Geology of Dayton, Ohio

Introduction

Dayton, Ohio is located in the southwest region of Ohio in the Miami Valley. The city’s geology has been shaped over millions of years by ancient seas, glaciers, and rivers.

This has resulted in a variety of rock formations and soil types across the Dayton area. Understanding the local geology gives insight into the natural resources, landforms, and hazards that impact the city.

Bedrock Geology

The bedrock underlying Dayton consists of sedimentary rocks formed during the Ordovician, Silurian, and Devonian periods between 444 and 359 million years ago. The main rock units include:

Ordovician Period (444-416 million years ago)

  • Shale: The oldest bedrock in the Dayton area is the Ordovician shale of the Martinsburg Formation. These shales formed from muddy sediments in a shallow inland sea covering Ohio during this time period. They can be found underlying western and southern parts of Dayton.
  • Limestone and Dolostone: Above the Martinsburg shales is the Ordovician Trenton Limestone, which is made up of skeletal limestone and dolostone. This unit is exposed at the surface in a band running southwest to northeast across central Dayton.

Silurian Period (416-359 million years ago)

  • Limestone and Dolostone: Dayton sits on the Silurian Lockport Dolomite, a formation composed of dolostone and limestone rich in fossils of marine organisms like brachiopods, bryozoans, and crinoids. This is the bedrock surface across much of Dayton.
  • Shale: The Silurian Cincinnatian Series shales, including the Kope and Fairview Formations, overlie the Lockport Dolomite in western Dayton. These soft gray to blue-gray shales formed from mud in shallow seas.

Devonian Period (359-318 million years ago)

  • Shale: Lastly, the Ohio Shale of the Devonian Period tops the bedrock sequence in far western Dayton near the Miami River. This black organic-rich shale formed from muds in a deep ocean environment.

Glacial Geology

Dayton’s landscape was reshaped over the last 2 million years by multiple glaciations during the Pleistocene Ice Age. As continental glaciers advanced over Ohio, they eroded and transported bedrock to form new sediment deposits.

Glacial Till

The ground moraine glacial till left behind by the glaciers covers most of Dayton. This till is a heterogeneous mixture of clay, silt, sand, gravel, and boulders transported and deposited by ice. The till deposits range from 10 to 100 feet thick.

Buried Valleys

Meltwater from the glaciers also carved large buried bedrock valleys that cut across western Dayton and are now filled with sediment. These ancient river valleys are hidden below the surface but influence groundwater flow.

Outwash Deposits

Glacial outwash consisting of stratified sand and gravel is found in the valleys of the Great Miami, Stillwater, and Mad Rivers flowing through Dayton. These deposits filled river valleys carrying glacial meltwater.

Kettle Lakes and Kames

In a few areas such as Hills and Dales Park, kettle lake basins and kame deposits formed when buried glacial ice melted and left depressions or mounds of stratified sand and gravel.

Recent Geology

Floodplain Alluvium

The modern floodplains of Dayton’s rivers contain sand, silt, and clay deposited during recent floods over the past thousands of years. These loose alluvial sediments are prone to flooding.

Loess

Loess is a blanket of wind-blown silt up to 15 feet thick covering glacial deposits on uplands around Dayton. This soft, porous silt originated from glacial outwash.

Landslides

The steep valley walls carved into shale and carbonate bedrock along the Great Miami River and other streams are prone to landslides and slope failures, especially after heavy rain.

Economic Geology

Dayton’s geology has provided key resources that supported the area’s growth.

  • Limestone: Abundant local limestone and dolostone from Ordovician and Silurian units provided building stone and aggregate for construction. Historic buildings across Dayton were built from quarried limestone.
  • Sand and Gravel: Glacial outwash provided sand and gravel for concrete and construction aggregate. This is still mined from river valleys.
  • Groundwater: Fractured bedrock, buried valleys, and glacial deposits provide groundwater resources, with wells tapping sand and gravel aquifers. However, shale bedrock has limited permeability.
  • Oil and Gas: Small quantities of petroleum and natural gas have been produced locally from fractured Silurian dolostone and shale units.

Geologic Hazards

Dayton’s geology also presents some hazards:

  • Flooding: The city’s location along several major rivers and on top of buried valleys makes it prone to significant flooding. Development in floodplains exacerbates risks.
  • Sinkholes and Subsidence: Limestones and dolostones are susceptible to dissolution, creating sinkholes. Abandoned quarries and mines also pose risks.
  • Landslides: Steep shale riverbanks fail as slumps or slides, like the 2019 Arcade landslide. Heavy rain increases risks.
  • Seismicity: Moderate earthquake hazard exists, with major faults running through southwest Ohio. Small quakes occur periodically.
  • Contaminated Sites: Industrial history left legacy contamination. Sites with lead, solvents, or other chemicals require cleanup.

Geologic Influences on Dayton

Dayton’s landscape reflects its geological history:

  • Rivers and Valleys: Bedrock valleys guide the Great Miami, Stillwater, and Mad Rivers through Dayton, which attracted settlement.
  • Floodplains: Level, fertile floodplains along these rivers provided space for expansion. However, proximity leads to flooding.
  • Hills and Glacial Deposits: Hilly northern Dayton sits on glacial moraine and kames and kettle lakes, like Hills and Dales Park.
  • Limestone Resources: Local limestone supported early cement production and building construction.
  • Springs and Fountains: Groundwater flowing from limestone and dolostone units feeds springs across Dayton, incorporated into fountains and attractions.
  • Transportation: River and buried bedrock valleys determined pathways for roads, railroads, and canals through Dayton region.

In summary, Dayton’s Ordovician to Devonian bedrock, overlain by glacial sediments and modified by recent river activity, made the area appealing for settlement but also presents significant geological hazards and constraints on development.

Understanding the geology provides critical insights on resources, land use, and engineering in the Dayton region.

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  • Start out going east on E 3rd St toward S Patterson Blvd in downtown Dayton. Turn right to merge onto S Patterson Blvd. Take I-75 N ramp on the left to Cincinnati. Merge onto I-75 N and drive for about 5 miles. Take exit 50A for Siebenthaler Ave toward N Fairfield Rd. Turn left onto Siebenthaler Ave. The destination will be on the right.
  • Begin at Riverscape MetroPark in downtown Dayton and head north on S Patterson Blvd. Take the I-75 N ramp on the left toward Cincinnati. Merge onto I-75 N and drive approximately 5 miles. Use the right 2 lanes to take exit 50A for Siebenthaler Ave. Turn left onto Siebenthaler Ave. Continue on Siebenthaler Ave for half a mile and the destination will be on your right.
  • Start at the Dayton Art Institute in downtown Dayton. Head east on E Monument Ave toward S Patterson Blvd. Turn right onto S Patterson Blvd. Take the I-75 N ramp on the left to Cincinnati. Merge onto I-75 N and drive for 5 miles. Take exit 50A for Siebenthaler Ave toward N Fairfield Rd. Turn left onto Siebenthaler Ave. 117 E Siebenthaler Ave will be on the right just past Danner Ave.