ORIFÍCIOS ORGANÓGENOS E ESTRUTURAS CORRELATAS NA FORMAÇÃO PALERMO (GRUPO TUBARÃO)

Some sedimentary features from the Palermo Formation (Upper Carboniferous of Southern Brazil), considered to be produced by the boring activity of worms are briefly discussed in this paper. The structures consist of cylindrical tubes which range from an almost vertical position to a sub-horizontal one. Usually, the borings begin in silty-clays and sandy-siltstones, with their length ranging from 1 to 8 em, while their diameter varies from 2 to 12 mm. The ratio of length to diameter ranges from 4:1 to 10,5:1. The average areal density is about three tubes per ten square centimeters. Some recondary structures, related with the boring activities, are also described. These refer mainly to the pseudo-nodular features, as well as to the extensive modification of the original bedding. Granulometric analysis of the reworked beds show relatively unsorted deposits probably connected with the mixing up of sediments by the organic activity The rate of sedimentation, as suggested by the burrows and related features, is also briefly discussed.