The Main-M1 sandstone is becoming an important exploration target for structural-lithological plays in the Oriente Basin of Ecuador,in which accurate prediction of sand distribution and pinch-out belt is the key to successful trap definition. Oriente Basin is a retro-arc thermally subsiding basin in the Late Cretaceous and a foreland basin in the Cenozoic. It can be divided into a fold-thrust zone in the west,a fore-deep zone in the middle,and a slope zone in the east. In the fore-deep zone,there are a series of nearly N-S oriented elongate anticlines. In the anticline of the study area,a carbonate build-up is developed,which is characterized by mounded,low-amplitude but relatively continuous seismic reflections,and thick,blocky and low-amplitude GR well log motifs. This build-up may indicate that during the time of its deposition in Campanian,the anticline had begun to uplift and push its top close to the paleo-sea level. This brought about locally favorable conditions for the development of the carbonate build-up. Palaeogeomorphic reconstruction based on the back-stripping method shows that the anticline had started to uplift in the Early Campanian,ranging in magnitude from 7 to 10 m. As the uplift and carbonate build-up were developed prior to the deposition of the Main-M1 sand reservoir,the palaeomorphology may thus influence the emplacement of Main-M1. According to the statistics of Main-M1 sand thickness in dozens of wells on the anticline,the top of the anticline is overall Main-M1 sand prone,but the sand becomes very thin or absent on top of the carbonate build-up. In the southern extension of the anticline,the Main-M1 sand is absent on the structural top but becomes thicker at the downdip to the east. It is thus proposed that anticlinal paleo-morphology could influence Main-M1 sand deposition and force it to accumulate on the structural flap. This model opens up a new way of identifying structural-lithological traps through palaeomorphology reconstruction in the fore-deep of the Oriente Basin.