Transcript Georgia Geology Notes

Georgia Geology Notes – 4 Provinces
Valley & Ridge*
Blue Ridge
Piedmont
Fall Line
Coastal Plain
*Some authors include part of the Appalachian
Plateau with the Valley & Ridge Province, while
others combine the Blue Ridge & Piedmont.
2
100 m.y. to 8,000 – Late
Cretaceous to Holocene
– Coastal Plain
220 m.y. to 190 m.y. –
Diabase Dikes
545 m.y. to 286 m.y. –
Cambrian – Pennsylvanian
Periods (Valley & Ridge)
1.1 b.y. to 360? m.y. –
Precambrian –
Devonian? (Blue
Ridge & Piedmont)
Geologic
Time Scale
3 Valley & Ridge Province – (incl.
Appalachian Plateau)
• Cambrian – Pennsylvanian folded
& faulted sedimentary rocks (544
to 286 m.y.)
• Fracture and karst aquifers
• Bounded by Cartersville and Great
Smoky Mt. faults
• Alternating anticlines & synclines,
thrust faults
• Cambrian – Ordovician sediments
deposited on passive margin.
Limestones, shales, sandstones.
• Ordovician – Pennsylvanian –
mostly clastics derived from rising
highlands. Sandstones, shales,
coal (Pennsylvanian Period)
Adapted from Ga.
Geologic Survey state
geologic map, 1977
4 Four Major Events in Appalachian History –
Late Precambrian – Iapetus Ocean rifting
Late Ordovician Period – Taconic Orogeny
Late Devonian Period – Acadian Orogeny
Pennsylvanian Period – Alleghenian Orogeny
Taconic Orogeny –
Shallow marine conditions
collision of Island Arc
& Laurentia continent
uplifted mountain
Foreland Basin
range “Taconic
Highlands”. Erosion of
highlands produced a
series of
northwestward
prograding “clastic
wedges” (river deltas).
Later orogenies
rejunvenated uplands.
Taconic Highlands
5 Interbedded shales and limestones, Ordovician
Lexington Ls., Kentucky. Similar rock types are
present in Valley and Ridge Province of NW Ga. ,
suggest passive margin deposition with a distant
clastic source.
6 Blue Ridge Province –
• Precambrian –
Devonian(?) igneous and
metamorphic rocks –
includes phyllites,
schists, gneisses,
metabasalts, other
metavolcanics, marble,
quartzite
• Fracture aquifers, except
for a few karst aquifers –
Murphy Syncline
• Highest topography in
Georgia – 28 peaks >
4,000 ft.
Combined Blue Ridge &
Piedmont geologic map
Piedmont Province – similar to Blue Ridge, except
topography is lower and there are more igneous rocks –
Pennsylvanian-aged granites & Triassic/Jurassic-aged
diabase dikes.
7
Piedmont & Blue Ridge features
Etowah River cave
Deformed gneiss on Ronald
Reagan Parkway
Triassic/Jurassic diabase (basalt) dike – Vulcan
quarry, Beaver Ruin Rd./I-85
Appalachian Mountains – a quick summary
Late Precambrian (600 m.y.) – Rifting of supercontinent, opening of Iapetus Ocean.
Late Ordovician (450 my.) – Island arc collision
with North America – Taconic Orogen y
Clastic wedges accumulate NW of Taconic
Highlands.
Late Devonian (410 to 380 m.y.) – Collision of
Baltica and North America – Acadian
Orogeny
Late Pennsylvanian (320 m.y.) – Collision of
N.A. with Africa, final deformation & uplift.
Stone Mt. and other granites emplaced – 300
m.y..
10 Fall Line – separates crystalline rocks of
Piedmont from present extent of softer
sediments of Coastal Plain.
Fall Line Cities – Columbus, Macon, Augusta
Marked by waterfalls and rapids.
Piedmont may have been partially covered by
Eocene and Oligocene transgressions (sea level
rises). Shoreline may have been low ridge of
Brevard Fault Zone. Evidence eroded away.
