Geology and Mineral Resources of Paraguay A Reconnaissance

58 GEOLOGY AND MINERAL RESOURCES OF PARAGUAYIf, as shown on plate 1 and discussed in the section onstructural geology, Harrington's concept of a grabenalong the depression is correct, then the fossiliferousbeds at Ypacaral may be anywhere within the Caacupeseries though almost certainly within the main arkosicsandstone unit and beneath the white saccharoidalsandstone.Paleontology. Much confusion exists as to the age ofthe Caacupe series and of the Itacurubi series, describedon succeeding pages. Available facts on identificationsand age assignments of the few fossils from these seriesthat have been made by various paleontologists aregiven below. It is evident from these conflicting reportsthat no satisfactory definition of the ages of the Caacupeand Itacurubi series can be made without studies oflarge collections of fossils that are tied to detailedgeologic maps. Indeed, it seems probable that solutionof the paleontologic problems may well have to awaitthe establishment, somewhere in South America, ofsome standard section of the Paleozoic rocks that canbe used as a point of reference throughout the continent.The first known fossils from what is here called theCaacupe series were from Cerro Aparipi, south ofArroyos y Esteros. They were collected and describedby Beder and Windhausen (1918). These authors alsocollected fossils from a pile of building stones in thetown of Arroyos y Esteros which they say were takenfrom a quarry a few kilometers north of the town.They identified the following species:Leptocoelia flabellites ConradCalmonia subseciva ClarkeTentaculites crotalinus SalterTropidoleptus carinatus ConradBeder and Windhausen's assignment of the bedsthat yielded these fossils to a Devonian age stood in theliterature until Harrington (1950) visited the samelocality and recognized the fauna to be of lower Silurianage. Harrington describes the following species fromCerro Aparipi and from the Vargas Peiia quarry atYpacarai:CerroAparipi YpacaraiLingula sp__________________________________ _ _ _ _ XAtrypina(!) paraguayensis Harrington__________ X _____Ctenodonta(l~) sp_____________________________ XPalaeoneilo constrictiformis Harrington________ ____ XNuculites opisthoxystomus Harrington__________ X XHyolithes sphenomorphus H arrington ___________ ____ XCalymene boettneri H arrington _________________ X XDalmanites sp_______________________________ ____ XClimacograptus innotatus var brasiliensis Rued- X XemannDiplograptus modestus Lapworth var ___________ ____ XHarrington points out that the trilobite describedby Beder and Windhausen as Acaste (Calmonia)subseciva Clarke is in reality the form he describes asCalymene boettneri Harrington.A J. Boucot of the U. S. Geological Survey has thefollowing comment concerning the faunal lists justgiven:The faunal list in Beder and Windhausen indicates lowerDevonian age for the Cerro Aparipi, and it is difficult to seehow they could have misidentified Leptocoelia flabellites. Onthe other hand the graptolites identified by Btilman (Harrington,1950) are certainly not of Devonian age. Is it possiblethat the flat-lying beds on the top of the hill are Devonian andthat the Silurian fossils could have been obtained from thebottom of the hill?Boucot's question can be answered in the negative.Harrington, in written communication to the author,states that there is but one tiny quarry on CerroAparipi and that it is certainly the place that yieldedBeder and Windhausen's collection as well as his owncollection that contained graptolites. He adds thathe is personally convinced that Beder and Windhausen'sidentification of Leptocoelia flabellites was in error.The present author, in company with Kicardo MazoU., failed to find the Cerro Aparipi locality, but likeBeder and Windhausen, did make a collection of fossilsfrom a large pile of building stone in a field 2 kilometerssouth of Arroyos y Esteros. Quite possibly thesestones came from the same quarry mentioned by theearlier workers. The rich fossil locality at the VargasPeiia clay pit near Ypacarai was found, quite accidentally,and a few fossils were found in a stone quarry1.5 kilometers southeast of Aregua and in pottery clayreported by the owner to come from a clay pit 3 kilometersnorth of Itaugua. The latter locality isprobably at about the same stratigraphic horizon asthat at the Vargas Pena quarry. The fossils collectedfrom these localities were examined by paleontologistsof the U. S. Geological Survey, whose reports follow:A. J. Boucot reports on a small lot of poorly preservedfossils from the stone quarry 1.5 kilometers southeastof Aregua as follows:This lot contains an unidentified plicated brachiopod, probablya rhynchonellid, whose brachial valve bears a median septum.It resembles the genus Camarotoechia. Also present is anunidentified smooth pelecypod and Tentaculites sp.A. K. Palmer reports as follows on trilobites fromthe same collection just noted:This collection contains a cephalon of a Phacopid trilobitethat could belong to either the subfamily Acastinae or Calmoninae.Trilobites of this type have not been reported fromrocks younger than lower Devonian. If a pygidium in thecollection belongs with the cephalon, then the general lack ofspines on the species would eliminate the subfamily Calmoninaefrom consideration.It is not possible to identify the genus within the Acastinaeto which the Paraguayan specimens might belong. The cephalon