CICLOESTRATIGRAFIA DO EOPERMIANO - ESTUDO DE CASO NO GRUPO ITARARÉ, BACIA DO PARANÁ (PARTE 2): EVIDÊNCIAS DE INDUÇÃO ASTRONÔMICA (ORBITAL E SOLAR) NO CLIMA E NA SEDIMENTAÇÃO

Abstract

The existence and nature of possible astronomic forcing of cyclicity in glacial sediments of the Itarare Group, Paraná Basin, during the Eopermian, were studied in core and gamma ray log data from two wells drilled by CPRM (Companhiade Pesquisa de Recursos Minerais) to coal research, one in Santa Catarina and other in Rio Grande do Sul. The distance between the original location of the cores (about 380 km) made it possible to test the astronomic forcing in this deposits in different locations of the basin. Two methods of data sampling were used, according to data scaleand the possible forcing: the gamma ray logs were digitized and sampled at I em intervals, in order to test the presence of orbital forcing (20,000 to 400,000 years) or other forcing phenomena (3,000 to 10,000 years), and the cores were scanned in the intervals with rhythmites and transformed in gray scale data sampled equally (0,2538 mm), in order to search for annual to centennial cycles. The harmonic analysis showed cyclicity in both scales: orbital cycles ranging from about 17,000 to 100,000 years and solar cycles ranging from about 22 to 1,000 years. The accumulation time calculated for one well in log and core data (about 9,400 years for the scanned interval and about 12,600 years for the same intervalin log data) showed a very high correlation. The accumulation rates calculated for the log data, ranging from 5,2 to 9,3 cm/ka, are very similar to the Pleistocene ones. The analysis also showed that the complete sedimentary record of the Itarare Group for one of the wells corresponds to about half precession cycle (12,342 years). As both astronomic forcing phenomena detected, the solar and the orbital cycles, affect climate on a global scale, certainly their influence on sedimentation occurred in other locations of the basin.