Coastal Plain Province –
Late Cretaceous to Holocene (Recent) deposits
at shoreline. Age – 70 m.y. - >10,000 yr.
Layered sediments, sands, clays, limestones.
Late Cretaceous sediments – mostly deltaic,
including Providence Sand.
Paleocene – Oligocene sediments – mostly
marine.
Miocene – Holocene – mostly continental
deltaic, fluvial and alluvial sediments,
except near coast.
Aquifers – uniform sediments, a few karst
wells.
Residuum of Paleocene Clayton Fm. over deltaic
Cretaceous Providence Sand
Resources
Valley & Ridge Province
Oil & Natural gas (other states), Coal,
Limestone, Barite.
Blue Ridge Province
Marble, minerals in pegmatites, Gold, Sulfide
minerals (including Copper), Talc, Corundum.
Piedmont Province
Granite, minor Gold, Copper, Feldspar,
minerals in pegmatites, minor Marble.
Coastal Plain
Limestone, Kaolin, Bauxite, Sand.
Georgia Geology Notes - Review
Valley and Ridge Province
Hard, compacted Paleozoic sedimentary rocks,
folded and faulted during uplift of Appalachian Mts.
Blue Ridge Province
Hard, Precambrian to Paleozoic metamorphic
rocks, folded, faulted, and metamorphosed during
uplift of Appalachian Mts.
Piedmont Province
Hard, Precambrian to Paleozoic metamorphic and
igneous rocks, similar to Blue Ridge Province.
Coastal Plain Province
Soft, uncompacted Late Cretaceous through
Cenozoic sediments, layers inclined gently toward
Atlantic Ocean and Gulf of Mexico (SW Ga.)
Georgia Geology Notes -
Groundwater Resources
Valley & Ridge Province –
Fracture zones, karst features (caverns,
enlarged fractures)
Blue Ridge Province –
Fracture zones, karst features (in Marble)
Piedmont Province –
Fracture zones
Coastal Plain Province –
More uniform aquifers (softer sand,
limestone, karst features – Regional
Floridan aquifer – Georgia and Florida.
Georgia Geology Notes -
Geology and Ecology
• Geologic structures affect topography and
stream channel distribution
• Rock types influence soil type
• Soil type influences nature of rainfall infiltration
• Soil type and topography influence vegetation
types
• Hardness of rock influences type of porosity
and permeability and aquifer types
• Topography influences climate and
microclimate
• Rock type influences chemistry and pathways of
ground water
Early Paleozoic Era Continental Shelf,
preserved as Early Cambrian – Middle
Ordovician (545 to 430 m.y.) sedimentary
rocks – Valley & Ridge Province
Rifted continental
margin – approx.
1.1 b.y.
Iapetus Ocean opening until Early
Ordovician Period
Initial collision of N. America (Laurentia) &
Island Arc System (Taconic Orogeny)
downwarped continental margin – created
Foreland Basin & Taconic Highlands.
Inland Sea to Northwest (mostly limestones)
Taconic
Highlands
Foreland Basin
Present-day Appalachian (Cumberland)
Plateau (left side) & Valley & Ridge Province
– folded, thrust-faulted Paleozoic Era
sedimentary rocks.
Compression during Continental Collisions
Change from passive margin to clastic
wedge is recorded in Taylor Ridge roadcut
on I-75 N @ Ringgold, GA.
Photo by P. Bouker
Late Mesozoic/Early Cenozoic Era
Continental Shelf, preserved as Late
Cretaceous – Recent sediments – Coastal
Plain Province
Continental Shelf deposits
Rifted continental
margin – eroded
Appalachian Mts.
Atlantic Ocean opening began during Late
Triassic Period
Valley &
Ridge
Fall Line
Coastal
Plain
Atlantic
Ocean
Blue Ridge &
Piedmont
Igneous &
Metamorphics