1911 Encyclopædia Britannica/Pliocene

by John Allan Howe

PLIOCENE (from the Gr. πλεῖων, more, and καινός, 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. 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 reformatory 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 opmion 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 time differences 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 (T railé de géolagze, 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 Formalionskunde (grd 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:-

Yoldza (Leda) myalzs bed (provisionally placed here). Forest-bed group and DCWllSh gravels with Elephas mendronahs.

Newer Weybourne crag (and Chillesford clay?). Pliocene Chillesford crag

Norwich crag and Scrobwularm crag.

Red crag of Butley

Red crag of Walton, Newbourn and Oakley.

St Erith and St Agnes beds.

Cora line crag

g}S)';ne 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 847

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 armquus, Mastadon arvernensrs, Equus stenoms, Cervus carnulorum, 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 molluses and a large number of mammals, many of which are extinct (Marhaeradus, Cams lufus, Ursus spelaeus, Hyaeua crocuta, Hrppapotamus amphzbrus, R moceros etruscus, Elephas armquus and E. merrdranahs, Brson bouasus, Ombos moschalus, numerous species of deer, Equus caballus and E. stenoms, 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 merrdronalrs 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 d1v1ded the local Pliocene into the following groups (from above downwards): Poederllan, Scaldisian, Casterlian, Diestian. F. W. Harmer (Quart. Journ. Geal. Soc., 1898 and 1900) proposed the following scheme for the Pliocene of Britain and the Low Countries:-

Cromerian = Forest-bed of Cromer.

(Iceno-Cromerlan = 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 atches 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, Béziers) marine marls and sands are ollowed by calcareous conglomerate (40 metres) or by marls and lignite; gravels and loams constitute the uppermost beds. In the Rhone basin the earliest deposits are the Congerla beds of Bollene (Vaucluse); this brackish ormation differs from the beds of the same name in Vienna, but resembles those of Italy and Rumania. Then followed a marine invasion (groupe de Sami-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 ryo metres above the sea, and even up to 350 m. in the neighbourhood o 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 (ISSOIFC), the fine tuffs (cine rites) with plants of Cantal, the lignitiferous sandstones beneath the basalt of Cézallier, 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 mars 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 Nagebiuh and Deckeuschotler, 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 reat 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 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 llgnites), the Florida group. and the Caloosharchis 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 1000 ft. thick, belong to this period. Other local formations of 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 arc 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 Mid- Pliocene 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.

TABLE OF PLIOCENE FORMATIONS.

Stages.

England.

Belgium

and Holland.

Rhone Basin.

Languedoc

and Roussillon.

Italy.

Eastern Europe.

Other Countries

Sicilian.

Cromer Forest

Bed. Fluvio-marine

Norwic h

crag. Red crag of

Suffolk.

Clays of Campine. Amstelian.

Astian,

Base of Red crag.

Poederlian.

Scaldisian sands with Tropkon antiquum.

Marls of St

Cosme. Gravels of

Chagny. Conglomerates of

Chambaran. Sands of Trc-

voux and

Mollon. Travertine of

Meximieux.

Durfort beds with EUphas nuridionalis.

Sands of Val d'Arno.

Limestones of Paler- mo and clays with northern mollusca.

Paludina (Vivipara)

Marine beds ef Entre Rios.

Volcanic tuffs d Sw Sumatra.

Conglomerates of Montpellicr and Fourrcs.

Sands of Rous- sillon with Ma s lodon arvernensis.

Marls of Val d'Arno with Mastodon arvernensis*

Yellow sands of Asti, Plaisantin, Monte Maria and Tuscany.

Conglomerates of Castrovillari.

Middle Paludina bods.

Petroleum-bearisf beds of Sumatra.

Marine sands U Moghara aad I Mokatta.

Plaisancian.

Coralline crag. Lenham beds.

Sands with Isocardia car. Diestian sandstones.

Marine marls of Brcsse, Hauterivcs.

Congeria beds olBollene.

Yellow sands of Montpellicr.

Blue marls of Millas.

Blue marls of Pia- cenza, Bologna, and Vatican.

Lower Paludina beds.

Marine beds ef

Florida. Lacustrine bed* ef

Rocky

tains.

Life of the Pliocene Period.—Sir C. Lyell denned the Pliocene strata as those which contained from 36–95% of living marine molluscs. This rule can no longer be strictly applied to the widely scattered marine deposits, and it is of course inapplicable to the very numerous formations of lacustrine and fluviatile origin. On the whole the marine organisms are very like their living representatives, and there is often practically no specific difference; Nassa, Valuta, Chenopus, Denmium, Fusus, Area, Peden, Pectunculus, Panopoea, Cyprina and Mactra may be mentioned among the marine genera; Congeria (Dreyssensia), Auricula, Paludina, Meianopsis ana Helix are found in the lacustrine deposits. One of the most interesting facts exposed by the study of the mollusca is the gradual lowering of the temperature of Europe during the period. In Britain the early Pliocene was, if anything, warmer than at present, but the percentage of northern forms ascends steadily through the higher beds, and finally arctic forms, such as Buccinum groenlandicum, Trichopteris borealis, Mya truncata, Cyprina islandica, &c, appear on the coasts of Norfolk and Suffolk, and some of the northern species even reached the Mediterranean (Sicily) at the close of the period. The flora exhibits the same gradual change, the large palms and camphor trees disappeared from Europe, the sabal palm lingered in Languedoc, and Chamerops humilis lived about Marseilles until the end; the sequoias and bamboos held on for some time, and the aspect of the vegetation in mid-Pliocene times was not unlike that of Portugal, Algeria and Japan of to-day. Not a few species that dwelt in Pliocene Europe are found in the forests of America. The flora of the Cromer forest beds is very like that of the same district at the present time. The mammals of the British Pliocene show a curious blending of northern and southern forms; they include Machaerodus (the sabre-toothed lion), hyenas, dogs, fox, wolf, glutton, marten, bears, Ursus arvernensus and the grizzly and cave bear, seals, whales, dolphins, bisons, musk ox, gazelle, the red deer and many others now extinct, the roebuck, pigs and wild boar, hippopotamus, hipparion and horse (Equus caballus and E. stenosis), several species of rhinoceros, tapir, hyrax, elephants (Elephas meridionalis and E. antiques), several mastodons, squirrel, beaver, hare, mice, voles, &c. The mastodon disappeared from Europe before the close of the period, but lived much longer in America. No generally accepted fossil man has been found in the Pliocene; Pithecanthropus erectus, found by E. Dubois in Java, is the nearest to the human type. Monkeys, Macacus and Semnopithecus, occur in the Pliocene of Europe. At this time the Pliocene mammals of North America were able to migrate into South America, and a few Of the southern forms travelled northwards.

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. Sec. London Annual, since 1893). (J. A. H.)