Origin and shallow-layer structure of the sediments in the Yellow Sea trough

On the basis of the analysis and study of the records of shallow-layer profiles and information from systematic analyses of some cores and their 14C datings, the sediments of Yellow Sea trough since the final slage the Late Pleistocene are found to have the following features. On the south slope of the trough, it is probably composed of island-shelf de posits. On the mouth of the trough, it is made up of eolian dunes and its deposits. In the centra! bottom region of the trough where intense desertization occurred in the early stage of the regression, there are parallel oblique beddings in the strata known as the 'angle of repose' texture, which demonstrates that the deposits there are composed of eolian sands. And in the late stage, thin derivative deposits developed in the northern part of the trough. On the north slope of the trough, thick-layer derivative deposits developed. This primary sedimentary pattern still remains unchanged since the occurrence of the Holocene transgression.

The Origin and Preservation of Suspended Barites near the 90°E Ridge in the Northeastern Indian Ocean

Suspended particulate barite crystals were detected in the water columns at four different stations near the 90°E ridge in the Indian Ocean.Four distinct morphological types of marine barites were distinguished:euhedral-subhedral crystals,oval or round crystals,rhombic crystals,and irregular crystals.The barite crystals in the study area are typically fine,with a dominant size of 1–3μm.The vertical distribution of barites is significantly affected by the formation and sedimentation processes.Barites begin to appear at a depth of 30 m and are formed primarily from the surface to the depth of 2000m with a concentration peak at the depth of 200m,where particles are coarser than those in the other layers.The barites begin to settle and dissolve once formed in the water column,resulting in finer barite particles and lower particle concentrations.The formation of barite crystals is related to biological processes associated with the decomposition of barium-rich skeletons in the microenvironment of decaying organic matter that is affected by the primary productivity and dissolved oxygen content in the water column.The dissolving process of barite crystals showed similar variation with the concentration of dissolved barium in ocean water,and the substitution of strontium for barite in crystals promotes the selective dissolution of barite and exerts an important impact on its morphology.It is approximately 33%of barites in the amount and 22%in the concentration to settle to the bottom of the water column compared to that observed in the main barite formation zone.