Taphonomic analysis on Neogene ostracods from Solimo tilde es formation, Borehole 1AS-5-AM, Brazil: A tool to the paleoenvironmental reconstitution

The taphonomic analysis on the Neogene ostracods from the Solimo similar to es Formation (core 1AS-5-AM, Atalaia do Norte, Brazil) reflect conditions predominantly of early (film mineralization and mold formation) and late (recrystallization, iron oxidation and secondary gypsum) diagenesis. Fragmentation, disarticulation (from death, ecdysis, and transport of ostracods), bioerosion (by the action of chitinolytic bacteria) and transport were observed during the biostratinomic process. Fossil-diagenetic analyzes through MEV, EDS, X-ray diffraction in sediments and ostracods valves and petrographic thin section, point to the non-replacement of the original chemical constitution of the most carapaces, but mineral filling with pyrite, dissolution, color change and recrystallization may occur. Based on these analyzes and on the lithological characteristics, the environment was interpreted as lacustrine, of low to moderate energy. The absence of evaporitic minerals and pyrite dispersed in the sediments attest to the low salinity of the environment. Three intervals were observed in the core according to the preservation patterns of the ostracods. In interval I (lake bottom), juvenile allochthonous ostracods suggest post-mortem transport. In interval II, the predominance of autochthonous fauna shows a low energy environment. Allochthonous and autochthonous (predominant) ostracods of interval III reflect energy variation in a scenario close to the coastal zone of lake.