Grain size characteristics of the carbonate-free fraction of surface sediments from the Southwest Indian Ridge area and
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Grain size characteristics of the carbonate-free fraction of surface sediments from the Southwest Indian Ridge area and its geological significance Qi Jia1, Dejiang Fan1, 2*, Xiaoxia Sun1, Ming Liu1, Wenqiang Zhang1, Zuosheng Yang1 1 Key Laboratory of Submarine Geosciences and Prospecting Techniques of Ministry of Education, Ocean University
of China, Qingdao 266100, China 2 Laboratory for Marine Geology and Environment, Pilot National Laboratory for Marine Science and Technology
(Qingdao), Qingdao 266061, China Received 5 January 2018; accepted 26 June 2018 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract
The carbonate-free fraction of 20 surface sediments collected from the ultraslow-spreading Southwest Indian Ridge (SWIR) was studied by grain size analysis and mineralogical analysis with X-ray powder diffraction (XRD), stereo microscopy and scanning electron microscopy (SEM). The characteristics of the carbonate-free fraction of the sediments were obtained, and related influential factors were discussed. The results show that the mean grain size of this fraction is in 1.96Φ–8.19Φ, with poorly sorting and unimodal, bimodal or irregular bimodal distribution patterns. Four grain size end members of the fraction are derived with the End Member Model method. The finest end member EM1 shows a significant contribution of terrigenous materials of the aeolian input and sediment carried by the bottom current. End member EM2 with medium size mainly reflects sediment of a siliceous bioclast origin. EM3 and EM4 are interpreted as representing the coarser volcanic materials related to bedrock weathering or volcanic activities. Multi-provenance is the dominant factor controlling the grain size pattern of the carbonate-free fraction of the sediments in that area. In addition, sediment transport processes such as the bottom current and wind are the minor factors that influence the grain size distribution of the carbonate-free fraction sediments. Key words: Southwest Indian Ocean, carbonate-free fraction, grain size distribution pattern, end member model, provenance Citation: Jia Qi, Fan Dejiang, Sun Xiaoxia, Liu Ming, Zhang Wenqiang, Yang Zuosheng. 2019. Grain size characteristics of the carbonatefree fraction of surface sediments from the Southwest Indian Ridge area and its geological significance. Acta Oceanologica Sinica, 38(2): 34–43, doi: 10.1007/s13131-018-1273-6
1 Introduction The carbonate-free fraction of sediments is the portion of sediments that contains no carbonate component and is also referred to as the “lithic fraction” (Revel et al., 1996). Compared to the carbonate fraction that usually contributes to the reconstruction of paleoclimatic evolution, although the noncarbonate fraction makes up only a small part of the deep sea sediment composed mainly of calcareous oozes, it is more efficient to record and provides diverse “lithic” information. This sediment fraction has different origins, such as terrestrial, volcanic and ice-rafted sources (McCave et
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