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JURASSIC
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JURASSIC , in See also:geology, the See also:middle See also:period of the Mesozoic era, that is to say, succeeding the Triassic and preceding the Cretaceous periods. The name Jurassic (See also:French jurassique; See also:German Juraformation or See also:Jura) was first employed by A. See also:Brongniart and A. von See also:Humboldt for the rocks of this See also:age in the western Jura mountains of See also:Switzerland, where they are well See also:developed. It was in See also:England, however, that they were first studied by See also: See also:Oppel, 1856–1858; and since then by many other workers: E. Benecke, E. See also:Hebert, W. See also:Waagen, and others. The study of Jurassic rocks has continued to attract the See also:attention of geologists, partly because the bedding is so well defined and See also:regular-the strata are little disturbed anywhere outside the Swiss Jura and the See also:Alps—and partly because the fossils are numerous and usually well-preserved. The result has been that no other See also:system of rocks has been so carefully examined throughout its entire thickness; many "zones" have been established by means of the fossils—principally by See also:ammonites—and these zones are not restricted to limited districts, but many of them hold See also:good' over wide areas. Oppel distinguished no fewer than See also:thirty-three zonal horizons, and since then many more sub-zonal divisions have been noted locally. The existence of faunal regions in Jurassic times was first pointed out by J. See also:Marcou; later M. See also:Neumayr greatly extended observations in this direction. According to Neumayr, three distinct See also:geographical regions of See also:deposit can be made out among the Jurassic rocks of See also:Europe: (I) The Mediterranean See also:province, embracing the See also:Pyrenees, Alps and Carpathians, with all the tracts lying to the See also:south. One of the biological characters of this See also:area was the See also:great abundance of ammonites belonging to the See also:groups of Heterophylli (Phylloceras) and Fimbriati (Lytoceras). (2) The central European province, comprising the tracts lying to the See also:north of the Alpine See also:ridge, and marked by the See also:comparative rarity of the ammonites just mentioned, which are replaced by others of the groups Inflati (Aspidoceras) and Oppelia, and by abundant reefs and masses of See also:coral. (3) The boreal or See also:Russian province, comprising the middle and north of See also:Russia, Spitzbergen and See also:Greenland. The See also:life in this area was much less varied than in the others, showing that in Jurassic times there was a perceptible diminution of temperature towards the north. The ammonites of the more See also:southern tracts here disappear, together with the See also:corals. The cause of these faunal regions Neumayr attributed to See also:climatic belts—such as exist to-See also:day—and in See also:part, at least, he was probably correct. It should be See also:borne in mind, however, that although Neumayr was able to trace a broad, warm See also:belt, some 6o° in width, right See also:round the See also:earth, with a narrower mild belt to the north and an See also:arctic or boreal belt beyond, and certain indications of a repetition of the climatic zones on the southern See also:side of the thermal See also:equator, more See also:recent discoveries of fossils seem to show that other influences must have been at work in determining their See also:distribution; in See also:short, the identity of the Neumayrian climatic boundaries becomes increasingly obscured by the advance of our knowledge. The Jurassic period was marked by a great See also:extension of the See also:sea, which commenced after the See also:close of the Trias and reached its maximum during the See also:Callovian and See also:Oxfordian stages; consequently, the Middle Jurassic rocks are much more widely spread than the See also:Lias. In Europe and elsewhere Triassic beds pass gradually up into the Jurassic, so that there is difficulty some-times in agreement as to the best See also:line for the See also:base of the latter; similarly at the See also:top of the sytsem there is a passage from the Jurassic to the Cretaceous rocks (Alps). Towards the close of the period See also:elevation began in certain regions; thus, in See also:America, the Sierras, Cascade Mountains, See also:Klamath