The Geochemistry and Bioturbation of Clay Sediments Associated with Amalgamated Crusts at the Gagua Ridge

Shuai Chen,Xiaoyuan Wang,Xuebo Yin,Bowen Zhu,Xin Huang,Kun Guo,Zhigang Zeng

doi:10.3390/min9030177

Abstract

Based on the analysis of geochemical and mineralogical compositions, deep sea clay sediment characteristics and their material sources were examined in the eastern flank of the Gagua Ridge. The mineralogy mainly consists of detrital clay minerals, quartz, and authigenic phillipsite. There is scarce biogenic debris (siliceous or calcareous). The consolidated sediments are more enriched in Si, Al, K, Na, Li, Sc, Cr, Rb, and Cs than the associated crusts and nodules. The unmixed sediment samples were mainlycontributed by Asian eolian dust. The onset of the outer Fe-Mn crust growth nearly coincides with the Central Asia aridification event at ~3.5 Ma, which resulted in an abrupt increase in eolian flux of Asian dust. Intensified surface primary productivity is assumed to bring more metals to deep waters, and eventually facilitate the outer Fe-Mn crust formation. Authigenic phillipsite may come from the alteration of local basic volcanic glasses and cause excess Al, high Al/Ti, and low Si/Al ratios. However, phillipsites hardly affect the abundance of rare earth elements (REEs) and their patterns. In addition, the investigation of two kinds of burrows inside the consolidated sediments reveals that the inner nodules of the amalgamated crusts may remain on the oxic sediment surface, due to frequent benthic activities.

Highlights

Fe-Mn nodules form by precipitation from both seawater and sediment pore waters on the sediment surface
The study area is located on the eastern flank of the Gagua Ridge, which lies on the westernmost edge of the Western Philippine Basin (WPB) (Figure 1)
We established the bulk geochemical and mineralogical data of the sediments associated with the amalgamated crusts of the eastern flank of the Gagua Ridge

Summary

Introduction

Fe-Mn nodules form by precipitation from both seawater and sediment pore waters on the sediment surface. In the Pacific Ocean, Elderfield et al (1981) [6] observed that the highest nodule rare earth elements (REEs) are associated with the lowest REEs of the associated sediments, and the nodules with the largest positive Ce anomalies are found on sediments with the smallest negative Ce anomalies, indicating competitive scavenging of REEs between the nodules and sediments Such a relation is not found within Central Indian Ocean Basin nodule-sediment pairs [11] or in the southwest Pacific Ocean [7]. Asian continental dust may contribute approximately 10–50% of the detrital fraction of Minerals 2019, 9, x FOR PEER REVIEW sediments on the Benham Rise, which lies ~300 km south of the Gagua Ridge in the WPB [26]. The main source of material in the Gagua Ridge would be a combination of eolian dust debris [3]

Objectives

Methods

Results

Discussion

Conclusion