Abstract:
The fossiliferous beds above the Pungo River
Formation (middle Miocene) in the Lee Creek
open pit mine in Beaufort County, North Carolina, are approximately 70 feet (21.3 m) thick.
This thickness includes 46 feet (14 m) that is
correlative with the Yorktown Formation of the
type area and is referred to that unit, and, above
the Yorktown, a fossiliferous section 23 feet (7 m)
thick that is assigned to the Croatan Formation.
The 149 species or subspecies of ostracodes
identified were from 16 samples from the Yorktown and Croatan. Coefficients of faunal similarity were calculated for all samples, and the resulting matrix was subjected to unweighted pair-
group cluster analysis. Three major faunal groupings were delineated. The principal faunal discontinuity occurs at the Yorktown-Croatan contact about 46 feet (14 m) above the base of the
Yorktown. The beds below this level belong to
the Pterygocythereis inexpectata and Orionina vaughani
ostracode assemblage zones. Correlation with
other Coastal Plain deposits containing planktonic foraminifers indicates that the Orionina
vaughani assemblage zone is planktonic foraminifer zones N19 and N20 in age and that the
Pterygocythereis inexpectata assemblage zone may
approximate the lowest part of planktonic zone
N19 in age. Thus, the Yorktown in the Lee Creek
Mine is of early Pliocene age. This is seemingly
corroborated by a K/Ar date of 4.4±0.2 my on
the Orionina vaughani assemblage zone in Virginia. A third major faunal assemblage is found in
the beds of the Croatan Formation, which are
referable to the Puriana mesacostalis ostracode assemblage zone. The upper part of the Croatan
can be correlated with rocks in Florida and North
Carolina that have been radiometrically dated by
the He/U method at about 1.8 to 1.9 mya. A
tentative He/U radiometric date of 2.4 mya was
obtained for the lower part of the Croatan at the
mine. If a date of about 2.0 mya is used for the
Pliocene-Pleistocene boundary, the Croatan as
used in the mine spans the Pliocene-Pleistocene
boundary.
