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

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

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

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

Briefing at The Oaks, Sun City

Age of the Rocks that we saw

Cretaceous Period

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

Geography when our limestones were formed about 115 million years ago

Berry Creek not eroded this deep

Rocks Exposed at Sun CityRocks Exposed at Sun City

missing by erosio

n

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

Bryozoa (sea moss) Stromatolites (Algae) Brachiopods (symmetrical shells)

Pelecypods (clams)(asymmetrical shells) Cephalopods & Ammonites

Gastropods (snails)

Corals

Fossils you may have stumbled over

On the road . . .

at Berry Creek PondStop 1 - Perched Water Table

Why is the water here?

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

Stop 2: Holding pond at Walgreens on Williams Dr

Why is

the water

here?

. . .the base of the pond is on impervious limestone!

Stop 2: Waxy Clay on weathered Georgetown LimestoneWalgreens on Williams Dr

What’s the black surface dirt?

black waxy clayblack waxy clay

weathered Georgetown limestone

un-weathered Georgetown limestone

Stop 2: Waxy Clay on weathered Georgetown LimestoneWalgreens on Williams Dr

Stop 2: Waxy Clay on weathered Georgetown Limestone

10,000 year old black waxy clays

weathered & eroded from Rocky Mountains

in New Mexico

Stop 3: layered limestone with rudist reefs

Lake Georgetown Spillway

What rocks are these?

Stop 3: layered limestone with rudist reefslayered limestone with rudist reefsLake Georgetown Spillway

Stromatolites cap layer

Stromatolite layer

Lake Georgetown Spillway North Rock Wall

Eoradiolites Rudist Debris Bank

Rudist Reef-forming Sea Shells

Lake Georgetown Rudists

Rudists: the exotic mound-building Rudist Clams that became extinct at the end of the Cretaceous

Length: 6 inches to 3 feet!

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.

Stromatolites: blue green algae

Modern Stromatolites Stromatolites preserved as rocks

Stromatolites grow in shallow water

Stop 3: layered limestone with rudist reefs

Stop 3: layered limestone with rudist reefs

Stop 3: layered limestone with rudist reefs

Lake Georgetown Spillway

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

Stop 5: rudist fossils in country rock, Texas grasses

Wolf Ranch Shaded Walk

Stop 6: Eagle Ford gas source rock, Buda cliff, Texas Crushed Stone Quarry, Balcones Faults

Celebration Church Overlook

Where’s the Balcones Fault?

UpUp

Down

Down

Inner SpaceCavern

Celebration overlook

Balcones FaultsBalcones Faults

Note: Black Waxy

Inner SpaceCavern

Celebration overlook

Balcones FaultsBalcones Faults

Lunch: French Quarter Grill: Round Rock

Stop 7: Inner Space Cavern Tour

Stop 7: Inner Space Cavern Tour

Balcones Fault

Flint

Dolomite

Limestone

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”..

The end of a perfect day!!!

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!!

Self-drive Field Stop: Blue Hole City Park Balcones Faults & Edwards Limestone Rudist Reef

University Blvd

Wolf Ranch

Blue Hole Park

Austin Ave

Self-drive Field Stop @ Blue Hole Park: Balcones Fault

Up Down

Blue Hole Park

University Blvd

Austin Ave

Self-drive Field Stop @ Blue Hole Park: Balcones Fault

Up Down

Blue Hole Park

Self-drive Field Stop @ Park: Edwards Rudist Reef