Jurassic coal maceral and deposition rate of peat in the northern Qaidam Basin

Abstract

To reveal peat accumulation characteristics of Jurassic coal seams in northern Qaidam Basin,coal petrology of the main coal seams and spectral analysis of coal seam No.7 in Gaoquan open-pit mine were investigated.Results show that the volume of organic macerals varies considerably(120 samples),the average content of vitrinine and inertinite are 49.9% and 41.1% respectively,the former mainly comprises collodetrinite (ave.19.1%) and telinite (ave.12.1%),and the later primarily comprises semifusinite (ave.19.3%) and inertodetrinite (ave.12.3%).Sporinite (ave.2.5%) is the major component of liptinite (ave.2.8%).Three effective thickness periods of 0.68 m,1.00 m and 1.82 m in coal No.7 were recognized through the spectrum analysis,and the ratio of them is similar to that of the peat development period precession and obliquity cycle.As a result,the variation of coal vitrinite and inertinite is affected by the precession and slop of Milankovitch astronomical cycle.The spectrum signal of three thickness periods were reconstructed by the Multi Taper Method (MTM),from which the total deposition time (approximately 371 ka) and the average peat sedimentation rate (ave.0.2 mm/a) of coal No.7 was obtained.The peat sedimentation rate of coal No.7 is lower than the highest rate(about 0.5~1.6 mm/a) of Holocene deposited in lower altitude area with similar latitude.

Keywords

• coal petrology
• peat deposition rate
• milankovitch
• jurassic
• qaidam