Reasons for a name

The Rupelian, introduced in 1850 by French-speaking Belgian geologist André Hubert Dumont, derives its name from a small tributary river to the Scheldt, Rupel in Belgium. A self-taught geologist, Dumont had made his appearance in the academic scene as a teen-ager, author of the prize-winning geological map of the Liége province. Launched in a career with the support of the great geologist d’Omalius d’Halloy, the young man believed that fossils alone, remains of organisms unevenly distributed on the surface of the earth, were unreliable tools of stratigraphy. Relative sealevel variations instead, interesting distant regions of the globe at the same time, and as revealed by the superposition of different facies, needed to be considered in rock correlation.

Jean Baptiste Julien d'Omalius d'Halloy (1783-1875)
Jean Baptiste Julien d’Omalius d’Halloy (1783-1875)
Choosing among three memories, in 1828 the Belgian Academy of Sciences presieded by Jean Baptiste Julien d’Omalius d’Halloy, found Dumont’s contribution as a surprisingly accurate rendition of a chaotic region.
When the Academy presented me with the three above-mentioned memories, I was astonished by what was new in one of them, but I wasn’t sure if this consisted in real discoveries or the inventions of a burning imagination. [When presented with Dumont] I was very surprised to find myself in front of a young man who didn’t seem to be more than fifteen-year-old.[…]Dumont has tried to demonstrate in 1851 that with the only help of stratigraphic notions, we can determine the limits of the seas during the different geological epoques and to judge the synchronicity of deposits.d'Omalius , 1858, p. 96-99
André Hubert Dumont (1809-1857)
André Hubert Dumont (1809-1857)
The relative age of the Boom Clay, in the West Flanders, was the object of Dumont’s enquiry since the late forties. The results of his field studies were presented to the Belgian Academy in a rapport of 10 November 1849. A case had stemmed from the purported analogy between the Boom Clay and the London Clay, in its turn coeval with the Coarse Limestone of the Paris Basin, typifying the Eocene. Dumont demonstrated instead that, notwithstanding superficial analogies, by the law of superposition his Rupelian had to be considered much younger than the British and French Eocene. This could be explained by differential uplift of North European regions, and by the different timings of marine transgression.
The Rupelian system has, in some localities, a bed of small thickness of sandy clays full of nucules, although more often starts with more or less clayey yellow sands. The upepr part is formed by very muddy sands and by schistose clays to which I relate the shelly sands of Rupelmonde, Boom, Hasselt, etc.Dumont, 1850, p. 370
A basculating movement uplifted the Belgian soil and downlifted that of Northern France, followed by a general lowering and a marine transgression towards Paris, producing on one side the marine marls and sands of Fontainebleau, the clays with Cyrena semi-striata, Cerithium plicatum, and the lower sands of the Rupelian system, so that synchronous strata in the two countries offer mineralogical and paleontological analogies. But such analogies were of short duration: a new vertical mouvement turned the Paris basin into a lake, producing a different effect in the Belgian marine basin, regressing its limits towards the North. Lacustrine deposits were deposited on the first, the marine clays of Boom on the other, thus explaining why the fauna in the vicinity of Rupel is missing in Paris, and that of the upper lacustrine deposit is wanting in Belgium.Dumont, 1851, p. 194-195
 
The Boom Clay Formation (from the website of Environment, Nature and Energy Department of the Flemish Government http://www.lne.be)
The Boom Clay Formation (from the website of Environment, Nature and Energy Department of the Flemish Government http://www.lne.be)
Nuculid bivalves of the Boom Clays (from Marquet 2010)
Nuculid bivalves of the Boom Clays (from Marquet 2010)
In 1852 Alcide d’Orbigny established the stage Stampian, from Étampes, in the Paris Basin, for the lower part of the Falunian (Oligocene). The Stampian is considered a synonym of Rupelian, which has priority (Lozouet, 2012). Learn more De Man E., Van Simaeys S., Vandenberghe N., Burleigh Harris W. & Wampler J.M. (2010). On the nature and chronostratigraphic position of the Rupelian and Chattian stratotypes in the southern North Sea basin. Episodes 33, 3-14. D’Omalius D’Halloy (1858). Notice sur André Dumont. Annuaire de l’Académie Royale de Belgique, des Lettres, et des Beaux-Arts de Belgique 24, 91-100. Dumont M.A. (1850). Rapport sur la carte géologique du Royaume de Belgique. Bulletin de l’Académie Royale de Sciences des Lettres et des Beaux-Arts de Belgique 16, 251–373. Dumont M.A. (1851). Note sur la position géologique de l’argile rupélienne et sur le synchronisme des formations tertiaires de la Belgique, de l’Angleterre et du Nord de la France. Bulletin de l’Académie royale de Belgique 18, 179-195. Lozouet, P. (coord., 2012). Stratotype Stampien. Muséum National d’Histoire Naturelle, Paris, 464 p. (Patrimoine géologique; 4). Marquet R. (2010). Reassessment of the Bivalvia (Mollusca) from the Boom Formation (Rupelian, Oligocene) of Belgium, with description of new species. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 80, 253-282.
Van Simaeys S. & Vandenbergh N. (2006). Rupelian. Geologica Belgica 9, 95-101.
Zittel K.A. (1901). History of geology and palaeontology to the end of the nineteenth century. London, Scott, 562 p. Links Flemish Government webpage on mineral resources 1850 note by A. Dumont to the Belgian Academy