Geology About Broken Arrow, Oklahoma

Broken Arrow, located in northeastern Oklahoma, has an interesting geologic history shaped by ancient seas, dynamic forces within the earth, and erosion from water and wind over millions of years. This article will explore the key geologic characteristics that define Broken Arrow and the surrounding region.

Bedrock Formations Underlying Broken Arrow

The bedrock underlying the Broken Arrow area contains sedimentary rocks deposited up to 500 million years ago during the Paleozoic Era when Oklahoma was covered by shallow inland seas.

Sandstones, Shales, and Limestones

The main bedrock formations include:

• Sandstones – deposited as beaches, dunes or river channels when the land surface was above sea level
• Shales – deposited as mud on the seafloor in low-oxygen environments
• Limestones – formed from calcium carbonate shells and marine life in clear, warm ocean water

These sedimentary rocks record the history of Oklahoma’s ancient ocean environments and ecology. They contain interesting fossils!

Depth and Structure of Bedrock

The bedrock layers underlying Broken Arrow are gently dipping to the west, descending from exposures at the surface in the east to depths over 8,000 feet deep along the border with Tulsa. Faulting and uplift has createduks and basins that trap oil and gas.

Surficial Geology Influencing Broken Arrow’s Terrain

Sandstone Bedrock Shapes Hills and Valleys

The sandstones and shales of the bedrock create a sequence of steep ridges and rolling hills aligned southwest-northeast, shaped by erosion from rivers and streams. Limestones underlie low, flat valleys. Resistant sandstone caps ridges while shale erodes to form valleys.

Top 5 Geologic Features Shaping Broken Arrow’s Terrain:

1. Fred Creek Valley – underlain by eroded shales
2. Broken Arrow Creek – cuts through sandstone ridges
3. Osage Hills – held up by hard sandstone layers
4. Glacial Erratics – granite boulders carried from the north
5. Alluvial Floodplains – deposited by creeks overflowing their banks

Glacial Erratics

Scattered across Broken Arrow are distinctive pink granitic boulders that originate from the Ozark Mountains far to the northeast. These “glacial erratics” were transported within flowing ice during the Illinoian Glaciation 300,000 years ago. As the climate warmed and ice melted, erratics were dumped randomly across the landscape.

Can you spot any glacial erratics while out exploring Broken Arrow’s hills?

Alluvial Plains and Terraces from Creeks

Broken Arrow Creek, Cat Creek, and other streams have deposited sandy alluvium in floodplains and terraces during floods over thousands of years. These level plains contrast with steeper hills capped by resistant sandstone. Floodplains supply fertile farmland but are vulnerable to future floods enhanced by climate change.

How Broken Arrow’s Geology Influences the City

Broken Arrow’s distinctive terrain and geology influence development patterns, economy, water and natural resources – essentially the city’s DNA!

Development Responds to Topography

• Ridgelines – desirable for hilltop estates to maximize views
• Valleys & Creek Corridors – transportation corridors, pipelines, trails
• Floodplains – set aside as parks and recreation areas

Sandstone ridges tend to have large residential lots while shale valleys and floodplains have municipal infrastructure. Know your property’s geology!

Bedrock Aquifers Supply Water

Water wells pump from porous sandstone and limestone bedrock units up to 500 feet deep. These fossil aquifers recharge very slowly from rainfall – faster pumping risks depletion! Help conserve groundwater.

Sand and Gravel Extraction

Creeks have deposited sand, gravel and aggregate used extensively for construction materials. Old borrow pits dot Broken Arrow but can fill with water creating small recreational lakes. Dig responsibly!

Oil and Gas Drilling

Drillers tap local oil and gas reservoirs trapped within fault zones and gentle folds in the deep bedrock, mainly the Viola Limestone Formation. New horizontal drilling techniques enhance production but can impact landscapes and communities through induced earthquakes if wastewater injection hits faults. Support smart energy policies!

Unique Local Geosites to Explore

Broken Arrow has easily accessible geosites where anyone can observe the local geology first-hand:

Fossil Collecting Locations

The shale member of the Ada Formation, found in creek beds west of the Creek Turnpike, contains marine fossils from Oklahoma’s shallow inland sea 310-320 million years ago including horn corals, brachiopods, pelecypods and crinoids. Search here after heavy rains (but avoid flash flooding)!

Glacial Erratic Boulders

A one-mile loop hiking trail in Nienhuis Park displays several massive pink granitic boulders dumped by glaciers 300,000 years ago. Can you spot glacial grooves and fractures from mountain glaciers? Bring the family!

Sandstone Ridge Trail

This great 2.2 mile public trail winds over a narrow sandstone ridge with panoramic views. See how water and wind erodes Currant Creek shale layers on the valley floor differently than the capping resistant Burbank sandstone. Don’t forget your camera!

Bedrock Road Cuts

Road cuts for highways 64 and 51 reveal steeply tilted red beds of the Permian Post Oak Conglomerate capped by the white Permian-aged Dog Creek Shale. Young geologists will enjoy interpreting uplift and erosion of units deposited 280 million years ago when Oklahoma underwent desert conditions. Mind the traffic!

By learning about the local geology, residents can gain a deeper appreciation of Broken Arrow’s natural beauty and landscape. We owe our city’s terrain and resources to over 500 million years of geologic history!