Mediadores de Centros de Ciências e os seus papéis durante as visitas escolares

In the present paper, it is presented a general view about who they are and the activities science centers and museums mediators develop. The literature points out to the diverse roles attributed to these actors and that the presence of this type of professional is a consolidated practice in non-formal educational institutions. Data obtained among the mediators of a science center during mediated school visits are also presented and discussed, focusing in the role attributed to these professionals, with the objective of characterizing their actions during these visits. The data obtained and analyzed showed that during school visits, the roles that are attributed to the mediators are: (a) mediation of the knowledge involved in the expositions; (b) explanation of the scientific concepts involved in the expositions; (c) presentation of the thematic spaces; (d) reception and organization of groups of visitors; (e) preservation of the physical and moral integrity of the visitors, and the integrity of the physical spaces and their equipments; (f) complementation of the school knowledge, and (g) diffusion of the scientific knowledge.

Microbialitos da formação Codó (Aptiano Superior) às margens do rio Tocantins em São Miguel do Tocantins (TO)

The southwestern region of the São Luís-Grajaú Basin has a rare outcrop of the Codó Formation (upper Aptian) with seven outstanding microbialite bioherms along the left margin of the Tocantins river, near Imperatriz (MA). Resting on sandstones of the Grajaú Formation, the Codó Formation presents: 1) a 20 cm thick basal calcilutite with gypsite pseudomorphs and some fossil tree stems; 2) metric dark shales with carbonate nodules and thin intercalated carbonate layers, enclosing some microbial laminites; 3) a 2 cm thick upper breccia composed of microbialite fragments and other carbonate clasts, with halite hoppers on the top; 4) the carbonate bioherms, which partially overlie the extensive shales and interrupt them laterally, as well as the breccia. The bioherms in the northern part of the outcrop are thicker (<2 m) and have interbedded dark shales, whereas the southern are thinner and continuous in the vertical direction. In general, they are composed of irregular gently to strongly wavy microbial laminites, sometimes with pseudocolumnar to conical lamination. All microbialites with highest synoptic relief (<20 cm) look like columnar stromatolites on weathered lateral expositions. In plan view, the horizontal sections of these microbialites are circular to slightly elliptic, sometimes forming very small channels (N60W) filled with fine breccia. The highest bed of the northern bioherm has mixed microbial laminites and columnar stromatolites, where intercolumnar spaces were filled with microbialite clasts, fish bones, plant fragments and very small probable crustacean coprolites. Several fractures and deformation in this upper bed indicate an initial brecciation process probably caused by subaerial exposure. In microscopic scale, the lamination is smooth, diffuse, defined by subtle granulation differences of very fine granular calcite crystals within micrite, but oxide levels, dissolution surfaces or thin precipitated calcite veneers...