Registro de variações ambientais dos últimos 3000 anos da Região da Ria do Mamanguá, Rio de Janeiro, utilizando marcadores orgânicos moleculares

Spera, Amanda Mattosinhos

doi:10.11606/d.21.2012.tde-28032013-104448

Cited by 1 publication

(1 citation statement)

References 23 publications

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“…Mamanguá Ría has restricted circulation and low intensity tidal variation, which ranges between 64 and 125 cm (Bernardes, ). The inner ría receives organic matter from land, like in an estuary, while the outer ría is influenced by marine production (Spera, ). Surface sediments are predominantly composed of clay and silt and are water saturated.…”

Section: Environmental Settingmentioning

confidence: 99%

Diagenetic Fate of Biogenic Soft and Hard Magnetite in Chemically Stratified Sedimentary Environments of Mamanguá Ría, Brazil

et al. 2019

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Magnetotactic bacteria (MTB) synthesize magnetite and greigite crystals under low oxygen conditions in the water column or uppermost sediment (greigite‐producing bacteria are found below the oxic‐anoxic transition). Dissolved iron and oxygen contents in local environments are known to be limiting factors for the production and preservation of biogenic magnetite. Understanding the processes that link MTB to their living environments is fundamental to reconstructing past chemical variations in the water column and sediment, and for using the magnetic properties of biogenic magnetite as environmental proxy indicators. Previous studies have suggested that the frequently identified biogenic soft (BS) and biogenic hard (BH) magnetite types are associated with equant and more elongated morphologies, respectively, and that their abundance varies in accordance with sedimentary oxygen content, where MTB that produce the BH component live in less oxygenated environments. We test this hypothesis in a high‐resolution integrated environmental magnetic and geochemical study of surface sediments from Mamanguá Ría, SE Brazil. Based on magnetic and pore water profiles, we demonstrate that both the BS and BH components occur within microaerobic environments and that as sediment oxygen content decreases with depth, the BS component disappears before the BH component. With continued burial into the sulfidic diagenetic zone, both components undergo progressive dissolution, but the BH component is more resistant to dissolution than the BS component. Our observations confirm previous inferences about the relative stability of these phases and provide a firmer basis for use of these two types of biogenic magnetite as paleoenvironmental proxies.

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Section: Environmental Settingmentioning

confidence: 99%