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mining. To understand, predict and identify the geologic formations that act as aquifers, sources for economically valuable deposits, or pollution pathways, the geologic framework must be described. As a research geologist and field mapper at the
NCGS, this is my job—to characterize the geologic framework of the Coastal Plain,
to discover what lies beneath a flat, nearly featureless landscape.
Another reason to study landforms and stratigraphy on the Coastal Plain is to
predict areas that may be subject to geologic hazards. The main geologic hazard that
impacts the Coastal Plain is flooding. Flooding is short-term and seasonal but
includes coastal storm surges originating on the oceanside and migrating up rivers,
riverine floods moving downstream along drainages towards the coast, and ponding
water that forms temporary lakes on uplands after significant rainfall events.
Flooding, of course, affects the youngest, active landforms, such as modern-day
barrier islands, salt marshes, swamps, river channels and point bars, and low-lying
terraces. What isn’t commonly known is that the older higher upland terraces with
their subtle, natural bowl-like configurations (like New Orleans during Hurricane
Katrina) may turn into lakes after significant rain fall events, causing widespread
flooding of farms, homes, and communities, in areas that are not directly connected
to the sea or rivers. During floods, landforms erode, and sediment is redeposited
elsewhere; inlets may open or close; channels may be cut or move; stream banks
may retreat; the oceanside shoreline may migrate inland. The impacts of long-term
flooding caused by sea-level rise will be even more devastating, as low-lying coastal
and riverine terraces that are currently dry land will be gradually inundated—permanently, on human time scales! Geologic maps based on landforms can be used
for strategic planning to define potentially hazardous, unsafe areas for living, and
potentially safe, stable areas that can support new economic development.
The Location of My Geological Field Work –
The Mid- Atlantic Coastal Plain
The Coastal Plain of eastern North Carolina is the emerged, landward portion of the
Atlantic continental shelf (Fig. 9.1). This landscape consists of low-relief, flat, eastward dipping marine terraces that are dissected by a series of river drainages. Its
surface is underlain by a seaward-thickening wedge of Cretaceous (145–66 million
years old) and Cenozoic (66 million years old to modern) rock and sediment that
thins westward to a feather edge along the Fall Line, the boundary of the Coastal
Plain with the adjacent, more-resistant to weathering, crystalline and metamorphic
bedrock of the Piedmont Province. The Coastal Plain wedge of sediment attains a
maximum known on-land thickness of about 3048 m (10,000 ft) beneath Cape
Hatteras (Fig. 9.1). Offshore from the Cape, greater thicknesses of sediment have
likely accumulated (7–10 km! or ~ 3–6 miles!) and underlie the offshore continental
shelf and rise; it is these deeper strata that may contain petroleum resources.
9 Drilling the North Carolina Coastal Plain – Discovering What Lies Beneath
mining. To understand, predict and identify the geologic formations that act as aquifers, sources for economically valuable deposits, or pollution pathways, the geologic framework must be described. As a research geologist and field mapper at the
NCGS, this is my job—to characterize the geologic framework of the Coastal Plain,
to discover what lies beneath a flat, nearly featureless landscape.
Another reason to study landforms and stratigraphy on the Coastal Plain is to
predict areas that may be subject to geologic hazards. The main geologic hazard that
impacts the Coastal Plain is flooding. Flooding is short-term and seasonal but
includes coastal storm surges originating on the oceanside and migrating up rivers,
riverine floods moving downstream along drainages towards the coast, and ponding
water that forms temporary lakes on uplands after significant rainfall events.
Flooding, of course, affects the youngest, active landforms, such as modern-day
barrier islands, salt marshes, swamps, river channels and point bars, and low-lying
terraces. What isn’t commonly known is that the older higher upland terraces with
their subtle, natural bowl-like configurations (like New Orleans during Hurricane
Katrina) may turn into lakes after significant rain fall events, causing widespread
flooding of farms, homes, and communities, in areas that are not directly connected
to the sea or rivers. During floods, landforms erode, and sediment is redeposited
elsewhere; inlets may open or close; channels may be cut or move; stream banks
may retreat; the oceanside shoreline may migrate inland. The impacts of long-term
flooding caused by sea-level rise will be even more devastating, as low-lying coastal
and riverine terraces that are currently dry land will be gradually inundated—permanently, on human time scales! Geologic maps based on landforms can be used
for strategic planning to define potentially hazardous, unsafe areas for living, and
potentially safe, stable areas that can support new economic development.
The Location of My Geological Field Work –
The Mid- Atlantic Coastal Plain
The Coastal Plain of eastern North Carolina is the emerged, landward portion of the
Atlantic continental shelf (Fig. 9.1). This landscape consists of low-relief, flat, eastward dipping marine terraces that are dissected by a series of river drainages. Its
surface is underlain by a seaward-thickening wedge of Cretaceous (145–66 million
years old) and Cenozoic (66 million years old to modern) rock and sediment that
thins westward to a feather edge along the Fall Line, the boundary of the Coastal
Plain with the adjacent, more-resistant to weathering, crystalline and metamorphic
bedrock of the Piedmont Province. The Coastal Plain wedge of sediment attains a
maximum known on-land thickness of about 3048 m (10,000 ft) beneath Cape
Hatteras (Fig. 9.1). Offshore from the Cape, greater thicknesses of sediment have
likely accumulated (7–10 km! or ~ 3–6 miles!) and underlie the offshore continental
shelf and rise; it is these deeper strata that may contain petroleum resources.
9 Drilling the North Carolina Coastal Plain – Discovering What Lies Beneath