Luminescence dating of quartz from ironstones of the Xingu River, Eastern Amazonia

Author(s)

Niyonzima, P. ^[1] ; Sawakuchi, A. O. ^[1] ; Bertassoli Jr, D. J. ; Pupim, F. N. ^[2] ; Porat, N. ^[3] ; Freire, M. P. ^[1] ; Goes, A. M. ^[1] ; Rodrigues, F. C. G. ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Geosci, Rua Lago 562, BR-05508080 Sao Paulo, SP - Brazil

^[2] Univ Fed Sao Paulo, Dept Environm Sci, Rua Sao Nicolau 210, BR-09913030 Sao Paulo, SP - Brazil

^[3] Geol Survey Israel, 32 Yeshayahu Leibowitz St, IL-9691200 Jerusalem - Israel

• Document type: Journal article
• Source: QUATERNARY GEOCHRONOLOGY; v. 67, FEB 2022.
• Web of Science Citations: 0

Abstract

This study reports on the first investigation into the potential of quartz luminescence dating to establish for-mation ages of ferruginous duricrust deposits (ironstones) of the Xingu River in Eastern Amazonia, Brazil. The studied ironstones comprise sand and gravel cemented by goethite (FeO(OH)), occurring as sandstones and conglomerates in the riverbed of the Xingu River, a major tributary of the Amazon River. The Xingu ironstones have a cavernous morphology and give origin to particular habitat for benthic biota in an area that hosts the largest rapids in Amazonia. So far, the Xingu ironstones have uncertain formation ages and their sedimentary origin is still poorly understood. In this way, seven samples of ironstones distributed along the lower Xingu River were collected for optically stimulated luminescence (OSL) dating of their detrital quartz sand grains. Addi-tionally, the organic content of some samples was dated by radiocarbon (C-14) for comparison with quartz OSL ages. The luminescence ages of the sand-sized quartz grains extracted from the ironstones were obtained from medium (100-300 grains) and small (10-20 grains) aliquots using the single aliquot regenerative-dose (SAR) protocol. Equivalent doses (D-e) distributions have varied overdispersion (OD) both for medium size aliquots (OD = 19-58 %) and small size aliquots (OD = 29-76 %). No significant trend was observed between D-e and aliquot size. The studied ironstones grow over the riverbed, but stay below or above water throughout the year due to the seasonal water level variation of the Xingu River. However, the effect of water saturation in dose rates is reduced due to relatively low porosity of ironstones. Water saturated dose rates (dry sample dose rates) range from 2.70 +/- 0.21 (2.79 +/- 0.22) Gy/ka to 12.34 +/- 0.97 (13.26 +/- 1.12) Gy/ka, which are relatively high when compared to values reported for Brazilian sandy sediments elsewhere (similar to 1 Gy/ka). Samples with high over-dispersion (>40 %) are mainly attributed to mixing of grains trapped in different time periods by goethite cementation. The obtained OSL ages for water saturated (dry) samples range from 3.4 +/- 0.3 (3.3 +/- 0.4) ka to 59.6 +/- 6.0 (58.1 +/- 6.4) ka, using D-e determined from medium size aliquots and dose response curves fitted by an exponential plus linear function. Radiocarbon ages of the bulk organic matter extracted from selected ironstone varied from ca. 4 cal ka BP to ca. 23 cal ka BP. Significant differences were observed between OSL and radio-carbon ages, suggesting asynchronous trapping of organic matter and detrital quartz within the ironstone matrix. These late Pleistocene to Holocene ages indicate that ironstones of the Xingu River result from an active surface geochemical system able to precipitate goethite and cement detrital sediments under transport. The obtained ages and differences between OSL and radiocarbon ages point out that the ironstones have multiphase and spatially heterogeneous growth across the Xingu riverbed. Our results also expand the application of lumines-cence dating to different sedimentary deposits. (AU)

• FAPESP's process: 16/02656-9 - The response of sedimentary dynamics of the Xingu and Tapajós rivers to climate changes and hydropower dams: risks for biodiversity conservation and energy production in Amazonia
• Grantee: André Oliveira Sawakuchi
• Support Opportunities: Research Program on Global Climate Change - Regular Grants
• FAPESP's process: 19/04059-6 - Characterization and application of violet stimulated luminescence signals of quartz for dating of fluvial sediments in Amazonia
• Grantee: Pontien Niyonzima
• Support Opportunities: Scholarships in Brazil - Doctorate
• 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: 19/24977-0 - Environmental signals recorded in modern sediments of tropical South American rivers
• Grantee: Dailson José Bertassoli Junior
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• 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: 16/11141-2 - Hydrologic variability and sediment supply of the Xingu and Tapajós rivers: climate change and anthropogenic impacts in eastern Amazon rivers during Holocene
• Grantee: Dailson José Bertassoli Junior
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 18/12472-8 - Origin and chronology of sandy substrates in Amazonia: implications for quaternary evolution of open vegetation ecosystems
• Grantee: Fernanda Costa Gonçalves Rodrigues
• Support Opportunities: Scholarships in Brazil - Doctorate