Micro-Mechanisms and Implications of Continental Red Beds

Abstract

Continental red beds, widely formed at various geologic timescales, are sedimentary rocks and sediments with red as the main color. Geoscientists have analyzed the geomorphology, paleomagnetism, paleoenvironments, paleontology, energy, and minerals in continental red beds. Despite the agreement that fine-grained hematite is closely related to the color of continental red beds, controversies and problems still exist regarding the micro-mechanism of their formation. As a review, this paper details the composition and color properties of pigmentation in red beds, analyzes the existence and distribution of authigenic hematite, and summarizes the iron sources and the formation of hematite. In addition, we introduce the fading phenomenon observed in continental red beds, including three types of secondary reduction zones: reduction spots, reduction strips, and reduction areas. Lastly, this paper summarizes the evolution of color in continental red beds, emphasizes the relationship between authigenic hematite and the diagenetic environment, and proposes possible research directions for future red bed-related issues.

Comparative geochemistry of Early Carboniferous marine red beds (MRBs) and their significance for deep time paleoceanographic reconstructions

“…This has been known and considered for some time in many Type-I and Type-II MRB studies, where a simple enrichment of Fe doesn't necessarily impart the red color in MRBs, such as Lajoie and Chagnon's (1973) red claystones, which contain approximately similar concentrations of Fe 2 O 3 as their green claystones (8 wt%), but higher Fe/Mn ratios and greater quantities of hematite and chamosite. The red color in red beds is not controlled by an elevated iron contentvery low iron oxide concentrations of <1 wt% are already sufficient to stain a sediment red (He et al, 2022). The red color appears to be dependent upon the size, distribution and crystallinity of the iron-oxide particles, which is largely controlled by diagenetic processes; for hematite the red color decreases when either the degree of hematite crystallinity or the grain size of the hematite particle increases (Hund, 1966;Cai et al, 2008;Li and Cai, 2013).…”