Straited surfaces and related features, developed by the gondwana ice sheets (state of Paraná, Brazil)

Abstract

The occurrence of striated floors, produced by the Gondwana ice sheets, is briefly described in this paper. Several striated localities crop out in the second plateua of the State of Paraná (Brazil), some of them being unusually well preserved. The striations occur on pre-Gondwana surfaces of the Devonian Furnas Formation, as well as on the periglacial deposits of the Itaaré Formation (Upper Carboniferous), which also bears the glacial sequences. Many outcrops are directly overlain by typical tillites, making possible a comparison between the direction of the glacial lineations, and the long axis pebble orientation of those rudaceous deposits. The average pebble long axis dip direction for the Cancela Tillite is S 11 ° E, while the glacial striations direction is S 2° E, the difference being only 9°. The ice movement deduced for the Cancela Tillite was toward N 11 ° W. Besides the results obtained from the tillite fabric, additional data were gathered from sedimentary structures of the periglacial deposits. Thus, crossbedding measurements, carried on in the outwash sandstones associated to several Gondwana glaciations, afforded the following average result: N 5° W. General results, as compared together, show a reasonable agreement between both the results of glacial deposits and of the periglacial ones. As the present writers are gathering more data, it is assumed that definite and more reliable results may be given in forthcoming papers.