Nellie Bly Outcrop
This is an EarthCache that will take you to a geological feature accessible from the Pathfinder walking trail. You’ll leave the paved trail and walk about 250 feet on (usually) mowed grass. The round trip walk from parking and back is about half a mile. Parking coordinates are provided for both southbound and northbound vehicles on Highway 75.
To get credit for this EarthCache:
You will identify and post a picture of a rock and send your answer describing how you identified it. You may log the find before you hear from the cache owner about your answer.
The rocks you see in this outcrop are part of a geological formation first identified near Nellie Bly Creek, which goes through the town of Ramona 15 miles south. This outcrop is near the edge of the formation where the rock changes to Alluvium (unconsolidated gravel, sand, silt, and clay) along the Caney River and Turkey Creek.
Geologic bedrock maps show the types of solid rock at the surface or just under the overlying material. The view below of a 1926 United States Geological Survey map shows the Nellie Bly formation in central Washington County.
The view below from the USGS Mineral Resources Online Spatial Data shows the Nellie Bly formation in tan and the Alluvium in yellow:
Geologic History
The Nellie Bly formation is from the Pennsylvanian subperiod of the late Carboniferous Period roughly 300 million years ago. The Carboniferous Period is known as the age of giant insects--before the age of dinosaurs during the Jurassic Period.
The Pennsylvanian subperiod was a time of climate change, with alternating land and sea. As the area transitioned from a marine environment, it became more terrestrial with swamp forests. The types of rocks deposited also transitioned from limestones to layers containing more sandstone and shale.
Alternating Layers of Shale and Sandstone
The Nellie Bly formation in this part of the State consists primarily of alternating layers of shale and sandstone--both sedimentary rocks. While shale forms from muddy deposits that settle out in slow-moving water, sandstone forms from sandy deposits.
At the base of this outcrop you will find piles of rocks that resemble broken plates and other rocks that are a variety of shapes and sizes.
Select a rock that you find interesting, and we’ll try to identify it.
Is it Shale?
Shale is a type of mudrock. It is made primarily of clay mineral flakes and silt-sized particles of other minerals, including quartz and mica.
Texture: The clay particles in shale are extremely fine-grained, so they are not visible without magnification.
Smell: When wet, shale may smell (and taste) like clay.
Shape: Because the clay particles are thin flakes that have a parallel orientation, when shale erodes, it typically breaks along parallel layers that are less than one centimeter thick.
Color: Shale is often a shade a gray. It can also be black, red, brown, green, or even bluish depending on the other minerals it contains. It has a dull surface. It may have tiny silvery flecks of mica.
Hardness: Shale is a soft and brittle rock that easily erodes and crumbles.
Is it Sandstone?
Sandstone is composed of sand-sized grains of various minerals, predominately quartz, and also feldspar, mica, and other minerals.
Texture: Sandstone can be distinguished from shale by its grains that are visible to the naked eye, and in most cases it is gritty to the touch.
Smell: Sandstone generally does not have a distinctive odor.
Shape: The grains in sandstone don’t have a parallel orientation and are cemented together, so sandstone breaks with an irregular fracture. It does not break along thin, parallel layers.
Color: Sandstone can come in a range of colors depending on its mineral content, including shades of yellow, brown, red, grey, and white.
Hardness: Sandstone’s hardness varies, depending on the mineral content.
Logging Tasks:
1) In your log, post a picture of the rock you found interesting.
2) In a message to the cache owner, answer these questions:
a) Do you think the rock is shale? Sandstone? Or something else?
b) Describe three qualities that indicate what kind of rock it is.
Acknowledgment
Thank you to Molly L. Yunker, Ph.D., Education & Outreach Coordinator, Oklahoma Geological Survey, University of Oklahoma.
Resources
Carpenter, E., Oil and Gas in Oklahoma, Geology of Washington County, Oklahoma Geological Survey, Bulletin No. 40-V (1928).
Gould, C. N., Index to the Stratigraphy of Oklahoma, Oklahoma Geological Survey Bulletin, No. 35, p.115 (1925).
Oakes, M. C., Geology and Mineral Resources of Washington County, Oklahoma, Oklahoma Geological Survey Bulletin, No. 62, p.208 (1940).
Tarbuck, E., & Lutgens, F., Earth Science, Prentice Hall (2006).
USGS Geologic Map of Oklahoma, Hugh D. Miser (1926).
USGS Mineral Resources Online Spatial Data available at https://mrdata.usgs.gov.