Late Miocene to Pliocene Delta Progradation in the Southern North Sea Basin

During the Late Miocene and Pliocene, northern Belgium and the Netherlands occupied the southern margin of the North Sea Basin, which was progressively infilled by a (north‐)westward migrating deltaic system. To date, the regional evolution and continuity of this system—transitioning from northern Belgium during the Late Miocene to the central Netherlands in the Pliocene—remain poorly constrained. This study clarifies this spatio‐temporal transition utilizing a well‐log correlation panel tied to biostratigraphically calibrated wells. The transect demonstrates that Upper Miocene successions, which attain thicknesses of up to 60 m in northernmost Belgium, pinch out northward and are completely absent in the southern Netherlands. Regional mapping reveals that the Upper Miocene deltaic progradation terminated just north of the Belgian–Dutch border along a roughly E‐W‐trending line. During the early Zanclean (Early Pliocene) transgression, a thin (5–10 m) sequence of Lower Pliocene fine‐grained sands was deposited above the relict delta topsets in northern Belgium. Northward and distal to this relict delta system, the Lower Pliocene units exhibit higher glauconite concentrations, probably reflecting increased depositional depths. Although these distal units locally thicken to 20–30 m, they failed to completely consume the available accommodation space. Complete infilling occurred during the late Zanclean to early Piacenzian, when deltaic progradation resumed with the deposition of highly bioclastic, coarsening‐upward sands. This shell‐rich unit remains thin (~4 m) where it overlies the relict Upper Miocene delta topsets in the south, but rapidly thickens to over 70 m as it filled the residual accommodation space further north. Because the residual accommodation space was largely filled by the early Piacenzian, subsequent younger Piacenzian sequences are significantly thinner and register a transition to a shallower‐marine depositional environment that covered a vast area across northern Belgium and the southern Netherlands.