TEE LAVA FIELD OF THE PARANA BASIN 67 



PREVOLCANIC SEDIMENTARY HISTORY 



The sedimentary history is relatively simple, exhibiting a rather 

 surprising uniformity of depositional conditions. Non-fossiliferous 

 basal conglomerates, shore-Hne sandstones, and alluvial deposits 

 are followed in the same depositional cycle by marine Lower 

 Devonian shales and sandstones, deposits of a sea which covered 

 a vast area in the interior of South America.^ There followed an 

 epoch of erosion which removed much of the Lower Devonian 

 and possibly older sediments. Then, if not, indeed, earlier (pre- 

 Devonian) it would appear that the approximate eastern and 

 northern Hmits of the Parana depositional basin were formed. 

 As yet, no great angular unconformity between Lower Devonian 

 and superjacent beds has been determined. 



Nearly all later sedimentation in this basin, so far as yet indicated 

 by outcropping rocks, was of the continental type, although some 

 diminutive brachiopods, presumably marine, have been found in the 

 lower coal measures in southern Parana, and mollusks, more probably 

 brackish-water or fresh-water forms, in the Estrada Nova beds of 

 both Sao Paulo and Parana. It is possible that some contempo- 

 raneous marine deposits were laid down in the now covered central 

 or western part of the geosyncline.^ I. C. White's stratigraphic 

 classification-^ applies to all the sedimentary region east of the basalt. 

 The first deposits of the continental sequence were of alluvial, 

 fluvio-glacial, glacial-morainic, floating ice, and palustrine origin, 

 and are found in the BraziHan states of Sao Paulo, Parana, and 



' Fossiliferous Lower Devonian has been found in the Falkland Islands, the 

 province of Buenos Aires, the eastern Andes of Bolivia, on both sides the lower Amazon 

 geosyncline, in Paraguay, and in the Brazilian states of Parana, Matto Grosso, and 

 Goyaz. In southern Goyaz, twelve miles north of the town of Rio Bonito, the writer 

 found shales lithologically similar to those of Ponta Grossa in Parana and carrying 

 Dalmanites. 



^ Siemiradski's {Geologische Reisebeohachtungen in Sudbrasilien, Sitz. Ber. Akad. 

 Wiss., Mat.— nat. CI., Bd. 107, Abt. i, pp. 23-39, figure and plate, Vienna, 1898) 

 locality and age determinations of some supposed Permian marine fossils from the 

 movmtains of the Matto Grosso-Paraguay frontier are doubtful. These fossUs were 

 worn as charms by Indians and may have come far distant from where Siemiradski 

 supposed. Also, they are not age-diagnostic; it is possible they are as old as Devonian. 



3 Report on the Coal Measures and Associated Rocks of South Brazil. In English 

 and Portuguese. Report to the Ministry of Industry, etc. Rio de Janeiro, 1908. 



