Late Pleistocene-Holocene fossils from Mirim Lake, southern Brazil, and their paleoenvironmental significance: II – Mollusks

Paleoecological characterization of ostracods in beachrocks from the Northern sector of the Rio Grande do Sul Coastal Plain, Brazil

“…That process causes the exposure and erosion of lagoon deposits on the shoreface due to landward migration of barriers on top of those deposits, as recorded in sectors of the Holocene Barrier IV, including the northern RSCP (Tomazelli & Villwock, 1991;Dillenburg, 1996;Campos et al, 2021;Lopes et al, 2022). The change from lagoon to fully marine environments is indicated by mixed Holocene assemblages of estuarine and marine invertebrates in Mirim and Patos Lagoons (Santos-Fischer et al, 2018;Lopes et al, 2021Lopes et al, , 2022. The available data, however, do not permit to infer the degree of temporal mixing, the proportion of reworked specimens, or their respective absolute ages.…”

“…In spite of the abundance of beachrocks along the Rio Grande do Sul Coastal Plain (RSCP), paleontological studies on these rocks are completely absent in the literature. Macroscopically, the main bioclastic constituents of the beachrocks are mollusk shells, in some cases associated with vertebrate remains (Lopes & Ferigolo, 2015), but microfossils (foraminifers and ostracods) were also found in coquinas of carbonate-cemented sand and shells formed in lagoon settings (Lopes et al, 2021). The presence of microfossils increases the importance of beachrocks for the reconstruction of depositional environments and paleoecological studies.…”

Fossiliferous sites of the southern coast of Rio Grande do Sul state, Brazil: geoheritage records of Quaternary sea-level, climate and environmental changes

“…The other known fossils discovered in Mirim Lagoon are marine organisms. These include a diverse assemblage of molluscan shells found along the western lagoon shore in Uruguay (Martínez 1989), whereas on the Brazilian side one oyster was retrieved from the bottom by fishermen close to the port of Santa Vitória do Palmar (Lopes et al 2021c). Other fossils found on the shore of Santiago Spit (Fig.…”

“…1D). This spit consists of a series of linear sand ridges developed on the northern end of Mirim Plateau, along the southern margin of the Taim Embayment (Abreu et al 1985;Lopes et al 2021c). These ridges contain a ~1-meterthick deposit close to the terrain surface, formed of denselypacked mollusk shells mined for years to obtain calcium (Fig.…”

“…9Q) are mainly of two species (the bivalve Erodona mactroides and the gastropod Heleobia australis) that today are abundant in brackish conditions in the estuary of Patos Lagoon. The fossils of marine species include the sciaenid fish Micropogonia furnieri (black drum or corvina) and several mollusks that inhabit the coast of Rio Grande do Sul today, but also include the bivalves Anomalocardia flexuosa and Cyrtopleura costata, which currently inhabit only warmer areas to the north (Lopes et al 2021c). The sedimentary succession described from cores (Abreu et al 1985) and hand auger samples (Lopes et al 2021c) at Latinos Spit and the fossils of estuarine and marine species indicate a marine incursion during the Middle Holocene, between ~8 and 3 ka ago based on radiocarbon and luminescence ages (Martínez and Rojas 2013;Lopes et al 2021c).…”