Sequence Stratigraphic Influence on Regional Diagenesis of a Non-Tropical Mixed Carbonate-Siliciclastic Passive Margin, Paleogene, North Carolina, U.S.A.

Brian Coffey
Simon Fraser University, Burnaby, BC

Cementation and dissolution related to regional diagenetic events can significantly alter the distribution of porosity and permeability in carbonate-prone systems. This study incorporates regional well cuttings-based sequence stratigraphic correlations (constrained by biostratigraphic, seismic, and wireline log data) to document the distribution of cementation and dissolution events across a mixed carbonate-siliciclastic passive margin. Cement stratigraphies were reconstructed from lithified cuttings fragments in thin sections, using staining methods (Dickson's solution), and cathodoluminescence.

Preliminary observations indicate that cement zonations were best preserved in mud-lean facies with extensive early primary porosity. Second order supersequence boundaries correspond closely with major cement dissolution events (presumably meteoric) that are best preserved as etched fabrics within syntaxial overgrowths on echinoderm grains. Multiple generations of cementation are associated with these intervals. Major flooding events above supersequence boundaries are associated with regional ferroan pore filling calcite cements. Third-order sequence boundaries commonly have undergone dissolution and extensive subsequent coarse mosaic calcite cementation. Coarse (100-200um) fabric replacive dolomite also commonly is associated with intervals interpreted to contain sequence boundaries. Abrupt changes in cement stratigraphies across many sequence boundaries may result from the deposition of regional aquitards during subsequent transgressive drowning of porous shallow to middle shelf facies, such that diagenetic leaching associated with subsequent eustatic fall was limited to the shallow, unconfined portion of the aquifer system.

This low-cost method demonstrates another means of validating sequence stratigraphic correlations in areas subjected to extensive, microfossil destructive meteoric diagenetic modification, while also providing insight into the post-depositional influence of eustatic variations on non-tropical, mixed carbonate-siliciclastic pore system configuration.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005