Chemical Properties and Geochemical Significance of Humic Acids and Kerogens in the Sediments from the Gannan Marsh

Key words: 
• marsh peat /
• humic acid /
• kerogen /
• elementary composition /
• infrared spec-trum

Abstract: Studied samples were collected from the Gannan marsh,southern Gansu Provice,where the climate is cold and moist,and organism consists mainly of herbs,for example,kobresia Humilis and Festuca sp. Peat distribution is wide and the mean peat thickness is about 4 m in this region. Sedimentary medium is acidic with a pH value of 5-5. 4. We here have studied chemical properties and geochemical significance of humic acids and kerogens by analyses of element and infrared spectra. Results show as follows:(1)The humic acids in the Gannan marsh sediment contain higher carbon content and lower hydro-gen and nitrogen contents as compared with those isolated from marine sediments. In-frayed spectra of humic acids in the studied samples show aromatic一rich and aliphatic一poor characteristics relative to those isolated from marine sediments. Those above indicate the features of land一marsh sedimentary enviroment. (2) With increasing depth,H/C,N/C and O/C atomic ratios and the carbohydrate content of infrared spectra for humic acids decrease,and the aromatic content of infrared spectra for humic acids increases,which shows an increase of condensation and aromaticity of humic acids with burial depth.(3) In the plot of O/C vs H/C atomic ratios,hmic acids and kerogens fall on the very im-mature region of maturation pathway of Type Ⅲ kerogen,while kerogens fall toward higher maturation than the corresponding humic acids. Infrared spectra show that kero-gens have a lower carbohydrate content and higher aromatic content relative to humic acids. Those above indicate the transformation of humic acids to kerogens,which under-ges condensation and aromaticity reactions.