BENTHIC FORAMINIFERAL PALEOECOLOGY OF THE LOWER JACKSON GROUP (EOCENE; BARTONIAN), HINDS COUNTY, MISSISSIPPI

Benthic foraminiferal assemblages were collected from the Moodys Branch and lower Yazoo Formations in the Mossy Grove core, Hinds County, Mississippi. The studied interval is 32 m (104 feet) thick and correlates with planktonic foraminiferal biozone P14. It represents Gulf Coast depositional sequence TE 3.2. This interval in the Mossy Grove core is of special interest as previous work has produced a detailed benthic oxygen and carbon isotope record. The benthic foraminifera were picked from the same samples used for the isotope analysis. These samples were collected at 0.6 m (2 foot) intervals throughout the studied interval.

The assemblages collected from the Moodys Branch are dominated by Siphonina advena, Siphonina jacksonensis, and Reussella moodysensis. Other important species in this assemblage includes Quinqueloculina mauricensis, Cibicidoides cocoaensis, and Anomalinoides bilateralis. Through the Moodys Branch interval and upwards into the Yazoo Clay, there is an increase in the abundance of Bolivina jacksonensis, Spiroplectammina mississippiensis, and Uvigerina jacksonensis.

The transition from the Siphonina-Reussella assemblage to the Uvigerina-Spiroplectammina assemblage is a gradual one through the studied interval. While species composition and abundance does vary from sample to sample, the overall character of the assemblages does not change. There is some correlation between fluctuation in Carbon and Oxygen isotope values and species composition in the samples. The controlling factors on the benthic foraminiferal assemblages in the studied interval, however, appear to be those associated with a transgressing epicontinental sea.