Miocene Unconformities, Chronostratigraphy, and Sea Level Cyclicity: Fine-Tuning Early Neogene Relative Coastal Onlap Curve for North Carolina Continental Margin

Stephen W. Synder, Albert C. Hine, Stanley R. Riggs, Scott W. Snyder

Stratigraphic interpretations of more than 21,000 km of high-resolution seismic reflection data have identified 18 discrete depositional sequences within the Miocene section of the North Carolina continental margin. Each sequence is bound by erosional unconformities, condensed sections, or a combination of both. These Miocene unconformities have been traced and mapped throughout the North Carolina continental margin, which demonstrates that they are regional chronostratigraphic hiatuses.

Biostratigraphic analyses (planktonic foraminifera and calcareous nannofossils) of more than 900 m of stratigraphic section recovered from 140 vibracores penetrating the Miocene sequences on the continental shelf have identified significant biostratigraphic gaps associated with four of the Miocene unconformities. These four major unconformities divide the Miocene sequences into three distinct ages, each generally correlative to the third-order cycles of relative coastal onlap proposed by Vail and Hardenbol.

Each third-order sequence consists of several fourth-order sequences. These higher frequency sea level events are interpreted to be driven by glacio-eustatic fluctuations throughout the Miocene. The duration and amplitudes of each third- and fourth-order sea level event are based on the biostratigraphic constraints, the identification of type 1 unconformities (marked by paleofluvial channels) versus type 2 unconformities (recognized by condensed sections characterized by bored, indurated, carbonate hardgrounds), as well as paleoenvironmental interpretations of benthic foraminiferal assemblages (maximum amplitudes).

Thus, these data allowed us to approximate the duration and amplitudes of Miocene sea level events identified within North Carolina, and to fine-tune the early Neogene relative coastal onlap curve for this segment of the western North Atlantic continental margin.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.