The study case is the source rocks of the Lower Cambrian Niutitang Formation in Guizhou area.Their trace element content is analyzed to accurately identify the hydrothermal sedimentation effect on source rocks and evaluate the intensity of the effect.The results show that(1)the diagram V/Sc-V/Cr can be used to judge whether hydrothermal sedimentation effect is a contributing factor for the composition of source rocks in the study area

which in turn

can reflect the redox environment change;(2)the slope Sc/Cr ratio is applicable for evaluating the intensity of hydrothermal sedimentation:when the Sc/Cr ratio is more than or equal to 0.144

normal sedimentation dominates and hydrothermal sedimentation effect is weak

and there is a linear correlation between V/Sc and V/Cr ratios

reflecting the redox environment change;when the Sc/Cr ratio is less than or equal to 0.120

hydrothermal sedimentation dominates

and the V/Cr ratio

which is distorted by the element content anomaly in the hydrothermal sediments

can not indicate the actual change of the redox environment

but remain useful to indicate the environment change;however

when the Sc/Cr ratio varies from 0.120 to 0.144(with both ends included)

both sedimentary processes function

and the value of V/Cr ratio is influenced by the hydrothermal sediments

but can still indicate the trend of redox environment change

and thus can be applied normally.The conclusion can be drawn that the diagram V/Sc-V/Cr can accurately identify the influence and indicate the intensity of the hydrothermal sedimentation on source rocks.