POSTED GZ IS IN NOW IN A FENCED CONSTRUCTION ZONE. SEE HINT FOR ALTERNATE VIEW POINT.
This earthcache is easy to get to and not far from parking which is available nearby in the Anderson Bonner Park. To do this EarthCache safely, DO NOT STAND on the edge of the overlook.
Most of the Dallas Metroplex is underlain by sedimentary rocks. These sediments were deposited as sea level rose through the Cretaceous time period, from about 110 to 65 million years ago, and covered the present Dallas Metroplex. Dinosaurs cavorted in this shoreline environment.
The sea 90 million years ago was deep enough to submerge all but the tallest Dallas skyscrapers. In this clear, warm sea, far removed from muddy shorelines, single-celled phytoplankton called coccolithophorae thrived. These creatures were armored with hubcap-shaped calcite plates that sank to the seafloor when the coccoliths died, accumulating on the seafloor as a gentle “snow” over millions of years to ultimately produce the 400-foot-thick Austin Chalk. The Austin Chalk is the bedrock that Dallas is built on.
Single-cell phytoplankton Coccolithophorae
Accumulated dead coccoliths - the basis of Austin Chalk
Chalk is a form of limestone. Chalk is subject to erosion, but it is more resistant to weathering than the clays and soils that usually top it. Being more resistant to weathering, chalk outcrops and cliffs appear as the other soils surrounding it are washed away. Chalk is a porous rock, meaning there are spaces within the material, which can actually hold a large volume of water. Water penetrates the chalk and is gradually released through drier seasons
White Rock Creek takes its name from the weathered-white Austin Chalk which lines its bed and banks. Outcrops of Austin Chalk are often exposed by erosion particularly on the outside of bends along creeks.
To claim credit for this EarthCache, send the answer to the following questions. DO NOT INCLUDE THE ANSWERS IN YOUR LOGS. Logs posted without providing answers to the questions will be deleted.
Questions:
1. About when and how was the Dallas bedrock geologically formed?
2. Describe what you see at this bend and how it differs on each side of the creek.
3. How high would you estimate the chalk cliff is at this spot?