Amazon mainstem sample are intermediate with prevalence of the Andean signal (7.7 wt ppm). The average defect water content correlates to the fraction of grains that are defect-water rich (> 10 wt ppm), ranging from 30 to 40 % for the Solimoes, Madeira, and Amazon Rivers down to 10-20 % for the Tapajo<acute accent>s and Negro Rivers. The average molecular-water signal exhibits a much clearer contrast than the OH-defect signal. Grains from cratonic tributaries (Negro, Tapajo<acute accent>s and Xingu rivers) exhibit significantly weaker molecular water signals than grains from Andean tributaries (Solimoes and Madeira rivers); slightly weaker than the latter is the signal from grains in the Amazon mainstem, reflecting a mixture of Solimoes and Negro rivers quartz in the Amazon mainstem sample. In contrast, trace-element concentrations widely overlap among samples, preventing any robust discrimination about the sources of quartz grains. Trace metals show a fair correlation between Li and Al in all samples; a weak correlation between Al and Ti (indicative of igneous origin) was observed in Negro, Xingu and Amazon River sands, but not in Solimoes, Madeira and Tapajo<acute accent>s sands. Boron correlates with Li in Tapajo<acute accent>s river and Amazon mainstem samples and with Al in Madeira and Tapajo<acute accent>s samples. Heavy-minerals are mostly amphibole, epidote, augitic clinopyroxene and hypersthene in Solimoes River sands largely derived from the Andes, and andalusite, amphibole and epidote in Madeira River sands. Cratonic tributaries contribute durable tourmaline and zircon with andalusite (Negro River) or staurolite and topaz (Tapajo<acute accent>s River). The higher content of OH defects and molecular water in quartz grains derived from the Andes than in those from cratonic areas indicates that this property can provide useful complementary information to discriminate the source of quartz grains, one of the thorniest tasks in provenance analysis. (AU)

• FAPESP's process: 19/24349-9 - Assessing the effects of past and future climate change on Amazonian biodiversity (CLAMBIO)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: BIOTA-FAPESP Program - Regular Research Grants
• FAPESP's process: 18/15123-4 - Past perspectives on tipping elements of the climate system: the Amazon Rainforest and the Atlantic Meridional Overturning Circulation (PPTEAM)
• Grantee: Cristiano Mazur Chiessi
• Support Opportunities: Research Grants - Research Program on Global Climate Change - Young Investigators - Phase 2
• FAPESP's process: 18/23899-2 - Trans-Amazon Drilling Project: origin and evolution of the forests, climate, and hydrology of the South American tropics
• Grantee: André Oliveira Sawakuchi
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants