Geology and Mineral Resources of Paraguay A Reconnaissance

SEDIMENTARY ROCKS 65at least three different localities in the Independenciabeds near Villarrica, in the small outlier betweenSan Jose and Valenzuela, and near Independencia.The stratigraphic position of these fossils within theseries is not known accurately, but those at Independenciaand perhaps the others, are believed byHarrington to be in the upper sandstone unit, not farabove the plant-bearing horizon.Beder (1923) found lamellibranchs on the southeastedge of Villarrica at a point where the road is cut inreddish-gray sandstone. This is 2 kilometers east ofthe Mesosaurus locality mentioned above in the descriptionof the Tubarao series. The fossils, which arepoorly preserved, were identified by Beder as Solenomorpha,probably S. similis Holdhaus and S. intermediaHoldhaus. Gerth (1932, pt. 2, p. 209-210) says thatBeder's Solenomorpha was later redescribed by Reedas Myophoria. Solenomorpha similis Holdhaus is nowcalled Leinzia similis (Holdhaus) Camargo Mendes(1951). Leanza (1948) calls attention to the fact thatWindhausen in 1931 added Sanguinolites to the list offossils from Villarrica; it accompanies Beder's Solenomorpha.Reed (1935, p. 41-42) describes and illustrates fossilscollected in 1924 by Windhausen from an outlier ofIndependencia beds between San Jose and Valenzuela.The only description of the geology is ofpinkish or buff-colored fine-grained sandstone containingnumerous poor impressions and internal casts of one or morekinds of small lamellibranchs.Reed classes these as Pinzonella cf. Ulusa Reed.Harrington (1950, p. 35) describes pelecypods from asmall abandoned quarry 800 meters south of HotelTilinsky in Independencia. The fossils are stratigraphicallyabove the plant-bearing beds but still inthe lower third of the upper sandstone unit. They weretaken from a light-gray to reddish-gray layer of sandstone,only 20 centimeters thick, that lies betweencrossbedded sandstone units. There are many individualfossils, but Harrington found only two speciesPinzonellopsis occidentalis (Reed) Camargo Mendesand pseudocorbtda anceps Reed.The paleontologic evidence, though somewhat sparse,convinces Harrington (1950) that the Independenciabeds of Paraguay are of late Permian age and stratigraphicallyequivalent to the Rio do Rasto group andthe Estrada Nova formation of the Brazilian Passa Doisseries (Gordon, 1947).TEIASSIC SYSTEMMISIONES SANDSTONEThe Misioiies sandstone was named by Harrington(1950, p. 37-40) for the Misiones region, between theRio Tebicuary and the Rio Parana, where it is particularlywell exposed. It consists of homogenous redsandstone, and probably of red clay or shale, and overlapsall, or nearly all, of the older rocks in the country.It is overlain by the Serra Geral basalt, and is possiblyinterbedded with it in part.One very large area of outcrop and several smallerones are shown on plate 1. The main outcrop occupiesa southward-trending band, 20 to 70 kilometers wide,that extends through the eastern part of Paraguay fromthe Rio Apa to the Rio Parana. At the latitude ofCaazapa the lower boundary of the belt trends abruptlywestward and the belt is broader, covering most of theextreme southwestern part of eastern Paraguay. Thedistribution as mapped is based partly on Harrington'smap, partly on sketch maps and descriptions by Carnier(191 Ic) and other earlier workers, and partly on observations,interpretations, and guesswork. The contactbetween the Triassic sandstone and the Serra Geral lavais believed to be one of the most accurate shown on theentire map (see p. 26 and pi. 1). The broad expanse ofTriassic rocks shown in the southwestern corner of thecountry is almost pure guesswork, however, for nearlyall of this area is marshland. Similarly, the northernhalf of the belt of outcrop is drawn as essentially conformableon the Independencia rocks; there are no mapsor descriptions known to the author to help determinewhether the Misiones beds there are conformable orwhether they overlap the older beds as they do farthersouth.A second fairly large area of outcrop lies in the areabetween Asuncion and Ypacarai, and extends as farsouth as Paraguari (pi. 1). Exposures are poor in mostof this area, and the soils are redder and thicker than inmany parts of the country. Good outcrops of massive,thick-bedded, reddish-brown sandstone are known atYaguaron, at Itapitapunta (a cliff on the Rio Paraguaysouth of Asuncion), in road cuts in and near Asuncionitself, and at a few other places. Harrington describesa striking angular unconformity between the Misionessandstone and the underlying Caacupe series. In aravine almost midway between Itaugua and Ypacarai,and about 200 meters north of the highway, he foundthe strike of the Misiones sandstone was almost duenorth and the dip 42° W. The actual contact is not exposed,but below the Misiones beds Harrington foundtypical Caacupe sandstone light-colored, crossbedded,and strongly brecciated that appeared to dip at 70° orhigher angles toward the west.A small inlier of sedimentary rocks along the RioParana near the colonies of Jesus and Trinidad (pi. 1)is referred to the Triassic with considerable hesitation.On the basis of several specimens of coal reported tohave come from that area, Harrington (1950) mappedthese rocks as above the Serra Geral lavas and as of