Foelsche is a partly buried

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 ...

(or

astrobleme 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 ...

), the eroded remnant of a former

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...

. It is situated about 85 km southeast of

Borroloola Borroloola ( local Aboriginal languages: ''Burrulula'') is a town in the Northern Territory of Australia. It is located on the McArthur River, about 50 km upstream from the Gulf of Carpentaria. Location Borroloola lies on the traditional c ...

in the

Northern Territory The Northern Territory (commonly abbreviated as NT; formally the Northern Territory of Australia) is an states and territories of Australia, Australian territory in the central and central northern regions of Australia. The Northern Territory ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

, and named after the nearby Foelsche River. Although little of it is exposed at the surface, and no crater shaped topography is evident, the circular nature of the feature is obvious on aeromagnetic images, a factor that led to its discovery.

Description

The impact occurred into flat-lying

Mesoproterozoic The Mesoproterozoic Era is a geologic era that occurred from . The Mesoproterozoic was the first era of Earth's history for which a fairly definitive geological record survives. Continents existed during the preceding era (the Paleoproterozoic), ...

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s of the

McArthur Basin The McArthur Basin is a large intracratonic sedimentary basin in northern Australia, with an exposed area of about 180,000 km2. Most of it lies within the northeastern Northern Territory, but extends over the border into the state of Qu ...

and most of the crater is covered by a semi-circular hill of flat-lying

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...

sedimentary rock. The only exposure of the crater itself are scattered outcrops of deformed

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and

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 di ...

around the northern edge of the overlying hill, which are inferred to be remnants of the crater rim. The rim is about 6 km in diameter. Evidence indicating an impact origin for the feature includes an abundance of

shocked quartz Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These pla ...

grains in the sedimentary rocks overlying the crater; these are assumed to have been eroded from the floor of the crater. The prominent circular aeromagnetic anomaly which marks the hidden crater is believed to have been caused by the disruption of a horizontal layer of magnetic rock (

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

sill) by the impact event,.
The age of Foelsche is not well constrained, but it must be younger than the

target rocks and older than the

rocks that partly fill the crater; it has been argued that the age is most likely Neoproterozoic because it appears that the crater was covered by sediments soon after the impact event.

Description

See also

References

Further reading