Callovian
CALLOVIAN (from Callovium, the Latinized form of Kellaways, a village not far from Chippenham in Wiltshire), in geology, the name introduced by d'Orbigny for the strata which constitute the base of the Oxfordian or lowermost stage of the Middle Oolites. The term used by d'Orbigny in 1844 was "Kellovien," subsequently altered to "Callovien" in 1849; William Smith wrote "Kellaways" or "Kelloways Stone" towards the close of the 18th century. In England it is now usual to speak of the Kellaways Beds; these comprise (1) the Kellaways Rock, alternating clays and sands with frequent but irregular concretionary calcareous sandstones, with abundant fossils; and (2) a lower division, the Kellaways Clay, which often contains much selenite but is poor in fossils. The lithological characters are impersistent, and the sandy phase encroaches sometimes more, sometimes less, upon the true Oxford Clay. The rocks may be traced from Wiltshire into Bedfordshire, Lincolnshire and Yorkshire, where they are well exposed in the cliffs at Scarborough and Gristhorpe, at Hackness (90 ft.), Newtondale (80 ft.) and Kepwick (100 ft.). In Yorkshire, however, the Callovian rocks lie upon a somewhat higher palaeontological horizon than in Wiltshire. In England, Kepplerites calloviensis is taken as the zone fossil; other common forms are Cosmoceras modiolare, C. gowerianum, Belemnites oweni, Ancyloceras calloviense, Nautilus calloviensis, Avicula ovalis, Gryphaea bilobata, etc.
On the European continent the "Callovien" stage is used in a sense that is not exactly synonymous with the English Callovian; it is employed to embrace beds that lie both higher and lower in the time-scale. Thus, the continental Callovien includes the following zones: -
Upper Callovien (Divesien) { Zone of Peltoceras athleta, Cosmoceras Duncani, Quenstedtoceras Lamberti and Q. mariae.
Lower Callovien { Zone of Reineckia anceps, Stephanoceras coronatum and Cosmoceras jason and a lower zone of C. gowerianum and
Macrocephalites macrocephalus.
Rocks of Callovian age (according to the continental classification) are widely spread in Europe, which, with the exception of numerous insular masses, was covered by the Callovian Sea. The largest of these land areas lay over Scandinavia and Finland, and extended eastward as far as the 40th meridian. In arctic regions these rocks have been discovered in Spitzbergen, Franz Josef Land, the east coast of Greenland, and Siberia. They occur in the Hebrides and Skye and in England as indicated above. In France they are well exposed on the coast of Calvados between Trouville and Dives, where the marls and clays are 200 ft. thick. In the Ardennes clays bearing pyrites and oolitic limonite are about 30 ft. thick. Around Poitiers the Callovian is 100 ft. thick, but the formation thins in the direction of the Jura.
Clays and shales with ferruginous oolites represent the Callovian of Germany; while in Russia the deposits of this age are mainly argillaceous. In North America Callovian fossils are found in California; in South America in Bolivia. In Africa they have been found in Algeria and Morocco, in Somaliland and Zanzibar, and on the west coast of Madagascar. In India they are represented by the shales and limestones of the Chari series of Cutch. Callovian rocks are also recorded from New Guinea and the Moluccas.
See Jurassic; also A. de Lapparent, Traité de géologie, vol. ii. (5th ed., 1906), and H.B. Woodward, "The Jurassic Rocks of Britain," Mem. Geol. Survey, vol. v.
(J. A. H.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)
