Senior University Geology Field Trip
November 5, 2012 8:45 am – 4:30 pm

with Don, Rocky, & Sandi
Explore , Photograph, & Sample . . . . .
world famous rocks modern perched water table modern aquifers supplying our drinking water
10, 000 years old black waxy glacial clays
135 million year old Rudist reefs
45 million year old Balcones Fault

Our Travel Schedule
8:45 to 9:00 am Briefing at The Oaks
9:10 to 9: 30 STOP 1 - Perched water table
9: 40 to 10:00
Berry Creek Pond
STOP 2 - Black Waxy clays
10:15 to 10:30
Walgreens, Williams Dr
STOP 3 - Rudist reefs
10:35 to 10:40
Lake Georgetown spillway
STOP 4 - Reef in D.B. Woods road cut
10:50 to 11:15 STOP 5 - Rudists and grasses
11:30 to 12:15
Wolf Ranch Mall
STOP 6 - Buda limestone cliff & faults
Celebration Church
12:30 to 1:30 LUNCH – French Quarter Grill
2:00 to 4:00 STOP 7 - nner Space Cavern
4:30 Return to Sun City

Mineral: natural occurring constituent of all rocks
Limestone: sedimentary rock composed of the mineral Calcite
Shale: sedimentary rock composed of one or more Clay minerals
Sandstone: sedimentary rock composed of the mineral quartz
Ground water: rain water filling rock voids
Water table: top of the ground water
Aquifer: 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

Eagleford Shale 120 feet
Buda Reef 60 feet
Del Rio Shale 60 feet
Georgetown Limestone 100 feet
Upper Dense limestone 30 feet
Rocks at the surface in Sun Cit y
Edwards Limestone 380 feet
Reef & Reef debris aquifer limestone 100 feet
Comanche Peak limestone 50 feet
Upper Walnut limestone 100 feet
Lower Walnut limestone 100 feet
Glen Rose Limestone 400 feet
Trinity sandstone 0 to 100feet
Ouachita Mountain complex folds and thrust faults
Trinity sandstone aquifer
0 to 100 feet

Geography when our limestones were formed about 115 million years ago

Rocks Exposed at Sun City
Berry Creek not eroded this deep

Springs

Fossils you may have stumbled over
Bryozoa (sea moss) Stromatolites (Algae)
Brachiopods
(symmetrical shells)
Gastropods (snails)
Pelecypods (clams)
(asymmetrical shells)
Cephalopods & Ammonites Corals

On the road . . .

Stop 1 - Perched Water Table at Berry Creek Pond

Stop 1 - Perched Water Table
Pavilion at Berry Creek Pond
Berry Creek Pond (stock tank)
Williams Dr. Gate
Village Center
Reef
Reef water filled=a perched water table

Stop 2: Holding pond at Walgreens on Williams Dr
. . .the base of the pond is on impervious limestone!

Stop 2: Waxy Clay on weathered Georgetown Limestone
Walgreens on Williams Dr
What’s the black surface dirt?

Stop 2: Waxy Clay on weathered Georgetown Limestone
Walgreens on Williams Dr black waxy clay weathered
Georgetown limestone un-weathered
Georgetown limestone

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
What rocks are these?
Lake
Georgetown
Spillway

Stop 3: layered limestone with rudist reefs
Lake Georgetown Spillway

Lake Georgetown Spillway North Rock Wall
Stromatolites cap layer
Eoradiolites Rudist Debris Bank
Stromatolite layer

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 weathersout leaving a round hole.

Stromatolites grow in shallow water
Modern Stromatolites Stromatolites preserved as rocks

Stop 3: layered limestone with rudist reefs

Stop 3: layered limestone with rudist reefs

Stop 3: layered limestone with rudist reefs
Lake Georgetown Spillway

Stop 4: Limestone Reef Outcrop
Road Cut, D.B. Woods Road
D. B. Woods Road - reef outcrop
. . . 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

Inner Space
Cavern
Balcones Faults
Up
Down
Up Down
Celebration overlook

Inner Space
Cavern
Balcones Faults
Note:
Black Waxy
Celebration overlook

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 ” ..

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 east of 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
Blue Hole Park
Austin Ave
Wolf Ranch

Self-drive Field Stop @ Blue Hole Park: Balcones Fault
Blue Hole Park
Up
Down
Austin Ave

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

Self-drive Field Stop @ Park: Edwards Rudist Reef