DISTINÇÃO DE TILITOS DENTRE OS MISTITOS DO SUBGRUPO ITARARÉ

PAULO M. B. LANDIM, MARIA BERNADETE R. BARROS

Resumo


Grain/matrix, sand fraction mean roundness and sand fraction mean sphericity were used in order to discriminate tillites among the mixtites from Itararé Subgroup. The results show that the variable grain/matrix is much more important than roundness or sphcricitv. Tillites present a high percent of matrix in relation to non-tillites samples, while roundness or sphericity values do not permit distinguish between the two sets of rocks. The absence of significative differences concerning roundness and sphericity may be explained reputing the tillites of the Itararé Subgroup as being constituted by sediments that , even deposited by ice, would not represent the first material transported by that agent, but a glacial reworking of sediments formerly deposited.

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