FLUVIAL FORCES IN ANCIENT ROCK The steep bedrock cliffs in Turkey Run State Park tell of two important chapters in its long geologic history. The first records the rock-building events by ancient rivers that took place about 300 million years ago. The second chapter records the erosional forces of glacial meltwater within the last million years.
E Wedge Rock B O E L B O L Wedge Rock on Trail 3 is an
N A excellent example of the erosional G I W A H phenomena known as freeze-thaw. N C I I G As water moves through joints M A S E BE in the rock, it freezes, expands, K LO A L IE and exerts pressure, causing the E R A E S INDIANA rock to fracture and fall into the T OHIO ILLINOIS W HIT canyons below. E
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Y R A ND U O B IN NS CO Y IS K W C - TU E EN PR K Records in Stone The inclined layers in the sandstone bedrock are known as cross beds. Formed by changes in depositional environment, the sand that eventually became rock at Turkey Run was deposited within a braided river channel system.
Cliffs and Quiet Valleys THE GEOLOGIC STORY Sandstone ridges rise almost vertically for 50 feet or more where glacial streams have cut of Turkey Run steep canyons into the bedrock. Boulders, waterfalls, potholes, and fallen rocks are found State Park in the stream valleys below the wooded cliffs.
Indiana Geological & Water Survey | Indiana University 611 N. Walnut Grove Ave., Bloomington, IN 47405-2208 812.855.7636 | [email protected] | igw s.indiana.edu Photos provided by the Ind. Dept. of Natural Resources and the Indiana Geological & Water Survey. Pennsylvanian Strata Carved by Glacial Meltwater The steep cliffs and deep gorges of Turkey Run State Hundreds of millions of years after it was formed, the Park offer a unique look at sedimentary rocks that sandstone bedrock was carved into today’s familiar formed more than 300 million years ago. During the landscape by the eroding action of glacial meltwater. Pennsylvanian Period of geologic time (318–299 mil- During the Pleistocene Epoch (2.6 million–12,000 Camping Area 4 Trail Number Entrance Station Parking lion years ago), large rivers flowed through this area years ago), a series of continental ice sheets flowed Lodging Picnic Area en route to a vast inland sea farther to the west, much southward from Canada and dynamically shaped Nature Center Picnic Shelter as the Mississippi River flows into the Gulf of Mexico the topography of Indiana. As the climate warmed today. Sand, mud, and gravel from the newly formed and the ice melted, thick deposits of gravel, sand, silt, Appalachian Mountains were carried hundreds of and clay were left behind. This sediment, called till, miles by these great rivers and deposited across south- blocked most of the pre-glacial drainage network. western Indiana. In time, the sediments compacted Meltwater eroded new channels, such as Sugar Creek, Rocky Hollow - and cemented to form the sandstone bedrock seen and cut the spectacular canyons in Turkey Run. today. As the ancient river changed course, water Stones of many sizes can be found in the ravines. Falls Canyon CREEK
volume, or sediment load, currents formed inclined
Many of these are igneous or metamorphic rocks such Camel’s
Back layers of sand and gravels. These features, called cross as basalt, granite, and gneiss that were washed out Nature Preserve L beds, were preserved as part of the sandstone. L from the till. These stones are called erratics because I M
Geologists have classified the bedrock exposed in they differ from the local sedimentary bedrock. GAR SU 10 the park as belonging to the Mansfield Formation, Erratics served as abrasive tools carried by meltwa- Punch Bowl 4 8 N 4 A a coarse-grained sandstone with beds of shale, occa- ter, wearing away the bedrock to create bowl-shaped R R 3 O sional quartz-pebble conglomerate, and thin seams features called potholes. Potholes can be seen in the W S
of coal near its base. Sandstone from the Mansfield streambed and along the canyon walls by the ladders
Narrows Rocky Formation is quarried nearby for building stone and on Trail 3. Large erratics can be seen in Boulder Can- Covered Hollow Wedge Bridge Rock aggregate sand. In the past, however, the stone was yon on Trail 9, and smaller stones rest in Sugar Creek. 10 R O 3 4 A quarried as a source of silica and used in the man- 8 1 D Boulder 9 Ladders 4 ufacture of glass. The iron content in the sandstone Joints, Ridges, and Waterfalls Canyon Bear Ice Goose Lusk tinted the glass, mostly used for bottles, green. The Hollow Box Fireplace 1 Rock Earth A prominent feature along the trails in the park is 5 Middle Box 2 Fill iron was deposited by groundwater and also causes Falls Canyon the smooth, nearly vertical character of the bedrock Canyon Canyon Gypsy SUGAR 5 Gulch the rust color seen in the sandstone cliffs. Cox Ford Newby CRE Tennis Gulch walls. This phenomenon is due to fractures, or joints, Covered EK Turkey Court There are few well-preserved fossils in the sandstone in the bedrock. The joints occur in nearly right angle Bridge 1 Run Canyon Turkey Run C Big Log at Turkey Run because most organisms that fell into pairs, forming a straight rectilinear pattern. Streams O Hollow 6 2
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u the rivers washed away or were tumbled and broken. 7 r in the park follow the joint pattern in many places F k O 11 e Gatehouse y R Col. Lieber
Occasionally, molds of ancient tree trunks and roots because this is the least resistant path for running D
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can be seen. These are the remains of extinct scale water. Excellent examples of joints are found along R
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A To Waveland trees (Lepidodendron) and giant rushes (Calamites) Trails 2 and 3. As water moves through the joints, D R that grew along the rivers and flood plains during the it helps to dissolve the cementing agent in the sand- un To U.S. 47 Pennsylvanian Period. Thin coal beds that crop out stone. When the water freezes, it expands and exerts Highway 41 in a few places near the base of the sandstone formed pressure on already weakened areas. Freezing and when lush vegetation was buried by other sediments thawing conditions during the last Ice Age were more 0 1/2 mile and transformed into coal. A thin coal bed can be severe than they are today, accelerating weathering. NORTH seen at creek level along Trail 4. Please remember Blocks of bedrock fractured and fell from the long 0 1/2 kilometer to take nothing but photographs, leave nothing but vertical cliffs as seen in the Devil’s Ice Box and Box footprints. Canyon. Huge blocks that tumbled into the gorges are seen throughout the park, for example Wedge Rock on Trail 3. Maps: Indiana Geological & Water Survey