Aspectos tafonômicos e o Efeito Lilliput em discinoideos do Devoniano da Bacia do Paraná, Sub-bacia Apucarana, Brasil

An earliest Givetian ''Lilliput Effect'' at So´tio Wolff and Sao Bento in the ParanaBasin occurred after an extinction event, possibly related to the latest Eifelian KAC y AK Event. The Malvinokaffric fauna was reduced from 65 genera before the extinction event to eight genera after the event. However, the abundance of the individual taxa is high. The size reduction of the surviving taxa was up to 90%. The palynomorphs during the extinction and post-extinction (''Lilliput Effect'') events are scarce. Nor- mal palynomorph abundance and diversity is restored later in the early Givetian immediately after the post-extinction event. The relictual fauna in the beds with the ''Lilliput Effect'' at So´tio Wolff and Sao Bento constitute the last survivors of the classical Malvinokaffric shelly fauna in the ParanaBasin, and are at these sites mixed with immigrants and alien elements (e.g. orthoconic nautiloids).

Chitinozoans from Middle and Upper Devonian strata have been investigated from the Parana Basin in southern Brazil and eastern Paraguay. These sequences are present in the Alto Garcas (north) and Apucarana (south) sub‐basins in Brazil, and the “East Paraguay Sub‐basin”; in eastern Paraguay. Marine communication between the sub‐basins was established during the early Givetian. Of the 49 chitinozoan species encountered, 28 species are retained in open nomenclature, and Ancyrochitina simplex is newly described. A chitinozoan biozonation, with five zones, is proposed for the investigated interval. The zones are from oldest to youngest: concurrent range zone of Alpenachitina eisenacki and Spinachitina biconstricta (late Eifelian?‐early Givetian); the interval range zone of Ancyrochitina taouratinensis (latest early‐middle Givetian); concurrent range zone of Fungochitina pilosa and Ancyrochitina langei (late Givetian); concurrent range zone of Hoegisphaera glabra and Ramochitina derbyi (early Frasnian)...

No contexto de modelos analogos, dados gamaespectrometricos de superficie da Formacao Ponta Grossa (FPG), Devoniano da Bacia do Parana, constituida pelos membros Jaguariaiva, Tibagi e Sao Domingos, permitiram melhor entender a distribuicao de seus litotipos e estabelecer correlacoes com os dados de radiacao gama derivados de perfis de pocos profundos. As medidas de superficie, espacadas de 50 cm nos arenitos e 100 cm nos folhelhos, foram adquiridas em quatro secoes: Arapoti, Tibagi, Jaguariaiva e Ponta Grossa, com extensoes respectivas de 30, 250, 12 e 16 metros. Os resultados mostraram que a tendencia de incremento gradativo da fracao argila na secao Arapoti (camadas de transicao das formacoes Furnas e Ponta Grossa) foi bem refletida nos perfis de raios gama em superficie e subsuperficie. No perfil Tibagi (Membro Jaguariaiva), os teores de carbono orgânico total (COT) guardaram relacao direta com o aumento da radiacao gama em superficie e em profundidade. Ainda neste perfil se constatou relacoes consistentes dos dados gamaespectrometricos de afloramentos e pocos com a secao granulometrica de 250 metros de exposicao da FPG. Na secao Jaguariaiva foi possivel notar com clareza a diminuicao das contagens nas camadas arenosas e a queda abrupta dos valores a partir do contato dos arenitos basais do Grupo Itarare. O Membro Tibagi, claramente mais arenoso, explicitou no perfil Ponta Grossa assinatura dos raios gama compativel a um padrao granocrescente ascendente, tambem verificada nos perfis de pocos. O Membro Sao Domingos, representativo de possante intervalo pelitico da FPG, foi tambem bem caracterizado atraves de altas contagens nos dois niveis de investigacao. O emprego de gamaespectrometria de superficie, em correspondencia a descricao pormenorizada de afloramentos e a dados de pocos profundos, apontou para o estabelecimento de modelos analogos da FPG na Bacia do Parana.

In the Parana Basin, dolines in sandstones occur in the Aquidauana Formation in Jardim (MS) and in the Furnas Formation in Ponta Grossa (PR). In the Ponta Grossa region, the retreat of arenitic rocks is marked by the “Furnas Formation Escarpment”, whereas in Jardim there is no associated escarpment. The dolines of the Jardim are generally extensive and shallow, and those of the Ponta Grossa deep and scarped. In Ponta Grossa, the dolines have had their origin associated, in most studies, with the subsurface erosion of sandstones, due to the presence of ruiniform relief features, the proximity of escarpments and the mistaken absence of carbonatic rocks in the basement of the basin. The Jardim and Ponta Grossa dolines are collapse phenomena generated by a piping process, brought about by the development of a subjacent karst system, at depth, in a phreatic environment, in the carbonatic basement rocks. The role of subjacent karst in doline formation in sandstones is demonstrated by: 1) rather than being distributed along all the arenitic units of the Parana Basin, dolines are restricted to only those locations with carbonatic rocks in the basement structures of the basin; 2) ruiniform relief features are surface structures originating from erosive or weathering processes in sandstones and can be attributed to pseudokarst, having no direct relationship with the dolines, which even when present at the surface, represent points of injection of meteoric water, connected at depth to the karst system; 3) besides being evidence of structural control in the sandstones, the alignment of surface features shows the direction of karst conduits at depth. The “Vila Velha Depression”, described for the first time in this study, which includes the dolines in the Ponta Grossa region, is a reflection of the piping process brought about by the subjacent karst. In the exposed karst area typical features are not very frequent or evident, due to dolomitic composition, and the dolines are more evident in sandstones than the actual carbonate rocks. However, in Jardim, the gradual geomorphological transition between sandstones and carbonate rocks makes the subjacent karst more visible, which exposed the karst features, in a different manner to the Ponta Grossa region, where the karst is encountered at a distance from the dolines and at greater depth.

