Ordovician seawater composition: evidence from fluid inclusions in halite

Authors

  • Fanwei Meng State Key Laboratory of Paleobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing
  • Yongsheng Zhang Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing
  • Anatoliy R. Galamay Institute of Geology and Geochemistry of Combustible Minerals，NAS of Ukraine, Lviv
  • Krzysztof Bukowski AGH University of Science and Technology, Faculty of Geology, Geophysics and Environment Protection
  • Pei Ni State Key Laboratory for Mineral Deposits Research, Institute of Geo-Fluid Research, School of Earth Sciences and Engineering, Nanjing University
  • Enyuan Xing Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing
  • Limin Ji Lanzhou Center for Oil and Gas Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou

DOI:

https://doi.org/10.7306/gq.1409

Keywords:

Ordovician, fluid inclusions, halite, seawater composition, calcite sea

Abstract

Fluid inclusions in halite can directly record the major composition of evaporated seawater; however, Ordovician halite is very rare. The Ordovician is a key time during the evolution history because profound changes occurred in the planet’s ecosystems. Marine life was characterized by a major diversification, the Great Ordovician Biodiversification Event and the Late Ordovician Mass Extinction, the first of the “big five” mass extinctions. However, so far there is no data on the Ordovician seawater. Data from the Ordovician-Silurian boundary were available only. In this study, we report the major compositions from Middle Ordovician halite in China to give the exact composition of Ordovician seawater. The basic ion composition (K+, Mg2+, Ca2+, and SO42-) of inclusion brines was established with the use of ultramicrochemical analysis. The data on the chemical composition of the brines in the primary inclusions indicated that the brines were of Na-K-Mg-Ca-Cl (Ca-rich) type, and cover a huge gap in the evolution of seawater chemistry. The chemical composition of the primary inclusion brine in halite confirmed the earlier results for the Cambrian and Silurian halite originating from other salt basins and the previous speculation of “calcite sea” during the Ordovician, indicating a higher potassium content in the Lower Paleozoic seawater than in the seawater of other periods of the Phanerozoic.

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Published

2018-05-08

Issue

Vol. 62 No. 2 (2018)

Section

Articles

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