Paper No. 8
Presentation Time: 10:05 AM
LATE PERMIAN THROUGH EARLY TRIASSIC MARINE REDOX AND CONTINENTAL WEATHERING FLUX PATTERNS INTERPRETED FROM U AND ND ISOTOPES: IMPLICATIONS FOR END-PERMIAN EXTINCTION MODELS
Marine anoxia was widespread during the end-Permian crisis, and it has recently been linked to hyperwarming related to Siberian Traps greenhouse gas emissions, although its timing, intensity, and causal relationships remain uncertain. Reducing conditions have been attributed to warm seawater temperatures and increased continental weathering fluxes (CWF) which stimulated marine primary productivity and increased demand on latest Permian seawater dissolved oxygen concentrations. In this study, we use U and Nd isotopes to assess these relationships. We analyzed deep-shelf carbonates of the Daxiakou section in Hubei Province, South China, ranging in age from the late Middle Permian (Capitanian) to the early Early Triassic (Induan). Nd-isotope trends show an increase across the Capitanian-Wujiapingian boundary to an early Wujiapingian maximum (εNd = -5), reflecting a regionally decreasing CWF or an increasing flux from juvenile Emeishan flood basalts. εNd then gradually decreased (to -10) until the mid-late Changhsingian; ~100 ky before the end-Permian extinction horizon (EH), there was an abrupt negative shift (to -14 to -16). Commencing at the EH and continuing at least until the Dienerian, εNd stabilized at -11 to -12. We interpret these trends to reflect slowly increasing regional CWF during most of the Late Permian, culminating in an episode of strongly elevated CWF. The U-isotope trend shows a peak in the early Wujiapingian (δ238U = +0.5‰) then a decrease and fairly uniform values (-0.2 to 0‰) during the mid- to late Late Permian. Values abruptly shifted to a minimum (‑0.6‰) at the EH, stabilized during the Griesbachian (-0.3‰), then increased during the Dienerian (to -0.1‰). The U-isotope record exhibits broadly positive covariation with the Nd-isotope record throughout the study interval, although the latest Permian negative εNd shift occurred ~100 ky earlier than the δ238U shift. The combined isotopic records suggest substantial variation in regional CWF and marine redox conditions during the Late Permian, with major increases in regional CWF leading (and possibly contributing to) intensified marine anoxia at the EH. Both proxies may ultimately have been responding to global climate trends, with the onset of a major warming episode ~100 ky prior to the EH.