BOSTON - OHIO, USA
MAY 31ST 2019
Cuyahoga Valley has been shaped by glacial forces and past river flows, Today the Cuyahoga River is mature and surrounded by wide river valleys along most of its banks. The younger rock layers from around the Jurassic and Eocene remain missing from the record because the valley was once carved out by an ancestral river before the ice age.
2 million years ago was the beginning of ice age, also named the Pleistocene Epoch. During that time ice advanced and melted back to the north, this happened in intervals till the Holocene10,000 years ago. Because glaciers displace sediment they are also responsible for the creation of several lakes including Lake Erie. After the Ice Age came to an end the Cuyahoga river started to retrace the old ancestral river after it was filled in by glacial sediment.
The Ledges trail consists of Sharon Conglomerate which was laid down during the Pennsylvanian age roughly around 310 million years ago. The Sharon Conglomerate is mainly comprised of sandstone, this is because those who named it may have been viewing the lower unit which is more of a conglomerate than the upper layers. Newly exposed sections look more yellow/orange in colour than the other moss-covered layers.
The Conglomerate is comprised of medium-grained quartz sandstone with layers of pebbles, the rock grades into a conglomerate. The conglomerate layers are narrow belts with a thickness ranging between 10-50 ft.
No other minerals are present besides quartz, the lack of igneous and metamorphic rock suggests that the individual grains have been through more than one cycle of sedimentation. Examination of a thin section shows inclusions in the quartz grains and pebbles which confirms that the quartz is from a metamorphic source.
Joints that form in the Ledges trail are from stress relief, the joints are responsible for the slot canyons and the caves in the area. Joints are orientated in two directions, they can also be perpendicular to each other and surprisingly form in very straight lines. These joints are very recognizable all throughout the Ledges trail but seem to fade out towards the north at Brandywine Falls.
The Ledges trail shows examples of cross-bedding of sandstone and layers of the conglomerate. Honeycomb weathering is also visible in some locations because the water flows down the conglomerate layers and weathers pebbles out of place. The slot canyons are strongly controlled by joints formed in the Sharon Conglomerate. The Sharon Conglomerate is very resistant to weathering and because of that, it forms steep ledges.
Slot Canyons (Cross-Bedding)
Sharon Conglomerate (Honeycomb Weathering)
Icebox Cave formed because of the joint sets and how they intersected. The cave floor is Meadville Shale and erodes much faster than the surrounding Sharon Conglomerate. At this time the cave is closed to visitors, the entrance is locked by metal gates designed to let bats fly in and out. The cave may not be reopened in the future because of White Nose Syndrome that affects the bat population and the possibility of spreading it further throughout the United States and Canada.
The Brandywine Falls are the highest waterfalls in the National park with a maximum height of 65 ft. Breca Sandstone forms the lip of the falls while Bedford and Cleveland shales lay beneath the sandstone.
The overhangs of Breca Sandstone collapse and fall to the base of the river, this is visible with sandstone boulders beside the water flow.
Layers (Rough measurements)
. Breca Sandstone - Top 8 Feet
. Bedford Shale - Middle 10 Feet
. Cleveland Shale - Bottom 17 Feet
Fossils present in the layers are Tabulate Corals which prove that part of the source is Middle Devonian in age. The clastic sediments most likely came from the Canadian Highlands and travelled down via streams and rivers and settled in a shallow basin formed by a river delta. The cross-bedding is also a good indicator that a stream deposited these layers.
Roadside Geology of Ohio
Mark J. Camp
Ohio Uplands - Allegheny Plateau
Page 201 - 205 (Newburg Heights and Vicinity)
Mountain Press Publishing Company (2006)
January 2nd, 2018
National Park Service
J. OSBORN FULLER; SOURCE OF SHARON CONGLOMERATE OF NORTHEASTERN OHIO. GSA Bulletin ; 66 (2): 159–176.
Robert G. Corbett and Barbara M. Manner, Department of Geology, The University of Akron, Akron, OH 44325 Geology and Habitats of the Cuyahoga National Recreation Area
OHIO J. SCI. 88 (1): 40-47, 1988