Xisheng Fang

Persistent effects of the Yellow River on the Chinese marginal seas began at least ~880 ka ago

The Yellow River (or Huanghe and also known as China’s Sorrow in ancient times), with the highest sediment load in the world, provides a key link between continental erosion and sediment accumulation in the western Pacific Ocean. However, the exact age of its influence on the marginal sea is highly controversial and uncertain. Here we present high-resolution records of clay minerals and lanthanum to samarium (La/Sm) ratio spanning the past ~1 million years (Myr) from the Bohai and Yellow Seas, the potential sedimentary sinks of the Yellow River. Our results show a climate-driven provenance shift from small, proximal mountain rivers-dominance to the Yellow River-dominance at ~880 ka, a time period consistent with the Mid-Pleistocene orbital shift from 41-kyr to 100-kyr cyclicity. We compare the age of this provenance shift with the available age data for Yellow River headwater integration into the marginal seas and suggest that the persistent influence of the Yellow River on the Chinese marginal seas must have occurred at least ~880 ka ago. To our knowledge, this study provides the first offshore evidence on the drainage history of the Yellow River within an accurate chronology framework.

Clay minerals in Arctic Kongsfjorden surface sediments and their implications on provenance and paleoenvironmental change

Kongsfjorden is a typical fjord on the edge of the ice cap of the Arctic Svalbard-Barents Sea. Its inner bay is connected with a modern glacier front along the direction of the fjord axis with a significant gradient change in the parameters of hydrology, sedimentation, and biology. In summer, ice and snow melt-water and floating ice collapse continuously and thus transport the weathering products on the surrounding land into the sea. Thus Kongsfjorden is regards as a natural laboratory for the study of unique sedimentation in polar fjords under modern glacial-sea water conditions. In this study, fifty-two surface sediments were collected in Kongsfjorden for clay mineral analysis to study the sediment source and sediment-transport process. Our results indicate that clay minerals in the surface sediments from Kongsfjorden are mainly composed of illite, chlorite, and kaolinite, and no smectite is found. Rocks from different periods exposed extensively in the surrounding areas of Kongsfjorden provide an important material basis for clay minerals in the Kongsfjorden. Kaolinite may be mainly derived from the fluvial deposits, weathered from reddish sandstones and conglomerates during the Carboniferous Period. Illite is mainly derived from Proterozoic low-grade and medium-grade metamorphic phyllite, mica schist, and gneiss. While chlorite is mainly from Proterozoic low-grade metamorphic phyllite and mica schist. In the direction from the fluvio-glacial estuary to the sea of the glacier front of Kongsfjorden, illite increase gradually, and the content of kaolinite declines gradually. However, the change pattern of chlorite is insignificant, which may be related to the provenance. Kongsfjorden detritus is mainly transported by the fluvio-glacial streams and icebergs into the sea and deposited in the inner bay. Coarse sediments are rapidly deposited in the glacier front, estuary, and near-shore areas. Clay fraction begins to deposit significantly by 200–400 m after flowing into the sea, which due to the crystal behavior of clay minerals, hydrodynamic condition and flocculation. Kaolinite and chlorite on the south of the bay near the Blomstrandhalvøya Island is mainly affected by ice-rafted detritus and thus can reveal the trajectory of transportation by the floating ice while entering the sea.

MINERALOGY OF SURFACE SEDIMENT IN THE EASTERN AREA OFF THE RYUKYU ISLANDS AND ITS GEOLOGICAL SIGNIFICANCE

The mineral composition of the bulk samples of the surface sediment in the eastern area off the Ryukyu Islands is studied with X-ray diffraction(XRD).It is found that the sediment consisting of smectite,illite+mica,kaolinite+chlorite,quartz,potash feldspar,plagioclase and calcite,is dominated by quartz,illite+mica,calcite and plagioclase,and kaolinite+chlorite and smectite occupy the second place with potash feldspar occasionally observed.According to the mineral composition,it is deduced that the sediment came from terrigenous,volcanic and biogenic sources.