Sequence stratigraphy and coal petrography applied to the Candiota Coal Field, Rio Grande do Sul, Brazil: A depositional model

The sedimentary rocks of the Candiota Coal Field which belong to the Rio Bonito Formation, Guata Group, Tubarao Supergroup, in the Parana Basin (Eopermian), were studied on the basis of sequence stratigraphy. Six fourth-order parasequences, designated ''A'' (the oldest) to ''F'', and a third-order sequence (''alpha'' sequence) were identified in outcrops, drill cores, and well logs. The rocks were deposited in an incised valley superimposed on the rocks of the Itarare Group, Tubarao Supergroup. Up to 23 coal seams have been observed; however, they do not extend through the entire coal field. The Gelification and the Tissue Preservation Indexes (based on maceral analysis; Diessel, 1986) were used to infer the depositional environments of the coal seams.