Geology and Mineral Resources of Paraguay A Reconnaissance

SEDIMENTARY ROCKS 57of red ochre that it gives a bright-red greasy streak.Poorly preserved fossils are widespread. At the northeastend of this exposure, 2.5 kilometers southwest of.Arroyos y Esteros, a fairly large collection of fossilswas made from a freshly quarried pile of building stoneidentical with that just described.Stratigraphically above the red micaceous sandstone,and extending 2 kilometers northeast of Arroyos yEsteros, is massive quartzose sandstone with little micaor feldspar. It is yellow to brown, but weathers to soilthat is nearly as red as that on the underlying red sandstonefarther southeast. This sandstone dips beneaththe valley of Rio Manduvira. It probably marks thetop of the Caacupe series and is overlain by softer andmore shaly beds of the Itacurubi series of DevonianFIGURE 47. Ocher quarry near Tobati. The white sandstone unit of the Caacupfiseries contains ocher-yellow clay between interstices of the sand grains.sive fauna, is on the east side of the Piribebuy valley,hence the beds described by these authors would seemto be stratigraphically above those of the main valley.Cerro Aparipi, which was not visited by the presentauthor, is a conical hill, 30 meters high and 300 meterslong, about 4 kilometers north of Rio Piribebuy andalmost due north of Tobati. According to Beder andWindhausen, the lower part of the hill is made up ofvery fine grained, highly micaceous sandstone, with afew intercalations of white to gray clay. This sandstoneis succeeded by 20 meters of white to grayishwhitefossiliferous clay, locally tinted yellow by veinletsof limonite. The layer of clay is overlain by mediumgrainedgrayish-red, thick-bedded sandstone that capsthe hill.The beds exposed on Cerro Aparipi are overlain by athick massive sandstone. This is exposed in a numberof places along the road between Tobati and Arroyos yEsteros between points 2.5 and 6.5 kilometers southwestof the latter town. The sandstone is soft, dullred, very micaceous, and contains such an abundanceThe author's interpretation of the Caacupe series, asgiven in preceding paragraphs and shown on the geologicmap, plate 1, differs somewhat from that of Harrington(1950, p. 19-24, fig. 3, and geologic map). The differenceshave to do with the place of the two major fossiliferouslocalities in the stratigraphic section, and withthe relative stratigraphic position of the white saccharoidalsandstone unit.Harrington's general description of the rocks of theCaacupe series is essentially the same as that givenabove. He says it is made up of a succession of lightcoloredsandstone beds that commence with a stronglydeveloped basal conglomerate. These basal beds hecalls "Paraguari conglomerate," using the name "Piri­bebuy sandstone" for the main part of the series. HisPiribebuy sandstone beds are crossbedded in the lowerpart and contain a few thin laj^ers of clay. They gradeupward to light-colored saccharoidal sandstone, whichcaps the Caacupe series.Harrington believes the fossiliferous clay of CerroAparipi and of the Vargas Pena clay pit at Ypacaraito be at or about the same stratigraphic horizon, whichhe places as probably high in the crossbedded sandstoneseries but beneath the saccharoidal sandstone unit.Unfortunately, the faunas from the two main localitiesshed no light on the problem. Unless there is an undiscoveredfault along the Rio Piribebuy that broughtthe beds at Cerro Aparipi up on its east side, and anotherbetween Arroyos y Esteros and the Rio Manduvira thatagain dropped the whole Caacupe section beneath thesurface, the facts available indicate that the fossiliferousclays at Cerro Aparipi are near the top of theseries and well above the saccharoidal sandstone unit.The place of the clay beds at Ypacarai is much moreopen to question than those just discussed. The authorbelieves they are very near the base of the Caacupeseries, but this is based more on his interpretation ofthe structure than on real knowledge of the stratigraphy.