Pliocene

Pliocene (from the Gr. 7rXd ov, more, and xacvos, recent), in geology, the name given by Sir C. Lyell to the formations above the Miocene and below the Pleistocene (Newer Pliocene) strata. During this period the great land masses of the earth were rapidly approaching to the configuration which they exhibit at the present day. The marine Pliocene deposits are limited to comparatively few areas; in Europe, in the beginning of the period, the sea.  washed the shores of East Anglia and parts of the south coast of England; it extended well into Belgium and Holland and just touched here and there on the northern and north-western coasts of France; it sent an arm some distance up the valley of the.

Guadalquivir and formed small bays on several points of the. southern coast of France; and up the Rhone basin a considerable gulf reached as far as Lyons. Early in the period the sea. covered much of Italy and Sicily; but the eastward extension of the ancient Mediterranean in south-east Europe, through the Danube basin, the Aral, north Caucasian and Caspian regions, continued to suffer the process of conversion to lagoons and large lakes which had begun in the Miocene.

Hypothetical continental outlines Pliocene Period  Generally all over the world the majority of Pliocene formations are non-marine, and the limited and local nature of the elevations since the inception of the period has exposed to view only the shallow marginal marine deposits. The principal exception to the last statement is to be found in the Pliocene of Italy and Sicily, where a continuous crustal depression permitted the accumulation of great thicknesses of material, which later on, towards the close of the period, were elevated some thousands of feet. With these deformatory movements are associated the Italian volcanoes; Etna certainly began its career beneath the sea, for its older tuffs are found interstratified with marine beds, and possibly some of the others had a similar origin. At the same time volcanic outbursts, some apparently .comparable to that of Martinique in recent times, were taking place in central France, while far away in southern Sumatra thousands of feet of submarine tuffs were being thrown out and deposited, and great lava flows were being erupted in Australasia.

Considerable differences of opinion are exhibited among geologists as to the lower limits of the Pliocene formations; this is partly to be accounted for by the absence of widely-spread marine deposits, and partly by the comparatively short timedifferences between one deposit and another, and hence the ,similarity of the faunas of contiguous strata-groups in local vertical series of beds. Following A. de Lapparent (Traite de geologie, 5th ed., 1906), we shall regard the Pliocene as divisible into three stages: an upper Sicilian stage, a middle Astian stage, and a lower Plaisancian stage. Other writers, however, have selected a different nomenclature, which often involves a different grouping of the formations; thus E. Kayser in his Formationskunde (3rd ed., 1908) distinguishes three stages under the names Arnian (upper), Astian (middle) and Messinian (lower) = Zanclean. The lower stage, however, includes the Pontian, Epplesheim, Pikermi and other formations which are here placed in the Miocene. This stage has been referred to a so-called Mio-Pliocene inter-period.

The Pliocene rocks of Britain now occupy but a small area in Norfolk, Suffolk and part of Essex; but from the presence of small outlying patches in Cornwall (St Erth and St Agnes), Dorsetshire (Dewlish) and Kent (Lenham), it is evident that the Pliocene Sea covered a considerable part of southern England. Moreover, these patches show by their present altitude above the sea that the Downs of Kent must have been elevated more than 850 ft., and the west coast of Cornwall 400 ft. since Pliocene times. The Pliocene rocks rest with strong unconformity upon the older strata in Britain. In the eastern counties the shelly, sandy beds are called "Crag"; this name has come into very general use for all the members of the series, and it is frequently employed as a synonym for Pliocene.

The English Pliocene strata are classified by the Geological Survey of England and Wales as follows: - Yoldia (Leda) myalis bed (provisionally placed here). Forest-bed group and Dewlish gravels with Elephas meridionalis.  Newer Weybourne crag (and Chillesford clay?).

Pliocene Chillesford crag.

Norwich crag and Scrobicularia crag.  Red crag of Butley.

Red crag of Walton, Newbourn and Oakley.

St Erth and St Agnes beds.

Coralline crag.

Lenham beds (Diestian).

Box-stones and phosphatic beds with derived early Pliocene and other fossils.

The box-stones are rounded pieces of brown earthy sandstone containing casts of fossils; the phosphatic beds contain the phosphatized bones of whale, deer, mastodon, pig, tapir, rhinoceros, &c., and have been worked as a source of manure. These basal conglomerate deposits underlie the red crag and sometimes the coralline crag. The last-named formation, known also as the "white" or "Suffolk crag," or as the "Bryozoan crag" (it was the presence of Bryozoa which led to the name coralline), is essentially a shell bank, which was accumulated at a depth of from 20 to 40 fathoms. It is best exposed near Aldeburgh and Gedgrave in Suffolk. The Red Crags are sandy, marine, shallow-water deposits, with an abundant fauna; they vary rapidly from point to point, and in general the more southern localities are richer in southern (older) forms than those farther north. The Norwich crag (fluvio-marine or mammaliferous crag) is not always very clearly marked off from the Red Crags. Marine fresh-water and land shells are found in these beds, together with many mammalian remains, including Elephas antiquus, Mastodon arvernensis, Equus stenonis, Cervus carnutorum, and dolphins, cod and other fish. The Forest-Bed group or Cromer forest-bed is exposed beneath the boulder clay cliffs of the Norfolk coast; it contains transported stumps of trees and many plants still familiar in Britain, many living fresh-water and estuarine molluscs and a large number of mammals, many of which are extinct (Machaerodus, Canis lupus, Ursus spelaeus, Hyaena crocuta, Hippopotamus am phibius, Rhinoceros etruscus, Elephas antiquus and E. meridionalis, Bison bonasus, Ovibos moschatus, numerous species of deer, Equus caballus and E. stenonis, Castor fiber, Talpa europaea and many others). The only record of Pliocene remains in the northern part of England consists of a few teeth of Elephas meridionalis found in a fissure in the limestone at Dove Holes, Derbyshire.

