Primitive equoid and tapiroid mammals: keys for interpreting the Ypresian – Lutetian transition in Belgium.

Terrestrial mammal teeth, pertaining to the primitive horses Hallensia louisi and Propachynolophus levei and the tapiroid Lophiodon remensis, have been discovered at the base of the marine Lede Formation in the Oosterzele and Balegem sandpits, 10 km southeast of Gent. According to its calcareous nannofossil NP15 dating, the basal Lede Formation in that area belongs to the Middle Lutetian. Comparison with in situ records in the Paris Basin suggests a latest Ypresian origin for the mammals (reference-level MPIO) and consequently reworking. The Oosterzele and Balegem specimens most probably originate from erosion of the continental Aalterbrugge Lignitic Horizon (uppermost Ypresian), which is cropping out nearby. The additional reworked faunal and lithological components at the base of the Lede Formation suggest that also the Aalter Formation (top NP13-base NP14) and the overlying Brussel Formation (NP14), or certain parts of these, were deposited but subsequently eroded in that area. The depositional history of the Lede Formation, resulting from the interplay of tectonic uplift and eustatic sea-level changes, is detailed.

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