Carlos Jaramillo

Sequence stratigraphic interpretations from palynofacies, dinocyst and lithological data of Upper Eocene-Lower Oligocene strata in southern Mississippi and Alabama, U.S. Gulf Coast

Abstract This paper presents new information on the sequence stratigraphy of the Upper Eocene–Lower Oligocene strata in southern Mississippi and Alabama, based on palynological and lithological data from five sections. By integrating lithological characteristics with palynofacies assemblages, several dinocyst paleoecological groups, the Deflandrea group, and the abundance of reworked dinocysts in samples, paleobathymetric curves were reconstructed and used to revise the sequence stratigraphy of the area. We identified a maximum flooding surface in the middle of the Shubuta Clay Formation in southern Mississippi, and dated it as latest Eocene. In southern Alabama, the Eocene–Oligocene boundary was placed within a condensed section representing about 0.19 Ma, and it coincided with the Shubuta Clay–Vicksburg Group contact. This condensed section is equivalent to the accumulation of the upper Shubuta and Red Bluff Formations in southern Mississippi. The Forest Hill–Mint Spring contact, which has been interpreted as a sequence boundary that merged with a transgressive surface, does not correlate with the Tejas A (TA) 4.3/4.4 sequence boundary of Haq et al. (1988) . The Pachuta Marl and lower Shubuta Clay Formations are constituents of a Late Eocene transgressive systems tract in southern Mississippi, but this systems tract extended to the Shubuta Clay–Vicksburg Group contact in southern Alabama. The overlying Early Oligocene highstand systems tract consisted of the upper Shubuta (in Mississippi), and the Red Bluff–Bumpnose–Forest Hill Formations. A thin sandstone in the Mint Spring was interpreted as a deposit of a possible lowstand systems tract above the sequence boundary in one southern Mississippi section. In general, the Mint Spring Marl and Marianna Limestone constituted a transgressive systems tract.