Abstract: Triassic/Jurassic Stratigraphy and Basement Structure along the Pensacola Arch/Conecuh Embayment Margin in Northwest Florida

Joel G. Duncan

Stratigraphic and structural analysis of deep borehole and seismic reflection data along the Pensacola Arch/Conecuh Embayment margin in eastern Santa Rosa County, Florida, reveals a series of grabens and horsts formed by northeast-trending faults that developed during continental rifting of Pangea in the Late Triassic and Early Jurassic. One apparent horst block, the Pensacola Arch, was a paleotopographic high that formed the southeastern boundary of the Middle to Late Jurassic Conecuh Embayment. A second graben, correlative with the Alabama-Arkansas fault system or regional basement rift system, trends northwest, roughly perpendicular to the northeast trending faults.

Upper Triassic synrift sediments that accumulated in a northeast-trending graben pinch out abruptly to the southeast against Suwannee Terrane basement at the Pensacola Arch. Middle to Upper Jurassic drift-stage strata of the Conecuh embayment progressively onlap the post-rift unconformity toward the southeast. Upper Jurassic Smackover Formation carbonates and evaporites overstep Triassic deposits and rest directly on quartzitic sandstone of the Suwannee Terrane near their depositional limit at the Pensacola Arch. The Smackover Formation thins significantly toward the southeast in association with the Triassic pinch out and rift-basin border fault at the Pensacola Arch.

Because the Louann Salt is absent along the margins of the Pensacola Arch, observed faulting in the Jurassic section must have originated in the basement rather than in the salt.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994