A Miocene age for the Molo Formation, Norwegian Sea shelf off Vestfjorden, based on marine palynology

Seven side-wall core samples from the lower part of the Mob Formation in exploration well 6610/3-1 off Vestfjorden/Lofoten have been reanalysed for marine palynomorphs. Description of new species from other studies and access to reference successions from nearby sites with an independent chronostratigraphy have enabled a more reliable depositional age constraint for the Mob Formation in its northern distribution area than previously achieved. The new data (e.g., the lowest occurrence of the dinoflagellate cysts Barssidinium graminosum and Barssidinium pliocenicum and the highest occurrence of the dinoflagellate cysts Minisphaeridium latirictum and Operculodinium piaseckii) provide incontrovertible evidence for a Miocene age for the Mob Formation in well 6610/3-1. Our data suggest that the Mob Formation in well 6610/3-1 started to accumulate after erosional activity which took place between the late middle Miocene and the late Miocene. The data (especially the presence of the dinoflagellate cyst A. andalouisiensis andalousiensis, the co-occurrence of the dinoflagellate cysts Barssidiniuni evangelineae and M. latirictum and the presence of the acritarch L. lucifer) suggest that the Mob Formation in well 6610/3 1 started to accumulate at around 8.8 / 8.7 Ma. The sediments were deposited in a warm temperate, high-energy environment influenced by river discharge. During deposition, older sediments, particularly from the Paleogene, became extensively eroded. The erosion and rapid accumulation were probably associated with the combined effects of eustatic sea-level fall and uplift/updoming of the hinterland/coastal zone.