ABSTRACT: Seismic Facies, Lithofacies, and Preservation Potential of Incised Valley-Fill Lithosomes: Quaternary Models from the North Carolina Continental Margin

SNYDER, STEPHEN W., North Carolina State University, Raleigh, NC, and ALBERT C. HINE, University of South Florida, St. Petersburg, FL

Stratigraphic interpretations from a dense network (>23,000 km) of very high resolution, seismic reflection profiles within the North Carolina continental margin have delineated a complex mosaic of Quaternary subbottom channel systems. The channels are incised valleys excavated by fluvial activity during lowstand events dictated by Quaternary glacioeustasy. The terms incised valley and paleofluvial channel are used interchangeably. Systematic analysis of the geometries and infill histories observed in the valley-fill lithosomes has yielded eight distinct seismic facies (SF) prototypes: (1) conformable; (2) mounded; (3) lateral accretion; (4) sigmoidal progradation; (5) horizontal onlap; (6) transparent; (7) chaotic; (8) multistage excavation and fill. Cores penetrating specific SF rototypes have facilitated the integration of lithologies and seismic facies. These data have allowed us to assess (1) the paleofluvial/estuarine environs and facies represented, (2) paleohydraulic behavior during submergence, and (3) generalized depositional infill histories. Our overall goal is to develop a model that depicts the most consistent lateral and vertical succession of paleoenvironments (facies) resulting from submergence induced by transgressive seas.

Although many of the channels lack cross-shelf-continuity, all of the channel-fill lithosomes identified are clearly paleofluvial in origin. The composite model for paleofluvial infilling consists of: a basal point bar depositional sequence (lateral accretion to prograded SF); capped by organic-rich, overbank and swamp sediments (high-amplitude, horizontal SF &/or chaotic SF); estuarine deltaic &/or turbidity max sediment regimes (most commonly mounded onlap SF); estuarine fill (complex facies consisting of a combination of horizontal, conformable, transparent, mounded, &/or chaotic SF--depending on the suite of estuarine microenvironments encountered); and rarely capped by subtidal sand bars (mounded SF), lagoonal sediments (conformable or horizontal SF), or distal flood idal-delta sediments (low-angle, sigmoidal progradation, mounded, or transparent SF). The lack of cross-shelf continuity of the paleofluvial channels is a consequence of stratigraphic incision by subsequent erosional transitional transgressions, leaving only the deeper channel infill facies preserved on the shelf.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)