Mountains, and Humboldt Range probably began to emerge. In England the estuarine See also:Portlandian resulted partly from elevation, but in the Alps marine conditions steadily persisted (in the Tithonian See also:stage). There appears to have been very little crustal disturbance or volcanic activity; tuffs are known in See also:Argentina and See also:California; volcanic rocks of this age occur also in See also:Skye and See also:Mull. The rocks of the Jurassic system See also:present great petrological diversity. In England the name " Oolites " was given to the middle and higher members of the system on See also:account of the prevalence of oolitic structure in the limestones and ironstones; the same See also:character is a See also:common feature in the rocks of See also:northern Europe and elsewhere, but it must not be overlooked that See also:clays and sandstones together bulk more largely in the aggregate than the oolites. The thickness of Jurassic rocks in England is 4000 to 5000 ft., and in Germany 2000 to 3000 ft. Most of therocks represent the deposits of shallow seas, but estuarine conditions and See also:land deposits occur as in the Purbeck beds of See also:Dorset and the coals of See also:Yorkshire. See also:Coal is a very important feature among Jurassic rocks, particularly in the Liassic See also:division; it is found in See also:Hungary, where there are twenty-five workable beds; in See also:Persia, See also:Turkestan, See also:Caucasus, south See also:Siberia, See also:China, See also:Japan, Further See also:India, New See also:Zealand and in many of the Pacific Islands. Being shallow See also:water formations, petrological changes come in rapidly as many of the beds are traced out; sandstones pass laterally into clays, and the latter into limestones, and so on, but a reliable See also:guide to the See also:classification and correlation is found in the fossil contents of the rocks. In the accompanying table a See also:list is given of some of the zonal fossils which regularly occur in the See also:order indicated; other forms are known that are equally useful. It will be noticed that while there is See also:general agreement as to the order in which the zonal forms occur, the line of division between one formation and another is liable to vary according to factors in the See also:personal See also:equation of the authors. The Jurassic formations stretch across England in a varying See also:band from the mouth of the See also:Tees to the See also:coast of See also:Dorsetshire. They consist of harder sandstones and limestones interstratified with softer clays and shales. Hence they give rise to a characteristic type of scenery—the more durable beds See also:standing out as See also:long ridges, sometimes even with See also:low cliffs, while the clays under-See also:lie the level spaces between. Jurassic rocks See also:cover a vast area in Central Europe. They rise from under the Cretaceous formations in the north-See also:east of France, whence they range southwards down the valleys of the See also:Saone and See also:Rhone to the Mediterranean. They appear as a broken border round the old crystalline See also:nucleus of See also:Auvergne. Eastwards they range through the Jura Mountains up to the high grounds of Bohemia. They appear in the See also:outer chains of the Alps on both sides, and on the south they rise along the centre of the See also:Apennines, and here and there over the See also:Spanish See also:Peninsula. Covered by more recent formations they underlie the great See also:plain of northern Germany, whence they range eastwards and occupy large tracts in central and eastern Russia. See also:Lower Jurassic rocks are absent from much of northern Russia, the stages represented being the Callovian, Oxfordian and Volgian (of See also:Professor S. See also:Nikitin) ; the See also:fauna differs considerably from that of western Europe, and the marine equivalents of the Purbeck beds are found in this region. In south Russia, the See also:Crimea and Caucasus, Lias and Lower Jurassic rocks are present. In the Alps, the Lower Jurassic rocks are intimately associated with the underlying Triassic formations, and resemble them in consisting largely of reddish limestones and See also:marbles; the ammonites in this region differ in certain respects from those of western and central Europe. The Oxfordian, Callovian, Cor2llian and Astartian stages are also present. The Upper Jurassic is mainly represented by a See also:uniform See also:series of limestones, with a See also:peculiar