Peffer Park Tour

enlarged photo of Peffer Park hillIf you hike along Collins' Run in Peffer Park (in Miami's Natural Areas) you can observe many geologic features, common in southwestern Ohio.

The wide, gently sloping valley in Peffer Park was created during the Pleistocene Epoch. Now, a fairly small creek, called Collins' Run, resides in this valley.

enlarged photo of Peffer Park stream bedLooking up the stream bed from the footbridge, the stream channel contains abundant rocks.

enlarged photo of stream bed rocksA closer look at the rocks shows that they are imbricated (or slanting) in the up-current direction. This configuration is the most stable one for flat rocks in a stream bed.

enlarged photo of clasts on tillFossil Stream Bed Deposits

Imbricated to jumbled gravel and larger clasts rest atop glacial till. These deposits are identical to modern stream deposits and represent a former channel of Collins' Run Creek.

enlarged photo of cut bankModern Stream Processes

If you look downstream along the cut bank, you will see that the glacial till forms a steep bank.

enlarged photo of point barsYou should be able to pick out point bars of sand and gravel (foreground) and a cut bank of glacial till (background).

enlarged photo of point bar sedimentsPoint Bar Features

Point bars in this stream are composed of fairly typical sediments, namely sand and gravel.

enlarged photo of point bar compositionLarger fragments of limestone and weathered shale are common, as are individual fossils weathered out of their enclosing rocks.

enlarged photo of cut bank with horizonsCut Bank Features

A close-up view of the cut bank shows soil horizons at its top and a weathered slump block at its base.

enlarged photo of unsorted till in cut bankAn even closer view of the cut bank shows the typical, unsorted clay-to-cobble-sized sediments in the till.

Glacial Till

enlarged photo of ovoid mass of tillThe ovoid mass of glacial till weathered out of the cut bank and fell into the stream.

enlarged photo of smaller ball of tillA slightly smaller "ball" of till was shaped by its journey down the stream bed, during which time it became armored by picking up several small rocks.

enlarged photo of fossiliferous limestoneRocks Along the Stream Bed

Fossiliferous limestone is representative of the local limestone bedrock. This particular bedrock contains numerous brachiopod fossils.

enlarged photo of glacial erraticOther rocks, usually the rounder ones without fossils, did not originate from the local bedrock. Instead, glaciers transported these rocks, called glacial erratics, from places far to the north, such as Canada.

enlarged photo of bedrock exposureBedrock Exposures

In some places, you can even see glacial till sitting directly on top of bedrock. Such places clearly show the "gap" in time, or unconformity, between the deposition of the bedrock (450 million years ago) and the till (24,000 years ago).

enlarged photo of bedrock in streamA little farther up Collins' Run, you will see bedrock exposed in the stream bank. This bedrock, composed of flat-lying limestone and shale (or mudstone), is about 450 million years old.

Fossils in Local Bedrock

The presence of fossils of marine creatures in the local bedrock indicates that the original sediments were deposited in a warm, shallow sea. About 450 million years ago, such a sea covered much of North America, and Ohio was south of the equator.

Marine fossils include:

enlarged photo of brachiopod fossilsBrachiopods

enlarged photo of trilobite fossilsTrilobites

enlarged photo of pelecypod fossilsPelecypods (clams)

enlarged photo of trace fossilsTrace Fossils

Not all fossils are shells or bones. Sometimes fossils are other materials that contain or reveal the tracks and other traces of animal activity. For example, the tracks of feeding marks left by marine worms are very common in local bedrock.

enlarged photo of the BluffsThe "Bluffs"

The "Bluffs" area is a high-cut bank that exposes about ten meters of till overlying a few meters of limestone and shale bedrock layers. If you look closely at the glacial till, you can see pieces of the Pleistocene (Ice-Age) wood that were incorporated into the till as the glacier rode over the landscape.

By using radiocarbon methods, geologists have been able to trace the date of this wood. They estimate this wood to be approximately 24,000 years old; this means that the till that encloses it is at least that old.

enlarged photo of Waynesville FormationLimestone and Shale Layers

In the Waynesville Formation, the limestone appears light colored and blocky, and the shale appears blue-gray and crumbly.

enlarged photo of limestone embedded in shaleA closer view shows two thin beds of limestone enclosed within shale.

enlarged photo of wood in hole in tillPleistocene Wood

Branches of what were probably spruce trees were overriden by the advancing glaciers during the latest glacial advance.

enlarged photo of Pleistocene wood in till

Glacial Erratics

enlarged photo of glacial erraticA boulder that originated from either Canada or Michigan can be seen near the creek. Glacial ice carried this boulder for hundreds of miles, depositing it here in Ohio.

enlarged photo of close-up of glacial erraticA close-up of the boulder's surface reveals curved cracks called chatter marks. These marks were caused by the boulder being dragged across solid rock during transport.