Abstract: The establishment of the marker bed in the petroliferous basins is the fundamental to further build the stratigraphic framework,conduct sedimentological study,and correlate the strata during the exploration and exploitation.Tuff layer,as the accumulation of volcanic ash with precise age information,is commonly widespread and characterized by its unique lithologic properties,so it can be used as the marker bed.As the only basin that has been discovered crude oil,the Lunpola Basin contains a tuff layer dated as ca.23.5Ma.Although the Lunpola Basin had undergone large scales of exploration,most of the boreholes did not recover cores,thus this tuff layer exposed in the outcrops has not been identified along the well logs.In this study,we analyze the logging data of the Wang-1 borehole and present the cyclostratigraphy of a part of middle-lower member of the Dingqinghu Formation.We correlate the Wang-1 result to that of the tuff-bearing measured section and accurately identify this tuff layer along the well log (853m).The tuff layer deposited in the Dingqinghu Formation is characterized by high natural gamma-ray values,acoustic traveltime,and resistivity and low spontaneous potential