and characteristic fauna, to which Oppel gave the name Tithonian." This includes most of the horizons from See also:Kimeridgian to Cretaceous; it is developed on the southern flanks of the Alps, Carpathians, Apennines, as well as in south France and other parts of the Mediterranean See also:basin. A characteristic formation on this See also:horizon is the " Diphya See also:limestone," so-called from the fossil Terebratula diphya (Pygope janitor) seen in the well-known escarpments (Hochgebirge See also:Kalk). Above the Diphya limestone comes the Stramberg limestone (Stramberg in See also:Moravia), with " Aptychus " beds and coral reefs. The rocks of the Mediterranean basin are on the whole more calcareous than those of corresponding age in north-See also:west Europe; thus the Lias is represented by 1500 ft. of See also: The best marine development is in See also:Cutch, where the following groups series = Bathonian. In the western See also:half of the See also:Salt Range and the Himalayas, See also:Spiti shales are the equivalents of the European Callovian and Kimeridgian. The upper part of the See also:Gondwana series is not improbably Jurassic. On the See also:African continent, Liassic strata are found in See also:Algeria, and Bathonian formations occur in See also:Abyssinia, See also:Somaliland, Cape See also:Colony and western See also:Madagascar. In See also:Australia the Permo-Carboniferous formations are succeeded in See also:Queensland and Western Australia by what may be termed the Jura-Trias, Stages 1 Ammonite Zones a Substages Von A. de See also:Lapparent, Trait, Alpine o, of Buch 5th ed. O Quenstedt E.% o See also:Purbeckian Perisphinctes transitorius e as Purbeckien a ar q O O Perisphinctes giganteus g , ., or ?; . a Ce Di h a Kalke a. Olcostephanus gigas 7 x Aquilonien o .o p Y Reineckia See also:eudoxus a 3 F' Acanthicus Oppelia tenuilobata 3' o a o Beds E2 m a) •-+ ° See also:ooh o as a) ..sa x c a) Portlandian Bononien Kimeridgian Virgulien '. 0 See also:gib _ Pteroceran Peltoceras bimammatum E as — See also:Corallian O a 72, Astartien I) Rauracien Oxfordian Peltoceras transversarium Aspidoceras perarmatum Peltoceras See also:athlete Cosmoceras See also:Jason Macrocephalites macrocephalus Argovien o 0 ,,.., a, k b O Neuvizien Callovian Upper Divesien a) Lower Divesien :=„-3: o Bathonian O v o Oppelia aspidoides ,. a a Bathonien o a a Posidonien Parkinsonia ferruginea co 3 o a a Beds S.Alps) Parkinsonia Parkinsoni bu ti o y m c' ( Cceloceras Hum hresianus o a a; l~ a Klauss Beds p Q b '4 ° (N. Alps) Sphaeroceras Sauzei w a' Sauzei-Kalke Sonninia Sowerbyi a W Oolite of See also:San Harpoceras Murchisonae Vigilio ° -k v ~ Ce v m ;a l~ o a U 0.'C a U pa Tr, ^ a) O Ba'ocian (InferiorOolite) Bajocien (passage beds) Harpoceras (Lioceras) opalinum Toarcien Upper Lias Lytoceras jurense .as b a Posidonia Bronni 7 a) Amaltheus spinatus 14 ,.a Amaltheus margaritatus a Dactylioceras Davoei Phylloceras See also:ibex Aegoceras Jamesoni Arietites raricostatus Oxynoticeras oxynotum Arietites obtusus Arietites Bucklandi Schlotheimia angulata Psiloceras planorbis Middle Lias Charmouthien Lower Lias Sinemourien Hettangien (part ) Hettangien (part) Rhetien are distinguished from above downwards: the Umia series=Portlandian and Tithonian of south Europe, passing upwards into the Neocomian; the Katrol series =Oxfordian (part) and Kimeridgian; the Chari series = Callovian and part of the Oxfordian; the Patcham 1 Purbeckian from the " Isle " of Purbeck. Aquilonien from Aquilo (See also:Nord). Bononien from See also:Bononia (See also:Boulogne). Virgulien from Exogyra virgula. Pteroceran from Pteroceras oceani. Astartien from See also:Astarte supracorallina. Rauracien from Rauracia (Jura). Argovien from Argovie (Switzerland). Neuvizien from Neuvizy (See also:Ardennes). Divesien from Dives (See also:Calvados). Bathonien from See also:Bath (England). Bajocien from See also:Bayeux (Calvados). Toarcien from Toarcium (See also:Tours). Charmouthien from Charmouth (England). Sinemourien from Sinemurum, Semur (See also:ate d'Or). Hettangien from Hettange (See also:Lorraine).which include the coal-bearing " See also:Ipswich " and " Burrum " formations of Queensland. In New Zealand there is a thick series of marine beds with terrestrial See also:plants, the Mataura series in the upper part of See also:Hutton's Hokanui system. See also:Sir J. See also:Hector included also the Putakaka series (as Middle Jurassic) and the See also:Flag series with the See also:Catlin's See also:River and See also:Bastion series below. Jurassic rocks have been recorded from New See also:Guinea and New See also:Caledonia. Life in the Jurassic Period.