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Mississippi's Revised Neogene Stratigraphy in Northern Gulf Context
Ervin G. Otvos
Reevaluation of Mississippi's Neogene coastal stratigraphy, based on a substantial body of new drill data, led to recognition of several marine intervals and the need to revise the old formation terminology that fails to meet modern standards. The Oligocene-Miocene series boundary cuts across the Heterostegina Zone. Subsequent regression resulted in a major hiatus (Zones N4b-8). Mid-Miocene deposits directly overlie upper Eocene sediments across a major unconformity surface. Deep neritic sedimentation (Hancock Formation) continued in the south and offshore. The most extensive Miocene transgression that peaked in Zone N9 led to significant shoreline shift. A deep-water trench, described first in offshore Alabama (Smith, 1991), crossed into present-day Mississippi. Recently documented thin lower and middle Miocene limestone units display considerable lithologic variety and correlate with carbonates in adjacent states.
A neritic embayment extended landward during the Tortonian transgression (N16) while Mississippi subdeltas freshened the offshore Gulf. Brackish paralic-to-terrestrial conditions prevailed during the rest of the Miocene and early Pliocene, producing a thick brackish inshore and alluvial-deltaic sequence. The proposed Pensacola Formation covers the entire sequence between the early middle Miocene and the pre-Citronelle Pliocene unconformities.
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