1911 Encyclopædia Britannica/Miocene

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MIOCENE, in geology, the system of strata which occurs between the Oligocene and the Pliocene. The term, derived from the Greek μεῖον, less, and καινός, recent, was introduced by Sir Charles Lyell, as indicating palaeontological a less percentage of recent species than is found in the Pliocene. Variable lacustrine, estuarine and marine deposits, especially characterized by soft calcareous sandstones and conglomerates (“ molasse ”) and sandy shell-beds (“ faluns ”), make up the Miocene system of the Neogene or newer Tertiary in Europe and western Asia, where it attains its fullest development. A. de Lapparent's classification is here adopted:—

V. Pontian or Pannonian.—Brackish- and fresh-water marls, limestones and gravels: occurring at Vienna, in the Caspian and eastern Mediterranean basins, and in southern France; mammalian deposits of Pikermi and the Siwalik Hills, with Hipparion gracile, Mastodon longirostris, Rhinoceros schleiermachi, numerous rummants, Congeria subglobosa. Marine beds of Belgium (Black Crag) and north Germany.

IV. Sarmatian.—More or less salt-water sands and marls of the same basins with Mastodon angustidens, Anchitherium aurelianense, Cerithium pictum, C. rubiginosum, Ostrea gingensis, Mactra podolica, Tapes gregarius. Stages IV. and V. represented in north-western France by marine sands (Cardita striatissima), and in Algeria and Morocco by marine marls and limestones.

III. Vindobonian.—Sub-stages:— (b) Tortonian: Marine marls with Ancillaria glandifarmis, Conus antiquus, Ranella marginata, Trochus patulus, Voluta rarispina. Laminated fresh-water limestones of Oeningen with fish, countless insects, and plants showing seasonal changes of the year in their successive layers (Acer trilobatum, Populus mutabilis, Juglans acuminata, Camphora, Podogonium); and the lacustrine deposits of central Spain. (a) Helvetian: Marine shelly sandstones and conglomerates (“ molasse " of Switzerland) with Ostrea gingensis, Carita jouanneti, Panopaea menardi, Conus ventricosus; the “faluns” of Touraine and Aquitaine; and the marine beds of Black Sea basin. At the base of the marine Helvetian in the Vienna basin clays (" Schlier ") with rock-salt and gypsum, and the lacustrine beds of Gascony (Calcaire de Simone with Mastodon tapiroides, M. simorrensis, Dinotherium giganteum) occur. II. Burdigalian or Langhian.-Marine “faluns” of Bordeaux (Oliva basteroti, Turritella terebralis); marls of Langhe in Liguria (Peclen burdigalensis); marine deposits of Vienna basin, Caspian region, Tunis and Algeria; fresh-water sands and marls of Orleans with Mastodon angustidens, M. tapiroides, Dinotherium cuvieri, Anthraxotherium onoideum; Littorinella clays of Mainz basin with Acerotherium incisivum Littorinella acuta, Dreyssenia brardi; freshwater grey “ molasse ” of Switzerland, with acacias, laurels, palms and sequoias.

I. Aquitanian.-Limestones, sands and marls of lakes and lagoons, with Anthracotherium, Anchitherium, Acerotherium inciswuiri, Palaeochoerus typus, Helix ramondi, Limnaea pachygaster, Planorbis coma, Potamides lamarcki; Quercus, Acacia, Ficus, Camphora, Cimzamomum, Taxodium, Glyptostrobus, Sequoia, Sabal, Phoenix, occur in central France (Caleaire de la Beauce); the plant-beds of Manosque; Mainz basin; lower “ molasse " of Switzerland with lignite, gypsum, red marls and conglomerates; “ brown-coal series " of north Germany with lignite. Intercalated marine sandstones occur in Aquitaine and near Marseilles; other marine developments occur in the “ faluns ” of Gascony (Lepidocyclina mantelli, Miogypsina burdigalensis), the upper Aquitanian of Bavaria and Austria-Hungary (0strea crassiassima, Pectunculus pilosus), and in southern Spain, Italy and Malta (Lepidocyclina and Lithothamnium). Basic tufis and lavas occur in Auvergne.

