Georgia's Fall Line -
Mesozoic Era Sedimentary Rocks &
Paleozoic Era Metamorphic Rocks
Tan and white layers of Mesozoic Era Period Pio Nono Formation
in Georgia's Coastal Plain Province.
Disconformity between upper, tan conglomerate and lower, white
sandstone units of the Pio Nono Formation. Erosional surface
and abrupt change in lithology (sandstone to conglomerate)
indicate disconformity. Time gap represented is probably
not very great, however, because both units are Cretaceous
Weathered gneiss exposed just beneath the Pio Nono Formation.
By definition, this is a nonconformity (sedimentary rocks
on top of metamorphic rocks). The origianl black bands
within the gneiss have undergone oxidation to hematite,
so they are now red.
Note that the foliation of the gneiss is nearly vertical,
in stark contrast to the origianl, horizontal layering
of the overlying Pio Nono Formation sedimentary rocks.
North of the fall line, only metamorphic rocks (more gneisses
& schists) and plutonic igneous rocks (such as Stone Mountain
Granite, pictured) are present, composing Georgia's
South of the fall line, only sediments and sedimentary rocks
(such as the Pio Nono Formation sedimentary rocks) are present,
composing Georgia's Coastal Plain.
Return to GEOL 1122 Home Page