DINOFLAGELLATE STRATIGRAPHY AND FACIES OF THE LATE CRETACEOUS – EARLY PALEOGENE (K/PG BOUNDARY) INTERVAL AT ODESSA, DELAWARE

Dinocyst assemblages from a 110-ft-deep wireline-cored borehole near Odessa, Delaware (site ID Fb25-15) provides valuable new insights into the stratigraphic record of the Cretaceous/Paleogene (K/Pg) boundary at an updip location in the U.S. Middle Atlantic Coastal Plain. The boundary interval in the study area includes, upward, the Mount Laurel, Navesink, Hornerstown, and Vincentown Formations. The K/Pg boundary has conventionally been placed between the Navesink and Hornerstown Formations and considered to be a major hiatus.

Two samples of shelly, slightly glauconitic sand from the Mount Laurel Formation yielded dinoflagellates. The upper, from 71.2 ft, includes Isabelidinium aff. I. cooksoniae, Deflandrea galatea and Alterbidinium acutulum. Together these suggest equivalence to the basal part of of calcareous nannofossil Zone CC25b, indicating the lower part of the upper Maastrichtian. A similar assemblage is also known from the Navesink and New Egypt Formations in New Jersey and the Severn Formation in Maryland.

Dinocysts in four samples (61.65, 56.3, 53.3, 50.7 ft) from glauconite-rich very silty sands and sandy silts of the Navesink Formation indicate a higher Maastrichtian position. The samples from 56.3 ft and 50.7 ft include Deflandrea galatea and Thalassiphora pelagica, which suggest correlation to nannofossil subzone CC 26a, indicating the middle part of the upper Maastrichtian. A similar assemblage is also present in the New Egypt Formation in New Jersey and the Severn Formation in Maryland.

Paleocene dinoflagellates were identified at 45.4 ft in a sample of dark, silty, very glauconitic sand from the Hornerstown Formation. The presence of Senoniasphaera inornata indicates this sample is lower Danian, correlative to planktonic foraminiferal zone P1 or lower.

The absence of Palynodinium grallator and Disphaerogena carposphaeropsis in the Navesink samples examined may be significant. These taxa indicate the uppermost part of the upper Maastrichtian in other Coastal Plain localities. In addition, the absence of the basal Paleocene marker Carpatella cornuta suggest the possibility that the basal Danian, equivalent to planktonic foraminiferal zones P0 and Pα, may be absent. If these intervals are indeed missing, these results suggest a short but clear K/Pg boundary hiatus.