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Accueil du site → Master → Portugal → Depósitos carbonatados da Sabkha Oum Dba (Saara Ocidental, Marrocos) : fácies, processos e comparação com o ambiente atual

Universidade de Coimbra (2018)

Depósitos carbonatados da Sabkha Oum Dba (Saara Ocidental, Marrocos) : fácies, processos e comparação com o ambiente atual

Brito, Marlisa Martinho de

Titre : Depósitos carbonatados da Sabkha Oum Dba (Saara Ocidental, Marrocos) : fácies, processos e comparação com o ambiente atual

Auteur : Brito, Marlisa Martinho de

Université de soutenance : Universidade de Coimbra

Grade : Mestrado em Geociências 2018

Résumé
The sabkha Oum Dba is a wide salt flat located approximately 35 Km north of the city of Laayoune, in Western Sahara (Morocco). Carbonate deposits were examined in detail for their geologic and microbiologic features in the southernmost sector of the sabkha, with the purpose of understanding the interactions between physico-chemical and biological processes that help in the production of non-marine carbonate deposits. Of the different continental environments in which carbonate deposits can precipitate, we focus on deposits accumulated in an ephemeral lake where a hydrological system sustained by ambient-temperature groundwater produced suitable conditions for the formation of microbial-derived carbonates that locally pass to travertine. This sabkha represents a typical example of a modern environment with ongoing calcium carbonate precipitation, where living microbial mats represent the biotic feature responsible for suitably influence the environment and leading to the formation of calcium carbonate precipitates. Microbial communities often form aggregates, biofilm, or mat communities in response to environmental stressful conditions such as hypersalinity. Extracellular polymeric substances (EPS), widely produced by microbes, accumulate outside cells to form a protective and adhesive matrix that attaches the microorganisms to substrates and provides physico-chemical protection and can also aid nutrient absorption. The optical microscope investigation of these carbonates has revealed many morphologies that can be attributable to microbially mediated processes. Petrographic observations suggest that microbial evidence include stromatolitic wavy and planar laminations, filamentous aggregates and isolated filaments, diatoms, EPS, microbial clots and peloids. The correct interpretation of the microbial mats, their interactions and features and the environmental conditions where they are formed are important to understand analogous structures in the past and can be applied in the interpretation of their remains – such morphological fossils and biominerals. This work sought to characterize the microbial mats and carbonate deposits from a biosedimentological perspective, in terms of their morphology, texture and composition, and through a direct field observation of the environment where the same carbonate morphologies are currently forming.

Mots clés  : Depósitos carbonatados ; Ambiente hipersalino ; Tapetes microbianos ; Microfácies ; Geomicrobiologia ; Carbonate deposits ; Hypersaline environment ; Microbial mats ; Microfacies ; Geomicrobiology

Présentation

Page publiée le 19 juin 2020