Detrital Mica Composition Quantitatively Indicates the Sediment Provenance along the Subei Coast to the Yangtze Estuary

The influence of large rivers on the Subei littoral plain area requires more research than the results that have been available up to now. Thus, specific diagnostic indices of detrital mica are successfully applied for the first time to identify the detritus of the Yangtze River and the ancient Yellow River and to analyze their influence on the coast in the Subei littoral plain area. Based on field investigation and sample collection, detrital mica minerals within the 0.063–0.125 mm grain size fraction were selected and identified. Their content/ratio differentiations and possible origins were analyzed. Moreover, specific diagnostic indices were evaluated for detritus identification considering these two large rivers in addition to their provenance influences on the Subei littoral plain area. The results indicate that the detrital mica contents in the Yangtze River Estuary differed from those in the ancient Yellow River Estuary. The mass percentage in the former (average value of 32.2%) was much higher than that in the latter (average value of 13.1%). The former contained abundant weathered mica, with a particle percentage of approximately 50.6%, while the latter contained abundant biotite (with a particle percentage of approximately 40.9%). Differences, including but not limited to those above, could be attributed to basic geological, climatic and hydrodynamic conditions. In particular, the mica indices were clearly distinguished between these two river estuaries. These indices constitute specific diagnostic indices for differentiating river detritus and quantitative contribution analysis of detritus provenance in the Subei littoral plain area. Finally, the changes and quantitative contributions of four diagnostic indices demonstrated that in the Subei littoral plain area, northward from the Yangtze River Estuary to sample site SBY11 located in Yangkou town, Rudong County, detrital micas were mainly affected by the Yangtze River, and southward from the ancient Yellow River Estuary to sample site SBY12 located in Bengcha town, Rudong County, detrital micas were largely affected by the ancient Yellow River. The main mixing area should be located between these two towns. This study provides both a good example and an efficient approach to the application of detrital mica in detritus identification, mixed zone determination, sediment provenance analysis and transport tracing