Stephen K. Boss

Influence of fluvial processes on the quaternary geologic framework of the continental shelf, North Carolina, USA

Abstract Digital, single-channel, high-resolution seismic reflection profiles were acquired from the insular continental shelf of North Carolina, USA along a data grid extending from Oregon Inlet northward 48 km to Duck, North Carolina and from the nearshore zone seaward approximately 28 km (total surveyed area=1334 km 2 ). These data were processed and interpreted to delineate principal reflecting horizons and develop a three-dimensional seismic stratigraphic framework for the continental shelf that was compared to stratigraphic data from the shoreward back-barrier (estuarine) and barrier island system. Six principal reflecting horizons (designated R 0 through R 5 ) were present within the upper 60 m of the shelf stratigraphic succession. Three-dimensional mapping of reflector R 1 demonstrated its origin from fluvial incision of the continental shelf during an episode (or episodes) of lowered sea-level. Fluvial processes during development of reflector R 1 were responsible for extensive reworking and re-deposition of sediment throughout most of the northern half of the study area. Five seismic stratigraphic units (designated S 1 through S 5 ) were tentatively correlated with depositional sequences previously identified from the North Carolina back-barrier (estuarine) and barrier island system. These five stratigraphic units span the Quaternary Period (S 1 =early Holocene; S 2 =51–78 ka; S 3 =330–530 ka; S 4 =1.1–1.8 Ma; S 5 =earliest Pleistocene). Unit S 1 is composed of fine-grained fluvial/estuarine sediment that back-filled incised streams during early Holocene sea-level rise. The four other stratigraphic units (S 2 –S 5 ) display tabular depositional geometries, low total relief, and thicken toward the east–southeast as their basal reflectors dip gently between 0.41 m km −1 (0.02°) and 0.54 m km −1 (0.03°). Knowledge of the three-dimensional subsurface stratigraphic architecture of the continental shelf enhances understanding of the development of shelf depositional successions and provides a framework for development of better Quaternary sea-level data, especially offshore North Carolina where such data are sparse.

Adventures in data analysis : The TAO Array and the 1997-1998 El Niño

Traditional undergraduate education in earth sciences does not emphasize data acquisition, analysis, or assessment. However, arrival of the information age dictates that earth sciences graduates be imbued with fundamental skills to organize, evaluate and process large data sets. Fortunately, the proliferation of remotely sensed data and its availability via the Internet provides many opportunities for earth science educators to meet these needs. Exercises to introduce students to data analysis have been designed utilizing data from the Tropical Atmosphere–Ocean (TAO) Array and the 1997–1998 El Niño episode in the tropical Pacific Ocean. The TAO Array is a grid of 69 buoys moored across the equatorial Pacific Ocean (8°N to 8°S and 95°W to 143°E) recording environmental data relevant to El Niño—Southern Oscillation (ENSO) processes. Data from the TAO Array is available in near-real-time (http://www.pmel.noaa.gov/toga-tao/realtime.html) or as archived ASCII files (http://www.pmel.noaa.gov/toga-tao/data-delivery.html) providing daily (sometimes hourly) records of environmental parameters for each buoy in the grid. Student exercises in data analysis begin with downloading data from buoy locations, parsing the data into spreadsheets, and organizing data by environmental parameter into yearly and monthly data sets. Analyses of reconstructed data include calculations of long-term averages of environmental parameters, seasonal climatologies, monthly climatologies and calculation of long-term, seasonal, and monthly anomalies. Finally, monthly anomaly maps produced by students are loaded sequentially into GIF-animation software to create time-series images illustrating the progress and development of the 1997–1998 El Niño event.