Day 4: June 12
We are continuing to see high quality results from the survey. We have strong reflections from signature layers far beneath us such as the Midway
Group (a.k.a. Porters Creek Clay). The Midway Group is the bottom unit to what we term the Tertiary section. This section begins ~250 ft beneath Memphis and extends downward to approximately
2400 ft below ground surface (~2200 ft thick). It is composed of sand and clay layers, the most important of which is a thick sandy
layer called the Memphis aquifer from where Memphis draws its drinking water.
At around 2400 to 3000 ft below ground surface we see reflections off the Cretaceous
contact. This is primarily a limestone deposit. In Tennessee, we see this outcrop (come up to the surface) at the TN River. Once this limestone is exposed to surface processes like rainfall infiltration, the
rock is s..l..o..w..l..y dissolved creating solution channels or caves. Blanchard Springs Caverns is a great nearby cavern in AR.
Further down at 3400 to 4000 ft we see faint signatures of the Paleozoic rocks. This
is about as far down as we can see with confidence. Our energy source discharges
15 in3 of air. In the ocean, the oil and gas industry use groups of energy sources that
can discharge more than 6000 in3 of air. Now that’s a lot of compressed air.