A new record of <i>Aratrocypris</i> Whatley <i>et al.</i>, 1985, Ostracoda, from the Lower Cretaceous of the North Sea: a range extension for the genus

Abstract

During analyses of ditch cuttings samples from wells 34/10-53A and 35/9-F-1H drilled by Statoil ASA in the North Viking Graben, North Sea, 16 specimens pertaining to Aratrocypris were found. One specimen was found at 1260 m (depth below KB) in 35/9- F-1H within an interval of Lower Paleocene claystones, and based on its white chalky preservation characteristics is considered reworked from Maastrichtian chalk. The remaining 15 specimens were found among ostracod-rich microfossil assemblages of Early Cretaceous age in a sample at 4190 m of 34/10-53A, and at 2166 m of 35/9-F-1H. Although these samples contain numerous ostracods, the occurrence at such a low stratigraphical level was unexpected since Aratrocypris , hitherto, has not been found older than Coniacian/Santonian. Their preservation condition as orange-stained opaque carapaces is the same as that of the remainder of the assemblage found at that level in the Lower Cretaceous. For this reason the possibility of it being caved from higher levels of the well is ruled out. The find, therefore, represents the earliest record of the genus, and is important also when considering its early zoogeographical distribution. Ostracods occur in well 35/9-F-1H at two levels: Lower Paleocene and Lower Barremian–Lower Hauterivian. Each assemblage has a very different style of preservation which allows them to be easily separated. Ostracod assemblages of the younger level are white, translucent carapaces, a preservational style consistent with the abundant foraminifera …