BENTHIC FORAMINIFERAL PALEOECOLOGY OF UPPER CRETACEOUS STRATA, DIXON CORE, NORTH CAROLINA

Foraminifers were examined from 58 samples taken from 630 feet of Santonian through Maastrichtian strata of the Tar Heel, Bladen, Donoho Creek, and Peedee Formations in the Dixon Core. More than 190 foraminiferal species were recognized from 8300 picked specimens. Approximately one hundred and twenty-four benthic species were recognized of which the genera Cibicides and Planulina were dominant, including Cibicides harperi (greater than 13 percent), C. stephensoni (6%) and Planulina taylorensis (6%). The foraminifer suborders observed included Rotaliina (77% of identified specimens), Lagenina (14%), Textulariina (8%) and one species of Robertinina (<1%).. Benthic foraminiferal abundance and textularid to rotalid ratio changes were used as a proxy for variations in environmental conditions; the former decreasing or increasing with falling or rising relative sea level, respectively, and the latter increasing or decreasing, respectively. In addition foraminiferal morphologies also vary with changes in sea level, with uncoiling and rectilinear forms increasing during a transgression and being replaced by more robust species such as Lenticulina, Nodosaria and Dentalina during a regression. Within the Tar Heel Formation benthic foraminiferal abundance increases four times with corresponding decreases in textularid to rotalid ratios, including two barren intervals, at 745.5 and 634.7 feet, both overlain by more populated samples and interpreted to be sequence boundaries. The presence of varied morphologies indicate a middle to outer neritic shelf environment. The overlying Bladen Formation samples have no textularids and a decreasing abundance of benthics and is interpreted as inner neritic. The younger Donoho Creek Formation includes one cycle of rising and falling benthic abundance and is seen as middle neritic; with the overlying Peedee Formation showing two increases in benthic abundance and very small textularid to rotalid ratios. The Peedee is interpreted to be inner to middle neritic with sea level falling prior the K-P boundary.