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landscape of the Coastal Plain into landforms, define the Quaternary (the last
2.58 million years) layers that underlie these landforms, and then group layers with
similar sedimentary properties into formations, which are the fundamental units
shown on geologic maps. I use two principal scientific techniques to make geologic
maps of the Coastal Plain: (1) remote sensing to interpret landforms from satellite
images and LiDAR elevation data, and (2) geologic core drilling to discover the
rocks or sediment that underlie the landforms. LiDAR, an acronym for Light
Detecting and Ranging, is an airborne surveying method, that uses laser light to collect elevation data. Remote sensing and geologic cores used together can help define
rock and sediment properties across broad areas of the Coastal Plain. And geologic
coring is one of the most interesting and rewarding endeavors for a working field
geologist because the core itself provides a window into hundreds to thousands to
millions of years of dynamic landscape evolution and Earth history that otherwise
would remain invisible to us humans who inhabit the Earth’s surface.
Several reasons drive us to study the stratigraphy and landforms of the North
Carolina Coastal Plain. In particular, geologists need to locate water resources, find
oil and gas reserves, discover economically valuable minerals and construction
materials, and identify areas subject to geologic hazards. We need the cores to
ground-truth the geology in areas where the underlying stratigraphy simply cannot
be viewed at the Earth’s surface.
The sediments and rocks beneath us provide the plumbing for fluids, such as
water, oil, and gas, to move through the Earth or to be stored underground in natural
holes or pore spaces. If pore spaces are connected, permeable conditions exist, and
fluids can move freely along underground pathways or conduits. The size of pore
space can range from very large caves that form in limestones to very small pores
between individual sand grains. Limestones may include vast networks of interconnected pore space because the rock dissolved from contact with subterranean acid
waters. In fact, some limestones include caves with flowing underground streams.
The ~40 million year-old Castle Hayne Limestone is an example of a partly dissolved permeable limestone that functions as the main aquifer that supplies clean
water for eastern North Carolina. In other Coastal Plain deposits, sands and gravels
also act as aquifers, but these store and transmit water through small pores between
grains. Impermeable strata such as muds and clays may act as confining units to trap
water and seal it in underground aquifers. Similar geologic conditions can also trap
oil and gas in underground ‘reservoirs’, that are natural underground holding tanks.
Pollutants originating at the ground surface can also move downward through the
geologic plumbing, mix with clean water and degrade its quality, and migrate outward through permeable strata, carrying contaminants far afield.
In addition to subterranean fluids, Coastal Plain deposits may contain other economically valuable resources. Gravels, sands and limestones are useful for construction; minerals such as titanium are needed for manufacturing steel, paint and
other products; and phosphorus-rich minerals are used to make fertilizer. While
mapping and drilling across eastern North Carolina, I routinely encounter ancient
beach deposits that contain heavy mineral sands, beds of phosphate nodules, and
large amounts of sand and gravel under river terraces, that may be suitable for
K. M. Farrell
landscape of the Coastal Plain into landforms, define the Quaternary (the last
2.58 million years) layers that underlie these landforms, and then group layers with
similar sedimentary properties into formations, which are the fundamental units
shown on geologic maps. I use two principal scientific techniques to make geologic
maps of the Coastal Plain: (1) remote sensing to interpret landforms from satellite
images and LiDAR elevation data, and (2) geologic core drilling to discover the
rocks or sediment that underlie the landforms. LiDAR, an acronym for Light
Detecting and Ranging, is an airborne surveying method, that uses laser light to collect elevation data. Remote sensing and geologic cores used together can help define
rock and sediment properties across broad areas of the Coastal Plain. And geologic
coring is one of the most interesting and rewarding endeavors for a working field
geologist because the core itself provides a window into hundreds to thousands to
millions of years of dynamic landscape evolution and Earth history that otherwise
would remain invisible to us humans who inhabit the Earth’s surface.
Several reasons drive us to study the stratigraphy and landforms of the North
Carolina Coastal Plain. In particular, geologists need to locate water resources, find
oil and gas reserves, discover economically valuable minerals and construction
materials, and identify areas subject to geologic hazards. We need the cores to
ground-truth the geology in areas where the underlying stratigraphy simply cannot
be viewed at the Earth’s surface.
The sediments and rocks beneath us provide the plumbing for fluids, such as
water, oil, and gas, to move through the Earth or to be stored underground in natural
holes or pore spaces. If pore spaces are connected, permeable conditions exist, and
fluids can move freely along underground pathways or conduits. The size of pore
space can range from very large caves that form in limestones to very small pores
between individual sand grains. Limestones may include vast networks of interconnected pore space because the rock dissolved from contact with subterranean acid
waters. In fact, some limestones include caves with flowing underground streams.
The ~40 million year-old Castle Hayne Limestone is an example of a partly dissolved permeable limestone that functions as the main aquifer that supplies clean
water for eastern North Carolina. In other Coastal Plain deposits, sands and gravels
also act as aquifers, but these store and transmit water through small pores between
grains. Impermeable strata such as muds and clays may act as confining units to trap
water and seal it in underground aquifers. Similar geologic conditions can also trap
oil and gas in underground ‘reservoirs’, that are natural underground holding tanks.
Pollutants originating at the ground surface can also move downward through the
geologic plumbing, mix with clean water and degrade its quality, and migrate outward through permeable strata, carrying contaminants far afield.
In addition to subterranean fluids, Coastal Plain deposits may contain other economically valuable resources. Gravels, sands and limestones are useful for construction; minerals such as titanium are needed for manufacturing steel, paint and
other products; and phosphorus-rich minerals are used to make fertilizer. While
mapping and drilling across eastern North Carolina, I routinely encounter ancient
beach deposits that contain heavy mineral sands, beds of phosphate nodules, and
large amounts of sand and gravel under river terraces, that may be suitable for
K. M. Farrell