Earth's youngest banded iron formation implies ferruginous conditions in the Early Cambrian ocean

• Published in: Scientific reports Vol. 8; no. 1; pp. 9970 - 10
• Main Authors: Li, Zhi-Quan, Zhang, Lian-Chang, Xue, Chun-Ji, Zheng, Meng-Tian, Zhu, Ming-Tian, Robbins, Leslie J, Slack, John F, Planavsky, Noah J, Konhauser, Kurt O
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 02.07.2018; Nature Publishing Group UK
• Subjects: Geological time; Iron; Marine environment; Sediments; Speciation
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-018-28187-2

It has been proposed that anoxic and iron-rich (ferruginous) marine conditions were common through most of Earth history. This view represents a major shift in our understanding of the evolution of marine chemistry. However, thus far, evidence for ferruginous conditions comes predominantly from Fe-speciation data. Given debate over these records, new evidence for Fe-rich marine conditions is a requisite if we are to shift our view regarding evolution of the marine redox landscape. Here we present strong evidence for ferruginous conditions by describing a suite of Fe-rich chemical sedimentary rocks-banded iron formation (BIF)--deposited during the Early Cambrian in western China. Specifically, we provide new U-Pb geochronological data that confirm a depositional age of ca. 527 Ma for this unit, as well as rare earth element (REE) data are consistent with anoxic deposition. Similar to many Algoma-type Precambrian iron formations, these Early Cambrian sediments precipitated in a back-arc rift basin setting, where hydrothermally sourced iron drove the deposition of a BIF-like protolith, the youngest ever reported of regional extent without direct links to volcanogenic massive sulphide (VMS) deposits. Their presence indicates that marine environments were still characterized by chemical- and redox-stratification, thus supporting the view that-despite a dearth of modern marine analogues-ferruginous conditions continued to locally be a feature of early Phanerozoic seawater.