32 Geomorphic Anomalies and Underlying Geologic Controls Identified from Surficial and Bedrock Mapping, Southeastern United States

Friday, 13 April 2018
1:30 PM - 5:30 PM
Room 300 D

USING HIGH-RESOLUTION LIDAR TO IDENTIFY ANOMALOUS GEOMORPHIC FEATURES THAT SUPPORT ALTERNATIVE GEOMORPHIC MODELS FOR DYNAMIC COASTAL PLAIN EVOLUTION, NORTH CAROLINA

Paper number: 32-10
Program: Theme Sessions
Time: 4:30 PM – 4:50 PM

Authors

Abstract

A four-quadrangle area that included the Early Pleistocene Surry Paleoshoreline complex was subjected to a comprehensive landscape analysis based on high-resolution LiDAR gridded elevation data (max. horizontal resolution = 20 cm), derived hillshade, slope and contours (0.5 and .025 m), and orthoimages. En lieu of interpreting the landscape in the context of existing geomorphic/stratigraphic models, the data itself defined the landform elements and hence the models. Some unexpected landscape features and relationships were identified. The focus is on four interrelated topics that include several unexpected features: 1) the Holocene depositional system and its landform elements; 2) arrays of terraces in drainages; 3) sinkholes, Carolina Bays and stratigraphy; and 4) landforms in ramp settings.

For incised valleys, the Holocene depositional system was differentiated first, as a series of landforms that define surface water flow paths from the upstream ends of the system on the interfluves (ramps) to the wetland bottom flat. An upstream-most feature is commonly a collection basin, Carolina Bay or sinkhole, which are interrelated. Also present are alluvial fans with incised feeder channels, valley margins with slope failures and colluvium, and disrupted drainage.

To map (middle to early) Pleistocene depositional systems in incised valleys, break points at the toes of steep slopes (“scarps”) were mapped in the drainages; these potentially define en echelon sets of terraces that step downstream every 1 to 2 meters. Some of these sets are connected to marine (ramp) terraces.

The Surry Paleoshoreline complex is interpreted as the boundary between normal and forced regression deposits. The shoreline is mainly depositional here, with no wave-cutting. The westernmost extent of the complex remains unknown. The relict shoreline in the map area likely formed at a sea levels of about 30-32 m. West of the scarp, a barrier island and relict tidal channels are preserved. Carolina Bays are best-developed in shoreline sands. East of the scarp are subtle Carolina Bays and muddier surficial deposits. Interfluve areas may exhibit subtle beach ridges. Geomorphologic evidence suggests that during the forced regression, the landscape stepped down continuously and subtly towards the coast and into drainages.

Geological Society of America Abstracts with Programs. Vol. 50, No. 3

doi: 10.1130/abs/2018SE-311987

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