Geochemical analysis of mass mortality events in the Cretaceous (Aptian) Konservatt-Lagerstätte of Crato paleolake, Brazil

Abstract

Geochemical records from the Cretaceous (Aptian) Crato paleolake in Brazil reveal the influence of volcanism and wet-dry paleoclimatic variations on the lake system and improve understanding of the mass mortalities represented by Konservat-Laggerstätte assemblages in the deposits. Specifically, we used paleoredox (Pb^EF, Mn^EF, U^EF, V^EF, Mo^EF, Fe^EF, V/Cr and U/Th ratios) and paleoproductivity (P^EF, Cu^EF, Zn^EF, Ni^EF, Ba^EF, and δ¹³C_VPDB) indexes to elucidate changes in detrital input (Al and Fe), paleoclimate (Sr/Cu, C- values, Sr/Al and Mg/Al), paleosalinity (Sr/Ba and Rb/K), and lake level (Fe/Mn and δ¹⁸O_VPDB), and their linkage to episodes of volcanism (Hg/Al and Hg/Fe). The mass mortalities of lacustrine organisms are found to be closely related to paleoclimatic variations. During dry episodes, the lake became more saline and alkaline, which impeded the larval development and the maturation of mayflies (Ephemeroptera), and triggered mass mortality events of these organisms. During wet periods, metal enrichment indicates that a rise in paleoproductivity may have caused hypoxia, thereby inducing the mass mortality events among Dastilbe fish. Mercury anomalies suggest that extrusion of Rajmahal-Kerguelen Plateau basalts in the late Aptian times influenced regional paleoclimatic and depositional processes, and may have been ultimately responsible for generating the Konservat-Lagerstätte of the Crato paleolake.