Weaubleau-Osceola structure
Encyclopedia
The Weaubleau-Osceola structure is thought to be a meteorite
impact
site in western Missouri
near the towns of Osceola
and Weaubleau
. It is believed to have been caused by a 1200-ft (366 m) meteoroid
between 310 and 340 million years ago during the late Mississippian period.
It is listed by the Impact Field Studies Group
as a "probable" impact structure.
The structure consists of an area of severe structural deformity and extensive breccia
tion that was poorly understood and had been thought to be the result of either faulting or of a cryptoexplosive
event. A 19-km-diameter (12 mi) circular structure was discovered by geologist
Kevin R. Evans through examination of digital elevation data
. Originally called the Weaubleau structure after Weaubleau Creek that cuts through it, now that its scope is better understood it is known as the Weaubleau-Osceola structure.
Because the site was covered by later Pennsylvanian period
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
, Missouri
, and Kansas
. These 38th parallel structures
are thought to possibly be the result of a serial impact, similar to that of comet
Shoemaker-Levy 9
on Jupiter
, an extremely unlikely event on Earth
. 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-Osceola structure.
The Weaubleau-Osceola structure is one of the fifty largest known impact crater
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
), are under water (Chesapeake Bay crater
), or have been subjected to orogeny
(Beaverhead crater
). Therefore the Weaubleau-Osceola structure is the largest exposed untectonized
impact crater in the US.
Long thought to be a glacial remnant, these conglomerate rocks
are found in the area of Osceola. They are nearly perfectly round, and are referred to locally simply as "round rocks" or "Missouri rock balls".
Current theory suggests that these rocks are chert
concretions, created when the impact threw pieces of shale
away from the center of the crater, and later silica-rich materials formed around the shale seeds.
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...
impact
Impact event
An impact event is the collision of a large meteorite, asteroid, comet, or other celestial object with the Earth or another planet. Throughout recorded history, hundreds of minor impact events have been reported, with some occurrences causing deaths, injuries, property damage or other significant...
site in western Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
near the towns of Osceola
Osceola, Missouri
Osceola is a city in St. Clair County, Missouri, United States. The population was 835 at the 2000 census. It is the county seat of St. Clair County.-History:...
and Weaubleau
Weaubleau, Missouri
Weaubleau is a city in Hickory County, Missouri, United States. The population was 518 at the 2000 census.-Geography:Weaubleau is located at ....
. It is believed to have been caused by a 1200-ft (366 m) meteoroid
Meteoroid
A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite...
between 310 and 340 million years ago during the late Mississippian period.
It is listed by the Impact Field Studies Group
Impact Field Studies Group
The Impact Field Studies Group is 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 involved in study of impact sites...
as a "probable" impact structure.
The structure consists of an area of severe structural deformity and extensive breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
tion that was poorly understood and had been thought to be the result of either faulting or of a cryptoexplosive
Cryptoexplosion
The term cryptoexplosion structure means an explosion of unknown cause. The term is now largely obsolete. It was once commonly used to describe sites where there was geological evidence of a large scale explosion within the Earth's crust, but no definitive evidence for the cause such as normal...
event. A 19-km-diameter (12 mi) circular structure was discovered by geologist
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
Kevin R. Evans through examination of digital elevation data
Digital elevation model
A digital elevation model is a digital model or 3-D representation of a terrain's surface — commonly for a planet , moon, or asteroid — created from terrain elevation data....
. Originally called the Weaubleau structure after Weaubleau Creek that cuts through it, now that its scope is better understood it is known as the Weaubleau-Osceola structure.
Because the site was covered by later Pennsylvanian period
Pennsylvanian
The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
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
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
, Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
, and Kansas
Kansas
Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...
. These 38th parallel structures
38th parallel structures
The 38th parallel structures, also known as the 38th parallel lineament, are a series of circular depressions or deformations stretching 700 km across southern Illinois and Missouri into eastern Kansas at a latitude of roughly 38 degrees north.Rampino and Volk postulated that these...
are thought to possibly be the result of a serial impact, similar to that of comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
Shoemaker-Levy 9
Comet Shoemaker-Levy 9
Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects. This generated a large amount of coverage in the popular media, and the comet was closely observed by...
on Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, an extremely unlikely event on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. 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-Osceola structure.
The Weaubleau-Osceola structure is one of the fifty largest known impact crater
Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...
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
Manson crater
The Manson impact crater is near the site of Manson, Iowa where an asteroid or comet nucleus struck the Earth during the Cretaceous Period, 74 Ma...
), are under water (Chesapeake Bay crater
Chesapeake Bay impact crater
The Chesapeake Bay impact crater was formed by a bolide that impacted the eastern shore of North America about 35 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" or marine impact craters, and the largest known impact crater in the U.S...
), or have been subjected to orogeny
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
(Beaverhead crater
Beaverhead crater
Beaverhead is an impact structure in central Idaho and western Montana in the United States.Estimated at in diameter, it is one of the largest impact craters on Earth...
). Therefore the Weaubleau-Osceola structure is the largest exposed untectonized
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
impact crater in the US.
Round rocks of Osceola
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
are found in the area of Osceola. They are nearly perfectly round, and are referred to locally simply as "round rocks" or "Missouri rock balls".
Current theory suggests that these rocks are chert
Chert
Chert is a fine-grained silica-rich microcrystalline, cryptocrystalline or microfibrous sedimentary rock that may contain small fossils. It varies greatly in color , but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements...
concretions, created when the impact threw pieces of shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
away from the center of the crater, and later silica-rich materials formed around the shale seeds.