Nilo Siguehiko Matsuda

UPPERMOST MISSISSIPPIAN BRACHIOPODS FROM THE BASAL ITAITUBA FORMATION OF THE AMAZON BASIN, BRAZIL

Abstract This paper describes 19 brachiopod species (including six indeterminate species) in 15 genera and one indeterminate genus from the basal Itaituba Formation at the Caima Quarry 1 section of Itaituba, Amazon Basin, Brazil. The faunal correlations of the brachiopods and the associated fusulinids and conodonts indicate a late Chesterian (late Serpukhovian) age for the described fauna, therefore confirming for the first time the presence of uppermost Mississippian rocks in the Amazon Basin. A new species, Composita caimaensis, is created, and two species, Inflatia cf. gracilis and Marginovatia cf. catinulus, are described for the first time from the Amazon Basin. The Amazon brachiopods appear to be of strong affinity with coeval faunas of the North American midcontinent.

Pennsylvanian (Carboniferous) brachiopods from the Itaituba Formation of the Amazon Basin, Brazil

A new brachiopod fauna is described from the lower Itaituba Formation at the Caima Quarry 2 section in the Itaituba area, Amazon Basin, Brazil. The Amazonoproductus amazonensis-Anthracospirifer oliveirai Assemblage is proposed for this fauna, which is considered early Pennsylvanian (Morrowan) as constrained by associated conodont and fusulinacean faunas. Nine brachiopod taxa are described herein, including Amazonoproductus amazonensis gen. et sp. nov., and Buxtonioides itaitubensis sp. nov. and Linoproductus caima sp. nov. The new tribe Marginovatini of the Linoproductoidea (the Productida) is also proposed.

Primeira ocorrência dos gêneros Ellisonia, Gondolella e Ubinates (Conodonts) para a Formação Itaituba, Pensilvaniano da Bacia do Amazonas, Brasil

This paper analyzes and describes a fi rst occurrence of the conodonts Ellisonia, Gondolella and Ubinates in Amazonas Basin, North of Brazil. The recovered material comes from two outcrops along the Tapajos River and from a limestone quarry of Itaituba Formation, whose levels are included in the Itaituba Formation, with a Pennsylvanian age. Those conodonts are relevant paleoecological indicators of water depth, salinity and environmental energy and have implications in the Late Carboniferous to Triassic biostratigraphy. The fossil remains represent M and S conodont elements, associated to Pa elements of the Idiognathodus, Idiognathoides, Neognathodus, Adetognathus, Hindeodus and Diplognathodus genus . Key words: conodonts, Amazonas Basin, Itaituba Formation, Pennsylvanian.

Ocorrência de dolomita em sela de rochas carbonáticas na mina Rio Bonito, Grupo Açungui (Paraná)

The dolomitization process which affected the carbonate rocks in the Acungui Group, exposed in the Rio Bonito quarry, occurred in two distinct episodes, namely of replacement and void-filling types. In the first case, the ancient limestone had its matrix largely substituted by dolomite with finely to averagely-grained crystals, primarily unimodal and secondarily polimodal distribution, in individuals of cloudy aspect. The void-filling type of dolomitization, responsible for the precipitation of micritic material (Dp1) of dolomitic and Fe-rich composition, originated from fluid in chemical disequilibrium with the fluid responsible for the previous dolomitization. The dolomitic cement Dp2 is constituted of saddle dolomite with non-planar individuals, coarsely-grained and with strong undulate extinction. Moreover, this type of dolomite occurs in the process of fracture-filling, in the breccia as well as in the dolomite marble, with generation posterior to that of the previous type. The dedolomitization process occurred in the dolomitic breccia, under superficial conditions, with the precipitation of late calcite as a void-filleing in association with the dolomite from Dp2 generation. Quartz completes the final phase of the void-filling process

NOTA BREVE: Ocorrência de dolomita em sela de rochas carbonáticas na mina Rio Bonito, Grupo Açungui (Paraná)

The dolomitization process which affected the carbonate rocks in the Acungui Group, exposed in the Rio Bonito quarry, occurred in two distinct episodes, namely of replacement and void-filling types. In the first case, the ancient limestone had its matrix largely substituted by dolomite with finely to averagely-grained crystals, primarily unimodal and secondarily polimodal distribution, in individuals of cloudy aspect. The void-filling type of dolomitization, responsible for the precipitation of micritic material (Dp1) of dolomitic and Fe-rich composition, originated from fluid in chemical disequilibrium with the fluid responsible for the previous dolomitization. The dolomitic cement Dp2 is constituted of saddle dolomite with non-planar individuals, coarsely-grained and with strong undulate extinction. Moreover, this type of dolomite occurs in the process of fracture-filling, in the breccia as well as in the dolomite marble, with generation posterior to that of the previous type. The dedolomitization process occurred in the dolomitic breccia, under superficial conditions, with the precipitation of late calcite as a void-filleing in association with the dolomite from Dp2 generation. Quartz completes the final phase of the void-filling process.