The Formation is subdivided into three member units: unnamed basal marine sandstone, the Neuburg Kieselerde Member, and an upper silicified conglomerate (Homsand facies).[2] Geographically, this formation is located in the central southernmost part of the Franconian Jura, on the left bank of the Danube, roughly between the towns of Wellheim and Neuburg in Bavaria. The formation is commercially quarried for siliceous earth, which has a variety of applications.
The formation infills karstic voids found in Upper Jurassic limestones. Its upper contact is with either MioceneUpper Freshwater Molasse clays and marls or Pleistocene glacial deposits[3] while the lower contact is with the Jurassic limestones, or the Lower Cretaceous Schutzfels Formation, a terrestrial unit which also infills the karstic terrain.
The Wellheim Formation was formed in a quiet water environment[4] by deposition of pelagic sediments into a number of submerged karsts in the ocean floor over several million years.[5] Wilmsen et al (2010) identified the primary sediment composition as sandy and spiculitic sediments, with notably little terrigenous input.[4] It has since been classified as an Opoka type marine deposit, a term that is primarily used to refer to Upper Cretaceous sponge spicule rich siliceous limestones found in Poland and western Ukraine.[6]
Lüttig (2007) called the scientific view of the formation of the Neuburg Kieselerde Member "contested"[lower-alpha 1][7] however that position has not been supported by subsequent authors.
The Wellheim Formation is fossiliferous with the Neuburg Kieselerde Member having one of the most diverse invertebrate assemblages in the Danubian Cretaceous Group.[8] Schneider et al. (2013) mapped fossil yielding localities associated with this member in a rough triangle between Wellheim, Rennertshofen and Neuburg.[9]
In 2015, 55,000 tons of the purified material were produced. This required the open-pit mining of 120,000 tons of raw siliceous earth.[19]
The producer has claimed a non-biogenic, mineral origin for their product,[18] while most other sources assert a biogenic origin for the material.[lower-alpha 2][8]
Substances called siliceous earths are usually defined as having a biogenic origin,[20] with material of a similar composition usually being termed diatomaceous earth.
The producer also has repeatedly claimed a unique "one-of-a-kind worldwide" status of their product,[21][22] but Lüttig refuted this in 2007 for the material that is produced, saying that several similar material deposits are known, naming Heiligenhafen Kieselgestein as an example. On the other hand he agreed that the very special formation circumstances could indeed be called unique.[7]
It has historically been used for the production of glass,[23] ceramics[17] and color pigments like ultramarine.
German: "nicht unumstritten",[7] referring to the dissenting view of the sole exploiting company
For example, Schneider et al., 2013 have this statement as the first sentence of their article's abstract: "With approximately 100 species, the invertebrate macrofauna of the Neuburg Kieselerde Member of the Wellheim Formation (Bavaria, southern Germany) is probably the most diverse fossil assemblage of the Danubian Cretaceous Group."[8]
Mushack, R.; Bachmann, W. (1996). "Neuburger Kieselerde: natürliche, funktionelle Füllstoffe" [Neuburg siliceous earth: natural, functional filler substances]. GAK: Gummi, Fasern, Kunststoffe; Fachmagazin für die Polymerindustrie (in German). 49 (8). Ratingen: Gupta: 620–629. ISSN0176-1625.
Niebuhr, B.; Pürner, T.; Wilmsen, M. (2009). "Lithostratigraphie der außeralpinen Kreide Bayerns"[Litho-stratigraphy of the ex-alpine Cretaceous of Bavaria]. Schriftenreihe der Deutschen Gesellschaft für Geowissenschaften (in German). 65. Stuttgart, Germany: Schweizerbart Science Publishers: 7–58.
Salvador, R. B.; Prieto, J.; Mayr, C.; Rasser, M. W. (2016). "New gastropod assemblages from the Early/Middle Miocene of Riedensheim and Adelschlag-Fasanerie, southern Germany". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 279 (2): 127–154. doi:10.1127/njgpa/2016/0546.
Wilmsen, Markus; Niebuhr, Birgit (2010). "On the age of the Upper Cretaceous transgression between Regensburg and Neuburg an der Donau". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen. 256 (3): 267–278. doi:10.1127/0077-7749/2010/0051.
Neuendorf, K.K.E.; Mehl, J.P. Jr.; Jackson, J.A., eds. (2011). Glossary of Geology (5thed.). Alexandria, Virginia: American Geological Institute. ISBN978-0922152896.
Stokes, W.L.; Varnes, V.J. (1955). Glossary of Selected Geologic Terms with special reference to their use in engineering. Denver, Colorado: Colorado Scientific Society. p.165.
Grout, F.F. (1932). Petrography and petrology, a textbook. New York, New York: McGraw-Hill Book Co. p.522.