Foraminíferos bentônicos recentes da plataforma continental amazônica associado ao Grande Sistema Recifal da Amazônia (GARS)

Abstract

In this research, 16 sediment samples from the Amazon continental shelf in the state of Pará were analyzed, 7 collected in the Central Sector (GAR transect) and 9 in the Southern Sector (LAG transect), in two expeditions in 2017 and 2018. The objectives were to analyze the distribution pattern of recent benthic foraminifera along the shelf to the mouth of the Amazon river, to relate the abundance of these organisms with environmental variables such as depth, organic matter, calcium carbonate and sediment granulometry, to analyze the taphonomy of the test and to correlate then with the fauna of the Caribbean region. The sediment samples were washed, sieved, quartered, weighed and screened for analysis under a magnifying glass. In 14 sediment samples, 2711 foraminifera were found in the LAG samples and 17158 in the GAR samples. Two samples did not show any carapace. 23 Families, 41 genera and 62 species were identified and described, with 354 species left open, distributed among the suborders Milioliina, Rotaliina, Textulariina, Lagenina and Spirilina. The most frequent species were Amphistegina lessonii, Globocasidulina subglobosa, Quinqueloculina lamarckiana, Cibicides refulgens, Q. bicostata, Hanzawaia concentrica, Miliolinella subrotunda, Triloculina bermudezi, Sigmavirgulina tortuosa, Cassidulina laevigata, Siphonina reticulata, Eponides repandus, Bigenerina nodosaria, Q. sulcata, Neoeponides antillarum, Q. bosciana and Textularia conica.Regarding the taphonomy of the tests, it was observed that in the shallower samples of the LAG transect, brown and mottled relict carapaces predominate, and in the GAR transect, white carapaces predominate, which suggests constant deposition. From the distribution of species patterns, four foraminifera associations were separated, two in each transect. These associations relate the species to the hydrodynamic energy of the environment, the composition and granulometry of the sediment. The benthic foraminiferal fauna described here is highly diverse and many species have a cosmopolitan distribution. More than 90% of the common species are seen in the modern fauna of the Caribbean Sea.