Late Pleistocene-Holocene fossils from Mirim Lake, southern Brazil, and their paleoenvironmental significance: II – Mollusks. (December 2021)

• Record Type: Journal Article
• Authors: Lopes, Renato Pereira; Pereira, Jamil Corrêa; Caron, Felipe; Ritter, Matias Do Nascimento; De Souza, Márcio Silva; Dillenburg, Sérgio Rebello; Barboza, Eduardo Guimarães; Tatumi, Sonia Hatsue; Yee, Márcio; Kinoshita, Angela; Baffa, Oswaldo
• Is Part Of: Journal of South American earth sciences. Volume 112:Part 1(2021)
• Publication Date: 2021-12
• Subjects: Quaternary -- Coastal evolution -- Paleoenvironment -- Geomorphology -- Mollusks -- Stable isotopes; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2021.103546
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: The fossil molluscan assemblages found on the shores of Mirim Lake, in southern Brazil and Uruguay, provide information about the environmental changes and geological evolution of that water body. The storm-generated shell deposits at Latinos Spit on the Brazilian shore are dominated by the estuarine bivalve Erodona mactroides, represented mostly by juveniles, and the gastropod Heleobia australis . Species previously unrecorded in this site include the marine gastropods Cylichnella bidentata, Buccinanops cochlidium and Pachycymbiola brasiliana, and the bivalves Tagelus plebeius, Ostrea puelchana, Crassostrea cf. praia, Mactra isabelleana, Anomalocardia flexuosa and Cyrtopleura costata . The two latter currently inhabit tropical areas to the north of Rio Grande do Sul, and their presence in Mirim Lake indicates average coastal water temperatures about 2–3 °C warmer than today. This condition promoted the precipitation of calcium carbonate from dissolved shells, thus cementing together sand and shells in the form of coquinas. The stratigraphic succession, OSL ages obtained in quartz sand from one coquina, radiocarbon dated shells, and δ 13 C and δ 18 O of five E . mactroides and five marine species indicate that Mirim Lake became a brackish lagoon around 7.6 ka ago, in response to the postglacial marine transgression (PMT), followed by fully marine conditions during the sea-level highstand of 6–5 ka BP. Marine influence was reduced after ∼4 ka BP as the result of sea-level fall and the closure of the connection with the ocean, related to the evolution of the sandy barrier that originated the modern shoreline. The environmental changes recorded in Mirim Lake help understand how coastal lagoons and their associated ecosystems respond to sea-level oscillations, which may be relevant to address future responses of these water bodies to the ongoing climate change. Highlights: Shell beds of Holocene marine and estuarine mollusks were found in Mirim Lake. Marine water and fauna invaded the lake during the Holocene sea-level highstand. The presence of extralimital mollusks indicate coastal waters ≥2 °C than today. Higher temperatures precipitated CaCO3 forming cemented coquinas in lagoon settings. Loss of connection with the ocean was driven by the formation of a coastal barrier.