Burial Records of Reactive Iron in Cretaceous Black Shales and Oceanic Red Beds from Southern Tibet

Abstract

One of the new directions in the field of Cretaceous research is to elucidate the mechanism of the sedimentary transition from the Cretaceous black shales to oceanic red beds. A chemical sequential extraction method was applied to these two types of rocks from southern Tibet to investigate the burial records of reactive iron. Results indicate that carbonate‐associated iron and pyrite are relatively enriched in the black shales, but depleted or absent in red beds. The main feature of the reactive iron in the red beds is relative enrichment of iron oxides (largely hematite), which occurred during syn‐depostion or early diagenesis. The ratio between iron oxides and the total iron indicates an oxygen‐enriched environment for red bed deposition. A comparison between the reactive iron burial records and proxies of paleo‐productivity suggests that paleo‐productivity decreases when the ratio between iron oxides and the total iron increases in the red beds. This phenomenon could imply that the relationship between marine redox and productivity might be one of the reasons for the sedimentary transition from Cretaceous black shale to oceanic red bed deposition.

Nonlinear Dynamic Study on Geomagnetic Polarity Reversal and Cretaceous Normal Superchron

“…So far, it has been gradually noticed that the geomagnetic field history would be linked with many global geological events and the Earth's interior evolution, such as the activity of mantle plumes, changes in the global heat flow, true polarity wander, seafloor spreading, the distribution of oil, global climate changes, the generation of oceanic plateau, seamount chains, continental flood basalts, marine magnetic anomalies, faunal extinction, mantle convection, etc. Especially, the Cretaceous normal superchron (CNS), during which the Earth's field showed no reversals, coincided well with some special changes, such as those in ocean-crust production, severe activity of the volcano, high-latitude sea surface paleotemperature and long-term sea level, wide distribution of black shale's deposition and world oil resources (Zhao, 2005;Huang et al, 2007).…”

Discovery of Pseudofrenelopsis gansuensis from the Lower Cretaceous of Wangqing, Jilin Province, and Its Significance in Correlation of Cretaceous Red Beds in China

“…In the Cretaceous time, continental deposits were dominated in almost the whole China except for the southern Tibet, eastern Heilongjiang and westermost Xinjiang where there were marine beds (Huang et al, 2007;Jiang et al, 2006). During the Early Cretaceous red beds developed well in a large area of China in which fossil plants, spores and pollen are rare.…”