Determining the Main Gas-generation Phase of Marine Organic Matters in Different Occurrence States using the Kinetic Method

This paper probes the determination of the main gas-generation phase of marine organic mattes using the kinetic method. The main gas-generation phase of marine organic matters was determined by coupling the gas generation yields and rates in geological history computed by the acquired kinetic parameters of typical marine organic matters （reservoir oil, residual bitumen, lowmaturity kerogen and residual kerogen） in both China and abroad and maturity by the EasyRo（%） method. Here, the main gas-generation phase was determined as Ro%=1.4%-2.4% for type Ⅰ kerogen, Ro%=1.5-3.0% for low-maturity type Ⅱ kerogen, Ro%=1.4-2.8% for residual kerogen, Ro%=1.5-3.2% for residual bitumen and Ro%=1.6-3.2% for reservoir oil cracking. The influences on the main gas-generation phase from the openness of the simulated system and the ＂dead line＂ of natural gas generation are also discussed. The results indicate that the openness of simulation system has a definite influence on computing the main gas-generation phase. The main gas-generation phase of type Ⅱ kerogen is Ro%=1.4-3.1% in an open system, which is earlier than that in a closed system. According to our results, the ＂dead line＂ of natural gas generation is determined as Ro=3.5 % for type Ⅰ kerogen, Ro=4.4-4.5% for type Ⅱ kerogen and Ro=4.6% for marine oil. Preliminary applications are presented taking the southwestern Tarim Basin as an example.

Biomarker evidence for changes in terrestrial organic matter input into the Yellow Sea mud area during the Holocene

We present lipid biomarker records of two cores （ZYI and ZY3） from the central South Yellow Sea mud area to investigate the changes in sources and transport processes of the sedimentary organic matter （OM） throughout the Holocene. Based on the analysis of marine biomarker content （EPB （Phytoplankton Biomarker, total content of brassicasterol, dinosterol and C37-alkenones） and crenarchaeol）, and terrestrial biomarkers （En-alkanols and brGDGTs） as well as TMBR＇ and BIT index values, the marine organic matter （MOM） and terrestrial organic matter （TOM） deposition history was reconstructed. Changes in TOM and MOM were related to variations in land vegetation density and marine productivity, as well as transport processes dominated by the oceanic circulation system. The marine biomarker contents from the South Yellow Sea have generally in- creased throughout the Holocene, indicating that the increased MOM contents were mainly controlled by the strengthening of the circulation system. The terrestrial biomarkers, on the other hand, were more variable, indicating more complex influence of TOM burial in the Yellow Sea. During the Early Holocene （7200-6000 cal yr BP）, the moderate TOM input revealed by the terrestrial proxy records may result from abundant land source supply by strong river transport despite the lack of transport via circulation system. The Mid-Holocene （6000-3000 cal yr BP） was characterized by decreased terrestrial biomarker contents. The balance between the decrease in land source supply and increase of transportation by the current system of the TOM resulted in the lower but stable contents of TOM. During the Late Holocene （3000 cal yr BP to present）, the TOM deposition in the South Yellow Sea increased as the current system was further enhanced and thus transported more TOM to the central South Yellow Sea, although the land supply of TOM was further reduced.