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Senior University Geology Field TripSenior University Geology Field Trip November 5, 2012 8:45 am – 4:30 pmNovember 5, 2012 8:45 am – 4:30 pm
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Georgetown’s Amazing Geologywith Don, Rocky, & Sandi
world famous rocks
Explore, Photograph, & Sample . . . . .
10, 000 years old black waxy glacial clays
modern perched water table
135 million year old Rudist reefs
45 million year old Balcones Fault
modern aquifers supplying our drinking water
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Our Travel Schedule
8:45 to 9:00 am8:45 to 9:00 am Briefing at The OaksBriefing at The Oaks9:10 to 9: 309:10 to 9: 30 STOP 1 - Perched water tableSTOP 1 - Perched water table
Berry Creek PondBerry Creek Pond9: 40 to 10:009: 40 to 10:00 STOP 2 - Black Waxy clays STOP 2 - Black Waxy clays
Walgreens, Williams DrWalgreens, Williams Dr10:15 to 10:3010:15 to 10:30 STOP 3 - Rudist reefsSTOP 3 - Rudist reefs
Lake Georgetown spillwayLake Georgetown spillway10:35 to 10:4010:35 to 10:40 STOP 4 - Reef in D.B. Woods road cutSTOP 4 - Reef in D.B. Woods road cut10:50 to 11:15 10:50 to 11:15 STOP 5 - Rudists and grassesSTOP 5 - Rudists and grasses
Wolf Ranch MallWolf Ranch Mall11:30 to 12:1511:30 to 12:15 STOP 6 - Buda limestone cliff & faultsSTOP 6 - Buda limestone cliff & faults
Celebration ChurchCelebration Church12:30 to 1:30 12:30 to 1:30 LUNCH – French Quarter Grill LUNCH – French Quarter Grill 2:00 to 4:00 2:00 to 4:00 STOP 7 - nner Space CavernSTOP 7 - nner Space Cavern 4:304:30 Return to Sun City Return to Sun City
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Definitions
Mineral: natural occurring constituent of all rocks
Limestone: sedimentary rock composed of the mineral CalciteShale: sedimentary rock composed of one or more Clay mineralsSandstone: sedimentary rock composed of the mineral quartz
Ground water: rain water filling rock voidsWater table: top of the ground waterAquifer: rock containing fresh water that can be recovered in a well
Normal fault: fracture in bed rock with measurable displacement
Stromatolites: Shallow water blue-green algae deposits
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Briefing at The Oaks, Sun City
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Age of the Rocks that we saw
Cretaceous Period
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Edwards Limestone 380 feet
Georgetown Limestone 100 feet
Del Rio Shale 60 feet
Buda Reef 60 feet
Eagleford Shale 120 feet
Glen Rose Limestone 400 feet
Ouachita Mountain complex folds and thrust faults
Upper Dense limestone 30 feet
Reef & Reef debris aquifer limestone 100 feet
Comanche Peak limestone 50 feet
Upper Walnut limestone 100 feet
Lower Walnut limestone 100 feet
Trinity sandstone aquifer0 to 100 feetTrinity sandstone 0 to 100feet
Rocks at the surface in Sun City
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Geography when our limestones were formed about 115 million years ago
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Berry Creek not eroded this deep
Rocks Exposed at Sun CityRocks Exposed at Sun City
missing by erosio
n
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Buda Lim
esto
ne cl
iff
Flin
t
Springs
Geological Cross Section Williamson County, Texas
Coman
che
Peak
Cliff
Sun City
outc
rop
Edwar
ds re
ef re
char
ge
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Bryozoa (sea moss) Stromatolites (Algae) Brachiopods (symmetrical shells)
Pelecypods (clams)(asymmetrical shells) Cephalopods & Ammonites
Gastropods (snails)
Corals
Fossils you may have stumbled over
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On the road . . .
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at Berry Creek PondStop 1 - Perched Water Table
Why is the water here?
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Pavilion at Berry Creek Pond
Reef
Berry Creek Pond (stock tank)
Village CenterWilliams Dr. Gate
Reef water filled=a perched water tableReef water filled=a perched water table
Stop 1 - Perched Water Table
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Stop 2: Holding pond at Walgreens on Williams Dr
Why is
the water
here?
. . .the base of the pond is on impervious limestone!
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Stop 2: Waxy Clay on weathered Georgetown LimestoneWalgreens on Williams Dr
What’s the black surface dirt?
