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The Stratigraphy and Geomorphology of the Hofmann Forest Pocosin¹

ABSTRACT

Hofmann Forest is a 34,000 ha pocosin (swamp-on-a-hill) that has about 25,000 ha of Histosols 0.4 to 2-m thick. The pocosin is about 17 m above sea level, and large organic areas are uncommon at these altitudes in North Carolina. A stratigraphic and geomorphic study of Hofmann Forest was made to determine what factors were responsible for the accumulation of organic materials.

The organic materials of the pocosin mantle a gentle undulating marine plain that was exposed to subaerial weathering about 220,000 years ago. Few streams drain the area and the organic materials occupy the undissected interstream divides where the distance between streams is from approximately 0.5 km to 8 km. Flux rates indicate that the very low hydraulic conductivity of the pre-Croatan formations and their closeness to the surface prevent significant removal of excess water through the permeable thin surficial beds to the adjacent streams. Rainfall exceeds evapotranspiration and the excess water must be removed primarily by overland flow to the streams.

The shallow depth to the pre-Croatan aquicludes, the large distance between streams, and an excess of rainfall over evapotranspiration are the three major reasons why organic materials mantle a gently undulating plain about 17 m above sea level. The first two have remained nearly unchanged over the major part of the Hofmann Forest organic areas for the last 220,000 years. These conditions make the pocosin a potential area for organic accumulation. It is possible that organic deposits have been discontinuous during the last 220,000 years because of wide fluctuations in temperature and presumably in rainfall.

¹ Joint contribution from the USDA-SCS and the Soil Sci. Dep., North Carolina Agric. Exp. Stn. Journal Ser. Pap. no. 5213., Raleigh, NC 27607.

² Soil Scientists, USDA-SCS and Soil Sci. Dep., North Carolina State Univ., Raleigh.

³ Professor of Geology, Univ. of North Carolina—Chapel Hill.

⁴ Soil Scientist, SCS, Natl. Soil Survey Lab., Lincoln, Nebr.

Received for publication March 14, 1977. Accepted for publication August 5, 1977.