ABSTRACT Beachrocks are a common feature along the Brazilian coast and although their occurrence in intertidal zones is concentrated in tropical regions, similar formations have been described submerged on the continental shelf in subtropical regions. In the state of Paraná, submerged sandstones are present on the continental shelf and their formation could be associated with the cementation of beach sediments. This would provide an excellent indicator of the stabilization of the coastline during lower sea-level periods. In this study, samples were identified and collected in Paraná State, Southern Brazil, at depths between 18 and 33 meters in the continental shelf and at 6 meters depth in the Paranaguá Bay inlet. As in situ observations proved problematic, analysis relied mainly on their petrography, mineralogy, ages and isotopic values (δ13C and δ18O). Whole rock dating demonstrated that the oldest acquired sample was formed 28109-26406 cal. years BP, being exposed to atmospheric conditions during the Last Glacial Maximum. This exposure is reflected in its cements, composed uniquely of microcrystalline and spar calcite, and on its δ18O/δ13C values, which indicates formation on a fresh water environment. Contrarily to most carbonate cemented products described along Brazilian coastline, δ13C values ranged between -26.36 and -51.07‰ on all other samples, interpreted as a result of cement precipitation prompted by methane, either: in a paleo-estuarine/ paleo-lagunar to transgressive environment buried under a pile of coarser material or; after transgression and drowning of organic-rich sediments by coarser sediments, and due to upward migration of methane on the sedimentary column. Both processes would result in cements identified on these samples, apart from the one collected closer to shore which indicates some freshwater influence. Two of the samples separated by 15km distance perpendicularly to the actual coastline and 11m depth difference yielded max and minimum ages of 7913 and 7452 cal. years BP. Such a short time span between these samples could be either the result of their formation on a linked environment or older carbon signature from drowned environments being present on younger cements.

ABSTRACT This study aimed to map habitats and species distribution in a benthoscape section of the Paranaguá Bay inlet, Paraná State, Southern Brazil. The degree of correspondence between maps independently generated through sidescan imagery and macrofauna and sediment samples was also evaluated. The study area had approximately 9km2 and was chosen considering both diverse landscape features and proximity to future port developments. Sampling was performed in 67 evenly distributed and unreplicated sites. Patterns related to backscatter intensity (high and low) and the presence or absence of bedforms were observed, as well as other large-scale features like sand waves and beach rock outcrops. Local sedimentary environments were represented in a mosaic used for comparisons with sedimentary and faunistic data. Cluster analysis using grain size data formed four groups with similar particle size distribution. A strong correspondence between habitats and grain size distribution was found in only one habitat class. Macrofauna around the deeper Poço Point region and the Mel Island shallower banks presented high species richness and number of individuals. These were considered habitats of high biological relevance. Regions with bedforms indicate higher rates of sand transport in which a few species can thrive. The navigation channel had the lowest number of species and individuals when compared to vicinal regions, indicating persistent impacts. The study evidenced local estuarine bottom heterogeneity and contributed to the understanding of local processes of both bottom sediments dynamics and their associate faunal components.