Acquisition, Processing, and Archiving of High-Quality Core Data, North Carolina Outer Banks

Rotosonic drilling technology was used to recover approximately 350 m of core (10 cm diameter) at eight different locations on the Outer Banks of North Carolina as part of a coastal geology cooperative research program. A combination of vibration and rotation of the drill pipe and casing is used to advance the hole. Water is used to wash out the casing, but is not circulated and no cuttings are brought to the surface. This leaves the site relatively undisturbed, so working in municipal areas is not a problem. Drill costs averaged about \$140/m. Coring runs are 3.3 m (10 ft) long, with each run recovering two 1.65 m (5 ft.) long polycarbonate tubes containing the core sample. In the laboratory, tubes are cut lengthwise with a circular saw and then split by pulling piano wire through the sediment. One half-core is used for sampling; the other half is used to create a detailed visual log and digital image, and is retained as an archive sample. The drilling recovered high-quality lithologic samples in unconsolidated sediments with recovery rates of over 90 percent in most holes. This allowed for thorough, detailed description and stratigraphic analysis, and closely controlled sampling for age dating and geochemical studies. High-resolution (2048 x 1536 pixel) digital images (TIFF format) of the cores are taken in a controlled setting. Lighting, camera settings, and core positioning are carefully monitored to ensure consistency. A tape measure is included in the frame to provide depth reference information in each image. Approximately 36cm of the core is imaged at a time (9 Mb file). To construct composited core images, each 36 cm-long segment is digitally stitched together using a software program written specifically for piecing together panoramic photographs. This process yields a high-resolution (TIFF format; 36 Mb) image showing the full 1.65 m (5 ft.) core tube. The composite image is then saved in JPEG format to reduce the file size to just over 4.5 Mb without unduly compromising the image quality. Lower-resolution images can be easily made for Internet distribution.