Distinguishing sediments from the Yangtze and Yellow Rivers, China: a mineral magnetic approach

The Yellow River and the Yangtze River contribute similar to 10% of the global fluvial sediment flux to the oceans. Proper characterization of the sediments of the two rivers is critical to the knowledge of their fate in the marginal seas of the west Pacific Ocean. Magnetic measurements have been made on bulk sediments as well as on separated particle size fractions of representative samples from the Yellow and Yangtze River estuaries, with the purpose of providing an efficient means of differentiating both groups of river sediments from each other. We found that on average the Yangtze River estuary sediments have relatively higher ferrimagnetic mineral contents and ferrimagnetic to antiferromagentic ratios compared with the Yellow River estuary sediments. A diagram of Saturated Isothermal Remanent Magnetization (SIRM) versus the demagnetization parameter S-100 can clearly distinguish sediments from the two rivers. Detailed magnetic measurements carried out on particle size fractions provide additional confirmation of magnetic contrasts between the two sets of river sediment samples. These contrasts reflect differences in lithology and weathering regimes in the catchments. To minimize possible biogenic and postdepositional diagenetic overprint in the marine environment, it is recommended that magnetic comparison on the coarser materials (eg, >4 mu m) be carried out in addition to bulk measurements. This study shows that the magnetic approach can therefore provide a potentially efficient means of discriminating sediment sources in the Yellow Sea and East China Sea. In view of the rapid variations in sediment load carried by these two rivers in recent years, the present data set also provides a baseline against which possible future variations in sediment composition resulting from catchment changes can be assessed.