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

Autor: Lian Chang Zhang, Mingtian Zhu, John F. Slack, Zhi Quan Li, Kurt O. Konhauser, Leslie J. Robbins, Noah J. Planavsky, Chun Ji Xue, Meng Tian Zheng
Rok vydání: 2018
Předmět:
Zdroj: Scientific Reports
Scientific Reports, Vol 8, Iss 1, Pp 1-10 (2018)
ISSN: 2045-2322
Popis: 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.
Databáze: OpenAIRE
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