Pyrite as a proxy for the identification of former coastal lagoons in semiarid NE Brazil

Abstract

This work aimed to test the suitability of pyrite (FeS 2 ) as a proxy for reconstructing past marine environmental conditions along the semiarid coast of Brazil. Morphological description combined with physicochemical analyses including Fe partitioning were conducted for soil depth profiles (30 and 60 cm depths) at three sites in two contrasting lagoons of the state of Ceará: a suspected former lagoon that would have been transformed into a freshwater Blake^at a site vegetated by Juncus effusus (site P1), and another lagoon with connection to the sea at sites vegetated by J. effusus (site P2) or Portulaca oleracea (site P3). Soil samples were collected in September 2010. Site P3 had more reducing conditions, reaching Eh values of -132 mV in the surface layer (0-10 cm), whereas minimum values for the P1 and P2 sites were +219 and +85 mV, respectively. Lower pyritic Fe values were found at site P1, with a degree of pyritization (DOP) ranging from 10 to 13%. At sites P2 and P3, DOP ranged from 9 to 67% and from 55 to 72%, respectively. These results are consistent with an interruption of tidal channels by eolian dune migration inducing strong changes in the hydrodynamics and physicochemical characteristics (lower salinity, oxidizing conditions) of these sites, causing the dieback of suspected former mangroves and a succession to freshwater marshes with an intermediate salt marsh stage. Together with other physicochemical signatures, pyrite can evidently serve as a useful proxy in tracking environmental changes in such ecotones, with implications for coastal management.

Hominin homelands of East Java: Revised stratigraphy and landscape reconstructions for Plio-Pleistocene Trinil

“…The massive and blocky-structured clays indicate thorough bioturbation and intermittent flooding. The clay contains dispersed fine pyrite crystals, which generally form under intermittent brackish water conditions, in combination with high bioavailability of organic matter and a dominant anaerobic environment (Pons et al, 1982;Weaver, 1989;Roychoudhury et al, 2003;Ferreira et al, 2015). This setting is supported by the occurrence of Melanoides aff.…”

Recovery of Soil Processes in Replanted Mangroves: Implications for Soil Functions

“…Mangrove forests are surrounded by dunes and by the sandy-clayey soils from the Barreiras geological formation, dominated by quartz and kaolinite, with minor amounts of Fe oxyhydroxides [40][41][42]. Mangrove soils are subjected to a daily mesotidal regime, ranging from 0.75 to 3.25 m (Table 1) [43], with redox potentials (Eh) ranging between +16 and +450 mV and pH values ranging from 6.3 to 7.7 (Table 1). Mature mangroves are composed of Avicennia germinans (L.) L., Laguncularia racemosa (L.) C. F., and Rhizophora mangle L. Revegetation was carried out using Rhizophora mangle L propagules.…”

Applying the Soil Management Assessment Framework (SMAF) to Assess Mangrove Soil Quality

“…The mangrove soils in the study area are characterized by sand-clay textures originating from the sedimentary deposits of the Barreiras Formation, as well as influence from the surrounding dunes [34][35][36]. Additionally, mangroves experience a daily to diurnal mesotidal regime, ranging from 0.75 to 3.25 m [37].…”