Genetic relationship between formation,accumulation and migration and dispersion of peat materials in Paleogene——Take the Qiongdongnan Basin as an example

Coal-type source rocks include both coal and terrigenous marine source rocks.By studying the distribution of secondary depressions,uplifts,as well as the characteristics of peat formation and accumulation in the northern marginal sea basin of the South China Sea,and combining them with coal formation characteristics observed in other basins,five genetic theories on the relationship between peat accumulation and dispersed organic matter accumulation are proposed.The northern marginal sea basin of the South China Sea is characterized by“disadvantageous coals formation and favorable terrigenous marine source rocks formation.”This paper provides a distribution map of coal seams and terrigenous marine source rocks in the Qiongdongnan Basin and determines their distribution patterns.Research shows that the migration of sedimentary facies in the basins and inner depressions led to the formation and migration of the peat accumulation centers.In addition,the vertical migration of the peat accumulation centers led to planar migration,which is actually a type of coupling relationship.Previous research results have revealed that the formation of coal-type source rock is multi-phased.The marginal sea basin is composed of several fault-depression basins,with each basin developing a second order of depression and uplift.There is no unified basin center or depositional center to be found.As a result,the concentration centers of coal-forming materials also vary greatly.Based on the distribution characteristics of coal-type source rocks in different basins within the marginal sea basins of the South China Sea,the research results have practical significance and provide guidance for exploring coal-type oil and gas reservoirs in this area.

REEs fractionation and sedimentary implication in surface sediments from eastern South China Sea

To get features of rare earth elements （REEs） fractionation, 106 surface sediment samples from eastern South China Sea were determined for REEs combined with major and trace elements by ICP-MS. The distribution pattern of REEs, strong correlation between REEs and Al, North American shale composite （NASC） normalization all suggest a dominant crustal source for REEs in the research area. However distinct fractionation among REEs was observed in surface sediment from area with water depth over 2000 m, confirmed by the strong positive correlation among light rare earth elements （LREEs） and among heavy rare earth elements （HREEs） but weaker relationship between LREEs and HREEs. Eluviation by Cl- might be a key role on the fiactionation of REEs, comparing with factors such as grain size, co-precipitation with Fe and Mn hydroxide, calcareous and siliceous biogenic precipitation. The fractionation among REEs could be used as index to illustrate the sedimentary environment in reverse.