—The expansion of the sea during this period, with the formation of broad sheets of shallow and probably warmish water, appears to have been favourable to many forms of marine life. Under these conditions several groups of organisms developed rapidly along new directions, so that the Jurassic period as a whole came to have a fauna differing clearly and distinctly from the preceding Palaeozoic or succeeding See also:Tertiary faunas. In the seas, all the See also:main groups were represented as they are to-day Corals were abundant, and in later portions of the period covered large areas in Europe; the See also:modern type of coral became dominant; besides See also:reef-See also:building forms such as Thamnastrea, Isastrea, Thecosmilia, there were numerous single forms like Montivaltia. Crinoids existed in great See also:numbers in some of the shallow seas; compared with Palaeozoic forms there is a marked reduction in the See also:size of the calyx with a great extension in the number of arms and pinnules; Pentacrinus, Eugeniacrinus, Apiocrinus are all well known; Antedon was a stalkless genus. Echinoids (urchins) were gradually developing the so-called " irregular " type, Echinobrissus, Holectypus, Collyrites, Clypeus, but the " regular " forms prevailed, Cidaris, Hemicidaris, Acrosalenia. See also:Sponges were important rock-builders in Upper Jurassic times (Spongilen Kalk) ; they include lithistids such as Cnemediastrum, Hyalotragus, Peronidella; hexactinellids, Tremadictyon, Craticularia; and horny sponges have been found in the Lias and 'Middle Jurassic. See also:Polyzoa are found abundantly in some of the beds, Stomatopora, Berenicia, &c. Brachiopods were represented principally by terebratulids (Terebratula, Waldheimia, Megerlea), and by rhynchonellids; Thecae, Lingula and Crania were also present. The Palaeozoic spirifirids and athyrids still lingered into the Lias. More important than the brachiopods were the pelecypods; Ostrea, Exogyra, Gryphaeawerevery abundant (Gryphite limestone, Gryphite grit); the genus Trigonia, now restricted to Australian See also:waters, was present in great variety; Aucella, See also:Lima, Pecten, Pseudomonotis Gervillia, Astarte, Diceras, Isocardia, Pleuromya may be mentioned out of many others. Amongst the gasteropods the Pleurotomariidae and Turbinidae reached their maximum development; the Palaeozoic Conularia lived to see the beginning of this period (Pleurotomaria, Nerinea, Pteroceras, Cerithium, Turritella). Cephalopods flourished everywhere; first in importance were the ammonites; the Triassic genera Phylloceras and Lytoceras were still found in the Jurassic waters, but all the other numerous genera were new, and their shells are found with every variation of size and ornamentation. Some are characteristic of the older Jurassic rocks, Arietites, Aegoceras, Amaltheus, Harpoceras, `Oxynoticeras, Stepheoceras, and the two genera mentioned above; in the middle stages are found Cosmoceras, Perisphinctes, Cardioceras, Kepplerites Aspidoceras; in the upper stages Olcostephanus, Perisphinctes, Reineckia, Oppelia. So regularly do certain forms characterize definite horizons in the rocks that some thirty zones have been distinguished in Europe, and many of them can be traced even as far as India. Another cephalopod See also:group, the belemnites, that had been dimly outlined in the preceding Trias, now advanced rapidly in numbers and in variety of See also:form, and they, like the ammonites, have proved of great value as See also:zone-indicators. The Sepioids or cuttlefish made their first See also:appearance in this period (Beloteuthis, Geoteuthis,) and their See also:ink-bags can still be traced in examples from the Lias and lithographic limestone. Nautiloids existed but they were somewhat rare. A great See also:change had come over the crustaceans; in See also:place of the Palaeozoic See also:trilobites we find long-tailed See also:lobster-like forms, Penaeus, Eryon, Magila, and the broad crab-like type first appeared in Prosopon. Isopods were represented by Archaeoniscus and others. See also:Insects have See also:left fairly abundant remains in the Lias of England, Schambelen (Switzerland) and Dobbertin (See also:Mecklenburg), and also in the English Purbeck. Neuropterous forms predominate, but See also:hemiptera occur from the Lias upwards; the earliest known flies ,(See also:Diptera) and ants (See also:Hymenoptera) appeared; See