{"id":2368,"date":"2020-10-26T19:36:26","date_gmt":"2020-10-26T19:36:26","guid":{"rendered":"https:\/\/blog.lib.uiowa.edu\/science\/?p=2368"},"modified":"2023-08-08T15:58:20","modified_gmt":"2023-08-08T15:58:20","slug":"iowa-rocks","status":"publish","type":"post","link":"https:\/\/blog.lib.uiowa.edu\/science\/2020\/10\/26\/iowa-rocks\/","title":{"rendered":"Iowa Rocks!"},"content":{"rendered":"\n

Iowa is not known for having an especially dramatic landscape. But in fact there are many hidden gems to be found in this particular plot of so-called flyover country. Among them is Wildcat Den State Park<\/a> in southeastern Iowa. According to Iowa DNR<\/a> it is one of the most photographed state parks in Iowa. If you\u2019ve not yet visited this state park to walk its trails<\/a> and view its remarkable geological features, take advantage of any opportunity to do so before it becomes snow and ice encrusted. The park is 12 miles northeast of the city of Muscatine; from the University of Iowa campus it\u2019s roughly an hour drive by car.<\/p>\n\n\n\n

The most prominent landscape feature at Wildcat Den are the spectacular sandstone cliffs and glens whose origins date back to the Middle Pennsylvanian period, or about 310 million years ago, when ancient rivers coursed through this landscape. What makes these cliffs on the south side of the park so visually arresting is due in part to cross-bedding*, as well as iron-oxide stained and cemented zones visible on the exposed sandstone. To walk the trail at the base of these cliffs is every bit as captivating as a visit to a fine arts museum. But there\u2019s much more to the geology at Wildcat Den.<\/p>\n\n\n\n

Brian Witzke\u2019s 1999 article in of Iowa Geology<\/a> (pages 16-19 ) provides a brief, but very informative introduction to the geology of this park, while \u201cThe Natural History of Wildcat Den State Park<\/a>,\u201c is a more detailed introduction to all aspects of the park, including its history, archaeology, vegetation, and wildlife. Its treatment of the park\u2019s geology is in-depth and somewhat technical, but would still be informative to the novice. In this Geological Society of Iowa (GSI) field trip guidebook Robert McKay details the geological phenomena of cross-bedding* that is so visible in the sandstone at Wildcat Den. It also includes discussions of all the stops on the 1997 GSI field trip, and could serve as either a preview of what to expect on a visit or a review to answer questions raised after first visiting the park.<\/p>\n\n\n\n

Two books published by the University of Iowa Press in its Bur Oak series would make excellent companion resources to help contextualize the geology of not only Wildcat Den State Park, but of geology all across the state: Jean Prior\u2019s Landforms of Iowa<\/a> and Wayne Anderson\u2019s Iowa\u2019s Geological Past: Three Billion Years of Earth History<\/a>. Both Prior and Anderson note the preponderance of sedimentary rock throughout Iowa in its exposed rock record, evidence of its early marine environment.<\/p>\n\n\n\n

Iowa Geology<\/a>, a small journal published by Iowa DNR Geological Survey Bureau from 1976 to 2001, offers a treasure trove of highly readable articles for a general audience on a variety of topics pertaining to Iowa geology one might imagine, including \u201cThe Midcontinent Rift,\u201d \u201cGlobal Climate Change and the Cretaceous Greenhouse World,\u201d and \u201cThe Age of Dinosaurs.\u201d All issues are available in PDF format from Iowa Research Online: The University of Iowa\u2019s Institutional Repository.<\/p>\n\n\n\n

For those who wish to explore Iowa\u2019s geology in other parts of the state, the Iowa Geological Survey (IGS) provides a beautiful suite of webpages called Parks of Iowa<\/a>, which also makes available guidebooks similar to \u201cThe Natural History of Wildcat Den State Park\u201d for 12 other Iowa state parks. In fact, IGS makes the Geological Society of Iowa Guidebooks<\/a> for field trips to over 70 diverse sites throughout Iowa freely available from its publications platform.<\/p>\n\n\n\n

Now it\u2019s time to go explore!<\/p>\n\n\n\n

Thank you to Kai Weatherman for writing this post, and a special thanks goes to Raymond Anderson<\/a> for his expert geologic commentary!<\/em><\/p>\n\n\n\n

Photographs of Sandstone Bluffs at Iowa\u2019s Wildcat Den State Park<\/strong><\/h2>\n\n\n\n

Photographs by Kai Weatherman with Text by Raymond R. Anderson<\/a><\/p>\n\n\n\n

The best-exposed rocks in Wildcat Den State Park are Pennsylvanian-age sandstones, originally deposited in a large river that was flowing to the southwest through the area.  The river was flowing through dense equatorial forests towards an arm of the sea that was advancing from the south into Iowa about 312 million years ago.  The sand formed sand bars and underwater dunes that were constantly being modified as river channels changed directions, eroding and cutting into existing bars and covering them with new sand layers (beds) from different directions creating the spectacular cross-bedding<\/em> that is displayed in most exposures.  Geologists identify these sandstones as the Spoon Formation<\/strong> of the Cherokee Group.  At some exposures, especially at the Devil\u2019s Punchbowl,<\/em> the sandstones are resting on a dark gray shale unit, the Caseyville Formation<\/strong>, the oldest Pennsylvanian unit in Iowa.  The Caseyville was deposited on a river delta that developed into an earlier advance of the Pennsylvanian sea into Iowa.<\/p>\n\n\n\n

