A Corrected Method of Using Vitrinite Reflectance Data to Estimate the Thickness of Sediment Removed at an Unconformity

Key words: 
• vitrinite reflectance /
• unconformity /
• organic maturation /

Abstract: Dow(1977) observed that vitrinite reflectance profiles that pass through an unconformity commonly exhibit an offset at the unconformity.And the offset could be used to estimate the amount of missing section.The estimation is accomplished graphically by projecting the preunconformity portion of the profile upward to the point where it attains a value equal to the vitrinite reflectance immediately above the unconformity.The vertical distance between this point and the unconformity was presented as the amount of missing section.This method has been widely used since the late 70's.And its inaccuracy is getting more and more apparent through further application.This paper presents a detailed study on the organic maturation of vitrinite during the burying-uplifting-reburing process.An organic maturity modeling,which integrates complete thermal and burial histories,is used.By the principle of reaction kinetics,it is assuned that the maturation process of the section below the unconformity continues during the erosional phase and the reburial phase.During the reburial phase,the sections above and below the unconformity undergo continued maturation (increases in cumulative TTI values) at different reaction rates,and results in a difference of organic maturation between the two sections. So the difference can be used to trace their burial histories of these sections.And then we proposes a corrected method to estimate the thickness of sediment removed at an unconformity using vitrinite reflectance data of the formations blow and above the unconformity.which can get a more accurate result than Dow's one.