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The Eifelian–Givetian (Middle Devonian) transition constituted an important paleoenvironmental event for the Malvinokaffric Realm in the Apucarana Sub-basin (Parana Basin). This study highlights integration between taphonomy and sequence stratigraphy, and four depositional sequences are identified during the transition. In Sequence 1, the presence of a typical normal-sized Malvinokaffric fauna is recorded. In the transgressive systems tract (TST) of Sequence 2, no benthic fossils are present, and this is interpreted as a stratigraphic marker of an event of significant paleoenvironmental change (KACAK Event). In Sequence 3, the TST has abundant bioclasts, which become rarer toward the top of the section, i.e., within the transgressive systems tract. The original habitat of this autochthonous to parautochthonous fauna was a low-energy environment between the fair weather wave base and the storm wave base of the Devonian epicontinental sea. In the highstand systems tract of this sequence, the presence of normal-sized Pennaia paulianna and lingulids demonstrates the return of more ambient conditions. Sequence 4 is of Carboniferous age. Its limit is a second-order sequence boundary recording a lowstand systems tract formed by a fluvial depositional system. The low diversity and the disappearance of taxa are not the result of a taphonomic bias, but reflect the post-KACAK Event.

The magnetotelluric geophysical method has been used effectively as a hydrocarbon exploration tool in the intracratonic Parana basin of South America. The Parana basin has an area of about 1,200,000 km2 (463,000 mi2), extending over portions of Brazil, Paraguay, Uruguay, Argentina, and Bolivia. The Paleozoic marine sedimentary rocks in the Parana basin are covered by the world's most extensive flood basalt complex, making geophysical exploration extremely difficult, although modern seismic techniques recently applied are achieving good results in some areas. The 1-2 km (3,300-6,600 ft) thick surface basalts and buried diabase sills pose no problem for the magnetotelluric method because the natural electromagnetic fields used as the energy source pass easily through the basalt. Data for the regional study were taken on six profiles with soundings spaced 8 to 15 km (5 to 9 mi) apart. The magnetotelluric sounding data outline a linear uplift known as the Ponta Grossa arch. This major structural feature cuts across the northeast-trending intracratonic basin almost perpendicularly, and is injected with numerous diabase dikes. Although its character is reasonably well known in the shallow, eastern parts of the basin, it is poorly delineated in the deeper parts of the basin where promising natural gas zones have been tested in several wells. In the survey area, MT interpretations show that basalts have aggregate thickness of as much as 2 km (6,600 ft), and basement may be as much as 6 km (20,000 ft) below the surface. Over most of the basin, the basalts are covered by Upper Cretaceous to Holocene continental sediments of a few hundred meters thickness and are underlain by 2 to 4 km (6,600 to 13,100 ft) thick Paleozoic sediments with possible hydrocarbon potential. The Ponta Grossa arch is interpreted to be the failed arm of a triple rift system that formed during the separation of the African and South American continents. Shales of the Devonian Ponta Grossa Formation are important Parana basin source rocks for hydrocarbons, as are several Permian units. Significant electrical contrasts occur between the Permian sediments and older units, so that magnetotelluric measurements can give an indication of the regional thickness of the Permian and younger sediments to aid in interpreting hydrocarbon migration patterns and possible trap areas.

What does the ‘Lilliput Effect’ mean?

Atualmente no Devoniano da Bacia do Paraná apenas duas espécies da superfamília Chonetoidea são reconhecidas formalmente: Australostrophia mesembria (Clarke, 1913) e Pleurochonetes falklandicus (Morris Sharpe,1846). Contudo, em outras localidades abrangidas igualmente pela Província Malvinocáfrica, a diversidade desta superfamília é significativamente maior. No presente artigo fez-se um estado da arte do estudo de Chonetoidea na Bacia do Paraná, com o intuito de compreender os motivos desta aparente baixa diversidade na referida bacia. Percebeu-se que embora já faça mais de um século desde os primeiros relatos, poucos estudos formais, tratando do tema, foram publicados até o presente momento. Este fato parece refletir na baixa diversidade registrada, tendo em vista que resultados obtidos em trabalhos não considerados publicações formais, tais como dissertações e teses, sugerem uma maior variedade de táxons. Portanto, concluiu-se que mais estudos formais, abordando este tema, são necessários a fim de caracterizar a real diversidade de Chonetoidea na Bacia do Paraná, contribuindo para um melhor entendimento da Província Malvinocáfrica como um todo.

