FÁCIES AMBIENTES E CARVÕES NA FORMAÇÃO RIO BONITO NO SUL DO ESTADO DO PARANÁ: UMA ANÁLISE ESTRATIGRÁFICA

Abstract (English)

The results obtained through stratigraphic analysis on a regional scale, in the Rio Bonito Formation (Lower Permian of the Parana Basin), are presented herein. The survey was performed over an area of about 3 000 km2, in the southern region of the State of Parana.The main purpose of the research was to analyse the faciologic and depositional parameters of the coal bearing deposit and the possibility of its economic exploitation. About 90 well logs and several field sections were studied. The interpretation of the sedimentary environment was made through the formats (curve shapes) of gamma rays and resistivity logs related to physical properties of the facies, supplemented by lithologic control from outcrop description and samples from strategically located wells. The lower member of Rio Bonito Formation (Triunfo Member) was originated in a deltaic province prograding over prodeltaic siltstones of an epicontinental shallow sea. The upper part of this member is of a retrogradacional nature, being covered by transgressive marine deposits of the Paraguacu Member. In the interdistributary bay of the deltaic plains of the Triunfo Member several peat swamps and marches were formed. Owing to high clastic influx and low subsidence rate, the peat accumulation was thin, being preserved as coal beds thinner than 50 cm with a high ash content. These elements justify the exclusion of about all the coal bearing layers ofthe area, as far as its economic exploitation is concerned.