ABSTRACT

The Claiborne-Jackson Group contact corresponds to a type 1 sequence boundary within the Bartonian Stage in southwestern Alabama and southeastern Mississippi. Transgressive glauconitic sandstones of the Gosport Sand (uppermost unit of the Claiborne Group in Alabama) are part of the TAGC 4.1 depositional sequence and disconformably overlie progradational, highstand regressive lignitic claystone of the Lisbon Formation of the Claiborne Group along a type 1 sequence boundary. These Lisbon claystones are part of the TAGC 3.4 depositional sequence in southwestern Alabama. The Gosport glauconitic sandstone is highly burrowed, contains a basal lag of shark teeth and phosphate and quartz pebbles, and is locally overlain by lignitic laminated clay. Transgressive glauconitic sandstone and marlstone of the Moodys Branch Formation (lowermost unit of the Jackson Group) are part of the TAGC 4.2 depositional sequence and disconformably overlie progradational, highstand regressive lignitic claystone and sandstone of the Gosport. In southeastern Mississippi, transgressive glauconitic sandstones and marlstones of the Moodys Branch Formation disconformably overlie progradational, highstand regressive lignitic claystone and sandstone of the Cockfield Formation (uppermost unit of the Claiborne Group in Mississippi) along a type 1 sequence boundary. The uppermost Cockfield beds are interpreted to be equivalent to the lignitic claystone and sandstone of the upper Gosport in Alabama. The uppermost beds of the Lisbon Formation, the Gosport Sand, and the Moodys Branch Formation have been assigned to the Bartonian planktonic foraminiferal Truncorotaloides rohri Interval Zone.