also:orthoptera, See also:cock-roaches, crickets, beetles, &c., are found in the Lias, Stonesfield See also:slate and Purbeck beds. Fishes were approaching the modern forms during this period, heterocercal ganoids becoming scarce (the Coelacanthidae reached their maximum development), while the homocercal forms were abundant (Gyrodus, Microdon, Lepidosteus, Lepidotus, Dapedius). The Chimaeridae, sea-See also:cats, made their appearance (Squaloraja). .The ancestors of the modern sturgeons, garpikes and See also:selachians, Hybodus, Acrodus were numerous. Bony-See also:fish were represented by the small Leptolepis. So important a place was occupied by See also:reptiles during this period that it has been well described as the " age of reptiles." In the seas the fish-shaped Ichthyosaurs and long-necked Plesiosaurs dwelt in great numbers and reached their maximum development; the latter ranged in size from 6 to 40 ft. in length. The Pterosaurs, with See also:bat-like wings and pneumatic bones and keeled See also:breast-See also:bone, flew over the land; Pterodactyl with short tail and Rhamphorhyncus with long tail are the best known. Curiously modified crocodilians appeared See also:late in the period (Mystriosaurus, Geosaurus, Steneosaurus, Teleosaurus). But even more striking than any of the above were the Dinosaurs; these ranged in size from a creature no larger than a See also:rabbit up to the gigantic Atlantosaurus, too ft. long, in the Jurassic of Wyoming. Both herbivorous and carnivorous forms were present; Brontosaurus, Megalosaurus, Stegosaurus, Cetiosaurus, Diplodocus, Ceratosaurus and Campsognathus are a few of the genera. By comparison with the Dinosaurs the mammals took a very subordinate position in Jurassic times; only a few jaws have been found, belonging to quite small creatures; they appear to have been marsupials and were probably insectivorous (Plagiaulax Bolodon, Trironodon, Phascolotherium, Stylacodon). Of great See also:interest are the remains of the earliest known See also:bird (See also:Archaeopteryx) from the Solenhofen slates of See also:Bavaria. Although this was a great advance beyond the Pterodactyls in avian characters, yet many reptilian features were retained.
Comparatively little change took place in the vegetation in the See also:time that elapsed between the close of the Triassic and the middle of the Jurassic periods. Cycads, Zamites, Podozamites, &c., appeared to reach their maximum; Equisetums were still found growing to a great size and Ginkgos occupied a prominent place; ferns were common ; so too were pines, yews, cypresses and other conifers, which while they outwardly resembled their modern representatives, were quite distinct in See also:species. No flowering plants had yet appeared, although a See also:primitive form of angiosperm has been reported from the Upper Jurassic of Portugal.
The economic products of the Jurassic system are of considerable importance; the valuable coals have already been noticed; the well-known See also:iron ores of the See also:Cleveland See also:district in Yorkshire and those of the See also:Northampton sands occur respectively in the Lias and Inferior Oolites. Oil shales are found in Germany, and several of the Jurassic formations in England contain some See also:petroleum. Building stones of great value are obtained from the Great Oolite, the Portlandian and the Inferior Oolite; large quantities of See also:hydraulic See also:cement and See also:lime have been made from the Lias. The celebrated lithographic See also: Oppel, See also:Die Juraformation Englands, Frankreichs and s.w. Deutschlands (1856-1858). For a good general account of the formations with many references to See also:original papers, see A. de Lapparent, Traite de geologie, vol. ii. 5th ed. (1906). The See also:standard work for Great See also:Britain is the series of See also:Memoirs of the See also:Geological Survey entitled The Jurassic Rocks of Britain, i and ii. " Yorkshire " (1892) ; iii. " The Lias of England and See also:Wales " (1893) ; iv. " The Lower Oolite Rocks of England (See also:York-See also:shire excepted)" (1894) ; v. " The Middle and Upper Oolitic Rocks of England (Yorkshire excepted)" (1895). The See also:map is after that of M. Neumayr, " Die geographische Verbreitung der Juraformation," Denkschr. d. k. Akad. d. Wiss., Wien, Math. u. Naturwiss., cl. L., Abth. i., Karte 1. (1885). (J. A. Additional information and CommentsThere are no comments yet for this article.
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