The Weaubleau structure is a probable

meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...

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

site in western

Missouri Missouri (''see #Etymology and pronunciation, pronunciation'') 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 border ...

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. In 19th-century accounts of the city in En ...

Osceola Osceola (1804 – January 30, 1838, Vsse Yvholv in Muscogee language, Creek, also spelled Asi-yahola), named Billy Powell at birth, was an influential leader of the Seminole people in Florida. His mother was Muscogee, and his great-grandfa ...

, and

Vista Vista may 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) a medical records system of the United States ...

. It is believed to have been caused by a

meteoroid A meteoroid ( ) is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than ''asteroids'', ranging in size from grains to objects up to wide. Objects smaller than meteoroids are classifie ...

between 335 and 340 million years ago during the middle Mississippian Period (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 invol ...

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 Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix. The word has its origins in the Italian language ...

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 syst ...

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 m ...

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 structure, composition, and History of Earth, history of Earth. Geologists incorporate techniques from physics, chemistry, biology, mathematics, and geography to perform research in the Field research, ...

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, on the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period (or the upper of two subsystems of the Carboniferous System). It last ...

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 U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

, and

Kansas Kansas ( ) is a landlocked U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Nebraska to the north; Missouri to the east; Oklahoma to the south; and Colorado to the west. Kansas is named a ...

. These 38th parallel structures 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 warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, an ...

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

, an extremely unlikely event on

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. 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 e ...

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 impact structure is an impact structure near the city 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 ha ...

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

orogeny Orogeny () is a mountain-mountain formation, building process that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is tectonic uplift, u ...

( Beaverhead impact structure). 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 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 prec ...

concretion A concretion is a hard and compact mass 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 shapes a ...

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 mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

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 b ...

s of the Northview Formation 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