ABSTRACT: Jurassic Sequence Stratigraphy in the Mississippi Interior Salt Basin of Alabama

Ernest A. Mancini, Berry H. Tew, Robert M. Mink

Three depositional sequences associated with cycles of eustatic sea-level change and coastal onlap can be identified in the Mississippi Interior Salt basin of Alabama. These depositional sequences probably correspond to the J2.4, J3.1, and J3.2 sequences of Vail and others for Callovian through Kimmeridgian strata. In the Mississippi Interior Salt basin, the lower depositional sequence is bounded by a basal unconformity and an upper Type 2 unconformity in the Callovian. This sequence includes Louann evaporites (transgressive deposits), Pine Hill anhydrites and shales (condensed section), and Norphlet eolian sandstones (progradational highstand regressive deposits). The middle depositional sequence reflects relative sea-level rise in the late Callovian. This sequence includes Norphlet arine sandstones and lower Smackover packstones and mudstones (transgressive deposits), middle Smackover mudstones (condensed section) and upper Smackover grainstones and anhydrites (progradational highstand regressive deposits). The sequence has an upper Type 2 unconformity indicating relative sea-level fall in the Oxfordian. The upper depositional sequence reflects relative sea-level rise in the late Oxfordian. This sequence includes lower Haynesville evaporites and clastics (transgressive deposits), middle Haynesville carbonate mudstones and shales (condensed section), and upper Haynesville updip continental sandstones and downdip shales, limestones, and anhydrites (progradational highstand regressive deposits). The sequence has an upper Type 1 unconformity indicating abrupt sea-level fall in the late Kimmeridgian. In these depositional sequences, progradational highstand regressive deposits are the principal petroleum reservoirs. Condensed section deposits have the potential to be source rocks if subjected to proper burial conditions; however, only the lower and middle Smackover mudstones were deposited and buried under conditions favorable for hydrocarbon generation and preservation. An understanding of sequence stratigraphy can serve as an aid to identifying potential hydrocarbon exploration targets.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990