Presentation on theme: "Senior University Geology Field Trip Senior University Geology Field Trip November 5, 2012 8:45 am – 4:30 pm November 5, 2012 8:45 am – 4:30 pm."— Presentation transcript:
Senior University Geology Field Trip Senior University Geology Field Trip November 5, :45 am – 4:30 pm November 5, :45 am – 4:30 pm
Georgetown’s Amazing Geology with Don, Rocky, & Sandi world famous rocks Explore, Photograph, & Sample , 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 amBriefing at The Oaks 9:10 to 9: 30STOP 1 - Perched water table Berry Creek Pond Berry Creek Pond 9: 40 to 10:00STOP 2 - Black Waxy clays Walgreens, Williams Dr Walgreens, Williams Dr 10:15 to 10:30STOP 3 - Rudist reefs Lake Georgetown spillway Lake Georgetown spillway 10:35 to 10:40STOP 4 - Reef in D.B. Woods road cut 10:50 to 11:15 STOP 5 - Rudists and grasses Wolf Ranch Mall Wolf Ranch Mall 11:30 to 12:15STOP 6 - Buda limestone cliff & faults Celebration Church Celebration Church 12:30 to 1:30 LUNCH – French Quarter Grill 2:00 to 4:00 STOP 7 - nner Space Cavern 2:00 to 4:00 STOP 7 - nner Space Cavern 4:30Return to Sun City 4:30Return to Sun City
Definitions 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
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 aquifer 0 to 100 feet Trinity sandstone 0 to 100feet Rocks at the surface in Sun Cit y
Geography when our limestones were formed about 115 million years ago
Berry Creek not eroded this deep Rocks Exposed at Sun City missing by erosion
Buda Limestone cliff Flint Springs Geological Cross Section Williamson County, Texas Comanche Peak Cliff Sun City outcrop Edwards reef recharge
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 Pond Stop 1 - Perched Water Table Why is the water here?
Pavilion at Berry Creek Pond Reef Berry Creek Pond (stock tank) Village Center Williams Dr. Gate Reef 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 Limestone Walgreens on Williams Dr What’s the black surface dirt?
black waxy clay weathered Georgetown limestone un-weathered Georgetown limestone Stop 2: Waxy Clay on weathered Georgetown Limestone Walgreens 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?
layered limestone with rudist reefs Stop 3: layered limestone with rudist reefs Lake 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 StromatolitesStromatolites preserved as rocks Stromatolites grow in shallow water
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?
Up Down Inner Space Cavern Celebration overlook Balcones Faults
Note: Black Waxy Inner Space Cavern Celebration overlook Balcones Faults
Lunch: French Quarter Grill: Round Rock
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 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 University Blvd Wolf Ranch Blue Hole Park Austin Ave
Self-drive Field Blue Hole Park: Balcones Fault Up Down Blue Hole Park University Blvd Austin Ave
Self-drive Field Blue Hole Park: Balcones Fault Up Down Blue Hole Park