Quartzite pebbles from an arenaceous siltstone with fine sand lenses have been found at two localities in the Campos Gerais region, Apucarana Sub-basin (Parana Basin), south Brazil. These pebbles were first interpreted as glacial diamictites, but their smooth surfaces and surrounding sediments indicate another origin. Two of the pebbles are associated with a small scale hummocky cross stratification in the top layer, and with laminated layers below, which is indicative of currents formed by oscillatory waves. None of the pebbles show any traces of encrustacion. The surrounding siltstone is affected by bioturbation and contain brachiopods ( Australospirifer ). Palynomorphs indicate that these storm deposits were deposited during an early Emsian maximum inundation.

This work presents petrological and geochemical results of the black shales interval from Permian and Devonian strata of the Parana Basin, Brazil and its relationships with fluoride of groundwater from Guarani Aquifer System. The Guarani Aquifer, located in South Brazil, Uruguay, Paraguay and Argentine, presents contents of fluoride higher than the Brazilian accepted potability limits. Several hypotheses have been presented for the origin of the fluoride in the groundwater of the Guarani Aquifer. Microcrystalline fluorite was registered in black shales of Ponta Grossa and Irati formations from Parana Basin. The results shown in this work suggest that fluoride present in groundwater of Guarani Aquifer can be originated in deeper groundwater that circulates in Ponta Grossa and Irati formations. The interaction of the groundwater coming from deeper black shales with the groundwater-bearing Aquifer Guarani System occurs through regional fragile structures (faults and fractures) that constitute excellent hydraulic connectors between the two sedimentary packages. The microcrystalline fluorite registered in Ponta Grossa and Irati Formations can be dissolved promoting fluoride enrichment in groundwater of these black shales and Guarani Aquifer System.

Insights into organic matter source and depositional environments of shales from the Ponta Grossa Formation in Parana basin, Brazil

Consistent trends towards decreasing body size in the aftermath of mass extinctions – Lilliput effects – imply a predictable response among unitary animals to these events. The occurrence of Lilliput effects has yet to be widely tested in colonial organisms, which are of particular interest as size change may potentially occur at the two hierarchical levels of the colony and the individual zooids. Bryozoans are particularly useful organisms in which to study colonial size response as they have well-defined zooids. Additionally, a number of analyses of present-day bryozoans have shown that zooid size reflects local environmental conditions, most notably seawater temperature and possibly also food supply. Following the hypothesised decline in primary productivity at the Cretaceous–Paleogene (K–Pg) mass extinction, it is predicted that bryozoan zooid size should decline in the early Paleogene, resulting in a Lilliput effect. To test this prediction, zooid size was compared across the K–Pg boundary at the assemblage level and also within 4 surviving genera. Analysis of 59 bryozoan species from assemblages on either side of the K–Pg boundary showed no significant change in zooid length. Zooid size was also measured in 98 Maastrichtian colonies and 162 Danian colonies belonging to four congeneric species. Only one of these genera showed a significant size decrease across the K–Pg boundary, the other three maintaining constant zooidal lengths, widths and areas. Additionally, the sizes of 210 Maastrichtian colonies and 163 Danian colonies did not show consistent size decrease across the K–Pg boundary in these same species, although maximum colony size did decline in three out of four genera. Furthermore, this lack of consistent size change is uniform between two distinct biogeographical regions, Denmark and the southeastern USA.

A tooth of Phoebodus cf. P. sophiae (Chondrichthyes, Elasmobranchii) was recovered from the Middle Devonian, Early Givetian, Rockport Quarry Limestone Formation in Alpena, Michigan. It is the first known record of the taxon in Michigan and the third known locality from North America. It is the oldest known record in North America, and possibly worldwide, and may extend the known temporal range of the genus. Previous known records for P. sophiae have been confined to the middle Givetian Polygnathus varcus conodont zone, and the taxon was thought to be a possible index fossil for the middle Givetian. The present record extends the taxon to the early Givetian P. hemiansatus conodont zone and, thus, complicates the use of P. sophiae as a proxy index fossil for the P. varcus zone.

A long-lived marine seaway between the Parnaiba and Parana basins occurred during a global marine transgression between Brazilian intracratonic basins (except for the Solimoes Basin) in the latest Eifelian/earliest Givetian (Middle Devonian). As a result of this transgression a catastrophic event (KACAK) in combination with the immigration of warm water Appalachian and Old World faunas contributed to the collapse of the Malvinokaffric Realm in the Parana Basin. In the Alto Garҫas and Apucarana sub-basins, the transgression is notable in the early Givetian with an impoverished shelly fauna following the KACAK post-extinction event in the earliest Givetian.