Abstract: Prediction of the developing zone of weathered clastic crust under the T1 unconformity is one of the key and critical issues
in the exploration of stratigraphic reservoirs in the Yongbei area, Dongying sag. Based on integrated analyses of high-precision 3D
seismic interpretation, core observation, thin section observation, logging interpretation and physical property testing, combined with
the setting of structural and burial histories, we investigate the special characteristics of seismic reflection of the upper layer of the Es3
Formation under the T1 unconformity surface in Yongbei area, Dongying sag, and further address their geological implications. Results
clay rocks and semi-weathered rocks. In the semi-weathered rocks, seismic event disappears to show blank reflection due to meteoric
weathering and solution. This results in an improvement of reservoir properties and an interface with underlying unweathered rocks. A
discontinuous angular unconformity surface was formed. In contrast, the unweathered and undissolved strata shows typical angular
unconformities. The evolution of seismic reflection characteristics could be divided into 4 phases, e.g., deposition of the Es3 Formation,
uplifting of the Es3 formation, early stage of the formation of the weathered clastic crust, and the main formation stage of the weathered
clastic crust. The development of the seismic blank zone is not smaller than that of the weathered clastic crust. It changes to normal
strata to the basinward. Development of weathered clastic crust improves reservoir properties largely, which could act as resrevoir space
and migration path for oil and gas. Therefore, such crusts are important exploration targets of stratigraphic reservoirs in the study area
for the next step.

Key words: seismic reflection characteristics, weathered clastic crust, unconformity, upper layer of the Es3 Formation, Yongbei area, Dongying Sag