Extensive occurrences of lower Cambrian red beds in South China: Composition, characteristics, and implications for global environmental change

Abstract

We present a systematic study of the petrological, mineralogical, sedimentological, and elemental geochemical characteristics of Cambrian Stage 3 red beds in the Hannan-Micangshan area of South China. The results show that red beds in the study area were mainly deposited in shallow marine environments, including the littoral and deeper neritic zones. Hematite and ferric hydroxides are the major pigmentary minerals in the red beds, and their origin is related to the contribution of iron-bearing minerals in the terrestrial fine-grained fraction during diagenetic transformation, based on evidence from many co-occurring iron-bearing terrestrial and clay minerals (e.g., ilmenite, chamosite, and glauconite), distinct diagenetically-altered characteristics, and close relationships between total Fe and Al, Mg, and Ti. The data also provide compelling evidence for presence of seawater-derived ferric hydroxides in shallow marine environments through in-situ technique analysis. Distinct lithological and sedimentological features in the study area allow the conclusion that diagenetic and hydrogenic ferric oxides/hydroxides jointly promoted the formation of the red beds. The present study found that the combination of active tectono-magmatic events, enhanced terrestrial fluxes, and improved dissolved oxygen conditions may have provided abundant iron sources and iron availability during the sedimentary and diagenetic processes, and thus facilitating the occurrence of red beds globally in Cambrian Stage 3.