FORAMINIFERAL PALEOECOLOGY AND SEQUENCE STRATIGRAPHY OF THE LOWER JACKSON GROUP (EOCENE; BARTONIAN), WAYNE COUNTY, MISSISSIPPI

The Moodys Branch Formation and the North Twistwood Creek Clay Member of the Yazoo Formation in the Mobil; #1 Young core, Wayne County, Mississippi, represents Gulf Coast depositional sequence TE 3.2 in eastern Mississippi. This interval is of special interest as previous work in the Mossy Grove core of western Mississippi has produced a detailed benthic oxygen and carbon isotope record which serves as a proxy for fluctuating relative sea-level. Foraminfera were picked from both the Moodys Branch Formation and the North Twistwood Creek Member in the Young core in order to calculate the planktonic:benthic (P:B) ratio and to identify the benthic foraminiferal assemblages throughout the interval. The P:B ratio and the benthic foraminiferal assemblages collected enable a direct comparison of the Moodys Branch and Yazoo Clay of eastern and western Mississippi.

The P:B ratio varies little in the Moodys Branch with planktonic foraminifera comprising less than 5% of the total foraminiferal fauna. In the lower 4 m of the North Twistwood Creek Clay Member, planktonic foraminifera comprise as much as 12% of the total fauna. The remainder of the North Twistwood Creek clay contains only a small percentage of planktonic foraminifera as a component of the foraminiferal fauna.

The benthic foraminiferal 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 Discorbis, Cibicidoides, Hanzawaia, Nonionella, and Spiroplectammina.

The P:B ratios and the benthic foraminiferal assemblages collected from the Young #1 core are consistent with the transgressive systems tract, the maximum flooding surface, and the increased sedimentation rate of the highstand systems tract. The results are similar to those obtained in western Mississippi although an abundance of Uvigerina and Bulimina in the Mossy Grove core indicate a deeper water environment. Additionally, higher P:B ratios in the lower Yazoo of the Mossy Grove core suggest a different sequence stratigraphic setting for the western sections.