Mineralogical constraints on the paleoenvironments of the Ediacaran Doushantuo Formation

Thomas F. Bristow, Martin J. Kennedy, Arkadiusz Derkowski, Mary L. Droser, Ganqing Jiang, Robert A. Creaser

Research output: Contribution to journalArticle

84 Citations (Scopus)

Abstract

Assemblages of clay minerals are routinely used as proxies for paleoclimatic change and paleoenvironmental conditions in Phanerozoic rocks. However, this tool is rarely applied in older sedimentary units. In this paper, the clay mineralogy of the Doushantuo Formation in South China is documented, providing constraints on depositional conditions of the Ediacaran Yangtze platform that host the earliest animal fossils in the geological record. In multiple sections from the Yangtze Gorges area, trioctahedral smectite (saponite) and its diagenetic products (mixed-layer chlorite/smectite, corrensite, and chlorite) are the dominant clays through the lower 80 m of the formation and constitute up to 30 wt% of the bulk rock. Saponite is interpreted as an in situ early diagenetic phase that formed in alkaline conditions (pH ≥ 9). The absence of saponite in stratigraphically equivalent basin sections, 200-400 km to the south, indicates that alkaline conditions were localized in a nonmarine basin near the Yangtze Gorges region. This interpretation is consistent with crustal abundances of redox-sensitive trace elements in saponitic mudstones deposited under anoxic conditions, as well as a 10‰ difference in the carbon isotope record between Yangtze Gorges and basin sections. Our findings suggest that nonmarine environments may have been hospitable for the fauna preserved in the Yangtze Gorges, which includes the oldest examples of animal embryo fossils and acanthomorphic acritarchs.

Original languageEnglish
Pages (from-to)13190-13195
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume106
Issue number32
DOIs
Publication statusPublished - 11 Aug 2009
Externally publishedYes

Fingerprint Dive into the research topics of 'Mineralogical constraints on the paleoenvironments of the Ediacaran Doushantuo Formation'. Together they form a unique fingerprint.

Cite this