5:15 PM - 6:30 PM
[MZZ46-P06] Lamina-scale analysis of chemical composition of the mid-Cretaceous northern Shimanto belt, Kochi, Japan: implications for formative processes of bedded ferromanganese deposits
Keywords:northern Shimanto belt, mid-Cretaceous, ferromanganese deposit
The mid-Cretaceous has been identified as a super-greenhouse world with tropical sea surface temperatures in excess of 35°C. In addition to the mid-Cretaceous climate being characterized by extreme warmth, it was also associated with significant tectonic, geochemical, and biotic perturbations1. Subsequently, it has been considered that the formation of the ferromanganese deposits occurred in the limited area in the marine environments2. However, available studies have mainly focused on the shallow marine sequences in North America and Africa. Data from the Pacific region are still limited despite the fact that the paleo-Pacific constituted the largest open ocean in the mid-Cretaceous, thus the Pacific region is critical for gaining a better understanding of the formation of metallic minerals in marine environments during the climatic evolution of the greenhouse Earth.
The mid-Cretaceous sequence of pelagic chert and ferromanganese deposits of the northern Shimanto-belt is widely distributed in the Aki area, Kochi, Japan. Bulk sample analysis of the northern Shimanto belt in the previous study3 suggested that the mineral component including metallic elements was of hydrothermal origin. To examine the more detailed formative processes of the ferromanganese deposits, we conducted observations of microstructures in the pelagic sequence and identified the tens-to-hundreds micrometer-scale lamina in the ferromanganese deposits. The elemental analysis by EPMA and laser ablation ICP-MS analyses indicated that the lamination is consists of (1) a high abundance of metallic elements such as iron and manganese and (2) metallic elements with silicate. Besides, we could identify the variations of the metallic element abundance in the chert sequence. Based on these results, we will discuss the formative processes of the ferromanganese minerals in the pelagic environment of the northwestern Pacific in the mid-Cretaceous.
References: Jenkyns, 2010. Gcubed; Roy, 2006, Earth-Sci Rev.; Fujinaga et al., 2011, Shigen Chishitsu.
The mid-Cretaceous sequence of pelagic chert and ferromanganese deposits of the northern Shimanto-belt is widely distributed in the Aki area, Kochi, Japan. Bulk sample analysis of the northern Shimanto belt in the previous study3 suggested that the mineral component including metallic elements was of hydrothermal origin. To examine the more detailed formative processes of the ferromanganese deposits, we conducted observations of microstructures in the pelagic sequence and identified the tens-to-hundreds micrometer-scale lamina in the ferromanganese deposits. The elemental analysis by EPMA and laser ablation ICP-MS analyses indicated that the lamination is consists of (1) a high abundance of metallic elements such as iron and manganese and (2) metallic elements with silicate. Besides, we could identify the variations of the metallic element abundance in the chert sequence. Based on these results, we will discuss the formative processes of the ferromanganese minerals in the pelagic environment of the northwestern Pacific in the mid-Cretaceous.
References: Jenkyns, 2010. Gcubed; Roy, 2006, Earth-Sci Rev.; Fujinaga et al., 2011, Shigen Chishitsu.