Matias do Nascimento Ritter

Fjords are considered biodiversity hotspots and aquatic critical zones, being extremely sensitive to climate change due to close oceanic, terrestrial, and glacial interactions. These ecosystems have received a great deal of attention in research on current and future anthropic impacts. Despite this, there is no analog in the geological record that presents icehouse-greenhouse biological and climatic changes. Here we present an analog, through a detailed taphonomic survey of the Lontras Shale Lagerstätte (Itararé Group, Paraná Basin, Brazil), related to a climatic optimum of the end of the Late Paleozoic Ice Age (Late Pennsylvanian), in which a temperate outer paleofjord with a rich well-preserved biota was installed. In the monotone layers of black shale, we find subtle variations of the dominant skeletal type, rates of fragmentation and disarticulation, and other taphonomic aspects that define distinct taphofacies. Each of them is the result of distinct time-averaging related to mass mortality events, turbidity, and depositional hiatus periods at different scales and intensities, mixing the ecologic census with short-term and long-term within-habitat assemblages. In addition, the rich paleobiota was reconstructed with autochthonous and allochthonous benthic fauna, many marine nektonic organisms, and intense continental contribution of terrestrial bioclasts, that proliferated and were exceptionally preserved by the establishment of an anoxic temperate outer fjord. The taphofacies show an evolution in a high-frequency sequence within a highstand systems tract, linked to climatic improvement. Furthermore, taphonomic detailing can be used as a comparison of deep marine and deep lacustrine taphofacies, in addition to serving as an analog for the short-time scale biological, biogeochemical, climatic, and stratigraphic changes associated with the icehouse–greenhouse transition in the past, present, and future.

At the beach, death assemblages are constantly reworked by wind and waves. One of the various consequences of this shore dynamic is the constant burial and exhumation of the shells, making them inappropriate for epibionts. However, some gastropod shells collected in the death assemblages arranged on the foreshore of the coastal plain of south Brazil were hardly encrusted. Olivancillaria urceus corresponds to 48.8% of all encrusted taxa, suggesting that some shell species may play a more striking role than others as available bioclasts. Therefore, the research aims to discuss the taphonomic implications for epibionts and bioerosion in gastropod shells. Abandoned gastropod shells were collected on 27 sites along a 150 km coastal strip in southernmost Brazil. Epibionts and bioerosion traces were identified, and their frequency was calculated considering their abundance, which taxa they occurred in, and their settlement on the different parts of the shells. At least 13 of 21 taxa were colonized by epibionts, of which 97% were by bryozoans. Other epibionts recognized were serpulid tubes, bivalves, and balanids. Fifteen taxa were bioeroded, showing traces made by worms (cf. Caulostrepsis), bryozoans (cf. Pennatichnus), balanids (cf. Rogerella), bivalves (cf. Gastrochaenolites), and sponges (cf. Entobia). The results reached in this survey suggest that the bryozoans have an advantage over other epibionts at colonizing the gastropod shells.