The term
karst describes a distinctive topography that indicates dissolution
(also called chemical solution) of underlying soluble rocks by
surface water or ground water. Although commonly associated with
carbonate rocks (limestone and dolomite) other highly soluble rocks
such as evaporates (gypsum and rock salt) can be sculpted into
karst terrain.
Precipitation infiltrates into the soil and flows
into the subsurface from higher elevations and generally toward a
stream at a lower elevation. Weak acids found naturally in rain and
soil water slowly dissolve the tiny fractures in the soluble
bedrock, enlarging the joints and bedding
planes.
One of the ways that springs are classified is by the volume of
the water they discharge. Many springs are measured regularly,
while some have never been measured. The largest springs are called
"first-magnitude," defined as meaning they discharge at least 100
cubic feet of water per second (cfs), or about 64.6 million gallons
per day (mgd).
The scale for spring flow is as follows:
- 0 Magnitude - no flow (sites of past/historic flow)
- 1st Magnitude - > 100 cubic feet per second (cfs)
- 2nd Magnitude - 10 -100 cfs
- 3rd Magnitude - 1 - 10 cfs
- 4th Magnitude - 100 gal/min (gallons per minute) - 1 cfs (448
gal/min)
- 5th Magnitude - 10 to 100 gal/min
- 6th Magnitude - 1 to 10 gal/min
- 7th Magnitude - 1 pint to 1 gal/min
- 8th Magnitude - Less than 1 pint/min
ECONOMIC GEOLOGY
ORDOVICIAN
Carbonate rocks of Middle Ordovician age are the second most
important sources of crushed stone for aggregates and agricultural
limestone in the State. Rock dust for coal mines is sometimes a
byproduct. Brought to or near the surface by the broad uplift of
the Cincinnati arch, the Lexington Limestone, Tyrone
Limestone, Oregon Formation, and Camp Nelson Limestone are the
principal sources of construction aggregate south of the Ohio River
in central Kentucky. Although the Tyrone, Oregon, and Camp Nelson
(High Bridge Group) are naturally exposed only along the deeply
incised valleys of the Kentucky River and its tributaries, detailed
examination of widely spaced cores suggests that large reserves of
industrial limestones are present at minable depths in the central
Kentucky area (Dever, 1981). Along the Ohio River in north-central
Kentucky, lime is being produced from the Camp Nelson Limestone
from two deep mines. One plant manufactures lime for use in
flue-gas desulfurization by coal-burning power-generating plants,
and the other plant makes high-calcium quicklime for steel-furnace
flux and chemical industries and hydrated lime for chemical
industries and water treatment.
Dolomitic limestone of the Oregon Formation and the Tyrone
Limestone were once used as building stones for central Kentucky
residences and commercial and public buildings. Because the dense,
finely crystalline dolomitic limestone of the Oregon Formation
could take a high polish, it was sometimes referred to in trade
circles as "Kentucky River marble."
Thin-bedded limestones of Late Ordovician age also were sources
of building stones in central Kentucky. Referred to by local
builders as "creekstone" and "fieldstone," these micrograined to
coarsely crystalline, locally fossiliferous gray limestones have
been used in a rough state for veneer, flagging, and numerous farm
fences. The beds of limestone are usually separated by partings or
layers of shale, thus allowing the stone to be obtained in thin,
irregular slabs. Stone came from dozens of small quarries,
creekbeds, and weathered slabs scattered across agricultural
land.
Ordovician rocks are also targets for oil and gas exploration.
Production has been obtained, principally in south-central
Kentucky, from stratigraphic correlatives of the Leipers and
Lexington Limestones and carbonates of the High Bridge
Group, as well as the deeper Knox Dolomite, which is not exposed at
the surface. (The deepest production in the State, in terms of both
depth and geologic age, is from a single well in Cambrian sandstone
at a depth of 7,598 ft in the Mavity Pool in Boyd County,
northeastern Kentucky.)
The outcrop of Middle Ordovician rocks coincides roughly with
the area referred to by some writers as the Central Kentucky
mineral district (Jolly and Heyl, 1964). Faults and related
fractures and joints associated with the Lexington and
Kentucky River fault systems are the focal points for numerous vein
deposits of barite, calcite, fluorite, galena, and sphalerite. The
veins are generally thin and the ore is commonly a mixed variety.
Limited mining has taken place. Very little mineralization has been
noted in rocks of Late Ordovician age in central and north-central
Kentucky, but a few mineral veins are exposed in Late Ordovician
carbonates on the Cumberland saddle portion of the Cincinnati arch
in south-central Kentucky.
Fertility of the residual soils in the Inner Bluegrass region is
enhanced by the presence of phosphate in the Lexington
Limestone. This area is the locale of the horse-farm industry
of central Kentucky. Phosphatic rock was mined on a small scale
approximately 60 years ago, but the deposits are limited and land
is more valuable for agricultural, industrial, and residential
uses.
Upper Ordovician strata of north-central Kentucky, particularly
the Kope Formation, contain soft, easily deformed shale.
Oversteepened slopes, artificial cuts, and highway fill containing
quantities of shale are subject to slump and sliding.
To log this cache:
1. Estimate, or collect and measure the rate of water flow from the
spring. What magnitude would you classify this spring?
2. At this karst landscape what type of rock is above the spring,
list the types you see.
3. Estimate the height and length of the rock outcropping above the
spring.
4. E-Mail me the answers, pictures of yourself with your GPSr are
appreciated and welcomed but not needed to
log.