期刊
RADIOCARBON
卷 60, 期 2, 页码 383-393出版社
UNIV ARIZONA DEPT GEOSCIENCES
DOI: 10.1017/RDC.2017.126
关键词
climate; radiocarbon AMS dating; stromatolite; X-ray diffraction
资金
- Brazilian financial agency CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico) [311354/2016-5, 305079/2014-0]
- Brazilian financial agency FAPERJ (Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro) [E-26/111.278/2014, E-26/110.138/2014, INCT-FNA464898/2014-5]
Among the oldest remains of living beings to have inhabited the Earth's surface, there are the stromatolites-laminated sedimentary rocks associated with lithified mats of layered phototrophic microbial communities-which grow in specific environmental conditions. In the present work, we study a recent carbonatic stromatolite from Lagoa Vermelha (Rio de Janeiro, Brazil), a shallow coastal hypersaline lagoon. X-ray diffraction was associated to a depth chronological model defining three different sections based on changes in mineral composition of the stromatolite with increased dolomite content. Although a mean growth rate of 0.19 +/- 0.03 mm/yr is observed, the model discloses decreasing growth rates among the sections. Since dolomite formation can be related to high availability of Mg+2, confirmed by an expressive presence of (Ca, Mg)CO3, the lower growth rates were associated to a more arid environment, until approximately 1440 cal AD, with higher temperatures and consequently promoting water evaporation and salinity enhancement.
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