Dinoflagellate cyst stratigraphy and paleoecology of the Upper Miocene and Pliocene, Rees Borehole, Northern Belgium

Abstract

Correlating and dating Neogene deposits along the southern margin of the North Sea Basin have historically been complicated by the fragmentary nature of the outcrops studied, the boreal aspect of the benthic foraminifera present, and scarcity of planktonic microfossils. Dinoflagellate cysts and other palynomorphs from the Rees Borehole, Campine area of northern Belgium, are therefore used to elucidate the paleoenvironmental history of the area. The borehole contains the Upper Miocene Diest and Kasterlee, mid-Pliocene Poederlee, and Pliocene Mol and Merksplas formations. For the Diest Formation, the presence of Achomosphaera andalousiensis andalousiensis, Barssidinium pliocenicum, Operculodinium? eirikianum, Operculodinium tegillatum, Selenopemphix armageddonensis and the acritarch Nannobarbophora walldalei are consistent with a late Late Miocene age. The dinoflagellate cyst assemblages of the Kasterlee Formation in the Rees borehole differ from those of the Kasterlee Formation in other areas, and are more similar to assemblages of the underlying Diest Formation. This may be explained by reworking of the Diest into the Kasterlee Formation. The Poederlee Formation assemblages include Achomosphaera andalousiensis suttonensis, Invertocysta lacrymosa, Operculodinium? eirikianum and, with the absence of Reticulatosphaera actinocoronata, Operculodinium tegillatum and Batiacasphaera minuta/micropapillata, point to a mid- to Late Pliocene age, between 3.7 and 2.7 Ma. For the first time, dinoflagellate cysts were found in the Merksplas Formation, indicating a marine influence. The presence of Achomosphaera andalousiensis suttonensis, Barssidinium pliocenicum, Capisocysta lyelli, Geonettia waltonensis, and Invertocysta lacrymosa within this formation collectively point towards a Late Pliocene age. Assemblages throughout the Rees Borehole reflect neritic deposition within a restricted marine basin under temperate climates.