2025-08-20 中国科学院（CAS）
Temporal distribution of Ordovician ferruginous ooids and its comparison with ocean temperature trends as revealed by multi-archive oxygen isotope compositions. (Image by NIGPAS)
＜関連情報＞
- https://english.cas.cn/newsroom/research_news/earth/202508/t20250820_1051102.shtml
- https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53374.1/660499/Upwelling-related-ferruginous-ooids-microbialites
上昇流に関連する鉄含有のオイド、微生物岩、およびオルドビス紀気候のダリウィリアン転換点
Upwelling-related ferruginous ooids, microbialites, and the Darriwilian tipping point of Ordovician climate
Xiaocong Luan;Colin D. Sproat;Jisuo Jin;Peir K. Pufahl;Rongchang Wu;Renbin Zhan
Geology Published:August 13, 2025
DOI:https://doi.org/10.1130/G53374.1
Cool-water settings characterize Ordovician occurrences of Phanerozoic ooidal ironstones (POIs), contrasting sharply with the warm and humid climate typical of other POIs. This geological puzzle was deciphered in this study based on a complex suite of Middle−Late Ordovician POIs in South China hosted in tropical sediments of a warm-water origin, and coeval ferruginous ooid-bearing sediments and ferruginous microbialites that accumulated in a relatively cool-water setting. Here, we demonstrate that, despite their different depositional settings, all Ordovician ferruginous deposits of South China share similar petrographic ultrastructures and δ56Fe isotopic signatures. This suggests that the formation of POIs was not likely controlled by water temperature but instead is attributable to a microbial iron factory, associated with active upwelling generated from frequent cool-water incursions from Gondwana. This model also explains the predominant occurrence of Ordovician ferruginous deposits in cool-water realms in peri-Gondwana. The Darriwilian peak of their abundance corresponds to the onset of an icehouse episode and a paleotropical cold-water tongue that created complex depositional environments across the South China plate.
