Updip Sequence Development on a Mixed Carbonate-Siliciclastic Continental Shelf, Paleogene, North Carolina, Eastern U.S.A.

Jenny LaGesse¹ and J. Fred Read^2
1 Colorado School of Mines, Golden, CO
² Virginia Tech, Blacksburg, VA

Cores, quarries and wells on the thin, updip part of the Paleogene shelf, NC, were studied to obtain a high resolution sequence framework to complement previous regional studies. The area spans the relatively positive Cape Fear Arch (Onslow Block), and the slowly subsiding (1.5 cm/ky) Albemarle Block to the north. The thin Paleocene sequence consists of a basal hardground, and deeper offshore, glauconitic fine sands to deeper marine silt-shale. Five Eocene sequences, 0-30 m thick, contain coastal sands, shoreface sandy-mollusk rudstones, offshore bryozoan grainstone-packstones and subwave base fine wackestone-packstone and marl. The Eocene sequences are bounded by hardgrounds (with condensed lags on the arch,), and have thin lowstand sands, a thin to absent transgressive unit, and a thicker highstand marine succession. The gently offlapping Oligocene succession has a single Lower Oligocene sequence of marl to fine foram sand on the arch, and downdip, two to three sequences capped by nearshore sandy molluscan facies. The upper Oligocene has three sequences of thin sands up into sandy mollusk rudstone. Deposition was influenced by differential movement of basement blocks (which localized fines in lows), increasing 3rd order-sea level changes and falling long term sea level as polar ice increased. Wave and current sweeping effectively decreased accommodation by 20-30 m, generated hardgrounds at sequence boundaries, and inhibited lowstand-transgressive deposition. Highstand deposits reflect high accommodation, with upward shallowing deposition that terminated at the depth of wave abrasion. This sequence stratigraphic development contrasts markedly with that from tropical shelves.

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