TEMPORAL VARIATIONS IN THE PALEOPEDOLOGY OF THE MID-CRETACEOUS HOPE PLANTATION CORE, BERTIE COUNTY, NORTH CAROLINA

In April 2004, the United States Geologic Survey (USGS) in cooperation with the North Carolina Geological Survey (NCGS) and the Raleigh Water Resources Discipline Carolina (WRD) completed a continuous deep core at Hope Plantation in Bertie County, North Carolina. The lower portions of this core offer an excellent chance to investigate the different facies within the early- to mid-Cretaceous Potomac Formation. This zone of interest consists of several sequences of very clay-rich deposits that coarsen upward to sand and disaggregate gravels. Of this section, 12 to 14 possible paleosols were identified and analyzed to determine changes in morphology during the change from the terrestrial Aptian/Albian into the marine-dominated Cenomanian. Macromorphology of these paleosols indicates that they can be grouped into three pedotypes: those that represent seasonally drained soil conditions (lower paleosols), those that are more consistently saturated (upper paleosols), and a combination of the two representing a transition form seasonal to saturated conditions. The lower paleosols are indicative of Udultic soils with hydromorphic conditions based on their strongly hued mottling, and pedogenic structure; while the upper paleosols appear to have experienced persistent saturated gleying conditions of an Aquept soil based on there drab hues and lack of distinct structures. Micromorphological analysis of these paleosols helps to confirm the macromorphological assessment. The lower paleosols contain well developed birefringent clay fabrics, including lattisepic and clino-bimasepic plasmic fabrics that are indicators of alternating wet and dry conditions. Argillans and translocated illuvial clays support this assessment. The upper paleosols contain fabrics that are more randomly oriented with weak birefringence. They also contain manganese and iron nodules, including sphaerosiderites, which indicate more water logged conditions. The macro- and micromorphological studies of this core support that this location changed temporally from a more terrestrial controlled fluvial system to a more marine dominated deltaic system.