In recent years, great achievements have been made in the mechanism of early-stage coalification and diagensis of organic matter as the results of the exploration and studies on the immature low mature oils and biogenic gas. In addition, the results of early-stage coalification and diagensis of organic matter are also an important factor for correctly identifying the macerals genesis and its matured process. The research advances are as follows:
(1) Advances in coal macerals and lithotypes origin, especilly the results form microscope observation of present peat. Through analysing petrologic and geochemical characteristics of varied salt and fresh water bogs; temperate zone, subtropical zone and the tropics bogs; herbaceous and woody plants peat and the peats formed varied sedimentary environments; Comparing similarities and differences of plant tissue and organ among present bogs surface layer, buried peat and plant relics in coal ball. Coal geologist have studied the degradation process of plant, and present possible cause of coal macerals formation from some plant tissue and organ during biochemical coalification and coalification.
(2) Geochemical advances in diagensis of sediementary organic matter. Through the analysis methods such as pyrolysis, thermal simulation experiment, infrared spectroscopic analysis, element analysis, 13CNMR, isotope assaying, GC-MS and so on, scientists have been studing organic molecules, such as humus, humic acid, fat acid, lignin etc, transition and mechanism during diagensis of sedimentary organic matter, and getting clearer understanding of kerogen chemical structure and mature process.
(3) Through artificial coalification of peat and the thermal simulation of present plant, analysing the physical-chemical transition process of sedimentary organic matter during earlystage coalification.
(4) There are two aspects of influence of bacteria on coal formation during early-stage coalification.
① A lot of microorganis were identified with investigation on peat bogs, and there are different microbiota from upper to bottom of peat bogs, and microorganis amount is also different. The influence of different bogs types and sedimentary environment on bacteria growth are also researched. The results show that microorganis play an important role on the plant relics degradation and transition of the bogs.
② Through analysing biomarker and petrologic characteristics, researching microorganis contribution and bacteria degradation degree on organic matter in sediment rocks.
Nevertheless there are also a lot of question in early-stage coalification:
Firstly, the origin of coal maceral and transition process are not completely be understood. As we know, it is qualitative change in geochemistry from plant relics to hard coal. The components and nature of peat and brown coal are very complicated, but those of hard coal are relatively simple, so there must bea lot of gas and liquid matter from the transition process, for example, gas in browl coal, immature oil and “transitional zone” gas and so on are possibility relate to early-stage coalification. In addition, the nature of coal macerals themselves must change very hard, for example, a lot of inertinite were produced during transition from browl coal to hard coal. At present, the transition process is also situated in finding out the why and wherefore.
Secondly, the influence of microorganis growth and activities on early-stage coalification. It is no doubt that microorganis degradated sedimentary organic matter, but how much organic carbon in sediment rocks come from microorganis, have disputed among scientiests because no enough proof showed that there were antidegradation bacteria components in sediment rocks.