The Pliocene deposits of Belgium and Holland and the northern extremity of France are closely related with those of Britain, though as a whole they are very much thicker. The older marine beds may be traced from Lenham across the Channel at Calais and through Cassel to Diest. The newer marine Pliocene runs in a parallel belt to the north of the older beds through Antwerp. Belgian geologists have divided the local Pliocene into the following groups (from above downwards): Poederlian, Scaldisian, Casterlian, Diestian. F. W. Harmer (Quart. Journ. Geol. Soc., 1898 and 1900) proposed the following scheme for the Pliocene of Britain and the Low Countries: Cromerian = Forest-bed of Cromer.

(Iceno-Cromerian = Chillesford beds and Weybourne crag. Icenian = marine crag of Norwich.

Amstelian = Red Crag, comprising the Newbournian and Butleyan sub-stages.

Waltonian = Walton crag and Poederlian and Scaldisian. Gedgravian = Coralline crag and Casterlian.

Lenhamian = Diestian.

In addition to the deposits just mentioned in French Flanders, the early Pliocene sea has left numerous small patches of marls and sands in Brittany and Normandy. In southern France marine sands, gravels and marls of Plaisancian and Astian ages occur in the depression of Roussillon, followed by Sicilian marls and gravels. In Languedoc (Montpellier, Nimes, Beziers) marine marls and sands are followed by calcareous conglomerate (40 metres) or by marls and lignite; gravels and loarns constitute the uppermost beds. In the Rhone basin the earliest deposits are the Congeria beds of Bollene (Vaucluse); this brackish formation differs from the beds of the same name in Vienna, but resembles those of Italy and Rumania. Then followed a marine invasion (groupe de Saint-Aries); these beds are now found at considerable elevations increasing northward and westward. The later formations in this area are fluviatile or lacustrine in origin, with remarkable torrential gravel deposits at several horizons. The marine Pliocene of the maritime Alps, consisting of blue and yellow clays and limestone, are now elevated 170 metres above the sea, and even up to 350 m. in the neighbourhood of Nice. In central France no marine beds are found, but many interesting and in some cases highly fossiliferous deposits occur in association with volcanic rocks, such as the lower conglomerate and upper trachytic breccia of Perrier (Issoire), the fine tuffs (cinerites) with plants of Cantal, the lignitiferous sandstones beneath the basalt of Cezallier, the diatomite of Ceyssac, &c. In Italy, Pliocene rocks form the low ranges of hills on both sides of the Apennines, hence the term "sub-Apennine" given to these rocks by A. d'Orbigny. They are marine marls and sands; the blue marls which crop out near Rome at the base of Mt Mario and Mt Vatican with the succeeding sands and gravels; the conglomerate followed by deep-sea marls of Calabria, and the marls, sands, limestones and blue clay of Sicily, all belong to the Plaisancian stage. To the next stage belong the yellow sands full of massive fossils, including the conglomerate of Castrovillari in Calabria and the white marls of the Val d'Arno. In the final (Sicilian) stage fluvio-lacustrine sands and gravels are found in Italy, except in Calabria and in Sicily where thick marine beds were formed. In Switzerland some of the deposits of Nagelfluh  and Deckenschotter, glacial plateau gravels, belong to the Sicilian stage. In south-eastern Europe a great series of sands and marls with lignites, termed the Paludina beds, rests directly upon the Pontian formation. From their great development in the Levant, they have been given the rank of a "Levantine stage" by F. von Hochstetter; they are found in Dalmatia, Croatia, Slavonia, Bosnia, Rumania, Bulgaria, southern Russia, the Cyclades, and the Caspian region. On the north coast of Africa marine and brackish sands and marls occur in Morocco, Algeria and Egypt; and the "rifts" of the Red Sea and Suez have been assigned to this period.

  


In North America marine W Pliocene is found fringing the coasts of California and the Gulf of - Mexico. In the latter region marine marls, clays and limestones are best developed in Florida and can be traced into the Carolinas and Virginia;; they have been classed as the Lafayette group (with lignites), the Florida group, and the Calooshatchis stage. On the Pacific coast the marine beds have attained great thicknesses, notably in the Merced series of San Francisco. In the San Luis Obispo region the non-marine Paso Robles beds, said to be moo ft. thick, belong to this period. Other local formations of Older Pliocene marine origin in California are those of San Diego and Wild Cat. In the Rocky Mountains are large lacustrine formations of considerable thickness, and certain conglomerates in Wyoming and Bishop Mountain are assigned to this age. The sands and clays with gypsum of Entre Rios in South America contain fossils of the Atlantic type.

Lignitiferous shale with petroleum and great thickness of volcanic tuffs have been found in southern Sumatra. In New South Wales Pliocene river terraces and alluvial deposits are covered by MidPliocene lavas and from these "deep leads" or buried river beds much gold has been obtained. In Victoria great basaltic and doleritic flows have filled up the Pliocene river valleys, and marine beds have been found at elevations of 1000 ft. above present sea-level. Very similar deposits and volcanic rock, belonging to the Wanganui system of F. W. Hutton, are found in New Zealand.

See C. Reid, "The Pliocene Deposits of Britain" (Mem. Geol. Survey, 1890); E. T. Newton, "The Vertebrates of the Pliocene Deposits of Britain" (Mem. Geol. Survey, 1891) (both contain a bibliography); C. Reid, Origin of the British Flora (1899); and "Geological Literature" (Geol. Soc. London Annual, since 1893).

(J. A. H.)