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black waxy clayblack waxy clay
weathered Georgetown limestone
un-weathered Georgetown limestone
Stop 2: Waxy Clay on weathered Georgetown LimestoneWalgreens on Williams Dr
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Stop 2: Waxy Clay on weathered Georgetown Limestone
10,000 year old black waxy clays
weathered & eroded from Rocky Mountains
in New Mexico
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Stop 3: layered limestone with rudist reefs
Lake Georgetown Spillway
What rocks are these?
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Stop 3: layered limestone with rudist reefslayered limestone with rudist reefsLake Georgetown Spillway
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Stromatolites cap layer
Stromatolite layer
Lake Georgetown Spillway North Rock Wall
Eoradiolites Rudist Debris Bank
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Rudist Reef-forming Sea Shells
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Lake Georgetown Rudists
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Rudists: the exotic mound-building Rudist Clams that became extinct at the end of the Cretaceous
Length: 6 inches to 3 feet!
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WHAT IS A RUDIST REEF?
A clam-like colonial (successive generations build on top of each other giving the reef vertical strength that minimizes compaction of the reef when buried). The rudist sea shell is shaped and sized like an inverted old fashioned glass Coke bottle. They occur in the Cretaceous Period 145 to 65 million years ago and are the equivalent of corals of today and other geological Periods.
The rudist fossil is the “limestone” shell of the marine organism and it is very delicate so it often weathers-out leaving a round hole.
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Stromatolites: blue green algae
Modern Stromatolites Stromatolites preserved as rocks
Stromatolites grow in shallow water
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Stop 3: layered limestone with rudist reefs
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Stop 3: layered limestone with rudist reefs
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Stop 3: layered limestone with rudist reefs
Lake Georgetown Spillway
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D. B. Woods Road - reef outcrop
Stop 4: Limestone Reef Outcrop Road Cut, D.B. Woods Road
Why are these layers curved?
. . . the reef ‘matrix’ resists compression from the rock layers above, maintaining its shape
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Stop 5: rudist fossils in country rock, Texas grasses
Wolf Ranch Shaded Walk
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Stop 6: Eagle Ford gas source rock, Buda cliff, Texas Crushed Stone Quarry, Balcones Faults
Celebration Church Overlook
Where’s the Balcones Fault?
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UpUp
Down
Down
Inner SpaceCavern
Celebration overlook
Balcones FaultsBalcones Faults
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Note: Black Waxy
Inner SpaceCavern
Celebration overlook
Balcones FaultsBalcones Faults
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Lunch: French Quarter Grill: Round Rock
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Stop 7: Inner Space Cavern Tour
Balcones Fault
Flint
Dolomite
Limestone
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ROCKS OF THE INNER SPACE CAVERNS
- Limestone is the original rock type which when buried can have the Ca partially replaced by Mg due to the movement of fluids being expelled by compaction of the whole rock column creating dolomite. - Dolomite does not “fizz” in acid until you scratch it into a powder, then if “fizzes”. Otherwise, it look just like limestone. - Flint is silicon dioxide and is thought to be the silicon dioxide of sponge quills called spicules sort of like the quills of a porcupine, but a marine animal that shared the reef with the Rudists and other reef organisms. The thin, discontinuous flint layers are thought to be formed when a storm swept a number of individual sponges off the reef and deposited their dead bodies in a “quiet” place out of the way of the waves and tides. Since the spicules become plastic as the organic sponge bodies decay, the plastic layers of flint during burial and compaction are often squeezed into “lumpy” and discontinuous “blobs”..
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The end of a perfect day!!!
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Self-drive Field Stop
The next 4 slides describe a self-drive field stop that you could do with family or friends. The destination is Blue Hole City Park in Georgetown.
On the drive from Wolf Ranch Shopping Center to the park, you will cross the Balcones Fault just eastof Interstate 35.
At Blue Hole Park, rudist fossils in the Edwards Limestone are visible on the rock outcrop (rock face). Enjoy!!
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Self-drive Field Stop: Blue Hole City Park Balcones Faults & Edwards Limestone Rudist Reef
University Blvd
Wolf Ranch
Blue Hole Park
Austin Ave
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Self-drive Field Stop @ Blue Hole Park: Balcones Fault
Up Down
Blue Hole Park
University Blvd
Austin Ave
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Self-drive Field Stop @ Blue Hole Park: Balcones Fault
Up Down
Blue Hole Park
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Self-drive Field Stop @ Park: Edwards Rudist Reef