Affiliation of Author(s):地球与行星科学学院

Journal:Precambrian Research

Key Words:Mesoproterozoic North China Calcium isotopes Strontium isotopes Continental weathering

Abstract:An increasing number of recent studies suggest that the Mesoproterozoic era potentially underwent short-term episodes of oceanic oxygenation, although oxygen levels remained generally low. These short-term pulses have been noted as potentially critical drivers for the evolution of eukaryotes. The causes of such episodic oceanic oxygenation events, however, as well as their relationships with the evolution of early eukaryotes and their long-term effects, remain unclear. Here, we report new δ44/40Ca, 87Sr/86Sr ratios, P concentrations and TOC from the early Mesoproterozoic (ca.1.6~1.54 Ga) Gaoyuzhuang Formation from the Pingquan section, North China, combined with previously published δ13Ccarb, δ13Corg, δ34SCAS isotopic data from the same section, to investigate the co-evolution of continental weathering, oceanic chemistry and biological innovation. Specifically, we find that a negative δ44/40Ca excursion (from 1.36‰ to 0.75‰) is coupled with a positive 87Sr/86Sr excursion (from 0.7091 to 0.7118) and an accompanying increase in concentrations of both P and TOC in the mid Gaoyuzhuang Formation. Combined, these signals suggest a transient increase in continental weathering flux, which may have promoted primary production via increasing P influx to the ocean and led to increase in organic carbon burial and potential oxygenation of the marine system. When compared to the carbon and sulfur isotope changes within the same section, we observe enhanced oceanic redox stratification at the onset of enhanced continental weathering. Regardless, this distinct oceanic oxidative pattern was likely related to globally low pO2 (generally < 2.5% PAL) and slow oceanic overturning circulation, but may preface that marine oxygenation was nearing a global threshold. Furthermore, the sharp and rapid δ44/40Ca fluctuations in the Gaoyuzhuang Formation indicate a large dissolved inorganic carbon (DIC) reservoir and high pCO2, which might have played an important role in compensating for the possible lower solar luminosity in the early Mesoproterozoic.

Co-author:靳松,杜远生,马鹏飞,周炼,余文超

First Author:Guo Hua

Indexed by:SCI

Translation or Not:no