\"Image
Image 01.  A view of a large block of Spoon Formation sandstone, popularly known as Steamboat Rock, that has broken free of the exposure bluff, sliding down-slope (probably on underlying Caseyville Formation shale).  The orange coloration is oxidized iron that coats quartz sand grains and sometimes cement them together.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 02.  A block of Spoon Formation sandstone that has broken free of the exposure bluff.  These broken blocks sometimes slide away from the base of the exposure creating a cave-like opening.  This action is called \u201cmechanical karst\u201d, different than the \u201csolutional karst\u201d that creates most Iowa caves by dissolving limestone.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 03.  This image shows an exposure of Spoon Formation sandstone that displays thick beds.  The cliff face displays an overall grayish coloration that is produced by calcium carbonate in groundwater that moved through the sandstone.  The water evaporates at the rock face, precipitating the calcium carbonate (calcite) that cements the sand grains together forming a thin surface crust that resists erosion.  This process is sometimes referred to as \u201ccase hardening\u201d. In the light brownish areas this cemented crust has fallen off (due to freeze-thaw or other mechanisms) exposing the fresh sandstone.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 04.  A closer look at the sandstone bluff showing the gray case-hardened areas surfaces and the light orange sandstone where the case hardening has fallen away.  The bluish colored areas are due to lichens coating the rock surface. This coloration can also be seen on image #3, which is the larger cliff face from which this image was taken, and may be accentuated by the photographic process. Some areas of the sandstone display a rust-red color where iron oxides coat or cement the grains more heavily.  The thin beds display a time of slower deposition punctuated by calmer water where silts and shales were deposited.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 05.  A close view of the Spoon Formation sandstone with gray case hardening on some surfaces and brownish fresh surfaces where the varying amounts of iron oxide coat and cement the sand grains.  A block of sandstone near the base has separated from the exposure creating a small scale example of mechanical karst.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 06.  An even closer look at the sandstone reveals cross-bedding, created by shifts in the river channel.  Areas of case-hardened surfaces appear gray and areas where it has fallen away appear brown or orange. The circular light colored spots are lichens and other plants that have grown on the sandstone.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 07.  Cross-bedded sandstone deposited by an ancient river.  Groundwater moving through the sand carries calcium carbonate that precipitated when the water evaporates at the rock face.  Large areas of this face were case-hardened, displaying the gray coloration.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 08.  Another good example of cross-bedding in the Spoon Formation sandstone deposited by an ancient river.  Each of the thin individual layers (or beds) represent a single event, with coarser-grained layers deposited by faster moving water and finer grains by water with less energy.  Each coarse layer represents a high energy event with increasingly finer sand grains deposited as the event dissipated. The coarser layers are slightly better cemented, so are less easily eroded and stand out in positive relief, the finer grains erode in from the face.  Groups of beds all trending the same direction were deposited as an underwater dune, with bundles of beds trending in different directions representing a change in water current direction, crossing the earlier beds; cross-bedding.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 09.   A cliff of sandstone originally deposited about 312 million years ago as sand in a large river that was flowing to the southwest.  A variety of bed thicknesses and orientations can be seen as can areas with gray case-hardening and other areas of brown freshly-exposed stone.  The beds are cut near the right side of the exposure by a near-vertical series of fractures.<\/figcaption><\/figure>\n\n\n\n
\"\"
Image 10:  A close-up of the sequence of roughly horizontal cross-bedded sandstones that was subsequently modified by tectonic activity that produced near-vertical fractures and deformed some of the beds.<\/figcaption><\/figure>\n\n\n\n
\"Image
Image 11.  An example of differential cementation created this honey-comb looking features.  Water bearing natural cements such as clay and lime moved preferentially through areas of coarser sand and sub-vertical fractures, cementing the sand grains as it moved.  In nearby areas where water did not move as freely the sand grains were not cemented as securely and eroded away when exposed to the weather. <\/figcaption><\/figure>\n\n\n\n
\"Image
Image 12.  This image is a wonderful example of thin-bedded sandstone (separated by thin silty layers) and cross-bedding (identified by the unconformable contact of one set of bedded layers with another set trending in a slightly different direction.<\/figcaption><\/figure>\n\n\n\n

Many of the photographs on this page were taken during the 2000\u2019s. So, some features may appear somewhat different now.<\/p>\n","protected":false},"excerpt":{"rendered":"

Iowa is not known for having an especially dramatic landscape. But in fact there are many hidden gems to be found in this particular plot of so-called flyover country. Among them is Wildcat Den State Park in southeastern Iowa. According to Iowa DNR it is one of the most photographed state parks in Iowa. IfContinue reading “Iowa Rocks!”<\/span><\/a><\/p>\n","protected":false},"author":223,"featured_media":2370,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[51,6],"tags":[222,223,224],"syndication":[41,37],"_links":{"self":[{"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/posts\/2368"}],"collection":[{"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/users\/223"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/comments?post=2368"}],"version-history":[{"count":12,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/posts\/2368\/revisions"}],"predecessor-version":[{"id":2791,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/posts\/2368\/revisions\/2791"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/media\/2370"}],"wp:attachment":[{"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/media?parent=2368"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/categories?post=2368"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/tags?post=2368"},{"taxonomy":"syndication","embeddable":true,"href":"https:\/\/blog.lib.uiowa.edu\/science\/wp-json\/wp\/v2\/syndication?post=2368"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}