QUATERNARY SEISMIC STRATIGRAPHIC FRAMEWORK OF THE SOUTHERN ALBEMARLE EMBAYMENT: THE SEQUENCE STRATIGRAPHIC RESPONSE TO EVOLVING PALEOTOPOGRAPHY

Over 750 km of high-resolution single channel seismic data were collected in Pamlico Sound, North Carolina, a drowned-river estuary located with the Albemarle Embayment regional depositional basin. The data show the regional geologic framework, including the distribution and character of Pliocene and Quaternary depositional sequences and associated incised paleodrainage systems. These deposits represent the updip component of transgressive and highstand systems tracts in a filling basin. Sequence boundaries are primarily Type 1 based on the observation of complex, incised channel-fill facies bounded by high amplitude seismic reflections. Additional surfaces (e.g,. marine flooding surfaces and ravinement surfaces) are also evident. At least 18 Quaternary seismic sequences can be identified within the basin. Quaternary sediments lie on a northward-dipping unconformity that is likely the top of Pliocene sediments, ranging from 75 meters below sea level (mbsl) in the north to approximately 37 mbsl in the south. The data reveal a complex Quaternary fill history characterized by multiple large (>30 m deep, several km wide) incised valleys and numerous smaller incised channels. Paleochannels provide information regarding the locations, sizes, geometries, orientations and fill history of the Quaternary fluvial systems that previously occupied this basin. Channel-fill facies seen in the data range from steeply dipping clinoforms to horizontal beds. Progradation of clinoforms dominantly trends to the east with few trending to the northwest. Understanding past basin dynamics in response to sea-level change will aid in refining regional sequence stratigraphic models.