Biominelalizations and biogeochemistry of iron, calcium and silica in the pampean coastal plains: their rol in the paleoenvironmental condition and sea level variations during the late cuaternary.

OSTERRIETH L. MARGARITA; FRAYSSINET, CELIA; FRAYSSINET, LUCRECIA

Simposio; The 14th International Symposium on Biomineralization (BIOMIN XIV) From Molecular and Nano-structural Analyses to Environmental Science; 2017

Different geomorphological settings: eolian dunes, estuarine, paleoestuarine, salt marsh,and fluvio-eolian plain sequencies Late Pleistocene- Holocene, was analized. Thestudy area is located in the Mar Chiquita region, Buenos Aires province. Disturbed andundisturbed samples were studied by means of routine procedures at different scalesof resolution: mesoscopic, microscopic and submicroscopic, using optical microscopySEM/EDX. Biomineralizations of iron in the form of framboidal and polyframboidal pyrite,greigite, mackinawite and iron oxyhydroxides were founded associated with gypsum,barite, calcite and halite, which permit us to define the redoxymorphic conditions inpaleoestuary pedosedimantary sequences. In the bioclastic and calcretized levels,calcium biomineralizations were founded associated with the processes of dissolution andreprecipitation of calcium carbonates and oxalates via biogenic action. The genetic sequenceof the calcite was defined via weddellite and whewellite associated with biomineralizinghyphas and bacteria in the soil, coexisting in the same pedosedimentary levels. Amorphoussilica biomineralizations of plants-silicophytoliths- presents, in the soils of the estuariesand paleoestuaries , (phytoliths of grasses and Cyperaceae), indicate a quite wet periodto marshy conditions, closely related to the advance and receding of the coastline duringthe Late Pleistocene-Late Holocene period. C4 plant communities were predominant,indicates a condition of greater salinity. The presence and complex interaction of calcium,iron and amorphous silica biomineralizations, demonstrate the complex biogeochemistrythat occurs in the temperate-wet paleoesturaries of the Pampean Plains. All this contributingto the understanding of taphonomic processes and their relevance to palaeoenvironmentalinterpretation of coastal environments. Knowledge of the evolution of palaeomarshes iscritical to understand the processes acting in the actual marshes, especially consideringurban development in coastal áreas and the consequences that different human activitiescould have, considering the active iron biogeochemistry and the possible acidificationprocesses generated by the oxidation of iron sulfides.