The Weaubleau structure is a probable

meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object en ...

impact Impact may refer to: * Impact (mechanics), a high force or shock (mechanics) over a short time period * Impact, Texas, a town in Taylor County, Texas, US Science and technology * Impact crater, a meteor crater caused by an impact event * Impac ...

site in western

Missouri Missouri is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Ranking List of U.S. states and territories by area, 21st in land area, it is bordered by eight states (tied for the most with Tennessee ...

near the towns of Gerster,

Iconium Konya () is a major city in central Turkey, on the southwestern edge of the Central Anatolian Plateau, and is the capital of Konya Province. During antiquity and into Seljuk times it was known as Iconium (), although the Seljuks also called it D ...

Osceola Osceola (1804 – January 30, 1838, Asi-yahola in Creek), named Billy Powell at birth in Alabama, became an influential leader of the Seminole people in Florida. His mother was Muscogee, and his great-grandfather was a Scotsman, James McQ ...

, and

Vista Vista usually refers to a distant view. Vista may also refer to: Software *Windows Vista, the line of Microsoft Windows client operating systems released in 2006 and 2007 * VistA, (Veterans Health Information Systems and Technology Architecture) ...

. It is believed to have been caused by a

meteoroid A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as mic ...

between 335 and 340 million years ago during the middle

Mississippian Period The Mississippian ( , also known as Lower Carboniferous or Early Carboniferous) is a subperiod in the geologic timescale or a subsystem of the geologic record. It is the earlier of two subperiods of the Carboniferous period lasting from roughl ...

(Latest Osagean to Earliest

Meramecian The Meramecian or Maramec stage is a sequence of Mississippian rocks in the Mississippi River Valley. It is named for the Meramec River in Missouri. Members Included are the St. Louis Limestone, Ste. Genevieve Limestone, Salem Limestone, and the ...

). It is listed by the

Impact Field Studies Group The Impact Field Studies Group (IFSG) was a scientific organization emphasizing geologic field research of suspected and confirmed sites of impact craters and impact structures. The group is composed of researchers, professionals and students invo ...

as a "probable" impact structure. The structure consists of an area of severe structural deformation and extensive

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...

tion that was poorly understood and had been thought to be the result of either

thrusting Thrust is a reaction force described quantitatively by Newton's third law. When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that ...

over a

dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a ...

or a cryptoexplosive event.Snyder, F.G., Gerdemann, P.E., Hendricks, H.E., Williams, J.H., Wallace, G., and Martin, J.A., 1965, Cryptoexplosive structures in Missouri: Guidebook, 1965 Annual Meeting of the Geological Society of America: Missouri Geological Survey and Water Resources, Report of Investigations No. 30, 73 p. A circular structure was discovered by

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, alt ...

Kevin R. Evans through examination of digital elevation data.Evans, Kevin R.; Mickus, Kevin L.; Rovey, Charles W. III; & Davis, George H. (2003). Field Trip I: The Weaubleau Structure: Evidence of a Mississippian Meteorite Impact in Southwestern Missouri. ''Association of Missouri Geologists Field Trip Guidebook, No. 26, 50th Annual Meeting'', pp. 1-30. Missouri Department of Natural Resources
PDF
/ref> The structure was originally called the Weaubleau-Osceola structure after Weaubleau Creek and

. It is now known as the Weaubleau structure. Because the site was covered by later

Pennsylvanian Period The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly . As with most oth ...

sediments, and only partially exposed to erosion relatively recently, its structure is well preserved, and its age can be determined with fair accuracy. It is one of a series of known or suspected impact sites along the 38th parallel in the states of

Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Roc ...

, and

Kansas Kansas () is a state in the Midwestern United States. Its capital is Topeka, and its largest city is Wichita. Kansas is a landlocked state bordered by Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to ...

. These

38th parallel structures The 38th parallel structures, also known as the 38th parallel lineament, are a series of seven circular depressions or deformations stretching across southern Illinois and Missouri and into eastern Kansas, in the United States, at a latitude of r ...

are thought to possibly be the result of a serial impact, similar to that of

comet Shoemaker-Levy 9 A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandt ...

, an extremely unlikely event on

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

. The argument for a serial strike would be greatly strengthened if the ages of the other 38th parallel structures could be constrained to the same period as the Weaubleau structure. The Weaubleau structure is one of the fifty largest known

impact structure An impact structure is a generally circular or craterlike geologic structure of deformed bedrock or sediment produced by impact on a planetary surface, whatever the stage of erosion of the structure. In contrast, an impact crater is the surface ...

s on earth and the fourth largest in the United States. The three larger ones in the US either have been glaciated and buried (

Manson crater The Manson crater is an impact crater near the site of Manson, Iowa where an asteroid or comet nucleus struck the Earth during the Cretaceous Period, approximately 74 Ma. It was one of the largest known impact events to have happened in No ...

), are under water ( Chesapeake Bay crater), or have been subjected to

orogeny Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An '' orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted ...

(

Beaverhead impact structure The Beaverhead impact structure is the 2nd largest impact structure within the U.S. It lies within the states of Idaho and Montana. Estimated at in diameter, it is the 9th largest impact crater on Earth. With an estimated age of 600 million ye ...

). Therefore, the Weaubleau structure is the largest exposed untectonized impact structure in the US.

Round rocks

Long thought to be a glacial remnant, these

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** C ...

rocks are found in the area of the Weaubleau structure. They are nearly perfectly round, and are referred to locally simply as "geodes", "round rocks", "Missouri rock balls", or "Weaubleau eggs". It has been suggested that the round rocks are

chert Chert () is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, the mineral form of silicon dioxide (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a ...

concretion A concretion is a hard, compact mass of matter formed by the precipitation of mineral cement within the spaces between particles, and is found in sedimentary rock or soil. Concretions are often ovoid or spherical in shape, although irregular ...

s or nodules. The round rocks may have formed when the impact threw

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

clast Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

s of the

Northview Formation The Northview Formation is a geologic formation in southwest Missouri. Its fauna includes brachiopods and abundant trace fossils of the Mississippian subperiod and Kinderhookian Series.The Stratigraphic Succession in Missouri, Missouri Geolog ...

away from the center of the impact structure and subsequent silica-saturated waters precipitated silica around the shale clasts. The formation of the round rocks is poorly understood and requires further research.

Round rocks

See also

References

Further reading