Marl Pit, Middletown, DE
Minerals/Soils/Coastal Plain Geology
Field Collecting Trip
[Postponed due to weather until May 26, 2018]
Where: Marl Pit, Middletown, DE
When: May 19, 2018: Marl Pit, Middletown, DE, 9:00 am to 1:00 pm
Rain delay or work delay, then
Sunday, May 20, 2018, 10:00am to 2:00pm
Contact: Tom Pankratz
Email me if you are interested in attending this trip. I’ll return a
confirmatory email. If you do not receive my confirmation, please
re-contact me. tjpankratz@verizon.net
Details
This is a working quarry so Monday’s through Friday are unavailable,
and if they have to work on Saturday, we'll rescheduled to Sunday. Though the starting time is
9am, you can arrive any time after 9 that you choose.
This trip is open to members of all ages. I think it’s a
particularly family-friendly site.
The site is called a ‘marl’ pit. Marl is a lime-rich (calcium
carbonate) mud or mudstone which contains variable amounts of clay
and silt. I do not know if this site really has, or ever has had,
marl of this definition. To me it looks mostly to be a sandy clay.
DGS Geosymposium 2017 Fieldtrip Guide.pdf
Two things make this site interesting. One is that it gives us a
rather rare look at the Delaware Coastal Plain. We’ve all travelled
over the coastal plain and even collected fossils at the canal and
by Odessa, but we’ve only really seen the topsoil, and then that’s
mostly covered with vegetation. Rarely do we get to see the
stratification caused by periodic oceanic flooding or the ice age
floods. I don’t really know which this site is due to. That it’s a
‘marl’ with calcium carbonate makes me think oceanic, but the
absence of fossils and the presence of a lot of river rounded rocks
makes me suspect ‘ice age’ floods. These rocks are the other thing
that makes this site interesting. Their variety is quite amazing and
I suspect just about every kind of rock in the greater Delaware
River drainage basin is here in stratified layers. The other ‘rock’
that’s most prevalent is ‘bog iron’. These layers are inches to
perhaps a foot or so thick and consists of a mix of goethite,
hematite and limonite iron oxide rocks with a variety of
configurations and colors. Very collectable! There may even be some
‘Indian Paintpots’ in the mix.
The site is easy to get into and we can drive right up to the
collecting and viewing areas. The quarry walls that are being
actively mined are perhaps 20 to 30 ft. high and consists of pretty
loose sand and clay..we’ll want to stay well back from these. But
elsewhere in the quarry the walls have been heavily eroded by
rainfall and we can safely walk and climb up and down them.
There are quite a few ‘rain wash gullies’ in these walls. Vegetation
cover is minimal in most places.
Safety:
Hard hats, safety vests and long pants are required for everybody.
Safety glasses are required if you are breaking rocks
Boots or ankle high shoes are required (safety boots are not
required; no open toe or heel shoes please)
Collecting equipment:
The soil is soft and easy to dig. Shovels, picks, screens, perhaps a
light weight hammer should be useful. I don’t think you find use for
sledge hammers, chisels or rock-busting equipment. Buckets and
wagons/hand carts will be useful.
I took and edited the following from the Delaware Geologic Survey
website:
The State of Delaware is located within two physiographic provinces,
the Appalachian Piedmont and the Atlantic Coastal Plain. Most of the
state lies within the Coastal Plain; it is only the hills of
northern New Castle County that lie within the Piedmont.
The rocks at the surface in the Piedmont are old, deformed,
metamorphic rocks that were once buried in the core of an ancient
mountain range. This range formed in a series of tectonic events
that built the Appalachians between about 543 and 250 million years
ago. All through that time and since, rivers and streams have
carried the erosional products, mostly sand, clay, and gravel, from
the mountains onto the Atlantic Coastal Plain.
Liability Waiver:
Please print, read, and sign the Liability
Waiver, and give it to Tom Pankratz at the site. Family members may
sign the same waiver. Marl Pit Liability Waiver
(PDF)
Fall Line
Delaware’s Piedmont ends at the Fall Line where the metamorphic
rocks dip under and disappear beneath the sediments of the Coastal
Plain. The Fall Line roughly follows Kirkwood Highway, Route 2,
across the state between Newark and Wilmington.
Atlantic Coastal Plain
Delaware’s Coastal Plain rises to about 100 feet above sea level.
Its streams drain into the Delaware River or Bay, and for much of
their length they are tidal. The Coastal Plain is made up of
sediments, mostly silt, sand, and gravel, that have been eroded off
the Piedmont and adjacent Appalachian Mountains. In cross section
these sediments form a southeastward thickening wedge that increases
from 0 feet at the Fall Line to over 10,000 feet along Delaware’s
coast.
During the time represented by this unconformity, the rocks we see
in the Piedmont today reached the earth’s surface as approximately 7
to 13 miles of overlying rock were removed by erosion allowing the
buried rocks to rise to the surface in compensation. The oldest
Coastal Plain sediments observed in Delaware are river-deposited
sediments. These sediments were eroded from the Appalachian
Mountains to the west, transported to the southeast by rivers, and
deposited where the rivers met the ocean to form a delta. On top of
the river sediments a sequence of marine silt and sand deposits
records the rise and fall of the sea level many times during a
period of over 80 million years, from the Late Cretaceous until the
end of the Tertiary Period, about 2 million years ago.
On top of all of these sediments is a thin veneer of young sand and
gravel that was carried into Delaware by glacial outwash during the
Ice Age. Glacial ice did not advance into Delaware, but melt-water
pouring off the glacier fronts carried great quantities of sand,
silt, and gravel over southern Pennsylvania and Delaware. Delaware’s
largest mineral resource is the sand and gravel deposited from the
glacial outwash.
Make yourself at home.