Some authors assign Stage I. to the Oligocene, Stage V. to the Pliocene; Stages I. and II. correspond to the first, and III. to the second Mediterranean Stage of E. Suess.

In Europe a general emergence of land in late Oligocene time resulted at the beginning of the Miocene (Aquitanian) in widespread lacustrine conditions throughout the western part of that continent, upon which the sea encroached at few points, though it had gained access to the Vienna basin and extended westward into Bavaria. Otherwise, marine Aquitanian deposits are confined to the Mediterranean basin and the south-west corner of France. Most of northern Europe, including the British Isles, remained dry land throughout Miocene time. During the Burdigalian period, with increasing elevation of the mountain regions and depression of the Mediterranean and Caspian basins, a marine invasion began, which passed its maximum in the Vindobonian. The Mediterranean reached eastward to Persia, and, still open to the Atlantic, submerged north Africa, most of Italy and the neighbouring islands. It ascended the Rhone valley, penetrated to the Mainz basin, and skirting the north fiank of the Alpine region passed into the Vienna basin and thence around the Carpathian tract into the Pontic and Caspian depression. The waters of the Atlantic further invaded the regions of the Garonne and the Loire, isolated Brittany and encroached upon north Europe between Belgium and Denmark.

The elevation of the Alps, and probably of the whole Alpine system of mountain folds from Morocco to Indo-China, though initiated by earlier Miocene and late Oligocene movements, took place mainly during the latter part of the Vindobonian period, and was completed in the Sarmatian. The waters of the ocean were then excluded from the Caspian and eastern Mediterranean basins, and replaced by vast fresh-water lakes; while brackish water lagoons occupied much of the western Mediterranean. This great retreat of the sea culminated in the Pontian stage, and land-connexion was established between North and South America. Outside the Eurasian region, Aquitanian deposits occur in Formosa, java, Borneo and Madagascar; while Burdigalian deposits are found in Mongolia. The Vindobonian ranges from Greenland, Iceland and Spitzbergen, where it contains lignite and plants denoting a temperate climate, by Japan, lava and India, to Victoria. It recurs in the Azores and the Antilles, and at intervals along the American continent from Patagonia to Alaska, where all three lower stages are represented, as also in the West Indies. Along the Atlantic slope of the United States and around the Gulf of Mexico the complete Miocene series is present, the Sarmatian and Pontian also occur in California.

The Miocene was a period of change, of mountain-building, climatic differentiation hitherto unprecedented, and of moderation in organic life, especially on land. The rich European flora indicates an equable and moist sub-tropical climate, slowly cooling, as witnessed by the gradual increase of trees with deciduous foliage amongst those characteristic of more tropical conditions. Oaks, maples, poplars, planes, willows, Cinnamomum, Camphora, Myrica, Sequoia, Taxodium, Glyptostrobus and palms, flourished together. The marine calcareous alga Lithothamnium became an important reef-building organism. Nummulites gave place to Lepidocyclina; lamellibranchs and particularly gastropods abounded in the shallow seas, of which the shark Carcharodon and the marine mammals Squalodon and Halitherium were amongst the largest denizens. The mammalian land-fauna of Europe made striking advances, and assumed a decidedly African aspect. Marsupials had disappeared from it before the Burdigalian period, during which primitive genera like Palaeachoerus, Hyopotamus, and the hornless ruminants Anthracotherium and Brachyopus, became extinct, while proboscideans (Mastodon, Dinotherium), rhinoceros and apes (Oreopithecus, Pliopithecus) came in, followed by antelopes, beavers and probably Machaerodus in the Vindobonian. The spread of turgforming grasses was succeeded in the Pontian by an enormous increase of herbivorous mammals, including Hipparion and horned ruminants (Helladotuherium, Antilope, Cervus, Camelopardalis, Palaeotragus), whose migrations were facilitated by the desiccation of the Mediterranean basin.  (C. B. W.*)