Geological and Dispositional History of the Starved Rocks, Illinois
Describe the clastic and carbonate facies you have discovered.
Starved Rock State covers about 200 miles and some 470 million years, from Ordovician sandstones to Pleistocene glacial till. The Ordovician St. Peter Formation sandstone was deposited across the midcontinent during the second major marine transgression of the Paleozoic Era. The first transgression deposited Upper Cambrian to Lower Ordovician clastics and carbonates. The clastic to carbonate rock transition is consistent with gradual sea level rise over the North American craton. Sea level dropped late in the early Ordovician, exposing the carbonate strata to ...view middle of the document...
These include small- and large-scale cross-stratification, low-angle planar bedding, high-angle planar-tabular cross-stratification, and horizontal laminations are preserved in the Starved Rock Member. There are coarsening-upward sequences preserved, with flooding surfaces represented by low-relief erosional contact of trough-cross-stratification (runnel) upon low-angle planar bedding (swash zone).
Starved rock and St. Peter Sandstone are an erosional remnant of Ordovician period. These remnants contain Pennsylvanian clastics that survived the washing out of the Illinois River at the end of the Ice Age. Evidence for swift, turbulent, and deep water includes gravel bars and erosional features as high as 160 feet above the current level of the river, massive cross bedded sand, and gravel deposits along the river course.
Identify the likely sedimentary environment where it might have been deposited.
There are 18 canyons at Starved Rock that were formed by glacial melt water and stream erosion. Starved Rock State Park is located along the south side of the Illinois River, one mile south of Utica and midway between the cities of LaSalle-Peru and Ottawa. The park is best known for its fascinating rock formations, including the St. Peter sandstone. It is located down in a huge low inland sea more than 425 million years ago and later brought to the surface.
The areas along the river are mainly forested; much of the area is a flat, gently rolling plain. The upland prairies were created during an intensive warming period several thousand years after the melting of the glaciers. The Illinois River Valley in the Starved Rock area is a major dissimilarity to the flatland. The valley was formed by a series of floods as glacial melt water broke through moraines, sending torrents of water surging across the land and deeply eroding the sandstone and other sedimentary rocks.
Sedimentation during Pennsylvanian time was influenced by structure of the land. The Canyon Rivers of Starved Rock and Matheisson State Parks were first established by the flood. Local drainage was lacking to keep up with the washing of the river valley by glacial melt water floods, creating hanging valleys and waterfalls that are certainly unusual in the Midwest. The enormous width of the river course corresponding to greater and frequently catastrophic late Pleistocene discharge is evident from the overlook at the Park.
The St. Peter sandstone is responsible for most of the elevation of Buffalo Rock. Lower Paleozoic strata here were exposed to erosion sometime in the middle to late Paleozoic and covered with...