The Late Paleozoic ice age termination in Southwestern Gondwana: New evidence from the Paraná Basin

Abstract

Records of diachronous ice spreading centers over the Gondwana supercontinent characterize the Late Paleozoic Ice Age (LPIA), which was the most intense and largest ice sheet expansion event of the Phanerozoic Eon. This study presents high-resolution paleoclimate and paleoenvironmental reconstructions of the LPIA termination interval in the southern Paraná Basin (Brazil) using a multiproxy approach that includes sedimentological and geochemical data from a ∼190 m long core. Geochemical proxies used here include elemental ratios, total organic carbon (TOC), stable carbon isotopes of bulk organic matter (δ¹³C_org), and biomarkers. The Gzhelian sedimentary succession recorded two third-order depositional sequences (DS), with significant sedimentological and geochemical changes. DS-1 recorded fining upward turbidite facies with sporadic outsized clasts, reduced chemical weathering intensity, brackish and oxic water conditions with marine influxes, and diminished organic matter accumulation derived from terrestrial and aquatic plant sources. The lower part of DS-2 records a transition from sandstone-rich rhythmite to organic-rich mudrocks, intensification of chemical weathering, and fully marine waters characterized by reducing bottom water conditions leading to increased TOC, with increased proportions of aquatic over terrestrial plant sources. The maximum flooding surface (MFS) within DS-2 records the apex of chemical weathering intensification, and dominance of aquatic over terrestrial plant sources. Above this interval, there is a coarsening upward trend of mudrocks to heterolithic facies with outsized clasts, and a gradual reduction in chemical weathering intensity, coupled with increased contribution of terrestrial plant sources. We suggest that the DS-1 succession formed in a transgressive estuarine environment under a relatively cold/arid climate with floating ice, whereas DS-2 records marine to fluvial-deltaic sedimentation and a climate transition to warmer/wetter conditions. These data support an abrupt climatic amelioration within the Gzhelian Stage in the southern Paraná Basin.