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Open-File Report 2008–1005

## Geomorphic Map of Worcester County, Maryland, Interpreted from a LIDAR-Based, Digital Elevation Model 

By Wayne L. Newell and Inga Clark 

| PDF Open-File Report 2008-1005 (896 KB, 34 pages)PDF Plate l - Geomorphic Map of Worcester County, Maryland (59,751 KB 1 page)PDF Plate ll - Geomorphic Map of Snow Hill (41,655 KB 1 page) |   | Abstract
A recently compiled mosaic of a LIDAR-based digital elevation model (DEM) is presented with geomorphic analysis of new macro-topographic details. The geologic framework of the surficial and near surface late Cenozoic deposits of the central uplands, Pocomoke River valley, and the Atlantic Coast includes Cenozoic to recent sediments from fluvial, estuarine, and littoral depositional environments. Extensive Pleistocene (cold climate) sandy dune fields are deposited over much of the terraced landscape. The macro details from the LIDAR image reveal 2 meter-scale resolution of details of the shapes of individual dunes, and fields of translocated sand sheets. Most terrace surfaces are overprinted with circular to elliptical rimmed basins that represent complex histories of ephemeral ponds that were formed, drained, and overprinted by younger basins. The terrains of composite ephemeral ponds and the dune fields are inter-shingled at their margins indicating contemporaneous erosion, deposition, and re-arrangement and possible internal deformation of the surficial deposits. The aggregate of these landform details and their deposits are interpreted as the products of arid, cold climate processes that were common to the mid-Atlantic region during the Last Glacial Maximum.

In the Pocomoke valley and its larger tributaries, erosional remnants of sandy flood plains with anastomosing channels indicate the dynamics of former hydrology and sediment load of the watershed that prevailed at the end of the Pleistocene. As the climate warmed and precipitation increased during the transition from late Pleistocene to Holocene, dune fields were stabilized by vegetation, and the stream discharge increased. The increased discharge and greater local relief of streams graded to lower sea levels stimulated down cutting and created the deeply incised valleys out onto the continental shelf. These incised valleys have been filling with fluvial to intertidal deposits that record the rising sea level and warmer, more humid climate in the mid-Atlantic region throughout the Holocene. Thus, the geomorphic details provided by the new LIDAR DEM actually record the response of the landscape to abrupt climate change. 

Holocene trends and land-use patterns from Colonial to modern times can also be interpreted from the local macro- scale details of the landscape. Beyond the obvious utility of these data for land-use planning and assessments of resources and hazards, the new map presents new details on the impact of climate changes on a mid-latitude, outer Coastal plain landscape. 
For more information concerning the report, please contact the author.
 
Contents- Abstract
- Introduction
- Physiography
- Geologic Framework
- The LIDAR-based DEM Map of Worcester County, MD
Methods

- New Details of Geomorphology and Stratigraphic
Windblown sand sheets and dunes
Terraces
Areas of raised-rim basins
- The Raised-rim basin terrains include the following newly described attributes

Details of flood plains, tidal wetlands, and erosional remnants of braided channel deposits

- Pleistocene to Holocene Contrasts
- Geomorphic features on Pleistocense and Holocene Transgressive
- History of the landscape interpreted from sequence of cross cutting
- Summary
- References
Figures- 1.      Location of Worcester County on the Delmarva Peninsula between the Chesapeake Bay and the Atlantic Ocean
- 2.      A complilation of Surficial Geology from Figure 2 of Bricker and others, 2003
- 3a.    Cross section of stratigraphic details of Nassawango Creek flood plain alluvium down stream from gaging station (see  Plate 2)
- 3b.   Schematic diagram of geomorphology of flood plain along Nassawango Creek where bog iron deposits  occur
Tables- Depositional  environments  and relative  ages  of  surficial  deposits  in Worchester           County  from  outcrop and corehole  data  and cross  cutting  relationships

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